Highlights
- The INCAPS 4 study reveals significant global disparities in radiation dose for noninvasive coronary artery disease (CAD) imaging, with median doses for CCTA being particularly high in low-income regions.
- Nuclear cardiology (SPECT and PET) generally achieves higher adherence to guideline-recommended dose limits (≤9 mSv) compared to CCTA.
- An inverse relationship exists between a country’s income level and the patient radiation dose, with the highest exposures observed in Africa and Latin America.
- The findings emphasize a critical global need for modernized equipment, standardized protocols, and specialized training to ensure diagnostic quality without excessive radiation risk.
Background
Coronary artery disease (CAD) remains a leading cause of global morbidity and mortality. To manage this burden, diagnostic imaging has expanded exponentially over the last two decades. Common modalities—Single-Photon Emission Computed Tomography (SPECT), Positron Emission Tomography (PET), Cardiac Computed Tomography for Calcium Scoring (CACS), and Coronary Computed Tomography Angiography (CCTA)—provide essential diagnostic and prognostic data. However, these techniques involve ionizing radiation, which carries a theoretical risk of long-term oncogenic effects. While international guidelines, such as those from the International Atomic Energy Agency (IAEA) and various cardiovascular societies, recommend keeping radiation doses “As Low As Reasonably Achievable” (ALARA), the degree to which these standards are met globally has historically been poorly documented. The INCAPS 4 (IAEA Network of Cardiology Protocols and Standards) study was designed to address this knowledge gap by providing a comprehensive cross-sectional analysis of real-world practice across 101 countries.
Key Content
Study Design and Global Participation
The INCAPS 4 study represented a massive undertaking in clinical data collection. In 2023, researchers conducted a worldwide cross-sectional study involving 19,302 adults undergoing noninvasive CAD diagnostic testing. Data were sourced from 742 centers across 101 countries during a single-week snapshot between October and December. The study captured a diverse demographic (44% female, median age 63 years) and evaluated four primary exposures: SPECT, PET, CACS, and CCTA. The primary outcome measure was the radiation effective dose (mSv) and the percentage of centers achieving a median effective dose of ≤9 mSv, a threshold often used to define high-quality, low-dose practice in nuclear and CT imaging.
Radiation Dose Variation by Modality
The analysis revealed marked differences in radiation exposure depending on the imaging modality utilized. CACS demonstrated the lowest median dose at 1.2 mSv (IQR, 0.7-2.2 mSv), followed by PET at 2.0 mSv (IQR, 1.6-2.4 mSv). These relatively low doses reflect the standardized nature of CACS and the efficient photon detection of modern PET scanners. In contrast, traditional nuclear cardiology (SPECT) showed a median dose of 6.5 mSv (IQR, 3.9-8.6 mSv).
The most concerning findings were associated with CCTA, which had a median dose of 7.4 mSv but exhibited a massive interquartile range (IQR, 3.5-15.5 mSv). This wide variation suggests that while CCTA can be performed at very low doses using modern techniques (like high-pitch spiral scanning or iterative reconstruction), it is often performed with outdated protocols or equipment that result in excessively high exposures.
The Socioeconomic and Geographic Gap
Perhaps the most striking finding of the INCAPS 4 study was the disparity based on geographic region and country income level. Western Europe consistently demonstrated the lowest doses (median 4.8 mSv for nuclear cardiology; 4.6 mSv for CCTA). Conversely, radiation doses were significantly higher in developing regions. For nuclear cardiology, Latin America recorded the highest median doses (7.8 mSv), while for CCTA, Africa recorded an alarmingly high median dose of 25.2 mSv (IQR, 14.7-35.3 mSv).
Regression modeling confirmed a significant inverse relationship between country income and dose. Specifically, patients in low- and middle-income countries (LMICs) received a 20% higher dose for nuclear cardiology and up to a 96% higher dose for CCTA compared to high-income countries. This “diagnostic divide” highlights a systemic inequality where patients in resource-limited settings are not only at risk of late diagnosis but are also exposed to higher procedural risks when they do receive care.
Adherence to Safety Guidelines
The guideline-recommended threshold of ≤9 mSv was met more frequently in nuclear cardiology centers than in CCTA centers (81% vs 56%, P < .001). This suggests that international efforts to standardize nuclear cardiology protocols (driven by previous INCAPS initiatives) may be yielding results, whereas CCTA protocol optimization remains inconsistent. The lack of adherence in the CCTA domain is particularly problematic given the modality's increasing use as a first-line diagnostic tool for stable chest pain.
Expert Commentary
The INCAPS 4 findings serve as a sobering reminder that technological advancement does not automatically translate to global clinical safety. The extreme variation in CCTA doses—ranging from near-negligible levels in some European centers to over 35 mSv in parts of Africa—reflects a failure of technology transfer and protocol standardization. From a mechanistic perspective, high CCTA doses are often the result of not using ECG-based tube current modulation, failing to adjust kVp based on patient body mass index (BMI), or the lack of iterative reconstruction software on older-generation scanners.
Furthermore, the socioeconomic disparity suggests that patients in LMICs are facing a “double hit”: they have a higher burden of cardiovascular risk factors and receive diagnostic services from centers with outdated equipment and less specialized training. Experts argue that reducing this gap requires more than just donating hardware; it necessitates a robust framework of “educational infrastructure,” including remote training for technologists and the implementation of automated dose-tracking software that can alert clinicians to protocol deviations in real-time.
Controversies remain regarding the absolute risk of these doses. While the risk of radiation-induced cancer at these levels is statistically small, the sheer volume of tests performed globally means that even minor reductions in median dose could prevent thousands of future cancer cases at a population level. The study underscores that the technology to provide safe imaging exists; the challenge is now one of equitable distribution and clinical education.
Conclusion
The INCAPS 4 study provides the most comprehensive map to date of the global landscape of cardiac imaging radiation. It reveals that while low-dose imaging is achievable, it is currently a privilege largely reserved for patients in high-income countries. The findings identify CCTA as a high-priority area for intervention, given its wide dose variation and lower rates of guideline adherence. To improve the quality of CAD diagnosis globally, international health organizations and professional societies must prioritize the dissemination of standardized low-dose protocols and advocate for the replacement of obsolete imaging equipment in underserved regions. Future research should focus on longitudinal assessments to determine if targeted educational interventions can successfully narrow the dose gap observed in this landmark study.
References
- Einstein AJ, Williams MC, Weir-McCall JR, et al. Worldwide Radiation Dose in Coronary Artery Disease Diagnostic Imaging. JAMA. 2026;285(8):e260703. doi:10.1001/jama.2026.0703. PMID: 41739468.
- Einstein AJ, et al. Current and Future Perspectives on Radiation Safety in Cardiac Imaging. JACC Cardiovasc Imaging. 2023;16(3):355-371.
- International Atomic Energy Agency (IAEA). Radiation Protection of Patients (RPOP) in Diagnostic Nuclear Medicine. 2024.
