Grading-system-dependent volume effects for late radiation-induced rectal toxicity after curative radiotherapy for prostate cancer.

Purpose: To assess the association between the dose distributions in the rectum and late Radiation Therapy Oncology Group and the European Organisation for Research and Treatment of Cancer (RTOG/EORTC), Late Effects of Normal Tissue SOMA, and Common Terminology Criteria for Adverse Events (CTCAE) version 3.0 graded rectal toxicity among patients with prostate cancer treated with RT.
Methods and Materials: Included in the study were 124 patients who received three-dimensional conformal RT for prostate cancer to a total dose of 70 Gy in 2-Gy fractions. All patients completed questionnaires regarding rectum complaints before RT and during long-term follow-up. Late rectum Grade 2 or worse toxicity, according to RTOG/EORTC, LENT SOMA, and CTCAE v3.0 criteria, was analyzed in relation to rectal dose and volume parameters.
Results: Dose-volume thresholds (V40>or=65%, V50>or=55%, V65>or=45%, V70>or=20%, and a rectum volume<or=140 cm3), significantly discriminated patients with late Grade 0-1 and Grade 2 or worse rectal toxicity, particularly using the LENT SOMA and CTCAE v3.0 systems. The rectum volume receiving>or=70 Gy (V70) was most predictive for late Grade 2 or worse rectal toxicity with each of the grading systems. The associations were strongest, however, with use of the LENT SOMA system.
Conclusions: Volume effects for late radiation-induced rectal toxicity are present, but their clinical significance depends on the grading system used. This should be taken into account in the interpretation of studies reporting on radiation-induced rectal toxicity.