EXPERT REACTION: CT scans could soon be responsible for 5% of new cancer cases every year

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Based on data from 61 million patients and 93 million CT examinations in 2023, this research paper establishes a direct link between ionising radiation from CT scans and annual cancer diagnoses. The projected number of radiation-induced cancers is 3 to 4 times higher than previously thought.

Improving patient radiation safety and mitigating radiation-induced cancer risk in Australia requires a three-pronged approach:
•    Medical school education: students must understand the harmful biological and health-related effects of ionising radiation and absorb basic principles of radiation safety.
•    Professional education: doctors requesting CT scans need to justify their request, know the indications, recognise appropriate imaging protocols and their radiation impact on patients; CT scans should be requested to answer a specific clinical question and not used as a screening tool.
•    Advocacy with health authorities and healthcare administrators, who should be aware of the health risks from CT-radiation exposure and consider improving patient access to low-dose options (e.g., photon counting CT, cone beam CT) or zero-radiation dose options (e.g., MRI, US). Cumulative assessment of patient radiation exposure, displaying the radiation dose of each CT exam within the patient’s radiology exam report, logging of these data into a central registry (e.g., electronic Medical Record, eMR), and individual exposure tracking through a radiation passport may provide great value. 

There have been several large-scale studies done about the link between cancer risk and CT dose. The current study analysed the largest cohort of over 61 million American patients’ data. Similar studies on 11 million Australian patients were done in 2013. Estimated overall cancer risks from CT radiation doses are similarly high. It is a well-established fact that high-energy radiation causes cancer.

But it is very difficult to determine the threshold of radiation that would cause cancer. Some biological effects are deterministic. For example, radiation exposure breaks DNA. Increased exposure would increase the DNA breakage and increase the severity. This will happen to everybody exposed to radiation. But cancer risk is not deterministic; rather stochastic. Not everyone who is exposed to radiation will get cancer.

Just based on mathematical formula using linear non-threshold model (that is, any amount of radiation can cause cancer) – the estimated risk sometimes can cause panic among the patients who are benefiting from radiation. Radiations are routinely used for diagnosis and treatment of cancer. This study has clearly established the importance of limiting the radiation dose where possible and of avoiding unnecessary CT scans if other low radiation or no radiation procedures can do the same job.

CT is an indispensable diagnostic tool in modern medicine which is widely used across Australian healthcare settings. It provides clinicians with rapid-high-resolution cross-sectional images of the body and plays a vital role in diagnosing trauma, cancer, cardiovascular disease, infections and many other conditions. It is often the preferred choice for acute and complex cases due to its speed, availability and diagnostic clarity.
 
Concerns over potential overuse are already understood among Australian radiologists and radiographers. While the long-term risks associated with CT radiation exposure require vigilant management, Australia already has a number of proactive measures to safeguard public health, such as the Australian Health Practitioner Regulation Agency, the Australian Radiation Protection and Nuclear Safety Agency and the Diagnostic Imaging Accreditation Scheme.
 
Although the findings highlight the need for vigilance around long-term radiation exposure, this should not discourage the use of CT imaging when clinically justified. In appropriately selected cases, the diagnostic and therapeutic value of CT scans significantly outweighs the potential radiation-associated risks.