SU‐E‐T‐879: Dosimetric Analysis of Proton Passive‐Scattering Stereotactic Body Radiotherapy (SBRT) of Treated Spine Lesions versus Photon SBRT

Abstract

Purpose: To investigate the trade‐off between spinal cord sparing and target coverage in spine patients treated with Proton Passive‐scattering Stereotactic Body Radiotherapy (SBRT) compared to Photon SBRT plans with IMRT and 3D‐CRT. Methods: Ten patients with spinal and paraspinal lesions have treated with Proton SBRT in our institution. Afterward, they were re‐planned with photon IMRT and 3D‐CRT SBRT protocol considering sufficient target coverage and sharp dose fall‐off at the margin of target and spinal cord. Dosimetric data obtained from the plans and were compared in target volume, spinal cord and other adjacent critical organs such as thecal sac, Cauda equina, esophagus. To test the validity of dose calculation in heterogeneous tissues for photon and proton, in house developed Monte Carlo has been used. Results: IMRT plans showed better coverage and conformity of the target volume compared to proton plans and 3D‐CRT. Dose fall‐off at the margin of spinal cord and target volume were comparable for IMRT, Proton and 3D‐CRT plans, however IMRT showed a better result. On the other hand, photon plans including IMRT and 3D‐CRT showed more exit dose to the beyond normal tissues. Conclusions: Proton plans showed wider beam penumbra at the margin of spinal cord and target volume due to multiple proton scatter events. The effect can leading to increase of spinal cord dose or decrease of target coverage and therefore risk of treatment failure.