Fano test, clinical proton beams and nuclear reactions

Abstract

Purpose

: A Fano test is implemented to prove the feasibility of the Monte Carlo simulation codes penh, fluka and topas for proton transport and, in particular, for the calculation of perturbation factors in ionization chambers used in proton-therapy. Optimal simulation parameters have been determined for penh and revised for topas and fluka.

Methods

: Simulations of proton beams with initial energies between 50 and $250\mathrm{MeV}$ have been performed. Fano test has been checked by locally absorbing secondary particles and switching off nuclear reactions. Particular attention has been paid to the role of the tracking parameters in the verification of the test. Results obtained in previous works have been revisited. The role of radiation production and nuclear reactions has been also investigated.

Results

: The results obtained for different materials conforming the simulation phantom indicate that penh verifies the test if the key parameter $W_{\mathrm{cc}}$ takes values of $10$keV at most: in this case other tracking parameters do not affect these findings. fluka verifies the test in all the cases analyzed. topas fails to accomplish the Fano test for initial proton energies larger than $100\mathrm{MeV}$, even if the optimal values of different tracking parameters suggested in previous publications are used. Nuclear reactions are responsible of most of the radiation yield produced; this yield makes the test to be violated in the three codes.

Conclusions

: The Fano test has permitted to establish the optimal values for the tracking parameters in case of penh. Using these values penh verifies the test in all cases studied. topas does not verify it for high initial proton energies, irrespective of the combinations of tracking parameters used.