Measurement of Neutron Dose Equivalent and its Dependence on Beam Configuration for a Passive Scattering Proton Delivery System

Journal Article · Thu Apr 15 04:00:00 EDT 2010 · International Journal of Radiation Oncology, Biology and Physics

DOI:https://doi.org/10.1016/j.ijrobp.2009.07.1732· OSTI ID:21372227

Xin, Wang; Sahoo, Narayan; Zhu, Ronald X; Zullo, John R ^[1]

---

1. Department of Radiation Physics, University of Texas M. D. Anderson Cancer Center, Houston, TX (United States)

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.

• OSTI ID: 21372227
• Journal Information: International Journal of Radiation Oncology, Biology and Physics, Journal Name: International Journal of Radiation Oncology, Biology and Physics Journal Issue: 5 Vol. 76; ISSN IOBPD3; ISSN 0360-3016
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
APERTURES
BARYONS
BEAMS
DOSE EQUIVALENTS
DOSES
ELEMENTARY PARTICLES
FERMIONS
HADRONS
MEDICINE
MOCKUP
NEUTRONS
NOZZLES
NUCLEAR MEDICINE
NUCLEONS
OPENINGS
PHANTOMS
PROTONS
RADIATION DOSES
RADIOLOGY
RADIOTHERAPY
SCATTERING
STRUCTURAL MODELS
THERAPY