- 01 Overview
- 02 How it Works
Housed at the opposite end of the Meson Hall from the 520 MeV cyclotron, the TR-13 is TRIUMF’s cyclotron specialized for the production of medical isotopes for both clinical use and research.
During the past twenty years, the TR-13, TRIUMF’s smallest cyclotron, has played a central role in the development of the University of British Columbia‘s world-class positron emission tomography (PET) clinical research program, and in the development of the BC Cancer’s use of medical isotopes in clinical programs.
The TR-13 was developed in the early 1990s in a technology transfer agreement with Richmond, B.C.-based heavy industry leader EBCO, a key builder of TRIUMF’s 520 MeV cyclotron. EBCO created the subsidiary Advanced Cyclotron Systems Inc. (ASCI) to commercialize a TRIUMF-designed, or TR-series, of compact medical cyclotrons. One of the prototypes was the TR-13.
The TR-13’s primary role is the production of the critical imaging isotopes carbon-11 (11C) and fluorine-18 (18F) for the UBC Hospital’s PET clinical and research program.
TRIUMF radiochemistry researchers also use the TR-13 for research into next-generation medical isotopes, and the targets to produce them. This includes the development of novel metal-salt solution liquid targets for the production of metal radioisotopes, including gallium-68 (68Ga), scandium-44 (44Sc), yttrium-86 (86Y), and zirconium-89 (89Zr) for use in diagnostic imaging, therapy and theranostics. Theranostics is a new field of personalized medicine which combines specific targeted therapy based on specific targeted diagnostic tests.
02 How it Works
The TR-13, at 1.75-meter-in-diameter, is a tiny version of the 18-meter-in-diameter 520 MeV cyclotron. Like its much larger neighbour, the TR-13 accelerates negative hydrogen ions, stripping the accelerated ions’ electrons to create accelerated protons to bombard targets. Unlike the 520 MeV cyclotron, the TR-13 is a fixed energy machine, always producing proton beams at 13 MeV.
The TR-13 operates as part of a precisely choreographed just-in-time radioisotope delivery system for the supply of medical isotopes to UBC Hospital.
The TR-13’s main product is carbon-11 (11C), a radioisotope with a half-life of just twenty minutes. This brief half-life means that 11C’s production must be tightly scheduled with that of the patient who’ll receive a PET scan using it.
Two or three times each weekday, while a patient is being prepped for scanning at UBC Hospital, the TR-13 operates for about 45 minutes to produce the 11C for the patient’s scan. The 11C is produced by bombarding a target that’s a mixture of oxygen and nitrogen gas. Some of the nitrogen is converted into the unstable isotope 11C. The gas is remotely channeled to a hot cell in one of TRIUMF’s radiochemistry labs, where it is converted into a liquid form of 11C.
For shipping, the11C is stored in a small vial which in turn is packed in a metal capsule. This is shipped to UBC Hospital via a dedicated, underground “rabbit line”- an air-pressurized, one-and-a-quarter inch diameter PVC pipe contained in two-square feet of radiation-shielding concrete. In the rabbit line (named for its rapid speed), the capsule makes the 2.5 km journey from TRIUMF to the UBC Hospital in just 130 seconds.
The TR-13 is also used to produce the radioisotope fluorine-18 (18F), used in PET scans at the UBC Hospital and the BC Cancer.
18F is produced by bombarding a liquid target of modified water in which 99.9% of the oxygen atoms, usually oxygen-16 (16O), are replaced with oxygen-18 (18O). When bombarded with protons, an oxygen nucleus absorbs a proton and loses a neutron, transforming into 18F, with nine protons and nine neutrons.
To create a radiopharmaceutical, the 18F is combined with glucose, to create the injectable radiopharmaceutical fludeoxyglucose (FDG), the most commonly used radiotracer in PET. This is done in either a TRIUMF radiochemistry lab or at the BC Cancer Agency.
Both 11C and 18F decay by emitting a positron, the anti-matter sibling of an electron. When a positron and electron in a patient interact, they annihilate to produce two gamma rays. The PET scanner, or camera, detects these coincident gamma rays, producing an image that pinpoints their location with the highest-precision of any medical imaging technology.
One key advantage of PET is that it provides information not just about organ structure, but also function. This enables early cancer detection and also otherwise impossible brain research. For example, tumor cells – because they are dividing rapidly – use more glucose than ordinary cells, and thus also uptake FDG more rapidly than surrounding tissues. This enables clinicians to identify tumor cells even when the tumor is too small to otherwise visualize. Similarly, PET’s ability to track metabolic changes means it’s also ideal for neurological imaging of Parkinson’s, Alzheimer’s and other dementia-related disorders.