Establishing dose planning in BNCT at the Finnish facility

The clinical trials of glioma patients with boron neutron capture therapy (BNCT) started in May 1999 at the Finnish Research Reactor (FiR 1). Epithermal neutrons are used with boronophenylalanine-fructose (BPA-F) as the 10B carrier. Before the clinical trials the dose planning system was established. The aim of the study was to 1) determine the FiR 1 epithermal neutron beam model 2) define the most suitable normal brain tissue material for NCT dosimetry 3) verify and normalise the beam model for clinical use 4) study the reliability of computational BNCT dose planning under in vivo conditions. The FiR 1 beam was modelled using DORT (Two Dimensional Discrete Ordinates Transport) code. The beam model was defined for the BNCT treatment planning program BNCT/Rtpe and its new version SERA (both INEEL/MSU, USA). The dosimetric characteristics of PMMA, water and two ICRU brain equivalent liquids as a phantom material were studied with computations to find a most suitable brain tissue sustitute for NCT dosimetry. The spectrum of the neutron beam model was verified in air with activation measurements. The neutron fluence/dose and gamma dose distributions in-phantoms were verified with activation dosimeters, ionisation chambers and TL dosemeters. The beam model of the treatment planning program was normalised to the measurements (activation foils) at the thermal neutron maximum in the PMMA phantom. The uncertainty of calculated reference doses are estimated in the brain with computational methods and around the brain with comparison to the measured values (activation foils and TL dosemeters) under in vivo conditions. The features of the dose planning system developed in the Finnish BNCT project will be exemplified by the treatment plans of the treated patients. [1] T.Serén, I.Auterinen, T.Seppälä, P.Kotiluoto, 15th European TRIGA Conference, (1999) 167. [2] T.Seppälä, T.Serén, I.Auterinen, Frontiers in Neutron Capture Therapy (2001) 219. [3] T.Seppälä, J.Vähätalo, I.Auterinen, A.Kosunen, D.W.Nigg, F.J.Wheeler, Radiat. Phys. Chem. (1999) 239. [4] A.Kosunen, M.Kortesniemi, H.Ylä-Mella, T.Seppälä, J.Lampinen, T.Serén, I.Auterinen, S.Savolainen, Radiat. Prot. Dosim. (1999) 187. [5] C.Aschan, M.Toivonen, S.Savolainen, T.Seppälä, I.Auterinen, Radiat. Prot. Dosim. (1999) 47. [6] T.Seppälä, I.Auterinen, C.Aschan, T.Serén, J.Benczik, M.Snellman, R.Huiskamp, U.Abo Ramadan, L.Kankaanranta, H.Joensuu, S.Savolainen, (under revision)