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The thermal neutron flux in a fast neutron therapy treatment unit is measured by a small ionization chamber coated inside with boron (10B). These measurements are compared with calculations of the thermal neutron flux made by a pencil beam algorithm, which can be used as a first approximation for treatment therapy planning. The additional dose for boron neutron capture therapy (BNCT) as a boost in a 14 MeV neutron generator is calculated from the measured thermal neutron flux.

Neutron and photon energy spectra were measured in different depths and lateral positions in tissue-equivalent phantoms exposed to a therapeutical 14.1 MeV neutron beam. Intensity weighted mass energy absorption coefficients were derived for application in ionization chamber dosimetry in mixed neutron-gamma fields. The resulting relative depth doses show that on the beam axis for depths in excess of 20 cm, gamma radiation contributes with more than 10% to the total dose; off the axis outside the direct beam neutron and gamma doses are comparable. The differences between these doses and those neglecting the spectra distribution increase with depth and with the distance from the beam axis.

The energy distribution of 3H(d, n)4He neutrons from a neutron therapy facility has been studied in different depths in a lucite phantom with two methods. Thin foils of 8 different target materials with well-known excitation functions and reaction thresholds between 1.8 and 12.6 MeV for the reactions to be observed have been activated. Secondly, recoil proton spectra have been measured with a small stilbene crystal. In both cases neutron energy spectra have been determined with unfolding methods. The two techniques are compared with respect to the application in neutron dosimetry and for monitoring purposes in neutron therapy.