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

Abstract

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. 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. 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. 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.