An In-vivo Comparative Study Between Standard and PET-Based Approach to Assess the Therapeutic Dose in Neutron Capture Therapies

Previous studies[l,2] dedicated to the evaluation of the best approach for a treatment plan more consistent with the clinical findings started a vexata quaestio, which is still an open issue as demonstrated by the fact that BNCT treatment plans are only partially based on the pre-evaluation of the macroscopic boron distribution. For example, the evaluation of the TIN ratio through pre-irradiation PET scanning is undoubtedly a major improvement[3]. The present article shows that the Treatment Planning System (TPS) response is evidently different if it is applied with two approaches: on one hand, the definition of the target and other regions takes into consideration the tumor morphology obtained through CT scanning (standard). On the other hand, the target and other regions definition is based on the evaluation of the PET scanning of the same patient (PET-based). In particular, the case study is a 74 years old woman, affected by parotid progressive cancer. The PET scanning permitted to evaluate a TIN ratio equal to 5. The same patient has been CT scanned for the morphology reconstruction in the TPS. BDTPS (Boron Distribution Treatment Planning System) is a TPS designed, implemented and in-phantom tested at JRC-IE in collaboration to University of Pisa. It is possible to use this TPS in both approaches. In particular, PET data are integrated directly by the system in the post-processing evaluation of the boron dose. The other doses (gamma, nitrogen and hydrogen) mainly present in BNCT are also calculated. The comparison between the two approaches gives a clear indication that the PET-based TPS offers more information in the peripheral area of the tumor, where the standard approach overestimates the boron dose. Consequently, the treatment plan calculates an irradiation time, insufficient to deliver a proper therapeutic dose in the area surrounding the main tumor core. The follow-up confirms the PET-based TPS findings. Additionally, the PET scanning helped to evaluate properly the TIN ratio, especially in zones where this ratio is too close to the unity. In this case, significant collateral damage occurs limiting the efficacy of BNCT. BDTPS can be applied to other capture therapies, such as GdNCT. Therefore, a PET-based treatment planning is a key for the most effective NCT.