Shielding verification and neutron dose evaluation of the Mevion S250 proton therapy unit

Abstract

For passive scattering proton therapy systems, neutron contamination is the main concern both from an occupational and patient safety perspective. The Mevion S250 compact proton therapy system is the first of its kind, offering an in‐room cyclotron design which prompts more concern for shielding assessment. The purpose of this study was to accomplish an in‐depth evaluation of both the shielding design and in‐room neutron production at our facility using both Monte Carlo simulation and measurement. We found that the shielding in place at our facility is adequate, with simulated annual neutron ambient dose equivalents at 30 cm outside wall/door perimeter ranging from background to 0.07 mSv and measured dose equivalents ranging from background to 0.06 mSv. The in‐room measurements reveal that the H*/D decreases when the distance from isocenter and field size increases. Furthermore, the H*/D generally increases when the angle around isocenter increases. Our results from in‐room measurements show consistent trends with our Monte Carlo model of the Mevion system.

Investigating neutron activated contrast agent imaging for tumor localization in proton therapy: a feasibility study for proton neutron gamma-x detection (PNGXD)

“…The treatment unit offers 24 different beam configurations organized into large, deep and small groups. The maximum achievable field size is 25 × 25 cm 2 with a greatest possible depth of 32 cm (Prusator et al 2018).…”

A dose voxel kernel method for rapid reconstruction of out-of-field neutron dose of patients in pencil beam scanning (PBS) proton therapy

“…3.1) (Perl et al 2012), an application built with the Geant4 MC toolkit (Allison et al 2016), was adopted for the DVK generations. The TOPAS MC code has been widely used in medical applications mainly for proton therapy (Lin et al 2014, Shin et al 2017, Hartman et al 2018 and validated against neutron measurements in proton treatment rooms (Lutz et al 2018, Prusator et al 2018. Figure 1 shows the beam irradiation conditions for the DVK generations.…”

Neutron radiation effects on microcomputers in radiation therapy environments

“…The Mevion S250 has been the first of its kind, offering an in-room cyclotron design with nominal energy of 232 MeV, therefore prompting more concerns for shielding. 7,8 The computers having 32-65 nm CPU process sizes used 4, 1 giga byte (GB), non-error correcting code (ECC), double data rate (DDR) memory. A 30 × 30 × 30 cm original solid water® (Sun Nuclear Gammex, Middleton; WI) block target (Figure 1) was set up with 100 cm source to surface distance (SSD) and was irradiated with proton beam with spread-out Bragg peak (SOBP) of range 25 cm, modulation of 20 cm and field size of 20 × 20 cm.…”