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Author Howell, Rebecca M. ♦ Burgett, Eric A. ♦ Isaacs, Daniel ♦ Price Hedrick, Samantha G. ♦ Reilly, Michael P. ♦ Rankine, Leith J. ♦ Grantham, Kevin K. ♦ Perkins, Stephanie ♦ Klein, Eric E.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword ISOTOPES AND RADIATION SOURCES ♦ DEPTH DOSE DISTRIBUTIONS ♦ DOSE EQUIVALENTS ♦ ENERGY SPECTRA ♦ EVAPORATION ♦ GY RANGE ♦ IRRADIATION ♦ MEV RANGE 10-100 ♦ NEUTRON BEAMS ♦ NEUTRON FLUENCE ♦ NEUTRON SPECTRA ♦ PEAKS ♦ PROTON BEAMS ♦ THERMAL NEUTRONS
Abstract Purpose: To measure, in the setting of typical passively scattered proton craniospinal irradiation (CSI) treatment, the secondary neutron spectra, and use these spectra to calculate dose equivalents for both internal and external neutrons delivered via a Mevion single-room compact proton system. Methods and Materials: Secondary neutron spectra were measured using extended-range Bonner spheres for whole brain, upper spine, and lower spine proton fields. The detector used can discriminate neutrons over the entire range of the energy spectrum encountered in proton therapy. To separately assess internally and externally generated neutrons, each of the fields was delivered with and without a phantom. Average neutron energy, total neutron fluence, and ambient dose equivalent [H* (10)] were calculated for each spectrum. Neutron dose equivalents as a function of depth were estimated by applying published neutron depth–dose data to in-air H* (10) values. Results: For CSI fields, neutron spectra were similar, with a high-energy direct neutron peak, an evaporation peak, a thermal peak, and an intermediate continuum between the evaporation and thermal peaks. Neutrons in the evaporation peak made the largest contribution to dose equivalent. Internal neutrons had a very low to negligible contribution to dose equivalent compared with external neutrons, largely attributed to the measurement location being far outside the primary proton beam. Average energies ranged from 8.6 to 14.5 MeV, whereas fluences ranged from 6.91 × 10{sup 6} to 1.04 × 10{sup 7} n/cm{sup 2}/Gy, and H* (10) ranged from 2.27 to 3.92 mSv/Gy. Conclusions: For CSI treatments delivered with a Mevion single-gantry proton therapy system, we found measured neutron dose was consistent with dose equivalents reported for CSI with other proton beamlines.
ISSN 03603016
Educational Use Research
Learning Resource Type Article
Publisher Date 2016-05-01
Publisher Place United States
Journal International Journal of Radiation Oncology, Biology and Physics
Volume Number 95
Issue Number 1


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