Helium 4He nuclei based radiotherapy.

Due to their advantageous physical and biological properties, ⁴He nuclei are the subject of growing interest in medicine. Low-energy ⁴He nuclei (α particles) are currently used in internal radiotherapy (IR) in the form of an implant in Diffusing Alpha-Emitters Radiation Therapy (DaRT) or radiopharmaceutical in Alpha - emitters based Radiopharmaceutical Therapy (αRT) and in binary therapy such as Boron Neutron Capture Therapy (BNCT) in a form of stable compound introduced into the body as a potential source of α particles in reaction with neutrons. High energy ⁴He ions were not used clinically since the 1990s. However, their application in external beam radiotherapy was extensively investigated and the first patient treatment was performed after a long time in 2021. The major challenging in dosimetry and treatment planning in radiation therapy with use of α particles is in vivo dose distribution monitoring in a body to get adequate information on biological response in cancerous and healthy tissues. The α particles, and in the case of BNCT also accompanying ⁷Li nuclei, cannot be measured directly, therefore suitable indirectly methods for imaging their distribution and concentration in tissues are emerging. Moreover, physical dose distribution imaging system shall be related to the specified biological response to allow real therapeutic effect determining and treatment plan establishment. Therefore, radiobiological parameters for weighting absorbed dose models taking into account synergic effects of different types of radiation in therapy are emerging. In the article general overview of used currently in clinics or being subject of pre-clinical studies ⁴He nuclei based therapies with particular emphasis on adequate methods of therapeutical dose imaging during therapy, was performed.