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Using Experimentally Determined Proton Spot Scanning Operation Parameters to Accurately Model the Beam Delivery Time

J Shen

J Shen1*, E Tryggestad2 , J Younkin1 , S Keole1 , K Furutani2 , Y Kang1 , M Herman2 , M Bues1 , (1) Mayo Clinic Arizona, Phoenix, AZ, (2) Mayo Clinic, Rochester, MN


SU-I-GPD-T-184 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To accurately model the beam delivery time (BDT) for a synchrotron proton spot scanning system using experimentally determined beam operation parameters.

Methods: A software tool to simulate the proton spot delivery sequences was constructed and BDT is calculated by the sum of time used for layer switch, spot switch and spot delivery. We designed specific proton beam test patterns/plans to isolate and quantify the relevant parameters in the operation cycle of the proton beam delivery. These parameters included the layer switching time, magnet preparation and verification time, average beam scanning speeds in x and y directions, proton spill rate and the maximum charge available for each spill. The experimentally-determined parameters, as well as the nominal values (initially provided by the vendor) were applied in the software tool to predict BDTs for 602 patient deliveries. The calculated BDTs were then compared with the actual BDTs recorded in the patient treatment delivery log files.

Results: The experimentally-determined layer switching time on all 97 energies is 1.912s (varying from 1.9s to 2.05s for beam energies from 71.3MeV to 228.8MeV), average magnet preparation and verification time is 1.87ms, the average scanning speeds are 5.9m/s (x direction) and 19.3m/s (y direction), the proton spill rate is 8.7MU/s and the maximum protons available for one acceleration is 19.4MU. Some of these measured parameters are quite different from the nominal values. The calculated BDTs using experimentally-determined parameters matched the recorded BDTs of 602 treatments (∆t=-0.7s±1.42s), which is significantly more accurate than BDTs calculated using nominal timing parameters (∆t=-20.5±16.7s).

Conclusion: An accurate model for BDT prediction was achieved by using the experimentally-determined proton delivery parameters, which is useful in many situations such as modeling the interplay effect, guidance on how to effectively reduce BDT, and identifying deteriorated machine performance.

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