Prog Med Phys.  2016 Sep;27(3):162-168. 10.14316/pmp.2016.27.3.162.

Secondary Neutron Dose Measurement for Proton Line Scanning Therapy

• Lee C
• Lee S
• Chung K
• Han Y
• Chung YH
• Kim JS

• KMID: 2376547
• DOI: http://doi.org/10.14316/pmp.2016.27.3.162

Abstract

Proton therapy is increasingly being actively used in the treatment of cancer. In contrast to photons, protons have the potential advantage of delivering higher doses to the cancerous tissue and lower doses to the surrounding normal tissue. However, a range shifter is needed to degrade the beam energy in order to apply the pencil beam scanning technique to tumors located close to the minimum range. The secondary neutrons are produced in the beam path including within the patient's body as a result of nuclear interactions. Therefore, unintended side effects may possibly occur. The research related to the secondary neutrons generated during proton therapy has been presented in a variety of studies worldwide, since 2007. In this study, we measured the magnitude of the secondary neutron dose depending on the location of the detector and the use of a range shifter at the beam nozzle of the proton scanning mode, which was recently installed. In addition, the production of secondary neutrons was measured and estimated as a function of the distance between the isocenter and detector. The neutron dose was measured using WENDI-II (Wide Energy Neutron Detection Instruments) and a Plastic Water phantom; a Zebra dosimeter and 4-cm-thick range shifter were also employed as a phantom. In conclusion, we need to consider the secondary neutron dose at proton scanning facilities to employ the range shifter reasonably and effectively.

Keyword

Proton therapy; Range shifter; Secondary neutron

MeSH Terms

Equidae
Neutrons*
Photons
Plastics
Proton Therapy
Protons*
Water
Plastics
Protons
Water

Figure

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  Fig. 1 Range shifter.

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  Fig. 2 WENDI-II detector.

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  Fig. 3 Schematic of first experiment.

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  Fig. 4 Schematic of second experiment.

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  Fig. 5 Two-dimensional dosage distribution within phantom irradiated by four proton scanning methods to assess neutron dose of range shifter.

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  Fig. 6 Measurement of secondary neutron using WENDI-II. Upper left and right: neutron emission measurements taken with a range shifter; lower left: emission measurement taken without a range shifter; lower right: emission measurements taken from a phantom.

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  Fig. 7 Secondary neutron dose on the radial axis from isocenter.

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  Fig. 8 Secondary neutron dose on the beam axis from the isocenter.

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  Fig. 9 Value of secondary neutron/Exp_1.

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  Fig. 10. Value of secondary neutron/Exp_2.

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