Ponente
Descripción
Introduction
We present an advanced pulse irradiation model (PIM) utilizing gMicroMC’s step-by- step algorithm (SBS) with the newly incorporated periodic boundary condition (PBC), along the modeling of the homogeneous stage with numerical ordinary differential equations (NumODEs). Our goal is to study the pulse structure effects on radical production during CONV and FLASH in pure water.
Methods
The PIMs input include the pulse dose rate (Drp), the average dose rate (Drav), and the pulse beam structure (frequency and width). To simulate the bulk characteristics of water, we implemented a PBC. The SBS is run during the beam-on time and for 1 μs after radiation stops to ensure the completion of the heterogenous stage. Meanwhile, the NumODEs are executed during the remaining beam-off time until the arrival of the next pulse (homogeneous stage). We define a Drav threshold for every Drp. Below the threshold (CONV), the concentration of radicals per unit of dose (G-yield) is constant; above it (FLASH), the G-yield depends on Drav.
Results
We irradiated pure water to a total dose of 20 Gy using a 70 MeV proton beam characterized by pulses with a duration of 1 μs. Figure 1 shows the G-yield of H2O2 as a Drav function. For Drp of 1.8·105 and 106 Gy/s, the Drav thresholds were ~10 Gy/s and ~100 Gy/s, respectively. In Figure 2, at the inception of every pulse, it can be observed a background yield (B-yield) of radicals. For CONV, the B-yield is constituted by H2 and H2O2, whereas for FLASH, it is a mixture of all the radicals.
Conclusions
Th B-yield determines the Dr threshold and, consequently the dependence of the G- yield with Drp and Drav. The FLASH effect has been demonstrated with comparable Drav thresholds for identical Drp [1]. Our findings suggest a potential correlation between the FLASH effect and radiochemistry.
Figure 1: https://www.dropbox.com/scl/fi/1fnjx1n0mvl1b3fldnzhw/Figure1_Miguel_Molina-Hernandez_Abstract.png?rlkey=qde35hga2u3oexl2knnr9vr3y&dl=0
Figure 2: https://www.dropbox.com/scl/fi/wjacutjakeh5e94hrjfrj/Figure2_Miguel_Molina-Hernandez_Abstract.png?rlkey=67a2ryx66c5h6bvj61qagc248&dl=0
[1] https://www.sciencedirect.com/science/article/pii/S0936655519301517
