Abstract
BackgroundWe measured and assessed ways to reduce the secondary neutron dose from a system for proton eye treatment.MethodsProton beams of 60.30 MeV were delivered through an eye-treatment snout in passive scattering mode. Allyl diglycol carbonate (CR-39) etch detectors were used to measure the neutron dose in the external field at 0.00, 1.64, and 6.00 cm depths in a water phantom. Secondary neutron doses were measured and compared between those with and without a high-hydrogen–boron-containing block. In addition, the neutron energy and vertices distribution were obtained by using a Geant4 Monte Carlo simulation.ResultsThe ratio of the maximum neutron dose equivalent to the proton absorbed dose (H(10)/D) at 2.00 cm from the beam field edge was 8.79 ± 1.28 mSv/Gy. The ratio of the neutron dose equivalent to the proton absorbed dose with and without a high hydrogen-boron containing block was 0.63 ± 0.06 to 1.15 ± 0.13 mSv/Gy at 2.00 cm from the edge of the field at depths of 0.00, 1.64, and 6.00 cm.ConclusionsWe found that the out-of-field secondary neutron dose in proton eye treatment with an eye snout is relatively small, and it can be further reduced by installing a borated neutron absorbing material.
Highlights
We measured and assessed ways to reduce the secondary neutron dose from a system for proton eye treatment
We found that about 60% of the secondary neutrons are generated at the eye snout
We concluded that the secondary neutron dose for a typical eye treatment beam in the National Cancer Center (NCC), Korea, ranges from 0.16 ± 0.01 mSv/Gy to 8.79 ± 1.28 mSv/Gy with the eye snout system when the displacement from the field edge ranges from 2.00 cm to 8.00 cm
Summary
We measured and assessed ways to reduce the secondary neutron dose from a system for proton eye treatment. Proton beam therapy and heavy ion therapy are increasingly used because of their excellent dose localization performance. This high-precision localization is achieved by the Bragg peak effect, which affords a sharp distal fall-off in depth dose distribution compared with normal photon therapy. One area of great interest is the extra dose emitted by secondary neutrons produced by nuclear interactions with the material in the beam path during proton and heavy ion therapy. The amount of the secondary neutron dose generated from the proton or heavy ion therapy machines can be dependent on the beam delivery system because neutron production is highly dependent on the material in the beam path and on the design of the beam line. Neutrons have high relative biological effectiveness (RBE) in that even a small dose of neutrons can have a large effect on the patient
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