ESTRO 2022 - Abstract Book

S916

Abstract book

ESTRO 2022

in 35 fractions over 7wks at 98% of dose coverage of corresponding planning target volume (PTVs) were prescribed. The DVH parameters evaluated for PTV were D 2 , D 95 , D 98 , V 95 and V 100 for both CECT and MRI based target volumes. In addition, %differences of GTVp, GTVn, GTVpn were computed along with concordance index (ConI), conformity index (CI) and homogeneity index (HI). ConI was ideally taken as 1. Results GTVp and GTVpn delineated on MRI was found to be significantly higher than the corresponding GTVs delineated (Fig). This resulted in significant differences in the D 2, D 95 , D 98 , V 95 , V 100 , CI and HI (Table). %differences of GTVp and GTVn of corresponding volumes delineated on CECT and MRI were significantly different. The mean ConI was 0.6 (±0.1) (p=0.01) and was inversely related to the %difference in GTVp (p=0.002) and GTVpn (p<0.001). For GTVn, a similar trend was observed. Concordance of GTVpn varied from good (ConI, ≥ 0.67, n=5), moderate (ConI 0.34-0.66, n=4) and poor (ConI ≤ 0.33, n=1).