New Advances in CT Dosimetry: The Planar Average Equilibrium Dose

Abstract

Background: The basis for the current output dose measurement in CT is the computer tomography dose index (CTDI). Modern CT scanners with helical scanning modes, dosage modulation, array detectors, multiple slice planes, or cone-beam irradiation geometries are incompatible with the conventional methods for measuring CT dosimetric performance. The AAPM TG 111 study acknowledged the shortcomings of the CTDI methods and suggested a new method that uses a short conventional ion chamber instead of a pencil chamber and better characterizes the dose profile from contemporary CT scanners.
 
 Materials and Methods: Three different anatomical regions (head, chest, and abdomen) of clinical scan sequences were used to build and characterize an in-house phantom design. The equilibrium dosage in our phantom was estimated to determine whether the attenuation of the beam was the same as that of the CTDI phantom. The obtained measurements were compared to those of the CTDI dose estimates made using a conventional pencil chamber.
 
 Results: The proposed method allowed the assessment of the equilibrium dosage as well as the accumulation dose for any clinical scan length. By contrast, the CTDI approach can underestimate the dose by 25% to 35% according to our revised methodology
 
 Conclusion: The CTDI measurements could no longer be sufficient, and the informed CTDI tends to underestimate the dose provided.