Is ¹¹B(p,α)2α nuclear reaction contributing in proton therapy?

In the last few years proton therapies have been increased exponentially due to the major advantage of protons to deposit most of their energy at the end of the range, forming a well-known Bragg Peak (BP). It has been suggested that ¹¹B accumulation in the tumor volume increases the dose at the BP, thus enhancing the benefits of proton therapy. The mechanism behind this increase is based on the proton-boron fusion that generates alpha particles, deposit their energy in the BP. The question remains on how many alpha particles are needed in order to achieve a significant dose enhancement given the low cross section of protons with ¹¹B. In this study we present a series of simulations in an effort to quantify the enhancement of the dose in the target volume originating from the p + ¹¹B → 3α nuclear reaction. We simulated via TOPAS MC the interaction of 75-250 MeV incident proton beam (10⁷ histories) in a phantom of cylindrical geometry that is filled with water and includes a Boron Uptake Region (BUR) that was placed based on the BP location of the incident energy. The thickness of BUR and boron concentration were varied. The number of produced alpha particles for the different setups was scored and comparisons between the different depth-dose curves will be presented. Work on clinical importance of the ¹¹B(p,α)2α is in progress.