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.