Program Information
Implementation of a Novel Sweeping Arc with Gantry Angle Dependent Modulation of Energy (SAME) for Proton Therapy Method
U Langner*, H Chung , K Langen , M Zhu , B Yi , Univ. of Maryland School Of Medicine, Baltimore, MD
Presentations
SU-I-GPD-T-192 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To investigate the efficacy and application of Sweeping Arc with gantry angle dependent Modulation of Energy (SAME) therapy with protons to tumors of different sizes and positions.
Methods: Proton arc therapy was simulated with Eclipse in a phantom study using a number of beams from equally spaced gantry angles and a single energy from the cyclotron. 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. These energies will vary depending on the tumor depth to produce a ~1cm SOBP ~5mm inside the distal edge of the tumor. A dose of 10Gy was delivered to a GTV of 1cm, 4cm, and 11cm diameter sphere inside a 25cm diameter water cylinder. PTV to GTV expansion was 5mm. Robustness evaluation of 2.5%/3mm was used as a metric. Plans were compared to 6X VMAT and 2 opposed SFO field plans.
Results: Worst case GTV robustness dose at 95% of the volume and worst case GTV robustness volume at 95% of the dose increased as the target volume increases and as the tumor shifts to the center of the volume. V20% and V50% was the smallest for SAME in all the cases and proton plans had markedly smaller integral doses to the volume compared to VMAT. Worst case robustness doses at 95 % of the volume was the best at 92.5% for the large GTV and the worst at 84% for the small GTV. This spread in robustness is caused by the inherent characteristic of this plan which will deliver only one energy plane per gantry angle.
Conclusion: SAME was more efficient for larger targets and closer to the CAX. Robustness can be increased for smaller targets by prescribing to lower isodose lines.
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