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Multiple Energy Extraction Reduces Beam Delivery Time for a Synchrotron-Based Proton Spot-Scanning System

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J Younkin

J Younkin*, M Bues , S Keole , J Stoker , J Shen , Mayo Clinic Arizona, Phoenix, AZ


SU-I-GPD-T-197 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Multiple energy extraction (MEE) is a technology recently introduced by Hitachi for its ProBeatV system that reduces beam delivery time (BDT) relative to traditional single energy extraction (SEE) by delivering several energy layers per accelerator spill. To determine whether this technique would significantly decrease beam-on time, we calculated BDT for a patient cohort in both SEE and MEE delivery modes.

Methods: A BDT model was developed to compute field delivery time. Actual BDTs from delivery logs of more than one thousand SEE treatment fields was used to validate this model. It was then used to compute delivery time for the same cohort of patient treatment fields in several MEE configurations, and the corresponding reductions in BDT were obtained. We then proposed and validated a method that other facilities can use to approximate MEE time savings without needing to re-implement our beam model.

Results: We accurately predicted BDT to within 1.66% ± 1.19% of measured SEE delivery time. An optimal MEE configuration with three energy layers per spill reduced total BDT for our patient sample by 41%. Additional layers provided limited BDT savings due to their diminishing effect on the number of spills required per field. BDT reduction for individual fields was strongly correlated with average MU per energy layer; among major sites, prostate with low MU/layer fields had 40% - 50% BDT reduction, but this dropped to 20% - 30% for breast treatment fields due to their higher average MU/layer. Approximations based on MU/layer predicted BDT savings to within 3%.

Conclusion: The MEE delivery technique resulted in a highly significant reduction in BDT for a sample of patient treatment fields. Upgrading synchrotrons to MEE will decrease total patient beam-on time at proton treatment centers considerably. Further study will determine the effect of this new technology on patient throughput.

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