Comparison of Radiation Doses and Best-Practice Use for Myocardial Perfusion Imaging in US and Non-US Laboratories: Findings From the IAEA (International Atomic Energy Agency) Nuclear Cardiology Protocols Study

Myocardial perfusion imaging (MPI) is integral to the diagnosis and management of known or suspected coronary artery disease^1,2 and is therefore performed on millions of US patients each year. However, the associated exposure to ionizing radiation has raised concerns about potential radiation-related health effects. The recent cross-sectional study of MPI practice conducted by the International Atomic Energy Agency (IAEA) demonstrated significant variations in radiation doses, and in the use of best practices that can help to reduce dose, among laboratories worldwide.³ Although survey data have described self-reported US use of different MPI protocols and some dose-reduction methods,⁴ no previous study, to our knowledge, has characterized actual US MPI radiation doses as well as use of best practices. We compared actual MPI practice and radiation doses in US and non-US laboratories and identified opportunities to improve radiation doses in the United States.

Data were collected as part of the IAEA Nuclear Cardiology Protocols Study (INCAPS).³ The INCAPS data included patient demographics, estimated effective radiation dose for each patient, and laboratory best practices that affect radiation dose, from 308 nuclear cardiology laboratories in 65 countries, including 50 US laboratories in 22 states encompassing all regions of the country. Each laboratory provided data on a consecutive series of patients undergoing MPI during a 1-week period from March 18 to April 22, 2013, yielding 7911 patients (including 1902 US patients). The study was approved by the institutional review board of Columbia University. Because no individually identifiable health information was collected, the board declared it exempt from the requirements of US federal regulations for the protection of human subjects.

An IAEA expert panel defined a priori 8 laboratory best practices affecting radiation doses.³ These included (1) avoiding thallium stress testing in patients 70 years or younger, because thallium has a long half-life (3 days) and exposes patients to more radiation than technetium Tc 99m–based radiopharmaceuticals used for MPI; (2) avoiding use of a dual-isotope (thallium and technetium Tc 99m) protocol in nonelderly patients; (3) avoiding too much technetium Tc 99m; (4) avoiding too much thallium; (5) performing stress-only imaging in some patient(s), rather than requiring every patient to have rest imaging and its attendant radiation dose even for studies with completely normal myocardial perfusion at stress; (6) using camera-based dose-reduction strategies, such as advanced hardware or software, or imaging in the supine and prone positions, which can clear false-positive perfusion defects owing to soft-tissue attenuation and thereby facilitate stress-only imaging; (7) applying weight-based dosing for technetium Tc 99m so that lighter patients receive less isotope; and (8) avoiding dosing that leads to residual counts from the first injection interfering with interpretation of the second scan, known as a shine-through artifact. Each laboratory was assigned a quality index score, defined as the number of best practices followed. Methodologic details regarding data collection, dose estimation, and best-practice definitions are presented elsewhere.³ The US laboratories included responded to an invitation distributed to contacts from lists provided by the IAEA, American Society of Nuclear Cardiology, and Intersocietal Accreditation Commission.

Median and mean patient and laboratory radiation doses and laboratory quality index scores were compared between US and non-US laboratories using Kruskal-Wallis tests and analysis of variance. The proportion of laboratories adhering to each best practice, 6 or more best practices, and a median radiation dose of no greater than 9 mSv (a threshold specified in professional society recommendations⁵) were compared using χ² tests. All analyses were performed with STATA/SE (version 13.1; StataCorp).

Compared with non-US patients, US patients undergoing MPI were older and included a greater proportion of women. The US radiation dose was higher (median, 11.6 vs 9.7 mSv; mean, 10.9 vs 9.7 mSv; P < .001 for both), and fewer US patients had a dose of 9 mSv or less (24.4% vs 43.3%; P < .001) (Table 1). The US patients were 7.6 times (95% CI, 6.1-9.4) more likely to undergo single-photon emission computed tomographic MPI using a 1-day protocol and 6.7 times (95% CI, 5.5-8.3) more likely to undergo positron emission tomography (P < .001 for both).

The median radiation dose ranged from 3.5 to 24.5 mSv among US laboratories. Only 7 of 50 US laboratories (14.0%) achieved a median dose of 9 mSv or less compared with 84 of 258 non-US laboratories (32.6%). Best-practice adherence was lower among US laboratories (Table 2), as reflected in a lower mean quality index (4.6 vs 5.6; P < .001) and the smaller proportion of laboratories with a quality index of 6 or better (15 of 50 [30.0%] vs 127 of 258 [49.2%]; P = .01). The US laboratories outperformed non-US laboratories in avoiding thallium stress imaging in patients younger than 70 years but underperformed in 4 of the other 7 practices.

We observed a 20% higher radiation dose to the typical patient undergoing MPI in a US laboratory compared with a patient in a non-US laboratory. This difference results in part from lower adherence to radiation-dose best practices among US laboratories. Practices such as weight-based dosing (16.0% vs 31.0%), judicious technetium Tc 99m use (56.0% vs 91.1%), and implementation of stress-only protocols in some patients (18.0% vs 32.6%) were adopted significantly less often in US facilities (Table 2). The higher radiation doses and less frequent use of these important best practices that we observed are coupled with markedly more frequent US use of MPI (2500 MPI studies per 100 000 population in a previous IAEA study⁶) than in other developed countries (eg, 1200, 364, 315, and 120 MPI studies per 100 000 population in Canada, Australia, Japan, and the United Kingdom, respectively⁶). Improvements in adherence to these best practices offer potential opportunities, that do not require any specific technology, to reduce the radiation burden of MPI in the United States through greater attention to patient-centered imaging.

Corresponding Author: Andrew J. Einstein, MD, PhD, Division of Cardiology, Department of Medicine, Columbia University Medical Center, New York–Presbyterian Hospital, 622 W 168th St, PH 10-203, New York, NY 10032 (andrew.einstein@columbia.edu).

Published Online: December 28, 2015. doi:10.1001/jamainternmed.2015.7102.

Author Contributions: Drs Mercuri and Einstein had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Mercuri, Pascual, Rehani, Paez, Einstein.

Acquisition, analysis, or interpretation of data: Mercuri, Pascual, Mahmarian, Shaw, Rehani, Einstein.

Drafting of the manuscript: Mercuri, Pascual, Shaw, Einstein.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Mercuri, Einstein.

Obtained funding: Einstein.

Administrative, technical, or material support: Mercuri, Pascual, Mahmarian, Paez, Einstein.

Study supervision: Pascual, Shaw, Paez, Einstein.

Conflict of Interest Disclosures: Dr Einstein reported receiving institutional research grants to Columbia University for other research from GE Healthcare, Philips Healthcare, Spectrum Dynamics, and Toshiba America Medical Systems. No other disclosures were reported.

Funding/Support: This study was supported by the International Atomic Energy Agency (IAEA), the Margaret Q. Landenberger Research Foundation in memory of A. Donny Strosberg, PhD, and the Irving Scholars Program.

Role of the Funder/Sponsor: Drs Pascual, Rehani, and Paez contributed as noted above. The other sponsors had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Group Information: The INCAPS Investigators Group includes executive committee members A. J. Einstein (chair), T. N. B. Pascual (IAEA project lead), D. Paez (IAEA section head), M. Dondi (IAEA section head); N. Better, S.E. Bouyoucef, G. Karthikeyan, R. Kashyap, V. Lele, F. Mut, V. P. C. Magboo, J. J. Mahmarian, M. Mercuri, M. M. Rehani, and J. V. Vitola, and regional coordinators E. Alexanderson (Latin America), A. Allam (Africa and Middle East), M. H. Al-Mallah (Middle East), N. Better (Oceania), S. E. Bouyoucef (Africa), H. Bom (East Asia), A. Flotats (Europe), S. Jerome (United States), P. A. Kaufmann (Europe), V. Lele (South Asia), O. Luxenburg (Israel), J. Mahmarian (North America), L. J. Shaw (North America), S. R. Underwood (United Kingdom), and J. Vitola (Latin America). Members by region include W. Amouri, H. Essabbah, S. S. Gassama, K. B. Makhdomi, G. I. E. El Mustapha, N. El Ouchdi, N. Qaïs, N. Soni, and W. Vangu (Africa); R. M. Abazid, B. Adams, V. Agarwal, M. A. Alfeeli, N. Alnafisi, L. Bernabe, G. G. Bural, T. Chaiwatanarat, J. M. Chandraguptha, G. J. Cheon, I. Cho, A. S. Dogan, M. Eftekhari, A. Frenkel, I. Garty, S. George, P. Geramifar, H. Golan, S. Habib, R. Hussain, H. Im, H-J. Jeon, T. Kalawat, W. J. Kang, F. Keng, A. Klaipetch, P. G. Kumar, J. Lee, W. W. Lee, I. Lim, C. M. M. Macaisa, G. Malhotra, B. R. Mittal, M. H. Mohammad, P. Mohan, I. D. Mulyanto, D. Nariman, U. N. Nayak, K. Niaz, G. Nikolov, J. M. Obaldo, E. Ozturk, J. M. Park, S. Park, C. D. Patel, H. K. Phuong, A. P. Quinon, T. R. Rajini, Y. Saengsuda, J. Santiago, H. B. Sayman, A. S. Shinto, V. Sivasubramaniyan, M. H. Son, P. Sudhakar, G. M. S. Syed, N. Tamaki, K. Thamnirat, T. Thientunyakit, S. Thongmak, D. N. Velasco, A. Verma, U. Vutrapongwatana, Y. Wang, K. S. Won, Z. Yao, T. Yingsa-nga, R. Yudistiro, K. T. Yue, and N. Zafrir (Asia); S. C. Adrian, D. Agostini, S. Aguadé, G. Armitage, M. Backlund, M. Backman, M. Baker, M. T. Balducci, C. Bavelaar, M. Berovic, F. Bertagna, R. Beuchel, A. Biggi, G. Bisi, R. Bonini, A. Bradley, L. Brudin, I. Bruno, E. Busnardo, R. Casoni, A. Choudhri, C. Cittanti, R. Clauss, D. C. Costa, M. Costa, K. Dixon, M. Dziuk, N. Egelic, I. Eriksson, G. Fagioli, D. B. de Faria, L. Florimonte, A. Francini, M. French, E. Gallagher, I. Garai, O. Geatti, D. Genovesi, L. Gianolli, A. Gimelli, E. del Giudice, S. Halliwell, M. J. Hansson, C. Harrison, F. Homans, F. Horton, D. Jędrzejuk, J. Jogi, A. Johansen, H. Johansson, M. Kalnina, M. Kaminek, A. Kiss, M. Kobylecka, M. Kostkiewicz, J. Kropp, R. Kullenberg, T. Lahoutte, O. Lang, Y. H. Larsson, M. Lázár, L. Leccisotti, N. Leners, O. Lindner, R. W. Lipp, A. Maenhout, L. Maffioli, C. Marcassa, B. Martins, P. Marzullo, G. Medolago, J. B. Meeks, C. G. Mendiguchía, S. Mirzaei, M. Mori, B. Nardi, S. Nazarenko, K. Nikoletic, R. Oleksa, T. Parviainen, J. Patrina, R. Peace, C. Pirich, H. Piwowarska-Bilska, S. Popa, V. Prakash, V. Pubul, L. Puklavec, S. Rac, M. Ratniece, S. A. Rogan, A. Romeo, M. Rossi, D. Ruiz, N. Sabharwal, B. G. Salobir, A. I. Santos, S. Saranovic, A. Sarkozi, R. P. Schneider, R. Sciagra, S. Scotti, Z. Servini, L. R. Setti, S.-Å. Starck, D. Vajauskas, J. Veselý, A. Vieni, A. Vignati, I. M. Vito, K. Weiss, D. Wild, and M. Zdraveska-Kochovska (Europe); R. N. Agüro, N. Alvarado, C. M. Barral, M. Beretta, I. Berrocal, J. F. Batista Cuellar, T.-M. Cabral Chang, L. O. Cabrera Rodríguez, J. Canessa, G. Castro Mora, A. C. Claudia, G. F. Clavelo, A. F. Cruz Jr, F. F. Faccio, K. M. Fernández, J. R. Gomez Garibo, U. Gonzalez, P. González, M. A. Guzzo, J. Jofre, M. Kapitán, G. Kempfer, J. L. Lopez, T. Massardo, I. Medeiros Colaco, C. T. Mesquita, M. Montecinos, S. Neubauer, L. M. Pabon, A. Puente, L. M. Rochela Vazquez, J. A. Serna Macias, A. G. Silva Pino, F. Z. Tártari Huber, A. P. Tovar, L. Vargas, and C. Wiefels (Latin America); A. Aljizeeri, R. J. Alvarez, D. Barger, W. Beardwood, J. Behrens, L. Brann, D. Brown, H. Carr, K. Churchwell, G. A. Comingore, J. Corbett, M. Costello, F. Cruz, T. Depinet, S. Dorbala, M. Earles, F. P. Esteves, E. Etherton, R. J. Fanning Jr, J. Fornace, L. Franks, H. Gewirtz, K. Gulanchyn, C.-L. Hannah, J. Hays, J. Hendrickson, J. Hester, K. Holmes, S. Jerome, A. Johnson, C. Jopek, H. Lewin, J. Lyons, C. Manley, J. Meden, S. Moore, W. H. Moore, V. Murthy, R. Nace, D. Neely, L. Nelson, O. Niedermaier, D. Rice, R. Rigs, K. Schiffer, E. Schockling, T. Schultz, T. Schumacker, B. Sheesley, A. Sheikh, B. Siegel, A. M. Slim, J. Smith, M. Szulc, N. Tanskersley, P. Tilkemeier, G. D. Valdez, R. Vrooman, D. Wawrowicz, and D. E. Winchester (North America); and A. Alcheikh, B. Allen, E. Atkins, J. Bevan, C. Bonomini, J. Christiansen, L. Clack, E. Craig, H. Dixson, I. Duncan, S. Fredericks, S. Gales, R. Hampson, T. Hanley, K. Hartcher, J. Hassall, B. Kelley, S. Kelly, T. Kidd, T. de Kort, G. Larcos, W. Macdonald, C. McGrath, E. Murdoch, S. O’Malley, M. O’Rourke, M. Pack, R. Pearce, R. Praehofer, S. Ramsay, L. Scarlett, K. Smidt, F. Souvannavong, K. Taubman, G. Taylor, K. Tse, S. Unger, and J. Weale (Oceania).

Additional Contributions: João Vitola, MD, PhD, Quanta Diagnóstico & Terapia, Curitiba, Brazil, Ganesan Karthikeyan, MBBS, MD, DM, Department of Cardiology, All India Institute of Medical Sciences, New Delhi, and Ravi Kashyap, MD, and Maurizio Dondi, MD, Section of Nuclear Medicine and Diagnostic Imaging, Division of Human Health, IAEA, Vienna, Austria, reviewed the manuscript. They received no compensation for this role. We thank the INCAPS executive committee, regional coordinators, and investigators group. Investigators group members were compensated for their time and effort involved in data collection.