Incidence of late rectal bleeding in high-dose conformal radiotherapy of prostate cancer using equivalent uniform dose–based and dose–volume–based normal tissue complication probability models

• DOI: 10.1016/j.ijrobp.2006.10.014
• Publication Date: 2007-01-27T12:13:59Z
• Authors: Matthias Söhn; Di Yan; Jian Liang; Elisa Meldolesi; Carlos Vargas; Markus Alber
• Keywords: Equivalent uniform dose; Male; Likelihood Functions; Prostate cancer; Models, Statistical; Dose–volume histograms; Rectum; Prostatic Neoplasms; Normal tissue complication probability; Dose-Response Relationship, Radiation; Risk Assessment; 3. Good health; 03 medical and health sciences; 0302 clinical medicine; Rectal toxicity; Volume effects; Confidence Intervals; Humans; Radiotherapy, Conformal; Gastrointestinal Hemorrhage; Radiation Injuries

Accurate modeling of rectal complications based on dose-volume histogram (DVH) data are necessary to allow safe dose escalation in radiotherapy of prostate cancer. We applied different equivalent uniform dose (EUD)-based and dose-volume-based normal tissue complication probability (NTCP) models to rectal wall DVHs and follow-up data for 319 prostate cancer patients to identify the dosimetric factors most predictive for Grade > or = 2 rectal bleeding.Data for 319 patients treated at the William Beaumont Hospital with three-dimensional conformal radiotherapy (3D-CRT) under an adaptive radiotherapy protocol were used for this study. The following models were considered: (1) Lyman model and (2) logit-formula with DVH reduced to generalized EUD, (3) serial reconstruction unit (RU) model, (4) Poisson-EUD model, and (5) mean dose- and (6) cutoff dose-logistic regression model. The parameters and their confidence intervals were determined using maximum likelihood estimation.Of the patients, 51 (16.0%) showed Grade 2 or higher bleeding. As assessed qualitatively and quantitatively, the Lyman- and Logit-EUD, serial RU, and Poisson-EUD model fitted the data very well. Rectal wall mean dose did not correlate to Grade 2 or higher bleeding. For the cutoff dose model, the volume receiving > 73.7 Gy showed most significant correlation to bleeding. However, this model fitted the data more poorly than the EUD-based models.Our study clearly confirms a volume effect for late rectal bleeding. This can be described very well by the EUD-like models, of which the serial RU- and Poisson-EUD model can describe the data with only two parameters. Dose-volume-based cutoff-dose models performed worse.