Keywords:
Radioprotection / Radiation dose, CT, Diagnostic procedure, Radiation safety, Dosimetric comparison
Authors:
P. GARCIA CASTAÑON, I. Salmerón Béliz, G. Paradela Díaz, R. Rosado del Castillo, P. Chamorro, S. HONORATO HERNANDEZ, C. PRIETO MARTIN
Results or findings
Table 2 shows the number of scans considered for each indication to evaluate median doses and the number of outliers extracted.
4 out of 10 indications presented a median DLP value above the corresponding EUCLID DRLs and have led to a revision of the protocol parameters: chronic sinusitis, coronary angiography, hepatocellular carcinoma staging and oncological staging of lung cancer. Table 3 shows median values compared to DRLs.
Doses from chronic sinusitis and oncological staging have been optimised by increasing the noise index, which was fixed for those protocols over the GE recommendations. For chronic sinusitis, this increase in the noise index was drastic, changing from 3.80 to 9.6. This index of 9.6 corresponds to neck protocols, and it has been chosen taking into account that imaging needs for a sinus CT is not comparable to a brain CT. Median dose fell from 730 mGy.cm to 139 mGy.cm (82%), and is now below EUCLID DRL. Besides, the aforementioned radiologists state that image quality remains adequate, according to a clinical evaluation.
For oncological staging of lung cancer, variation in the noise index has been slighter. Abdomen series have not been modified for the moment, with noise index already at the suggested value of 15.86, but for thorax series, it has been raised from 12 to 15.86, a value also recommended for chest protocols. The overall dose reduction was of about 19%, yield in a median value of 850 mGy.cm, which is still over the EUCLID DRL. A further optimization is currently being developed, based on other parameters like level of iteration or kV. At the moment, radiologists also consider image quality optimal.
Since abdomen series are actually at the recommended noise index, the optimization of hepatocellular carcinoma requires further investigation. We are working on the effect of slice width and other parameters such as the number of series performed within a protocol.
For coronary angiography, doses have not been yet optimized because it involves some extra complexity and it will be performed throughout this year.