Radiation Safety in Medical Imaging
Radiation safety in medical imaging is ensured through a three-phase approach: performing only justified procedures on appropriate patients before imaging, optimizing radiation dose during the procedure using ALARA principles, and maintaining robust quality assurance programs with proper equipment calibration and personnel training.
Pre-Imaging: Justification and Appropriate Use
The foundation of radiation safety begins before any imaging occurs. Tests utilizing ionizing radiation should be performed in the right patient, for the right reason, at the right time, with consideration of non-radiation alternatives 1.
Use appropriate use criteria frameworks to ensure procedures are justified, as the 600% increase in population radiation exposure from 1980-2006 resulted entirely from increased utilization rather than higher doses per test 1.
Consider patient-specific factors that modulate stochastic risk: younger patients without comorbidities face higher lifetime cancer risk than older patients with limited life expectancy 1.
For younger patients, alternative imaging modalities without ionizing radiation (cardiac MRI, echocardiography) should be preferentially selected when clinically feasible 1.
Educate ordering physicians on radiation risks and appropriate use criteria before they request imaging studies 1.
During Imaging: Dose Optimization (ALARA Principle)
Every procedure must be optimized to use the smallest necessary radiation dose that provides diagnostic image quality—the ALARA (As Low As Reasonably Achievable) principle 1.
Protocol Selection and Technical Factors
Select imaging protocols with the lowest detector dose and frame rate that still yield diagnostic quality images 1.
Limit beam-on time, use proper beam collimation, and optimize system positioning to minimize exposure to both patients and nearby personnel 1.
Restrict the examination field to only the body region of clinical interest 1.
For nuclear cardiology, select radionuclide species delivering the least radiation while answering the clinical question, and administer the smallest radiopharmaceutical activities ensuring diagnostic quality 1.
Use stress-first imaging for patients with reasonable pretest probability of normal studies; reserve rest-first imaging for challenging subjects likely to have abnormal results 1.
Addressing Practice Variation
The need for standardization is critical, as radiation doses for similar procedures vary up to 13-fold within and across institutions 1. This variation demonstrates inadequate optimization and represents a major safety concern.
Quality Assurance and Facility Management
Facility directors must establish comprehensive quality assurance programs monitoring patient and personnel exposures, with equipment calibration verified by radiological physicists 1.
Equipment Standards
Radiological equipment requiring greater than current state-of-the-art doses to generate quality images should be considered obsolete and either replaced or renovated 1.
Equipment must provide user control of imaging dose parameters allowing operators to select protocols balancing image quality and dose 1.
Collaborate with equipment service engineers and institutional physicists to verify optimal calibration 1.
Monitoring and Benchmarking
Tabulate patient procedure doses and personnel exposures to verify they remain within guideline levels 1.
Compare facility doses to benchmark reference levels developed by professional societies for quality assurance 1.
Investigate and explain individual large outlier exposures, taking corrective action when indicated 1.
Implement dose index registries permitting comparison to regional and national values 1.
Personnel Training and Safety Culture
Proper training of all personnel is essential to ensure understanding of radiation physics, radiation biology, and radiation protection principles 1.
Training should create a culture of respect for radiation hazard and commitment to minimize exposure and maximize protection 1.
All personnel performing radiation-based procedures must understand determinants of patient dose and adjust conduct to achieve diagnosis with minimal necessary exposure 1.
Physicians managing radiation facilities are responsible for fostering a culture minimizing patient exposure and maximizing personnel protection 1.
Understanding Radiation Risk
Biological Effects
Radiation effects fall into two categories 1:
- Deterministic effects occur predictably above dose thresholds (skin erythema, epilation, direct cardiac toxicity)
- Stochastic effects involve potential malignancy development at later times, with risk remaining controversial at medical imaging dose levels
Risk Modeling Limitations
The Linear No-Threshold (LNT) model estimates 5-7.9% lifetime cancer mortality risk per 1000 mSv effective dose, but this was developed for occupational protection, not medical imaging 1.
Prospective studies have not unequivocally confirmed increased solid cancer risk from low-dose radiation (<100 mSv) delivered over years, neither confirming nor refuting LNT 1.
Stochastic risks decrease with increasing age and are lower in men than women—particularly relevant for coronary artery disease populations 1.
Patient Dose Tracking
Current understanding of radiation biology does not support clinical utility of longitudinal patient dose tracking 1. Based on LNT concepts, incremental cancer risk from a particular exposure is independent of prior exposure magnitude, providing no additional clinical decision-making value 1. The principal value of tracking programs would be providing data for future research to define dose-risk relationships more precisely 1.
Common Pitfalls to Avoid
- Performing imaging without considering non-radiation alternatives in younger patients
- Failing to optimize protocols for individual patient characteristics
- Using outdated equipment requiring excessive doses
- Neglecting to monitor and benchmark facility performance
- Inadequate personnel training on dose-reduction techniques
- Ordering studies without clear clinical justification