(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: Multiple channels cylinders (MCC) have replaced single channel cylinders (SCC) in 3D image-guided HDR brachytherapy to accommodate asymmetry targets and anatomic changes during each HDR insertion. We assess the dosimetry benefits by comparing plans using MCC and SCC applicators and then search approaches to optimize HDR plans.
Methods: HDR plans are optimized by covering > 90% of the high risk CTV (HRCVT) with the prescription dose (PD) while controlling the equivalent dose EQD2Gy at the tolerance of nearby bladder and recto-sigmoid in addition to external beam doses. Plans using MCC for twenty-three patients with 30 Gy in 5 fractions and twelve patients with 12 Gy in two fractions were all optimized with evaluation of D90% of HRCTV minus applicator (HRCTV-app) and bladder wall since the applicator and packing materials and the content of the bladder are biological irrelevant. HDR plans using SCC are planned for having the same D10cc to the bladder and recto-sigmoid.
Results: Average doses of D90% of HRCTV and HRCTV-App are 105% and 97% of PD from MCC plans but only 99% and 89% from SCC plans, respectively. Hotspot doses of D2cc to the bladder and recto-sigmoid are 77% and 76% in MCC plans but increased to 79% and 82% in SCC plans. D10cc to the bladder wall is also increased from 48% in MCC plans to 51% in SCC plans. Hotspot dose of D1cc to HRCTV-App in MCC plans is 170% that is 30% higher than that of SCC plans. D90% for HRCTV-app has been improved from 88% to 97% after using HRCTV-App.
Conclusion: Benefits of 3% to OARs and 6-8% to targets using MCC had been approved from hundreds of HDR plans. Definition of HRCTV-app and hotspot doses to the bladder wall and recto-sigmoid wall if needed had significantly improved our HDR plans.
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