SU-E-J-29: Evaluation of Effectiveness of Immobilization Devices for Radiation Therapy with Repeated CBCT Studies

Medical Physics
H LiX Zhu

Abstract

To evaluate the effectiveness of three different immobilization devices for lung radiation therapy with daily and/or weekly cone-beam CTs (CBCT). Three different immobilization devices, short (IM1) and long (Im(2) ) Vac-lok cushion with wing boards (Civco), BodyFix (Im(3) , Elekta), were investigated. Repeated CBCT images for 3 SBRT patients immobilized with Im(3) , and 6 IMRT patients immobilized with IM1 and Im(2) (3 each) were acquired. Each SBRT patient received 70 Gy in 10 fractions and setup daily with CBCT, while IM1 and Im(2) patients were setup daily with orthogonal kV, and weekly CBCT (week 0-6). The day 1, 6 and 10 CBCT for Im(3) were considered week 0-2 CBCT. Patient setup was first based on skins markers then shifts were made based on bony landmarks in kV and GTV with CBCT. Skin contours, which are further away from the isocenter and thus more sensitive to rotation and skin folding, were extracted in each CBCT data set and the difference on skin contours were investigated for both before and after shifts. Over 2 weeks of treatment, Im(3) has the smallest standard deviation for setup shifts (0.09, 0.16, 0.20 cm on LR, UD and IO directions) compared to IM1 (0.29, 0.35, 0.34 cm) and Im(2) (0.11, 0.19, 0.40 cm), which ...Continue Reading

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