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Comparison of the Dosimetric Accuracy of Proton Breast Plans Delivered with VisionRT and CBCT Setup

M MacFarlane1*, K Jiang1, M Mundis1, E Nichols1, S Chen1, N Biswal1, (1) University of Maryland School of Medicine, Baltimore, MD,


(Wednesday, 7/15/2020) 10:30 AM - 11:30 AM [Eastern Time (GMT-4)]

Room: Track 3

Purpose: Surface guided radiation therapy (SGRT) systems i.e. VisionRT, tracks a patient’s position before and during radiation therapy to aid in setup and treatment accuracy. In this study, we evaluate the dosimetric accuracy of VisionRT and CBCT setup in proton breast plans.

Methods: 20 patients were retrospectively analyzed in this IRB-approved study. Patients were typically setup with both CBCT and VisionRT for the first three fractions, then daily VisionRT and weekly CBCT thereafter. Each patient underwent a QA-CT scan midway through their treatment course to assess for anatomical changes. To emulate the VisionRT and CBCT setup, the planning CT and QA-CT were registered in two ways: 1) by registering the volume within the CTs covered by the CBCT, and 2) by contouring and registering the surface surveyed by the VisionRT system. The original plan was copied onto these two datasets and the dose was recalculated. The dosimetric parameters evaluated in this study were CTV: V95%; Heart: V25Gy, V15Gy, and mean dose; and Lung: V20Gy, V10Gy, and V5Gy.

Results: One-way repeated measures MANOVA (p < 0.001) and post-hoc ANOVA omnibus tests found that the CTV V95% (p < 0.001) and heart V25Gy (p = 0.029) were significantly different between datasets. Pairwise t-tests showed that, specifically, there was no significant difference in CTV V95% between the CBCT and VisionRT registered QA-CTs (p = 0.50) but both QA-CT’s were significantly lower (p < 0.001) than the planning CT’s by 3.7% on average. The heart V25Gy was significantly higher in the VisionRT plan compared to the planning CT (p = 0.01, albeit by 0.2%) but no significant difference was found between the planning CT and CBCT setup (p = 0.23), and the CBCT and VisionRT setup (p = 0.12).

Conclusion: This study supports that SGRT systems provide accurate delivery of proton breast treatment plans.


Surface Matching, Protons, Cone-beam CT


TH- External Beam- Particle/high LET therapy: Proton therapy - Motion management - interfraction

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