Prostate position variability and dose-volume histograms in radiotherapy for prostate cancer with full and empty bladder.

PURPOSE

To evaluate prostate position variability and dose-volume histograms in prostate radiotherapy with full bladder (FB) and empty bladder (EB).

METHODS AND MATERIALS

Thirty patients underwent planning computed tomography scans in a supine position with FB and EB before and after 4 and 8 weeks of radiation therapy. The scans were matched by alignment of pelvic bones. Displacements of the prostate/seminal vesicle organ borders and center of mass were determined. Treatment plans (FB vs. EB) were compared.

RESULTS

Compared with the primary scan, FB volume varied more than EB volume (standard deviation, 106 cm3 vs. 47 cm3), but the prostate/seminal vesicle center of mass position variability was the same (> 3 mm deviation in right-left, anterior-posterior, and superior-inferior directions in 0, 41%, and 33%, respectively, with FB vs. 0, 44%, and 33% with EB). The bladder volume treated with 90% of the prescription dose was significantly larger with EB (39% +/- 14% vs. 22% +/- 10%; p < 0.01). Bowel loops received > or = 90% of prescription dose in 37% (3% with FB; p < 0.01).

CONCLUSION

Despite the larger variability of bladder filling, prostate position stability was the same with FB compared with EB. An increased amount of bladder volume in the high-dose region and a higher dose to bowel loops result from treatment plans with EB.