Positron emission tomography users seeking less expensive equipmentfor producing PET radiopharmaceuticals have several options. Sometechnologies, however, are closer to commercial and clinical realitythan others. Several cyclotron manufactures are
Positron emission tomography users seeking less expensive equipmentfor producing PET radiopharmaceuticals have several options. Sometechnologies, however, are closer to commercial and clinical realitythan others.
Several cyclotron manufactures are coming out with compact,negative-ion cyclotrons:
Cyclotron manufacturers accelerate negative rather than positiveions in order to make their machines smaller, said Dr. MichaelPhelps, chief of nuclear medicine at the University of Californiaat Los Angeles. PET isotopes can be manufactured this way withoutproducing radiation within the equipment, thus enabling the useof self-shielded technology.
Shielding requirements are reduced further in a patented linearaccelerator, introduced commercially at the SNM meeting. Theremay be technical drawbacks, however, to the manner in which thisreduction has been achieved.
The Tandem Cascade Accelerator has been under development forthe past three years by Science Research Laboratories of Somerville,MA. This effort was funded at first by the National Institutesof Health and later as part of the Strategic Defense Initiativeresearch program, said Ruth E. Shefer, president of AcceleratorApplications.
ACCELERATOR APPLICATIONS, a separate company from SRL, was formedlast year to commercialize the TCA system. While AA says it isready to take orders for production of the accelerator, the firstclinical installation--at Mallinckrodt Institute--is not expecteduntil early next year, Shefer said.
The TCA requires only 4.5 tons of shielding, largely becauseof the lower bombarding energy used to produce the PET radioisotopes.A fully shielded cyclotron weighs about 40 tons, including 20tons of shielding, she said. The weight of the electromagnet inJSW's self-shielded cyclotron is 27 tons, according to the vendor'sspecifications.
Cyclotrons typically use 8 MeV of energy to accelerate deuteronsand 19 MeV for protons. TCA bombards its targets with 3.7 MeVof energy for protons or deuterons, Shefer said. The JSW unituses 10 MeV of energy for deuterons and 17 MeV for protons.
Lower energy requirements also mean that the TCA consumes atenth of the electrical power of a cyclotron and can be pluggedinto a standard 220-volt outlet, Shefer said.
Cyclotrons are compact accelerators that use spiral coils forparticle acceleration, Phelps said. A linear accelerator usesa straight path instead. More energetic particles could be usedin a linear accelerator, but the length of the system would beexcessive, he said.
The catch in using a lower bombarding energy is that--if allelse is the same--the radioisotope yield will be less. SRL's challengewas to boost the yields while keeping the energy level low. Itsolution was to use a higher beam current, Shefer said.
The effects of boosting the beam current are still not clear,Phelps said.
"As you raise the intensity of the beam, it produces heatingproblems and causes unusual chemical reactions," he said.
SRL has had to develop targetry technology to prevent the increasedheat from harming the targets. It still has to prove these innovations,he said.
"We need facts," Phelps said. "There is a differentprinciple (involved with the TCA) and real possibilities withit, but we need some data."
Four common PET agents have been produced in the TCA--18-fluorodeoxyglucose(FDG), carbon-11, nitrogen-13 and oxygen-15--in yields equivalentto present-generation cyclotrons, Shefer said.
The system will be sold first only with an oxygen-15 target,but AA hopes to complete development on the other three targetsand offer them for sale within the next year. The TCA is expectedto sell for $750,000 versus $1.5 million for a PET cyclotron,Shefer said.