Monte Carlo study of radiation dose enhancement by gadolinium in megavoltage and high dose rate radiotherapy.

Daniel G Zhang,Eduardo G Moros,Vladimir Feygelman,Geoffrey G Zhang,Kujtim Latifi,Mohammed Yousfi

doi:10.1371/journal.pone.0109389

Daniel G Zhang, Eduardo G Moros + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0109389

Copy DOI

Abstract

MRI is often used in tumor localization for radiotherapy treatment planning, with gadolinium (Gd)-containing materials often introduced as a contrast agent. Motexafin gadolinium is a novel radiosensitizer currently being studied in clinical trials. The nanoparticle technologies can target tumors with high concentration of high-Z materials. This Monte Carlo study is the first detailed quantitative investigation of high-Z material Gd-induced dose enhancement in megavoltage external beam photon therapy. BEAMnrc, a radiotherapy Monte Carlo simulation package, was used to calculate dose enhancement as a function of Gd concentration. Published phase space files for the TrueBeam flattening filter free (FFF) and conventional flattened 6MV photon beams were used. High dose rate (HDR) brachytherapy with Ir-192 source was also investigated as a reference. The energy spectra difference caused a dose enhancement difference between the two beams. Since the Ir-192 photons have lower energy yet, the photoelectric effect in the presence of Gd leads to even higher dose enhancement in HDR. At depth of 1.8 cm, the percent mean dose enhancement for the FFF beam was 0.38±0.12, 1.39±0.21, 2.51±0.34, 3.59±0.26, and 4.59±0.34 for Gd concentrations of 1, 5, 10, 15, and 20 mg/mL, respectively. The corresponding values for the flattened beam were 0.09±0.14, 0.50±0.28, 1.19±0.29, 1.68±0.39, and 2.34±0.24. For Ir-192 with direct contact, the enhanced were 0.50±0.14, 2.79±0.17, 5.49±0.12, 8.19±0.14, and 10.80±0.13. Gd-containing materials used in MRI as contrast agents can also potentially serve as radiosensitizers in radiotherapy. This study demonstrates that Gd can be used to enhance radiation dose in target volumes not only in HDR brachytherapy, but also in 6 MV FFF external beam radiotherapy, but higher than the currently used clinical concentration (>5 mg/mL) would be needed.

Highlights

Magnetic resonance imaging (MRI) is often used in tumor localization for radiotherapy treatment planning, and gadoliniumcontaining materials are often applied to enhance contrast for tumor volumes
BEAMnrc [24] version V4r2.3.2, a Monte Carlo simulation package designed for radiotherapy applications which has been applied in many medical physics research projects, was used to calculate dose enhancement as a function of Gd concentration
This study demonstrates that the dose enhancement is higher for the flattening filter free (FFF) beams compared to the conventional flattened beams, but lower than the Ir-192 brachytherapy for the same reason

Summary

Introduction

Magnetic resonance imaging (MRI) is often used in tumor localization for radiotherapy treatment planning, and gadoliniumcontaining materials are often applied to enhance contrast for tumor volumes. The concentration of gadolinium used for MRI is reported to be about 2.4 mM [3]. In addition to imaging, using gadolinium-containing materials as radiosensitizers have been reported. As an avid electron acceptor, MGd depletes the pool of DNA repair substrates that are unavailable to repair the oxidative damage to DNA induced by radiation [6,7]. It increases intracellular oxygen levels, thereby potentially overcoming hypoxia and allowing ‘‘fixation’’ of radiation damage [8]. The plasma concentration was up to 77.1 mg/ mL with a single intravenous administration of 6.3 mg/kg MGd [9]

Methods

Results

Discussion

Conclusion