Neutron measurements around medical electron accelerators by active and passive detection techniques. 1991

G Tosi, and A Torresin, and S Agosteo, and A Foglio Para, and V Sangiust, and L Zeni, and M Silari
Servizio di Fisica Sanitaria, Ospedale Niguarda Ca'Granda, Piazza Ospedale Maggiore, Milano, Italy.

Passive and active detection techniques have been employed in order to measure neutron fluence rates and corresponding exposure rates around medical electron accelerators operating at energies well above the neutron binding energies of the structural materials. In these conditions from the treatment head, in the direct photon flux and from the shielded region, a fast neutron flux emerges which is partly absorbed and partly scattered by the walls, eventually establishing a nearly uniform thermal and epithermal flux in the room. Both direct and scattered flux contribute to the dose to the patient. A smaller neutron dose rate can also be found outside the treatment room, where the therapy staff works. Passive detectors, of moderation type, have been employed in the treatment room and 3He active detectors in the external zones. For the treatment room the activation data were compared with results of Monte Carlo simulation of the neutron transport in the room. Technical features of the two measures are briefly presented and results obtained around three different types of accelerators are reported. At the higher beam energies, i.e., 25 MV, a neutron dose of 0.36 Sv was estimated in the treatment field in addition to a therapeutic x-ray dose of 50 Gy. At lower energies or out of the treatment field the neutron dose drops significantly. In the external zones the dose rates everywhere are below the recommended limits and normally very low, the highest values being recorded in positions very close to the access door of the treatment room.

UI MeSH Term Description Entries
D009502 Neutrons Electrically neutral elementary particles found in all atomic nuclei except light hydrogen; the mass is equal to that of the proton and electron combined and they are unstable when isolated from the nucleus, undergoing beta decay. Slow, thermal, epithermal, and fast neutrons refer to the energy levels with which the neutrons are ejected from heavier nuclei during their decay. Neutron
D010315 Particle Accelerators Devices which accelerate electrically charged atomic or subatomic particles, such as electrons, protons or ions, to high velocities so they have high kinetic energy. Betatrons,Linear Accelerators,Accelerator, Linear,Accelerator, Particle,Accelerators, Linear,Accelerators, Particle,Betatron,Linear Accelerator,Particle Accelerator
D011829 Radiation Dosage The amount of radiation energy that is deposited in a unit mass of material, such as tissues of plants or animal. In RADIOTHERAPY, radiation dosage is expressed in gray units (Gy). In RADIOLOGIC HEALTH, the dosage is expressed by the product of absorbed dose (Gy) and quality factor (a function of linear energy transfer), and is called radiation dose equivalent in sievert units (Sv). Sievert Units,Dosage, Radiation,Gray Units,Gy Radiation,Sv Radiation Dose Equivalent,Dosages, Radiation,Radiation Dosages,Units, Gray,Units, Sievert
D011835 Radiation Protection Methods and practices adopted to protect against RADIATION. Protection, Radiation
D011874 Radiometry The measurement of radiation by photography, as in x-ray film and film badge, by Geiger-Mueller tube, and by SCINTILLATION COUNTING. Geiger-Mueller Counters,Nuclear Track Detection,Radiation Dosimetry,Dosimetry, Radiation,Geiger Counter,Geiger-Mueller Counter Tube,Geiger-Mueller Probe,Geiger-Mueller Tube,Radiation Counter,Counter Tube, Geiger-Mueller,Counter Tubes, Geiger-Mueller,Counter, Geiger,Counter, Radiation,Counters, Geiger,Counters, Geiger-Mueller,Counters, Radiation,Detection, Nuclear Track,Dosimetries, Radiation,Geiger Counters,Geiger Mueller Counter Tube,Geiger Mueller Counters,Geiger Mueller Probe,Geiger Mueller Tube,Geiger-Mueller Counter Tubes,Geiger-Mueller Probes,Geiger-Mueller Tubes,Probe, Geiger-Mueller,Probes, Geiger-Mueller,Radiation Counters,Radiation Dosimetries,Tube, Geiger-Mueller,Tube, Geiger-Mueller Counter,Tubes, Geiger-Mueller,Tubes, Geiger-Mueller Counter
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man

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