Microwave and millimeter-wave sensing has become one of the most promising non-invasive routes to skin cancer diagnosis. The technique exploits a simple physical fact: malignant lesions such as basal cell carcinoma, squamous cell carcinoma, and melanoma contain more water than healthy skin, and water-rich tissue has a higher dielectric permittivity at microwave frequencies. By placing a transmitter and a receiver antenna in contact with the skin and exciting electromagnetic surface waves that travel along the skin-air interface, the system can detect the extra attenuation and phase shift introduced by a tumor. The approach is non-ionizing, painless, low-cost, and capable of real-time readout, and recent advances in antenna design and deep-learning signal processing have pushed spatial resolution and diagnostic reliability steadily upward.

Yet safety has lagged behind performance. Most previous evaluations of skin-cancer detectors relied on a single-tissue model representing a single anatomical site, typically the forearm or abdomen, and most assessed safety solely through the specific absorption rate, or SAR, the standard metric that quantifies how much electromagnetic energy is dissipated per kilogram of tissue. The McGill team argues that both shortcuts are problematic. Anatomical differences in skin and subcutaneous structure across the body strongly influence the electric-field distribution at microwave frequencies, so a single-site assessment may not reflect the actual risk during clinical deployment. And SAR itself, while codified in regulatory frameworks, does not capture exposure duration, tissue perfusion, or heat diffusion, all of which determine the physiological outcome that actually matters: how much the tissue warms up.

The two antennas under study were both built on 50-micrometer-thick flexible Kapton substrates chosen for biocompatibility and good skin contact. The monopole antenna, the team’s first-generation design, measures 20 by 20 millimeters and operates from 2 to 5 gigahertz, with a standard SMA connector on the reverse side for repeatable measurements. The newer Vivaldi antenna, measuring 26 by 17 millimeters and operating from 3 to 6 gigahertz, was selected for its end-fire radiation pattern and wide bandwidth, which confine energy along the skin surface. Because biological tissue has a high permittivity, both antennas are far smaller than their free-space counterparts, a key advantage for wearable and point-of-care deployment.

To capture anatomical reality, the researchers constructed nine multilayer tissue models in Ansys HFSS, each consisting of skin, fat, muscle, and, where relevant, bone. Layer thicknesses came from published anatomical measurements: skin thicknesses ranged from 0.9 millimeters on the forehead to 1.7 millimeters on the buttock, while fat thickness varied from a mere 0.3 millimeters on the palm to 12.1 millimeters on the buttock. For the forehead, palm, and sole, all four layers were included because soft tissue is thin enough for the waves to reach bone. At the other six sites, where soft tissue exceeds 20 millimeters, the bone layer was omitted, since microwave penetration depth in soft tissue at 2 to 6 gigahertz is less than 20 millimeters and the waves attenuate before reaching bone. Each model shared identical lateral dimensions of 12 by 6 centimeters, large enough to accommodate the compact antennas.

The full-wave simulations revealed a consistent pattern for both antennas: the peak electric field, and therefore the SAR hot spot, always appears in a small area on the skin surface directly beneath the transmitting antenna. But the magnitude of that hot spot varies enormously with anatomy. The forehead model, with only about 5.1 millimeters of soft tissue over bone, produced the strongest fields, because the wave reflects strongly at the bone interface and constructively reinforces the field at the surface. Sites with much thicker soft tissue, roughly 11 to 33 millimeters, showed far weaker surface fields. At 6 gigahertz, the peak SAR in the forehead model approached nearly twice that of the sole or neck models at identical input power, and the monopole results showed the same trend, with all other sites registering 43 to 54 percent lower peak SAR than the forehead.

Frequency matters as well. Across the operating bands, peak SAR rose steadily with frequency in every tissue model. The explanation lies in the dispersive nature of tissue dielectric properties: as frequency increases, conductivity rises while permittivity falls, which strengthens the skin effect and confines the electromagnetic field ever more tightly to the superficial layers. Because SAR is proportional to the square of the local electric field times conductivity, the combination of higher conductivity and a more surface-localized field drives peak absorption upward at higher frequencies.

The temperature analysis, performed by solving Pennes’ bioheat equation with an explicit finite-difference scheme in MATLAB, added a twist that SAR alone could never reveal. Under a 10-dBm Vivaldi scan over 100 seconds, the palm model heated the most, reaching a peak rise of 2.47 degrees Celsius, while the buttock model, despite having the second-highest peak SAR of all nine sites, produced the smallest temperature rise, about 20 percent lower. The ranking of temperature rise simply does not follow the ranking of SAR, because heating depends not only on the absorption hot spot but also on the spatial and temporal distribution of deposited power, the thermal properties of each layer, and heat diffusion. Even in a short 10-second exposure, comparable to a real clinical scan, the differences persisted: the arm model showed the highest rise at 0.516 degrees Celsius, roughly 16 percent above the buttock. The authors note that at most sites the 1-degree-Celsius safety threshold adopted by IEEE Standard C95.1 would be reached within 30 seconds at 10 dBm, meaning that power level is simply too high for practical use.

From the SAR results, the team derived site-specific power limits that keep the peak spatial-average SAR below the 1.6 watts-per-kilogram threshold mandated by both the U.S. FCC guidelines and Health Canada’s Safety Code 6, averaged over 1 gram of tissue. For the Vivaldi antenna, allowable power ranged from as low as 2.2 dBm at the forehead up to 4.9 dBm at the sole, so the researchers adopted the strictest value, 2.2 dBm, as the global limit for full-body use. Thermal verification confirmed the conservativeness of that choice: after a 10-second exposure at 2.2 dBm, the highest temperature rise anywhere was only about 0.068 degrees Celsius, negligible by any clinical standard. For the monopole antenna, the corresponding global limit was 2.9 dBm, again set by the forehead, and the worst-case 10-second temperature rise at that power stayed below 0.09 degrees Celsius, occurring at the palm.

The authors are careful to note the limitations of their thermal model, which omits blood perfusion, metabolic heat, and convective cooling at the skin-air interface, making the temperature predictions deliberately conservative upper bounds. Future work will incorporate perfusion and heterogeneous boundary effects. Even so, the study delivers something the field has lacked: a standardized workflow, from electric-field mapping and SAR calculation to temperature-rise evaluation and power-limit derivation, that bridges electromagnetic design and biomedical safety. For a technology racing toward clinical integration, the message is clear. A safety assessment based on a single body site is not a safety assessment at all, and the device that scans your forehead may need very different power settings from the one that scans your sole.

Subject of Research: Radiation safety analysis of microwave surface-wave antennas for skin cancer detection across nine anatomical sites

Article Title: Site-dependent numerical safety analysis in microwave skin spectroscopy: comparison of monopole and vivaldi antennas

Article References: Shang, S., & Popović, M. (2025). Site-dependent numerical safety analysis in microwave skin spectroscopy: comparison of monopole and vivaldi antennas. Frontiers in Antennas and Propagation, 3, Article 1714578. https://doi.org/10.3389/fanpr.2025.1714578

Image Credits: AI Generated

DOI: 10.3389/fanpr.2025.1714578

Keywords: microwave sensing, skin cancer detection, specific absorption rate, antenna safety, temperature rise, bioheat equation, Vivaldi antenna, monopole antenna, wearable devices, electromagnetic simulation, radiation exposure, tissue modeling

The research, conducted at Shohadaye-Khalije-Fars Teaching Hospital in Bushehr and published in BMC Infectious Diseases, examined the medical records of 428 hospitalized patients with RT-PCR-confirmed SARS-CoV-2 infection admitted during 2020, all of whom underwent at least one chest HRCT scan during their stay. Across this cohort, a total of 463 HRCT examinations were performed. The researchers, led by Atefeh Esfandiari and Hedayat Salari of Bushehr University of Medical Sciences, judged each scan against the indications laid out in the Iranian national COVID-19 guidelines, using a structured checklist to extract clinical data from the charts. By these criteria, 188 of the 463 scans, or 40.6 percent, were classified as inappropriate.

The distinction between appropriate and inappropriate imaging rests on well-established principles of radiological stewardship. Reverse transcription polymerase chain reaction remains the reference standard for diagnosing SARS-CoV-2 infection, detecting viral RNA with high specificity. HRCT is meant to serve as a complementary tool, reserved for situations such as diagnostic uncertainty, suspected complications, or significant deterioration in a patient’s respiratory status. When a scan is ordered outside these documented indications, the patient absorbs ionizing radiation without a corresponding benefit, and the health system absorbs the cost. The American College of Radiology and similar bodies worldwide have long warned that indiscriminate imaging of this kind erodes both safety and economic efficiency.

To understand why so many scans fell outside guideline recommendations, the team turned to multivariable logistic regression, a statistical technique that isolates the independent effect of each potential predictor while controlling for the others. The results were striking. The strongest driver of inappropriate ordering was symptom duration of seven days or less at the time the scan was requested, with an adjusted odds ratio of 47.15 and a p-value below 0.001. In practical terms, patients scanned very early in the course of illness were dramatically more likely to have been imaged without a guideline-supported reason, a pattern consistent with clinicians reaching for CT before the disease’s characteristic radiological evolution had even had time to develop.

Two other independent predictors emerged from the analysis. Requests originating from hospital-based general practitioners working in the emergency department carried an adjusted odds ratio of 9.64 for inappropriateness, compared with requests from subspecialists, suggesting that the ordering physician’s level of training shaped adherence to imaging criteria. Patient age also mattered: those younger than 30 years faced an adjusted odds ratio of 8.97 for receiving an inappropriate scan relative to patients older than 65. Younger patients with COVID-19 generally have milder disease and lower baseline risk, which may explain why imaging them often lacked a defensible clinical indication, yet the scanners were still frequently rolled out.

Repeat imaging added another layer of concern. Among the 35 repeat HRCT examinations performed during the study period, 12 were judged inappropriate. Serial chest CT is sometimes justified to track disease progression or response to therapy, but each additional scan compounds the cumulative radiation dose. In the context of a respiratory illness where many follow-up scans yield little actionable information, the finding underscores how easily a resource-intensive test can become routine rather than reasoned.

The economic analysis translated these clinical lapses into monetary terms, calculated from three distinct perspectives. The unnecessary financial burden attributable to inappropriate HRCT utilization was estimated at 56,047,000 Iranian rials, approximately 2,156 US dollars, borne by patients themselves. From the governmental healthcare system perspective, the burden rose to 182,360,000 rials, roughly 7,014 US dollars. Under the private tariff, the figure climbed to 328,812,000 rials, or about 12,646 US dollars. While these sums may appear modest in absolute global terms, they represent pure waste, expenditure on imaging that delivered no clinical value, and they scale rapidly when projected across the thousands of hospitals and millions of admissions that defined the pandemic era.

The study’s methodology deserves attention for what it reveals about health services research during public health emergencies. As a retrospective, analytical, cross-sectional investigation conducted in 2022, it reviewed records rather than prospectively guiding care, which means the findings describe practice as it happened rather than testing an intervention. Descriptive statistics and chi-square or Fisher’s exact tests were used to compare groups, and the appropriateness judgment depended on documented clinical indications in the chart, an approach that ties the assessment to the paper trail each ordering clinician left behind. The work was approved by the ethics committee of Bushehr University of Medical Sciences, with informed consent waived due to the retrospective design and all patient data fully anonymized.

Why does this matter beyond a single hospital in Bushehr? The pandemic placed unprecedented pressure on diagnostic infrastructure everywhere, and the temptation to image broadly, to see what the lungs looked like rather than to answer a specific clinical question, was felt in emergency departments across the globe. Guidelines from national health authorities and professional societies consistently urged restraint, recommending CT primarily when RT-PCR results were unavailable or discordant with clinical findings, or when complications were suspected. The Iranian data provide a quantified case study of what happens when that restraint slips: more than four in ten scans ordered without indication, a clear gradient of risk tied to early symptom duration, junior ordering patterns, and young age, and a measurable bill attached to every unnecessary exposure.

The authors conclude that strengthening adherence to evidence-based imaging indications could reduce unnecessary utilization without compromising clinical care. Their findings point toward practical remedies: decision-support tools embedded in electronic ordering systems, clearer escalation pathways that involve subspecialist judgment before advanced imaging, and audit-and-feedback mechanisms that show clinicians how their ordering behavior compares with guideline expectations. As health systems worldwide continue to digest the lessons of COVID-19, the Bushehr study offers a reminder that the cost of a pandemic is measured not only in lives and lockdowns but also in the quiet accumulation of tests that were never needed, doses of radiation that were never justified, and funds that could have strengthened care elsewhere.

Subject of Research: Clinical appropriateness and economic burden of high-resolution chest CT scanning in hospitalized COVID-19 patients

Article Title: Evaluating the clinical appropriateness of high-resolution chest CT scans in hospitalized patients with COVID-19 and the economic burden: a retrospective study in southern Iran

Article References: Esfandiari, A., Amiri, B., Abbasi, F., Esfandiari, S., & Salari, H. (2026). Evaluating the clinical appropriateness of high-resolution chest CT scans in hospitalized patients with COVID-19 and the economic burden: a retrospective study in southern Iran. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14582-y

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14582-y

Keywords: COVID-19, SARS-CoV-2, high-resolution computed tomography, HRCT, RT-PCR, medical imaging, imaging appropriateness, healthcare costs, radiation exposure, Iran, retrospective study, clinical guidelines

The study, published in the Western Journal of Emergency Medicine, was led by co-senior authors David Thompson, MD, an associate professor of clinical emergency medicine and director of quality improvement and patient safety in the UC College of Medicine’s Department of Emergency Medicine, and Anita Goel, MD, also an associate professor of clinical emergency medicine. Over a 23-month campaign spanning the emergency departments of University of Cincinnati Medical Center and West Chester Hospital, the team tracked what happened when clinicians were given the training, tools and encouragement to apply validated clinical decision rules before ordering head and cervical spine CT scans in low-risk trauma patients. The outcome was striking: an estimated 3,542 CT scans were avoided, roughly $6.2 million in patient healthcare charges were saved, and more than 14,000 hours of cumulative patient waiting time were eliminated, all with no identifiable patient harm.

The technical foundation of the campaign rested on clinical decision rules that have become core components of emergency medicine training and standards of care nationwide. These rules, which guide clinicians in determining which head or neck trauma patients genuinely need cross-sectional imaging, incorporate carefully weighted risk indicators. Patients who fall from height, are ejected from motor vehicles, experience limb weakness or numbness, present with blood in the ear, vomit after the injury or show signs of confusion are considered high risk and proceed to imaging. Patients without such red flags, including many with concussions, are classified as low risk, and in those cases the rules support withholding the CT scan and monitoring the patient instead. The rationale is grounded in both radiation biology and health economics: each head or cervical spine CT delivers a meaningful ionizing radiation dose to tissues that are inherently radiosensitive, and the diagnostic yield in truly low-risk populations is exceptionally low.

The numbers quantify just how much low-value imaging was being avoided. At an estimated cost of approximately $1,750 per scan, the 3,542 avoided CT examinations translated into $6.2 million in patient charges that were never incurred. At an average of about four hours of waiting per scan, the campaign spared patients a cumulative 14,168 hours of time spent in the emergency department. Perhaps most striking from a radiation safety perspective, the avoided scans eliminated an estimated 6,021.4 millisieverts of collective radiation dose, a figure the researchers note corresponds to roughly 2,000 years of typical natural background radiation exposure for a single person. In an era when medical imaging accounts for a substantial fraction of the population’s cumulative exposure to ionizing radiation, reductions of this magnitude carry genuine public health significance.

Crucially, the campaign’s safety review found no downside. When the team examined their data at the conclusion of the intervention period, they identified zero missed injuries, meaning every avoided scan had indeed been medically unnecessary and no patient had been sent home with an undetected serious head or spinal injury. This finding addresses the central concern that has historically slowed the adoption of imaging-reduction programs: the fear that trimming CT utilization will inevitably let dangerous pathology slip through. Thompson emphasized that the guidelines, when followed, reliably protect against missed serious injuries, and the campaign’s own outcome data provided direct, institution-level confirmation of that claim across two busy emergency departments.

The intervention itself was deliberately multifaceted, reflecting modern implementation science rather than a single blunt policy. Continuing education sessions were delivered to emergency medicine providers, reinforcing the decision rules and the research evidence behind them so that clinicians understood not just what to do but why. Simultaneously, the CT decision rules were embedded directly into the electronic health record used to order patient testing, so that the point of ordering became a structured prompt for appropriate test selection. This combination of provider education and clinical decision support embedded in the workflow is widely regarded as the most durable way to change ordering behavior, because it reduces reliance on individual memory or judgment at moments of time pressure and standardizes the application of evidence across the entire provider pool.

The campaign also extended its educational efforts to patients, recognizing that a significant fraction of unnecessary imaging is driven not by clinician uncertainty but by patient expectation. Some injured patients arrive convinced that a CT scan is required, even after a physician has determined that their risk profile does not warrant one. To address this, the team created informational handouts designed to reassure patients that declining a scan in their situation reflects careful, evidence-based medicine rather than corner-cutting. As Thompson explained, not everyone with a head or neck injury needs a CT scan; some do and some do not, and the department’s goal is to provide the right care for every patient using the tools available to make those distinctions accurately.

The setting in which these results were achieved amplifies their importance. University of Cincinnati Medical Center is the Greater Cincinnati region’s only academic medical center and its only Level I adult trauma center, functioning as a major tertiary referral hub with an 81-bed emergency department that Thompson described as almost always at capacity. West Chester Hospital adds further patient volume to the health system’s emergency care footprint. Demonstrating that imaging reduction can be achieved in such a demanding, high-acuity environment undercuts a common objection, namely that evidence-based imaging restraint works only in smaller or calmer settings. The UC experience suggests the opposite: precisely because high-volume departments face the greatest pressures of throughput, cost and radiation burden, they may have the most to gain from rigorously applied decision support.

By the end of the 23-month period, all measured outcome indicators showed reductions in the rate of head and cervical spine CT scanning at both participating hospitals, and the absence of any identified missed injuries confirmed that the avoided imaging was truly discretionary. The research team, which included co-first authors Jude C. Luke, an emergency medicine resident physician, and Rebecca N. Kubick, a medical student, alongside biostatistician Heidi J. Sucharew, Natalie E. Kreitzer, and performance improvement specialists Kayla Winkler and Mary L. Giles, framed the project as a win for both physicians and patients. Doctors retain the reassurance that validated rules protect against missed injuries, while patients receive faster care, smaller bills and less radiation. If replicated at scale, the model offers a template for how emergency departments everywhere can convert well-established clinical decision rules from guidelines on paper into measurable reductions in low-value care.

Subject of Research: A quality improvement campaign reducing head and cervical spine CT imaging in low-risk trauma patients

Article Title: University of Cincinnati emergency medicine physicians safely eliminate thousands of unnecessary CT scans

Article References: University of Cincinnati emergency medicine physicians safely eliminate thousands of unnecessary CT scans. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: emergency medicine, CT scans, quality improvement, clinical decision rules, trauma, radiation exposure, healthcare costs, University of Cincinnati, patient safety, low-value care, electronic health records, concussion

The study was conducted by Dr. Roy Yaniv of the Hebrew University of Jerusalem and Sheba Medical Center, together with Prof. Yoav Yair of Reichman University and Prof. Colin Price of Tel Aviv University. Rather than relying solely on models or measurements taken at ground level, the team sent radiation sensors aloft on balloons launched from southern Israel on six occasions between 2014 and 2016. The balloons climbed to approximately 35 kilometres, well above the roughly 10-kilometre ceiling at which most passenger aircraft cruise, allowing the researchers to trace how atmospheric ionization and radiation change continuously from near the surface to the upper stratosphere.

The vertical structure that emerged from the measurements was strikingly clear. As the balloons ascended, radiation levels climbed steadily, reaching a pronounced maximum at around 17 to 20 kilometres above Earth before declining again at even greater heights. This peak is a well-known feature of atmospheric physics called the Regener-Pfotzer maximum. It arises because high-energy cosmic rays entering the atmosphere collide with molecules of air and generate cascades of secondary particles. Near the top of the atmosphere the incoming radiation is intense, but the air is too thin to produce many secondary particles; deeper down, the cascade is fully developed but the overlying atmosphere has already absorbed much of the primary flux. The result is an altitude band where radiation dose rates are at their highest, sitting comfortably above the cruising levels of civil aviation but close enough to influence the environment aircraft operate in.

At approximately 10 kilometres, the altitude at which commercial aircraft typically cruise, the researchers measured gamma-equivalent radiation dose rates of roughly 0.9 to 1.3 microsieverts per hour. Those numbers may sound modest, but they accumulate meaningfully over the thousands of hours that pilots, cabin crews and frequent flyers spend airborne each year. Notably, the levels recorded over Israel were relatively low compared with some higher-latitude regions, a difference the researchers attribute to the stronger geomagnetic shielding found over the Eastern Mediterranean. Earth’s magnetic field deflects charged cosmic particles, and its protective effect is strongest near the equator and weakest near the poles, so geography matters as much as altitude when estimating exposure.

Altitude, however, was only part of the story. The team also found that radiation levels varied systematically with the solar cycle. When the Sun is highly active, its magnetic field is carried outward by the solar wind and forms a protective bubble around the entire solar system, deflecting many of the galactic cosmic rays that would otherwise reach Earth. During periods of low solar activity, this shield weakens, and more of the energetic particles streaming from beyond the solar system penetrate the atmosphere. The balloon measurements reflected this modulation directly: the researchers observed higher radiation levels when solar activity was lower, quantifying the relationship with a negative correlation of r = -0.71. The authors are careful to stress that with only six balloon flights, the number of observations is limited, and the correlation should therefore be considered indicative rather than statistically definitive.

Extrapolating the observed relationship to solar-minimum conditions suggested that radiation levels at commercial aviation altitudes could rise by approximately 40 to 60 percent compared with solar-maximum conditions. The researchers caution that this estimate rests on extrapolation rather than on direct measurements taken under the most extreme quiet-Sun conditions, but the direction and rough magnitude of the effect are consistent with what is known about cosmic-ray modulation. The finding carries practical weight because the Sun is currently progressing through the declining phase of its activity cycle, and solar minima recur roughly every eleven years, meaning the aviation sector periodically operates in precisely the conditions where exposure is greatest.

We tend to think of the atmosphere above us as relatively stable, but the radiation environment at flight altitude is continuously shaped by processes taking place far beyond Earth, the researchers said. Our measurements show that the solar cycle has a measurable effect on the radiation environment experienced at aviation altitudes. By combining direct balloon observations with atmospheric radiation models, we can better understand when and where these levels change and improve the tools used to assess long-term exposure for aircrew and frequent flyers.

To test how well their observations aligned with established prediction tools, the team compared the balloon data with the EXPACS/PARMA atmospheric radiation model. The measured values closely matched the model’s predicted electromagnetic radiation component, generally agreeing within about 10 to 15 percent. The comparison also revealed an important nuance about what the instruments were actually measuring. According to the model, electromagnetic radiation represents only part of the total radiation environment at flight altitude: neutrons account for roughly 40 to 45 percent of the modeled total ambient dose, while photons, electrons and positrons contribute approximately 35 to 40 percent. The Geiger-Müller detectors carried by the balloons were primarily sensitive to photons and charged particles and had little direct sensitivity to neutrons. The reported measurements should therefore not be interpreted as the total radiation dose received by an airline passenger or crew member, but rather as a reliable indicator of the electromagnetic component of the atmospheric radiation field, one that can be used to anchor and validate broader dose assessments.

The findings have particular relevance for aviation, where flight crews and frequent flyers spend extended periods at altitudes where atmospheric protection from cosmic radiation is considerably weaker than at ground level. Occupational exposure limits apply to aircrew in many jurisdictions, and accurate assessment of cumulative dose depends on knowing how radiation varies with altitude, geographical location and solar conditions. The researchers note that continued monitoring is important for understanding long-term occupational exposure, especially as radiation levels shift over the solar cycle and differ substantially between polar and equatorial routes. Beyond aviation, the work offers a clearer picture of how radiation from space interacts with Earth’s atmosphere, and the researchers suggest that similar approaches, pairing relatively inexpensive balloon-borne measurements with established radiation models, could be used to track changes in the atmospheric radiation environment as solar conditions evolve over the coming years.

Subject of Research: Solar-cycle modulation of cosmic radiation dose rates at civil aviation altitudes measured by high-altitude balloons over Israel

Article Title: Cosmic radiation at flight altitudes rises when the sun is less active

Article References: Cosmic radiation at flight altitudes rises when the sun is less active. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: cosmic radiation, solar cycle, aviation, high-altitude balloons, galactic cosmic rays, Regener-Pfotzer maximum, radiation exposure, aircrew, atmospheric ionization, EXPACS/PARMA model, geomagnetic shielding, solar minimum