Neutron capture therapy of cancer

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). 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.

Boron neutron capture therapy

History

James Chadwick discovered the neutron in 1932. Shortly thereafter, H. J. Taylor reported that boron-10 nuclei had a high propensity to capture low-energy thermal neutrons.