Evaluation of Gold Nanoparticle Size Effect on Dose Enhancement Factor in Megavoltage Beam Radiotherapy Using MAGICA Polymer Gel Dosimete

Gold nanoparticles (GNPs) are among the most promising radio-
sensitive materials in radiotherapy. Studying the effective sensitizing factors such
as nanoparticle size, concentration, surface features, radiation energy and cell type
can help to optimize the effect and possible clinical application of GNPs in radiation
therapy. In this study, the radiation sensitive polymer gel was used to investigate the
dosimetric effect of GNP size in megavoltage (MV) photon beam radiotherapy.
Material and Methods: GNPs with the size of 30nm, 50nm and 100nm in
diameter were used. Transmission electron microscope (TEM) and dynamic light
scattering (DLS) were applied to analyze the size of nanoparticles. The MAGICA
polymer gel was synthesized and impregnated with different sizes of GNPs. The
samples were irradiated with 6MV photon beam and 24 hours after irradiation, they
were read using a Magnetic Resonance Imaging (MRI) scanner. Macroscopic Dose
Enhancement Factor (DEF) was measured to compare the effect of GNP size. The
MAGICA response of the 6MV x-ray beam was verified comparing Percentage
Depth Dose (PDD) curve extracted from polymer gel dosimetry and Treatment Plan-
ning System (TPS).
Results: MAGICA polymer gel dose response curve was linear in the range of 0
to 10 Gy. DEFs by adding 30nm, 50nm and 100nm GNPs were 1.1, 1.17 and 1.12,
respectively. PDD curves of polymer gel dosimeter and treatment planning system
were in good agreement.
Conclusion: The results indicated a substantial increase in DEF uses a MV pho-
ton beam in combination with GNPs of different sizes and it was inconsistent with
previous radiobiological studies. The maximum DEF was achieved for 50nm GNPs
in comparison with 30nm and 100nm leading to the assumption of self-absorption ef-
fect by larger diameters. According to the outcomes of this work, MAGICA polymer
gel can be recommended as a reliable dosimeter to investigate the dosimetric effect
of GNP size and also a useful method to validate the current radiobiological and
simulation studies.