Evidence for photoneutron production in the lead shielding of a dedicated intra-operative electron only facility.
A dedicated electron-only intra-operative suite has just been completed at the Massachusetts General Hospital. This suite is located on the 3rd floor with the shielding consisting entirely of lead and borated polyethylene, except for concrete in the floor and ceiling to support the lead and on the finished floor. The radiation protection barriers for this facility were calculated on the basis of a maximum permissible dose of 10 microSv wk(-1) for photons and 10 microSv wk(-1) for neutrons, based on a quality factor of 10 (this factor is specified in the regulations of the Commonwealth of Massachusetts). This even split was predicated on the basis that, except for the primary beam, the neutron leakage from the machine was generally about the same as for x rays. The initial survey showed that the neutron dose equivalent outside all barriers, except below the floor, was within the calculated values, < 10 microSv wk(-1). However, the neutron dose equivalent measured directly below the floor was found to be 35 microSv wk(-1) for the highest electron energy, a difference of > 25 microSv wk(-1). The neutron dose equivalent, for neutrons produced by bremsstrahlung photon interactions in the lead and based on a 3% photon background in the electron beam, was calculated to be 25 microSv wk(-1), in good agreement with this difference.
Biggs
P J
PJ
Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
D004583:Electrons; D004865:Equipment and Supplies, Hospital; D007432:Intraoperative Period; D007854:Lead; D009873:Operating Rooms; D017785:Photons; D011835:Radiation Protection / Q000295:instrumentation* / Q000379:methods
D007854:Lead