Phenomenological Study of Intra-Spill Break Spots In Dose-Driven Continuous Scanning Proton Therapy
Abstract
Purpose
Dose Driven Continous Scanning proton therapy offers reduced beam delivery time compared to discrete spot scanning but requires accurate characterization of temporal beam parameters for precise dose calculation. This study quantified rise time (trise) and plateau beam current (I0,measured) variations across a complete spill cycle and assessed their impact on average beam current (Iavg) per spot.
Methods
Beam current measurements were performed using a CROSSmini 2D detector array at 50 μs temporal resolution across three proton energies (70.2, 150.2, 228.7 MeV) and three nominal beam currents (8, 14, 20 MU/s) with break points implemented at every spot. Piecewise function fitting was applied to extract trise and I0,measured parameters for each spot across complete spill duration. Sensitivity analysis was conducted using partial derivatives and experimental validation to quantify the relative impact of the temporal parameter variations on Iavg. Moving averages over 20-spot windows were calculated to characterize intra-spill parameter changes.
Results
I0,measured observe a decreasing trend throughout spills before a steep terminal decline. Mean trise was 1.43 ± 0.71 ms across all conditions. Sensitivity analysis reveal Iavg exhibited substantially higher sensitivity to trise variations than I0,measured changes, with trise variations producing up to 80% changes in Iavg compared to <2% for I0,measured variations across spill.
Conclusion
We have characterized trise and I0,measured within a spill and the impact of the variation of these parameters on Iavg. These findings provide an essential basis for improving dose calculation accuracy in DDCS delivery.