The impact of Internal Bremsstrahlung on the Dose Point Kernel: The case of $^{90}Y$.

Internal Bremsstrahlung (IB) is a process accompanying beta decay and consisting in the emission of photons with continuous energy up to the end-point of the beta spectrum. It is usually neglected when Dose Point Kernels (DPKs) are estimated for beta emitting radioisotopes. In this study, the DPK for $^{90}Y$ was re-calculated including IB in Monte Carlo (MC) simulations, so that the contribution of IB to DPK was assessed. GAMOS MC simulations were carried out scoring the energy deposited in concentric spherical shells, made of water, having radii ranging from $0.01 {mm}$ to $30 {mm}$. Results show that the contribution of IB photons to DPK is negligible for distances within the beta-particle range, where the contribution of beta particles is dominant; for larger distances, IB photon contribution becomes higher than $20%$ thus confirming the relevant role of Internal Bremsstrahlung emission when estimating DPK at distances larger than beta-particle range. Consequently, the inclusion of IB photons as an additional source term in MC simulations is advisable for $^{90}Y$ DPK estimation.