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

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Monte Carlo Simulation

^{3}was irradiated by 105 kVp and 220 kVp photon beams. The field size was 5 cm in diameter, and the SSD was 20 cm. The chosen simulation geometry was specifically designed to focus on the depth dose variations along the central beam axis while mitigating the potential impacts of other parameters such as phantom heterogeneity, beam quality, and angle. The phantom was composed of pure water or a mixture of water and nanoparticles at concentrations ranging from 3 to 40 mg/mL. The simulation utilized gold, platinum, iodine, silver, and iron oxide nanoparticle materials added to the water phantom. By varying the photon beam energy, nanoparticle material, and concentration, Monte Carlo simulation using the EGSnrc-based DOSXYZ code determined depth doses up to 10 cm along the central beam axis of the phantom. The macroscopic approach was employed in the simulation. By employing a substantial number of histories, specifically 200 million for each simulation [26,27], we were able to attain a statistical uncertainty of ±1% for the depth dose in our simulations. This number of histories proved effective in minimizing statistical variations and ensuring a higher level of accuracy in the obtained depth dose results.

#### 2.2. Calculation of Dose Enhancement Ratio

## 3. Results

## 4. Discussion

#### 4.1. Dependence of Dose Enhancement on the Phantom Depth

#### 4.2. Dependence of Dose Enhancement on the Nanoparticle Material

^{n}, where Z is the atomic number, and n is between 4 and 5 [8]. In addition, it is important to note that iron oxide nanoparticles are magnetic and can enhance image contrast in magnetic resonance imaging, making them useful for image-guided radiotherapy [34,35].

#### 4.3. Dependences of Dose Enhancement on Nanoparticle Concentration

#### 4.4. Dependences of Dose Enhancement on the Photon Beam Energy

^{3.5}, where E represents the energy of the radiation beam [8]. For other nanoparticles, it was found that the DER values for platinum, iodine, silver, and iron oxide were 3.67%, 2.78%, 1.18%, and 1.17% higher, respectively, when the photon beam energy was changed from 220 kVp to 105 kVp. The lower values of the percentage increase can be attributed to the decrease in compositional atomic number within the phantom.

## 5. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Schematic diagrams (not to scale) showing the heterogeneous phantom used in Monte Carlo simulations. The dimensions of the phantoms were equal to 12 × 10 × 10 cm

^{3}. The phantoms were irradiated by the 105 kVp and 220 kVp photon beams with field size equal to 5 cm diameter. The source-to-surface distance was equal to 200 cm.

**Figure 2.**Relationships of dose enhancement ratio and phantom depth with variation of nanoparticle (NP) concentration using the 105 kVp photon beams for (

**a**) gold, (

**b**) platinum, (

**c**) iodine, (

**d**) silver, and (

**e**) iron oxide.

**Figure 3.**Relationships of dose enhancement ratio and phantom depth with variation of nanoparticle (NP) concentration using the 220 kVp photon beams for (

**a**) gold, (

**b**) platinum, (

**c**) iodine, (

**d**) silver, and (

**e**) iron oxide.

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**MDPI and ACS Style**

Chow, J.C.L.; Jubran, S.
Depth Dose Enhancement in Orthovoltage Nanoparticle-Enhanced Radiotherapy: A Monte Carlo Phantom Study. *Micromachines* **2023**, *14*, 1230.
https://doi.org/10.3390/mi14061230

**AMA Style**

Chow JCL, Jubran S.
Depth Dose Enhancement in Orthovoltage Nanoparticle-Enhanced Radiotherapy: A Monte Carlo Phantom Study. *Micromachines*. 2023; 14(6):1230.
https://doi.org/10.3390/mi14061230

**Chicago/Turabian Style**

Chow, James C. L., and Sama Jubran.
2023. "Depth Dose Enhancement in Orthovoltage Nanoparticle-Enhanced Radiotherapy: A Monte Carlo Phantom Study" *Micromachines* 14, no. 6: 1230.
https://doi.org/10.3390/mi14061230