WE-EF-303-02: BEST IN PHYSICS (JOINT IMAGING- THERAPY): A Comprehensive Simulation of Image Guided Beam Gating for XXXX Treatments Using Scanned Proton Therapy.

@entity1 @entity343 @entity1493 @entity96
PURPOSE: To evaluate the effectiveness of image guided beam gating for PBS liver treatments under realistic breathing conditions. METHODS: We have previously proposed a Beams' Eye View ( @entity1493 ) X-ray image system as an online motion monitoring device for deriving a gating signal for PBS proton therapy. Using dedicated 4D dose calculations (4DDC), in this work we have simulated gated liver treatments using three amplitude-based gating windows (10/5/3mm) based on motion extracted from @entity1493 imaging of fiducial markers or the diaphragm. In order to improve motion mitigation, @entity1493 guided gating has also been combined with either volumetric (VS) or layered (LS) rescanning. Nine 4DCT(MRI) liver data-sets have been used for the investigation, which not only consider realistic @entity1 geometries but also motion variations between different breathing cycles. All 4D plans have been quantified in terms of plan homogeneity in the @entity343 (D5-D95), the total estimated treatment time and the beam-on duty cycle. RESULTS: Neither gating nor rescanning can fully retrieve a comparable plan homogeneity to the static case, and considerable reductions of the duty cycle (<10%) were observed as a Result motion variations when small gating windows are used. However, once combined with rescanning, dose homogeneity within 1% of the static plan could be achieved with reasonable prolongation of the treatment time for all 9 subjects. No differences were observed between the efficacy of layered or volumetric re-scanning, or of gating signals extracted from fiducial or diaphragm motions. However, layered rescanning may be preferred over volumetric rescanning when performed in combination with gating as it is generally more time-efficient and dosimetrically robust to @entity1 and motion variations CONCLUSION: Combining @entity1493 beam gating with rescanning is an efficient and effective approach to treating @entity96 , and is equally effective if either the diaphragm or fiducial markers are used as motion surrogates.
