Alpha emitters are small particles used in the treatment of cancer. They are nuclear particles that
typically travel short distances and attack cancer cells only.
New research has produced alpha particles with a special coating that enables them to differentiate
between healthy cells and cancer cells. The coating identifies the cancer cell and introduces the
alpha particle into the cell; when the alpha particle is inside the cell, it gives off radiation and
destroys the cancer cell. After a short period of time, the alpha particle stops emitting, causing no
significant collateral damage to the healthy cells.
This requires targeted delivery to the desired site of action. Scientists are working with the
radioactive element thorium, which emits alpha-particles. “Thorium emits energy-rich radiation,
albeit over a short distance, it cannot even penetrate through a sheet of paper,” explains Dr. Alan
Cuthbertson, head of Thorium Research at Bayer in Oslo, Norway.
His team is working on a means of transporting thorium directly to a tumour where the
radioisotope first accumulates and then decays, releasing the alpha particles. “The alpha particles
then destroys the cancer cells without damaging the surrounding healthy tissue too severely,” he
To do this, the thorium-derived radionuclide is attached to an antibody which delivers the
radioisotope directly to its site of action in the tumour. “We have selected specific antigens
expressed on the surface of the tumour cells to which the thorium-antibodies dock with high
affinity,” says Dr Cuthbertson.
This radioimmunotherapy approach could be a source of new hope for patients with lymph node,
prostate or breast cancer.
As this treatment develops, the requirement for Alpha emitters will grow. However, there is a
shortage of these emitters, which can only be manufactured in a nuclear reactor cyclotron and
worldwide production is insufficient to meet the growing demand. Now a solution has been found to
produce these alpha particles from the natural decay of thorium, an emitter of alpha particles.
In a world first, Thor Medical in Norway is studying the feasibility of producing alpha emitters as a
by-product of the natural thorium decay process. The thorium required could be supplied by the
Steenkampskraal rare earths mine in the Western Cape.
Trevor Blench, chairman of Steenkampskraal Holdings, says the company plans to supply thorium to
Thor Medical. The mineral resource estimate indicates that the Steenkampskraal mine contains 11
700 tons of thorium.
In October 2014, the Colorado School of Mines published a report entitled ‘Thorium: Does Crustal
Abundance Lead to Economic Availability? The report includes studies of where the thorium would
be sourced and states that the Steenkampskraal mine in South Africa will be the lowest cost
producer of thorium in the world, with an estimated production cost of USD3,56 per kilo.
“Once the mine is in production we will be able to increase output in a relatively short time to meet
this demand. This will be in addition to the rare earths that will be mined that are typically used in
electronic components, electric vehicles, magnets, electric motors and defence systems, for which
we are seeing increased demand,” he said.