Comparison between measured (in vivo) and calculated neutron fluences and gamma doses in the Finnish BNCT clinical trials

Two clinical phase I/II protocols (P01, P03) on boron neutron capture therapy (BNCT) for the treatment of glioblastoma started at the Finnish BNCT facility in May 1999 (P01) and in February 2001(P03). For the reliability of BNCT it was regarded useful to verify actual patient doses by making comparisons between the doses calculated with the treatment planning programs and the doses measured with independent detectors. In this work the measured and calculated gamma doses and thermal neutron fluences were compared with each other for the 21 patients (18 in P01 and 3 in P03) treated so far. For neutron fluence and gamma dose measurements in vivo activation detectors and thermoluminescent (TL) dosimeters can be used. The methods of measuring gamma doses in BNCT beams have been published in detail elsewhere [1, 2]. Diluted Mn-Al activation foils (1%, Æ 12 mm 0.2 mm, ECN Petten) and wires (2.4 %, Reactor Experiments Inc.) were used for neutron fluence measurements and 7LiF:Mg,Cu,P TL detectors of type MCP-7s (TLD Niewiadomski & Co., Krakow, Poland) for the measurement of absorbed gamma doses. Detector pairs were placed at several points on the beam entry surface on patients' head in order to verify treatment planning. 55Mn reaction rates and gamma dose rates were calculated with two treatment planning softwares, namely BNCT_Rtpe (P01) and SERA (P03) (both INEEL/MSU, USA). In SERA dose planning also the air cavities were included to the head model unlike in BNCT_Rtpe because of SERA's advanced geometry tool and its shorter calculation time. The methods and the results of the comparisons will be presented. [1] C. Aschan, M Toivonen et al, Radiat. Prot. Dosim. 81 (1999) 47 - 56. [2] C. Aschan, M. Toivonen et al, Radiat. Prot. Dosim. 82 (1999) 65 - 69