Stereotactic Radiosurgery for the Treatment of Primary and Secondary Ocular Malignancies

Abstract

isocenter radiosurgery for either single or multiple targets utilizing a flattening filter free LINAC operating at up to 2400 MU/min. The most common treatment geometry was two non-coplanar arcs requiring one room entry. Patients were immobilized in an Aquaplast mask. Imaging workflow included KV-KV 6DOF alignment, CBCT 6DOF alignment, and then a repeat CBCT 6DOF alignment prior to treatment. The magnitudes of the residual translation vector and corrections around each rotation axis were calculated between the KV and first CBCT (CT1) and then between the first and second CBCT (CT2). Results: As shown in the table below, CT1 alignment showed significant residual error after KV only alignment. CT2 alignment demonstrated stability of the patient over a mean imaging interval of 3.19 min between the two CBCT scans including one CBCT acquisition, registration, physician review and movement of the couch. The mean time after the second CBCT until beam-off was 6.44 minutes. Conclusion: The automated KV algorithm did not perform accurately enough to omit CBCT alignment for radiosurgery. CBCT alignment demonstrated stability even though patients were immobilized with only an Aquaplast mask. This data suggests that frameless radiosurgery with 6DOF alignment is feasible without invasive immobilization if treatment time is short. Stable rotational corrections to less than 0.5 degrees are feasible and facilitate single isocenter treatments of multiple targets. Author Disclosure: J. Fiveash: Research Grant; Varian Medical Systems. Consultant; Varian Medical Systems. C.D. Willey: None. M. Bredel: None. R. Popple: Research Grant; Varian Medical Systems. S.A. Spencer: None. K. Dempsey: None. J. Markert: None. K. Riley: None. M.C. Dobelbower: Research Grant; Varian Medical Systems.