Interstitial high dose rate brachytherapy boost in early-stage breast cancer: deformable image registration for defining target volume

Purpose: optimization of the technique of additional irradiation of the removed tumor bed using high-dose brachytherapy for breast cancer. Material and Methods: the results of treatment of 28 patients diagnosed with breast cancer were analyzed. After surgical treatment and a course of external radiation therapy, all patients underwent additional irradiation of the removed tumor bed using high-dose brachytherapy. The assessment of the operation protocols, the data of the pathomorphological conclusion was carried out, and on the basis of pre- and postoperative CT images, the formation of irradiation fields for high-dose brachytherapy was carried out. Results: After deformable (nonrigid) registration of pre- and postoperative CT images of 28 patients, it was revealed that in 18 women (64.3% of cases) the location of interstitial markers and the primary tumor focus does not match topographically, which can cause incorrect formation of borders irradiation. In 35.7% of cases, radiopaque markers were located on the chest wall (on the pectoralis major muscle) when the primary tumor was located in the breast tissue. In 25% of cases, the markers were located cranial or caudal to the topography of the primary tumor focus. Label migration occurred in 3.6% of cases. In 35.7% of cases, the topography of the primary tumor node and marks completely coincided. Conclusions: The use of deformable (non-rigid) registration of pre- and postoperative CT images is a simpler method to determine the topography of the removed tumor bed, which subsequently leads to a more accurate formation of the clinical volume of irradiation.