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Sweeping Arc with Gantry Angle Dependent Modulation of Energy (SAME) for Proton Therapy: A Proof of Principle

U Langner

U Langner*, H Chung , W D'Souza , K Langen , M Zhu , B Yi , Univ. of Maryland School Of Medicine, Baltimore, MD


SU-I-GPD-T-191 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To develop a method to deliver efficient Sweeping Arc with gantry angle dependent Modulation of Energy (SAME) therapy with protons. A phantom planning study was done to illustrate the proof of principle.

Methods: Proton arc therapy was simulated with Eclipse using 24 beams from equally spaced gantry angles. Each angle represents a control point where energy will be modulated according to predetermined depths inside the target volume with an energy modulator (EM) attached to the snout. A single energy is allowed from the cyclotron per plan and additional energies will be produced using the EM, resulting in a plane inside the target volume that will be swept across as the arc is completed. A dose of 10Gy was delivered to a 4cm diameter sphere centered in a 25cm diameter water cylinder, using an energy of 141MeV (corresponding range: ~14.2cm) for every other gantry angle and 135MeV (corresponding range: ~13.2cm) for remaining angles. Plans were compared to a 6X VMAT plan and a 2 opposed SFO fields plan.

Results: The SFO plan produced 1619 spots and 51 270 MUs, while the SAME plan produced 2023 spots, and 47 332 MUs. V5% for the phantom was 30.4% for VMAT, 10.7% for SFO, and 16.2% for the SAME method. The V20% and V50% was the least for the SAME method at 15.5%, 7.8%, and 3.1% for V20% and 2.5%, 1.8%, and 1.7% for V50% for the VMAT, SFO and SAME methods, respectively. The integral doses were markedly less for both proton plans compared to VMAT (>50%). Integral doses less than 100cGy were larger for the SAME method than the SFO method, but increased slower as higher doses were included in the integral.

Conclusion: The SAME method is feasible and provide a decrease in integral dose at higher doses than the other methods.

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