Dosimetric impact of bladder volume on organs at risk during external beam radiotherapy of cervical cancer.

This study aimed to investigate the effect of bladder volume on the dosimetry of pelvic organs at risk (OARs) in patients treated with external beam radiation therapy. Twenty patients with locally advanced cervical cancer were selected. Two computed tomography-simulation scans were obtained, one with an empty bladder followed by one with a full bladder. The acquired images were transferred to the treatment planning system. Target and OARs were contoured in both images, and treatment plans were performed for each computed tomography image. The delivered doses to target and OARs were determined using dose-volume histograms. The mean dose of the bowel bag in the empty and full bladder were 35.06 ± 4.13 (Gy) and 31.59 ± 3.86 (Gy), respectively. Furthermore, the V45 of the bowel bag in the empty bladder was 364.27 ± 154.39 (cc) and in the full bladder, it was 240.84 ± 129.66 (cc). The mean dose of the rectum in the empty and full bladder were 49.50 ± 1.95 (Gy) and 49.18 ± 1.03 (Gy), respectively. The rectal V50 (%) was 52.82 ± 21.84 (%) in the empty bladder and 45.49 ± 29.55 (%) in the full bladder. The mean dose and V45 of the bowel bag, also V50 of the rectum, had significantly decreased in the full bladder status (p-value < 0.05). The results showed that the bladder volume significantly affected the delivered dose to the bowel bag and rectum. The average bowel bag V45 and rectum V50 in the full bladder were significantly decreased. Bladder distention is an effective method to improve the dosimetric parameters of pelvic OARs.