Ultrasound Combination to Improve the Efficacy of Current Boron Neutron Capture Therapy for Head and Neck Cancer

Boron neutron capture therapy (BNCT) is radiotherapy in which a nuclear reaction between boron-10 (¹⁰B) in tumor cells and neutrons produces alpha particles and recoiling ⁷Li nuclei with an extremely short range, leading to the destruction of the tumor cells. Although the neutron source has traditionally been a nuclear reactor, accelerators to generate neutron beams have been developed and commercialized. Therefore, this treatment will become more widespread. Recurrent head and neck cancer (HNC) close to the body surface is considered a candidate for BNCT using the boron compound boronophenylalanine (BPA) and has been found to be highly responsive to this treatment. However, some cases recur early after the completion of the treatment, which needs to be addressed. Ultrasound is a highly safe diagnostic method. Ultrasound with microbubbles is expected to promote the uptake of BPA into tumor cells. Ultrasound also has the ability to improve the sensitivity of tumor cells to radiotherapy. In addition, high-intensity focused ultrasound may improve the efficacy of BNCT via its thermal and mechanical effects. This review is not systematic but outlines the current status of BPA-based BNCT and proposes plans to reduce the recurrence rate of HNC after BNCT in combination with ultrasound.