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Session: Therapy General ePoster Viewing [Return to Session]

Comparison of Three Cushion Types for Gamma Knife Icon Mask Treatment

D Luo*, T Briere, E Han, M McAleer, UT MD Anderson Cancer Center, Houston, TX


PO-GePV-T-58 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: For mask treatment on Gamma Knife Icon, our clinic uses Moldcare cushion (QFix, Avondale, PA, USA) to mold underneath the patient’s head and upper neck for comfort and reproducibility inside the mask adaptor before a thermoplastic mask is molded around their face for immobilization. In order to treat an anterior lesion, the mold is made very thin to avoid collision. Occasionally the lesion is so anterior that, instead of the moldable cushion, a 3-mm bolus, as readily available in all radiation oncology department, or a grip shelf liner, a common consumer product, may be used to further reduce the distance between the skull and the mask adaptor.This study investigates the relative dosimetric effect from the two non-conventional material compared to the Moldcare cushion.

Methods: Two plans were delivered to an anthropomorphic head phantom with an ionization chamber inside. Plan-A had one shot of all 8 sectors of 16-mm collimation centered at the ion chamber. Plan-B has 3 posterior sectors at 16-mm and the rest at Block position. The phantom was placed inside Moldcare, or on top of the 3-mm bolus, or the grip shelf liner.

Results: Compared to Moldcare, both plans delivers > 1% less dose when the phantom is on top of the 3-mm bolus. One layer of liner received the same dose as the Moldcare from Plan-A, but 0.8% more dose from Plan-B. The 3-layer liner configuration received the same dose as the Moldcare from Plan-B.

Conclusion: The 3-mm bolus, while more accessible and easy to use, has more than 1% dose difference from the standard of care. The grip shelf liner is very easy to use and has less attenuation than the Moldcare. While all measured dose are lower than the planned dose, the dose from the liner is the closest to planned.


Gamma Knife, Immobilization


TH- External Beam- Photons: gammaknife

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