Imaging and profiling of absorbed dose in neutron capture therapy

Imaging and profiling of the absorbed dose in tissue-equivalent gel phantoms exposed to thermal neutrons were performed at the TAPIRO fast reactor (ENEA, Italy). The proposed method, aimed at supporting the planning of neutron capture therapy, allows measurement of three-dimensional distributions of the therapy dose not only in tumors but also in normal tissue. This feature is very important, because the value of the maximum fluence admitted for therapy is limited by the dose absorbed in the healthy tissue. Fricke-infused gel phantoms were designed that allow imaging of the absorbed dose by means of optical analysis, based on the detection of visible-light absorbance with a charge-coupled device camera. Moreover, the various components of the secondary radiation contributing to the dose can be separated through the differential analysis of images obtained with gels with different elemental compositions. Dose mapping in a phantom was also performed with thermoluminescent dosimeters (TLDs). A method for separating the different dose contributions was studied. based on the analysis of the glow-curve shapes of different kinds of TLDs. The agreement of the results obtained with the two techniques confirmed the validity of the methods. Fluence measurements performed with activation techniques and Monte Carlo simulations gave further support.