What 5.2 Million CT Scans Taught Us About Patient Radiation Dose | Tom Griglock & Kalpana Kanal
September 18, 2026
In this episode of Rethink Imaging, host Chris St. John sits down with Dr. Kalpana Kanal and Dr. Thomas Griglock to discuss the newly updated Diagnostic Reference Levels (DRLs) and Achievable Doses (ADs) published ten years after the benchmark 2014 study. Analyzing a massive dataset of 5.2 million CT exams from 2025, they break down the 22% reduction in national DRLs, explain why low dose isn't always good dose, and emphasize why clinical optimization and diagnostic image quality must take precedence over endless dose reduction.
Over the past decade, healthcare providers have worked relentlessly to lower radiation exposure in computed tomography (CT). But is continually dropping radiation doses always in the best interest of the patient?
In this episode of Rethink Imaging, host Chris St. John is joined by Dr. Kalpana Kanal, lead author on the original 2014 Diagnostic Reference Level (DRL) study and its 10-year follow-up, along with co-author Dr. Thomas Griglock. Together, they break down the findings from a modern dataset of 5.2 million CT exams, a substantial leap from the 1.3 million exams analyzed in 2014.
The guests detail how national DRLs dropped by 22% and achievable doses fell by 9%, signaling tighter protocol management across facilities nationwide. However, both experts caution against the public and media obsession with endless dose reduction. They explain why anatomy-specific constraints, such as the dense bone of the skull and the vital need for gray-white matter differentiation, place a natural floor on dose reduction for head CTs compared to body scans. Finally, they provide a practical roadmap for facilities using both modern optimization platforms and legacy equipment to benchmark their protocols responsibly without sacrificing diagnostic image quality.
What You'll Learn:
- The 10-Year CT Dose Trajectory: How national DRLs dropped 22% and achievable doses dropped 9% across 5.2 million CT exams over a decade.
- Optimization Over Reduction: Why lowering dose endlessly can compromise diagnostic image quality and why "optimization" is the true goal of radiation safety.
- Anatomy-Specific Physics Limits: Why body CT doses have plummeted (down 31% for chest CTs) while head CT doses remained steady due to skull attenuation and gray-white matter resolution requirements.
- Real-Time Benchmarking & Data Curation: How modern analytics platforms allow real-time national benchmarking and acquisition-level parsing without discarding multi-phase trauma data.
- Benchmarking Without High-End Tech: Practical steps for small or community facilities with legacy equipment to evaluate internal protocols against national standards.
Youtube Chapters:
- 00:00 - Intro / Welcome to Rethink Imaging
- 00:30 - Defining DRLs and Achievable Dose: Explaining the 75th percentile threshold vs. 50th percentile target.
- 02:16 - The 10-Year Data Shift: Analyzing the 22% reduction in DRLs and 9% drop in achievable doses.
- 04:06 - Practical Benchmarking: How facilities can compare internal doses against national peer data.
- 05:39 - 1.3M to 5.2M Exams: Real-time data processing and state-of-the-art patient sizing methods.
- 11:41 - Data Quality & Curation: Comparing ACR Dose Index Registry workflows with real-time platforms.
- 17:11 - Dose Reduction vs. Dose Optimization: Why lowering dose too far threatens diagnostic image quality.
- 18:58 - Head Scans vs. Body Scans: Why chest CT doses dropped 31% while head CT doses barely moved.
- 25:20 - Responding to High Doses: Justifying higher protocols for neuroradiology vs. irresponsible knee-jerk cuts.
- 29:51 - Navigating Legacy Equipment: How facilities with older scanners can maintain optimized protocols.
- 36:21 - Unexpected Discoveries: Uncovering a 35% overall radiation drop since 2006.
- 40:53 - What's Next in Research: Upcoming pediatric and cardiac DRL studies evaluating dose alongside image quality.
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