Determining and reporting the doses in the treatment of glioma patients in the epithermal neutron beam at the Finnish BNCT facility (FIR 1)

The clinical trials of glioma patients at the Finnish boron neutron capture therapy (BNCT) facility (FiR 1) started in May 1999. The doses of the patient in tumour, target volume and sensitive tissues are calculated individually. The calculated doses are calibrated to the reference monitor units according to the ratio of the independently measured and calculated 197Au(n,g) reactions rates at the depth of 20 mm on the central axis of a cylindracal PMMA phantom chosen as the reference geometry. Absorbed doses to the head and body are monitored individually using in vivo dosimeters. In BNCT the total dose is the weighted sum of the absorbed doses originating from the neutron and gamma interactions in tissues. The material compositions of the head model for the neutron-gamma transport calculation and kema factors are based on the ICRU report 46. The doses in the clinical research of BNCT should be reported in such a way that the doses are comparable, traceable and can be recalculated, if underlying information, like weighting factors for dose components, are replaced by new ones. The minimum, average and reference doses are reported for the tumour, target and normal brain. In addition to the total weighted doses the dose components (boron, gamma, nitrogen, and fast neutron dose), weighting factors and estimated boron concentration in these tissues are reported. There are no international recommendations available for BNCT dose calculation or reporting. Therefore the BNCT doses reported in the literature may not be comparable and a careless use of values can lead to over- or underdosing. There is an obvious need for standardisation in the medical application of BNCT. In this paper the methods of dose calculation and reporting of the glioma patients at FiR 1 are described.