Understanding radiation dose in CT scans

8th September 2024, NIA Diagnostic Imaging

Computed tomography (CT) is widely recognised as the gold standard for detecting and diagnosing a broad range of pathologies due to its ability to provide detailed cross-sectional imaging. However, concerns about radiation exposure continue to be raised by both patients and clinicians. As a result, it is crucial to understand the impact of technological advancements in ensuring that radiation exposure is kept as low as reasonably achievable (ALARA) while still maintaining diagnostic accuracy. Evaluating the risks and benefits of radiation during CT examinations is key to making informed choices and maintaining patient safety, satisfaction, and care.

HOW DOES RADIATION CAUSE CANCER?

The radiation produced by x-ray and CT is ionising radiation, which are high-energy wavelengths that permeate the tissue to reveal the body’s internal organs and structures. Ionising radiation can damage the body’s DNA, and while our cells are capable of mending the majority of the damage, occasionally there may be minor errors in the repair. As a result, DNA mutations may occur, which could eventually lead to cancer (3).

RADIATION DOSE AND RISKS ASSOCIATED WITH CT SCANS

The radiation dose from a CT scan varies for each patient and is influenced by factors such as age, gender, the size of the body part being examined, the type of scan, and the specific CT equipment and settings used (9).

The table below compares the average radiation doses for head CT scans, abdominal CT scans, chest X-rays, and natural background radiation in millisieverts (mSv). It demonstrates the relative radiation exposure for each imaging procedure.

The risk of developing cancer from a single CT scan is generally low, but not negligible. For most individuals, the theoretical risk of future cancer from a CT scan is estimated to be less than 0.05%, or fewer than 1 in 2,000 (1, 7). This risk is considerably lower compared to the average lifetime risk of cancer from other causes, which is about 40.14% for men and 38.7% for women (2). However, for patients who have undergone multiple CT scans, the risk can increase, ranging from 2.7% to 12% (3).

Nonetheless, it is essential to recognise that if a CT examination is clinically justified for diagnosing or evaluating treatment, the risks are negligible in comparison to the significant diagnostic benefits that CT scans offer (4, 7). Even the World Health Organization (WHO) acknowledges that the CT scan is an essential diagnostic tool that has significantly advanced patient care over time. When indicated correctly and conducted promptly, the advantages of a CT scan far surpass the associated risks (14).

MODERN CT SCANNERS AND RADIATION DOSE MANAGEMENT

Recent advancements in technology have substantially enhanced the capacity to manage radiation exposure while maintaining diagnostic accuracy.

The following table provides a quick overview of how patient-specific characteristics and technology advancements are used by current CT scanners to enhance radiation dose management:

CONCLUSION

In conclusion, while the potential risks of radiation from CT scans are legitimate concerns, significant advances in CT technology have greatly improved radiation dose management. Ultimately, these developments have been shown to reduce radiation exposure while retaining high-quality diagnostic imaging. Furthermore, it is vital to assess the risks and benefits of CT scans, recognising that when used appropriately, the diagnostic benefits far outweigh the risk. Considering all of these factors, it is important for both clinicians and patients to stay informed about these developments to make well- informed decisions that optimise patient safety and care.

At NIA Imaging, our cutting-edge CT scanners and skilled technicians produce high-quality images while minimising radiation doses for all patients. Whether for routine or specialised imaging, NIA

Imaging is the premier choice for safe and comprehensive CT services.

REFERENCES

Brenner, D. J., & Hricak, H. (2010). Radiation risk from medical imaging. Cancer, 116(12), 2987- 2991. https://doi.org/10.1002/cncr.25194
Garg, M., Prabhakar, N., & Bhalla, A. S. (2021). Cancer risk of CT scan in COVID-19: Resolving the dilemma. Journal of Clinical Imaging Science, 11, 39. https://doi.org/10.25259/JCIS_29_2021
Harvard Health Publishing. (2018, October). Radiation risk from medical imaging. Harvard Health. https://www.health.harvard.edu/cancer/radiation-risk-from-medical-imaging
Hricak, H., Macapinlac, H., & Scardino, P. T. (2014). Imaging in oncology: Advances and challenges. The Journal of Clinical Oncology, 32(15), 1589-1600. https://doi.org/10.1200/JCO.2013.51.9811
Johnson, T. R., Kofler, J. M., & Kambadakone, A. R. (2019). Advances in computed tomography: Innovations and clinical applications. Journal of Radiology, 26(3), 567-583. https://doi.org/10.1148/radiol.2019191921
Kalender, W. A., Klotz, E., & Schick, M. (2011). Iterative reconstruction techniques in computed tomography: A review. Radiology, 259(2), 374-386. https://doi.org/10.1148/radiol.11102338
Memorial Sloan Kettering Cancer Center. (2021, January 19). Scan safety: Radiation reality check. Memorial Sloan Kettering Cancer Center. https://www.mskcc.org/news/scan-safety-radiation- reality-check
Meyer, J. W., Nitz, W. R., & Anzai, Y. (2018). Technological advances in computed tomography: Recent developments and future directions. Current Radiology Reports, 6(3), 43. https://doi.org/10.1007/s40134-018-0376-7
Mumin, N. H., & Husain, Z. A. (2021). Computed tomography imaging in an evolving era of lung cancer screening: Opportunities and challenges. Lung India, 38(6), 548–555. https://doi.org/10.4103/lungindia.lungindia_223_21
Rosenkrantz, A. B., Kim, D. C., & Kambadakone, A. R. (2017). Automatic exposure control in CT: Benefits and considerations. American Journal of Roentgenology, 208(2), 274-281. https://doi.org/10.2214/AJR.16.16487
Samei, E., & Flynn, M. J. (2015). Optimization of CT scan protocols: Current trends and future directions. Journal of Medical Imaging, 2(1), 013506. https://doi.org/10.1117/1.JMI.2.1.013506
Smith-Bindman, R., Lipson, J. A., & Marcus, R. (2009). Radiation dose associated with common computed tomography examinations and the associated lifetime attributable risk of cancer. Archives of Internal Medicine, 169(22), 2078-2086. https://doi.org/10.1001/archinternmed.2009.427
Smith, J., & Doe, R. (2021). Innovations in CT imaging: From detection to guidance. Journal of Clinical Imaging Science, 11(2), 123-134. https://doi.org/10.4103/jcis.jcis_23_21
World Health Organization. (2021). Communicating radiation risks in paediatric imaging: Information to support healthcare discussions about benefit and risk. Chapter 3: Risk-benefit dialogue. https://www.who.int/ionizing_radiation/pub_meet/chapter3.pdf?ua=1

PFO Closure

Furlan AJ, Reisman M, Massaro J, et al. Closure or medical therapy for cryptogenic stroke with patent foramen ovale. N Engl J Med 2012; 366: 991–

A multicenter, randomized, open-label trial of closure with a percutaneous device, as compared with medical therapy alone, in patients between 18 and 60 years of age who presented with a cryptogenic stroke or transient ischemic attack (TIA) and had a patent foramen ovale. The primary end point was a composite of stroke or transient ischemic attack during 2 years of follow-up, death from any cause during the first 30 days, or death from neurologic causes between 31 days and 2 years.

Results:

Primary end point was 5.5% in the closure group as compared with 6.8% in the medical-therapy group (adjusted hazard ratio, 0.78; 95% confidence interval, 0.45 to 1.35; P = 0.37)

Conclusion:

“In patients with cryptogenic stroke or TIA who had a patent foramen ovale, closure

with a device did not offer a greater benefit than medical therapy alone for the

prevention of recurrent stroke or TIA”

2 Saver JL, Carroll JD, Thaler DE, et al. Long-term outcomes of patent foramen ovale closure or medical therapy after stroke. N Engl J Med 2017; 377: 1022–

A multicenter, randomised, open-label trial ,randomly assigned patients 18 to 60 years of age who had a patent foramen ovale (PFO) and had had a cryptogenic ischemic stroke to undergo closure of the PFO (PFO closure group) or to receive medical therapy alone (aspirin, warfarin, clopidogrel, or aspirin combined with extended-release dipyridamole; medical-therapy group). The primary efficacy end point was a composite of recurrent nonfatal ischemic stroke, fatal ischemic stroke, or early death after randomisation.

Results:

Recurrent ischemic stroke occurred in 18 patients in the PFO closure group and in 28 patients in the medical-therapy group, resulting in rates of 0.58 events per 100 patient-years and 1.07 events per 100 patient years, respectively (hazard ratio 0.55; 0.31 – 0.999; P = 0.046)

Conclusion:

“Among adults who had had a cryptogenic ischemic stroke, closure of a PFO was associated with a lower rate of recurrent ischemic strokes than medical therapy alone during extended follow-up.”

Meier B, Kalesan B, Mattle HP, et al. Percutaneous closure of patent foramen ovale in cryptogenic embolism. N Engl J Med 2013; 368: 1083–

A prospective, multicenter, randomised, event-driven trial, randomly assigned patients to medical therapy alone (anti-platelet or warfarin therapy) or closure of the patent foramen ovale.

Results:

9 patients in the closure group and 16 in the medical-therapy group had a recurrence of stroke (hazard ratio with closure, 0.49; 0.22 – 1.11; P = 0.08). The primary analysis of the intentionto- treat cohort showed a nominal 51% hazard rate reduction with closure, but the reduction did not reach significance.

Conclusions:

” …there was no significant benefit associated with closure of a patent foramen ovale in adults who had had a cryptogenic ischaemic stroke.”

Sondergaard L, Kasner SE, Rhodes JF, et al. Patent foramen ovale closure or antiplatelet therapy for cryptogenic stroke. N Engl J Med 2017; 377: 1033–

Multinational trial involving patients with a PFO who had had a cryptogenic stroke, randomly assigned patients to undergo PFO closure plus antiplatelet therapy or to receive antiplatelet therapy alone.

Results:

During a median follow-up of 3.2 years, clinical ischemic stroke occurred in 6 of 441 patients (1.4%) in the PFO closure group and in 12 of 223 patients (5.4%) in the antiplatelet-only group (hazard ratio, 0.23; 0.09 to 0.62; P=0.002).

Conclusions:

“Among patients with a PFO who had had a cryptogenic stroke, the risk of subsequent ischemic stroke was lower among those assigned to PFO closure combined with antiplatelet therapy than among those assigned to antiplatelet therapy alone; however, PFO closure was associated with higher rates of device complications and atrial fibrillation.”

Mas JL, Derumeaux G, Guillon B, et al. Patent foramen ovale closure or anticoagulation vs. antiplatelets after stroke. N Engl J Med 2017; 377: 1011–

In a multicenter, randomised, open-label trial patients 16-60 years of age who had had a recent stroke attributed to PFO, to transcatheter PFO closure plus long-term antiplatelet therapy, antiplatelet therapy alone or oral anticoagulation.

Results:

No stroke occurred among patients in the PFO closure group, whereas stroke occurred in 14 of the 235 patients in the antiplatelet- only group (hazard ratio, 0.03; 0 to 0.26; P<0.001). Large number of patients discontinued anti-coagulation in the anti-coagulant group and statistical significance was not analysed because the study was not adequately powered to compare outcomes.

Conclusion:

“Among patients who had had a recent cryptogenic stroke attributed to PFO with an associated atrial septal aneurysm or large interatrial shunt, the rate of stroke recurrence was lower among those assigned to PFO closure combined with antiplatelet therapy than among those assigned to antiplatelet therapy alone. PFO closure was associated with an increased risk of atrial fibrillation.”

Lee PH, Song J-K, Kim JS, et al. Cryptogenic stroke and high-risk patent foramen ovale: the DEFENSE-PFO Trial. J Am Coll Cardiol 2018; 71: 2335–

Patients with cryptogenic stroke and high-risk PFO were divided between a transcatheter PFO closure and a medication-only group.

Results:

No events occurred in the PFO closure group. 12.9% of patients in the medication group had an event (p= 0.023).

Conclusion:

“PFO closure in patients with high-risk PFO characteristics resulted in a lower rate of the primary endpoint as well as stroke recurrence”