Shielding calculation for the Proton-Therapy-Center in Prague, Czech Republic

Abstract

The study of radiation fields around the cyclotron room was carried out for the Proton-Therapy-Center in Prague (Czech Republic). The 230 MeV proton cyclotron will be installed there as well as additional components located along the beampath. The ambient doses were computed by taking into account 3 major sources of secondary radiation (neutron and photon) -the cyclotron, energy degrader and its collimator. The fluxes of neutrons/photons produced by protons were computed using Monte Carlo code MCNPX TM 2.5.0. Energy and angular distributions were computed for various targets and proton beam energies. Different physical models of high-energy proton interactions were studied as well. The annual charge at the cyclotron exit was based on the "patient model" (distribution of treatment type) established for a similar therapy center in Essen (Germany). Calculated data were used as an approximation of the radiation field of the most significant sources of radiation (graphite degrader, tantalum collimator). Fluence-to-dose conversion factors from ICRP-74 were used for the annual dose equivalent evaluation. With these results, the shielding analysis in the Therapy-Center was performed in the context of the current legislation requirements.

Monte Carlo Neutron Dose Measurement in Proton Therapy for Healthcare Worker Radiation Safety

“…In this study, PHITS was used to calculate three things; firstly, it calculated the neutron fluence, using the [T-cross] card, that passed the shielding; secondly, the neutron fluence from the selected phantom; and lastly, it calculated, around the treatment room using the [T-point] card, the ambient equivalent dose rate at 30 cm. In the PHITS program, the "multiplier" parameter combines the [T-point] card with the corresponding [Multiplier] card and converts the calculation results into the ambient equivalent dose rate H* (10), which is the depth of 10 mm from the body's surface, indicates the equivalent dose received by the whole body. The calculation results in the PHITS output file are normalized per source particle, representing the contribution of each proton to the total ambient equivalent dose rate and neutron fluence.…”

“…In the PHITS program simulation process, the error value must be below 3% to achieve statistical uncertainty, with the number of proton histories performed in the simulation being 10 9 . Following International Commission on Radiological Protection (ICRP) and International Committee for Radiological Units (ICRU), the conversion function h(E), whose value depends on neutron energy, considers 20 neutron energy groups in the neutron fluence calculus from 10 -9 MeV to 230 MeV 10 .…”

“…In the analytical model, the dose at the target location is assumed to be produced by a point source 7,8,9 . Meanwhile, the Monte Carlo method evaluates and tracks primary and secondary particles' interactions with materials by considering the particle database information and the material properties 10,11 . When analytical method data is obtained from the Monte Carlo method, the combination is called the hybrid method 12 .…”

“…Moreover, the calculation must be verified 13 at the commissioning stage by comparing its results to experimental measurements at the facility using detectors 14 . In order to evaluate proton therapy bunker performance, this study aims to assess and estimate the neutron dose outside the shielding wall in the operator room and CPCT door by calculating the ambient equivalent dose H* (10). The calculation is done through a stochastic approach using Monte Carlo-based PHITS software by calculating the neutrons' secondary radiation produced from the protons to a water phantom interaction.…”

A torus source and its application for non-primary radiation evaluation

“…Different from the traditional photon radiation therapy system, typical PT systems are composed of several subsystems in different rooms, such as an accelerator, a beam transport line (BTL), and a scanning nozzle (Addendum 2009, Smith et al 2009, Schippers and Lomax 2011). These subsystems are potential sources of nonprimary radiation doses, as secondary particles, especially neutrons, are generated by high-energy proton loss in matter during beam transport (Agosteo et al 1998, Carnicer et al 2012, Urban and Kluson 2012. Typically, an inner shielding wall between the patient and accelerator/BTL is built in the traditional shielding design of PT facilities to reduce non-primary dose in treatment rooms (Addendum 2009).…”