TY - JOUR
T1 - Measurement of Neutron Dose Equivalent and its Dependence on Beam Configuration for a Passive Scattering Proton Delivery System
AU - Wang, Xin
AU - Sahoo, Narayan
AU - Zhu, Ronald X.
AU - Zullo, John R.
AU - Gillin, Michael T.
N1 - Copyright:
Copyright 2010 Elsevier B.V., All rights reserved.
PY - 2010/4
Y1 - 2010/4
N2 - Purpose: To measure the neutron dose equivalent per therapeutic proton dose (H/D) in a passive scattering proton therapy system and study its dependence on the proton energy, aperture-to-isocenter distance, spread-out Bragg peak (SOBP) width, and field size. Methods and Materials: We performed four experiments of varying proton energies, aperture-to-isocenter distances, SOBP widths, and field sizes. Etched track detectors were used to measure the neutron dose equivalent at both an in-field (isocenter, beyond the protons' range) and out-of-field (30 cm lateral to the isocenter) location in air. Results: For a nonmodulated beam with all the protons stopping in the aperture and an aperture-to-isocenter distance of 30 cm, the H/D values measured at the isocenter were approximately 0.3 mSv/Gy for all snouts with a 100-MeV beam. The H/D values increased to 10.7, 14.5, and 15.1 mSv/Gy, respectively, for small, medium, and large snouts when the beam energy increased to 250 MeV. At the out-of-field location, H/D values increased from 0.1 to 2.7, 3.0, and 3.2 mSv/Gy, respectively, for small, medium, and large snouts. When the aperture-to-isocenter distance was changed from 10 to 40 cm, the H/D value at the isocenter dropped 70%. The H/D value doubled for the modulated beam relative to the nonmodulated beam. Open apertures reduced the neutrons produced in the nozzle, but increased those produced in the phantom. Conclusions: Our data showed that changes in the four factors studied affect the H/D value in predictable ways which permits an estimate of a patient's neutron exposure.
AB - Purpose: To measure the neutron dose equivalent per therapeutic proton dose (H/D) in a passive scattering proton therapy system and study its dependence on the proton energy, aperture-to-isocenter distance, spread-out Bragg peak (SOBP) width, and field size. Methods and Materials: We performed four experiments of varying proton energies, aperture-to-isocenter distances, SOBP widths, and field sizes. Etched track detectors were used to measure the neutron dose equivalent at both an in-field (isocenter, beyond the protons' range) and out-of-field (30 cm lateral to the isocenter) location in air. Results: For a nonmodulated beam with all the protons stopping in the aperture and an aperture-to-isocenter distance of 30 cm, the H/D values measured at the isocenter were approximately 0.3 mSv/Gy for all snouts with a 100-MeV beam. The H/D values increased to 10.7, 14.5, and 15.1 mSv/Gy, respectively, for small, medium, and large snouts when the beam energy increased to 250 MeV. At the out-of-field location, H/D values increased from 0.1 to 2.7, 3.0, and 3.2 mSv/Gy, respectively, for small, medium, and large snouts. When the aperture-to-isocenter distance was changed from 10 to 40 cm, the H/D value at the isocenter dropped 70%. The H/D value doubled for the modulated beam relative to the nonmodulated beam. Open apertures reduced the neutrons produced in the nozzle, but increased those produced in the phantom. Conclusions: Our data showed that changes in the four factors studied affect the H/D value in predictable ways which permits an estimate of a patient's neutron exposure.
KW - Neutron dose equivalent
KW - Passive scattering
KW - Proton therapy
KW - measurement
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U2 - 10.1016/j.ijrobp.2009.07.1732
DO - 10.1016/j.ijrobp.2009.07.1732
M3 - Article
C2 - 20097484
AN - SCOPUS:77949562089
SN - 0360-3016
VL - 76
SP - 1563
EP - 1570
JO - International Journal of Radiation Oncology Biology Physics
JF - International Journal of Radiation Oncology Biology Physics
IS - 5
ER -