**1. Introduction**

Boron neutron capture therapy (BNCT) for head and neck cancer was approved in Japan in 2020, using the world's first accelerator-type neutron generator, (BNCT treatment system NeuCure® Sumitomo Heavy Industries, Ltd.) along with the boron drug for BNCT (Borofaran (10B), and Steboronin® Stella Pharma Co., Ltd.) [1]. It has attracted a lot of interest due to its potential for advancement and widespread use in general medical practice.

Recent developments in quantum-based medicine are remarkable worldwide, and representative particle therapy devices are expected to expand their application range due to their excellent beam quality and biological effects, as well as technological improvements in disease adaptability such as beam shaping technology, rotation of gantry, and diagnostic image-guided irradiation and focal tracking irradiation, which precede X-ray therapy devices. Neutron capture therapy is a representative method for applying quantum to medical treatment using neutron capture reactions with atoms, in addition to therapies that control and apply direct cellular damage of these quanta to living organisms. Neutron capture reactions occur between various atoms, but the stable isotope of boron, boron-10 (10B), which is the most suitable condition for medical applications, is used and is called boron neutron capture therapy. Since naturally existing boron consists of two stable isotopes (11B and 10B), where 11B accounts for 80%, special technology and equipment are required to produce concentrated 10B used for BNCT.

BNCT is a particle therapy that biologically targets tumor cells [2]. By selectively introducing boron drugs containing 10B atoms into tumors and irradiating them with thermal neutrons, charged particles are generated by neutron capture ( 10B + n → α + 7 Li or 10B (n, α) 7 Li). The resulting alpha particles and recoil lithium (Li) nuclei are high LET (linear energy transfer) particles that emit all their energy over a short range corresponding to the size of a cell. If boron compounds are selectively introduced, the reaction occurs only in cancer cells and is an ideal "cell-selective treatment" in which surrounding normal cells are preserved. The characteristic of this treatment is that the boron compounds to be administered and the neutrons to be irradiated are non- to low-toxic, respectively, and the treatment is completed by a two-step approach, "neutron capture reaction," in which the effects of both compounds are shown for the first time in vivo (**Figure 1**).

Unlike other advances in radiotherapy that spatially add changes to the distribution of doses, it is necessary to note that there are different distributions of biological effects in the same irradiation field in BNCT. In the case of BNCT for glioma, we mainly examine the distribution dose of the tumor and the distribution dose of the normal brain for medical care. In the case of neutron irradiation, it is necessary to add and calculate other doses mixed in the neutron field to be irradiated, as well as the biological effects of the radiation quality and tissue reaction, respectively. There are

#### **Figure 1.**

*In boron neutron capture therapy (BNCT), 10B compounds are administered followed by low-energy neutron irradiation, which causes a nuclear reaction between the 10B and the neutrons. The resulting helium nuclei (alpha particles) and lithium recoil nuclei selectively destroy tumor cells from within even in the infiltrated area.*

## *Boron Compounds for Neutron Capture Therapy in the Treatment of Brain Tumors DOI: http://dx.doi.org/10.5772/intechopen.106202*

some peculiarities in these calculations, but the results are easy to understand because they are visualized as X-ray equivalent doses (**Figure 2**).

The practice of providing medical care by considering the biological effects of radiotherapy is the same in the current general-purpose radiotherapy devices. The wide range of invasion areas of glioma is sometimes targeted as a tumor or as a risk organ, and different biological effects have been induced by the difference of the number of fractions and the dose at one time in the assumed tissues, which are each subject. For details, refer to the guidelines for radiotherapy and the Guidance on Evaluation of Accelerator Neutron Irradiation Device System for Boron Neutron Capture Therapy (BNCT Review Working Group, National Institute of Health

**Figure 2.**

*In BNCT, organ-specific dose distributions are calculated simultaneously (upper: Dose distribution, right: Lower: Dose volume histogram (DVH) for normal and tumor tissue). The SERA calculation engine used in many reactor-based BNCT facilities combines a proprietary Monte Carlo calculation code.*

Sciences, Japan) [3]. This knowledge is necessary not only for BNCT, but also for conventional X-ray irradiation (2Gy 30 fractions) (for example, in combination with intensity-modulated irradiation, stereotactic irradiation, reirradiation at the time of recurrence, etc.), and is a sense to be acquired.
