Inter- and Intrafraction Patient Positioning Uncertainties for Intracranial Radiotherapy: A Study of Four Frameless, Thermoplastic Mask-Based Immobilization Strategies Using Daily Cone-Beam CT

摘要: Purpose To determine whether frameless thermoplastic mask-based immobilization is adequate for image-guided cranial radiosurgery. Methods and Materials Cone-beam CT localization data from patients with intracranial tumors were studied using daily pre- posttreatment scans. The systems ( 1 ) Type-S IMRT (head only) mask (Civco) head cushion; 2 Uni-Frame cushion, coupled a BlueBag body immobilizer (Medical Intelligence); 3 shoulder cushion (Civco); 4 same as previous, mouthpiece. comparative metrics translational shift magnitude average rotation angle; systematic inter-, random intrafraction positioning error was computed. For strategies 1–4, respectively, the analysis interfraction variability included 20, 9, 81, 11 patients, whereas that subset of 7, 16, 8 patients. results compared statistical significance an variance test. Results Immobilization system provided best overall accuracy stability. mean shifts (± SD) 2.3 1.4), 2.2 1.1), 2.7 1.5), 2.1 1.0) mm motion 1.1 1.2), 0.7 0.9), 0.8) devices respectively. No significant correlation between treatment time evident, although not purely random. Conclusions We find all are viable solutions With pretreatment corrections, symmetric PTV margins would likely be if ideal radiation planning targeting available.