Three methods for clinical implementation of BNCT irradiations in Finland

Boron neutron capture therapy (BNCT) is a radiotherapy method which utilises an epithermal neutron beam together with specific 10B compounds accumulating in cancer cells to treat malignant tumour patients. The ICRU states that the radiotherapeutic dose to the patient should be realised within 5% accuracy of the planned dose. The aim of this study was to 1) develop the dosimetry system for the FiR 1 BNCT beam, 2) present an estimate of the blood boron level after a boronphenylalanine (BPA) infusion and 3) develop a patient positioning system for the Finnish BNCT facility. These individual phases are combined in the implementation of BNCT treatments at the Finnish BNCT facility. The physical neutron and gamma doses were determined with different dosimetrical methods. Different phantom materials and geometries were used in dose assessments to provide comprehensive data. Measured and calculated doses were compared to verify the source model and the treatment planning system. The blood boron level influences the boron concentration in the healthy tissue and in the tumour cells. It is then essential to predict the blood boron level during the treatment. A bi-exponential model was created to produce an estimate of the blood boron level during the irradiation using the measured blood boron data as reference values. At the Finnish BNCT facility the planned irradiation fields are carried out with a horizontal static beam aperture. Thus all the beam directions have to be realised solely by positioning the patient instead of moving the beam. A special system was developed to facilitate the patient positioning in BNCT in which the positioning techniques used in traditional radiotherapy cannot be applied. The methods involved in dosimetry, boron estimation and positioning all contribute to the reliability of the eventual patient dose. The methods described here provide practical means for BNCT and have been established in studies and actual treatment situations. [1] M. Kortesniemi, A. Kosunen et al., Frontiers in Neutron Capture Therapy (2001) 659. [2] P. Ryynänen, M. Kortesniemi et al., Int J Radiat Oncol. Biol. Phys. (2000) 1145. [3] T. Seppälä, M. Kortesniemi et al., Med. & Biol. Eng. & Comp. (1999) 402.