ESTRO 2024 - Abstract Book

S3258

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

For the 28 analysed FLASH treatments, the determined positions of Probe 1 and 2 on the mouse holder indicated a set-up uncertainty with standard deviations of 0.9 mm horizontally and 2.0 mm vertically. This indicates that the mouse holder was placed in the beam in a reproducible manner. The probe on the foot displayed slightly larger variations of 1.8mm horizontally and 3.1mm vertically [Fig 2]. However, the measurements showed that the mouse leg was consistently placed centrally in the spot pattern. The mean difference between the measured total dose and the expected dose at the probe position was (-2.2 ± 2.5)% of the total dose for Probe 1, (3.4 ± 0.7)% for Probe 2 and (0.9 ± 0.7)% for Probe 3 [Fig.2]. Probe 1 received (91 ± 18)% of the prescribed dose, whereas Probe 2 received (102 ± 1)% and Probe 3 (97 ± 19)%. This confirms that the mouse foot target was indeed well within the high-dose area while the joint target was closer to the penumbra region in the top part of the field.

Conclusion:

The detector system was successfully calibrated for absolute dose measurements in the SOBP and provided time resolved in vivo dose rate measurements in the SOBP for proton beam FLASH. It allowed for the verification of the accumulated dose and the mouse leg positions in the treatment field.

Keywords: FLASH dosimetry, in vivo, spread-out Bragg peak

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