Related Experiment Video
Updated: Jun 24, 2026

Proton Therapy Delivery and Its Clinical Application in Select Solid Tumor Malignancies
Published on: February 6, 2019
Secondary neutron doses for several beam configurations for proton therapy
Dongho Shin1, Myonggeun Yoon, Jungwon Kwak
1Proton Therapy Center, National Cancer Center, Goyang, Korea.
Purpose:
To compare possible neutron doses produced in scanning and scattering modes, with the latter assessed using a newly built passive-scattering proton beam line.
Methods And Materials:
A 40 x 30.5 x 30-cm water phantom was irradiated with 230-MeV proton beams using a gantry angle of 270 degrees , a 10-cm-diameter snout, and a brass aperture with a diameter of 7 cm and a thickness of 6.5 cm. The secondary neutron doses during irradiation were measured at various points using CR-39 detectors, and these measurements were cross-checked using a neutron survey meter with a 22-cm range and a 5-cm spread-out Bragg peak.
Results:
The maximum doses due to secondary neutrons produced by a scattering beam-delivery system were on the order of 0.152 mSv/Gy and 1.17 mSv/Gy at 50 cm from the beam isocenter in the longitudinal (0 degrees ) and perpendicular (90 degrees ) directions, respectively. The neutron dose equivalent to the proton absorbed dose, measured from 10 cm to 100 cm from the isocenter, ranged from 0.071 mSv/Gy to 1.96 mSv/Gy in the direction of the beam line (i.e., phi = 0 degrees ). The largest neutron dose, of 3.88 mSv/Gy, was observed at 135 degrees and 25 cm from the isocenter.
Conclusions:
Although the secondary neutron doses in proton therapy were higher when a scattering mode rather than a scanning mode was used, they did not exceed the scattered photon dose in typical photon treatments.
Related Concept Videos
Nuclear Stability
To hold positively charged protons together in the...
Nuclear Transmutation
Biological Effects of Radiation
Types of Radioactivity
Alpha (α) decay is the emission of an α particle from the nucleus. For example, polonium-210 undergoes α decay:
Radioactivity and Nuclear Equations
A nuclide of an element has a specific number of protons and...
Nuclear Power
Nuclear Fuels
Nuclear fuel consists of a fissile isotope, such as uranium-235, which must be present in sufficient quantity to provide a...
