Biological-effective versus conventional dose volume histograms correlated with late genitourinary and gastrointestinal toxicity after external beam radiotherapy for prostate cancer: A matched pair analysis

Abstract

Background: To determine whether the dose-volume histograms (DVH's) for the rectum and bladder constructed using biological-effective dose (BED-DVH's) better correlate with late gastrointestinal (GI) and genitourinary (GU) toxicity after treatment with external beam radiotherapy for prostate cancer than conventional DVH's (C-DVH's). Methods: The charts of 190 patients treated with external beam radiotherapy with a minimum follow-up of 2 years were reviewed. Six patients (3.2%) were found to have RTOG grade 3 GI toxicity, and similarly 6 patients (3.2%) were found to have RTOG grade 3 GU toxicity. Average late C-DVH's and BED-DVH's of the bladder and rectum were computed for these patients as well as for matched-pair control patients. For each matched pair the following measures of normalized difference in the DVH's were computed: (a) δAUC = (Area Under Curve [AUC] in grade 3 patient - AUC in grade 0 patient)/(AUC in grade 0 patient) and (b) δV60 = (Percent volume receiving = 60 Gy [V60] in grade 3 patient - V60 in grade 0 patient)/(V60 in grade 0 patient). Results: As expected, the grade 3 curve is to the right of and above the grade 0 curve for all four sets of average DVH's - suggesting that both the C-DVH and the BED-DVH can be used for predicting late toxicity. δAUC was higher for the BED-DVH's than for the C-DVH's - 0.27 vs 0.23 (p = 0.036) for the rectum and 0.24 vs 0.20 (p = 0.065) for the bladder. δV60 was also higher for the BED-DVH's than for the C-DVH's - 2.73 vs 1.49 for the rectum (p = 0.021) and 1.64 vs 0.71 (p = 0.021) for the bladder. Conclusions: When considering well-established dosimetric endpoints used in evaluating treatment plans, BED-DVH's for the rectum and bladder correlate better with late toxicity than CDVH's and should be considered when attempting to minimize late GI and GU toxicity after external beam radiotherapy for prostate cancer. © 2003 Jani et al; licensee BioMed Central Ltd.