Is radiation exposure cumulative?

From the Guidelines

Yes, radiation exposure is cumulative in the human body, and this cumulative effect is a significant concern for both patients and medical personnel. When a person is exposed to ionizing radiation, the biological damage adds up over time from multiple exposures, causing damage to DNA and cellular structures that may not be fully repaired between exposures 1. The body keeps a "running total" of radiation damage, which is why there are lifetime exposure limits for radiation workers and why medical professionals track patients' radiation exposure from diagnostic procedures. Different tissues respond differently to radiation accumulation, with some being more sensitive than others.

Key Points to Consider

• The cumulative nature of radiation exposure is particularly important for people who undergo multiple medical imaging procedures involving radiation, work in radiation-related fields, or receive radiation therapy for cancer 1.
• Healthcare providers often consider a patient's radiation history before ordering additional tests, and radiation workers wear dosimeters to monitor their total exposure over time 1.
• The risk of radiation-caused cancer is not uniform across the entire population, with patient characteristics such as age, gender, and comorbidities modulating the risk associated with a particular radiation exposure 1.
• The potential for radiation-induced cancer is less relevant in patients with shorter life expectancies and important comorbidities, but it is most important for children and young adults with a long life expectancy, particularly females, in addition to those with congenital heart disease who have an ongoing need for evaluation and risk an increased lifetime cumulative exposure 1.

Implications for Clinical Practice

• Tracking cumulative radiation exposure is essential for both patients and medical personnel, as it allows for the assessment of the attendant risk and the implementation of strategies to mitigate it 1.
• The use of technology to measure and track cumulative radiation dose for both patients and occupationally exposed healthcare workers is crucial for their protection and can indicate a need for corrective action when necessary 1.
• Healthcare providers should consider the cumulative nature of radiation exposure when ordering diagnostic procedures and take steps to minimize exposure whenever possible, while also weighing the clinical value of the procedure against the potential risks 1.

From the Research

Radiation Exposure Cumulativity

• The cumulativity of radiation exposure is a topic of interest in the field of radiological protection, with studies suggesting that cumulative doses of ionising radiation can increase the risk of subsequent cancer in exposed individuals 2.
• Research has shown that the risk of second primary cancer consequent to high/very high doses of radiation is likely due to repopulation of heavily irradiated tissues by surviving stem cells, some of which will have been malignantly transformed by radiation exposure 2.
• The concept of lifetime radiation risk of stochastic effects is important in contemporary radiation protection, with the lifetime attributable risk (AR) being an approximation to more general lifetime risk quantities, but only valid for exposures under 1 Gy 3.
• Alternative quantities, such as radiation-attributed decrease of survival (RADS), have been recommended for applications in space and medicine to represent the cumulative radiation risk conditional on survival until a certain age 3.

Epidemiological Evidence

• Recent epidemiological evidence suggests that low doses of ionising radiation, of the order of 100 mGy, can cause cancer, with substantial evidence found from studies including several million individuals, many of them followed-up for more than half a century 4.
• A retrospective cohort study of workers in France, the United Kingdom, and the United States found a linear increase in the rate of cancer with increasing radiation exposure, with an estimated rate of mortality from all cancers excluding leukaemia increasing by 48% per Gy 5.
• The study provides a direct estimate of the association between protracted low dose exposure to ionising radiation and solid cancer mortality, with the risk per unit of radiation dose for cancer among radiation workers similar to estimates derived from studies of Japanese atomic bomb survivors 5.

Cumulative Dose and Cancer Risk

• The cumulative dose received during a course of radiation treatment can be sufficiently high to increase the risk of second primary cancer, with studies showing a linear dose-response for second primary solid cancers over a cumulative gamma radiation dose range of tens of gray 2.
• Recurrent medical imaging can result in cumulative doses above 100 mSv, with evidence existing for cancer risk elevation, and around one in five patients estimated to be under the age of 50 6.
• The radiation protection framework needs to respond to the challenge of recurrent imaging and high individual doses, with the integration of clinical and exposure history data supporting improved knowledge about radiation risks from low doses and individual radiosensitivity 6.