Radiation doses from routine dental imaging often raise questions and concerns among patients. As dentists increasingly embrace advanced dental imaging techniques, it's crucial to describe how these techniques differ in radiation doses compared to conventional intraoral and extraoral dental imaging.
The effective dose is the primary metric for describing radiation dose, as it factors in tissue weighing in the human body and signifies the probability of stochastic, or cancer-causing, effects. It's units are sieverts, which can then be compared to background radiation equivalent time, or low levels of radiation exposure from non-intentional radiation sources.
Consider this: An FMX with a digital (CCD) sensor using rectangular collimation has an effective dose of 20 microsieverts (µSv), equivalent to 2.5 days of background radiation. A panoramic radiograph has an effective dose of 20 µSv, also equivalent to 2.5 days of background radiation.
When delving into CBCT, the effective dose is contingent on various factors
- Field of view
- Resolution
- kVp, mA, and time (modifiable depending on the machine)
- Pre-set low-dose or high-dose protocols, machine-dependent
- Pre-set parameters for kids, small, medium, or large adults
- Specific CBCT models
For the Carestream CS 9300 model, an adult low dose CBCT scan of 5 x 5cm has an effective dose of 3 µSv, or 8.5 hours of equivalent background radiation. A larger volume size, such as a 10 x 10cm, is 75 µSv, or 9 days.
Source: https://www.carestreamdental.c...
Let's compare the Planmeca ProMax 3D Classic as well. For a small field of view CBCT volume such as a 4 x 5 cm, it would be 13 µSv or 1.5 days worth. To capture both arches with an 8 x 8 cm field of view, it would be 36 µSv or 4 days worth.
Source: https://www.planmeca.com/globa...
Image quality and effective dose are interconnected. For superior spatial resolution and better visualization of fine details, effective dose must increase. This is usually recommended if scans are taken for endodontic purposes. To trace small canals more clearly, a high-resolution scan should be taken which would increase the effective dose. On the other hand, if a scan is required for implant planning and assessment of bony arcithecture and alveolar ridge dimensions, fine details may be less critical and dentists can opt for a lower-resolution setting.
Protecting patients and limiting necessary radiation dose is a paramount duty. The principles of ALARA/ALADA (As Low As Reasonably Achievable/As Low As Diagnostically Acceptable) apply when prescribing radiographs. Dentists should minimize the radiation dose to patients if possible while obtaining diagnostically acceptable radiographs. Selection criteria and using the right parameters for CBCT scans should adapt depending on the patient and purpose at hand.
References: Table 3.2 in White and Pharoah's Oral Radiology 8th Edition is written by Sanjay Mallya, Ernest Lam