Novel intraocular shielding device for eye plaque brachytherapy using magnetite nanoparticles: A proof-of-concept study using radiochromic film and Monte Carlo simulations.

PURPOSE: Eye plaque brachytherapy is a mainstay treatment for uveal melanomas despite potential toxicities to normal tissues. This work proposes a nanoparticle ferrofluid as a novel intraocular shielding device. With a modified magnetic plaque, the shielding particles are drawn to the tumor surface, attenuating dose beyond the tumor while maintaining prescription dose to the target. METHODS AND MATERIALS: Ferromagnetic nanoparticles suspended in a silicone polymer were synthesized to provide a high-density shielding medium. The ferrofluid's half-value layer (HVL) was quantified for 125I photons using radiochromic film and Monte Carlo methods. A magnetic COMS plaque was created and evaluated in its ability to attract ferrofluid over the tumor. Two ferrofluid shielding mediums were evaluated in their ability to attenuate dose at adjacent structures with in vitro measurements using radiochromic film, in addition to Monte Carlo studies. RESULTS: The shielding medium's HVL measured approximately 1.3 mm for an 125I photon spectrum, using film and Monte Carlo methods. With 0.8 mL of shielding medium added to the vitreous humor, it proved to be effective at reducing dose to normal tissues of the eye. Monte Carlo-calculated dose reductions of 65%, 80%, and 78% at lateral distances 5, 10, and 18 mm from a tumor (5-mm apical height) in a modeled 20-mm COMS plaque. CONCLUSIONS: The magnitude of dose reduction could reduce the likelihood of normal tissue side effects for plaque brachytherapy patients, including patients with normal tissues close to the plaque or tumor. Additional studies, safety considerations, and preclinical work must supplement these findings before use.

Dosimetric characterization of a novel 90Y source for use in the conformal superficial brachytherapy device.

PURPOSE: To characterize the dose distribution in water of a novel beta-emitting brachytherapy source for use in a Conformal Superficial Brachytherapy (CSBT) device. METHODS AND MATERIALS: Yttrium-90 (90Y) sources were designed for use with a uniquely designed CSBT device. Depth dose and planar dose measurements were performed for bare sources and sources housed within a 3D printed source holder. Monte Carlo simulated dose rate distributions were compared to film-based measurements. Gamma analysis was performed to compare simulated and measured dose rates from seven 90Y sources placed simultaneously using the CSBT device. RESULTS: The film-based maximum measured surface dose rate for a bare source in contact with the surface was 3.35 × 10-7 cGy s-1 Bq-1. When placed in the source holder, the maximum measured dose rate was 1.41 × 10-7 cGy s-1 Bq-1. The Monte Carlo simulated depth dose rates were within 10% or 0.02 cm of the measured dose rates for each depth of measurement. The maximum film surface dose rate measured using a seven-source configuration within the CSBT device was 1.78 × 10-7 cGy s-1 Bq-1. Measured and simulated dose rate distribution of the seven-source configuration were compared by gamma analysis and yielded a passing rate of 94.08%. The gamma criteria were 3% for dose-difference and 0.07056 cm for distance-to-agreement. The estimated measured dose rate uncertainty was 5.34%. CONCLUSIONS: 90Y is a unique source that can be optimally designed for a customized CSBT device. The rapid dose falloff provided a high dose gradient, ideal for treatment of superficial lesions. The dose rate uncertainty of the 90Y-based CSBT device was within acceptable brachytherapy standards and warrants further investigation.

A novel conformal superficial high-dose-rate brachytherapy device for the treatment of nonmelanoma skin cancer and keloids.

PURPOSE: To develop a novel conformal superficial brachytherapy (CSBT) device as a treatment option for the patient-specific radiation therapy of conditions including superficial lesions, postsurgical positive margins, Dupuytren's contractures, keloid scars, and complex anatomic sites (eyelids, nose, ears, etc.). METHODS AND MATERIALS: A preliminary CSBT device prototype was designed, built, and tested using readily available radioactive seeds. Iodine-125 (125I) seeds were independently guided to the treatment surface to conform to the target. Treatment planning was performed via BrachyVision Planning System (BPS) and dose distributions measured with Gafchromic EBT3 film. Percent depth dose curves and profiles for Praseodymium-142 (142Pr), and Strontium-90/Yttrium-90 (90Sr-90Y) were also investigated as potential sources. Results achieved with 90Sr-90Y and electron external beam radiation therapy were compared and Monte Carlo N-Particle eXtended 2.6 simulations of 142Pr seeds were validated. RESULTS: BPS was able to predict clinical dose distributions for a multiple seeds matrix. Calculated and measured doses for the 125I seed matrix were 500 cGy and 473.5 cGy at 5 mm depth, and 171.0 cGy and 201.0 cGy at 10 mm depth, respectively. Results of 90Sr-90Y tests demonstrate a more conformal dose than electron EBRT (1.6 mm compared to 4.3 mm penumbra). Measured 142Pr doses were 500 cGy at surface and 17.4 cGy at 5 mm depth. CONCLUSIONS: The CSBT device provides a highly conformal dose to small surface areas. Commercially available BPS can be used for treatment planning, and Monte Carlo simulation can be used for plans using beta-emitting sources and complex anatomies. Various radionuclides may be used in this device to suit prescription depths and treatment areas.