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Online Adaptive VMAT Planning Based On Deformed Dose

R Qiu

R Qiu*, A Vassil , A Godley , Cleveland Clinic, Cleveland, OH


SU-F-J-107 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Prostate treatment with volumetric-modulated arc therapy (VMAT) in conjunction with small PTV margins, allows the dose to the rectum and bladder to be minimized, at the potential cost of prostate coverage. Coverage can be restored by online adaptive planning. Here, the deformed planning dose is used as the goal for adaptive plan optimization.

Methods: 9 prostate patients with CT-on-Rails (CTOR) imaging were re-planned using Monaco (Elekta AB, Stockholm, Sweden) with 2 VMAT arcs, and 70 Gy to 95% of the PTV. A variable margin of 4-6 mm was used. The planning CT was deformably registered to each CTOR, the resulting deformation field was then applied to morph the structures and dose to the CTORs, using ADMIRE (Elekta AB, Stockholm Sweden). The deformed dose, edited contours and CTOR were imported into Monaco, and the dose referred as a guide for plan optimization. The original treatment plan was also copied to the CTOR, keeping the center of the prostate as the isocenter, to mimic the current repositioning based therapy.

Results: The deformed dose guided optimization maintained the prostate coverage and the sparing of OAR. The shifted plan was unable to do both. The mean percentage volume covered by 100% isodose line increased from 96.11±2.04 to 99.74±0.10 for prostate, and 83.48±2.63 to 94.61±0.34 for PTV by adapting the deformed dose guided optimization. PTV coverage is of some interest, as there still needs to be some margin for intra-fraction motion. Besides, the resulting lower inter-fraction dose variation of optimized plan implied a better dose delivery consistency.

Conclusion: Using the planned dose, deformed to the daily CTOR provided a successful goal for adaptive optimization, allowing reduced margins, increased OAR sparing, and maintained prostate coverage.

Funding Support, Disclosures, and Conflict of Interest: Godley receives research grant from Elekta.

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