Results of 10 y of radiation protection dosimetry at the neutrontherapy facility in Louvain-la-Neuve.
After 10 y of routine operation, radiation hazards to the neutron therapy staff at Louvain-la-Neuve were evaluated. These hazards to the staff in neutron therapy are a matter of concern, not only because of the dose levels due to induced activation after treatment but also because of the difficulty of evaluating adequately the dose equivalent rates (including the quality factor, QF) during the irradiation. Build-up of radioactivity near the collimator and in the therapy room is reported. In the beam axis, dose rates due to activation can amount up to 5 mGy h-1. However, these rates are efficiently reduced to 0.3 mGy h-1 by automatically withdrawing the target after irradiation. Other problems of radioactive contamination (for instance, the choice of the Fe composition of the collimator) are discussed. Dose equivalent rates were determined during treatment at different positions inside and outside the treatment room. At these locations, neutrons of widely varying energies are present, accompanied by a significant proportion of gamma rays. The measurements of neutron-dose equivalent rates were performed with three commercial neutron detectors: a BF3 and a He3 remcounter (Nuclear Enterprises and Nardeux) and the Dineutron multisphere remcounter (Nardeux). The Dineutron also allowed the evaluation of QF. The results of these detectors were compared with the results of the integration of microdosimetry spectra obtained in free air with a TE proportional counter (Far West Technology). For the p(65) + Be neutrons, the dose equivalent rate was equal to 0.4 Sv h-1 in the treatment room (at 2.5 m from the collimator) and was reduced to 2-3 microSv h-1 at the room entrance. The gamma component increased from 55% to 95% at the same positions, respectively. Ratios of the responses of all detectors and QF values are compared and discussed at the different positions. The whole-body dose equivalents to the neutron therapy staff over the 10 y considered are presented; although they are higher than for conventional radiotherapy, they remain far below the ICRP recommended dose limits.
Vynckier
S
S
Unité de Radiothérapie et de Neutronthérapie, UCL--Cliniques Universitaires St-Luc, Bruxelles, Belgium.
Pihet
P
P
Wambersie
A
A
D005214:Fast Neutrons; D006280:Health Workforce; D006801:Humans; D009502:Neutrons; D011829:Radiation Dosage; D011878:Radiotherapy