Neutron flux density and secondary-particle energy spectra at the 184-inch synchrocyclotron medical facility
Helium ions, with an energy of 920 MeV, produced by the 184-inch synchrocyclotron of the Lawrence Berkeley Laboratory are now being used in a pilot series to determine their efficacy in the treatment of tumors of large volume. The techniques for production of the large uniform radiation fields required for these treatments involve the use of beam-limiting collimators and energy degraders. Interaction of the primary beam with these beam components produces secondary charged particles and neutrons. The sources of neutron production in the beam transport system of the alpha-particle beam have been identified and their magnitudes have been determined. Measurements with activation detectors and pulse counters of differing energy responses have been used to determine secondary particle spectra at various locations on the patient table. These spectra are compared to a calculation of neutron production based on best estimates derived from published cross sections. Agreement between the calculated spectra and those derived from experimental measurements is obtained (at the 10 to 20% level) when the presence of charged particles is taken into account. The adsorbed dose in soft tissue is not very sensitive to the shape of the incident neutron energy spectrum, and the values obtained from unfolding the experimental measurements agree with the values obtained from the calculated spectra within the estimated uncertainty of +-25%. These values are about 3 x 10/sup -3/ rad on the beam axis and about 1 x 10/sup -3/ rad at 20 cm or more from the beam axis, per rad deposited by the incident alpha-particle beam. Estimates of upper limit dose to the lens of the eye and red bone marrow are approximately 10 rad and approximately 1 rad, respectively, for a typical treatment plan. The absorbed dose to the lens of the eye is thus well below the threshold value for cataractogenesis estimated for fission neutrons. An upper limit for the risk of leukemia is estimated to be approximately 0.04%.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6612587
- Report Number(s):
- LBL-6721; TRN: 78-019434
- Country of Publication:
- United States
- Language:
- English
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63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ALPHA PARTICLES
ABSORPTION
BONE MARROW
RADIATION DOSES
CHARGED PARTICLES
ENERGY SPECTRA
COLLIMATORS
CHARGED-PARTICLE TRANSPORT
CRYSTALLINE LENS
FISSION NEUTRONS
NEUTRON DOSIMETRY
HELIUM IONS
RADIOTHERAPY
NEUTRONS
BERKELEY SYNCHROCYCLOTRON
FLUX DENSITY
MEV RANGE 100-1000
NEUTRON FLUX
PATIENTS
ACCELERATORS
BARYONS
BODY
CYCLIC ACCELERATORS
DOSES
DOSIMETRY
ELEMENTARY PARTICLES
ENERGY RANGE
EYES
FERMIONS
HADRONS
HEMATOPOIETIC SYSTEM
MEDICINE
MEV RANGE
NUCLEAR MEDICINE
NUCLEONS
ORGANS
RADIATION FLUX
RADIATION TRANSPORT
RADIOLOGY
SENSE ORGANS
SPECTRA
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