engleski

Which dose index should be used for establishing DRL in dental CBCT?

BACKGROUND/INTRODUCTION: Different performance of devices used in case of patients undergoing dental cone beam computed tomography (CBCT) examinations as well as procedure itself may result in complex dose distribution within the patient. At the moment, depending on publication, three dosimetric quantities (dose indices) are suggested to be used as representation of patient dose: CT dose index (CTDI), CBCT dose indices (CBCTDI1 and CBCTDI2) or dose-area product (DAP). Since it was previously explained why CTDI should not be used as dose index in case of dental CBCT, the aim of study was to investigate DAP and CBCT dose indices and to propose one which should be used for establishing diagnostic reference levels (DRLs) in dental CBCT. DESCRIPTION OF ACTIVITY AND WORK PERFORMED: For the purpose of investigation, Monte Carlo simulation was used and experimental measurements were performed. CBCT dental unit was simulated using Monte Carlo N-Particle transport code (MCNP® 6.1.1beta) and model verification was performed using PMMA head CTDI phantom and radiochromic films. For calculation of organ doses and for the assessment of effective doses computational anthropomorphic phantom was used („Zubal“). Most often clinical protocols involving different exposure geometries including sizes and positions of fields of view (FOV) and different tube current-exposure time products (mAs) were simulated. Simulations were performed for both, 180o and 360o of X-ray tube rotation and in all cases for the X-ray tube voltage of 90 kV. DAP was measured using DAP-meter (VacuTec, Germany). CBCT dose indices were calculated using doses obtained by simulation. In case of CBCTDI1, simulations were performed in 15 points along the diameter line. Measured DAP and calculated CBCT dose indices were compared to effective doses for every exposure geometry and analysed. A strong linear correlation between DAP and effective dose exists for all FOVs. Better correlation was found in cases of FOVs positioned on maxilla which can be explained by strong influence of distance of the FOV position from thyroid gland. In case of CBCT dose indices, correlation between these dose indices and effective dose is weaker. As described earlier, obtaining values of CBCT dose indices requires more time and more complex measuring and calculating procedure when compared to obtaining values of DAP. Since dose index used to represent the dose to the patient should be easily measurable, based on the results of this study, we propose DAP to be used as dose index in case of dental CBCT examinations. CONCLUSION AND RECOMMENDATIONS: Because DAP is easily measurable and it shows strong linear correlation with effective dose, it should be used for establishing DRL in case of dental CBCT examinations.

Clinical diagnostic reference levels (DRLs), Radiation physics, Cone beam CT, Diagnostic procedure

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