Program Information
Online Adaptive VMAT Planning Based On Deformed Dose for Patients Undergoing Concurrent Prostate, Seminal Vesicle and Lymph Node Treatment
L Qiu*, A Vassil , A Godley , The Cleveland Clinic, Cleveland, OH
Presentations
TU-C1-GePD-J(B)-2 (Tuesday, August 1, 2017) 9:30 AM - 10:00 AM Room: Joint Imaging-Therapy ePoster Lounge - B
Purpose: VMAT in conjunction with small PTV margins allows the dose to the rectum, bowel and bladder to be minimized, at the potential cost of prostate, seminal vesicle (SV) or lymph nodes (LN) coverage. Coverage to all three can be maintained by adaptive planning. Here, we use the deformed planning dose as the goal for plan adaptation.
Methods: Nine prostate, SV and LNs patients with CT-on-Rails (CTOR) imaging were re-planned using Monaco (Monaco, Elekta AB, Stockholm, Sweden) with 2 10MV VMAT arcs, 70 Gy to 95% of the prostate PTV, 56 Gy to 95% of the SV PTV and 50.4 Gy to 95% of the LNs PTV. A variable PTV margin of 4-6 mm was used. The planning CT was deformably registered to each CTOR, the resulting deformation field was applied to morph the dose to the CTORs. The deformed dose and CTOR were imported into Monaco, and the dose guided the plan adaptation. The original treatment plan was shifted to the CTOR, aligning the center of the LNs to mimic bony alignment, and to ensure LN coverage. CTORs were extended to ninety slices by replicating the first and last slices, to increase the scattered dose.
Results: The deformed dose guided adaptation maintained the prostate, SV & LNs coverage and the sparing of organs at risk (OAR). The shifted plan was unable to do both. On average the percentage volume covered by 100% isodose line increased from 95.5 to 99.4 for prostate, 84.4 to 93.1 for prostate PTV, 91.8 to 98.6 for SV, and 87.5 to 96.8 for SV PTV by the deformed dose guided adaptation. PTV coverage is partially required to account for intra-fraction motion.
Conclusion: Using the planned dose deformed to the daily CTOR provided a successful goal for adaptive optimization, and maintained prostate and SV PTV coverage.
Funding Support, Disclosures, and Conflict of Interest: A. Godley receives a research grant from Elekta AB, Stockholm, Sweden
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