A comparative dosimetry study of an alanine dosimeter with a PTW PinPoint chamber at ultra-high dose rates of synchrotron radiation

The use of synchrotron X-ray sources provides innovative approaches in radiation therapy. The unique possibility to generate quasi-parallel beams promoted the development of microbeam radiation therapy (MRT), an innovative approach able to reduce damages to normal tissues while delivering considerable doses in the lesion. Accurate dosimetry in broad-beam configuration (prior to the spatial fractionation of the incident X-ray fan) is very challenging at ultra-high dose rate synchrotron sources. The available reference dosimetry protocol based on the use of a PTW PinPoint ionization chamber was compared with alanine dosimetry at the European Synchrotron Radiation Facility (ESRF) ID17 Biomedical beamline, an orthovoltage X-ray source with an average dose rate of 11.6 kGy/s. Reference dose measurements of the alanine pellets were performed at the National Centre for Radiation Research and Technology (NCRRT) Co-60 facility in Egypt. All alanine dosimeters were analysed by an electron paramagnetic resonance spectrometer. We determined a relative response r(ESRF) = 0.932 +/- 0.027 (1s) of the alanine pellets irradiated at the ESRF compared to the Co-60 facility. Considering the appropriate corrections for the ESRF polychromatic spectrum and the different field size used, our result is in agreement with the previous work of Waldeland et al. for which the utilised alanine contained the same amount of binder, and it is consistent with the works of Anton et al. and Butler et al. for which the utilised alanine contained a higher amount of binder. We confirm that alanine is an appropriate dosimeter for ultra-high dose rate calibration of orthovoltage X-ray sources.