ABC | Volume 114, Nº2, February 2020

Update Update of the Brazilian Guideline on Nuclear Cardiology – 2020 Arq Bras Cardiol. 2020; 114(2):325-429 Table 27 – Strategies for reducing radiation exposure 1 Divulgate and apply appropriate exam indication criteria 2 Give preference to tracers that result in lower exposure to radiation. It is currently recommended to use technetium-99m ( 99m Tc), which has a physical half-life of 6 hours, in comparison with thallium-201 ( 201 Tl), whose half-life of 73 hours results in unfavorable dosimetry 3 Avoid protocols that inject both radioisotopes, 201 Tl and 99m Tc, in the same study (dual-isotope protocol), also considered an unfavorable dosimetry in combination 4 Avoid injecting any dose of 99m Tc which is > 36 mCi or which results in an exposure dose of > 15 mSv for the complete exam 5 In the event that it is necessary to use 201 Tl, avoid doses over 3.5 mCi 6 Attempt to decrease the number of patients who perform both stress and resting phases. In some cases, it is possible to answer the clinical question with the stress injection, provided that images are perfectly normal during this phase 7 Utilize more sensitive equipment which is able to detect lower injected doses of radiopharmaceutical, such as new gamma cameras with solid cadmium-zinc- telluride (CZT) detectors, as well as software which improves imaging quality, even at lower administered doses 8 Apply the dose adjustment table based on patient’s size or body mass index (BMI) (Tables 28 and 29) 9 Avoid shine through. This phenomenon occurs in perfusion studies with 99m Tc (one-day protocol, resting and stress phases) when the dose of the second injection is less than 3 times the first dose, and the residual activity in this step may interfere with interpretation of images corresponding to the second injection. This situation may result in a non-diagnostic study, making new investigations necessary and thus increasing the patient’s total received dosage. nuclear imaging, this means obtaining the principal exam information, most commonly MPS, using the minimum amount of radiation necessary to maintain diagnostic quality. This involves not only the choice of radiotracer, but also the best technique and the best protocol that may be adjusted to minimize radiation exposure. Furthermore, 2 other important principles guide the application of ionizing radiation for medical imaging: “ justification” and “ optimization.” Justification signifies that a study should be well indicated and justified as adequate, in following with appropriate criteria, as described in these guidelines. The best way to minimize a patient’s exposure to radiation is not to recommend an exam that is not appropriately indicated. This situation, however, is often beyond the control of the doctor responsible for performing the exam and should be understood by the referring doctor, who should have a basic grasp on the scientific literature. It is important to emphasize that the risk of a patient dying due to cardiovascular disease (the leading cause of death in Brazil), without undergoing a well indicated exam, is much higher than any eventual risk owing to radiation exposure. The risks of a patient with suspected coronary disease who has an appropriate indication for an exam are not theoretical, but rather real, and they are higher than the risks resulting from radiation use. The other principle which demands our attention is optimization , which represents adjustments to protocols, including the use of the best technological resources available (modern software and hardware) to perform an exam. This task is the responsibility of a multiprofessional team, made up of physicians, supervising nurses, nursing technicians, radiology technologists, biomedical specialists, biologists trained to manipulate radioactive material, professionals with training in radiopharmacy, and a team of medical physicists. The risks of deleterious effects of radiation involving patients, provided that the multiprofessional team uses the best technique and consistently observes the principles of justification and optimization, are minimal, and they are, at times, the fruit of theoretical elaboration with no consolidated practical base. The INCAPS Nuclear Cardiology Protocols Cross- Sectional Study (INCAPS), an important, recently conducted international study coordinated by the International Atomic Energy Agency (IAEA), involving 65 countries, including Brazil, verified that radiation exposure may be different when comparing patients living in different countries, given the diversity of implemented protocols in nuclear cardiology practice worldwide. 317 Innumerous opportunities have been found to improve the application of nuclear cardiology comprehensively worldwide, basically using the principle of optimization . It has generally been identified that with simple, low-cost orientations, such as adjusting dose to BMI, it is possible to reduce the administered dose of radiation and patient exposure significantly. Latin America is an example, 318 where there are opportunities to improve protocols. It has been recommended that the majority of patients undergoing MPS have a maximum estimated radiation exposure of 9 mSv. This goal is feasible to reach when applying the recommendations listed in Table 27, which are strategies supported by the IAEA. 24 In the Brazilian centers that participated in the INCAPS study, average doses were observed to vary between 8.4 and 17.8 mSv, thus demonstrating the possibility of optimizing protocols in the country, which has been undertaken since the publication of INCAPS. 318 12.1. Reducing Radiation Using New Technologies, Image Quality, and Reliability of Findings Given that exposure to high doses is a source of concern, considering the possibility of biological effects of ionizing radiation, which are known as deterministic (those which occur above certain limits of absorbed dose in a determined tissue, including skin erythema, loss of hair, and, possibly, direct cardiac toxicity) and stochastic (those whose radiation causes damage that may lead to malignancy which is generally long-term), 319,320 there has been a demand for new technology to reduce doses of radiotracers, maintaining image quality and diagnostic accuracy. In this context, new cameras with CZT detectors have been launched in recent years. Differently from traditional Anger cameras, gamma radiation 396