Assessing the Effect of Directional Bremsstrahlung Splitting on the Output Spectra and Parameters Using BEAMnrc Monte Carlo Simulation Package.

Introduction: EGSnrc software package is one of the computational packages for Monte Carlo simulation in radiation therapy and has several subset codes. Directional bremsstrahlung splitting (DBS) is a technique that applies braking radiations in interactions in this software. This study aimed to evaluate the effect of this technique on the simulation time, uncertainty, particle number of phase-space data, and photon beam spectrum resulting from a medical linear accelerator (LINAC). Materials and methods: The gantry of the accelerator, including the materials and geometries of different parts, was simulated using the BEAMnrc code (a subset code in the EGSnrc package). The phase-space data were recorded in different parts of the LINAC. The DBS values (1, 10, 100, and 1000) were changed, and their effects were evaluated on the simulation parameters and output spectra. Results: Increasing the DBS value from 1 to 1000 resulted in an increase in the simulation time from 1.778 to 11.310 hours, and increasing the number of particles in the phase-space plane (5 590 732-180 328 382). When the DBS had been picked up from 1 to 100, the simulation uncertainty decreased by about 1.29%. In addition, the DBS increment value from 100 to 1000 leads to an increase in uncertainty and simulation time of about 0.71% and 315%, respectively. Conclusion: Although using the DBS technique reduces the simulation time or uncertainty, increasing the DBS from a specific value, equal to 100 in our study, increases simulation uncertainties and times. Therefore, we propose considering a specific DBS value as we obtained for the Monte Carlo simulation of photon beams produced by linear accelerators.

Therapeutic effect of cold atmospheric plasma and its combination with radiation as a novel approach on inhibiting cervical cancer cell growth (HeLa cells).

Cervical cancer is one of the important cancers in women. Research on novel treatment approach can reduce the mortality and burden. Although radiotherapy is a common treatment, its negative side effects have concerned physician. In our study, we studied impact of cold atmospheric pressure plasma on the Hela cancer cells, as an alternative treatment. The effect of three different types of such plasma; dielectric barrier discharge (DBD), plasma jet, and afterglow plasma, on the cancer cells were studied. Moreover, some effective operating parameters such as exposure time, applied voltage, composition of working gas in plasma treatment were investigated on the survival of the afterglow plasma. Finally, treatments by the afterglow plasma, gamma radiation (1 Gy), and combination of both were compared. Analysis showed that DBD and plasma jet (direct exposure) effectively killed the cancer cells, even by a minimum applied voltage. But a fraction of the cells survived after the exposure of indirect diffused afterglow plasma. In the case of this plasma, we realized that higher applied voltage and exposure time led to less cell viability. Fewer fractions of survival cells were detected in the case of argon afterglow plasma comparing to oxygen afterglow. Cold atmospheric plasma and its combination with radiation therapy showed a significant decrease in viability of the cells, comparing to the radiation alone. Our research showed that plasma and its combination with radiation therapy have superiority over radiation therapy.