Stereotactic Body Radiation Therapy of Ventricular Tachycardia Using 4pi-Optimized Arc Trajectories.

PURPOSE/OBJECTIVE(S) To investigate dose sparing of organs at risk (OARs) by using 4pi-optimized arc trajectories in stereotactic body radiation therapy for treating ventricular tachycardia (VT-SBRT). MATERIALS/METHODS Computed tomography (CT) datasets of the thorax of 15 patients were used for contouring and planning. A 4pi algorithm was implemented into a treatment planning system via a specific program for generating the optimized trajectories. Optimization is based on geometric penalty of arc overlap with OARs, weighted by relative OAR priority. Following VMAT optimization applied to optimized trajectories, dosimetric results were compared to a conventional trajectory (two full arc) plans. RESULTS On average, a significant reduction in maximum dose was observed for esophagus (18%), spinal cord (26%) and trachea (22%) with the 4pi-optimized trajectory when compared to the conventional one. Mean doses were also found to decrease for esophagus (19%), spinal cord (33%), skin (18%), liver (59%), lungs (19%), trachea (43%), aorta (11%), inferior vena cava (25%), superior vena cava (33%) and pulmonary trunk (26%). Improvement in dose sparing in terms of median dose was also observed for esophagus (40%), spinal cord (48%), skin (36%), liver (72%), lungs (41%), stomach (45%), trachea (53%), aorta (45%), superior vena cava (38%), pulmonary veins (32%) and pulmonary trunk (39%). No statistically significant differences of maximum dose (P = 0.650) or homogeneity index (P = 0.156) were observed for target volumes. Conformity index was comparable between optimized and non-optimized trajectory plans. CONCLUSION While preserving target volume coverage, 4pi-optimized trajectories can provide significant dose reduction to OARs and cardiac substructures especially in terms of mean and median doses. Ours results show that 4pi-optimized arc trajectories represent a promising delivery option for VT-SBRT.