Image-based three-dimensional treatment planning of intracavitary brachytherapy for cancer of the cervix: dose-volume histograms of the bladder, rectum, sigmoid colon, and small bowel.

ABSTRACT

PURPOSE: The purpose of this study was to evaluate dose-volume histograms (DVHs) of bladder, rectum, sigmoid colon, and small bowel using image-based three-dimensional treatment planning for intracavitary brachytherapy. METHODS AND MATERIALS Between 2001 and 2003, 22 patients with cancer of the cervix (1 IB1, 5 IB2, 11 IIB, 5 IIIB) were treated with computerized tomography (CT)-compatible high-dose-rate intracavitary applicators and underwent postimplant pelvic CT scans with the applicator in place. The volumes of organs at risk were digitized. For radiography-based planning, International Commission on Radiation Units and Measurements (ICRU) bladder and rectum point doses were calculated. For the CT-based planning, the DVHs were computed for the bladder, rectum, sigmoid colon, and small bowel. To compare doses to organs at risk, the minimum dose in 2.0cm(3) volume receiving the highest dose (D(2)) was determined from DVHs. These D(2) doses were compared with radiography-based ICRU point doses. RESULTS: The mean ICRU bladder point dose (401cGy) was markedly underestimated compared to the mean bladder D(2) dose (484cGy). However, the mean ICRU rectal point dose (412cGy) did not differ significantly from the mean rectal D(2) dose (373cGy). The most frequent organ receiving the highest D(2) dose was the sigmoid colon in 9 of 22 patients (41%) followed by the rectum in 7 of 22 patients (32%) and small bowel in 6 of 22 patients (27%). CONCLUSIONS: From CT-based three-dimensional (3-D) evaluation, the ICRU bladder point dose was substantially lower than bladder D(2) dose. Special attention should also be given to the areas of proximal rectum and sigmoid colon due to more frequent high D(2) dose in these areas.