Radiological characteristics of MRI-based VIP polymer gel under carbon beam irradiation

• We study the radiological characteristics of VIP gel dosimeters under carbon beam irradiation.
• Linear energy transfer dependence was evaluated and discussed with simulation code PHITS.
• Contribution from secondly ion can explain results with different incident beam energy.

We study the radiological characteristics of VIP polymer gel dosimeters under carbon beam irradiation with energy of 135 and 290 AMeV. To evaluate dose response of VIP polymer gels, the transverse (or spin–spin) relaxation rate R2 of the dosimeters measured by magnetic resonance imaging (MRI) as a function of linear energy transfer (LET), rather than penetration depth, as is usually done in previous reports. LET is evaluated by use of the particle transport simulation code PHITS. Our results reveal that the dose response decreases with increasing dose-averaged LET and that the dose response–LET relation also varies with incident carbon beam energy. The latter can be explained by taking into account the contribution from fragmentation products.