Evaluation of CT Scatter and Attenuation for Fast Kvp-Switching, Tin-Filtered, and Dual-Source CT Scanners
Abstract
Purpose
Assess whether current shielding methods for reducing scattered X-ray radiation in CT scans are appropriate for newer CT technologies, such as systems that use rapidly alternating X-ray tube voltage (fast kVp-switching), tin-filtered, or dual X-ray sources (dual-source) CT scanners.
Methods
Multiple acquisition modes were used on two CT scanners: the GE CT750HD and the Siemens Force. These modes included fast kVp-switching, tin filtration, dual-source, and conventional 120kVp operation. The maximum scatter fraction (μSv/DLP) at 1m was found and compared with the British Institute of Radiology (BIR) shielding guidance values. A wooden box lined with 1.6mm Pb (3.0mm Pb on the side facing the scanner) was built and positioned 1.5m from the CT scanning isocenter. The box had an opening fitted to a pressurized survey meter. Different thicknesses of lead sheets were placed over the opening to measure transmission values and then compared to the NCRP Transmission models.
Results
Both systems showed maximum scatter fractions below the BIR guideline, with the exception of the tin-filtered 120kVp. For the GE system, transmission for single and fast kVp-switching stayed below the NCRP reference model. On the Siemens machine, scatter from single and dual-source scanning also remained below this threshold. However, when using tin-filter modes, scatter transmission exceeded the NCRP model.
Conclusion
This study demonstrates that fast kVp-switching and dual-source CT scanners meet established shielding requirements and stay below NCRP transmission model curves and the BIR max scatter fraction. In contrast, tin-filtered modes demand thicker lead than these models predict. Scanners frequently using tin filtration, such as those in lung screenings, might require additional lead shielding to protect staff and the public from scattered radiation. Future studies will evaluate other advanced CT technologies, including split-filter and photon-counting systems, and the impact of thicker lead shielding.