An overview on the developments and improvements of a treatment planning system for BNCT

Boron Neutron Capture Therapy (BNCT) is a radiation therapy for cancer that employs a neutron beam and a ¹⁰B-loaded drug to selectively kill tumor cells whilst sparing surrounding healthy tissues (HT). In conventional radiation therapy, treatment planning systems (TPSs) implementing simplified models of radiation transport and dose deposition allow to efficiently optimize all the relevant parameters prior to the patient\´s irradiation. This simplified approach is not feasible in BNCT, because the presence of neutrons requires the use of more complex radiation transport models. For this reason, current BNCT TPSs routinely perform several radiation transport simulations based on the Monte Carlo method. Our team has been involved in BNCT TPS research since 1996, introducing the original trait of employing in the simulation a three-dimensional map of the highly heterogeneous boron distribution in tissues, obtained through PET scanning of the target region. This approach differs markedly from the standard one, in which boron concentration is assumed to be uniform in each "macro region" within the patient\´s head, and its value is estimated on the basis of blood sampling. The first result of this research was the prototype software CARONTE, employed to test the feasibility of the new approach and to carry out a comparative study by applying the two different approaches to the same test case. The results, presented in this paper in terms of the computed physical dose rate due to the ¹⁰B reaction, show how the different assumptions made in the two approaches can significantly influence important TP parameters. This led to the development of Boron Distribution TP Software (BDTPS), an original and complete TPS. The different phases of the experimental validation of BDTPS, which included the design and construction of an ad hoc phantom able to host a number of vials loaded with ¹⁰B solutions, is presented here. The phantom, which subsequently underwent computed tomography (CT) and positron emission tomography (PET) scanning, was irradiated in the High Flux Reactor (HFR) at JRC, Petten, The Netherlands.