TY - JOUR
T1 - Measured Neutron Spectra and Dose Equivalents from a Mevion Single-Room, Passively Scattered Proton System Used for Craniospinal Irradiation
AU - Howell, Rebecca M.
AU - Burgett, Eric A.
AU - Isaacs, Daniel
AU - Price Hedrick, Samantha G.
AU - Reilly, Michael P.
AU - Rankine, Leith J.
AU - Grantham, Kevin K.
AU - Perkins, Stephanie
AU - Klein, Eric E.
N1 - Publisher Copyright:
© 2016 The Authors.
PY - 2016/5/1
Y1 - 2016/5/1
N2 - 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 × 106 to 1.04 × 107 n/cm2/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.
AB - 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 × 106 to 1.04 × 107 n/cm2/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.
UR - http://www.scopus.com/inward/record.url?scp=84963569403&partnerID=8YFLogxK
U2 - 10.1016/j.ijrobp.2015.12.356
DO - 10.1016/j.ijrobp.2015.12.356
M3 - Article
C2 - 27084645
AN - SCOPUS:84963569403
SN - 0360-3016
VL - 95
SP - 249
EP - 257
JO - International Journal of Radiation Oncology Biology Physics
JF - International Journal of Radiation Oncology Biology Physics
IS - 1
ER -