Dosimetric Impact on the Flattening Filter and Addition of Gold Nanoparticles in Radiotherapy: A Monte Carlo Study on Depth Dose Using the 6 and 10 MV FFF Photon Beams

Dosimetric parameters calculation for 18 MV photon beam in flattening filter (FF) and flattening filter free (FFF) linear accelerators with and without magnetic deflector and lead filter

Dosimetric characteristics of the flattening filter (FF) and flattening filter free (FFF) modes of 18 MV therapeutic photon beam were investigated with and without the magnetic deflector (MD) and lead filter. MCNP version 6.1.0 Monte Carlo (MC) code was used to simulate the 18 MV photon beam of 2100 C/D-Varian linear accelerator (LINAC) for the FF and FFF modes. The MD (uniform magnetic flux density of 1 Tesla) and lead filter (thickness of 1 mm) were modeled to remove contaminant electrons. The dosimetric parameters for different scenarios of LINAC's head were calculated. Removing the flattening filter in the FFF mode increased the dose rate, electron contamination, skin dose, out-of-field dose, and un-flatness compared to the FF mode. While the lead filter decreased the contaminant electrons significantly, using the MD removed all secondary electrons from the beam line. The surface dose was decreased by 8.3% and 11.2% for the magnetic deflector (MD) and lead filter in the FF mode, respectively. The surface dose was decreased by 16.8% and 20.3% for the MD and lead filter scenarios in the FFF mode, respectively. The MD and lead filter decreased surface penumbra by 15.5% and 11.5% compared to the FFF mode. Removing the flattening filter from the LINAC's head improves most of the dosimetric characteristics of the 18MV therapeutic beam. The use of a lead filter and magnetic deflector preserves the skin-sparing property of megavoltage beams that deteriorate in FFF mode. However, using a magnetic deflector does not reduce photon fluence and dose rate.

Depth Dose Enhancement in Orthovoltage Nanoparticle-Enhanced Radiotherapy: A Monte Carlo Phantom Study

BACKGROUND

This study was to examine the depth dose enhancement in orthovoltage nanoparticle-enhanced radiotherapy for skin treatment by investigating the impact of various photon beam energies, nanoparticle materials, and nanoparticle concentrations.

METHODS

A water phantom was utilized, and different nanoparticle materials (gold, platinum, iodine, silver, iron oxide) were added to determine the depth doses through Monte Carlo simulation. The clinical 105 kVp and 220 kVp photon beams were used to compute the depth doses of the phantom at different nanoparticle concentrations (ranging from 3 mg/mL to 40 mg/mL). The dose enhancement ratio (DER), which represents the ratio of the dose with nanoparticles to the dose without nanoparticles at the same depth in the phantom, was calculated to determine the dose enhancement.

RESULTS

The study found that gold nanoparticles outperformed the other nanoparticle materials, with a maximum DER value of 3.77 at a concentration of 40 mg/mL. Iron oxide nanoparticles exhibited the lowest DER value, equal to 1, when compared to other nanoparticles. Additionally, the DER value increased with higher nanoparticle concentrations and lower photon beam energy.

CONCLUSIONS

It is concluded in this study that gold nanoparticles are the most effective in enhancing the depth dose in orthovoltage nanoparticle-enhanced skin therapy. Furthermore, the results suggest that increasing nanoparticle concentration and decreasing photon beam energy lead to increased dose enhancement.

Enhanced electron beam and X-ray beam therapy by applying nanoparticle heterojunctions: A Monte Carlo simulation

Cancer has become one of the major diseases that seriously threaten human health. In order to improve the therapeutic gain ratio (TGF) of conventional X-ray and electron beams, we studied the dose enhancement effect and secondary electrons emission of Au-Fe nanoparticle heterostructures by Monte Carlo method. Under the irradiation of 6 MeV photon and 6 MeV electron beams, the Au-Fe mixture has a dose enhancement effect. For this reason, we explored the secondary electrons production that leads to dose enhancement. For 6 MeV electron beam irradiation, Au-Fe nanoparticle heterojunctions have an higher electrons emission than Au and Fe nanoparticles. When cubic, spherical and cylindrical heterogeneous structures are considered, the electron emission of the columnar Au-Fe nanoparticles is the highest, with a maximum value of 0.00024. For 6 MV X-ray beam irradiation, Au nanoparticle and Au-Fe nanoparticle heterojunction have similar electrons emission, while Fe nanoparticle has the lowest one. When cubic, spherical and cylindrical heterogeneous structures are considered, the electron emission of the columnar Au-Fe nanoparticles is the highest, with a maximum value of 0.000118. This study contributes to improve the tumor-killing effect of conventional X-ray radiotherapy treatment and has guiding significance for the research of new nanoparticles.