Formation and Dosimetry of Proton Beams for Flash Therapy Study

Purpose: To develop methods for tuning and dosimetry of proton beams in the widest possible range of proton current, including flash therapy modes with extremely high dose rates. Studies of flash therapy patterns, which have become much more active in recent years, have increased interest in the methods of forming therapeutic proton beams, including the method of passive proton scattering used in this work. Material and methods: The characteristics of the highcurrent linear proton accelerator of the INR RAS make it a unique facility and allow work with proton beams of record intensity. The therapeutic beam formation system is developed based on the principle of double passive proton scattering, which allows instantaneous irradiation of biological objects of significant size with a uniform dose regardless of the beam intensity. The primary adjustment of the formation system is performed using a standard MP-3 water phantom (PTW, Germany) at low proton currents, i.e. in the conventional irradiation mode. The proposed method of setting up the beam formation system allows combining the secondary shaped scatterer with the beam center and finding the optimal angle of the energy modulator, thereby optimizing the depth dose distribution. The used methods of dosimetry and beam control with film detectors and a Cherenkov monitor are also applicable at high proton currents, which allows setting up the beam formation system and irradiating biological objects in flash therapy modes. Results and conclusion: The work developed methods for the formation and dosimetry of proton beams applicable in the widest possible range of proton beam intensities, up to proton current values of about 10 mA. The main practical result of the work is the implemented irradiation of biological targets weighing up to 100 g with protons in a single pulse with a record average dose rate for protons per fraction of about 106Gy/s. For this purpose, original methods for setting up the beam formation system elements and Cherenkov beam monitors were used.