Use of fractional dose-volume histograms to model risk of acute rectal toxicity among patients treated on RTOG 94-06.
OBJECTIVE
For toxicities occurring during the course of radiotherapy, it is conceptually inaccurate to perform normal-tissue complication probability analyses using the complete dose-volume histogram. The goal of this study was to analyze acute rectal toxicity using a novel approach in which the fit of the Lyman-Kutcher-Burman (LKB) model is based on the fractional rectal dose-volume histogram (DVH).


METHODS
Grade ≥2 acute rectal toxicity was analyzed in 509 patients treated on Radiation Therapy Oncology Group (RTOG) protocol 94-06. These patients had no field reductions or treatment-plan revisions during therapy, allowing the fractional rectal DVH to be estimated from the complete rectal DVH based on the total number of dose fractions delivered.


RESULTS
The majority of patients experiencing Grade ≥2 acute rectal toxicity did so before completion of radiotherapy (70/80=88%). Acute rectal toxicity depends on fractional mean rectal dose, with no significant improvement in the LKB model fit when the volume parameter differs from n=1. The incidence of toxicity was significantly lower for patients who received hormone therapy (P=0.024).


CONCLUSIONS
Variations in fractional mean dose explain the differences in incidence of acute rectal toxicity, with no detectable effect seen here for differences in numbers of dose fractions delivered.
Department of Bioinformatics and Computational Biology – Unit 1410, The University of Texas MD Anderson Cancer Center, P.O. Box 301402, Houston, TX 77230, USA. sltucker@mdanderson.org
Susan L
SL
Tucker
Jeff M
JM
Michalski
Walter R
WR
Bosch
Radhe
R
Mohan
Lei
L
Dong
Kathryn
K
Winter
James A
JA
Purdy
James D
JD
Cox
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011878:Radiotherapy / Q000009:adverse effects; D012007:Rectum / Q000187:drug effects / Q000528:radiation effects*; D012306:Risk