Dosimetric analysis of the effects of the bladder volume on organs at risk (OAR) in high-dose-rate intracavitary brachytherapy in carcinoma cervix – an institutional study

Purpose
The purpose of this study was to establish a dosimetric correlation between the bladder volume and its effects on the dose received by the organs at risk (OARs) (urinary bladder, rectum, and sigmoid) during computed tomography (CT)-guided high-dose-rate (HDR) brachytherapy in carcinoma cervix, and to determine an optimum bladder volume to limit the dose to OARs.

Material and methods
Seventy-five intracavitary applications in patients of carcinoma cervix (stage IIB, IIIA, IIIB, IVA) treated with external beam radiotherapy with concurrent chemotherapy followed by CT-based HDR intracavitary brachytherapy (tandem and ovoid type) at our institute between July 2014 to January 2016 were studied. The bladder volume at the time of imaging was noted and was correlated with the radiation dose received by bladder, rectum, and sigmoid colon.

Results
Dose volume histogram (DVH) parameters of the bladder increases by elevating the volume of the bladder. Rectum dose does not follow a continuous increasing trend. It increases up to a bladder volume of 110 cc and then starts decreasing. The highest rectal dose observed was in the bladder volume, range 70-110 cc. The minimum doses were recorded when the bladder volume was > 170 cc. Sigmoid colon DVH parameters follow a similar trend as that of the rectum.

Conclusions
A relationship exists between the volume of the OARs and the dose received by them. A bladder volume of about 70 cm³ or less proved better for achieving the prescribed dose limits of bladder, rectum, and sigmoid. The correlations between the bladder volume and the doses received by the OARs were not significant.