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

Introduction: This study aims to investigate the dosimetric impact of bladder volumetric changes during helical radiotherapy (RT) for rectal cancer (RC).Material and Methods: 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.Results: 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).Conclusion: 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