Determination of the optimal ultra-low dose protocol in CT-guided transthoracic lung biopsy and evaluation of the effectiveness of this protocol

Objective: The standard protocol routinely applied in CT-guided transthoracic lung biopsy procedure previously and the ultra-low-dose transthoracic CT protocols we have been using from one year were correlated with; technical success rates performing biopsy procedure, reaching diagnosis, comparative evaluation of exposed X-ray doses. Material and Methods: As with other CT procedures, CT-guided lung biopsy procedures in also; scanning parameters such as tube voltage, tube current, pitch value were changed, and a low-dose protocol was developed with iterative reconstruction algorithm modification. Since November 2017, 40 of 183 CT-guided transthoracic lung biopsies were performed with low-dose protocol and 143 with standard protocol over a 3-year period. Image quality was evaluated using subjective and objective methods in both protocols. Histopathological materials of all patients were re-evaluated by microscopic methods and cellular analysis was performed. Diagnostic performance, complication rate and radiation dose were compared in the procedures performed with both protocol groups. Results: The mean effective radiation dose was reduced by 96.8% with the UDD protocol (p <0.001). Although there was a statistically significant deterioration in image quality in the images taken with the UDD protocol in the subjective evaluation, no significant difference was found between the two groups in terms of complication rates, pathological material adequacy and cellular analysis evaluation criteria. In the objective evaluation of image calyste, SNR and CNR ratios in both lung and vertebral corps were significantly higher in the control group (standard dose), while SNR and CNR rates in pectoral muscle and axillary fat tissue were significantly higher in the study group(ultra low dose).Although no statistically significant difference was found between the average number of scans performed during the procedure in both groups (p = 0.296), there was a statistically significant difference between the mean processing times (p <0.001), It was observed that the average time was longer in the procedüres performed with the UDP protocol.Regardless of patient group as the size of the lesion increased, the mean procedure time, effective radiation dose, pneumothorax and parenchymal bleeding decreased. A statistically significant relationship was found between the lengthening of the lesion-to-pleura distance and the increase in the complication rates of pneumothorax and parenchymal hemorrhage. Conclusion: In this TTB protocol using 80 kV tube voltage and 30 mAs tube current, it was found that the the effective radiation dose to which the patient is exposed was significantly reduced without compromising patient-procedure safety and histopathological diagnostic performance. The procedure time and dose was higher in small lesions than in large lesions. Keywords: CT-guided lung biopsy, low-dose, objective image quality, iterative reconstruction, cellular analysis