From the Guidelines
The typical radiation dose for a lumbosacral CT scan ranges from 5 to 10 millisieverts (mSv), though this can vary depending on the specific protocol, equipment, and patient factors. This dose is higher than a standard X-ray (which delivers about 1.5 mSv for the lumbar spine) but lower than many other CT examinations. The radiation exposure occurs because CT scanners use X-rays to create detailed cross-sectional images of the spine, allowing visualization of bone, soft tissue, and neural structures. Factors that affect the radiation dose include the scan length, slice thickness, tube current, and whether dose reduction techniques are employed. Modern CT scanners often incorporate dose reduction technologies such as iterative reconstruction algorithms and automatic exposure control to minimize radiation while maintaining diagnostic image quality. For context, the average person receives about 3 mSv annually from natural background radiation. While the benefits of obtaining accurate diagnostic information typically outweigh the risks of radiation exposure for patients with appropriate clinical indications, healthcare providers should follow the ALARA principle (As Low As Reasonably Achievable) when ordering imaging studies to minimize unnecessary radiation exposure, as supported by the American College of Cardiology task force on expert consensus decision pathways 1.
Some key considerations for minimizing radiation dose in CT scans include:
- Scan length: keeping the scan length to a minimum to encompass only the anatomy of interest
- X-ray beam intensity: adjusting the x-ray tube potential and current to minimize radiation exposure
- Rotation time: selecting the optimal rotation time to minimize exposure
- X-ray beam filtration: using filters to selectively attenuate low-energy x-rays that contribute to radiation dose
- Scan acquisition mode: selecting the acquisition mode that delivers the lowest dose while producing similar images, as discussed in the 2018 ACC/HRS/NASCI/SCAI/SCCT expert consensus document on optimal use of ionizing radiation in cardiovascular imaging 1.
It's worth noting that the risks associated with radiation exposure from CT scans are still being studied, and while there is evidence that high doses of radiation can increase the risk of cancer, the risks associated with lower doses are still unclear, as discussed in the American College of Radiology white paper on radiation dose in medicine 1 and the Radiation Dose Summit proceedings 1. However, by following the ALARA principle and using dose reduction techniques, healthcare providers can minimize unnecessary radiation exposure and reduce the risks associated with CT scans.
From the Research
Radiation Dose for Lumbosacral CT Scan
- The radiation dose for a lumbosacral (lower back and sacrum) Computed Tomography (CT) scan can be reduced by using various techniques such as automatic exposure control (AEC) and considering the patient's body mass index (BMI) 2.
- A study found that the combined use of BMI and AEC can reduce the radiation dose of CT volume scans of the lumbar spine without compromising image quality 2.
- The effective dose for low dose CT of the lumbar spine can be as low as 1.0-1.1 mSv, which is comparable to or even lower than the dose from radiography (0.7 mSv) 3.
- Task-specific CBCT protocols for lumbar bone visualization can have a dose as low as 3.2 mGy, while soft-tissue visualization protocols can have a dose of 10.6 mGy or lower (5.1 mGy for lower-resolution protocols) 4.
- General guiding principles for reducing dose in CT scans include tailoring the scan to the patient, minimizing scan length, using tube current modulation, and minimizing tube current and potential 5.
Dose Reduction Techniques
- Dose reduction techniques such as iterative reconstruction and periodic review of CT studies can also be effective in reducing radiation dose 5, 6.
- The use of artificial intelligence and photon counting CT may also have potential for dose reduction in the future 6.
- Organized efforts for standardization of CT protocols, led by professional societies, can help minimize dose while maintaining image quality 5.