Dosimetric impact of bladder filling on organs at risk with barium contrast in the small bowel for adjuvant vaginal cuff brachytherapy

Introduction
The aim of this prospective study was to analyze dosimetric impact of modifying bladder filling on dose distribution in organs at risk (OARs) when using contrast in the small bowel of patients under adjuvant therapy with high-dose-rate vaginal cuff brachytherapy (HDR-VCB) for endometrial cancer.

Material and methods
This research included 19 patients who underwent laparoscopic surgery. They were treated with HDR-VCB and 2.5-3.5 cm diameter cylinders. Two successive computerized tomography (CT) scans were performed, with empty bladder and with bladder filled with 180 cc of saline solution. Bladder, rectum, sigmoid, and small bowel were delineated as OARs. Oral barium contrast was used to clearly visualize small bowel loops. Prescription dose was 7 Gy. Dose-volume histograms were generated for each OAR, with full and empty bladder to compare doses received.

Results
Bladder distension had no dosimetric impact on the bladder, rectum, or sigmoid, unlike the small bowel. With full bladder, mean minimum dose at 2 cc (D2cc) was not significantly higher for full vs. empty bladder (5.56 vs. 5.06 Gy, p = 0.07), whereas there was a significant reduction in the small bowel (1.68 vs. 2.70 Gy, p < 0.001). With full bladder, the dose increased to 50% of the volume (D50%) of the bladder (2.11 vs. 1.28 Gy, p < 0.001), and decreased in the small bowel (0.70 vs. 1.09 Gy, p < 0.001).

Conclusions
The present study describes the dose received by organs at risk during HDR-VCB, making it possible to define the dose received by small bowel loops, when visualized with oral barium contrast. In patients undergoing laparoscopic surgery, a full bladder during HDR-VCB reduces the dose to the small bowel without a clinically relevant dose increase in the bladder, and no dose increase in other OARs.