Online 2D dose verification required in UHDR-FLASH preclinical research: challenges and possibilities

Document Type

Conference Proceeding

Publication Date

5-1-2025

Publication Title

Radiother Oncol

Keywords

2D real-time dosimetry, UHDR-FLASH dosimetry, Oncology, Radiology, Nuclear Medicine & Medical Imaging

Abstract

Purpose/Objective: The increasing interest in FLASH-RT has lead to both the development of new, and the conversion of existing linear accelerators to enable ultra-high dose rate (UHDR) irradiations for preclinical research. Dosimetry in this setting remains challenging with several crucial aspects missing. This work shows the challenges and need for real-time 2D UHDR dosimetry, and presents a solution in the context of preclinical irradiations in a non-homogeneous electron beam.Material/Methods: An experimental camera-scintillation combination, and radiochromic film, were used to investigate the spatial dose distribution of two UHDR electron LINACS: a converted Varian Trilogy™ (16 MeV; 25x25 cm²) and a Sordina IORT Technologies ElectronFlash (9 MeV; Ø=12 cm). The challenges of real-time 2D dosimetry with scintillating coatings were assessed by irradiation of 1) an ex-vivo rat brain with the Varian Trilogy™, with the skull at an SSD of 80 cm, using a field size of 2x2 cm² and delivering 30 pulses of 0.39 Gy at an average dose rate (DR) of 44.9 Gy/s; and 2) a 3D printed mouse phantom with the ElectronFlash, using an SSD of 138.7 cm, a circular field with a diameter of 120 mm and delivering 10 pulses of 1.98 Gy at a DR of 198 Gy/s.Results: The field homogeneity, assessed using film is shown in Figure 1 for the gaussian shaped Varian Trilogy™ field and the flattened ElectronFlash. The coating showed a linear dose response in the flattened field (R²>0.999) and linear response with pulses in the gaussian field (R²=0.998). Calibration in the non-homogeneous field (Trilogy™) is challenging and requires a 2D reference dosimeter and perfect alignment. As an example, the intensity difference between 2 regions of interest, separated by 3 cm, is 18.31% in the gaussian field (Trilogy™) and 0.65% in the flattened field (ElectronFlash). The ex-vivo use of the flexible coatings is shown in Figure 2. The left panel shows the rat brain with coating (top), overlayed with the signal (middle) and with overlying film (bottom). The right panel shows the 3D printed mouse phantom (top), with the flexible coating (middle), overlayed with the signal (bottom). The flexible coating was capable of assessing the signal per pulse in each point. Rotation of the rat resulted in a maximal response difference of 3.2%. Conclusion: We showed the need for 2D real-time dosimetry to determine beam characteristics in non-homogeneous UHDR beams using a preclinical FLASH radiotherapy setting; one solution is scintillating based dosimetry.

Volume

206

First Page

S2590

Last Page

S2592

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