Use of Positron Emission Tomography (PET) to improve radiation dosimetry for Boron Neutron Capture Therapy (BNCT)

The purpose of this work is to enhance dosimetry for BNCT by incorporating positron emission tomography (PET) into treatment planning. Currently, the INEEL code, BNCT Radiation Treatment Planning Environment (BNCT_RTPE) is used by some research institutions to determine patient specific dose to and around the tumor. Non-uniform rational B-spline (NURBS) geometry with Monte Carlo techniques are used to generate the three dimensional geometry and to determine dosimetry based on magnetic resonance imaging (MRI) and/or computed tomography (CT) [9,13]. During treatment planning homogeneous distribution of boron concentration in tumor cells and normal brain cells is assumed to be constant throughout the brain in BNCT_RTPE. A technique has been developed that allows for the incorporation of detailed patient specific boron biodistribution provided by PET to post process the dose based on the homogeneous distribution used in BNCT_RTPE. The method allows for three dimensional geometrical reconstruction with PET in BNCT_RTPE followed by peak to average scaling of the boron dose. Differences between the BNCT_RTPE boron dose and PET adjusted boron dose are presented. Results of the dose adjustment indicate remarkable differences between the conventional way of determining the dose and the PET adjusted boron dose, especially around the boundaries of the tumor. Based on data in 3 patients and the analysis done using BNCT_RTPE, the differences between conventional approach of radiation treatment planning and PET based treatment planning are as much as 20 - 80 %. Much of the differences indicate an over prediction by conventional methods in the amount of dose predicted in and around the tumor boundary regions. In conclusion, the use of PET data is shown to enhance existing methods for predicting the dosimetry for BNCT in existing codes. Improvements in dosimetry and the pharmacokinetic information provided by PET taken together with better boron compounds can significantly improve the efficacy of BNCT.