Bladder distension improves the dosimetry of organs at risk during intracavitary cervical high-dose-rate brachytherapy.

PURPOSE: To evaluate dose-volume histograms (DVHs) and dose-surface histograms (DSHs) to analyze bladder distension during cervical brachytherapy.

METHODS: Twenty brachytherapy fractions from five cervical cancer patients were selected. For each fraction, empty and full (200cc of contrasted saline) bladder simulation CT scans existed, one of which was used to plan treatment. An alternative plan was then created with the unused scan. DVH for each fraction was generated for the bladder, rectum, sigmoid colon, and small bowel. Mean DVH dose, D0.1cc, and D2cc were calculated for each organ at risk. Plans were then exported to a MATLAB-based program to generate a DSH.

RESULTS: Full bladder plans showed no difference in bladder D2cc or D0.1cc compared with empty bladder plans; however, bladder mean DVH dose and DSH dose were both significantly reduced. Full bladder plans showed a significant reduction in small intestine D2cc from 2.81 Gy to 1.83 Gy and reduction in D0.1cc from 4.07 Gy to 2.57 Gy (p < 0.05); similarly, sigmoid D2cc was significantly reduced from 4.24 Gy to 3.87 Gy (p < 0.05) and D0.1cc was reduced from 6.12 Gy to 5.61 Gy (p < 0.05) in full bladder plans. Both small intestine and sigmoid also showed reduced mean DVH and DSH dose in full bladder plans. The rectum showed no significant difference in D2cc, D0.1cc, mean DVH, or DSH dose between plans.

CONCLUSIONS: Bladder distension during cervical brachytherapy significantly reduced dose in all DVH and DSH parameters for sigmoid and small intestine with no change in bladder parameters. It reduces dose to organ at risk, but the correlation to toxicity requires further investigation.