PubMed · 2493946
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1989-02-11. Radiotherapy's second setback.. https://pubmed.ncbi.nlm.nih.gov/2493946/
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A hybrid detector for measuring fast neutrons in mixed gamma-neutron fields is discussed in this paper. The detector consists of an ionization chamber with components made from a plastic scintillator. Its operation is based on the two detection systems thus combined. Its parameters and domain of applicability are explained. This paper proposes a rapid integral method for measuring the neutron-dose equivalent based on this detector, which allows a good separation of the gamma component.
The external radiation hazard to radiographers from the use of high-energy neutrons in radiotherapy has been investigated. The contributions from neutron-induced activity in the therapy gantry, the treatment room, the patient and ancillary equipment have been analysed as has the whole-body dose equivalent to radiographers. It was found that there are significant levels of gamma radiation throughout the treatment room, which increase both in the vicinity of the walls in line with the beam axis and in close proximity to the neutron therapy gantry. The mean dose equivalent to radiographers per field treated was found to be 5.1 +/- 1.8 microSv. The dose per field also varied considerably with the particular site being treated but it was found that the dose equivalent per field per minute of set-up time was approximately constant. It was also found that the dose per field increased with the number of patients treated per day commensurate with a build-up of induced activity. The studies also showed that the dose equivalent to radiography staff was comparable to that at other high-energy neutron facilities but significantly greater than that recorded at facilities with low-energy beams.
The treatment planning for radiotherapy with fast neutrons requires modifications of the planning systems used for photons. The neutron- and photon-component of the treatment fields must be determined and can then be used for separate calculations. The corrections for inhomogeneities are performed by use of attenuation coefficients and the corresponding corrections for changes in the kerma. The treatment planning system MEVAPLAN (Siemens) was modified to follow these requirements. Thus treatment planning for 14 MeV DT-neutrons could be performed. The multiplanar option is used to calculate 3D-dose distributions based on up to 40 serial CT slices. The generated three-dimensional dose matrix and the CT data are transferred via magnetic tape to the visualization system VOXEL-MAN developed at the University Hospital of Hamburg. This system uses a ray casting algorithm based on the generalized Voxel-model to display detailed 3D-images of human anatomy together with the calculated dose distribution. Different treatment plans for neutrons and photons are calculated and visualized. Various manipulations of the data-sets are displayed to improve the critical examination of the simulated dose distribution and to discern the quality of treatment techniques.