Case-control studycited by the Tayebat archiveabstract only checked★ key study A-CHM-04 in-depth review

Radiation dose to the heart during breast-cancer radiotherapy raises later heart-attack risk

Risk of ischemic heart disease in women after radiotherapy for breast cancer.

Overview

Darby SC et al.. N Engl J Med 2013 · PMID 23484825 · DOI 10.1056/NEJMoa1209825

Each extra Gray of average heart dose increased the rate of major coronary events by about 7%.

Does the study support the specific claim? Yes · Methodological quality: high

Study explained simply

What did the researchers want to find out?: Measure heart risk by radiation dose.
How was the study done?: Case-control with dose reconstruction.
How many people, animals or samples were studied?: 2,168 women.
What was actually found?: +7.4% per Gy, linear.
How large was the observed effect?: ERR 7.4%/Gy (2.9-14.5).
What do the results mean in everyday life?: Keep heart dose as low as possible; control cardiac risk factors.
What are the study's limitations?: Historical doses; relative measure.
What does it say about Elawady's specific claim?: Confirms the archive number.
Do the results apply to Germany and Europe?: High.
What can explicitly not be concluded from this study?: That radiotherapy does net harm.

Authors: Darby SC, Ewertz M, McGale P, Bennet AM, Blom-Goldman U, Brønnum D, Correa C, Cutter D, Gagliardi G, Gigante B, Jensen MB, Nisbet A, Peto R, Rahimi K, Taylor C, Hall P
Journal: N Engl J Med
Year: 2013
Identifier: PMID 23484825 DOI 10.1056/NEJMoa1209825
Verification: verified – PubMed E-utilities efetch, 2026-10-25
Retracted: no
Corrections: none
Extent checked: abstract only
Conflicts of interest and funding: not stated in abstract | Grants: British Heart Foundation, Cancer Research UK, Department of Health, Medical Research Council

Dose-response between incidental cardiac radiation in breast cancer radiotherapy and ischaemic heart disease.

Study design: Case-control study – Population-based case-control study with individual dosimetry
Population: Women irradiated for breast cancer 1958-2001
Country: Sweden and Denmark
Period: 1958-2001
Sample size: 2,168 (963 cases with major coronary events, 1,205 controls)
Inclusion and exclusion criteria: Women who underwent breast-cancer radiotherapy; cases with MI, revascularisation or IHD death

Exposure / intervention: Mean radiation dose to the whole heart (average 4.9 Gy, range 0.03-27.72)
Comparator: Lower heart doses
Endpoints: Major coronary events
Statistical methods: Conditional logistic regression; excess relative risk per Gy

Results: Major coronary events increased linearly by 7.4% per Gy mean heart dose (95% CI 2.9-14.5; P<0.001), no apparent threshold; increase began within 5 years and continued into the third decade. Proportional increase similar with and without cardiac risk factors.
Absolute risks: Not given numerically in abstract; authors state women with pre-existing cardiac risk factors have greater absolute increases.
Authors' conclusion: Cardiac exposure increases IHD proportionally to mean heart dose, beginning within a few years and lasting at least 20 years.

Orienting tool: ROBINS-E
Type of assessment: simplified assessment (abstract only)
Full formal assessment: no
Overall risk of bias: low
Rationale: Dosimetry blinded to outcome is likely; residual confounding limited because comparison is within irradiated women.

7.4% is a relative increase per Gy; with modern mean heart doses of a few Gy the absolute excess is small for most women (see I-CHM-06).

Core evidence for radiation-related heart disease.

I-CHM-06 (modern doses: approx. 0.3% cardiac mortality risk in non-smokers); I-CHM-02 (radiotherapy reduces breast-cancer death).

High; modern techniques lower heart doses.

Landmark study, correctly quoted; needs absolute-risk and benefit context.

Multidimensional assessment
Multidimensional assessment
Authenticity of the source	verified
Methodological quality	high
Risk of bias	low
Precision of results	moderate
Directness	direct
Reproducibility	replicated
Consistency with the overall evidence	consistent
Regional transferability	high
Adequacy of the interpretation (by the archive)	essentially correct but incomplete

Risk at modern very low heart doses (breath-hold, proton).

Note: according to the archive, the studies were compiled by the archive operators. Whether Dr. Elawady himself cited this study is not established.

What the archive says about the study: Darby 2013 NEJM: in 2,168 breast-cancer radiotherapy patients, major coronary events rose 7.4% per Gray of mean heart dose, linearly, with no threshold ('the heaviest blow').
A. What was actually studied?: Heart dose vs coronary events.
B. What did the authors find?: Linear 7.4%/Gy relative increase.
C. What conclusions do the authors themselves draw?: Heart exposure should be minimised; absolute risk is greater with pre-existing risk factors.
D. What does the archive derive from it?: Radiotherapy causes ischaemic heart disease.
E. Is this derivation scientifically justified?: Correct figure. The Arabic summary speaks of 'per Gray of chest irradiation', but the unit is mean dose to the heart. The archive does not translate the relative figure into absolute risk or mention the breast-cancer deaths prevented by radiotherapy (I-CHM-02).
Adequacy of the interpretation (by the archive): essentially correct but incomplete