A Monte Carlo evaluation of dose distribution of commercial treatment planning systems in heterogeneous media.

INTRODUCTION: Calculations from a treatment planning system (TPS) in heterogeneous regions may present significant inaccuracies due to loss of electronic equilibrium. The purpose of this study is to evaluate and quantify the differences of dose distributions computed by some of the newest dose calculation algorithms, including collapsed cone convolution (CCC), fast Fourier transform (FFT) convolution, and superposition convolution, in heterogeneity of the lung. MATERIALS AND METHODS: A 6-MV Siemens Primus linear accelerator was simulated by MCNPX Monte Carlo (MC) code, and the results of percentage depth dose (PDD) and dose profile values were compared with measured data. The ISOgray TPS was used and PDDs of CCC, FFT, and superposition convolution algorithms were compared with the results obtained by MCNPX code. CT2MCNP software was used to convert the computed tomography images of the lung tissue to MC input files, and dose distributions from the three algorithms were compared to MC method. RESULTS: For PDD curves in buildup region, the maximum underdosage of ISOgray TPS was at the surface (19%) and comes in closer agreement when depth increases (average 7.08%). Dose differences (DD) between different algorithms and MC were typically 4.81% (range: 1.95% to 7.30%), -1.55% (range: -5.14% to 5.26%) and 4.96% (range: 2.00% to 7.4%) in the lung for the CCC, FFT, and superposition algorithms, respectively. The difference between monitor units and maximum dose calculated using the three algorithms were 0.5% and 1.61%, respectively. The maximum DD of 7% was observed between MC and TPS results. CONCLUSION: Significant differences were found when the calculation algorithms were compared with MC method in lung tissue, and this difference is not negligible. It is recommended to use of MC-based TPS for the treatment fields including lung tissue.

Evaluating the Incidence Rate of an Accelerated Short Course High Dose Rate Intravaginal Brachytherapy Complications in Patients with Endometrial Cancer.

Background: Brachytherapy in treatment of endometrial cancer patients is growing and therefore, evaluation of more feasible schedule has become of great importance. The purpose of current study was to evaluate the complications of accelerated short course high dose rate intravaginal brachytherapy (HDR IVB), a new brachytherapy approach which is a more feasible treatment option in developing countries. Method: From 2017 to 2018, 54 patients diagnosed with endometrial cancer and FIGO stages IA to IIB who underwent total abdominal hysterectomy with a bilateral salpingo-oophorectomy were enrolled in present study. They were treated with a total dose of 25 Gy in 5 fractions which was prescribed daily. A dose of 5 Gy was prescribed at a depth of 0.5 cm in the upper third and middle third of vagina. Adverse effects related to organs at risk consist of bladder, vagina and rectum were documented based on the Common Terminology Criteria for Adverse Events v3.0 (CTCAE v3.0). Results: The accelerated short course HDR IVB was well tolerated and no grade 3 or higher toxicities was reported for patients during the follow up period. There were no chronic rectal toxicities and only one patient showed chronic urinary toxicities. However, the incidence rate of vaginal toxicities at the end of 4-month and 8-month follow up periods was higher than acute toxicities and significantly lower in elderly group compared to younger group. Conclusion: Overall, the accelerated HDR IVB was safe and was well tolerated in endometrial cancer patients and the incidence rate of undue complications were equal, if not less, in elderly patients compared to the younger ones.

High-dose-rate brachytherapy in treatment of non-melanoma skin cancer of head and neck region: preliminary results of a prospective single institution study.

PURPOSE: Skin cancers are the most common human malignancy with increasing incidence. Currently, surgery is standard of care treatment for non-melanoma skin cancers. However, brachytherapy is a growing modality in the management of skin cancers. Therefore, we aimed to assess the outcome of patients with non-melanoma skin cancers treated by high-dose-rate (HDR) brachytherapy with surface mold technique. MATERIAL AND METHODS: In this prospective study, we recruited patients with basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) of the skin who were candidates for definitive or adjuvant brachytherapy during 2013-2014. Alginate was used for making the individualized surface molds for each patient. Patients were treated with afterloading radionuclide HDR brachytherapy machine, with a total dose of 30-52 Gy in 10-13 fractions. Participants were followed for 2 years for radiation toxicity, cosmetic results, and local failures. RESULTS: A total of 60 patients (66.7% male; median age, 71 years) were included, of which 42 (70.0%) underwent definitive radiotherapy. Seventy-five percent of lesions were BCC. The mean total dose was 39.6 ± 5.4 Gy. Of patients in definitive group, 40/42 (95.2%) experienced complete clinical response after 3 months. The recurrence rate was 2/18 (11.11%) and 1/42 (2.38%) in adjuvant and definitive groups, respectively. The percentage of grade 3-4 acute (3-month post-treatment) and late toxicities (2 years post-treatment) was 6.7% and 0%, respectively. The cosmetic results were good/excellent in 96.2% of patients after 2 years of follow-up. CONCLUSIONS: With appropriate patient selection and choosing as lowest dose per fraction as possible, HDR brachytherapy with customized surface molds yields good oncological and cosmetic results for the treatment of localized skin BCC and SCC.

Adjuvant high-dose-rate brachytherapy in the management of oral cavity cancers: 5 years of experience in Iran.

PURPOSE: Brachytherapy is a cost-effective method for the management of oral cavity cancers in low to middle income countries. We aimed to evaluate the clinical outcomes of high-dose-rate interstitial brachytherapy (HDR-IBT) in patients with oral cavity cancer. MATERIAL AND METHODS: From 2009 to 2013, 78 patients (49 combined external beam radiotherapy [EBRT] plus IBT and 29 IBT monotherapy) with oral cavity cancers had been treated in our center. Slightly more than half the patients were male, and the median age was 54 years. The treatment was planned based on the Paris system. The main outcomes were disease-free and overall survival. RESULTS: The median follow-up duration was 36.5 months (range, 1.17-54.23). The actuarial four-year overall and disease-free survival rates were 83% and 65%, respectively. The local and locoregional control was achieved among 89.74% and 87.17% of patients, respectively. None of the factors including tumor size, node status, gender, and radiation modality (IBT alone vs. IBT + EBRT) had a significant statistical correlation to the local control rate. All the patients tolerated the planned treatment in the IBT alone group. Late complications included a case of trismus and three cases of catheter insertion site fibrosis. CONCLUSIONS: HDR-IBT as a monotherapy or in combination with EBRT is an appropriate option for the management of oral cavity squamous cell carcinomas, and supports the improvement in treatment outcomes and toxicity profiles in adjuvant settings.