Abstract

Ionizing radiation are widely employed in the medical field both for diagnosis and for radiotherapy treatments, where it is often required to measure the precise dose delivered along with radiation distribution in the target volume. This is even more important in emerging techniques such as the FLASH radiotherapy [1], in which very high dose rates (e.g. >40 Gy/s) are delivered over short times (<1 s). Quality Assurance in the FLASH radiotherapy planning process is essential to ensure the accurate dose delivery to the patient and to minimize the possibility of accidental exposure. In this framework, commissioning procedures involve the characterization of radiation beam using a water phantom during the simulated treatment. Furthermore, periodical tests are carried out in a similar way to ensure that there are no drifts in the machine performance, ensuring that measured and calculated doses lie within the agreement criteria. The characterization of the beam in the water phantom is performed by probes such as ionization chambers or scintillators that map the dose distribution in the target volume. A possible more convenient alternative for in-situ, real-time dose profiling is represented by optical fibres used as radiation sensors. However, standard silicate optical fibres for telecom applications exhibit little sensitivity to ionizing radiations. This issue can be addressed by developing ad-hoc silicate fibres, like those doped with aluminium or magnesium nanoparticles, which for their higher Rayleigh scattering behaviour have been named Enhanced Backscattering Fibres (EBFs). In a previous work [2], it was demonstrated the possibility to recover the radiation profile of an X-ray beam through the Radiation Induced Refractive Index Change (RRIC) in EBFs, by means of Optical Frequency Domain Reflectometry (OFDR).

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