One of the main goals of diagnostic radiology is to acquire high-quality images with a low dose of radiation, as high-quality images enable radiologists to make meaningful diagnoses, and low doses of radiation keep patients safe.

But what exactly defines a “low-dose CT scan”? Is it 10 mGy, 12 mSv, or 1 rad? Or 300 mGy-cm? What is considered a concerning amount of radiation? Understanding radiation dosage can be complicated, even for radiologists.¹

Radiation dosage calculator—putting patient safety concerns into perspective

Although humans are exposed to radiation from many sources, medical imaging comprises the largest total source of radiation exposure for most people. For example, the US agency in charge of radiation estimates that a typical chest CT scan may come with an absorbed dose of 7 mGy.²

To put it into perspective, the average annual dose of radiation to a person in the US from all sources (excluding medical imaging) is around 620 mrem (6.2 mGy)—less than a single “typical” chest CT.² To find a rough estimate of your yearly radiation exposure, try this dosage calculator from the EPA.

Large government organizations and public health initiatives rely on the average or typical dosage, but in reality, there is a huge degree of variation. One recent study that reported the range of radiation dosages for chest CT scans included values from 5 mGy to 24 mGy. Some of this variation is accounted for by the patient’s diameter, the use of contrast materials, and whether angiography was performed.³ However, significant differences persist both within and between facilities, though exactly how much difference depends on how it is measured.

Thinking about radiation dosages—the science behind variation

Radiation energy creates measurable effects on the materials it passes through, but since these effects vary based on the type of material and are measured in different ways, it’s difficult to assign a simple, single unit of radiation dosage. Unfortunately, dosing radiation is just not as simple as dosing a medication measured in grams.

The table below helps compare how radiation units are used. When CT scanners are calibrated, the radiation output is measured in air, and using a phantom, or Lucite (polymethylmethacrylate) tube of a given length and width. Although phantoms scatter energy beams in a way somewhat like a human body would, they are obviously imperfect.⁴

Table adapted from https://pubs.rsna.org/doi/full/10.1148/radiol.14132328.

To more accurately reflect cancer risks to patients, an effective dose or dose equivalent can be calculated. The effective dose of radiation a patient is exposed to may vary quite dramatically even with the same emitted dose and type of radiation, based on the patient’s size, density, the organs scanned, and the length of the scan. In fact, the CTDI may underestimate or overestimate a patient’s exposure to radiation, sometimes by as much as 40%.⁴

Despite this amount of possible variation, most machines report CTDI which makes it a useful metric to compare machines, protocols, and facilities.

How does my hospital perform?

Since 2011, facilities have had the option to submit their radiation data to the Dose Index Registry, a collection of CTDI information across facilities, maintained by the American College of Radiology (ACR).

There are many reasons a facility may choose to do this, including ensuring patient safety, accessing national data for research, fulfilling Merit-Based Incentive Performance System (MIPS) requirements, and Joint Commission benchmarks as well as meeting Maintenance of Certification (MOC) Part IV for individual radiologists.

Since the registry’s inception, the amount of variation between facilities has been quantified across all types of CT scans, and some of that data can be seen here.

As alluded to earlier, there are large differences between and within facilities regarding radiation dosage and dose reduction efforts. One study found dosage differences of 13-fold, on average, within each CT study type.³

Maintaining diagnostic image quality

Many facilities have found ways to achieve acceptable images with lower doses of radiation. Perhaps some of them have newer scanners, or better radiologists. It’s likely that differing protocols impact results as well, especially when decisions about settings are made without understanding how they impact the patient’s total radiation exposure.¹

However, there is one solution that no one concerned with patient safety should overlook—reconstruction algorithms—specifically PixelShine^®. This vendor-agnostic, AI-driven solution provides high-quality images by de-noising  noisy images, works with older CT scanners, and likely fits within imaging facility's  budget.

For more information or to set up a demonstration, contact us today.

References

1. Mayo-Smith WW, Hara AK, Mahesh M, Sahani DV, Pavlicek W. How I do it: Managing radiation dose in CT. Radiology. 2014;273(3):657-672. https://doi.org/10.1148/radiol.14132328
2. US Nuclear Radiation Commission. Doses in our daily lives. NRC Web. https://www.nrc.gov/about-nrc/radiation/around-us/doses-daily-lives.html
3. Smith-Bindman R, Lipson J, Marcus R, et al. Radiation dose associated with common computed tomography examinations and the associated lifetime attributable risk of cancer. Arch Intern Med. 2009;169(22):2078-2086. https://dx.doi.org/10.1001%2Farchinternmed.2009.427
4. McCollough CH, Leng S, Yu L, Cody DD, Boone JM, McNitt-Gray MF. CT dose index and patient dose: They are not the same thing. Radiology. 2011;259(2):311-316. https://doi.org/10.1148/radiol.11101800
5. Kessler C, Burns D. MEASURING CONDITIONS AND UNCERTAINTIES FOR THE COMPARISON AND CALIBRATION OF NATIONAL DOSIMETRIC STANDARDS AT THE BIPM. BUREAU INTERNATIONAL DES POIDS ET MESURES; 2018. https://www.bipm.org/documents/20126/27085544/bipm+publication-ID-3145.pdf/ccddce92-aa6c-07ab-3792-4b3c88d8340a. (https://www.bipm.org/en/dosimetry)