Late rectal toxicity on RTOG 94-06: Analysis using a mixture lyman model

Susan L. Tucker, Lei Dong, Walter R. Bosch, Jeff Michalski, Kathryn Winter, Radhe Mohan, James A. Purdy, Deborah Kuban, Andrew K. Lee, M. Rex Cheung, Howard D. Thames, James D. Cox

Research output: Contribution to journalArticlepeer-review

47 Scopus citations

Abstract

Purpose: To estimate the parameters of the Lyman normal-tissue complication probability model using censored time-to-event data for Grade ≥2 late rectal toxicity among patients treated on Radiation Therapy Oncology Group 94-06, a dose-escalation trial designed to determine the maximum tolerated dose for three-dimensional conformal radiotherapy of prostate cancer. Methods and Materials: The Lyman normal-tissue complication probability model was fitted to data from 1,010 of the 1,084 patients accrued on Radiation Therapy Oncology Group 94-06 using an approach that accounts for censored observations. Separate fits were obtained using dose-volume histograms for whole rectum and dose-wall histograms for rectal wall. Results: With a median follow-up of 7.2 years, the crude incidence of Grade ≥2 late rectal toxicity was 15% (n = 148). The parameters of the Lyman model fitted to dose-volume histograms data, with 95% profile-likelihood confidence intervals, were TD50 = 79.1 Gy (75.3 Gy, 84.3 Gy), m = 0.146 (0.107, 0.225), and n = 0.077 (0.041, 0.156). The fit based on dose-wall histogram data was not significantly different. Patients with cardiovascular disease had a significantly higher incidence of late rectal toxicity (p = 0.015), corresponding to a dose-modifying factor of 5.3%. No significant association with late rectal toxicity was found for diabetes, hypertension, rectal volume, rectal length, neoadjuvant hormone therapy, or prescribed dose per fraction (1.8 Gy vs. 2 Gy). Conclusions: These results, based on a large cohort of patients from a multi-institutional trial, are expected to be widely representative of the ability of the Lyman model to describe the long-term risk of Grade ≥2 late rectal toxicity after three-dimensional conformal radiotherapy of prostate cancer.

Original languageEnglish
Pages (from-to)1253-1260
Number of pages8
JournalInternational Journal of Radiation Oncology Biology Physics
Volume78
Issue number4
DOIs
StatePublished - Nov 4 2010

Keywords

  • Dose-volume histogram
  • Lyman model
  • Prostate cancer
  • Radiation Therapy Oncology Group
  • Rectal toxicity

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