A Scientific Answer Based on Landmark Research

                                                                                                 Author | Wencheng WANG | Senior Food Engineer | Senior Nutritionist  |https://www.cazzicteca.com

Abstract: A large-scale study published inJAMA Internal Medicine（https://jamanetwork.com/journals/jamainternalmedicine）in 2025 has sparked intense public debate — suggesting that CT scans may be responsible for up to 5% of newly diagnosed cancers. But what does this number actually mean? Is undergoing a CT scan safe for the average person? This article deciphers the truth behind the data in plain language.

Keywords: CT radiation safety, JAMA Internal Medicine（https://jamanetwork.com/journals/jamainternalmedicine）、radiation-induced cancer risk, 100 mSv safety threshold, ALARA principle.

I. What Does "CT Scans Cause 5% of Cancers" Actually Mean?

In April 2025, a research team led by Rebecca Smith-Bindman at the University of California, San Francisco (UCSF)（https://www.ucsf.edu/） published a landmark study in JAMA Internal Medicine.

The team analyzed data from approximately 93 million CT examinations performed on 61.51 million patients in the United States in 2023. Using a risk prediction model, they estimated that if current CT utilization patterns remain unchanged, these scans could result in approximately 103,000 lifetime radiation-associated cancers — roughly 5% of the approximately 1.95 million new cancer cases diagnosed annually in the U.S.

However, it is critical to note: this does not mean "you have a 5% chance of getting cancer from a single CT scan."

This figure represents a population-attributable risk projection. By analogy, stating that "100,000 people die in traffic accidents nationwide each year" does not imply that every individual faces an extremely high risk each time they go outside. The absolute cancer risk for the vast majority of patients undergoing a single CT examination is exceedingly low — approximately 0.01% to 0.05%. The 5% aggregate figure is predominantly driven by high-frequency scanning populations, such as patients with chronic diseases or those undergoing longitudinal oncological follow-up with repeated multi-site CT imaging.

II. What Dosage Is Considered Safe?

The consensus in the international radiation protection community is clear: at cumulative doses below 100 mSv (millisieverts), no epidemiological evidence has conclusively demonstrated an increase in cancer incidence.

This 100 mSv threshold is derived from three major cohort studies:

· Japanese Atomic Bomb Survivor Cohort (LSS): The Radiation Effects Research Foundation has followed approximately 87,000 survivors for over 47 years. In the dose range below approximately 100 mSv, no statistically significant excess cancer risk has been detected.

· Nuclear Industry Worker Cohorts: Multi-national epidemiological studies of nuclear industry workers have similarly failed to demonstrate a clear excess cancer risk among populations with chronic exposure below 100 mSv.

· Pediatric Medical Exposure Cohort: A large-scale cohort study published in Nature Medicine in 2023 found that hematological malignancy risks became statistically significant only when cumulative bone marrow doses reached ≥30 mGy.

So how much radiation does a single CT scan actually deliver?

The global average annual natural background radiation exposure is approximately 2.4–3.0 mSv. In other words, a single conventional chest CT is roughly equivalent to 2–3 years of additional "natural" radiation exposure.

Based on the 100 mSv annual safety threshold, a simple calculation yields: no more than 6–7 conventional CT scans or 5 contrast-enhanced CT scans per year falls within the safe range.

III. Do the Benefits of CT Far Outweigh the Risks?

The answer is: yes, when there is a clear clinical indication.

In the context of lung cancer screening with low-dose CT, data from the U.S. National Lung Screening Trial (NLST) demonstrate that the ratio of lives saved through CT screening to radiation-induced cancer deaths is approximately 16:1. The European ITALUNG study reported an even more favorable benefit-to-risk ratio of 63:1.

In other words, for every one cancer potentially induced by radiation, CT screening simultaneously saves 16 to 63 lives. For acute trauma, suspected stroke, visceral hemorrhage, and tumor staging, the rapid diagnostic value of CT is irreplaceable.

IV. What Should We Really Be Concerned About?

Not "doing CT scans" per se, but rather "performing CT scans without clinical justification."

An editorial published alongside the study sharply noted that the research's intent was not to discourage the public from undergoing CT examinations, but rather to urge clinicians to rigorously assess the necessity of every scan ordered.

If you or a family member are facing frequent CT examinations, the following evidence-based recommendations may be helpful:

· Ask proactively: "Is this CT scan truly necessary? Are there alternatives such as ultrasound or MRI?"

· Bring prior imaging: Carry recent imaging records when seeking referrals to avoid redundant cross-institutional examinations.

· Disclose special conditions: Pediatric, pregnant, and preconception patients should request low-dose scanning protocols. Modern CT technology can reduce radiation doses by 30%–50%.

· Maintain a radiation log: Retain the dose metrics (DLP or CTDIvol) from each CT report. When cumulative exposure approaches 100 mSv, proactively remind your physician to reassess necessity.

· Do not let fear delay critical care: Refusing medically necessary examinations out of radiation anxiety poses a far greater risk than the radiation exposure itself.

One-Sentence Summary

CT is neither a monster to be feared nor a tool to be滥用 (abused). When clinically indicated, proceed with confidence; when unjustified, dare to question — this is the most scientifically sound approach to CT imaging.

References

1. Smith-Bindman R, et al. Projected lifetime cancer risks from current computed tomography imaging. JAMA Intern Med. 2025;185:710-719.

2. Moghanaki D, et al. Misleading concerns about computed tomography scans. JAMA Intern Med. 2025.

3. Bosch de Basea Gomez M, et al. Risk of hematological malignancies from CT radiation exposure. Nat Med. 2023;29(12):3111-3119.

4. Hendrick RE, Smith MA. Benefit-risk analysis of lung cancer CT screening. 2024.

5. Ozasa K, et al. Studies of mortality of atomic bomb survivors, Report 14. Radiat Res. 2012;177(3):229-243.

Disclaimer: This article is intended for educational and informational purposes only and does not constitute medical advice. Individualized imaging decisions should be made in consultation with qualified healthcare professionals.

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About Author: http://en.cnsoc.org/)

Mr.Wencheng WANG

Senior Food Engineer

Senior Nutritionist certified by the Chinese Nutrition Society.(https://en.cnsoc.org/)

He currently serves as  Director of the Research Center at Classic (Xiamen) Technology Co., Ltd. https://www.cazzicteca.com/

A 1995 graduate of Nanchang University(https://english.ncu.edu.cn/)—ranked third in China for its Food Science program—Mr. Wang has dedicated his career to food R&D, food testing, and food safety. From 1995 to 2002, he held various positions at the Jiujiang Product Quality Supervision and Inspection Institute in Jiangxi Province, including Food Inspector, Investigator, Laboratory Director, Quality Manager, and Deputy Director of the Institute. He has also served as Quality Control Director and Technical Director for foreign-invested enterprises in Australia and France.

 He published over 10 papers in national core journals and provincial/ministerial journals. Pls see another page the masterwork .

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