A clinical comparison of patient setup and intra-fraction motion using frame-based radiosurgery versus a frameless image-guided radiosurgery system for intracranial lesions

Background and purposeA comparison of patient positioning and intra-fraction motion using invasive frame-based radiosurgery with a frameless X-ray image-guided system utilizing a thermoplastic mask for immobilization.Materials and methodsOverall system accuracy was determined using 57 hidden-target tests. Positioning agreement between invasive frame-based setup and image-guided (IG) setup, and intra-fraction displacement, was evaluated for 102 frame-based SRS treatments. Pre and post-treatment imaging was also acquired for 7 patients (110 treatments) immobilized with an aquaplast mask receiving fractionated IG treatment.ResultsThe hidden-target tests demonstrated a mean error magnitude of 0.7 mm (SD = 0.3 mm). For SRS treatments, mean deviation between frame-based and image-guided initial positioning was 1.0 mm (SD = 0.5 mm). Fusion failures were observed among 3 patients resulting in aberrant predicted shifts. The image-guidance system detected frame slippage in one case. The mean intra-fraction shift magnitude observed for the BRW frame was 0.4 mm (SD = 0.3 mm) compared to 0.7 mm (SD = 0.5 mm) for the fractionated patients with the mask system.ConclusionsThe overall system accuracy is similar to that reported for invasive frame-based SRS. The intra-fraction motion was larger with mask-immobilization, but remains within a range appropriate for stereotactic treatment. These results support clinical implementation of frameless radiosurgery using the Novalis Body Exac-Trac system.