ESTRO 2025 - Abstract Book

S2589

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

Material/Methods: The Xstrahl CIX system is equipped with two rotating anode X-ray tubes, producing radiation in the orthovoltage energy range (150 kVp). The source-to-sample distance (SDD) is adjustable between 5 and 25 cm. Customized 3D printed holders allow the use of conformal and multi-slit collimators (MSCs). For this study, MSCs with 500 and 200 µm wide apertures, spaced 1000 and 800 µm centre-to-centre, were fabricated for preclinical experiments. Film dosimetry was employed to characterize dose profiles at various depths in a 60×60×20 mm³ water-equivalent phantom. For initial measurements, only one tube was used. Results: The use of MSCs allowed for sub-millimetric modulation of the dose distribution. Despite a decrease in dose rate when using SFRT, the system achieved beam doses of up to several tens of Gy in a single 6-second irradiation at a 6 cm SSD. Films irradiated at depths of 1, 10, and 19 mm into the phantom using the 200-800 µm MSC showed a peak-to-valley dose ratio (PVDR), which is defined as the ratio between the beam (peak) dose and the scattered (valley) dose between the beams, of 13 to 7 within the first 10 mm of the phantom. This demonstrates the system’s ability to modulate the dose distribution despite beam divergence and radiation attenuation.

Conclusion: The Xstrahl CIX FLASH system can generate arrays of sub-millimetric X-ray beamlets, making it suitable for preclinical SFRT studies. The system is effective for in vitro models and superficial tumors in small animal models, particularly mice. Ongoing work aims to enhance the system by designing a setup that operates both X-ray tubes in SFRT mode and by developing MSCs with apertures of 100 µm or smaller. The latest developments of this system will be presented.

Keywords: SFRT, FLASH Compact X-ray Source, Film Dosimetry