Room: AAPM ePoster Library
Purpose: Ocular melanoma patients undergoing brachytherapy receive extremely high doses to normal structures of the eye, causing unwanted side effects such as blindness and loss of vision. We propose an intraocular shielding method using ferrous magnetite nanoparticles in a polymer fluid, known as ferrofluid (PDMS-Fe3O4). The particles are drawn toward the tumor with a magnetic plaque, creating a ferrofluid shield for normal tissue structures. To evaluate the effectiveness of the ferrofluid as a radiation shield, we studied its attenuation properties using Monte Carlo simulation and film dosimetry methods.
Methods: An IsoAid Advantage™ Iodine-125 brachytherapy seed was simulated using GAMOS, a GEANT4 Monte Carlo code, and benchmarked versus standard TG-43 parameters. EBT3 Gafchromic films were used for attenuation measurements using a single calibrated I-125 seed. The linear attenuation coefficient of PDMS-Fe3O4 was determined using film, GAMOS, and analytically using attenuation coefficients based on the elemental composition.
Results: GAMOS-simulated dose rate constant, radial dose, and anisotropy functions for IsoAid I-125 were validated with published MCNP Monte Carlo data. The linear attenuation coefficients obtained by film and GAMOS simulation were 0.529 and 0.530 mm?¹ respectively. The analytically derived linear attenuation coefficient for PDMS-Fe3O4 was 0.551 mm?¹, which differs from our measured attenuation by ~4%. Based on the measured attenuation, 1.0-mm layer of ferrofluid can reduce dose to normal eye structures by 40%. This magnitude of dose reduction to the lens, macula, and optic nerve can reduce the incidence of radiation-induced side effects.
Conclusion: An I-125 seed was modeled with GAMOS and validated versus previously reported Monte Carlo data. Our determined linear attenuation coefficient for PDMS-Fe3O4 was approximately 0.53 mm?¹. Therefore, a 1.0-mm layer of this ferrofluid can attenuate photons by 40%, making the material an effective shield to protect the structures of the eye from excessive dose during intraocular brachytherapy.