The Dose–Volume Relationship of Small Bowel Irradiation and Acute Grade 3 Diarrhea During Chemoradiotherapy for Rectal Cancer

• DOI: 10.1016/j.ijrobp.2007.06.066
• Publication Date: 2007-10-02T15:18:11Z
• Authors: John M. Robertson; David Lockman; Di Yan; Michelle Wallace
• Keywords: Diarrhea; Male; Antimetabolites, Antineoplastic; Rectal Neoplasms; Radiation Dosage; Combined Modality Therapy; Pelvis; 3. Good health; 03 medical and health sciences; 0302 clinical medicine; Acute Disease; Intestine, Small; Humans; Female; Fluorouracil

Previous work has found a highly significant relationship between the irradiated small-bowel volume and development of Grade 3 small-bowel toxicity in patients with rectal cancer. This study tested the previously defined parameters in a much larger group of patients.A total of 96 consecutive patients receiving pelvic radiation therapy for rectal cancer had treatment planning computed tomographic scans with small-bowel contrast that allowed the small bowel to be outlined with calculation of a small-bowel dose-volume histogram for the initial intended pelvic treatment to 45 Gy. Patients with at least one parameter above the previously determined dose-volume parameters were considered high risk, whereas those with all parameters below these levels were low risk. The grade of diarrhea and presence of liquid stool was determined prospectively.There was a highly significant association with small-bowel dose-volume and Grade 3 diarrhea (p < or = 0.008). The high-risk and low-risk parameters were predictive with Grade 3 diarrhea in 16 of 51 high-risk patients and in 4 of 45 low-risk patients (p = 0.01). Patients who had undergone irradiation preoperatively had a lower incidence of Grade 3 diarrhea than those treated postoperatively (18% vs. 28%; p = 0.31); however, the predictive ability of the high-risk/low-risk parameters was better for preoperatively (p = 0.03) than for postoperatively treated patients (p = 0.15). Revised risk parameters were derived that improved the overall predictive ability (p = 0.004).The highly significant dose-volume relationship and validity of the high-risk and low-risk parameters were confirmed in a large group of patients. The risk parameters provided better modeling for the preoperative patients than for the postoperative patients.