PET without cyclotron

Autor: Ahmad Mushtaq
Rok vydání: 2009
Předmět:
Zdroj: Annals of Nuclear Medicine. 23:321-323
ISSN: 1864-6433
0914-7187
DOI: 10.1007/s12149-009-0231-y
Popis: Positron emission tomography (PET) has been well established noninvasive imaging technique for diagnosis, staging/ restaging and monitoring of therapy response in oncology. Molecular imaging using positron emitting radionuclides kinetics provides quantitative in vivo assessment of biological and physiological processes involved in the earlier stages of disease progression. Because of the short life time (hours) of many of the PET radioisotopes, a cyclotron and radiocompound synthesis facility is required. One of the most widely recognized advantages of PET is the use of the positron emitting biologic radiotracers, e.g., C (T = 20 min), N (T = 10 min), O (T = 2 min), and most important F (T = 110 min) that mimic natural substrate. However, due to relatively short half-lives, they are unable to be transported to sites at great distances from the production facility. The production of radioisotopes using a cyclotron/accelerator demands a knowledge of excitation functions (reaction cross section), development of high current targets, radiochemical separations at no-carrier added level, recovery of enriched target materials in most of the cases, remote control and highly trained manpower for running, repair and maintenance. Cyclotrons are generally used for production of short-lived radioisotopes; however, long-lived isotopes are also produced which can be used at distant places. Fast and high resolution imaging method, such as single photon emission computed tomography (SPECT) is now commonly available for diagnostic studies in developing countries, whereas PET facility is rarely employed for patient management due to non-availability of cyclotron in these countries. Positron emission tomography has two major advantages over SPECT, namely, better spatial resolution and greater sensitivity. The number of positron emitting radionuclides is large. However, most of the PET studies are performed near to cyclotron production facility with short-lived positron emitters (C, O, N, and F). A tabulation of 157 positron emitting radionuclides which have the physical characteristics deemed appropriate for radiopharmaceutical use is provided by Lambrecht [1]. Some cyclotron produced generator radionuclides have also been listed by Qaim [2]. Table 1 presents the generator produced positron emitters, which can be utilized far from production site for PET studies. Production route of parent in a cyclotron and separation of daughter is discussed elsewhere [3]. Antibody-PET imaging might be of value for the selection of radioimmunotherapy (RIT) candidates to confirm tumor targeting and to estimate radiation doses to tumor and normal tissues. One of the requirements to be set for such a scouting procedure is that the biodistributions of the diagnostic and therapeutic radioimmunoconjugates should be similar. The potential of the positron emitters zirconium-89 (Zr) and iodine-124 (I) for this approach, as these radionuclides have a relatively long half-life that matches with the kinetics of MAbs in vivo (T1/2 3.27 and 4.18 days, respectively), were evaluated [4]. Other long-lived positron emitters, which may be used at distant places are, V (T = 16 d), Mn (T = 5.59 days), As (T = 17.78 days), and Au (T = 39.5 h). Through the supply of a long-lived parent radionuclide, from which a short-lived daughter radionuclide can be milked off periodically at hospitals, it has become possible A. Mushtaq (&) Isotope Production Division, Pakistan Institute of Nuclear Science and Technology, P.O. Nilore, Islamabad, Pakistan e-mail: mushtaqa@pinstech.org.pk
Databáze: OpenAIRE
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