A Method for the Prediction of Late Organ-at-Risk Toxicity After Radiotherapy of the Prostate Using Equivalent Uniform Dose

Purpose: To evaluate the predictive value of equivalent uniform doses (EUD) for late bladder and rectal toxicity after high-dose three-dimensional conformal radiation therapy (3D-CRT) to the prostate. Materials and Methods: Using the method developed by Kutcher et al., EUDs for whole bladder and rectum were calculated from the dose-volume histograms of 180 patients with localized prostate cancer treated to 70-74 Gy with 3D-CRT. Late complications were recorded using the Radiation Therapy Oncology Group scale, correlated against EUD and known physical predictive indicators. Results: EUD is an independent prognostic factor for Grade 2+ long-term rectal and bladder toxicity after radiation treatment to the prostate. Patients receiving an EUD >63.1 Gy to the rectum have a statistically significant (10% vs. 30%; p = 0.002) higher risk of developing Grade 2+ late complications. Patients receiving an EUD >53.4 Gy to the bladder have a statistically significant (10% vs. 33%; p = 0.001) higher risk of developing Grade 2+ late complications. Conclusions: It has been demonstrated that EUD is a strong independent predictive factor for Grade 2+ late complications after 3D-CRT to the prostate. Threshold values have been demonstrated for both bladder and rectum, above which there is a clinically significant increased risk of complications.