Neutron shielding for a new projected proton therapy facility: A Geant4 simulation study

DOSE CALCULATION OF PROTON THERAPY BASED ON MONTE CARLO AND EMPIRICAL FORMULA

In this work, we used the Monte Carlo-based TOPAS simulation software to calculate the ambient dose equivalents and annual effective dose due to the secondary neutron field produced in proton therapy, also we introduced a USTC phantom to access the organ equivalent dose. The ambient dose equivalent and annual effective dose were calculated in several positions of interest inside and outside the facility. The simulation results were compared qualitatively to the results of the Empirical Formula, showing that the Empirical Formula calculations overestimated the dose, 28.95 times higher than the MC simulations, on average, which would lead to over shielding. In addition, the highest equivalent dose rate of a single radiation-sensitive organ simulated by TOPAS was 1.50 × 10-9 mSv/a for the eye lens, 2.36 × 10-3 mSv/a for limbs and 1.01 × 10-3 mSv/a for skin, which also meets the limits. Therefore, MC simulation has great advantages in shielding design and safety evaluation. And this work presents a new method to calculate the dose, introducing a more anthropogenic phantom can get more realistic results.

Monte Carlo Simulations of Neutron Ambient Dose Equivalent in a Novel Proton Therapy Facility Design

Purpose

The neutron shielding properties of the concrete structures of a proposed proton therapy facility were evaluated with help of the Monte Carlo technique. The planned facility's design omits the typical maze-structured entrances to the treatment rooms to facilitate more efficient access and, instead, proposes the use of massive concrete/steel doors. Furthermore, straight conduits in the treatment room walls were used in the design of the facility, necessitating a detailed investigation of the neutron radiation outside the rooms to determine if the design can be applied without violating existing radiation protection regulations. This study was performed to investigate whether the operation of a proton therapy unit using such a facility design will be in compliance with radiation protection requirements.

Methods

A detailed model of the planned proton therapy expansion project of the University of Texas, M. D. Anderson Cancer Center in Houston, Texas, was produced to simulate secondary neutron production from clinical proton beams using the MCNPX Monte Carlo radiation transport code. Neutron spectral fluences were collected at locations of interest and converted to ambient dose equivalents using an in-house code based on fluence to dose-conversion factors provided by the International Commission on Radiological Protection.

Results and Conclusions

At all investigated locations of interest, the ambient dose equivalent values were below the occupational dose limits and the dose limits for individual members of the public. The impact of straight conduits was negligible because their location and orientation were such that no line of sight to the neutron sources (ie, the isocenter locations) was established. Finally, the treatment room doors were specially designed to provide spatial efficiency and, compared with traditional maze designs, showed that while it would be possible to achieve a lower neutron ambient dose equivalent with a maze, the increased spatial (and financial) requirements may offset this advantage.

Transversal dose distribution optimization for laser-accelerated proton beam medical applications by means of Geant4

The main purpose of this paper is to quantitatively study the possibility of delivering dose distributions of clinical relevance with laser-driven proton beams. A Monte Carlo application has been developed with the Geant4 toolkit, simulating the ELIMED (MEDical and multidisciplinary application at ELI-Beamlines) transport and dosimetry beam line which is being currently installed at the ELI-Beamlines in Prague (CZ). The beam line will be used to perform irradiations for multidisciplinary studies, with the purpose of demonstrating the possible use of optically accelerated ion beams for therapeutic purposes. The ELIMED Geant4-based application, already validated against reference transport codes, accurately simulates each single element of the beam line, necessary to collect the accelerated beams and to select them in energy. Transversal dose distributions at the irradiation point have been studied and optimized to try to quantitatively answer the question if such kind of beam lines, and specifically the systems developed for ELIMED in Prague, will be actually able to transport ion beams not only for multidisciplinary applications, such as pitcher-catcher nuclear reactions (e.g. neutrons), PIXE analysis for cultural heritage and space radiation, but also for delivering dose patterns of clinical relevance in a future perspective of possible medical applications.