Yielding medical isotopes is an expensive business, with even 1 g of the target material used to produce them costing thousands of dollars. But these short-lived isotopes are essential for treating cancer and imaging processes in the body, which is why demand for radioisotopes in Turkey has rocketed over the last 10 years. Back in 2000, for example, Turkey imported 39 500 milliCurie (mCi) of thallium-201 (1 Ci is 3.7 × 1010 decays per second, or 37 × 109 Bq) but by 2010 that figure had more than quadrupled to 149 000 mCi.
In early 2011 TAEK therefore began work on the €20 m Proton Accelerator Facility (PAF) at SANAEM to put an end to Turkey's dependence on importing isotopes for medical use. At the heart of the facility is a 15–30 MeV cyclotron – built by the Belgium firm Ion Beam Applications (IBA) – that will produce medical isotopes by accelerating negatively charged hydrogen ions in a 2.7 m diameter cyclotron and then smashing them into a variety of liquid, gas or solid targets. With an operating proton current of 1.2 mA, the facility can produce radioisotopes more quickly than those with a lower current.
With construction now complete, TAEK researchers finally began putting the 60-tonne cyclotron through its paces last October. They hope that once PAF is fully operational later this year it will produce more than 150 000 mCi of thallium-201 – easily outstripping demand of that particular isotope and so ending Turkey's import dependence on it and a range of other medical isotopes. Indeed, Ali Tanrikut, project manager and acting director of SANAEM, believes Turkey may actually be able to export them in the future.
Medical matters
According to estimates from the International Atomic Energy Agency, there are currently about 350 cyclotrons in the world that are used for radioisotope production, with the US alone running about 70. Turkey's new facility is therefore nothing out of the ordinary – indeed the country already operates eight smaller cyclotrons with lower proton energies for producing medical isotopes. However, those facilities are all based at hospitals and mostly produce only one isotope – fluorine-18 – which is used in PET to produce a 3D image of processes in the body.
But in addition to fluorine-18, PAF will also aim to create four other key medical radioisotopes for use in hospitals, namely thallium-201, iodine-123, indium-111 and gallium-67. These other radioisotopes can all be used for SPECT, which involves injecting isotopes into the blood stream and then imaging the gamma rays emitted from the radioisotopes.
The protons that are essential to the production of the isotopes will be created at PAF by first heating tantalum filaments in the ion source of the cyclotron. The released energetic electrons from the filaments ionize and excite the hydrogen gas in the ion source to produce negatively charged hydrogen anions. These are then accelerated to high energies before being passed through a "carbon stripper", which takes away two electrons, leaving just protons. The protons are finally sent down four separate beamlines to various targets, with three of the beamlines being used to produce medical isotopes and the fourth for research and development.
Patients will not actually be treated at the facility, which in effect will be one large radioisotope production line. Instead, the radioisotopes, once created, will be sent to handling stations elsewhere in the facility where they will be bounded into various chemicals that can be used in a clinical setting. Quality-control checks will also be carried out at the facility including monitoring the radioactivity and the chemical and microbiological quality of the radioisotopes. Once ready for use, samples will be sent by helicopter around the country – speed being of the essence with fluorine-18, for example, which has a half-life of barely 100 minutes.
Ken Peach, co-director of the Particle Therapy Cancer Research Institute at the University of Oxford in the UK, says he was "very impressed" after a visit to the facility last year when it was nearing completion. "This is a major investment, with advanced radioisotope-handling equipment that will have a big impact on medical diagnosis and treatment," he says. "It will contribute significantly to the development of research capability in Turkey."
As well as producing large quantities of radioisotopes, Tanrikut also has great hopes for PAF's research beamline. He anticipates that the beamline will be able to produce other radioisotopes such as palladium-103 and cobalt-57 that are trickier to make, as they require higher proton currents. Palladium-103 can be used to treat prostate cancer, while cobalt-57 is used for a "Schilling test" to investigate patients who have a deficiency of vitamin B12.
But perhaps the main legacy of the facility will be its impact on the next generation of researchers in Turkey, who can now be trained in how to make and handle radioisotopes. "Education and training cannot be done without infrastructure", says Tanrikut. "We will now be able to design our own beamlines and help students learn how to play with these protons."