Comparison of effect of rectal volume delineation methods on dose constraint endpoints in the treatment of prostate cancer with intensity-modulated radiation therapy

Abstract

Objective: Identifying a reliable method of rectal volume delineation (RVD) for prostate cancer treatment planning using intensity-modulated radiation therapy (IMRT) is invaluable for clinical and investigational purposes. We analyzed rectal dose constraint outcomes utilizing commonly used RVD methods. Methods: Sixty-two prostate cancer patients treated with IMRT from August 2008 to March 2010 were reviewed. RVD either included the entire rectal volume (ERV) or limited the volume to a 3 mm rectal wall (3 MM). V50, the percentage of rectal volume receiving 50 Gy, V65, V70, and V75.6 were determined and analyzed for differences. We analyzed factors including definitive and postoperative treatment, rectal volume, and length. Results: For definitive treatment, using ERV, the mean rectal V50, V65, V70, and V75.6 was 41.3, 21.6, 15.1, and 7.0 %, respectively. Using 3 MM, the mean V50, V65, V70, and V75.6 was 37.3, 23.4, 18.5, and 10.3 %, respectively. The V65, V70, and V75.6 were significantly lower in ERV than 3 MM (p < 0.01), while V50 was significantly higher (p < 0.01). Similar findings were noted with rectal volumes <100 cm 3 and length <10 cm. There was no difference in V50 and V65 with rectal length ≥10 cm. For postoperative treatment, using ERV, the mean rectal V50, V65, and V70 was 30.2, 12.9, and 2.7 %, respectively. Using 3 MM, the mean V50, V65, and V70 was 30.6, 16.5, and 4.7 %, respectively. The V65 and V70 were lower in ERV than 3 MM (p < 0.01), but not V50. Similar findings were observed with volumes <100 cm 3 and length ≥10 cm. Conclusion: We identified different rectal dose-volume endpoints when using common methods of RVD. The differences in dose-volume outcomes are dependent upon prescribed dose, rectal volume, and length. Further analysis, incorporating larger numbers and long-term toxicity outcomes, will contribute to the standardization of contouring and dose-volume analysis for treatment planning. © 2013 Springer-Verlag Berlin Heidelberg.