Purpose: To experimentally validate theoretical Monte Carlo (MC) simulations of surface profile dose and depth dose of a novel 90Y source for use in a Conformal Superficial Brachytherapy (CSBT) device for the treatment of non-melanoma skin cancers and keloids.
Methods: A newly designed brachytherapy source was created by activating â?¸â?¹Y disks to â?¹â?°Y by neutron bombardment at the University of Missouri Research Reactor (MURR). Each â?¹â?°Y disk source has a 1 mm radius and 1 mm thickness. Dose profiles and depth doses were evaluated for single and multiple sources. Measurements were made using Gafchromic EBT3 film dosimetry in a Solid WaterÂ® HE phantom. Simulations were performed with the Monte Carlo n-particle transport code (MCNP5) in photon, electron mode. The simulation space contained a 125 cmÂ³ water phantom cube composed of 1.25x10â?»â?´ cmÂ³ cubic tally voxels. A polyenergetic electron source pertaining to the â?¹â?°Y spectrum was emitted randomly within the source volume. The outputs of the simulations were the probability distributions of the energy deposited in each tally voxel for a single emitted electron (MCNP: *F8 tally). Additional measurements and MC simulations were performed at 0.1 cm depth with eight sources placed in a hexagonal distribution directly on the phantom.
Results: Using film dosimetry techniques, a single source placed directly on the film yielded a dose rate of 0.0976 Gy/s at the surface and dose rates of 0.0171 Gy/s, 0.0084 Gy/s, 0.0028 Gy/s, and 0.0006 Gy/s for 1, 2, 3, and 5 mm depths, respectively. Normalizing the MC simulations to the measured surface dose rate resulted in a 14.3% difference from the measured dose rate at 1 mm depth and a total correlation of r=0.982.
Conclusion: MC simulations were quantitatively validated and provide a basis for further investigation of â?¹â?°Y for conformal brachytherapy.