Phenomenological Study of Intra-Spill Break Spots in Dose-Driven Continuous Scanning Proton Therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Particle Therapy

Background:

• Dose Driven Continuous Scanning (DDCS) proton therapy offers faster beam delivery than discrete scanning.
• Accurate dose calculation in DDCS requires precise characterization of temporal beam parameters.
• Understanding beam current variations within a spill is essential for optimizing DDCS delivery.

Purpose of the Study:

• To quantify the variations in beam rise time (t_rise) and plateau beam current (I_0,measured) during a complete spill cycle in DDCS proton therapy.
• To assess the impact of these temporal parameter variations on the average beam current per spot (I_avg).
• To provide a basis for improving dose calculation accuracy in DDCS.

Main Methods:

• Beam current measurements were performed using a CROSSmini 2D detector array with 50 μs temporal resolution.
• Piecewise function fitting was used to extract t_rise and I_0,measured parameters for each spot.
• Sensitivity analysis and experimental validation quantified the impact of temporal variations on I_avg.

Main Results:

• Measured I_0,measured showed a decreasing trend throughout spills, with a steep terminal decline.
• The mean t_rise was 1.43 ± 0.71 ms across all tested conditions.
• I_avg was significantly more sensitive to t_rise variations (up to 80% change) than to I_0,measured variations (less than 2% change).

Conclusions:

• The study successfully characterized temporal beam parameters (t_rise, I_0,measured) within a spill cycle for DDCS proton therapy.
• Variations in beam rise time have a substantial impact on average beam current, significantly influencing dose calculation accuracy.
• These findings are critical for enhancing the precision of dose delivery in DDCS proton therapy.