Measured Neutron Spectra and Dose Equivalents From a Mevion Single-Room, Passively Scattered Proton System Used for Craniospinal Irradiation.

Autor:	Howell RM; Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas. Electronic address: rhowell@mdanderson.org., Burgett EA; Department of Nuclear Engineering, Idaho State University, Pocatello, Idaho., Isaacs D; Department of Nuclear Engineering, Idaho State University, Pocatello, Idaho., Price Hedrick SG; Department of Radiation Oncology, Washington University, St. Louis, Missouri., Reilly MP; Department of Radiation Oncology, Washington University, St. Louis, Missouri., Rankine LJ; Department of Radiation Oncology, Washington University, St. Louis, Missouri., Grantham KK; Department of Radiation Oncology, Washington University, St. Louis, Missouri., Perkins S; Department of Radiation Oncology, Washington University, St. Louis, Missouri., Klein EE; Department of Radiation Oncology, Washington University, St. Louis, Missouri.
Jazyk:	angličtina
Zdroj:	International journal of radiation oncology, biology, physics [Int J Radiat Oncol Biol Phys] 2016 May 01; Vol. 95 (1), pp. 249-257. Date of Electronic Publication: 2015 Dec 19.
DOI:	10.1016/j.ijrobp.2015.12.356
Abstrakt:	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(6) to 1.04 × 10(7) n/cm(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. (Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.)
Databáze:	MEDLINE
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