BNCT dosimetry for brain cancer based on the nuclear research reactor NUR and the modified MIRD phantom by introducing the eye lens: Simulation study

Abstract

The Glioblastoma Multiforme (GBM) is one of the most aggressive type of the brain cancer, as well as resistant to treatments combining surgery and concomitant sessions of radiotherapy, based on X-rays, and chemotherapy. The Boron Neutron Capture Therapy (BNCT) has been elected as a radical solution to this type of cancer. This present work focuses on the dosimetric study of the GBM using the therapeutic BNCT beam based on the NUR nuclear research reactor of the Draria Nuclear Research Center (CRND) that has been already optimized in a previous research. In this context, the simulations have been done using the Monte Carlo Code (MCNP5) and the Medical Internal Radiation Dose (MIRD) phantom with an assumption of a brain tumor of 1.5 cm radius situated at different depth ranging from 4 to 10 cm and centered with respect to the neutron beam. In addition, the calculation of the absorbed dose by the tumor, the healthy brain tissue, the skin around head and neck (skin), the pharynx and the thyroid was performed for the different locations of the tumor using the ICRU 46 to determine the elemental composition and the flux to Kerma conversion coefficients for each tissue. However, the recent epidemiological studies show that cataract can occur at a dose lower than 200 cGy, as it can be a stochastic effect and not a deterministic one. To this end, a calculation of the absorbed dose by the lens of the eye and more precisely by its most radiosensitive part (germinative zone) was developed by modifying the MIRD phantom to model the entire eye based on the equations of later studies. The obtained results show that the absorbed dose rate calculated for the tumor increases each time its depth rises, which is not the case for the dose rate calculated for the healthy organs where it remains approximately constant. The absorbed dose by the germinative zone varies from (68.37 ± 0.89) cGy for tumor depth of 4 cm to (733.92 ± 15.96) cGy for a tumor situated at 10 cm of depth.