Comparing two Monte Carlo codes to simulate the ideal activity of a phosphorus-32 film source using dose rate obtained by clinical applications

Abstract

Introduction: Phosphorus-32 encapsulated in a polymeric base is a promising source for brachytherapy, especially for intracavitary brachytherapy (IBT) [1, 2]. From the clinical studies published, a good dose rate for this source to have is 1 Gy/min [3, 4, 5]. A similar source has been developed with a new formulation. In this work, two Monte Carlo codes were compared to evaluate the ideal activity this source must have to deliver a 1 Gy/min dose rate. Materials & Methods: TOPAS 3.8 [6] and MCNP6.2 [7] were used to model two simulations, both with the source centered in the origin point, above an isotropic volume of water 1 mm deep (2.5 cm³). The source has the decay properties of phosphorus-32, whose beta emission spectrum was extracted from the IAEA website. For TOPAS, EnergyDeposit scoring was used, and tally*F8 for MCNP. Dividing dose per decay by the dose rate of 1 Gy/min, the simulated source’s total activity can be obtained. Results: Table 1 shows the results for both simulations. Therefore, the source’s initial activity must be between 2.13 × 109 Bq (57.44 mCi) and 2.19 × 109 Bq (59.06 mCi) to obtain the 1 Gy/min dose rate.With only a 2.8% difference between both codes’ results, it is safe to assume that the simulations are reliable. Summary: These results facilitate the source manufacturing, and, with them, it is possible to minimize the patient’s exposure to radiation, while ensuring the quality of the treatment.