Predicting grade 3 acute diarrhea during radiation therapy for rectal cancer using a cutoff-dose logistic regression normal tissue complication probability model.
OBJECTIVE
Understanding the dose-volume relationship of small bowel irradiation and severe acute diarrhea may help reduce the incidence of this side effect during adjuvant treatment for rectal cancer.


METHODS
Consecutive patients treated curatively for rectal cancer were reviewed, and the maximum grade of acute diarrhea was determined. The small bowel was outlined on the treatment planning CT scan, and a dose-volume histogram was calculated for the initial pelvic treatment (45 Gy). Logistic regression models were fitted for varying cutoff-dose levels from 5 to 45 Gy in 5-Gy increments. The model with the highest LogLikelihood was used to develop a cutoff-dose normal tissue complication probability (NTCP) model.


RESULTS
There were a total of 152 patients (48% preoperative, 47% postoperative, 5% other), predominantly treated prone (95%) with a three-field technique (94%) and a protracted venous infusion of 5-fluorouracil (78%). Acute Grade 3 diarrhea occurred in 21%. The largest LogLikelihood was found for the cutoff-dose logistic regression model with 15 Gy as the cutoff-dose, although the models for 20 Gy and 25 Gy had similar significance. According to this model, highly significant correlations (p <0.001) between small bowel volumes receiving at least 15 Gy and toxicity exist in the considered patient population. Similar findings applied to both the preoperatively (p = 0.001) and postoperatively irradiated groups (p = 0.001).


CONCLUSIONS
The incidence of Grade 3 diarrhea was significantly correlated with the volume of small bowel receiving at least 15 Gy using a cutoff-dose NTCP model.
Robertson
John M
JM
William Beaumont Hospital, Department of Radiation Oncology, Royal Oak, Michigan 48073, USA. jrobertson@beaumont.edu
Söhn
Matthias
M
Yan
Di
D
D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage; D003967:Diarrhea / Q000453:epidemiology / Q000209:etiology*; D004307:Dose-Response Relationship, Radiation; D005472:Fluorouracil / Q000008:administration & dosage; D006801:Humans; D015994:Incidence; D007421:Intestine, Small / Q000000981:diagnostic imaging / Q000528:radiation effects*; D016013:Likelihood Functions; D016015:Logistic Models; D015233:Models, Statistical; D011832:Radiation Injuries / Q000150:complications / Q000517:prevention & control; D011859:Radiography; D011879:Radiotherapy Dosage; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000532:radiotherapy*
D000964:Antimetabolites, Antineoplastic; D005472:Fluorouracil