ESTRO 2023 - Abstract Book

S1547

Digital Posters

ESTRO 2023

anaesthetic using a transperineal approach. PTV margin was 2 mm in all direction to CTV. Rectum, bladder, femoral heads, bowel were defined as OARs. 8 helical tomotherapy plans created for each patient based on 4 different HFRT approach to deliver the prescribed dose to cover 95% of PTV. In the tomotherapy plans, a 2.5 cm dynamic jaw was used and modulation factor and the pith were 2.5 and 0.287 respectively. The rectal dosimetry improvement with the use of hydrogel SpaceOAR was evaluated via Elekta ProKnow DS. For the statistical analysis, scorecards with scoring tables were created based on dose criteria and plans quality were analyzed in terms of radiation dosimetry to determine the optimum HFRT with the use of hydrogel SpaceOAR and without hydrogel SpaceOAR. Results All plans were evaluated for PTV coverage and OARs dose especially for rectal dosimetry improvement. All helical tomotherapy plans, the prescribed doses were delivered to PTV with a minimum coverage of 95%. Helical tomotherapy can generate highly conformal plans as expected. The mean CI was 1.03 and mean HI was 0.095 from all HFRT plans. Considering all HFRT plans, the % volume of rectum that received 50% of the prescribed dose was ≈ 11% less when hydrogel SpaceOAR was injected between prostate and rectum. Figure 1 represents the rectum dose comparison for all HFRT plans from all patients. Additionally, the multiple dose criteria for rectum were evaluated and the dosimetric analysis was listed in Table 1. As a result, all plans meet these criteria when hydrogel SpaceOAR was used. Moreover, when hydrogel SpaceOAR was injected, all HFRT plans are eligible to reduce radiation toxicity for rectum (mean plan score was 175 out of 195), however, some of the criteria were not met for rectum when the hydrogel SpaceOAR was not injected (mean plan score 155 out of 195).