Estudo computacional do efeito da focalização na radioterapia VHEE

Abstract

Cancer is an increasingly relevant public health problem on the world stage. For it’s treatment, some types of radiotherapy are used, in order to deliver, through the use of beams of ionizing radiation, a quantity of dose in the tumor region while minimize it in the health tissue. Radiation therapy with very high energy electrons (VHEE), between 50 and 250 MeV, proved to be an interesting technique in this regard. Recently it was observed that, by combining VHEE beams with different focuses, it is possible to obtain percentage depth dose (PDD) curves similar to those of protontherapy, which minimize damage to healthy tissue, at a potentially lower cost. This work analyzes the effect of focusing VHEE beams on PDD, in order to obtain a PDD with a dose deposition peak well located at a certain depth, and with low dose deposition in adjacent healthy tissues. For this purpose, Monte Carlo simulations were performed with TOPAS for unfocused and focused VHEE beams in a simulating object composed of water. For the focused case, two cases were considered, the case where the beam is symmetrically focused and the case where the beam is asymmetrically focused. Simulations were performed using VHEE beams composed of 107 particles, with Gaussian spatial distribution in x and y with averages at x = 0 and y = 0, and standard deviations σx = 4 mm and σy = 4 mm; with Gaussian distribution of energies, with an average energy of 250 MeV and a standard deviation of 0.75% of this average value, and with initial divergence of 3.2 mrad. The simulations were performed with the same parameters of the reference article (WHITMORE et al., 2021). This choice allowed the validation of the results obtained by comparison with the data presented in that same article.