ESTRO 2025 - Abstract Book

S2688

Physics - Dose calculation algorithms

ESTRO 2025

spots following break-spots require a finite beam rise time (T rise ) to reach full intensity. While T rise measurement using high-resolution oscilloscope is challenging due to signal noise, understanding its impact on delivery time is crucial for system optimization. This preliminary study evaluates DDCS delivery time sensitivity to T rise variations across different beam energies and spot patterns. Material/Methods: Using the NCCS proton beam delivery system, we developed a computational model to analyse the impact of ±10% and ±40% variations in T rise (nominal: 2.0 ms, estimated from oscilloscope measurements) across multiple beam energies from a prostate treatment plan. The analysis examined the relationship between beam current (1-20 MU/s) and total delivery time for 24 different energies, with Fig. 1 showing results for five representative energies (135.5 180.3 MeV).

Results:

Analysis revealed that delivery times stabilize at higher beam currents (>15 MU/s). Higher energies showed reduced sensitivity to T rise variations, with ±40% variations converging toward nominal delivery times as energy increased (Fig. 1a). Despite large T rise variations of ±40%, total delivery time remained within ±10% bounds across all energies (Fig. 1c). Lower energies exhibited higher relative sensitivity due to shorter absolute delivery times, but even at 10% T rise variation, relative sensitivity stayed below 3% (Fig. 1b), suggesting this as a practical tolerance limit for T rise measurement precision.