Gamma and neutron doses of the epithermal neutron beam at the Finnish BNCT facility

In radiotherapy, uncertainty regarding the the absorbed dose in a patient has to be on a level such that the effects of a treatment can be estimated reliably beforehand and analysed after the treatment. The physical dose must also have a metrologically traceable link to national and international dosimetry standards so that comparisons with other radiotherapy modalities are possible. Although most of the uncertainties in boron neutron capture therapy (BNCT) are related to determinations of boron distribution at the target area and the biological response to radiation, the accuracy of the physical dose is still of great importance. Accurately characterized spectrum, fluence rate and absorbed dose distributions in a phantom forms the basis for a reliable dose delivery to a patient and are also essential for biological studies at the BNCT beam.

The presence of both neutron and gamma‐radiation in the epithermal neutron beam and the spread of the neutron energy and fluence in tissue or tissue substitute phantom make dosimetry of BNCT complicated. Several type of dosemeters together with the calculational methods are needed for accurate and reliable dose chacterization of an epithermal neutron beam. At the FiR1 BNCT beam diluted Au and Mg activation foils, tissue equivalent and Mg ionization chambers, LiF:Mg,Ti and 7LiF:Mg,Cu,P thermoluminescent dosemeters and SiLi semiconductor were used in measurements and DORT, MCNP and rtt_MC codes in radiation transport calculations. The preliminary results indicate approximately 6% and 12% compatibility with different dosimetric methods for gamma and neutron doses respectively.

In this work, a summary of the results of the dose determinations will be presented.