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Experimentally determined proton discrete spot scanning time structures for an improved synchrotron-based PBS spot
James Kuan Huei Lee1,2, Clifford Ghee Ann Chua2,3, Kah Seng Lew2,3
1Department of Physics, National University Singapore, Singapore, Singapore.
Medical Physics
|June 25, 2026
Summary
An accurate beam delivery time model for proton therapy was developed using oscilloscope measurements. This model incorporates multi-energy extraction characteristics for improved 4D dose accumulation calculations.
Area of Science:
- Medical Physics
- Radiation Oncology
- Particle Accelerator Physics
Background:
- Accurate discrete spot scanning (DSS) beam delivery time (BDT) models are crucial for 4D dynamic dose accumulation in proton therapy.
- Reliable interplay evaluation in 4D dose calculations depends on machine-specific BDT models.
Purpose of the Study:
- To develop a BDT model for a synchrotron-based Hitachi Probeat PBS proton system.
- To characterize key BDT structures and multi-energy extraction (MEE) using oscilloscope measurements.
Main Methods:
- Oscilloscope measurements and delivery log files were used to characterize BDT structures.
- Spot-to-spot scanning trajectories were visualized using a CROSSmini 2D strip ionization chamber.
- MEE design, charge recapture efficiencies, and the impact of spot number were investigated.
Main Results:
- An improved BDT model incorporating dead times between RFK and HSST signals was derived.
- Spot-to-spot movement exhibits "hockey-stick" behavior, governed by the slower axis.
- Energy-dependent MEE layer variations and reduced charge fraction/MEE efficiency with increased spot numbers were observed.
Conclusions:
- MEE characteristics must be included in synchrotron-based time models for accurate proton beam delivery modeling.
- The presented methodology offers a framework for developing machine-specific delivery time models.
