Application of computed tomography dose index as dosimetric parameter in dental tomography

Aplicação do índice de dose em tomografia computadorizada como parâmetro dosimétrico em tomografia odontológica

ABSTRACT

Objective

Quantify the CTDI from a reference beam, correcting this value for several beam widths from the ratio of CTDI₁₀₀ values measured in the air, and verifying the underestimation of the dose comparing CTDI₁₀₀ and CTDI₃₀₀, applied to dental CBCT.

Methods

i-CAT and Prexion 3D tomographs, 100mm pencil ionization chamber, electrometer. Firstly for beam above 40 mm, CTDI_W,NT from CTDI_W,Ref, multiplied by the ratio of CTDI_AR measurements to N.T widths and reference, was estimated. In second, CTDI₁₀₀ and CTDI₃₀₀ are obtained by displacing the ionization chamber along the beam with spacing intervals equal to 100 mm to cover sufficiently large integration intervals for CBCT protocols, and a comparison is made through the modified efficiency.

Results

CTDI_AR,100,Ref averaged 53% higher than CTDI_W,Ref, due to attenuation of the beam by the simulator object, and the ratio between CTDI_AR,100,Ref and CTDI_W,Ref is greater than 1, being this constant relationship and validating the method for dosimetry in quality control tests. For the second method, CTDI₁₀₀ greatly underestimates the dose deposited on the central axis, where CTDI₃₀₀ covers all beam sizes and stands out in relation to CTDI₁₀₀ to more accurately quantify the radiation levels emitted.

Conclusions

The IEC method is applicable to quality control, facilitating practice, and optimizing time and resources. CTDI₃₀₀ is a better dose descriptor than CTDI₁₀₀, and should be implemented for CBCT modalities when used.

Indexing terms
Cone-beam computed tomography; Dentistry; Dosimetry; Radiography