AUA QI Summit 2017: Practical Issues in CT Dose Optimization

Linthicum, Maryland ( Dr. George Fung, who is the CT R&D Collaboration Manager at Siemens, as well as an adjunct Assistant Professor of Radiology at Johns Hopkins University, discussed practical issues in CT dose optimization, noting that the historical perspective of CT imaging started with the introduction of brain scans in the 1970’s, whole body CTs in the 1980’s, spiral CT scans in the 1990’s, and radiation dose awareness/dose reduction technology in the 2000s. Through the 1970’s up until the late 1990’s there was a general trend for increasing mSv dose per CT scan (1.3 mSv to 8.5 mSv), but with the dose reduction technology in the early/mid 2000’s the mean dose has now decreased to 7.4 mSv. This is secondary (and will lead to continued improvement) to innovative development of CT technology aiming at higher dose efficiency, including (i) tube current modulation, (ii) optimization of x-ray spectra, (iii) x-ray beam collimation, (iv) iterative image reconstruction, and (v) more efficient x-ray detectors.

Tube current modulation allows (i) a mAs setting to automatically adapt to patient size (adult vs pediatric), (ii) full mAs variation over the patient’s long axis, and (iii) real-time modulation during tube rotation. This allows several benefits, including same scan protocols for slim/obese patients, optimal diagnostic image quality in every slice, and images achieved at the lowest dose levels. Optimization of x-ray spectra automatically adjusts for the tube voltage to be tailored to the individual patient size (as low as 70kv for children), the system capabilities, and the clinical task desired. X-ray beam collimation is a technology based on precise, fast and independent movement of both collimator blades, which limits over-ranging and only irradiates the targeted tissues of clinical interest. The most recent improvements in iterative reconstruction include the advanced modeled iterative reconstruction (ADMIRE). The benefits of ADMIRE are (i) exceptionally low radiation levels, providing enhanced image quality with a natural image impression at doses that weren’t possible in the past, (ii) excellent image quality, offering great delineation and sharpness of the organs and structures of interest, and (iii) everyday suitability, allowing image availability immediately after the examination is complete.

Dr. Fung concludes with hypothesizing that the dose reduction seen in 2007 (mean 7.4 mSv/scan) should continue to drop precipitously, with an estimated 40% further dose reduction based on the aforementioned technological advances.

Speaker(s): George Fung, Siemens AG, Pittsburgh, PA, USA

Written by: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto, Princess Margaret Cancer Centre, Twitter: @zklaassen_md, at the AUA Quality Improvement Summit - October 21, 2017- Linthicum, Maryland