Monte Carlo Assessment of Pediatric Patient Dose In Tin-Filtered High-Pitch CT
Abstract
Purpose
High-pitch dual-source acquisition (“FLASH”) with tin spectral filtration has substantially reduced radiation dose while minimizing patient motion, both of which are particularly important for pediatric imaging. However, in adults, tin-filtered spectra have been shown to yield higher radiation dose conversion coefficients compared with conventional spectra. The purpose of this study was to use Monte Carlo simulation to quantify pediatric organ and effective doses in tin-filtered FLASH CT protocols across common anatomic regions.
Methods
A previously validated Monte Carlo framework modeling a dual-source CT system (SOMATOM Force, Siemens Healthineers) was used to simulate CT examinations using ICRP reference pediatric extended cardiac–torso (XCAT) phantoms representing ages of newborn, 1, 5, 10, and 15 years. High-pitch FLASH acquisitions (pitch = 3) were simulated using conventional spectra (100 kV and 120 kV) and tin-filtered spectra (100Sn and 150Sn) for head, neck, head-neck, chest, abdomen-pelvis, pelvis, and chest-abdomen-pelvis examinations. To reduce angular bias, each scan was repeated with 12 uniformly-distributed tube starting angles. Angle-averaged CTDIvol-normalized organ doses (h-factor) and DLP-normalized effective doses (k-factor) were compared across the different spectra.
Results
Across all anatomic regions, pediatric k-factors decreased with increasing age, with reductions of 26.2%–41.5% between successive age groups. The dependence of k-factors on beam hardness was age dependent: k-factors decreased with increasing beam hardness (100 kV, 120 kV, 100Sn, 150Sn) for newborn, were relatively insensitive to beam hardness for 1-year, and increased with increasing beam hardness for 5-, 10-, and 15-year. Pediatric h-factors demonstrated similar age- and beam-hardness–dependent behavior, with most organs exhibiting a crossover in beam-hardness dependence near the 1-year phantom. Breast tissue showed increasing h-factors with beam hardness across all ages, whereas bone surface showed decreasing h-factors.
Conclusion
Radiation dose conversion coefficients for tin-filtered FLASH CT are strongly age dependent in pediatric imaging, with trends differing from those reported in adult studies.