The essential role of radiobiological figures of merit for the assessment and comparison of beam performances in boron neutron capture therapy

Purpose: Boron Neutron Capture Therapy (BNCT) is a treatment modality that uses an external neutron beam to selectively inactive boron10-loaded tumor cells. This work presents the development and innovative use of radiobiological probability models to adequately evaluate and compare the therapeutic potential and versatility of beams presenting different neutron energy spectra. M&M: Aforementioned characteristics, collectively refer to as the performance of a beam, were defined on the basis of radiobiological probability models for the first time in BNCT. A model of uncomplicated tumor control probability (UTCP) for HN cancer was introduced. This model considers a NTCP able to predict severe mucositis and a TCP for non-uniform doses derived herein. A systematic study comprising a simplified HN cancer model is presented as a practical application of the introduced radiobiological figures of merit (FOM) for assessing and comparing the performance of different clinical beams. Applications involving treated HN cancer patients were also analyzed. Results: The maximum UTCP proved suitable and sensitive to assess the performance of a beam, revealing particularities of the studied sources that the physical FOMs do not highlight. The radiobiological FOMs evaluated in patients showed to be useful tools both for retrospective analysis of the BNCT treatments, and for prospective studies of beam optimization and feasibility. Conclusions: The presented developments and applications demonstrated that it is possible to assess and compare performances of completely different beams fairly and adequately by assessing the radiobiological FOM UTCP. Thus, this figure would be a practical and essential aid to guide treatment decisions.