Optimal beam arrangement for stereotactic body radiation therapy delivery in lung tumors.

PURPOSE: To compare the different beam arrangement and delivery techniques for stereotactic body radiation therapy (SBRT) of lung lesions using the criteria of Radiation Therapy Oncology Group (RTOG) 0236 protocol. MATERIAL AND METHODS: Thirty-seven medically inoperable lung cancers were evaluated with various planning techniques including multiple coplanar multiple static beams, multiple non-coplanar static beams and arc delivery. Twelve plans were evaluated for each case, including five plans using coplanar fixed beams, six plans using non-coplanar fixed beams and one plan using arc therapy. These plans were compared using the target prescription isodose coverage, high and low dose volumes, and critical organ dose-volume limits. RESULTS: The prescription isodose coverage, high dose evaluation criteria and dose to critical organs were similar among treatment delivery techniques. However, there were differences in low dose criteria, especially in the ratio of the volume of 50% isodose of the prescription dose to the volume of planning treatment volume (R(50%)). The R(50%) in plans using non-coplanar static beams was lower than other plans in 30 of 37 cases (81%). CONCLUSION: Based on the dosimetric criteria outlined in RTOG 0236, the treatment technique using non-coplanar static beams showed the most preferable results for SBRT of lung lesions.