(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: To examine dosimetric performance of the Venezia?? applicator used for boosting treatment in cervical adenocarcinoma.
Methods: We evaluated 125 plans from 36 patients. The Venezia applicator was utilized with interstitial needles to cover large target volumes and/or irregular shapes; since its ring-guide directs needles parallel to or 30-degrees oblique from the tandem. Additionally, the perineal template allows needle channels beyond the maximum in the ring guide. Plans were inverse-optimized to an expanded target structure including the area around the ring, and parts of the Intermediate risk CTV. Results included D90 of the High-Risk-Clinical-Target-Volume (HRCTV), and doses to 2cm³ of bladder, rectum, sigmoid, and bowel. Prescription dose coverage was assessed with the conformity index. Trends in usage and dosimetric effectiveness over time were evaluated.
Results: Average HRCTV volume was 97.4 cm³ (23.4-296.7cm³) compared to average 100% IDL volume for a standard point-A tandem and ring loading without needles (83-93cm³). Average volume of the optimization structure was 129.1cm³. Target volumes were appropriately covered; only 6 plans had D90% HRCTV < 100%. In 25 patients, the number of needles used varied between fractions, and in 31 patients only some fractions used the Venezia instead of tandem and ring. This demonstrated the treatment adaptation that occurred over the course of the boost. The average number of needle channels placed per fraction was 10.1 (0-21). Most common needle placements were 8, 10, or 12. Conformity of the dose to the optimization structure was consistent with average of 0.71 (±0.05).
Conclusion: Using the Venezia applicator to include interstitial channels showed consistent quality target coverage for large and/or asymmetrical targets while maintaining acceptable critical structure dose levels. Treatments involving interstitial needles are feasible for repeated placement and removal over a full-fractionated treatment permitting high adaptability to compensate observed dosimetric underperformance from using tandem and ring alone.
Keywords
Brachytherapy, Interstitial Brachytherapy, Intracavitary Brachytherapy
Taxonomy
TH- Brachytherapy: GYN Intracavity Brachytherapy
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