ESTRO 2024 - Abstract Book

S2573

Clinical - Urology

ESTRO 2024

and V36Gy <1cc. DVCs for bladder were V18.1Gy <40% and V37Gy <10cc. A minimally clinically important change (MCIC) in EPIC QOL was defined as a decrease of 5 points for bowel toxicity and 6 for urinary toxicity as previously published [4]. EPIC QOL data were not available for one patient. Correlation between dose/volume constraints and toxicities were examined using Spearman’s rank correlation coefficient (significant p<0.05).

Results:

41.4% (12/29) and 58.6% (17/29) of patients experienced a MCIC change in acute EPIC bowel and urinary summary scores respectively. 41.4% (12/29) and 75.9% (22/29) of patients experienced a MCIC change in late EPIC bowel and urinary summary scores respectively. Correlations between acute bowel QOL and the V18.1Gy (r=-0.3167, p=0.0882), V29 Gy (r=-0.3658, p=0.0468) and V36Gy (r=-0.2387, p=0.2039) calculated from averaged CBCT data were stronger than correlations between acute bowel QOL and the same dosimetric parameters calculated from the planning CT (r=-0.08756, p=0.6455; r=-0.2261, p=0.2296 and r=-0.03707, p=0.8458 respectively). For late bowel QOL, correlations were greater based on averaged CBCT data for V36Gy (r=-0.1681, p=0.3833) versus planned CBCT data (r=-0.08356, p=0.6665) (Fig. 1). When the outlier value of V36Gy=12.40cc from the averaged CBCT data (present due to persistent rectal dilation throughout treatment) was removed, correlations of V36Gy decreased to r=-0.1742, p=0.3660 and r=-0.1059, p=0.5918 for acute and late bowel toxicity respectively, however, they remained greater than the corresponding correlations associated with planning CT data. Correlations between V18.1 Gy and acute urinary QOL were greater based on average CBCT data (r=-0.2245, p=0.2331) versus planning CT data (r=-0.007141, p=0.9701). Correlations between V37Gy and acute and late urinary QOL were greater based on planning CT data (r=0.2639, p=0.1587 and r=0.1830, p=0.3331 respectively) versus average CBCT data (r=0.1400, p=0.4605 and r=0.08138, p=0.6690 respectively), however, the direction of correlation was paradoxical in that a greater volume of the bladder received V37Gy among those who experienced less of a decline in urinary QOL score from the first fraction than those who experienced a greater decline in urinary QOL score (Fig. 2). The strength of these correlations between V37Gy and acute and late urinary QOL declined, however, when a single outlier was removed from both the planning CT (r=0.2170, p = 0.2583 and r=0.1304, p=0.5002 respectively) and averaged CBCT datasets (r=0.07599, p=0.6952 and r=0.02354, p=0.9035 respectively). All coefficients of determination were low at <0.11.