Upper limit of magnetic effect on α/β ratio

Abstract

Magnetic resonance imaging (MRI) is being integrated into radiotherapy delivery for MRI-guided radiotherapy. The purpose of this work is to investigate theoretically the upper limit of any potential magnetic effect on the α/β ratio, an important radiobiological parameter in radiation therapy. Based on the theory of dual radiation action, the α/β ratio can be expressed by an integral of the product of two microdosimetry quantities and , where is the probability that two energy transfers, a distance x apart, results in a lesion, and is the proximity function, which is the energy-weighted point-pair distribution of distances between energy transfer points in a track. The quantity depends on the applied magnetic field. An analytical approach has been used to derive a formula that can be used to calculate the α/β ratio in an extremely strong magnetic field, which gives the upper limit of the potential changes of the α/β ratio due to the presence of a magnetic field. For V79 Chinese hamster cells the upper limit of the increase of the α/β ratio with a magnetic field has been found to be 2.90 times for Pd-103, 2.97 times for I-125 and 2.3 times for Co-60 sources.