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SU‐E‐T‐551: Analysis of a Non‐Invasive Patient Mask Immobilization System for Cranial SRS with TomoTherapy
Author(s) -
Bichay T,
Kane J,
Ebrom P,
Chen C
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612513
Subject(s) - tomotherapy , nuclear medicine , radiosurgery , medicine , image guided radiation therapy , medical imaging , radiation therapy , surgery , radiology
Purpose: Purpose: Patient treatment setup accuracy is dependent on at least two parameters; localization and immobilization. Localization can be carried out with high resolution IGRT while immobilization can be accomplished with a non‐invasive mask. In this study we carried out an analysis of the reliability of a radiosurgery mask system to immobilize the patient during the SRS treatment session. Methods: Patients were fitted with a thermoplastic mask and customized pillow designed for SRS. TomoTherapy MVCT using 1 mm slice thickness was carried out prior to treatment. The required shifts, based on bony anatomy, were applied to the patient position, and the SRS treatment was then delivered. Typical treatment time varied from 20–30 minutes. At the completion of the treatment a second MVCT was carried out to determine if any patient movement had taken place. A total of 23 patients were analyzed. Some patients received more than one treatment fraction. A total of 32 MVCT measurements were included in this study. Results: The mean absolute shift for the 32 measurements is 0.42 mm (SD=0.29) lateral, 0.77 mm (SD=1.02) longitudinal, and 0.47 mm (SD=0.43 mm) in the vertical direction. Overall the average vector displacement is 1.23 mm (SD=0.87). The variation in shifts between different patients was significant. Two patients had a vector shift of greater than 3.0 mm largely due to a longitudinal displacement. Conclusions: This study demonstrates quantitatively the reliability of a non‐invasive mask system for patient immobilization during cranial radiosurgery. Our program routinely applies a 3 mm PRV and PTV to account for patient position uncertainty. These results suggest that this expansion should be adequate for most patients. Care in the initial molding of the mask, and customized pillow, may be key in ensuring minimal patient motion during cranial SRS.