ESTRO 2025 - Abstract Book

S2607

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

1 Division of Radiation Oncology, National Cancer Centre Singapore, Singapore, Singapore. 2 Division of Physics and Applied Physics, Nanyang Technological University, Singapore, Singapore. 3 Oncology Academic Clinical Programme, Duke-NUS Medical School, Singapore, Singapore Purpose/Objective: Dose-driven continuous scanning (DDCS) is a form of beam delivery where the proton beam is scanned continuously across spots. DDCS is planned to be commissioned in National Cancer Centre Singapore and will be the first clinical DDCS for proton therapy in the world. This study aims to quantitatively characterize crucial beam delivery parameters for commissioning of the DDCS delivery system. Material/Methods: Break spots are defined as spot for which the beam is turned off between spots due violation of specific constraints. Irradiation experiments with and without break spots were conducted at three different energies (70.2, 150.2 and 228.7 MeV), with three different beam intensity, and 5 different spot doses. An oscilloscope was used to measure the time for the dose monitor (DM) signals to fully ramp up to the target beam current ( t rise ) and the minimum time between consecutive break spots ( t RFK ). The temporal resolution of the oscilloscope is 0.5 ms. The t rise is defined as the time taken for the DM signal to reach plateau when the radiofrequency knock (RFK) signal is turned on and is fitted with a piece-wise function that is optimised using least square fit. The minimum break spot time ( t RFK ) is the time between RFK off signal and RFK on signal for the next spot. The beam ramp up region and signal measured are illustrated in Figure 1.

Figure 1: a) Schematic illustration of beam ramp up region. The square waveform of the RFK signal indicates when the beam is turned on and off. b) Shows the measured RFK signals during irradiation at CAX with break spots for 70.2 MeV at 8 MU/s. c) Shows the measured RFK and DM signal when beam is turned on during irradiation at CAX without break spot for 70.2 MeV at 8 MU/s. Results: We have observed that t RFK between break spots to be 1.67 (±0.02) ms across all energy, beam intensity, and spot dose combinations. Figure 2 summarise the t rise found for all energy and beam intensity.