Radiation therapy of post-mastectomy patients with positive nodes using fixed beam tomotherapy

Purposes: To develop an optimized dosimetric class solution for post-mastectomy irradiation for fixed beam tomotherapy (FBT). Methods and materials: CT simulation scans from 10 post-mastectomy patients were used to generate plans with planning target volumes (PTVs) that included the chest wall, axillary nodes and supraclavical nodes using FBT and helical tomotherapy (HT) with 3D and IMRT modes and the resultant dosimetry was compared to conventional IMRT. FBT IMRT plans were analyzed with both 4 (4FBT) and 11-field (11FBT) plans. Important organs at risk (OARs) included the heart, ipsilateral and contralateral lungs, esophagus and contralateral breast. In all plans, the spinal cord and contralateral lung were completely blocked while the heart and ipsilateral lung were directionally blocked. Doses to the contralateral breast were minimized. Each plan was evaluated for its delivery time, percentile volume of lung receiving x Gy (Vx) and dose received by x percent volume (Dx). D1 and D5 were used to measure the maximum dose to the OAR or PTV, D95 and D99 were used to measure the minimal dose to the PTV. Results: Compared to the conventional IMRT technique, HT IMRT, 11FBT IMRT and 11FBT 3D significantly reduced the D1 of the heart in cases of left-sided tumors by 13%, 41% and 36%, and the V10 of ipsilateral lung in all cases by 26%, 49% and 46%, respectively. A close to 90% reduction in the contralateral breast dose was also observed with the 11FBT plans. Target dose homogeneity of 11FBT 3D plans is inferior to that of the HT and conventional IMRT plans but the treatment delivery time, 7.59 min, was significantly shorter by 3 min. 4FBT IMRT resulted in clinically unacceptable heterogeneity with high dose regions in both the PTV and normal tissue. Conclusions: A class solution based on an 11 beam configuration was established to optimize the dosimetry of fixed beam tomotherapy planning for post-mastectomy patients. The 11FBT plans were deliverable in clinically efficient treatment times.