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Does Custom Made Immobilization Improve Patient Setup? Analysis of Vacuum Bag Vs Off the Shelf Immobilization for Pelvis and Thorax Treatments

S Hadley*, Y Sun, The University of Michigan, Ann Arbor, MI


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Customized vacuum bags are assumed to perform better for patient setup and immobilization as compared to flat table top & off the shelf immobilization. With the advent of CBCT and 6DOF couches, we put this assumption to the test.
Methods: We perform 6DOF image registration of treatment CBCTs to assess the quality of reproducing patient position using custom made vacuum bags compared to conventional immobilization equipment. For thorax treatments, we compare the Elekta BodyFix (28 pts, 81 CBCTs), Civco vacuum bags (11,120) and, Civco Thorax Board (5,125). For pelvis we compared Civco vacuum bags (20,100) to thin pads on the flat table (11,89). A 6DOF alignment was performed for each CBCT to the planning CT to align the boney anatomy. Statistical analyses of the rotation angles of the alignment were used to compare the different immobilization techniques to determine which is best at reproducing patient position.

Results: A flat table with a thorax board outperforms both BodyFix and vacuum bags in terms of minimizing rotations needed to align a CBCT to the planning CT. For pelvis setups, the blue pad with flat table outperform a vacuum bag, even though both methods are substandard at positioning the pelvis. The thorax board and BodyFix required repositioning 4% and 5% of the setups while the vacuum bag required repositioning 32% of setups. For pelvic setups the blue pad and vacuum bag preformed poorly, requiring patient repositioning in 10% of setups.

Conclusion: These results show us that for treatments in the thorax, custom vacuum bags perform worse than a standard thorax board placed on a flat table. For the flat table vs the custom vacuum bag, neither system was significantly better for pelvic setups. The variation in rotation needed to align the pelvic bone was large, indicating both systems were equally unsatisfactory.


Patient Positioning, Immobilization, Image-guided Therapy


TH- External Beam- Photons: Motion management - interfraction

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