The presence of contrast agent increases organ radiation dose in contrast-enhanced CT
Mahta Mazloumi, Gert Van Gompel, Veerle Kersemans, Johan De Mey, Nico Buls
Abstract
Abstract Objectives Routine dosimetry calculations do not account for the presence of iodine in organs and tissues during CT acquisition. This study aims to investigate the impact of contrast agent (CA) on radiation dose. Methods First, relation between absorbed radiation dose and iodine concentrations was investigated using a cylindrical water phantom with iodine-saline dilution insertions. Subsequently, a retrospective study on abdominal dual-energy CT (DECT) patient data was performed to assess the increase of the local absorbed radiation dose compared to a non-contrast scan. Absorbed doses were estimated with Monte Carlo simulations using the individual CT voxel data of phantom and patients. Further, organ segmentations were performed to obtain the dose in liver, liver parenchyma, left kidney, right kidney, aorta, and spleen. Results In the phantom study, a linear relation was observed between the radiation dose normalized by computed tomography dose index (CTDI) and CA concentrations I conc (mg/ml) for three tube voltages; $$ \frac{D_{80 kVp}}{CTDI_{vol}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mfrac><mml:msub><mml:mi>D</mml:mi><mml:mrow><mml:mn>80</mml:mn><mml:mi>kVp</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mtext>CTDI</mml:mtext><mml:mi>vol</mml:mi></mml:msub></mml:mfrac></mml:math> = 0.14 × I conc + 1.02, $$ \frac{D_{120 kVp}}{CTDI_{vol}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mfrac><mml:msub><mml:mi>D</mml:mi><mml:mrow><mml:mn>120</mml:mn><mml:mi>kVp</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mtext>CTDI</mml:mtext><mml:mi>vol</mml:mi></mml:msub></mml:mfrac></mml:math> = 0.16 × I conc + 1.21, $$ \frac{D_{140 kVp}}{CTDI_{vol}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mfrac><mml:msub><mml:mi>D</mml:mi><mml:mrow><mml:mn>140</mml:mn><mml:mi>kVp</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mtext>CTDI</mml:mtext><mml:mi>vol</mml:mi></mml:msub></mml:mfrac></mml:math> = 0.16 × I conc + 1.24, and for DECT acquisition; $$ \frac{D_{DECT}}{CTDI_{vol}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mfrac><mml:msub><mml:mi>D</mml:mi><mml:mtext>DECT</mml:mtext></mml:msub><mml:msub><mml:mtext>CTDI</mml:mtext><mml:mi>vol</mml:mi></mml:msub></mml:mfrac></mml:math> = 0.15 × I conc + 1.09. Similarly, a linear relation was observed between the dose increase and the organ iodine contents ( R 2 = 0.86 and p value < 0.01) in the patient study. The relative doses increased in the liver (21 ± 5%), liver parenchyma (20 ± 5%), right kidney (37 ± 7%), left kidney (39 ± 7%), aorta (34 ± 6%) and spleen (26 ± 4%). In addition, the local dose distributions changed based on patient’s anatomy and physiology. Conclusions Compared to a non-contrast scan, the organ doses increase by 30% in contrast-enhanced abdominal CT. This study suggests considering CA in dosimetry calculations, epidemiological studies, and organ dose estimations while developing new CT protocols. Key Points • The presence of contrast media increases radiation absorption in CT, and this increase is related to the iodine content in the organs. • The increased radiation absorption due to contrast media can lead to an average 30% increase in absorbed organ dose. • Iodine should be considered in CT radiation safety studies .