Radiologic assessment of a self-shield with boron-containing water for a compact medical cyclotron

Abstract

The cyclotron at our hospital has a self-shield of boron-containing water. The amount of induced radioactivity in the boron-containing water shield of a compact medical cyclotron has not yet been reported. In this study, we measured the photon and neutron dose rates outside the self-shield during cyclotron operation. We estimated the induced radioactivities of the boron-containing water used for the self-shield and then measured them. We estimated the activation of concrete outside the self-shield in the cyclotron laboratory. The thermal neutron flux during cyclotron operation was estimated to be 4.72 × 102 cm−2 s−1, and the activation of concrete in a cyclotron laboratory was about three orders of magnitude lower than the clearance level of RS-G-1.7 (IAEA). The activity concentration of the boron-containing water did not exceed the concentration limit for radioactive isotopes in drainage in Japan and the exemption level for Basic Safety Standards. Consequently, the boron-containing water is treatable as non-radioactive waste. Neutrons were effectively shielded by the self-shield during cyclotron operation.

Hybridised production of technetium-99m and technetium-101 with fluorine-18 on a low-energy biomedical cyclotron

“…The neutron energy distribution ranged from 1 MeV with a relative flux of ∼1.1 × 10 11 n/s and extended to over 10 MeV with a gradual drop in flux to ∼1.1 × 10 8 n/s; the majority of the flux focused in the neutron energy range from 1 MeV to 4 MeV. This value is similar to the one reported by Horitsugi et al from the GE Healthcare ALARA reports as 7.13 × 10 11 n/s at 80 μ A during dual port irradiation [ 16 , 17 ]. Figure 2 shows the correlation between proton beam current and the resulting neutron flux (n/s) for 16.5 and 18.5 MeV cyclotrons from reported values in the literature.…”

Representation and illustration of the initial parameters in GATE 8.1 monte carlo simulation of an Elekta Versa-HD linear accelerator

“…Papadimitroulas showed GATE to reliable and efficient in various dosimetry, brachytherapy, and particle therapy applications Papadimitroulas (2017). Several other studies were carried out to validate GATE in dosimetry (Horitsugi et al, 2012;Laoues et al, 2015), proton therapy (Grevillot et al, 2011a;Zarifi et al, 2019), and brachytherapy (Thiam et al, 2008). Many studies sufficiently showed GATE to have great potential in aiding treatment planning systems (Arbor et al, 2019) and in IMRT treatment planning (Benhalouche et al, 2013).…”

Effectiveness of self-shielding type cyclotrons

“…The reduction of neutron activation is also important for the radiation control of materials surrounding the cyclotron and decommissioning of facility. Several authors used activation detectors to measure the neutron flux [3][4][5]. In this work, we used the activation detectors Au foil, TLD, and CR-39 to monitor neutron fluence inside the cyclotron vault in five types of cyclotrons covered with self-shields.…”