Exploring the potential of mixed-source brachytherapy for the treatment of cervical cancer using high-dose rate 192Ir and/or 50 kV electronic sources.

PURPOSE: In this study, computer modeling was used to compare the relative doses with the bladder, rectum, and bowel when two different brachytherapy modalities were used to treat cervical cancer with a tandem and ovoid applicator. A standard high-dose rate (HDR) (192)Ir treatment plan was compared with a "mixed-source" brachytherapy (MSB) treatment plan in which a 50 kV electronic brachytherapy X-ray source was substituted for (192)Ir as the tandem source. METHODS AND MATERIALS: A total of 15 three-dimensional CT data sets from cervical cancer patients previously treated with tandem and ovoid applicator were evaluated for the study. Bladder, rectum, bowel, and target volumes were contoured and separate treatment plans were created for MSB and HDR (192)Ir applications. Dose-volume histograms were analyzed for each organ at risk. RESULTS: The mean %V(25) for the bladder was 43% vs. 70% for MSB and HDR (192)Ir methods, respectively. Similarly, for the rectum mean %V(25) was 34% vs. 48% for MSB and HDR (192)Ir. For the bowel, the mean %V(25) was 28% vs. 43% for the MSB and HDR (192)Ir methods, respectively. In 16 of 45 organs at risk, %D(2 cc) values were higher for MSB than HDR (192)Ir. CONCLUSIONS: MSB is capable of providing target coverage to the cervix, uterus, and paracervical regions equivalent to that provided by HDR (192)Ir, while significantly reducing the overall dose to the bladder, rectum, and bowel. This reduction is associated with small regions of increased dose in a significant proportion of patients.