Dosimetric characteristics of accelerated partial breast irradiation with CT image–based multicatheter interstitial brachytherapy: A single institution’s experience

Abstract

Purpose To present dosimetric assessment of CT-based high-dose-rate interstitial brachytherapy of breast cancer including dose–volume histogram analysis of dose to critical structures. Methods and Materials Treatment plans of 49 patients with early-stage breast cancer enrolled to the Groupe Européen de Curiethérapie-European Society for Therapeutic Radiology and Oncology trial and treated with interstitial partial breast irradiation were selected for the study. Treatment planning was performed with the use of pre- and postimplant CT imaging. Quantitative dosimetry on target volume including calculation of target volume coverage, dose homogeneity, and conformality indices was performed. Dose nonuniformity ratio was defined as ratio of volumes encompassed by 1.5 times the prescribed dose (PD) and the PD. Dose homogeneity index was defined as ( V100– V150)/ V100. Detailed dose–volume histogram analysis was carried out for the breast, lung and heart. Results Three-, four-, five-, and six-plane implants were used in 17, 21, 10, and 1 patients, respectively. The median number of catheters was 15 (range, 6–28). The mean volume of the planning target volume (PTV) was 66.4 cm 3 (range, 15.5–176 cm 3). On average, 92% (range, 90–96%) of the PTV received the PD. The mean values for dose nonuniformity ratio and dose homogeneity index were 0.32 (range, 0.25–0.41) and 0.65 (range, 0.50–0.76), respectively. The mean conformal index was 0.68 (range, 0.51–0.82) and breast tissue volume around PTV, which received at least the PD ranged between 5.3 and 51 cm 3. The mean maximum doses to skin, lung, and heart were 55%, 44%, and 21%, respectively. Volumes of the lung and heart receiving 5 Gy were 50.6 and 21.0 cm 3, respectively. Conclusions Our implant technique based on two sets of CT scanning resulted in acceptable dose distributions with respect to target coverage, dose homogeneity, and conformality.