T Giaddui*, B Wang, J Price, C Heese, C Miyamoto, B Micaily, S Li, Temple University Hospital, Phila., PA

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  T Giaddui

PO-GePV-P-17 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: To analyze the major variations among the volumes and doses of interest for patients underwent Multi channel vaginal cylinders (MCVC) High Dose Rate (HDR) Brachytherapy

Methods: Data was collected for ten patients treated using MCVC HDR, eight patients receiving treatments over 5 fractions and two patients over 2 fractions. The prescription dose was 500 cGy for one patients, 550 cGy for one patient, 600 cGy for 6 patients and 700 cGy for 2 patients. High risk CTV (HRCTV), bladder, rectum, bowel and sigmoid volumes were delineated by the treating physician on the CT scan for each fraction (44 fractions in total). Plans were developed using Oncentra treatment planning system. Inverse planning by simulated annealing (IPSA) optimization was performed first, followed by manual optimizations for all cases. The HRCTV D90%, D10cc and D2cc for the bladder, rectum, bowel and sigmoid were evaluated for each fraction and their volume and dose variations are quantified by the ratio of the standard deviations to the mean values.

Results: Variations of delineated volumes ranged from:3-14% for HRCTV; 4-27% for bladder and rectum, 3 to 67% for bowel and 20 to 115% for sigmoid. Doses for HRCTVs and all OARs met their constraints (using American Brachytherapy society (ABS) guidelines). However, there were over 10% dose variations to OARs from one fraction to another. The variations increased over 50% for bowel and sigmoid with shape changes and location while the variation in hotspot dose to the 2cc of bladder and rectum were typically less than 10% but may have been in different locations for individual fractions.

Conclusion: The range of fractional variations in dosimetric parameters suggests consistency in HDR planning by considering only the HRCTV, rectum and bladder doses but if sigmoid and bowel doses are involved, it is important to individualize planning for each fraction.

Keywords

Brachytherapy

Taxonomy

TH- Brachytherapy: HDR Brachytherapy

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