Evaluation of a single-isocenter technique for axillary radiotherapy in breast cancer

The aim of this study was to develop a technique for axillary radiotherapy that minimizes the risk of radiation-induced damage to the surrounding normal tissue (i.e., arm, shoulder, lung, esophagus, and spinal cord) while keeping the risk of a nodal recurrence to a minimum. A planning study was performed in 20 breast cancer patients. The target volume of the axillary treatment encompassed the periclavicular and axillary lymph node areas. The 3-dimensional (3D) computed tomography (CT) information in this study was used to outline the lymph node areas and the organs at risk (i.e., the esophagus, spinal cord, brachial plexus, and lung). A conventional AP-PA technique (with a transmission plate placed in the AP beam) was evaluated. In addition, a new single-isocenter technique consisting of AP/PA fields using a gantry rotation of +/-20 degrees and a medial AP segment was developed. Both techniques were compared by evaluation of the calculated dose distributions and the dose-volume histograms of the target volume and surrounding organs at risk. The field borders and humeral shielding were redefined based on the 3D anatomical references. Adapting the humeral shielding reduced the irradiated volume by 19% and might contribute to a reduction of the incidence of arm edema and impairment of shoulder function. The maximum radiation dose in the esophagus and spinal cord was reduced by more than 50% using the single-isocenter technique. The difference between both techniques with respect to the mean doses in the target volume and lung, and the maximum dose in brachial plexus, was not statistically significant. Moreover, the single-isocenter technique allowed a fast and easy treatment preparation and reduced the execution time considerably (with approximately 10 minutes per fraction).