High-dose-rate interstitial brachytherapy using inverse planning for locally advanced cervical cancer

A 56-year-old woman with bulky cervical cancer was treated with high-dose-rate interstitial brachytherapy combined with external beam irradiation and chemotherapy. Inverse planning (IP) was used in the treatment planning for brachytherapy. Source dwell positions were selected automatically, once the required information had been input, for example, to prohibit dwelling inside the organs at risk (OARs) and to permit dwelling inside the planning target volume with a 2-mm inner margin. IP was compared with conventional geometrical optimization (GO) and dose point optimization (DO). The dwell positions of 3 plannings (IP, GOIP, and DOIP) were the same as IP, while in the other 2 plannings (GOConv and DOConv) dwell positions had the same length in all the applicators without concern for anatomy. D90 was equalized in all plannings as 100% prescription dose, and so the coverage index was always 90%. There was no definite tendency in dose non-uniformity ratio in the 5 plannings. As for sparing OARs such as the bladder, urethra, and rectum, IP showed the best % V75. The calculation time of the computer was fast enough. This is the first report in Japan on the clinical use of IP in interstitial brachytherapy, and it implies the usefulness of IP.