Theoretical Analysis of Proton Therapy for Prostate Cancer

Abstract

The dependence of high proton energies has been investigated for proton therapy, which are governed by essential physical factors such as ion ranges and stopping powers. In addition, the volume of prostate is another variable factor varies according to human age and types of tumor. The aim of this theoretical study is about bombardment the prostate tumor by normal incidence protons from Medical Cyclotron at room temperature and energy ranges 60-250 MeV. It was studied by means of calculating Stopping Powers, 3D Ion ranges (longitudinal, lateral and radial) and the total target damage as a function of proton energies, which are calculated by TRIM computer code. The electronic stopping powers were calculated by Bethe-Bloch model, which have showed good coincidence with the TRIM results with 0.99 correlation factor. The ionization process is predominated through track of protons in tissues of the prostate, which yields a steep increase in total stopping power with penetration distance leading to the Bragg peak close to the end of range of the proton beams. The skewness and kurtosis are calculated, the negative sign of skewness for all spectra indicated that left tail (towards the surface of incidence protons) is larger than right (away from the surface) leading to reduce side effects to the neighboring normal tissues. The positive value of kurtosis means that the spectra are peaked. This indicates that the precise dose localization is delivered to the tissues. Proton therapy offers the benefit of specified dose localization and has favorable dose-depth distributions, compared with photon beam radiotherapy.

The angular distribution of protons with different energies are studied to reach the tumor in any position in prostate, it is noticed that at angle of 45 degree, there is equidimensional ion ranges. The total target damage increases with proton energies with values (0.58 - 1.7) KeV/ion for ranges energy (60 - 250) MeV respectively. In order to reach the tumor, the proton beam direction could be changed in definite steps or turned on and off very quickly.Volumes of the different shapes of prostates change according to age and kinds of the tumor, which are prolate ellipsoid, prolate spheroid, or spherical shape. This leads to select the precise proton energy to prevent the spread of radiation outside the prostate.This theoretical study can be considered as a tool and an indication to determine the precise proton energy required for prostate cancer treatment to minimize the side effects. Proton therapy is a promising technology as a result of the rapid development of nuclear accelerators.