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 2.0cm³ volume receiving the highest dose (D₂) was determined from DVHs. These D₂ 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 D₂ dose (484cGy). However, the mean ICRU rectal point dose (412cGy) did not differ significantly from the mean rectal D₂ dose (373cGy). The most frequent organ receiving the highest D₂ 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 D₂ dose. Special attention should also be given to the areas of proximal rectum and sigmoid colon due to more frequent high D₂ dose in these areas.

Keywords: Cervical cancer, Brachytherapy, Image-based treatment planning, Dose-volume histogram, Organs at risk