4π Noncoplanar Stereotactic Body Radiation Therapy for Centrally Located or Larger Lung Tumors

Purpose: To investigate the dosimetric improvements in stereotactic body radiation therapy for patients with larger or central lung tumors using a highly noncoplanar 4 pi planning system. Methods and Materials: This study involved 12 patients with centrally located or larger lung tumors previously treated with 7- to 9-field static beam intensity modulated radiation therapy to 50 Gy. They were replanned using volumetric modulated arc therapy and 4 pi plans, in which a column generation method was used to optimize the beam orientation and the fluence map. Maximum doses to the heart, esophagus, trachea/bronchus, and spinal cord, as well as the 50% isodose volume, the lung volumes receiving 20, 10, and 5 Gy were minimized and compared against the clinical plans. A dose escalation study was performed to determine whether a higher prescription dose to the tumor would be achievable using 4 pi without violating dose limits set by the clinical plans. The deliverability of 4 pi plans was preliminarily tested. Results: Using 4 pi plans, the maximum heart, esophagus, trachea, bronchus and spinal cord doses were reduced by 32%, 72%, 37%, 44%, and 53% (P <= .001), respectively, and R-50 was reduced by more than 50%. Lung V-20, V-10, and V-5 were reduced by 64%, 53%, and 32% (P <= .001), respectively. The improved sparing of organs at risk was achieved while also improving planning target volume (PTV) coverage. The minimal PTV doses were increased by the 4 pi plans by 12% (P =. 002). Consequently, escalated PTV doses of 68 to 70 Gy were achieved in all patients. Conclusions: We have shown that there is a large potential for plan quality improvement and dose escalation for patients with larger or centrally located lung tumors using noncoplanar beams with sufficient quality and quantity. Compared against the clinical volumetric modulated arc therapy and static intensity modulated radiation therapy plans, the 4 pi plans yielded significantly and consistently improved tumor coverage and critical organ sparing. Given the known challenges in central structure dose constraints in stereotactic body radiation therapy to the lung, 4 pi planning may increase efficacy and reduce toxicity. (C) 2013 Elsevier Inc.