SU‐E‐T‐455: Novel Planning Techniques for Lung SBRT

Two new planning techniques in lung SBRT are presented. The first technique involves a differential dosing strategy for patients with compromised pulmonary function. The second technique compares supine vs prone setup for extreme posterior lesions. CyberKnife™(CK) prone setup is complicated due to patient discomfort from longer treatment times and the inability to track without fiducials.CK(G.3) Multiplan™(V3.5). Synchrony™, XSight™ Lung Tracking Systems. Our lung SBRT patients are tracked using fiducials with Synchrony or without fiducials with XSight using a 60 Gy in three fractions scheme. If the ray-tracing optimized plan results in V15Gy greater than 10% we employ the differential dosing technique. A new PTV is created to encompass the 54 Gy isodose surface. A more conformal plan with a dose constraint of 60Gy to CTV and 54Gy to PTV is created appreciably lowering the V15Gy. Alternatively a 54Gy PTV can be created from measured respiration excursions. For the prone/supine comparison, plans were generated for both positions then evaluated.Patients planned with the differential dose technique have a good tumor response as evidenced by a follow-up PET. Although prone setup is preferred for extremely posterior tumors, a dosimetrically comparable supine plan can be created to replicate the prone plan. The supine low dose spillage was only slightly greater than in the prone case.We conclude that the 54Gy/60Gy dosed patients have almost the same tumor response as the standard 60 Gy treatment. A dosimetrically similar supine plan obviates the need for a prone delivery.