Linear particle accelerators work, as the name suggests, by accelerating particle in a straight line. Cyclic particle accelerators, such as cyclotron, make the ...
Cyclotron Radionuclides for Health Care A. Mushtaq Isotope Production Division, Pakistan Institute of Nuclear Science and Technology, P.O. Nilore, Islamabad, Pakistan Abstract Cyclotron produced radionuclides are gaining increasing significance in diagnostic investigations via positron emission tomography (PET) and single photon emission computed tomography (SPECT) as well as in some therapeutic applications. Pakistan is importing cyclotron-produced isotopes from abroad. Establishing a first cyclotron facility for production of isotopes for health care is overdue. To meet the current and near future radionuclide demands in Pakistan availability of a cyclotron with 30 MeV proton acceleration capabilities may allow the routine and cost effective production of a range of radionuclides. An advantage of a cyclotron facility located at PINSTECH is also described. 1. INTRODUCTION Transforming a stable nuclide into an unstable state by irradiation with neutrons, protons, deutrons, alphas, gammas or other nuclear particles creates the majority of radionuclides. The source of these particles may be a radionuclide, a nuclear reactor, or a particle accelerator/cyclotron. The tremendous variety of man-made radionuclides has given rise to many applications in physics, biology and, of course, medicine. The nuclear reactor produced radionuclides are generally neutron excess nuclides. They mostly decay by - emission and suitable for therapy purposes. The cyclotron produced radionuclides, on the other hand, are often neutron deficient and decay mainly by electron capture or +emission. They are especially suitable for diagnostic studies. Today more than 250 cyclotrons exist worldwide (cf. Directory of Cyclotrons, IAEA-DCRP/CD, 2002) and radionuclide production science and technology at cyclotrons has become a very important feature of modern nuclear medicine. Cyclotrons belong to a class of machines called particle accelerator. These exist in two varieties, linear and cyclic. Both create charged particles and accelerate them to high velocities to bombard target materials. Linear particle accelerators work, as the name suggests, by accelerating particle in a straight line. Cyclic particle accelerators, such as cyclotron, make the particles travel many times around a central point, thus achieving higher acceleration than is possible with linear accelerators. Charged particles (ions) created from a suitable source material are injected into the center of the cyclotron at the Ion Injection point. Once inside the cyclotron, the ions are forced to travel in a circular path around a central point and repeatedly accelerated by electrical fields. During acceleration, the charged ions are forced by a strong magnetic field to travel in an outward spiral path, in an evacuated gap between magnetic poles. As the speed of the particle beam increases, the spiral path of the particles increases in the radius until, when the desired speed is reached, the beam is extracted from the machine at the Ion Extraction Point. Magnets guide the extracted beam to one of several possible targets. When the beam of particles bombards the target, a nuclear reaction occurs, altering the physical
composition of the target material and producing reactivity. When, for example, nitrogen gas is used as a target some of it is converted into radioactive carbon. Cyclotrons do not use uranium or produce difficult to dispose of fission product waste. When operating, the cyclotron is surrounded by an intense field of radiation, but this disappears quickly when the machine is switched off. To protect the operators and the environment Medical Cyclotron is housed in a massive concrete vault with 2.3 meter thick walls. 2. TYPES OF CYCLOTRONS The smallest machine is a cyclotron to accelerate only deuterons up to 4 MeV. It is used in a hospital environment to produce 15O. Small linear accelerator for p and d particles with energies below 3.7 MeV has also been developed but its use has been limited. The next stage is a single particle negative ion machine for proton acceleration up to energy of 11-12 MeV. It can be used to produce four major +emitters, viz. 11C, 13 N, 15O and 18F. The next higher group of machines is generally a two particle machine with Ep 20 MeV and Ed 10 MeV. The even higher energy machines have capabilities of producing many more radionuclides; in particular when besides p and d, also 3He and alpha particle beams are available. On the other hand, when energies above 100 MeV are under consideration, only the proton beam is of interest. Table 1 summarizes the types of accelerators developed to meet the specific demands of radionuclide production. Table 1. Types of accelerators used for radionuclide production Classification Characteristics Level I Level II Level III Level IV
Level V Level VI
Single particle (d) Single particle (p) Single or two particle (p, d) Single or multiple particle (p, d, 3He, 4He) Single or multiple particle (p, d, 3He, 4He) Single particle (p)
Energy Major radionuclides produced [MeV] 15 2000 sqm is needed that may be acquired/built in Phase II of PINSTECH.
5. PERSPECTIVES Radionuclide production technology at cyclotrons has been well developed, especially for short-lived positron emitters, commonly used SPECT radionuclides and a few therapeutic radionuclides. In this regard, all components of the technology, i.e. cyclotron, high current irradiation targets and automated or remotely controlled chemical processing units can now be purchased from international market. The number of radionuclides potentially interesting for health care is relatively large. For production of commonly used positron emitters and many new radionuclides the necessity of an intermediate energy (30 MeV) cyclotron is inevitable.
6. BIBLIOGRAPHY 1. S. M. Qaim, Cyclotron Production of Medical radionuclides. In Handbook of Nuclear Chemistry. Volume 4. Kluwer Academic Publishers London (2003). 2. A. P. Wolf and W. B. Jones, Cyclotrons for Biomedical Radioisotope Production. Radiochimica acta 34. 1-7 (1983). 3. A. Arzumanov et al., radioisotope Production at The Kazakhstan cyclotron. J. Radioanal. Nucl. Chem. Vol.257, No.1, 215-218 (2003). 4. S. M. Qaim, Nuclear Data Relevant to Cyclotron Produced Short Lived Medical Radioisotopes. Radiochimica acta 30. 147-162 (1982). 5. C. Birattari et al., Review of cyclotron production and quality control of “High Specific activity” Radionuclides for Biomedical, Biological, Industrial and
6. 7.
8. 9.
Environmental Applications at INFA-LASA. Cyclotrons and their Applications 2001,16th International Conferece, Edited by F. Marti (2001). D.Visvikis et al., PET Technology: current trends and future developments. The Brit. J. Radiol. 77, 906-910 (2004). F. Tarkanyi et al., Status of the database for production of medical radioisotopes of 103Pd, 123,124I, 201Tl by using Rh, Te and Tl targets. J. Nucl. Sci. Tech. Supplement 2, 1318-1321 (2002). R. J. Nickles, the production of a broader palette of PET tracers. J. Label. Compd. Radiopharm. 46, 1-27 (2003). CYCLONE 30, Main Features and Benefits, IBA, Belgium (http://www.iba.be.)
