Physics of Nuclear Medicine
Nuclear medicine is the branch of medical imaging that uses small amounts of radioactive materials for diagnosis, staging of disease, therapy and monitoring the response of a disease process . The tracer principle is used in nuclear medicine because of its ability to utilize small amounts of radioactive substance in living organisms without significant pharmacological effect on the body. The practice of nuclear medicine involves administering small amounts of radio-labeled compounds called radiopharmaceuticals (radioactive substance+drug). The radiopharmaceutical administered to the patient orally, intravenously or by inhaling localizes in the target cell for either diagnostic or therapeutic purposes. Diagnostic radiopharmaceuticals yield information about where they are localized which can help imaging of the organ of interest or disease site in patient using special gamma cameras such single photon emission tomography (SPECT) or positron emission tomography (PET) imaging system. On the other hand, therapeutic radiopharmaceuticals target specific tumors, such as thyroid, lymphomas or bone metastases, delivering radiation to tumorous lesions for the purpose of curing, destroying, mitigating or controlling the disease  .
Accurate measurement of the activity of a radiopharmaceutical is done with the use of a well-type ionization chamber called radionuclide dose calibrator. The accuracy of measurements of this instrument is critical to achieve the desired result for diagnosis or treatment of the patient. Although some manufacturers of the dose calibrators claim high accuracy and reproducibility for the radioactivity measurements, yet few studies have reported variations in these parameters. Errors ranging from 64 to 144% of the expected activity using calibration factors supplied by manufacturers of radionuclide dose calibrators have been observed  .
A clinically higher than actual dosage of activity implies that, the patient will be given a higher than prescribed dosage activity being unnecessarily burdened with extra radiation. On the other hand, a lower dosage of administered activity will be inadequate, demanding repetition of the process which implies extra dose to the patient and occupationally exposed staff. A nuclear medicine facility should have suitably qualified Medical Physicist therefore to that ensure dose calibrators are regularly checked for any calibration errors to ensure that assay errors of prescribed dosage fall within recommended limits  .
Medical physicists together with other health care professionals are at the forefront of research in nuclear medicine focused on quality control on dose calibrator which include; daily constancy test, a quarterly linearity test, an annual accuracy check and periodic reassessment of its calibration, traceable to secondary standards   . Research is also ongoing on prostate-specific membrane antigen imaging, advances in radionuclide therapy, [F-18] fluorodeoxyglucose positron-emission tomography (PET) for dementia, quantitative PET assessment of myocardial perfusion, and iodine-124 (I-124) and many more others   .
Author: Elias Mwape (Medical Physicist)
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