Room: Exhibit Hall | Forum 1
Purpose: CT colonography (CTC) is a less invasive alternative to colonoscopy for colorectal cancer screening. Because there is no iodinated contrast used in CTC, spectral pre-filtration with a tin filter has the potential to reduce dose while maintaining image quality by removing low-energy photons from the spectrum normally needed in contrast-enhanced CT scans to increase contrast signal. The purpose of this study is to investigate the effect of the hardened energy spectra on organ and effective dose across a wide range of patient sizes for potential use in CTC.
Methods: Our study included 53 patient models from the extended cardiac-torso family (weight: 126.8-287.5 lbs, diameter: 23-39 cm). Using a Monte Carlo program previously validated for a 96-row CT system (SOMATOM Force, Siemens Healthineers, Forchheim, Germany), CTC scans were simulated to cover the abdomen-pelvis region. Simulations were performed for each patient model and three spectra: the conventional 120kV, 100kV with tin (100Sn), and 150kV with tin (150Sn). Colon dose and effective dose were normalized by volume CT dose index (CTDI(vol)) and dose length product (DLP), respectively, and compared for the spectra.
Results: For a given spectrum, CTDI(vol)-normalized colon dose generally decreased with increasing patient diameter. Compared to 120 kV, the rate of dose decrease was slower for the pre-filtered spectra (100Sn and 150Sn kV). For a given patient model, CTDI(vol)-normalized colon dose was generally the highest at 150Sn kV and the lowest at 120 kV; however, these were many exceptions to this general trend. In contrast, DLP-normalized effective dose increased consistently with increasing spectral hardness. Compared to 120 kV, normalized effective dose was 6-26% higher at 100Sn kV and 11-41% higher at 150Sn kV.
Conclusion: In CT colonography, spectral pre-filtration generally results in higher colon dose for the same CTDI(vol) and consistently higher effective dose for the same DLP.