Highlights
- •MC calculations were used to assess neutron doses to healthy organs.
- •Lateral incidences induce more neutron doses than the anterior–superior incidence.
- •Impact of some irradiation parameters on neutron doses changes with beam incidence.
- •Investigations on internal neutron fluence and doses were carried out.
- •Beam incidence impacts the fluence and energy of neutrons reaching the patient.
Abstract
Purpose
In scattering proton therapy, the beam incidence, i.e. the patient’s orientation with
respect to the beam axis, can significantly influence stray neutron doses although
it is almost not documented in the literature.
Methods
MCNPX calculations were carried out to estimate stray neutron doses to 25 healthy
organs of a 10-year-old female phantom treated for an intracranial tumor. Two beam
incidences were considered in this article, namely a superior (SUP) field and a right
lateral (RLAT) field. For both fields, a parametric study was performed varying proton
beam energy, modulation width, collimator aperture and thickness, compensator thickness
and air gap size.
Results
Using a standard beam line configuration for a craniopharyngioma treatment, neutron
absorbed doses per therapeutic dose of 63 μGy Gy−1 and 149 μGy Gy−1 were found at the heart for the SUP and the RLAT fields, respectively. This dose
discrepancy was explained by the different patient’s orientations leading to changes
in the distance between organs and the final collimator where external neutrons are
mainly produced. Moreover, investigations on neutron spectral fluence at the heart
showed that the number of neutrons was 2.5 times higher for the RLAT field compared against the SUP field. Finally, the influence
of some irradiation parameters on neutron doses was found to be different according
to the beam incidence.
Conclusion
Beam incidence was thus found to induce large variations in stray neutron doses, proving
that this parameter could be optimized to enhance the radiation protection of the
patient.
Keywords
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Article info
Publication history
Published online: April 02, 2016
Accepted:
March 14,
2016
Received in revised form:
February 5,
2016
Received:
October 26,
2015
Identification
Copyright
© 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
