Diamond detectors for dose and instantaneous dose‐rate measurements for ultra‐high dose‐rate scanned helium ion beams

Abstract

BackgroundThe possible emergence of the FLASH effect—the sparing of normal tissue while maintaining tumor control—after irradiations at dose‐rates exceeding several tens of Gy per second, has recently spurred a surge of studies attempting to characterize and rationalize the phenomenon. Investigating and reporting the dose and instantaneous dose‐rate of ultra‐high dose‐rate (UHDR) particle radiotherapy beams is crucial for understanding and assessing the FLASH effect, towards pre‐clinical application and quality assurance programs.PurposeThe purpose of the present work is to investigate a novel diamond‐based detector system for dose and instantaneous dose‐rate measurements in UHDR particle beams.MethodsTwo types of diamond detectors, a microDiamond (PTW 60019) and a diamond detector prototype specifically designed for operation in UHDR beams (flashDiamond), and two different readout electronic chains, were investigated for absorbed dose and instantaneous dose‐rate measurements. The detectors were irradiated with a helium beam of 145.7 MeV/u under conventional and UHDR delivery. Dose‐rate delivery records by the monitoring ionization chamber and diamond detectors were studied for single spot irradiations. Dose linearity at 5 cm depth and in‐depth dose response from 2 to 16 cm were investigated for both measurement chains and both detectors in a water tank. Measurements with cylindrical and plane‐parallel ionization chambers as well as Monte‐Carlo simulations were performed for comparisons.ResultsDiamond detectors allowed for recording the temporal structure of the beam, in good agreement with the one obtained by the monitoring ionization chamber. A better time resolution of the order of few μs was observed as compared to the approximately 50 μs of the monitoring ionization chamber. Both diamonds detectors show an excellent linearity response in both delivery modalities. Dose values derived by integrating the measured instantaneous dose‐rates are in very good agreement with the ones obtained by the standard electrometer readings. Bragg peak curves confirmed the consistency of the charge measurements by the two systems.ConclusionsThe proposed novel dosimetric system allows for a detailed investigation of the temporal evolution of UHDR beams. As a result, reliable and accurate determinations of dose and instantaneous dose‐rate are possible, both required for a comprehensive characterization of UHDR beams and relevant for FLASH effect assessment in clinical treatments.

Development and benchmarking of a dose rate engine for raster‐scanned FLASH helium ions

“…The delivery and measurement of dose and dose rate was performed at HIT, following experimental procedure for instantaneous dose rate acquisition. 24 For each investigated plan, the delivery time structure of the irradiated spill was recorded by the beam monitor chamber with a 50 µs time resolution for a helium ion beam irradiation with an energy of 145. (range in water of approximatively 14.6 cm).…”

“…Dose rate measurements were performed with diamond prototype detectors (sensitive volume 1.1 mm in diameter, 1 µm thick, PTW) coupled with a transconductance amplifier (DLPCA200-FEMTO) and a digital oscilloscope. 24,25 To investigate the performance of the dose rate engine in-depth along the beam, a 2 cm × 2 cm field with a 2 mm spot separation in x and y, resulting in 121 individual spots was used. The number of particles was set to 2.2 × 10 9 , close to the maximum number of particles deliverable in one spill with helium ions at HIT at the time of the study.…”

Metrology for advanced radiotherapy using particle beams with ultra-high dose rates

“…By using a transimpedance amplifier and a digital oscilloscope, a temporal resolution in the range of a few ns could be achieved (Marinelli et al 2023). Additionally, the temporal structure of scanned pencil beams can also be detected (Tessonnier et al 2023).…”