Low-Dose and Ultra-Low Dose Chest CT Australia: What Does “Low Dose” and “Ultra-Low Dose” Mean?

“Low dose” and “ultra-low dose” are increasingly appearing on radiology websites. These terms should mean something. Patients should be able to ask what radiation dose was actually delivered – and what diagnostic information was retained to achieve it.

Australia’s National Lung Cancer Screening Program (NLCSP) has made low-dose chest CT, or LDCT, much more familiar to patients and referrers.

That is an important advance. Lung cancer screening can identify small lung cancers before they become symptomatic, while exposing patients to substantially less radiation than a conventional diagnostic chest CT.

But it has also created a new advertising problem.

Search radiology websites and you will increasingly find phrases such as:

“low-dose CT”
“ultra-low-dose CT”
“significantly lower radiation”
“without compromising image quality”

These sound impressive. But in medicine, these words cannot simply mean “our scanner uses less radiation than it otherwise could.”

If a medical imaging provider advertises a scan as low dose or ultra-low dose, patients should reasonably be entitled to ask:

How low?

Australia now has a definition for low-dose lung screening CT

For the Australian National Lung Cancer Screening Program, a low-dose chest CT should use a CTDIvol of no more than 3.0 mGy for a standard-sized patient, with appropriate reduction for smaller patients and increase for larger patients.

Importantly, Australia also defines what is meant by the standard-sized patient used for this comparison:

Approximately 170 cm tall and 70 kg

This matters because CT radiation exposure depends substantially on body habitus.

A 50 kg patient and a 120 kg patient should not necessarily receive the same scanner output. A larger body requires more X-ray photons to maintain equivalent image quality.

So whenever we quote an approximate radiation dose in this article, the comparison is based on a standard-sized adult of approximately 170 cm and 70 kg, unless otherwise stated.

Australia’s current ARPANSA Diagnostic Reference Level for NLCSP low-dose chest CT is:

Australian NLCSP LDCT	Reference value
CTDIvol	3 mGy
DLP	90 mGy·cm

These are not rigid dose limits for every individual patient. They are national reference levels used to benchmark and optimise practice.

But they mean that “low-dose CT” is no longer just a vague advertising adjective in Australian lung screening. There is an objective technical benchmark behind it.

What about ultra-low-dose CT?

Australia does not currently have a separate legislated or NLCSP definition for ultra-low-dose CT.

The medical literature, however, generally places modern ultra-low-dose chest CT in the region of approximately 0.2 mSv or less, although protocols vary.

A 2024 systematic review of 15 studies found a mean ULDCT effective dose of 0.22 ± 0.10 mSv, compared with 2.84 ± 1.80 mSv for the reference CT examinations. Nodule detection ranged from 86.1% to 100%.

An earlier systematic review similarly found average doses of approximately:

standard-dose chest CT: 3.17 mSv
low-dose CT: 1.22 mSv
ultra-low-dose CT: 0.22 mSv.

For practical communication with patients, we therefore regard:

≤0.2 mSv as a sensible contemporary description of an ultra-low-dose chest CT.

What do these radiation numbers mean in everyday life?

Millisieverts are not particularly intuitive.

ARPANSA estimates that Australians receive approximately 1.7 mSv every year from natural background radiation simply through normal life.

ARPANSA also gives approximate exposures of:

0.06 mSv for a two-view chest X-ray
0.11 mSv for a return Melbourne–London flight
approximately 5 mSv as a broad public-information estimate for a conventional chest CT.

That makes the scale easier to understand:

Examination or exposure	Approximate dose	Everyday equivalent
*Ultra-low-dose chest CT*	<0.2 mSv	Less than ~6 weeks of normal Australian background radiation
		About 3 two-view chest X-rays
		Less than 2 Melbourne–London return flights
*MBR Health low-dose spectral chest CT*	~0.7 mSv	About 5 months of natural Australian background radiation
		About 12 two-view chest X-rays
		About 6 Melbourne–London return flights
*Traditional low-dose CT protocols*	~1–1.5 mSv	Roughly 7–11 months of Australian background radiation
*Conventional chest CT – broad ARPANSA comparison*	~5 mSv	Almost 3 years of Australian background radiation

These are approximate comparisons only. Radiation from a medical examination is not biologically identical to radiation accumulated slowly from the environment or during air travel.

They simply help patients understand the scale.

“Ultra-low dose without compromising image quality” is a significant medical claim

This is where radiology advertising needs greater scrutiny.

Statements such as:

“Our ultra-low-dose CT technology minimises exposure while maintaining diagnostic image quality.”

or:

“Ultra-low radiation dose scans without compromising image quality.”

sound reassuring.

But what exactly does “without compromising image quality” mean?

Image quality is not an on/off switch.

Diagnostic fidelity depends upon what we are trying to see. You can read more on why MBR Health choses to provide the technically most advanced radiology in Australia in our Insights post titled Best, Not Standard: Why We Chose A Different Approach to Advanced Radiology and Regenerative Medicine.

At extremely low doses, modern reconstruction technology can preserve remarkable image quality, particularly for pulmonary nodule detection. But published studies still show differences depending on nodule size, density and the pathology being assessed.

A systematic review found ULDCT nodule detection ranging from 86.1% to 100%, while malignant nodule classification remained less certain.

Another review found considerable variation in ULDCT sensitivity for nodules and some other pulmonary abnormalities.

So a blanket statement that radiation has been reduced “without compromising image quality” needs evidence.

A provider should be able to explain:

the actual CTDIvol
the actual DLP
the approximate effective dose
the patient size on which any advertised dose is based
what clinical task the protocol has been validated for
and what diagnostic compromises, if any, are associated with that protocol.

Without those numbers, the words “low dose” and “ultra-low dose” tell patients very little.

Medical advertising has rules

This is not simply semantics between radiologists. Under the National Law, advertising a regulated health service must not be false, misleading or deceptive, or likely to be misleading or deceptive.

Ahpra specifically warns that advertising may be misleading when it:

provides only partial information or omits important details
makes effectiveness claims unsupported by acceptable evidence
understates risks or limitations
makes unsupported comparisons about quality or outcomes
or claims to provide a superior health service without adequate evidence.

The Australian Consumer Law applies as well.

The ACCC states that claims about the benefits, qualities or performance of a service must be accurate, based on reasonable grounds and capable of being proved. Importantly, the overall impression of the advertising matters – not merely whether an individual sentence can technically be defended.

That has obvious relevance to radiology.

If you describe a CT as “ultra-low dose”, there should be an actual ultra-low dose.

If you say there is “no compromise in image quality”, you should have evidence supporting that statement for the diagnostic task being advertised.

If you call something “low dose”, patients should not have to guess whether that means 0.7 mSv, 1.5 mSv, 3 mSv or something else entirely.

Medical terminology should inform patients, not simply reassure them – or worse mislead them.

The dose is recorded

The useful thing about CT radiation is that this discussion does not have to rely on marketing.

The scanner records the dose information.

CT examinations generate objective dose metrics including:

CTDIvol, in mGy
DLP, in mGy·cm.

These are normally recorded with the examination, including within the DICOM dose information or Radiation Dose Structured Report.

CTDIvol is a scanner-output measure rather than an individual’s exact absorbed dose, and effective dose in mSv is subsequently estimated rather than directly measured. A useful tool to perform this estimation is the:

Simple Calculator for Effective Dose in CT (DLP -> Eff Dose): Radiologic Technologist’s guide to Effective Dose (mSv) in CT from Dose Length Product (mGy cm)

You can obtain your DLP from your DICOM data and enter the data into the calculator. At MBR Health we publish the CT dose in the report.

Low dose and good imaging are not the same thing

Radiation optimisation is a balance.

If we reduce radiation dose sufficiently, fewer X-ray photons reach the detector and image noise increases. Modern scanners compensate using better detectors, iterative reconstruction and increasingly sophisticated reconstruction algorithms. This is why modern ultra-low-dose CT can perform remarkably well. But the objective of radiology is not to achieve the smallest possible number on the radiation dose report.

The objective is:

the lowest appropriate radiation dose that still answers the clinical question accurately.

A screening examination needs enough fidelity to detect the abnormalities it is designed to find.

A patient with symptoms, known malignancy, complex infection, interstitial lung disease, pulmonary vascular disease or mediastinal pathology may need substantially more diagnostic information (cancer detection) than a screening CT is designed to provide.

Low-dose screening CT is not a full diagnostic chest CT

This is another distinction that should not disappear in advertising.

Australia’s NLCSP low-dose CT is specifically a non-contrast lung cancer screening examination in eligible asymptomatic patients. ARPANSA’s protocol specification describes the scan range from the lung apices to the bottom of the lungs and specifically excludes chest protocols that would not qualify for the NLCSP.

It is an excellent examination for the task for which it is designed.

That does not make it the most accurate examination for every thoracic disease.

Sometimes additional radiation exposure, contrast administration or more sophisticated CT data is justified because the diagnostic question is different.

Where MBR Health fits

At MBR Health, we perform both.

Our low-dose chest CT is approximately 0.7 mSv in a standard-sized patient and retains spectral CT data, providing additional material and energy-dependent information beyond conventional single-energy CT.

We also perform an ultra-low-dose chest CT at <0.2 mSv where the clinical question is appropriate, with screening-level diagnostic fidelity comparable to conventional LDCT — at approximately an order of magnitude less radiation than many traditional 1–2 mSv low-dose protocols.

The point is not simply to advertise the smallest number.

It is to select the right acquisition for the patient.

A sensible way to think about chest CT

CT examination	Practical dose concept	Purpose
Ultra-low-dose CT	~0.2 mSv or less	Selected screening or surveillance where diagnostic fidelity can be preserved
Low-dose lung screening CT	CTDIvol ≤3 mGy for a 170 cm/~70 kg standard patient	Nodule detection and lung cancer screening
MBR low-dose spectral CT	~0.7 mSv	A lower radiation exposure than the low-dose screening program requirement but includes both conventional and spectral data
Diagnostic chest CT	Usually several mSv	Broader diagnostic assessment where higher image fidelity and/or contrast may be required

The question patients should ask

If a radiology provider advertises low-dose or ultra-low-dose CT, ask:

“What is the actual radiation dose for a standard 170 cm, 70 kg patient?”

Then ask:

“What are your CTDIvol and DLP values?”

And perhaps most importantly:

“Has the image quality at that dose been validated for what you are trying to diagnose?”

Those are reasonable questions.

The answers should be numbers and evidence — not adjectives.

Low-Dose and Ultra-Low-Dose Chest CT on the Gold Coast

MBR Health provides both low-dose Spectral CT chest imaging and ultra-low-dose chest CT on the Gold Coast. The appropriate protocol depends on whether the clinical question is screening, surveillance or more detailed diagnostic assessment. Learn more about MBR Health Lung Health & Screening and our advanced Spectral CT imaging.

Author: Dr Kirralee Sherif (PhD)

References

Australian Government Department of Health, Disability and Ageing. Medicare Benefits Schedule Item 57410: Low-dose CT chest for the National Lung Cancer Screening Program. MBS Online.
Australian Society of Medical Imaging and Radiation Therapy. Early detection: National Lung Cancer Screening Program. Australian NLCSP technical guidance describes CTDIvol ≤3.0 mGy for a standard-sized patient of 170 cm and approximately 70 kg, adjusted for patient size.
Australian Radiation Protection and Nuclear Safety Agency. Current Australian National Diagnostic Reference Levels for Multi Detector Computed Tomography. LDCT chest NLCSP DRL: CTDIvol 3 mGy; DLP 90 mGy·cm.
ARPANSA. What is background radiation? Average natural background radiation in Australia is approximately 1.7 mSv/year; two-view chest X-ray approximately 0.06 mSv; Melbourne–London return flight approximately 0.11 mSv; broad chest CT comparison approximately 5 mSv.
Pan Z, Zhang Y, Zhang L, Wang L, Zhao K, Li Q, Wang A, Hu Y, Xie X. Detection, measurement, and diagnosis of lung nodules by ultra-low-dose CT in lung cancer screening: a systematic review. BJR Open. 2024 Nov 22;6(1):tzae041. doi: 10.1093/bjro/tzae041. PMID: 39665102; PMCID: PMC11634541.
Tækker M, Kristjánsdóttir B, Graumann O, Laursen CB, Pietersen PI. Diagnostic accuracy of low-dose and ultra-low-dose CT in detection of chest pathology: a systematic review. Clin Imaging. 2021 Jun;74:139-148. doi: 10.1016/j.clinimag.2020.12.041. Epub 2021 Jan 6. PMID: 33517021.
Australian Health Practitioner Regulation Agency. Guidelines for advertising a regulated health service. Section 133 of the National Law prohibits false, misleading or deceptive advertising of regulated health services.
Australian Competition and Consumer Commission. False or misleading claims. Advertising claims must be truthful, accurate, based on reasonable grounds and capable of substantiation.