Status of Study in Dental Cone Beam Computed Tomography Dose Estimation Modes

Flat-panel detector based cone beam computed tomography (CBCT) dental medical imaging (dental CBCT) possesses the characteristics as X-ray beam wide-collimated at Z direction (refer to direction parallel to CT rotation axis), 180 to 360 degree selectable scan angle range, adjustable field of view size, and selectable full-fan or half-fan detector offset modes. Absorbed dose distributions in patient's head caused by dental CBCT are more complex than that caused by multi-detector CT (MDCT) and other clinical CBCTs (eg. CBCT applied to image-guided radiotherapy and interventional surgery etc.). Therefore, an effective and agreed internationally dental CBCT dose estimation mode has not been raised yet. This paper reviews researches on CT dose estimation, and concludes that dental CBCT dose estimation mode consists two interacted layers of dose index and patient medical radiation dose (which indicates effective dose based on population mean dataset and patient specific organ dose). Meanwhile, this review reaches results as follows. The key problem for dental CBCT dose index is how to depict absorbed dose distributions at phantom central plane being vertical to Z direction when an uniform cylindrical phantom is scanned. Area average absorbed dose is the most promising dose index to this problem. Dental CBCT can apply MDCT's patient medical radiation dose estimation theories directly, except for one problem remains to be solved. That is how to get exact patient's attenuation information for specific X-ray source. Meanwhile, dental CBCT dose estimation mode should explore the influence caused by heel effect and cone angle effect of cone shape X-ray beam.