Neutron capture therapy of cancer

Neutron capture therapy of cancer
a. BNCT is based on the neutron capture and decay reactions that occur when boron-10 is irradiated with low-energy (0.0025 eV) thermal neutrons. The resulting 10B(n,α)7Li capture reaction yields high linear energy transfer (LET) α particles (stripped down helium nuclei [4He]) and recoiling lithium-7 (7Li) atoms. b. The short range (5-9 μm) of the α particles limits the destructive effects to the boron-containing cells. In theory, BNCT can selectively destroy malignant cells while sparing adjacent normal tissue if the requisite amounts of 10B and neutrons are delivered to the tumor cells. Reprinted from Barth RF, Mi P, Yang W (June 2018). "Boron delivery agents for neutron capture therapy of cancer". Cancer Communications. 38 (1): 35. doi:10.1186/s40880-018-0299-7 PMC 6006782. PMID 29914561).
Specialty	oncology
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Neutron capture therapy (NCT) is a type of radiotherapy for treating locally invasive malignant tumors such as primary brain tumors, recurrent cancers of the head and neck region, and cutaneous and extracutaneous melanomas. It is a two-step process: first, the patient is injected with a tumor-localizing drug containing the stable isotope boron-10 (¹⁰B), which has a high propensity to capture low energy "thermal" neutrons. The neutron cross section of ¹⁰B (3,837 barns) is 1,000 times more than that of other elements, such as nitrogen, hydrogen, or oxygen, that occur in tissue. In the second step, the patient is radiated with epithermal neutrons, the sources of which in the past have been nuclear reactors and now are accelerators that produce higher energy epithermal neutrons. After losing energy as they penetrate tissue, the resultant low energy "thermal" neutrons are captured by the ¹⁰B atoms. The resulting decay reaction yields high-energy alpha particles that kill the cancer cells that have taken up enough ¹⁰B.

All clinical experience with NCT to date is with boron-10; hence this method is known as boron neutron capture therapy (BNCT).^[1] Use of another non-radioactive isotope, such as gadolinium, has been limited to experimental animal studies and has not been done clinically. BNCT has been evaluated as an alternative to conventional radiation therapy for malignant brain tumors such as glioblastomas, which presently are incurable, and more recently, locally advanced recurrent cancers of the head and neck region and, much less often, superficial melanomas mainly involving the skin and genital region.^[1][2][3]