Ionizing Radiation

Function

Electromagnetic and particulate radiation can produce ion pairs by interaction with matter. Through ionizing radiation, clinicians can obtain high-quality images to assist in making a diagnosis. Ionizing radiation uses gamma, x, alpha particles, neutrons, beta rays, charged nuclei, and positron radiation.

Life on Earth has thrived for approximately 4 billion years amid the constant presence of natural ionizing radiation. There is a high probability that this radiation has played and continues to play a role in shaping the current state of life. The natural background radiation remains minimal, measuring just a few millisieverts per year (mSv/y).[1]

Natural sources of ionizing radiation include solar, cosmic, and radioactive elements such as uranium and gamma rays. Natural radiation is the primary source of human exposure to ionizing radiation, especially in areas with high natural background radiation such as (i) Guarapari, Brazil; (ii) Kerala, India; (iii) Ramsar, Iran; (iv) Yangjiang, China.[2] Ionizing radiation is found in consumer products and radioactive substances and is spread by improper disposal of radioactive waste.[3]

Radiation is an important part of modern medicine and is used in diagnostic radiology in x-rays, CT imaging, and interventional radiology when different procedures are performed under fluoroscopic guidance. Radiation is also used in the treatment of certain types of cancers.

Currently, 46% of ionizing radiation is from a medical source, as opposed to only 15% in the past. The dosimetry of ionizing radiation is a well-established and mature branch of physical sciences.[4] Dosimetry calculates the safe and effective dose for the patient during radiotherapy and monitors the chronic exposure of clinicians. The radiation dosage is measured in rad, sievert, and grey units. Factors that impact exposure are

• Radiation exposure time
• Distance from the radioactive source
• Degree of radioactivity or rate of energy emission

Issues of Concern

The lifetime cancer mortality risk from a pediatric CT scan is higher than in adults; the lifetime attributable risk to children of CT-induced cancer is estimated to be 1 in 1000.[3] Results from recent studies have demonstrated that pediatric CT scans are directly associated with an increased incidence of solid tumors, leukemia, lymphoma, and myelodysplasia. Results from another study that extrapolated epidemiological data from survivors of an atomic bomb radiation exposure estimated there may be a risk of 1 fatal cancer for every 1000 CT scans performed in young children.[5] 

Moreover, the discussion on radiation risks in imaging should consider the significant misdiagnosis issue, with an irreducible error rate of 3% to 4%. Providing a balanced analysis, considering the potential risks and benefits of imaging procedures, is essential to address patient concerns about radiation exposure.[6] Additionally, extensive imaging, such as whole-body CT in patients with trauma, revealed an incidental finding in one-third of the scans. Less than 1% of patients required urgent medical attention, and less than 3% had follow-up. Incidentalomas may increase patient anxiety in the long term.[7]

The overutilization of CT scans can significantly raise healthcare costs. Frequent and unnecessary CT imaging incurs expenses for each scan, leading to downstream costs, including repeat scans, follow-up procedures, and potential overdiagnosis, resulting in overtreatment and higher healthcare utilization.[7]

Cellphones, AM/FM radio, microwaves, sunbathing, and lighting are all nonionizing radiation sources. These are extremely low doses of ionizing radiation with no detectable health effects. However, long-term exposure may lead to cancer and other adverse health events.

Clinical Significance

Acute radiation sickness occurs at high-dose (1-12 Gray, Gy) exposures.[8] Acute radiation poisoning is a clinical condition encompassing 4 organ systems, leading to the development of specific subsyndromes: 

• Hematopoietic syndrome
• Gastrointestinal subsyndrome
• Neurovascular subsyndrome
• Cutaneous subsyndrome 

Countermeasures of potential benefit include

• Cytokines
• Hematopoietic stem cell transplantation 
• Fluoroquinolones 
• Bowel decontamination 
• Serotonin receptor antagonists
• Loperamide
• Enteral nutrition 
• Topical steroids
• Antihistamines
• Antibiotics
• Surgical excision/grafting for skin changes [9][10]

Chronic effects may persist for several years. Radiation can increase many malignant, circulatory, age-related, and neurodegenerative diseases.[11][12] Some researchers reported a link between increased exposure to ionized radiation and the risk of tuberculosis, viral infections, diseases of the digestive system (chronic liver disease in particular), cataracts, and Down syndrome.[2][13] 

Over the past several decades, there has been increasing evidence regarding the carcinogenic risk of exposure to ionizing radiation. Several studies utilizing data from nuclear disasters have attempted to estimate cancer risk based on specific doses of ionizing radiation. Reducing radiation dose during imaging at a hospital is one way to limit excess exposure to ionizing radiation in patients. Children are at increased risk of receiving higher doses of ionizing radiation than adults due to their body habitus, and the risk to a fetus is recognized before any imaging in pregnant patients. Evaluate the appropriateness of imaging to minimize harm to the patient.[14]

The negative effect on the human body is via cell damage. In most cases, the cell can repair itself, but the damage to core DNA and repair mechanisms can render the cell unable to operate normally. Cells die and can slough off the mucosa. A high radiation dose over a short span spread across multiple doses is thought to optimize cell repair than prolonged exposure at a low dose. Teratogenic effects are associated with ionizing radiation. Direct radiation, especially to a fetus in the first trimester, predisposes a high level of teratogenicity and may result in fetal death.

Other Issues

Ionizing radiation is being evaluated not only as a risk factor for malignancy but also as one of the sources of high healthcare costs.[15] There is a push for clinicians to utilize their clinical skills to diagnose patients rather than relying on computerized tomography and other imaging modalities in making a diagnosis. Knowing there is no safe dose of ionizing radiation is essential.

There is a movement in health care known as ALARA (as low as reasonably achievable), where the exposure to ionizing radiation is limited while still achieving quality imaging. Radiation exposure to healthcare workers is higher than in the general population. The measurement of the effective radiation dose on the human body is in roentgen equivalent man (or rem). The average dose of radiation per year in a healthcare worker is 5 rem/year compared to a member of the public, which is 0.1 rem/year. Healthcare workers limiting their radiation exposure time whenever possible is essential. When not possible, those who work with radiation should use appropriate shielding and distance themselves during imaging procedures. 

Note that radiation also has beneficial uses in healthcare. Radiation therapy in cancer treatment decreases recurrence rates and minimizes the need for increased tissue resection, leaving the patient with potentially increased levels of physical disfiguration (as with breast cancer).[16] Radiation also improves survival rates in many malignancies, including breast, prostate, gastric, esophageal, testicular, and pancreatic cancers. 

Enhancing Healthcare Team Outcomes

The International Commission on Radiological Protection (ICRP) is dedicated to safeguarding people and the environment from the adverse effects of ionizing radiation exposure. This safeguarding involves managing radiation doses effectively, which hinges on a comprehensive grasp of dose quantities. For more than 90 years, the system of radiological protection has evolved to align with scientific advancements in radiation exposure knowledge concurrent with the discovery of radiation imaging modalities. The primary goals are preventing harmful tissue reactions (deterministic effects) by keeping doses to organs and tissues below certain thresholds and managing the likelihood of stochastic effects.[17]

The system relies on 3 dose quantities: absorbed, equivalent, and effective. Absorbed dose is the fundamental measure that sets the limits for tissue reaction prevention. Effective dose combines equivalent doses to protect against stochastic effects. The ICRP now considers absorbed dose the most suitable measure for limiting tissue reaction doses, distinguishing them from limits for stochastic effects, which are set in effective dose.[17]

Clinicians should strive to decrease ionizing radiation exposure to themselves and their patients, particularly those at risk. One way to decide whether or not a test is needed is to ask oneself, "Will this extra imaging test change the outcome or treatment for the patient?" If yes, the test may be indicated, but radiation-minimizing strategies described above should be employed. If the answer is no, the imaging test is unnecessary.[16]

With the rise of interventional radiology and the number of procedures under fluoroscopic guidance, the assessment of the attitudes of interventional radiologists toward personal radiation protection and the utilization of radiation protection devices is important. Results from a survey of 504 members of the Society of Interventional Radiology revealed that while many radiologists use radiation safety devices such as lead aprons and thyroid shields, some devices like leaded eyeglasses, ceiling-suspended shields, and rolling shields are less commonly used. Reasons for avoiding specific devices were comfort, ease of use, and availability. The study suggests further investigation into the barriers to device usage and the availability of protective tools in interventional radiology practice.[18] Protocol-based healthcare implementations, such as protocols to decrease the dose of ionizing radiation administered, are a great way to improve outcomes in patient safety and enhance team performance.[5] Current advancements in artificial intelligence, such as machine learning algorithms, enable precise dose optimization and continuous monitoring, decreasing radiation doses to patients and operators during medical procedures.[19]