Room: AAPM ePoster Library
Purpose: The aim of this study is to evaluate the risk of radiation exposure from kilovoltage cone-beam computed tomography (kV-CBCT), when using gold nanoparticles as contrast agent in image-guided radiotherapy. Monte Carlo simulation (macroscopic approach for radiotherapy) was used to determine the imaging dose from a phantom.
Methods: The imaging dose enhancement ratio (IDER), defined as the ratio of the imaging dose without addition of gold nanoparticles to the tumour to the dose with addition of gold nanoparticles to the tumour, was calculated using Monte Carlo simulation (EGSnrc-based codes) based on an X-ray Volumetric Imager (XVI, Elekta Oncology Systems). The photon beam energy from the CBCT and nanoparticle concentration were varied in the range of 120 – 140 kVp and 3 – 40 mg/ml, respectively. An oval-shaped phantom with dimension similar to a Rando phantom (pelvis section) was used. The materials of the phantom were set to water, and water plus gold nanoparticles, to determine the imaging dose with and without addition of gold nanoparticles in the CBCT-based image-guided radiotherapy.
Results: It is found that the IDER value increased with a decrease of photon beam energy, and increase of nanoparticle concentration. Based on the maximum IDER of 1.6, with photon beam energy and nanoparticle concentration equal to 120 kVp and 40 mg/ml determined in this study, and the experimental imaging dosimetry of the similar phantom with CBCT irradiation, the imaging dose was estimated to be 0.63% of the typical therapeutic dose of 2 Gy per fraction used in radiotherapy. This is within the standard uncertainty of ±5% in radiation dose delivery.
Conclusion: From the results of risk assessment using IDER predicted by Monte Carlo simulation, it is concluded that the radiation exposure from kV-CBCT with addition of gold nanoparticles as contrast agent is within the dose delivery uncertainty in image-guided radiotherapy.