Dosimetric Impact of Bladder Volumetric Changes During Helical Radiotherapy for Rectal Cancer

This study aims to investigate the dosimetric impact of bladder volumetric changes during helical radiotherapy (RT) for rectal cancer (RC).

A total of 42 RC patients' helical RT treatment plans were analyzed. The bladder volumes were divided into 3 groups (Group1: V<100ml, Group2 100ml≤V≤200ml, and Group3V>200ml). Planning target volume (PTV), PTV boost, bladder, bowel, right, and left femoral head dose values were analyzed and compared between groups. Statistical analysis was done with a one-way ANOVA test in SPSS18.0 program. A value of p <0.05 was considered statistically significant.

The median age of the patients was 59 (range:22-87) and bladder volume ranged from 41.44ml-620.82ml. In the dosimetric data comparison of the patient groups with different bladder volumes, the D50 dose values of PTV and PTV boost volume was highest in Group 3 (p=0.039). No statistical significance was found between PTV and PTV boost’ doses of D98 and D2 ​​and groups. The optimum PTV dose value was in Group2. Bowel doses were highest in Group 1. As the bladder volume increased, the Dmax, Dmean, V15%, and V30% values of the bowel doses decreased. There was a statistically significant relationship between bladder Dmax doses and groups (p = 0.024). Femoral heads doses increased in proportion to increasing bladder volume groups and these results were statistically significant for V5% and V30% (p <0.05).

In our study, as the bladder volume increased, there was an inversely proportional decrease in the bowel doses and a directly proportional increase in the femoral head and bladder doses. Bladder volume values significantly affected values of the target and critical organs dose during helical RT for RC