Brachytherapy - Articles in Press

Hypofractionated accelerated computed tomography–guided interstitial high-dose-rate brachytherapy for liver malignancies - Corrected Proof

2012-05-10

Abstract: Purpose: To report our results of computed tomography (CT)–guided interstitial high-dose-rate (HDR) brachytherapy (BRT) in the local treatment of inoperable primary and secondary liver malignancies.Methods and Materials: Between 2000 and 2009, 31 patients underwent a total of 42 BRT procedures for 36 hepatic lesions exceeding 4cm and located adjacent to the liver hilum and bile duct bifurcation. The median tumor volume was 99cm3 (range, 46–1348cm3). The median age was 64 years (range, 27–85 years). The HDR-BRT delivered a median total physical dose of 13.0Gy (range, 7.0–32.0Gy) in twice daily fractions of median 7.0Gy (range, 4.0–10.0Gy) in 14 patients and in once daily fractions of median 8.0Gy (range, 7.0–14.0Gy) in 17 patients.Results: The median followup was 13.3 months with an overall survival rate of 66% at 1 year. The local control rate for patients with metastatic lesions was 79%, 59%, and 59%, and for the subgroup with primary hepatic tumors 88%, 50%, and 50% at 1, 2, and 3 years, respectively. Severe side effects occurred in 4.7% of BRT procedures with no treatment-related deaths.Conclusions: Our results confirm CT–guided interstitial HDR-BRT to be a safe procedure for the local treatment of inoperable liver malignancies unsuitable for thermal ablation.

Patient-reported long-term rectal function after permanent interstitial brachytherapy for clinically localized prostate cancer - Corrected Proof

2012-05-07

Abstract: Purpose: To evaluate the effect of permanent interstitial brachytherapy with or without supplemental therapies on long-term rectal function using a patient-administered quality-of-life instrument.Methods and Materials: One hundred thirty four of the initial 219 prostate brachytherapy patients who remain alive and have participated in a prospective evaluation of rectal function were mailed the rectal function assessment score (R-FAS). Of the 134 patients, 3 have a colostomy because of colorectal cancer, 2 failed to respond, and 129 (99.2% of eligible patients) returned a completed R-FAS. R-FAS ranges from 0 to 27 with lower scores indicative of better bowel function. Median followup was 14 years. Multiple clinical, treatment, and dosimetric parameters were evaluated for impact on bowel function.Results: For the current cohort, R-FAS was 3.35, which was comparable to the 1999 (4.29), 2002 (3.92), and 2006 (4.00) surveys. In the 2011 survey, 10 (7.8%), 17 (13.1%), and 102 (78.3%) patients reported bowel function to be worse, improved, or unchanged after brachytherapy. No patient has developed a rectal ulcer or fistula. The number of preimplant bowel movements, tobacco, and diabetes mellitus correlated with R-FAS. Consistent with the previous thee surveys, patient’s perception of overall rectal quality of life was inversely related to the use of supplemental external beam radiation.Conclusions: Long-term rectal function after prostate brachytherapy is favorable with a small number of patients reporting deterioration in bowel function. The judicious use of supplemental external beam radiation with particular attention to rectal doses may further improve long-term function.

Urethral strictures following high-dose-rate brachytherapy for prostate cancer: Analysis of risk factors - Corrected Proof

Benjamin R. Hindson, Jeremy L. Millar, Bronwyn Matheson — 2012-05-07

Abstract: Purpose: High-dose-rate brachytherapy is an established technique to deliver a conformal dose of radiation to patients with prostate cancer. The William Buckland Radiotherapy Center has been performing high-dose-rate brachytherapy with external beam radiation treatment for prostate cancer since 1998 and has an extensive prospective database on all patients treated. The purpose of this analysis was to assess the risk of stricture formation and identify the predictive or causative factors.Methods and Materials: Three hundred fifty-four patients were treated between 1998 and 2008. Patients received one of three differing dose schedules: 20Gy in four treatments (20Gy/4), 18Gy/3, and 19Gy/2 during three sequential time periods. Nelson–Aalen cumulative hazard modeling was used to estimate risk of events over time. Potential risk factors, including dose, were identified and used in the analysis.Results: There were 45 patients who developed at least one stricture, an overall risk of 8.2% at 2 years. The 2-year risk of stricture formation was 3.4%, 2.3%, and 31.6% for 18Gy/3, 20Gy/4, and 19Gy/2, respectively. Most strictures occurred in the bulbomembranous urethra (50%) or external sphincter region (33%). On multivariable analysis, the dose schedule used was the only significant predictor for increased stricture formation.Conclusions: In our patients, those who received 19Gy/2 were at a significantly higher risk of stricture formation. Most of these strictures were mild, requiring only one intervention but a 2-year stricture risk of 31.6% was striking, and we have modified our protocol.

Seed migration in prostate brachytherapy depends on experience and technique - Corrected Proof

2012-04-30

Abstract: Purpose: To determine seed loss and pulmonary migration rate over time in permanent seed prostate brachytherapy.Methods and Materials: We analyzed the first 495 patients treated in our department. All patients were treated with loose 125I seeds with automated seed delivery system and real-time intraoperative planning. Pelvic fluoroscopic imaging was done 30 days after the implant. Patients were divided into five groups of 100 patients according to the order they were treated, and groups were compared using χ2 test and one-way analysis of variance.Results: A total of 22.8% of patients lost at least one seed. The highest percentage of patients losing any number of seeds was in the first 100. Thirty-eight percent lost at least one seed. This number decreased gradually and was only 9% in Patients 400–499. The mean total seed loss rate (number of seeds lost/number seeds implanted) changed significantly over time (p<0.001). There was a continuous significant (p<0.001) decline after the first 100 patients (1.25% for the first 100 patients) followed by a rise in Patients 300–399, followed by another decline (0.21% for the last 100 patients). The seed loss rate to the thorax changed significantly over time (p=0.009). It rose after an initial rate of 0.25–0.42% in Patients 200–299 and 300–399 and declined later to a rate of 0.21% in the last 100 patients.Conclusions: We found a learning curve for seed migration. Avoiding implanting seeds outside of the capsule and modern transrectal ultrasound imaging can help decrease migration.

High-dose-rate brachytherapy for prostate cancer in a previously radiated patient with polyethylene glycol hydrogel spacing to reduce rectal dose: Case report and review of the literature - Corrected Proof

2012-04-30

Abstract: Purpose: To describe the use of a temporary spacer to reduce rectal dose prior to prostate radiation in a man with prior pelvic radiotherapy and review the relevant literature.Methods and materials: A healthy 57-year-old man presented with high-risk prostate cancer (Gleason score of 8, prostate-specific antigen level [PSA] 12.6 ng/mL, T3a by magnetic resonance imaging [MRI]), only 2.5 years after a low anterior resection followed by pelvic chemo-radiotherapy to 50.4 Gy for a locally advanced rectal cancer. Due to the prior radiation, he was not felt to be a candidate for surgery or external beam radiation, so he chose long-term androgen deprivation therapy (ADT) plus high-dose-rate brachytherapy to 36 Gy in 6 fractions. To reduce the radiation dose to the anterior rectal wall, 10 mL of a polyethylene glycol hydrogel spacer was injected between the prostate and rectum and created between 1.4 and 1.5 cm of separation along the length of the prostate.Results: Two randomized trials demonstrating that local therapy plus ADT improves overall survival compared to ADT alone provided the rationale for additional prostate radiotherapy in this otherwise healthy patient. Salvage brachytherapy is associated with a 3.4% rate of rectal fistula among the 251 cases reported in the literature from 2000–2007, with rates as high as 12% in one series. The spacer allowed the rectal dose constraint goals to be easily met.Conclusions: Injecting an absorbable polyethylene glycol hydrogel to separate the prostate and rectum appears to be associated with decreased maximum and mean rectal doses, and may have particular utility in previously irradiated patients.

High-dose-rate interstitial computed tomography–based brachytherapy for the treatment of cervical cancer: Early results - Corrected Proof

2012-04-18

Abstract: Purpose: There is limited published data on high-dose-rate interstitial brachytherapy (HDRBT) for cervical cancer resulting in no consensus on a fractionation schedule. This study reports our experience of CT-based HDRBT for treating locally advanced cervical cancer.Methods and Materials: Forty-seven patients diagnosed with Stage IIB–IVA cervical cancer not suitable for intracavitary brachytherapy were treated with HDRBT from March 2005 to November 2010. All patients received external beam radiation therapy with a median dose of 45Gy and all had one interstitial implantation followed by 3.75–5Gy×5 fractions in a twice daily (BID) schedule. Total doses for clinical target volume and organs at risk, including rectum, bladder, and sigmoid, were summated and normalized to a biologically equivalent dose of 2Gy per fraction. At 3 months posttherapy, early response was assessed with clinical examination and positron emission tomography (PET/CT) imaging.Results: Median clinical target volume D90 (dose delivered to 90% of the clinical target volume) was 76.3 (59.0–86.9) Gy and the 2cc dose to the bladder, rectum, and sigmoid colon organs were 70.2 (55.9–77.7), 65.8 (54.9–80.6), and 56.5 (45.0–71.2) Gy, respectively. Posttreatment, 12 patients had evidence of persistent disease on PET/CT. Eleven of the 35 patients who had complete response developed recurrences. Two patients developed late Radiation Therapy Oncology Group ≥3 rectal toxicities. Two-year actuarial local control, disease-free survival, overall survival, and Grade ≥3 toxicities were 61%, 43%, 59%, and 10%, respectively.Conclusion: Our approach of a single implantation procedure followed by five fractions of HDRBT was well tolerated with early results demonstrating a moderate response and local control rate with acceptable toxicities.

Defining a magnetic resonance scan sequence for permanent seed prostate brachytherapy postimplant assessment - Corrected Proof

David Bowes, Juanita Crook, Rasika Rajapakshe, Cynthia Araujo, Brent Parker — 2012-04-18

Abstract: Purpose: We describe a magnetic resonance (MR) scan sequence for prostate brachytherapy postimplant assessment.Methods and Materials: One brachytherapy team at the British Columbia Cancer Agency has incorporated MR–CT fusion into their permanent seed prostate brachytherapy quality assurance procedure. Several attempts were required to ensure that the diagnostic MR scanner at the adjoining general hospital performed the desired sequence, providing many examples of suboptimal scans and underlining the pitfalls for a center trying to incorporate the use of MR scanning into their brachytherapy program.Results: The recommended sequence (Fast Spin Echo T2-weighted, repetition time [TR]/echo time [TE] 4500/90, echo train length [ETL] 10, 20×20 field of view [FOV], 80 bandwidth [BW]) is associated with superior edge detection when compared with those images in which a typical diagnostic sequence was used. The use of a low bandwidth sequence does not compromise edge detection or seed identification when compared with a higher bandwidth.Conclusions: We have defined a magnetic resonance imaging sequence, which appears to optimize both prostate delineation and identification of seeds, lending itself to straightforward fusion with CT images and allowing for less uncertainty in permanent seed prostate brachytherapy quality assurance.

A phantom study to assess accuracy of needle identification in real-time planning of ultrasound-guided high-dose-rate prostate implants - Corrected Proof

2012-04-18

Abstract: Purpose: High-dose-rate brachytherapy of the prostate is commonly performed using transrectal ultrasound (US) guidance, with CT imaging used for needle reconstruction and treatment planning. Transrectal ultrasound images can, however, be used for the entire process, allowing treatment without changes in the patient position. This study assesses needle reconstruction accuracy using US images.Methods and Materials: Prostate phantoms were implanted with 10–18 needles. Three-dimensional US images were acquired, and needles were reconstructed using specialized software. A CT scan was also obtained. The image sets were registered and needle reconstruction errors were assessed. A dose plan was obtained using the US images and the dwell times were transferred to the CT reconstruction to obtain the true “delivered dose,” which was evaluated using standard dosimetric parameters.Results: Two sources of error were identified. First, reconstruction based on the bright echoes in the US images introduces a systematic error because these echoes correspond to the proximal wall of the needle, and not the center of the needle channel. If left uncorrected, this shift can lead to an underestimate of urethral doses. Second, incorrect needle tip identification can occur in the cranial–caudal direction. Errors up to 5.8mm were observed. A measurement of needle lengths protruding beyond the template can be used to compensate for this.Conclusions: Factors limiting the accuracy of US-based needle reconstruction have been identified. Once recognized, these errors can be corrected for, resulting in accurate implant geometry. This facilitates a treatment technique combining excellent anatomic definition, minimal prostate motion, and accurate dose planning and delivery.

Phase I/II trial of single-fraction high-dose-rate brachytherapy–boosted hypofractionated intensity-modulated radiation therapy for localized adenocarcinoma of the prostate - Corrected Proof

2012-04-05

Abstract: Purpose: A Phase I/II protocol was conducted to examine the toxicity and efficacy of the combination of intensity-modulated radiation therapy (IMRT) with a single-fraction high-dose-rate (HDR) brachytherapy implant.Methods and materials: From 2001 through 2006, 26 consecutive patients were treated on the trial. The primary objective was to demonstrate a high rate of completion without experiencing a treatment-limiting toxicity. Eligibility was limited to patients with T stage ≤2b, prostate-specific antigen (PSA) ≤20, and Gleason score ≤7. Treatment began with a single HDR fraction of 6Gy to the entire prostate and 9Gy to the peripheral zone, followed by IMRT optimized to deliver in 28 fractions with a normalized total dose of 70Gy. Patients received 50.4Gy to the pelvic lymph node. The prostate dose (IMRT and HDR) resulted in an average biologic equivalent dose >128Gy (α/β=3). Patients whose pretreatment PSA was ≥10ng/mL, Gleason score 7, or stage ≥T2b received short-term androgen ablation.Results: Median followup was 53 months (9–68 months). There were no biochemical failures by either the American Society of Therapeutic Radiology and Oncology or the Phoenix definitions. The median nadir PSA was 0.32ng/mL. All the 26 patients completed the treatment as prescribed. The rate of Grade 3 late genitourinary toxicity was 3.8% consisting of a urethral stricture. There was no other Grade 3 or 4 genitourinary or gastrointestinal toxicities.Conclusions: Single-fraction HDR-boosted IMRT is a safe effective method of dose escalation for localized prostate cancer.

Brachytherapy for prostate cancer does not influence long-term depression rate - Corrected Proof

2012-03-29

Abstract: Purpose: Current literature describes concern for an increase in depression owing to treatment of prostate cancer. Here, depression and coping up to 8 years posttreatment are described for patients treated with 125I brachytherapy for localized prostate cancer.Methods and Materials: Between December 2000 and June 2010, 132 patients received questionnaires at: baseline, 1 month, 6 months, 1 year, and 8 years posttreatment. The measures included the Center for Epidemiologic Studies Depression Scale (CES-D) and the Utrecht Coping List. Also general quality of life measures were used: the Short Form Health Survey (RAND-36), the European Organization for Research and Treatment of Cancer C30 questionnaire (EORTC QLQ-C30+3) and a prostate cancer specific questionnaire (EORTC-PR25). Descriptive statistics were performed and correlations among depression, coping, and general quality of life measures were investigated.Results: At baseline and all follow-up moments, approximately 10% of the patients had a CES-D score of 16 or more, indicating a clinically significant level of depressive symptoms. Depression did not seem to change in time. Active coping was the most predominant style of coping in problem situations. Coping strategy did not change in time. No relevant correlations were found between coping and depression. No significant associations were found between CES-D mean score and patient characteristics (medical and demographic). Relevant negative correlations were found between depression and HRQOL variables vitality, emotional functioning, and mental health (ρ>0.5).Conclusion: Prostate brachytherapy does not contribute to an increased risk of depression.

Tumor control, eye preservation, and visual outcomes of ruthenium plaque brachytherapy for choroidal melanoma - Corrected Proof

2012-03-22

Abstract: Purpose: To evaluate outcomes in patients with posterior choroidal melanoma treated with ruthenium (106Ru) brachytherapy.Methods and Materials: A retrospective single institutional analysis of 83 of 94 consecutive patients who underwent 106Ru brachytherapy was performed. Disease was mainly staged as small- and medium-sized nonmetastatic melanoma. The main parameters evaluated were tumor control (local control [LC] and progression-free survival [PFS]) and ocular preservation (enucleation-free survival [EFS]). Besides, functional evaluation was performed and complications were described.Results: The median follow-up was 39 (6–83) months. The median values of height and maximal basal diameter were 4.3 and 9.3mm, respectively. Median apical and basal doses were 100 and 307Gy, respectively. The actuarial 2-year LC, PFS, and EFS were 96.2%, 96.2%, and 95.5%, respectively. Actuarial 5-year LC, PFS, and EFS were 93.6%, 93.6%, and 84.1%, respectively. Preinsertion visual acuity (VA) maintenance was 34% (equal or better than before treatment). Approximately 56% of patients stayed with a minimum functional VA of 0.1 or more, from whom more than half stayed with 0.5 or more. Cataract was seen in 16% of treated eyes, and glaucoma was the rarest complication, with an incidence of 3%.Conclusions: Small- and medium-sized choroidal melanomas can be adequately treated with 106Ru brachytherapy, with high rates of tumor control and ocular preservation. Moreover, acceptable incidence of complications such as glaucoma and cataract are seen, and a reasonable part of patients stay with a minimum functional VA.

Evaluation of the visibility of a new thinner 125I radioactive source for permanent prostate brachytherapy - Corrected Proof

Gemma Roberts, Bashar Al-Qaisieh, Peter Bownes — 2012-03-21

Abstract: Purpose: The 125I source currently used for prostate brachytherapy at St. James’s Institute of Oncology is a standard size seed (≈4.5mm in length and 0.8mm in diameter). A new, thinner seed is under evaluation. This is designed to be implanted using narrower needles, potentially reducing edema and improving the dose distribution. This study investigated the visibility of the thinner source on multimodality images and compared it with that of standard size seeds.Methods and Materials: Images of dummy seeds of both thinner and standard size models were taken using ultrasound, fluoroscopy, computed tomography (CT), and magnetic resonance (MR) imaging. The ultrasound, fluoroscopy, and CT images were acquired with the seeds inserted into phantoms positioned in a water tank. The MR images were acquired using phantoms containing single seeds. The images were analyzed visually and quantitatively. The resolution of closely spaced seeds on CT images was investigated.Results: The visibility of both seeds was similar on ultrasound, fluoroscopy, and MR images. On CT images, the thinner seeds give reduced artifacts and better resolution.Conclusions: The use of the thinner seed would have minimal effect on ultrasound and fluoroscopy imaging during treatment. However on CT images, the use of the thinner seeds may improve seed identification for post-treatment dosimetry. Further study is required into the suitability of MR images alone for post-treatment dosimetry.

Brachytherapy catheter spacing and stabilization technique - Corrected Proof

2012-03-21

Abstract: Purpose/Objectives: To facilitate catheter spacing, implant stability, and patient comfort during multicatheter interstitial brachytherapy.Methods and Materials: Uniform and consistent spacing of multiple interstitial implant catheters can be difficult because individual catheters may become displaced during the course of treatment. The authors have developed a brachytherapy catheter fixation method using Jackson-Pratt (JP) drains that can be used within wounds to maintain catheter spacing or on the skin surface for applicator fixation. JP drains are threaded over the implant needles to space and stabilize the implant geometry. The needles are then replaced with the usual brachytherapy catheters.Results: Surgically directed (“open”) placement of implant catheters is less prone to displacement when a drain connects and spaces the catheters in the wound. Fixation on the skin surface can also be achieved with the JP drains, which make the friction buttons optional. The soft drain material helps avoid discomfort and pressure injury sometimes associated with hard plastic buttons. Small (10 French) round JP drains are suitable for breast, and head and neck sites and larger 7×10-mm flat JP drains for extremity sarcomas, abdominal, or thoracic tumors.Conclusions: The complex brachytherapy devices fashioned from widely available surgical drains effectively guide and maintain geometry for multicatheter interstitial implants. Stable implant geometry leads to more reliable implementation of brachytherapy dosimetry. Patient comfort is improved and soft tissue injury from hard-edged buttons is avoided.

Long-term outcome for very high-risk prostate cancer treated primarily with a triple modality approach to include permanent interstitial brachytherapy - Corrected Proof

2012-03-21

Abstract: Purpose: To evaluate outcome in the most unfavorable subset of high-risk prostate cancer patients treated with a combination of supplemental external beam radiation therapy (EBRT) and brachytherapy.Methods and Materials: Very high-risk prostate cancer was defined as follows: any Gleason score 10, Gleason score 8–9 with >50% of the biopsy cores positive for malignancy, Gleason score 8–9 with a prostate-specific antigen (PSA) >20ng/mL, any clinical stage T3, or any PSA >40ng/mL. One hundred thirty-one patients were identified who met the aforementioned criteria. The median followup was 6.6 years. One hundred twenty (91.6%) patients received supplemental EBRT and 100 (76.4%) received androgen deprivation therapy (median duration, 19.5 months; range, 4–36 months). The median postimplant day 0 D90 (i.e., the minimum percentage of the prescription dose that covers the planning target volume) was 121.9% of prescription dose. Multiple clinical treatment and dosimetric parameters were evaluated for impact on the evaluated survival parameters.Results: The median pretreatment PSA and Gleason score were 11.0ng/mL and 8. One hundred ten (84%) patients had a Gleason score ≥8. At 9 and 12 years, the cause-specific survival, biochemical progression-free survival, and overall survival were 91.0% and 86.5%, 87.3% and 87.3%, and 70.5% and 60.5%, respectively. The most common cause of death was heart disease (22.2%) with deaths from nonprostate cancer (12.7%) and prostate cancer (8.3%) being less likely.Conclusions: Permanent interstitial brachytherapy usually with supplemental EBRT and androgen deprivation therapy results in excellent biochemical control and cause-specific survival in the most unfavorable subset of high-risk prostate cancer patients. Death from diseases of the heart was more than twice as likely as death from prostate cancer.

Calculating prescription doses for new sources by biologically effective dose matching - Corrected Proof

2012-03-21

Abstract: Purpose: In current clinical practice, single isotopes, such as 125I or 103Pd, are used as single sources in prostate seed implants. A mixture of two radionuclides in the seeds has been proposed for prostate cancer treatment. This study investigates a method for determining the prescription dose for these new seeds using the biological effective dose (BED).Methods: Ten prostate cancer cases previously treated using single radionuclide seeds were selected for this study. The BED distribution for these cases was calculated. Plans using other radionuclides were then calculated based on this BED distribution. Prescription values could then be obtained for the calculated plans. The method was verified by calculating the prescription dose for 103Pd and 125I and comparing to clinical values. The method was then applied to a hybrid seed that consisted of a mixture of 125I and 103Pd radionuclides, which deliver equal dose to 1cm from the source in water (50/50D@1cm). A prescription BED value was also calculated.Results: A prescription BED of 110Gy was found to correlate to a prescription dose of 145, 120, and 137Gy for 125I, 103Pd, and 50/50D@1cm hybrid seeds, respectively.Conclusion: The method introduced in this article allows one to calculate the prescription dose for new and novel sources in brachytherapy. The method was verified by calculating a prescription dose for 125I and 103Pd radionuclides that coincides with values used clinically.

Prognostic importance of tobacco use in men receiving definitive prostate brachytherapy - Corrected Proof

2012-03-14

Abstract: Purpose: Several prominent publications have identified an overall association between tobacco use and an increased risk of disease recurrence and disease-specific mortality in prostate cancer patients. The authors explored whether tobacco use adversely impacts treatment outcomes in men treated with permanent interstitial brachytherapy.Methods and Materials: From April 1995 to August 2008, 2057 patients underwent brachytherapy by a single brachytherapist. Median follow-up was 7.5 years. The role of tobacco use as a prognostic factor for biochemical progression-free survival, cause-specific survival, and overall survival was investigated. Differences in survival between smokers and nonsmokers were compared using Kaplan–Meier curves and log-rank tests.Results: Current smokers presented with a lower body mass index (p<0.001), smaller prostate size (p=0.003), younger age (p<0.001), higher prostate-specific antigen level (p=0.002), a trend toward higher percentage biopsy core involvement (p=0.08), higher incidence of perineural invasion (p=0.015), and higher risk disease (p<0.001) than former or nonsmokers. There was no difference in biochemical progression-free survival (p=0.30) or cause-specific survival (p=0.72) at 10 years for smokers compared with nonsmokers. On univariate and multivariate analysis, tobacco use was an adverse risk factor for overall survival (p<0.001). There was no association between smoking and any prostate cancer-specific outcome.Conclusions: Smokers treated with brachytherapy have excellent outcomes and are at no higher risk of treatment failure than men who are nonsmokers.

The dosimetric impact of heterogeneity corrections in high-dose rate 192Ir brachytherapy for cervical cancer: Investigation of both conventional Point-A and volume-optimized plans - Corrected Proof

Daniel E. Hyer, Arshin Sheybani, Geraldine M. Jacobson, Yusung Kim — 2012-03-05

Abstract: Purpose: To evaluate the dosimetric impact of heterogeneity corrections on both conventional and volume-optimized high-dose rate (HDR) 192Ir brachytherapy tandem-and-ovoid treatment plans.Methods and Materials: Both conventional and volume-optimized treatment plans were retrospectively created using eight unique CT data sets. In the volume-optimized plans, the clinical target volume (CTV) and organs-at-risk (rectum, bladder, and sigmoid) were contoured on the CT data sets by a single physician. For each plan, dose calculations representing homogeneous water medium were performed using the Task Group (TG-43) formalism and dose calculations with heterogeneity corrections were performed using a commercially available treatment planning system.Results: For the conventional plans, the change in dose between TG-43 and heterogeneity-corrected calculations was assessed for the following points: Point-A (left and right) and International Commission on Radiation Units and Measurements (ICRU) 38 defined rectum and bladder points. It was found that the dose to the ICRU bladder decreased the most (−2.2±0.9%), whereas ICRU rectum (−1.7±0.8%), Point-A right (−1.1±0.4%), and Point-A left (−1.0±0.3%) also showed decreases with heterogeneity-corrected calculations. For the volume-optimized plans, the change in dose between TG-43 and heterogeneity-corrected calculations was assessed for the following dose–volume histogram parameters: D90 of the CTV and D2cc of the rectum, bladder, and sigmoid. It was found that D90 of the CTV decreased by −1.9±0.7% and D2cc decreased by −2.6±1.4%, −1.0±0.4%, and −2.0±0.6% for the rectum, bladder and sigmoid, respectively, with heterogeneity-corrected calculations.Conclusions: Heterogeneity corrections on high-dose rate plans were found to have only a small dosimetric impact over TG-43-based dose calculations for both conventional Point-A and volume-optimized plans.

Comparison of survival and regional failure between accelerated partial breast irradiation and whole breast irradiation - Corrected Proof

2012-03-02

Abstract: Purpose: To compare rates of regional recurrence (RR) and overall survival (OS) between a pooled set of 1400 patients treated on the American Society of Breast Surgeons MammoSite (Hologic, Inc., Bedford, MA) Registry Trial to a cohort of 3600 patients treated with whole breast irradiation (WBI).Methods and Materials: A total of 1440 women underwent accelerated partial breast irradiation (APBI) between 2002 and 2004 as part of the American Society of Breast Surgeons Registry Trial and a total of 3593 patients who received WBI were evaluated from the Surveillance Epidemiology and End Results database with treatment received between 1980 and 2009. A matched-pair analysis was performed based on age, receipt of hormonal therapy, chemotherapy, nodal status, and tumor size (1051 patients per arm). Rates of RR and OS were then analyzed for each group.Results: After the match, no differences in patient characteristics were noted when tumor size was evaluated as a continuous variable. Rates of RR and OS were similar between the WBI and APBI groups. A Cox regression model found no difference between WBI and APBI with regard to RR; however, OS was improved in the APBI cohort (hazard ratio 0.008, p<0.0001).Conclusions: With one of the largest patient populations to date comparing WBI and APBI, no difference in RR or OS was noted between WBI and APBI treatment. Until the publication of prospective Phase III trials, these data support the continued use of APBI on protocol and off protocol in appropriately selected patients.

Endobronchial brachytherapy provides excellent long-term control of recurrent granulation tissue after tracheal stenosis - Corrected Proof

2012-03-01

Abstract: Purpose: To review the experience of using endobronchial brachytherapy (EBB) as a treatment for recurrent tracheal granulation tissue.Methods and Materials: Patients referred for EBB at the Rabin Medical Center for benign stenosis were reviewed with institutional review board approval. Patients underwent bronchoscopic resection of granulation tissue followed by insertion of self-expanding metallic stents. After stenting, repeat laser resection was done at least 1 week before brachytherapy. After CT simulation, patients had three-dimensional brachytherapy treatment planning. A single 10-Gy dose was prescribed to 1.0cm from the source and treatment was delivered using high-dose-rate afterloader with 192Ir source. Patients were followedup with bronchoscopy every 3 months after the completion of therapy.Results: From November 2001 to January 2009, 29 patients were treated with EBB to prevent granulation tissue reformation. Median age was 70 years and 55% of patients were male. Ninety percent of patients were treated to the trachea and the remaining patients had stenoses in the main stem bronchi. The primary cause of stenosis was prolonged mechanical ventilation (76%). The median time from stent placement to brachytherapy was 69 days. Median active length of treatment was 7cm. With a median followup of 36 months, 66% (19 of 29) of patients remained free of granulation tissue. Forty-eight percent of patients have died, with all except 1 patient dying of their underlying condition. A single patient experienced death from tracheoesophageal fistula.Conclusion: EBB is an effective and safe treatment to prevent recurrent granulation tissue formation after endobronchial resection and should be considered in patients who are unable to undergo surgical resection.

External validation of the pretreatment nomogram to predict acute urinary retention after 125I prostate brachytherapy - Corrected Proof

2012-02-20

Abstract: Purpose: Acute urinary retention (AUR) after 125I prostate brachytherapy has a negative impact on quality of life. Recently, the authors developed a nomogram to predict the risk of AUR preoperatively. The aim of this study was to assess the external validity of the nomogram.Methods and Materials: The nomogram was initially developed on 714 patients treated with 125I prostate brachytherapy at the University Medical Center Utrecht, the Netherlands. Predictive factors included in the nomogram were prostate volume, international prostate symptom score, neoadjuvant hormonal treatment, and prostate protrusion. For external validation, the data of 715 consecutive patients treated between January 2003 and July 2008 at the Princess Margaret Hospital, Toronto, were used. The performance of the nomogram was evaluated by discrimination (ability to distinguish between patients who develop AUR yes or no) and calibration (agreement between observed and predicted numbers of AUR).Results: Of the 715 patients treated at the Princess Margaret Hospital, 67 patients (9.4%) developed AUR compared with 8.0% in the University Medical Center Utrecht cohort. In the validation data set, the discriminatory ability of the nomogram was good (receive operating characteristic area: 0.86; 95% confidence interval: 0.82–0.91), and comparable to the derivation data set (receive operating characteristic area: 0.82; 95% confidence interval: 0.77–0.88). Comparison between the predicted risks and the observed frequencies of AUR showed underestimation of the nomogram in the validation data set for high AUR risks values. Still, the negative predictive value for the risk of AUR, using a cutoff value of 5%, was high (98.1%).Conclusion: External validation of the nomogram shows adequate discrimination of patients with and without AUR. Therefore, the nomogram can aid in individualized treatment decision making.

Impact of MRI-based postimplant dosimetric assessment in prostate brachytherapy using contrast-enhanced T1-weighted images - Corrected Proof

2012-02-13

Abstract: Purpose: To compare contrast-enhanced T1-weighted (CE-T1WI) magnetic resonance imaging (MRI) with computed tomography (CT) for postimplant dosimetry and seed recognition in prostate brachytherapy.Methods and Materials: A total of 245 patients who received 125I prostate brachytherapy with or without external beam radiotherapy were enrolled. For postimplant analysis, CT and MRI scans were obtained at 1 month after seed implantation. For MRI-based dosimetry, T2-weighted images were fused with the CE-T1WI; the prostate was delineated on the T2-weighted images, and the seed detection was performed manually on the CE-T1WI. In CT-based dosimetry, the seed detection was essentially performed automatically. The dosimetric results obtained by MRI-based and CT-based dosimetry were compared.Results: The mean prostate D90 (the minimum dose received by 90% of the prostate volume) estimated by MRI-based and CT-based dosimetry were 113% and 115%, respectively, with no significant difference. The mean prostate V100 (the percent volume of the postimplant prostate receiving 100% of the prescribed dose) estimated by MRI-based and CT-based dosimetry were 95.2% and 95.8%, respectively, again with no significant difference. The mean prostate V150 (the percent volume of the postimplant prostate receiving 150% of the prescribed dose) estimated by MRI-based and CT-based dosimetry were 52.8% and 57.0%, respectively (p<0.01). In all of the 35 patients (14%) in whom the MRI-based V150 were at least 10% lower than the CT-based results, the seed detection by CT-based dosimetry was overestimated in highly seed-clustered areas or in the areas close to calcifications because of reconstruction artifacts in CT images.Conclusions: MRI-based dosimetry using CE-T1WI appears to be acceptable. Our results suggest that MRI-based dosimetry is a practical method for estimation of the higher dose distribution, especially if seeds are clustered together or when they are close to calcifications.

A survey of current clinical practice in permanent and temporary prostate brachytherapy: 2010 update - Corrected Proof

2012-02-13

Abstract: Purpose: To help establish patterns of care and standards of care of interstitial permanent low-dose-rate (LDR) and temporary high-dose-rate brachytherapy for prostate cancer and to compare the results with a similar 1998 American Brachytherapy Society (ABS) survey.Methods and Materials: A comprehensive questionnaire intended to survey specific details of current clinical brachytherapy practice was provided to the participants of the seventh ABS Prostate Brachytherapy School. Responses were tabulated and descriptive statistics are reported.Results: Sixty-five brachytherapy practitioners responded to the survey. Eighty-nine percent (89%) of respondents performed LDR and 49% perform high-dose-rate brachytherapy. The median number of years of experience for LDR brachytherapists increased from 5 to 10 years over the course of the 12 years since the preceding survey. Compared with the first ABS, a smaller proportion of respondents received formal brachytherapy residency training (43% vs. 56%) or formal “hands-on” brachytherapy training (15% vs. 63%). There has been a marked decline in the utilization of the Mick applicator (Mick Radio-Nuclear Instruments, Inc., Mount Vernon, NY, USA) (60% vs. 28%) and an increase in the use of stranded seeds (40% vs. 11%). Compliance with postimplant dosimetry was higher in the 2010 survey.Conclusion: This survey does suggest an evolution in the practice of LDR brachytherapy since 1998 and aids in identifying aspects that require further progress or investigation. ABS guidelines and other practice recommendations appear to impact the practice of brachytherapy.

Pacemaker/implantable cardioverter–defibrillator dose in balloon high-dose-rate brachytherapy for breast cancer treatment - Corrected Proof

Yongbok Kim, Youssef Arshoun, Mark G. Trombetta — 2012-02-13

Abstract: Purpose: To retrospectively report pacemaker (PM)/implantable cardioverter–defibrillator (ICD) dose in balloon high-dose-rate (HDR) brachytherapy and provide distance–dose graph and table to approximately estimate the maximal device dose.Methods and Materials: For 3 patients (A, B, and C), PM/ICD was retrospectively contoured on planning computed tomography images and its maximal dose was extracted from a dose–volume histogram. The surface of 1cm expansion from balloon was prescribed to 34Gy and the inverse square law was dominant factor in dose calculation. Therefore, the maximal PM/ICD dose was approximately estimated from the distance–dose graph or table and compared with that of the treatment plan.Results: The minimal device–balloon surface distance was 10.9, 18.4, and 4.3cm for patient A, B, and C, respectively. The maximal dose estimated from the proposed table/graph was 2.1 vs. 1.61Gy for patient A, 0.87 vs. 0.49Gy for patient B, and 8.9 vs. 9.14Gy for patient C compared with that from the treatment plan.Conclusions: Depending on the location of PM/ICD relative to the tumor bed, balloon HDR brachytherapy is feasible if the maximal dose is less than or equal to the dose limit. The proposed distance–dose graph and/or table enable to approximately predict the maximal device dose based on the measurement of minimal distance between lumpectomy and the device before balloon implantation for the suitability of balloon HDR brachytherapy.

Biopsy and implantation of the seminal vesicles - Corrected Proof

Nelson N. Stone, Vassilios M. Skouteris, Richard G. Stock — 2012-02-06

Abstract: Purpose: To describe the technique and outcomes of seminal vesicle biopsy (SVB) and permanent implantation in patients with T3b prostate cancer.Methods and Materials: Intermediate- and high-risk prostate cancer patients who elected brachytherapy as their treatment of choice were offered SVB for either Gleason score ≥7, prostate-specific antigen levels >10ng/mL, or clinical stage ≥T2b. Three cores were taken from both seminal vesicles at the base of the prostate using transrectal ultrasound. Patients with a positive SVB and either a negative pelvic lymph node dissection or pelvic computerized tomogram were treated with a combination of a partial implant followed by 45Gy of external beam irradiation therapy. During the seed implant, sources were positioned in the anterior wall of the seminal vesicles using intraoperative dosimetry to guide placement. Biochemical freedom from failure was determined using a definition of >0.2ng/mL. Survival was measured using the Kaplan–Meier and Cox proportions projections.Results: Of 526 patients who underwent SVB, 52 (9.9%) were positive for prostate cancer invasion. Clinical stage, prostate-specific antigen levels, and Gleason score were all predictive of a positive SVB (p<0.001). The 10-year biochemical freedom from failure was 64%. Cox regression demonstrated Gleason score (p=0.044) and biologic effective dose (p=0.013) as significant.Conclusions: Patients with pathologically confirmed seminal vesicle involvement of prostate cancer can be successfully identified and managed by a combined approach of permanent seed implantation to the prostate and seminal vesicles followed by external beam irradiation therapy. SVB should be encouraged in men with high-risk prostate cancer and aggressively treated when encountered.

Is there any advantage to three-dimensional planning for vaginal cuff brachytherapy? - Corrected Proof

Hyun Kim, Hayeon Kim, Christopher Houser, Sushil Beriwal — 2012-02-03

Abstract: Purpose: To evaluate whether the three-dimensional (3D) CT-based high-dose rate planning for vaginal cuff brachytherapy offers any advantage over the 2D orthogonal film-based library plans for adjuvant treatment of endometrial cancers.Methods and Materials: Eighty-four consecutive postoperative patients with endometrial cancers treated with vaginal brachytherapy as an adjuvant treatment were analyzed. Patients had CT imaging-based plans. Clinical target volume (CTV) was defined by expanding the upper 2.5cm of the cylinder by 5mm in all directions and editing to exclude any bladder and rectum. The dose prescribed was 7Gy with three fractions at 5mm depth with a goal of D90 ≥100% for CTV. All dosimetric parameters were compared with library-based plans.Results: Both the 2D- and 3D-based plans allowed sufficient dosage to the CTV (D90 for CTV ≥95%). The doses of 0.1, 1, and 2cc to rectum and bladder were significantly higher for 2D-based plans (p≤0.001 in each parameter). D2 cc with 2D plan for rectum and bladder was >100% (range: 103–116%) in 7 (8%) and 6 (7%) patients, respectively. In contrast, no patients had D2 cc >100% with 3D planning for both organs.Conclusion: Three-dimensional CT-based planning for high-dose rate vaginal cuff brachytherapy helps to decrease dose to critical organs without compromising coverage of CTV by customizing the dosimetry according to individual patient anatomy.

Radioactive seed migration after transperineal interstitial prostate brachytherapy and associated development of small-cell lung cancer - Corrected Proof

William C. Chen, Jerald Katcher, Carlos Nunez, Ali M. Tirgan, Rodney J. Ellis — 2012-01-16

Abstract: Purpose: We report a case of lung carcinoma developing in the location of a migrated prostate brachytherapy seed.Methods and Materials: A 57-year-old male nonsmoker was originally diagnosed with prostate adenocarcinoma Group IIB in October 1999. Treatment was completed at an outside local hospital and consisted of hormone suppression, pelvic external beam radiation, and transperineal interstitial permanent prostate brachytherapy with loose iodine-125 seeds.Results: The treatment was unremarkable for any complications, and immediate postimplant evaluation did not reveal any loose seeds. The patient remained clinically without evidence of disease and was asymptomatic until an isolated episode of hematuria in December 2009. Radiographic evaluation noted an incidental right lower lobe lung mass with a 4-mm hyperdensity slightly off-center. Biopsy confirmed Stage IB limited-stage small-cell lung cancer, and he underwent thoracic radiation with concurrent systemic chemotherapy. The mass remained mildly avid on a positron emission tomographic scan after treatment, and he underwent surgical evaluation with final pathology demonstrating no residual tumor but a metal rod-like implant consistent with a migrated radioactive brachytherapy seed.Conclusions: To our knowledge, this is the first case of a long-term adverse sequela seen in the location of a migrated brachytherapy seed. Although reported incidence of pulmonary seed emboli remains low with little measurable consequence on pulmonary function, we must appreciate that a theoretical risk for secondary malignancy remains not only locally within the periprostatic region but also at any site of seed migration.

Dosimetry comparison between TG-43 and Monte Carlo calculations using the Freiburg flap for skin high-dose-rate brachytherapy - Corrected Proof

2012-01-09

Abstract: Purpose: The purpose of this work was to evaluate whether the delivered dose to the skin surface and at the prescription depth when using a Freiburg flap applicator is in agreement with the one predicted by the treatment planning system (TPS) using the TG-43 dose-calculation formalism.Methods and Materials: Monte Carlo (MC) simulations and radiochromic film measurements have been performed to obtain dose distributions with the source located at the center of one of the spheres and between two spheres. Primary and scatter dose contributions were evaluated to understand the role played by the scatter component. A standard treatment plan was generated using MC- and TG-43-based TPS applying the superposition principle.Results: The MC model has been validated by performing additional simulations in the same conditions but transforming air and Freiburg flap materials into water to match TG-43 parameters. Both dose distributions differ less than 1%. Scatter defect compared with TG-43 data is up to 15% when the source is located at the center of the sphere and up to 25% when the source is between two spheres. Maximum deviations between TPS- and MC-based distributions are of 5%.Conclusions: The deviations in the TG-43-based dose distributions for a standard treatment plan with respect to the MC dose distribution calculated taking into account the composition and shape of the applicator and the surrounding air are lower than 5%. Therefore, this study supports the validity of the TPS used in clinical practice.

Reirradiation of paraaortic lymph node metastasis by brachytherapy with hyaluronate injection via paravertebral approach: With DVH comparison to IMRT - Corrected Proof

2011-12-30

Abstract: Purpose/Introduction: To safely irradiate retroperitoneal targets as paraaortic lymph node by separating abdominal at-risk organs from the target during irradiation, we created a percutaneous paravertebral approach of high-dose-rate brachytherapy with hyaluronate gel injection (HGI). We report a case treated with this technique.Methods and Materials: We encountered a patient with symptomatic regrowth of paraaortic lymph node metastasis from prostatic cancer. He had previously received 58.4Gy of radiotherapy to the same region 12 months prior. Brachytherapy needles and a HGI needle were deployed via the paravertebral approach under local anesthesia at our outpatient clinic.Results: A single dose of 22.5Gy (equivalent to 60.94Gy in 2Gy per fraction schedule calculated at α/β=10) was delivered to the target, with preservation of the surrounding small intestine by HGI with D2cc (minimum dose to the most irradiated volume of 2mL) of 5.05Gy. Therapeutic ratio was 3.64 times higher for this brachytherapy plan compared with an intensity-modulated radiation therapy plan. At followup at 1 year after brachytherapy, the symptoms had disappeared, tumor size had reduced with no fluorodeoxyglucose accumulation, and prostate-specific antigen level had decreased.Conclusion: We consider that high-dose-rate brachytherapy with the HGI procedure offers effective treatment even in this type of reirradiation situation.

Comparison of prostate volume, shape, and contouring variability determined from preimplant magnetic resonance and transrectal ultrasound images - Corrected Proof

2011-12-26

Abstract: Purpose: To compare preimplant prostate contours and contouring variability between magnetic resonance (MR) and transrectal ultrasound images.Methods and Materials: Twenty-three patients were imaged using ultrasound (US) and MR before permanent brachytherapy treatment. Images were anonymized, randomized, and duplicated, and the prostate was independently delineated by five radiation oncologists. Contours were compared in terms of volume, dimensions, posterior rectal indentation, and observer variability. The Jaccard index quantified spatial overlap between contours from duplicated images.Results: The mean US/MR volume ratio was 0.99±0.08 (p=0.5). The width, height, and length ratios for the prostate were 0.98±0.06 (p=0.09), 0.99±0.08 (p=0.4), and 1.05±0.14 (p=0.1). Rectal indentation was larger on US by 0.18mL (p=0.01) and correlated with prostate volume (p<0.01). MR and US interobserver variability in volume were similar at 3.5±1.7 and 3.3±1.9mL (p=0.6). Intraobserver variability was smaller on US at 1.4±1.1mL compared with MR at 2.4±2.2mL (p=0.01). Local intraobserver variability was lower on US at the midgland slice (p<0.01) but lower on MR at the base (p<0.01) and apex (p<0.01) slices.Conclusions: US is comparable to MR for preimplant prostate delineation, with no significant difference in volume and dimensions. Rectal indentation because of the transrectal ultrasound probe was measurable, although the effects were small. Intraobserver variability was lower on US for the prostate volume but was lower on MR locally at the base and apex. However, the difference was not observed for the interobserver variability, which was similar between MR and US.

Initial clinical experience with multilumen brachytherapy catheters for accelerated partial breast irradiation - Corrected Proof

2011-12-23

Abstract: Purpose: To review the initial experience of three institutions using multilumen catheters to deliver accelerated partial breast irradiation (APBI) and evaluate dosimetric improvements.Methods and materials: Patients were eligible for this analysis if they met criteria for accelerated partial breast irradiation at their respective institution and were not enrolled on the national Phase III trial. Minimum guidelines for treatment planning from the National Surgical Adjuvant Breast and Bowel Project B-39/Radiation Therapy Oncology Group 0413 protocol were followed. Toxicities were coded using common toxicity criteria version 3.0 criteria.Results: Sixty-two patients were analyzed as part of this study. Median skin spacing was 11mm with a median skin dose of 86.9% (% of prescription dose [PD]). Median rib dose was 76.1% of the PD (range, 4.3–155.7%). The V90, V95, and V100 of the PD for the planning target volume evaluation was 95.4%, 95.2%, and 80.3%, respectively. Seven patients had both skin and rib spacing <7mm, with the median skin dose and rib dose being 113.4% and 130.9% of the PD. For these cases, the median V90, V95, and V100 of the PD was 99.2%, 94.3%, and 81.1%, respectively, whereas the median V150 and V200 were 22.5cc and 7.4cc. Overall, Grade I and II radiation dermatitis were noted in 41.9% and 6.5% of patients.Conclusion: The multilumen device led to improvements in target coverage and normal structure doses compared with traditionally accepted guidelines. Similar toxicities were seen compared with single-lumen devices, even in patients with skin and rib spacing <7mm.

A comparison of the impact of isotope (125I vs. 103Pd) on toxicity and biochemical outcome after interstitial brachytherapy and external beam radiation therapy for clinically localized prostate cancer - Corrected Proof

2011-12-23

Abstract: Purpose: To compare biochemical outcomes and morbidity associated with iodine-125 (125I) and palladium-103 (103Pd) brachytherapy as part of combined modality therapy for clinically localized prostate cancer.Methods and materials: Between October 2002 and December 2008, 259 patients underwent prostate brachytherapy (125I prescription dose, 110Gy: n=199; 103Pd prescription dose, 100Gy: n=60) followed by external beam radiotherapy (median dose, 50.4Gy). Eighty-seven patients also received neoadjuvant androgen deprivation therapy. Toxicities were recorded with CTCAE v 3.0, International Prostate Symptoms Score (IPSS), and International Index of Erectile Function questionnaires.Results: Overall, acute Grade ≥2 genitourinary toxicity occurred in 21% and 30% of patients treated with 125I and 103Pd, respectively (p=0.16). There were no significant differences in IPSS change or urinary quality-of-life scores between the isotopes at 4, 6, or 12 months (p=0.20, 0.21, and 1.0, respectively). IPSS resolution occurred at a median of 11 and 6 months for 125I and 103Pd patients, respectively (p=0.03). On multivariate analysis, only the use of neoadjuvant androgen deprivation therapy was predictive of time to IPSS resolution (p=0.046). Late Grade ≥2 gastrointestinal toxicity occurred in 7% of 125I patients and 6% of patients treated with 103Pd. Of 129 potent patients at baseline, there was better erectile function in patients who received 103Pd (p=0.02); however, the followup was shorter for these patients. The 5-year prostate-specific antigen relapse-free survival for 125I and 103Pd patients was 95.2% and 98.2% (p=0.73), respectively.Conclusion: There were no differences in acute or long-term genitourinary or gastrointestinal toxicity between 125I and 103Pd in combined modality therapy for prostate cancer. There may be less erectile toxicity with the use of 103Pd; however, additional followup of these patients is needed. There was no significant difference in 5-year prostate-specific antigen relapse-free survival between 103Pd and 125I.

Prostate brachytherapy seed migration to a left varicocele - Corrected Proof

2011-12-23

Abstract: Purpose: To report a rare case of seed migration to a left varicocele after transperineal interstitial prostate brachytherapy with loose iodine-125 (125I) seeds.Methods and Materials: A 73-year-old man presented with a serum prostate-specific antigen level of 5.21ng/mL, Gleason score of 7 (3+4), and clinical T1c adenocarcinoma of the prostate. The patient underwent transperineal interstitial prostate brachytherapy with loose 125I seeds followed by external beam radiation therapy. Two weeks after seed implantation, a followup pelvic radiograph was obtained. One month after seed implantation, a pelvic computed tomography scan for postimplant dosimetric analysis was carried out. Subsequent ultrasound examination of the scrotum was undertaken.Results: Two weeks after seed implantation, an anteroposterior pelvic radiograph showed that a migrated seed was overlapped by the scrotum. Postimplant pelvic computed tomography revealed that a seed had migrated to the left side of the scrotum. Subsequent ultrasound examination of the scrotum revealed that the patient had a left varicocele to which the seed had migrated. The patient had no symptoms related to the migrated seed.Conclusions: This is the first report of seed migration to a left varicocele after transperineal interstitial prostate brachytherapy with loose 125I seeds. For the present case, we suggest that the seed moved from the prostate to the left varicocele through the pelvic veins, bypassing the systemic circulation.

Is prostate-specific antigen percentage decrease predictive of clinical outcome after permanent iodine-125 interstitial brachytherapy for prostate cancer? - Corrected Proof

2011-12-05

Abstract: Objective: To determine the usefulness of prostate-specific antigen (PSA) percentage (vs. pretreatment value assumed as 100%) in prediction of biochemical relapse, after iodine-125 (125I) permanent brachytherapy for prostate cancer, to employ a parameter independent by the initial PSA amount and by the individual prostatic volume.Methods and materials: Our study included 133 patients, 102 still disease free (Group A) and 31 who experienced proven biochemical recurrence (Group B). PSA levels before and after 125I brachytherapy were recorded, and PSA percentage vs. pretreatment values were calculated. Cox regression model, receiver operating characteristic curves, and Kaplan–Meier regression model with log-rank test were calculated.Results: We observed that, in patients submitted to brachytherapy for prostate cancer, a PSA percentage >20% of pretreatment value is highly associated with relapse risk (p<0.0001) and that this association is strongly present since t=6 months of followup (p<0.0001), with a hazard ratio near to five times (4.965), a sensitivity of 72.4%, and specificity of 79.8% related to the chosen cutoff.Discussion: Despite the amount of PSA is the only parameter that the clinicians can deploy to monitor patient’s followup after permanent interstitial brachytherapy for prostate cancer, its evolution in time seems unable to predict early biochemical relapse as it is influenced by prostatic volume and initial PSA amount.Conclusions: Our data suggest that a PSA percentage >20% of pretreatment value at 6 months might represent an early, inexpensive, and useful predictive tool of bad outcome in patients after permanent brachytherapy.

Experimental characterization of the dosimetric properties of a newly designed I-Seed model AgX100 125I interstitial brachytherapy source - Corrected Proof

Zhe Chen, Paul Bongiorni, Ravinder Nath — 2011-11-21

Abstract: Purpose: To measure the dosimetric properties of the Model AgX100 125I source for interstitial brachytherapy.Methods and Materials: The photon energy spectrum emitted by the AgX100 source was measured using a high-resolution germanium spectrometer customized for low-energy brachytherapy source spectrometry. The dose distribution around the source was measured using the 1×1×1mm3 lithium fluoride thermoluminescent dosimeters in water-equivalent solid phantoms. The dosimetric parameters needed for dose calculation using the American Association of Physicists in Medicine Task Group No. 43 (TG-43) formalism were determined and compared with the results of a Monte Carlo simulation by an independent research group and with the TG-43 consensus values of the well-established model 6711 source.Results: It was found that (1) the photon energy spectrum emitted by the AgX100 source was nearly identical to that emitted by the model 6711, (2) the dose-rate constant determined by the photon spectrometry technique (0.957±0.037cGy·h−1·U−1) and by the thermoluminescent dosimeter technique (0.995±0.066cGy·h−1·U−1) was within 1.5% of the corresponding values determined for the model 6711 source, and (3) the radial dose function and the anisotropy function of the AgX100 source were also found to be similar to the consensus data established for the model 6711 source in the TG-43 update report.Conclusions: A comprehensive dosimetric characterization has been carried out for the model AgX100 125I source. The American Association of Physicists in Medicine TG-43 dosimetry parameters for this source has been determined from the experimental data.

Tumor bed-to-skin distance using accelerated partial-breast irradiation with the strut-adjusted volume implant device - Corrected Proof

2011-11-21

Abstract: Purpose: Because of the risk of skin toxicity with single dwell position, single-lumen brachytherapy devices are sometimes contraindicated for tumor cavities 5–7mm from the skin surface. We discuss the use of multicatheter device to treat patients with tumor bed-to-skin distances <7mm.Methods and Materials: We treated 117 patients with accelerated partial-breast irradiation brachytherapy: 77 single-lumen and 40 multicatheter devices. A subset of 12 patients treated with SAVI® had bed-to-skin spacing <7mm. All patients had Tis-2N0 ductal carcinoma with negative margins. A total dose of 34.0Gy in 10 fractions was delivered twice daily. Planning target volume was created using computed tomography–based three-dimensional planning with a 1.0-cm expansion of the lumpectomy cavity. Skin dose was measured dosimetrically, with skin constraints <125% of the prescription. Toxicities were graded, and patients were assessed at various intervals.Results: Of the patients treated with the multicatheter device, 0% (0/12) had their device pulled. At 2 weeks after treatment, fewer than 50% of the patients had skin toxicities of Grades 1–2, all of which resolved by 6 months. The cosmetic outcome was good to excellent at followup.Conclusions: Multicatheter devices permit well-tolerated accelerated partial-breast irradiation in patients with tumor cavities near the skin surface for which the single-lumen device may not be appropriate.

Image-guided vulvovaginal interstitial brachytherapy in the treatment of primary and recurrent gynecological malignancies - Corrected Proof

2011-10-13

Abstract: Purpose: Evaluation of interstitial high-dose-rate brachytherapy (HDRB) to the vulvovaginal region both alone and in combination with external beam radiotherapy (EBRT) for primary or recurrent gynecological malignancy.Methods and Materials: From 1998 to 2009, 37 women with a mean age of 68 years were treated with transperineal interstitial HDRB. Fifteen patients (40.5%) were treated for primary disease, whereas 22 (59.5%) patients were treated for recurrent disease. Median time to local recurrence was 31 months (2–312 months). Primary sites included endometrium (12), vulva (11), vagina (10), vulvovagina (1), cervix (1), and bladder (2). Thirty-one patients (83.7%) in this series were treated with radical intent, whereas 6 (16.3%) were treated with palliative intent. Radically treated patients received between 45 and 60Gy (median, 45Gy) of EBRT. The median number of days from EBRT to HDR boost was 5 days (1–35 days). The HDRB doses ranged from 11Gy in two fractions to 42Gy in six fractions (dose per fraction varied from 4 to 8.5Gy) and fractions were given at least 6–8h apart.Results: Eight of the 31 patients (26%) treated with radical intent relapsed locally. Eleven of 37 patients (30%) treated with either radical or palliative intent recurred locally. The 2- and 5-year local progression-free survival was 74% and 63.4%, respectively. The total progression-free survival, which includes local, locoregional/nodal, and distant recurrence, at 2 and 5 years, was 73.6% and 45.6%, respectively. With a mean follow-up of 27 months (3.8–111.9 months), the median survival for the patient group was 16.6 months with a 2- and 5-year overall survival of 47.7% and 36.4%, respectively. Acute Grade 3 toxicity was seen in 13 (35%) of the 37 patients (skin: 10, urinary: 2, genital: 2, gastrointestinal: 0). No acute Grade 4 toxicities were seen. A total of 10 of the 37 patients (27%) developed late Grade 3 toxicities. Five of the 22 patients (22%) treated for recurrent disease with radical intent developed Grade 3 toxicity (skin: 4, urinary: 2, genital: 1, radiation-induced fracture of acetabulum: 1, and gastrointestinal: 0), whereas 1 of the 6 patients treated with palliative intent had Grade 3 toxicity affecting skin. No late Grade 4 toxicities were seen.Conclusion: This retrospective series suggests that interstitial perineal HDRB is a safe and effective treatment option for primary or locally recurrent gynecological malignancies. It is a valuable option in patients who have received previous EBRT to the pelvis, achieving good local control with acceptable late treatment-related side effects.

A comparison of the biological effective dose of 50-kV electronic brachytherapy with 192Ir high-dose-rate brachytherapy for vaginal cuff irradiation - Corrected Proof

2011-10-13

Abstract: Purpose: Advantages for electronic brachytherapy (EBT) of the vaginal cuff include decreased physical dose to the bladder and rectum. Here we compare 192Ir with EBT using biological effective dose (BED) to account for the different radiobiological effectiveness (RBE) predicted for low-energy x-rays.Methods and Materials: Fifteen data sets from five consecutive postoperative endometrial cancer patients treated with EBT were analyzed. Treatment planning was performed using PLATO software. The dose was prescribed as 21Gy in three fractions to a depth of 0.5cm. Physical dose, BED3, and BED10 were evaluated for the mucosa, bladder, and rectum. An RBE value of 1.5 was used for BED calculations.Results: Mucosal physical dose is 28.4% greater with EBT (36.6 vs. 28.5Gy, p<0.05). However, the BED10 is increased by 79.1% (55.6 vs. 99.6Gy, p<0.05) and the BED3 by 71.5% (118.8 vs. 203.7Gy, p<0.05). The physical dose (dose to 50% volume of the organ) to the bladder (9.3 vs. 6.6Gy, p<0.05) and rectum (7.2 vs. 4.2Gy, p<0.05) are reduced with EBT. BED3 to the rectum and bladder are also reduced but to a lesser extent (13 vs. 8.3Gy, p<0.05; 18.9 vs. 14.7Gy, p=0.06, respectively).Conclusions: BED takes into account the higher RBE of low-energy photons generated with EBT and provides a more accurate estimate of the biological effect. When using EBT, physical dose may underestimate the biological effect on the vaginal mucosa and overestimate the benefit for the bladder and rectum. Dose adjustment for EBT based on BED should be considered.

Quantitative evaluation of lower urinary tract symptoms using a visual analog scale in men undergoing permanent brachytherapy - Corrected Proof

2011-10-13

Abstract: Purpose: A previous study showed that a visual analog scale (VAS) that measures quality of life (QOL) in relation to each of the seven items on the International Prostate Symptom Score (IPSS) was found to be significantly more able to identify a patient’s chief complaint. The aim of this study was to assess the two questionnaires with special reference to the symptom that the patient most wants treated via the concomitant use of the IPSS and VAS after permanent brachytherapy (PBT).Methods and Materials: A total of 156 men undergoing PBT were enrolled. The IPSS and VAS were evaluated at the preimplantation stage and at 1–3 months, 6–9 months, and 1 year after PBT. The correlations between the IPSS-QOL score and the total for the 14 symptoms questions included in the IPSS and VAS were statistically calculated. Multivariate analysis was used to investigate which factors could be used to predict the IPSS-QOL after PBT.Results: The correlation coefficients between the IPSS-QOL score and the seven questions on the VAS were higher than those between the IPSS-QOL and the seven questions on the IPSS. Multivariate analysis showed that the strongest factor for determining IPSS-QOL at each time point was nocturia on the VAS.Conclusions: The VAS scale reflected the change in the patients’ QOL more precisely than the IPSS, which examines the frequency of lower urinary tract symptoms. Nocturia plays a key role in determining QOL. VAS could be a promising tool for assessing satisfaction in patients with lower urinary tract symptoms after PBT.

Semiautomatic segmentation for prostate brachytherapy: Dosimetric evaluation - Corrected Proof

2011-09-26

Abstract: Purpose: To demonstrate that manual prostate segmentation in transrectal ultrasound images can be replaced with semiautomatic segmentation.Methods and Materials: Semiautomatic segmentation using a tapered ellipsoid model was applied to transrectal ultrasound images. Region-based volumetric evaluation was performed between original and physician-reviewed semiautomatic contours. For dosimetric assessment, treatment plans generated on semiautomatic contours were overlaid on physician-reviewed semiautomatic contours and dose parameters were computed. To establish a threshold for the acceptable amount of dosimetric degradation below which the adoption of semiautomatic planning is unacceptable, the range of variability in dosimetric quality attributed to manual variability was obtained and compared with that of semiautomatic contours.Results: An average volume error (1—Dice similarity coefficient) of less than 7% between semiautomatic and manual volumes (140 cases) was obtained. The difference between the mean V100 of plans created for semiautomatic contours then overlaid on physician-reviewed semiautomatic contours and the original V100 values, that is, before overlaying on the physician-reviewed contours (41 cases) was lower than 5%. An average total duration of 2–4min, which includes algorithm initialization, 11.67±3.57s algorithm time, and contour modification is required per case. This algorithm is being used at the British Columbia Cancer Agency and to this date has been applied for the treatment of more than 600 patients.Conclusions: In terms of volumetric and dosimetric accuracy, the proposed algorithm is a suitable replacement for manual segmentation in the context of our planning technique. The benefits are shorter segmentation times; greater consistency; less reliance on user experience; and smooth, symmetric contours.

Urethra low-dose tunnels: Validation of and class solution for generating urethra-sparing dose plans using inverse planning simulated annealing for prostate high-dose-rate brachytherapy - Corrected Proof

2011-09-22

Abstract: Purpose: Urethral dose is related to severity of genitourinary toxicity in patients treated with brachytherapy for prostate cancer. This work describes a dose planning method that uses inverse planning to create a low-dose tunnel around the urethra and presents a class solution to achieve this additional dose sparing of the urethra.Methods: Fifteen patients on the Radiation Therapy Oncology Group (RTOG) 0321 protocol were treated for prostate cancer with a high-dose-rate brachytherapy dose boost to an external beam radiation treatment regimen. All were treated with 9.5Gy for each of the two fractions after 45Gy of the external beam radiation. The inverse-planning algorithm, inverse planning simulated annealing (IPSA), was used to create both the standard RTOG protocol (SRP) plan for treatment and the a posteriori urethra dose sparing (UDS) plan consisting of a dose tunnel along the urethra. Both plans maintained the protocol parameters: prostate V100 (volume receiving 100% of prescribed dose)>90% and bladder and rectum V75<1 cm3. In the SRP plans, the urethra surface was optimized to receive <125% of the prescription dose and in the UDS plans <100%. Dose-volume histograms for the clinical treatment volume, bladder, rectum, penile bulb, and urethra for both plans are compared using a paired sample t test with significance claimed for probability values<0.05.Results: UDS planning reduced the urethra V100 from 88% to 58% on average (p<0.01) and the V125 from 3.3% to 0.2% (p < 0.01). Bladder and rectum V75 were maintained at <1 cm3 and not significantly different between plans. Prostate coverage was maintained per protocol at V100>90%, with mean for the SRP V100=93% versus UDS plan V100=90%. Prostate D90 for SRP was 104% versus UDS plan D90=101%. For all patients, the UDS achieved a dose tunnel surrounding the length of the intraprostatic urethra. The class solution for generating UDS is presented.Conclusions: A urethral sparing–focused planning solution using IPSA reduces mean urethral dose by 34%, as compared with IPSA-generated plans based on the RTOG 0321 protocol. This is done while maintaining prostate coverage and critical structure dose. This technique can be applied to all patients in whom urethra toxicity is of particular concern.

Two-step transurethral surgery of the prostate and permanent implant brachytherapy for patients with lower urinary tract symptoms and low- to intermediate-risk prostate cancer - Corrected Proof

2011-09-22

Abstract: Purpose: Prostate brachytherapy is an increasingly used treatment option for low- to intermediate-risk prostate cancer (PCa). However, patients with preexisting lower urinary tract symptoms (LUTS) and PCa, who would otherwise be good brachytherapy candidates, are often contraindicated because of the risk of postoperative urinary morbidity. We report our clinical experience with limited transurethral resection of the prostate (LTURP) and/or transurethral incision of the prostate (TUIP) months before brachytherapy to treat patients with LUTS and low- to intermediate-risk PCa.Methods and Materials: Of 258 men undergoing prostate brachytherapy at our institution between 1998 and 2011, 42 were treated with planned LTURP and/or TUIP well before (mean, 5.7 months) seed implantation. Transurethral surgery was considered before brachytherapy for patients who at presentation required α-blocker therapy for LUTS, had an International Prostate Symptom Score greater than 14 off α-blockers, or had an elevated postvoid residual (>100mL). Patients only proceeded to brachytherapy once LUTS resolved.Results: All 42 patients in our series underwent TUIP (25), LTURP (7), or TUIP/LTURP (10) with mean 5.7 months before prostate brachytherapy for low- or intermediate-risk PCa. Mean International Prostate Symptom Score, peak flow rate, and postvoid residual significantly improved after transurethral surgery, and improvement persisted at the latest followup. No patient developed retention, urethral necrosis, or urinary incontinence after transurethral surgery or brachytherapy (median followup, 39 months and range, 1–121).Conclusions: Planned LTURP and/or TUIP more than 4 months before brachytherapy is a safe and effective treatment strategy for men with LUTS and low- to intermediate-risk PCa.

Three-year clinical outcome using the Contura multilumen balloon breast brachytherapy catheter to deliver accelerated partial breast irradiation (APBI): Improving radiation standards for the optimal application of APBI - Corrected Proof

2011-09-19

Abstract: Purpose: We reviewed our institution’s 3-year clinical experience in treating patients with the Contura multilumen balloon (SenoRx, Inc., Aliso Viejo, CA) breast brachytherapy catheter to deliver accelerated partial breast irradiation (APBI).Methods and Materials: Forty-six patients treated with breast-conserving therapy received adjuvant radiation using the Contura catheter (34Gy in 3.4Gy fractions). Fourteen patients had Stage 0, 24 had Stage I, and 8 had Stage II breast cancer. Median follow-up was 36 months (range, 1–44 months).Results: Only one local recurrence developed (2%). The rate of persistent seroma formation at latest reported follow-up was 4.3% (2 patients) and the incidence of any clinically detectable telengiectasias was 2.2%. No major toxicities (0% Grade III) have occurred. The median skin dose (% of the prescribed dose) was 99.7. The median dose to 95% of the planning target volume for evaluation was 98.8%. The percentage of patients with excellent/good cosmetic results at 24 (n=23) and 36 (n=22) months was 100% and 97%, respectively.Conclusion: Adjuvant APBI using the Contura multilumen balloon catheter exhibited similar locoregional control, cosmesis, and toxicities to other forms of APBI with similar lengths of follow-up. In addition, improved radiation standards for the delivery of APBI were demonstrated.

Predicting biochemical tumor control after brachytherapy for clinically localized prostate cancer: The Memorial Sloan-Kettering Cancer Center experience - Corrected Proof

2011-09-19

Abstract: Purpose: To identify predictors of biochemical tumor control and present an updated prognostic nomogram for patients with clinically localized prostate cancer treated with brachytherapy.Methods and Materials: One thousand four hundred sixty-six patients with clinically localized prostate cancer were treated with brachytherapy alone or along with supplemental conformal radiotherapy. Nine hundred one patients (61%) were treated with Iodine-125 (125I) monotherapy to a prescribed dose of 144Gy, and 41 (4.5%) were treated with Palladium-103 (103Pd) monotherapy to a prescribed dose of 125Gy. In patients with higher risk features (n=715), a combined modality approach was used, which comprised 125I or 103Pd seed implantation or Iridium-192 high–dose rate brachytherapy followed 1–2 months later by supplemental intensity-modulated image-guided radiotherapy to the prostate.Results: The 5-year prostate-specific antigen relapse-free survival (PSA-RFS) outcomes for favorable-, intermediate-, and high-risk patients were 98%, 95%, and 80%, respectively (p<0.001). Multivariate Cox regression analysis identified Gleason score (p<0.001) and pretreatment PSA (p=0.04) as predictors for PSA tumor control. In this cohort of patients, the use of neoadjuvant and concurrent androgen deprivation therapy did not influence biochemical tumor control outcomes. In the subset of patients treated with 125I monotherapy, D90>140Gy compared with lower doses was associated with improved PSA-RFS. A nomogram predicting PSA-RFS was developed based on these predictors and had a concordance index of 0.70.Conclusions: Results with brachytherapy for all treatment groups were excellent. D90 higher than 140Gy was associated with improved biochemical tumor control compared with lower doses. Androgen deprivation therapy use did not impact on tumor control outcomes in these patients.

Timing of postseed imaging influences rectal dose–volume parameters for cesium-131 prostate seed implants - Corrected Proof

2011-08-25

Abstract: Purpose: To study the influence of timing of postseed implant imaging on rectal dose–volume parameters for cesium-131 (131Cs) seed prostate implants.Methods and Materials: Fifteen patients were treated in our institution with combination 131Cs brachytherapy followed by pelvic external beam radiation therapy for intermediate to high-risk prostate cancers. For all patients, CT scans were scheduled at 7 days (CT7) and again at 2 months for external beam radiation therapy simulation purpose (CT60) postseed implantation. Comprehensive postseed implant dosimetry was performed for both CT7 and CT60 scans. In each case, dose–volume histogram parameters, rectal separation (the distance between the center of posterior most seed and most anterior rectal wall), and posterior row activity (the total activity implanted within 2–4mm anterior to the posterior wall of the prostate) data were collected. The absolute rectal volumes receiving 100% and 110% prescription dose were also collected.Results: Rectal dose correlated strongly with rectal separation (p<0.001). The mean change in rectal separation between CT7 and CT60 scans was 1.1 (±1.7) mm, and the corresponding change in 0.1-cc rectal dose was 18 (±26.5) Gy. Posterior row activity did not correlate with rectal dose (p=0.51). The mean volume of rectum that receives between 100% and 110% of the prescription dose (RV100 and RV110) increased twofold, between CT7 and CT60 evaluations (0.03 [±0.06] cc vs. 0.07 (±0.05) cc, respectively, p=0.06).Conclusions: Our study has demonstrated that rectal doses after 131Cs seed implants are influenced by the timing of postseed imaging. This may be a consequence of prostatic and periprostatic edema resolution.

Interfraction accumulation of seroma during accelerated partial breast irradiation: Preliminary results of a prospective study - Corrected Proof

2011-08-08

Abstract: Purpose: To quantify and characterize the process of seroma accumulation during accelerated partial breast irradiation using multicatheter balloon brachytherapy.Materials and Methods: Twenty-two patients were treated using the Contura Multilumen brachytherapy catheter to a dose of 34Gy in 10 fractions over 5 treatment days. Serial aspirations of the vacuum port of the catheter were performed at the time of CT simulation and before each treatment. Volume and characteristics of fluid drawn were recorded. Univariate analysis was performed to evaluate various factors predictive of seroma formation.Results: Median patient age was 59.5 years, body mass index was 31, and volume of surgical specimen was 62.4cm3. Median time from breast conservation surgery to placement of Contura catheter was 18.5 days. Pericatheter seroma, typically scant with a median volume of 0.75mL, was noted in 91% of patients at CT simulation. A total of 203 aspirations were performed with a median-aspirated seroma volume of 4.05mL. There was no significant correlation between the volume of seroma and histology (invasive vs. in situ), quadrant of location, body mass index, reexcision or reoperation, days from breast conservation surgery to balloon placement, or the volume of specimen removed. Radiation treatment factors, including balloon volume, balloon to skin distance, and planning target volume evaluation, also did not correlate with aspirated seroma.Conclusions: Interfraction seroma accumulation has a variable pattern of development with no discernible predictors of occurrence. Routine pretreatment aspirations via vacuum port may potentially improve dosimetric reproducibility for a minority of patients.

Objective automated assessment of time trends in prostate edema after 125I implantation - Corrected Proof

2011-08-04

Abstract: Purpose: To present an objective automated method to determine time trends in prostatic edema resulting from iodine-125 brachytherapy.Methods and Materials: We followed 20 patients, implanted with stranded seeds, with seven consecutive CT scans to establish a time trend in prostate edema. Seed positions were obtained automatically from the CT series. The change in seed positions was used as surrogate for edema. Two approaches were applied to model changes in volume. (1) A cylindrical model: seeds from the compared distribution were linked to the reference distribution of Day 28. After alignment, the compared distribution was scaled in cylindrical coordinates, leading to the changes in radial and craniocaudal directions. The volume changes were calculated using these scaling factors. (2) A spherical model: distances of seeds to the center of gravity of all seeds were used as a measure to model volume changes.Results: With Day 28 as reference, the observed volume changes were smaller than 18% ± 6% (1 standard deviation) for the cylindrical model and 12% ± 7% for the spherical model. One day after implantation, the implanted prostate was less than 10% larger than in the reference scan for both models. Apart from Day 0, both models showed similar volume changes.Conclusions: We present an objective automated method to determine changes in the implanted prostate volume, eliminating the influence of an observer in the assessment of the prostate size. The implanted volume change was less than 18% ± 7% for the studied group of 20 patients. Edema was 9% ± 5% from 1 day after implantation onward.

Experimental measurements and Monte Carlo simulations of dose perturbation around a nonradioactive brachytherapy seed due to 6- and 18-MV photons - Corrected Proof

James Paul Steinman, Mohammad Bakhtiari, Harish Kumar Malhotra — 2011-07-08

Abstract: Purpose: Radioactive seeds used in permanent prostate brachytherapy are composed of high-Z metals and may exceed 100 in a patient. If supplemental external beam treatment is administered afterward, the seeds may cause substantial dose perturbation, which is being investigated in this article.Methods and Materials: Film measurements using 6-MV beam were primarily carried out using Kodak XV2 film layered above and below a nonradioactive iodine-125 (125I) seed. Monte Carlo simulations were carried out using DOSXYZnrc. Other experimental comparisons looked at changing beam energy, depth, and field size, including two opposing fields’ pair. Effect of multiple seeds spatially spaced 0.5cm vertically was also studied.Results: For a single 125I seed, on XV film, there is a localized dose enhancement of 6.3% upstream and −10.9% downstream. With two opposing fields, a cold spot around the seed of ∼3% was noticed. Increasing beam energy and field size decreased the magnitude of this effect, whereas the effect was found to increase with the increasing Z of material. DOSXYZnrc and EBT-2 film verified maximum dose enhancement of +15% upstream and −20% downstream of the 125I seed surface.Conclusions: In general, the dose perturbation because of the seeds was spatially limited to ∼2mm upstream and ∼5mm downstream to the incident beam. Similar to other heterogeneities, the seeds perturbation depends on incident beam energy, field size, and its Z. With multiple seeds spatially apart and multiple radiation fields routinely used in external beam radiotherapy, the cumulative effect may not result in clinically significant dose perturbation.