Boron Neutron Capture Therapy
Encyclopedia
Boron neutron capture therapy (BNCT) is an experimental form of radiotherapy that uses a neutron
beam that interacts with boron
injected into a patient. BNCT depends on the interaction of slow neutrons with boron-10 to produce alpha particles and lithium nuclei, without producing other types of ionizing radiation.
Patients are first given an intravenous injection of a boron-10 containing chemical that preferentially binds to tumor cells. In clinical trials performed so far the neutrons are created in a nuclear reactor
, but particle accelerators may also be used to collide protons into targets made of lithium
or beryllium
.
The neutrons pass through a neutron moderator
, which shapes the neutron energy spectrum suitable for BNCT treatment. Before entering the patient the neutron beam is shaped by a beam collimator
. While passing through the tissue of the patient, the neutrons are slowed by collisions and become low energy thermal neutrons. The thermal neutrons undergo reaction with the boron-10 nuclei, forming a compound nucleus (excited boron-11) which then promptly disintegrates to lithium-7 and an alpha particle. Both the alpha particle and the lithium ion produce closely spaced ionizations in the immediate vicinity of the reaction, with a range of approximately 5-9 micrometres, or roughly the thickness of one cell diameter. This technique is advantageous since the radiation damage occurs over a short range and thus normal tissues can be spared.
BNCT has been experimentally tested primarily as an alternative treatment for malignant brain tumors called glioblastoma multiforme
as well as recurrent, locally advanced head and neck cancer
. Although there are reports of some successful outcomes, this approach has not yet been shown to be superior to other current therapies. Hence, BNCT has not entered routine clinical use.
(Italy
) on a 42 years old man to treat liver cancer
.
His liver
has been explanted, has been subjected to the treatment, and has been reimplanted.
The first clinical trial of BNCT in Argentina were performed on 9 October 2003. BNCT has been used in Japan for head and neck cancers in 2009. Taiwan
BNCT group also started treating head and neck cancers at the Tsing Hua Open-pool Reactor (THOR) of National Tsing Hua University
on 11 August 2010.
, a study by H. J. Taylor in 1935 showed the ability of the boron-10 nuclei to capture thermal neutrons. The neutron capture initiated the fission
of the boron-10 nuclei into helium-4 alpha particles as well as lithium-7 particles. In 1936, Locher realised the potential of this discovery in the field of medicine and subsequently suggested that neutron capture could be used to treat tumours. A binary system uses two separate components for the therapy of cancer. Each component in itself is relatively harmless to the cells, but when combined together for treatment they produce a highly cytocidal effect which is lethal. As development on neutron capture therapy continued, other radioactive isotopes such as uranium-235 were researched. However, studies in the late 1950s by Lussenhop et al. showed that the amounts of uranium needed for successful neutron capture therapy was too toxic for human use.
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
beam that interacts with boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
injected into a patient. BNCT depends on the interaction of slow neutrons with boron-10 to produce alpha particles and lithium nuclei, without producing other types of ionizing radiation.
Patients are first given an intravenous injection of a boron-10 containing chemical that preferentially binds to tumor cells. In clinical trials performed so far the neutrons are created in a nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
, but particle accelerators may also be used to collide protons into targets made of lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
or beryllium
Beryllium
Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...
.
The neutrons pass through a neutron moderator
Neutron moderator
In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235....
, which shapes the neutron energy spectrum suitable for BNCT treatment. Before entering the patient the neutron beam is shaped by a beam collimator
Collimator
A collimator is a device that narrows a beam of particles or waves. To "narrow" can mean either to cause the directions of motion to become more aligned in a specific direction or to cause the spatial cross section of the beam to become smaller.- Optical collimators :In optics, a collimator may...
. While passing through the tissue of the patient, the neutrons are slowed by collisions and become low energy thermal neutrons. The thermal neutrons undergo reaction with the boron-10 nuclei, forming a compound nucleus (excited boron-11) which then promptly disintegrates to lithium-7 and an alpha particle. Both the alpha particle and the lithium ion produce closely spaced ionizations in the immediate vicinity of the reaction, with a range of approximately 5-9 micrometres, or roughly the thickness of one cell diameter. This technique is advantageous since the radiation damage occurs over a short range and thus normal tissues can be spared.
BNCT has been experimentally tested primarily as an alternative treatment for malignant brain tumors called glioblastoma multiforme
Glioblastoma multiforme
Glioblastoma multiforme is the most common and most aggressive malignant primary brain tumor in humans, involving glial cells and accounting for 52% of all functional tissue brain tumor cases and 20% of all intracranial tumors. Despite being the most prevalent form of primary brain tumor, GBMs...
as well as recurrent, locally advanced head and neck cancer
Head and neck cancer
Head and neck cancer refers to a group of biologically similar cancers that start in the upper aerodigestive tract, including the lip, oral cavity , nasal cavity , paranasal sinuses, pharynx, and larynx. 90% of head and neck cancers are squamous cell carcinomas , originating from the mucosal lining...
. Although there are reports of some successful outcomes, this approach has not yet been shown to be superior to other current therapies. Hence, BNCT has not entered routine clinical use.
Recent applications
On 19 December 2001, BNCT has been successfully used for the first time in PaviaPavia
Pavia , the ancient Ticinum, is a town and comune of south-western Lombardy, northern Italy, 35 km south of Milan on the lower Ticino river near its confluence with the Po. It is the capital of the province of Pavia. It has a population of c. 71,000...
(Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
) on a 42 years old man to treat liver cancer
Liver cancer
Liver tumors or hepatic tumors are tumors or growths on or in the liver . Several distinct types of tumors can develop in the liver because the liver is made up of various cell types. These growths can be benign or malignant...
.
His liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
has been explanted, has been subjected to the treatment, and has been reimplanted.
The first clinical trial of BNCT in Argentina were performed on 9 October 2003. BNCT has been used in Japan for head and neck cancers in 2009. Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
BNCT group also started treating head and neck cancers at the Tsing Hua Open-pool Reactor (THOR) of National Tsing Hua University
National Tsing Hua University
National Tsing Hua University is one of the most prestigious universities in Taiwan. The university has a strong reputation in the studies of science and engineering. Times Higher Education - World University Rankings is107in the world. Engineering and Science are the best in Taiwan...
on 11 August 2010.
Early history of neutron capture therapy
After the initial discovery of the neutron in 1932 by Sir James ChadwickJames Chadwick
Sir James Chadwick CH FRS was an English Nobel laureate in physics awarded for his discovery of the neutron....
, a study by H. J. Taylor in 1935 showed the ability of the boron-10 nuclei to capture thermal neutrons. The neutron capture initiated the fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
of the boron-10 nuclei into helium-4 alpha particles as well as lithium-7 particles. In 1936, Locher realised the potential of this discovery in the field of medicine and subsequently suggested that neutron capture could be used to treat tumours. A binary system uses two separate components for the therapy of cancer. Each component in itself is relatively harmless to the cells, but when combined together for treatment they produce a highly cytocidal effect which is lethal. As development on neutron capture therapy continued, other radioactive isotopes such as uranium-235 were researched. However, studies in the late 1950s by Lussenhop et al. showed that the amounts of uranium needed for successful neutron capture therapy was too toxic for human use.