Dose-volume response analyses of late rectal bleeding after radiotherapy for prostate cancer.
OBJECTIVE
To compare the fits of various normal tissue complication probability (NTCP) models to a common set of late rectal toxicity data, with the aim of identifying the best model for predicting late rectal injury after irradiation.


METHODS
Late toxicity data from 128 prostate cancer patients treated on protocol with three-dimensional conformal radiotherapy at The University of Texas M.D. Anderson Cancer Center (UTMDACC) were analyzed. The dose-volume histogram for total rectal volume, including contents, was obtained for each patient, and the presence or absence of Grade 2 or worse rectal bleeding within 2 years of treatment was scored. Five different NTCP models were fitted to the data using maximum likelihood analysis: the Lyman model, the mean dose model, a parallel architecture model, and models based on either a cutoff dose or a cutoff volume.


RESULTS
All five of the NTCP models considered provided very similar fits to the UTMDACC rectal bleeding data. In particular, none of the more highly parameterized models (the four-parameter parallel model, three-parameter Lyman model, or three-parameter cutoff dose and volume models) provided a better fit than the simplest of the models, the two-parameter NTCP model describing rectal bleeding as a probit function of mean dose to rectum.


CONCLUSIONS
No dose-volume response model has yet been identified that provides a better description of the UTMDACC rectal toxicity data than the mean dose model. Because this model has relatively low predictive accuracy, the need to identify a better model remains.
Tucker
Susan L
SL
Department of Biostatistics and Applied Mathematics, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA. sltucker@mdanderson.org
Cheung
Rex
R
Dong
Lei
L
Liu
H Helen
HH
Thames
Howard D
HD
Huang
Eugene H
EH
Kuban
Deborah
D
Mohan
Radhe
R
D004307:Dose-Response Relationship, Radiation; D006471:Gastrointestinal Hemorrhage / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D015233:Models, Statistical; D011336:Probability; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000150:complications*; D020266:Radiotherapy, Conformal / Q000009:adverse effects; D012002:Rectal Diseases / Q000209:etiology*; D012007:Rectum / Q000528:radiation effects*; D012189:Retrospective Studies