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

Journal Article · Tue Jan 01 04:00:00 EST 1991 · Medical Physics; (USA)

DOI:https://doi.org/10.1118/1.596751· OSTI ID:6148423

Tosi, G; Torresin, A ^[1]; Agosteo, S; Para, A F; Sangiust, V; Zeni, L ^[2]; Silari, M ^[3]

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1. Servizio di Fisica Sanitaria, Ospedale Niguarda Ca'Granda, Piazza Ospedale Maggiore 3, 20162 Milano (Italy)
2. Instituto di Ingegneria Nucleare-CeSNEF, Politecnico di Milano, Via Ponzio 34/3, 20133 Milano (Italy)
3. Consiglio Nazionale delle Ricerche, Istituto Tecnologie Biomediche Avanzate, Via Ampere 56, 20131 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 {sup 3}He 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.

• OSTI ID: 6148423
• Journal Information: Medical Physics; (USA), Journal Name: Medical Physics; (USA) Vol. 18:1; ISSN 0094-2405; ISSN MPHYA
• Country of Publication: United States
• Language: English

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