Room: AAPM ePoster Library
Purpose: The Dual Energy Monoenergetic Algorithm (DEMA) (Siemens AG) allows for the creation of virtual monoenergetic CT images (VMIs) from dual energy CT (DECT) scans. A VMI dataset produced at 120 keV containing materials of various densities was evaluated to determine the feasibility of using 120 keV VMIs for radiation therapy treatment planning with a standard 120 kVp CT-density curve.
Methods: The DEMA calculates VMIs by projecting the HU values from the DECT-scans (80 kVp and 140 kVp) to new HU values from known reference curves. A Siemens SOMATOM Confidence RT Pro was used to scan a phantom with calibrated Gammex inserts representing 12 different mass densities, ranging from 0.320 g cm?³ to 1.824 g cm?³. First, a scan of the phantom was taken using a tube potential of 120 kVp. Next, two consecutive scans were collected for the DECT with tube potentials of 80 and 140 kVp. VMIs were created from the DECT scans using the DEMA set to 120 keV. Mean HU values were then obtained for each insert from both the standard 120 kVp and 120 keV VMI scans. Mass density vs HU value was plotted for each scan type. The curves were compared and HU differences between the two scan types were tabulated.
Results: For mass densities = 1.095 g cm?³ mean HU values differed by less than 16.3 ± 34.9 HU. However, for mass densities = 1.139 g cm?³, differences increased, ranging from 82.2 ± 38.9 to 405.9 ± 40.9 HU.
Conclusion: Caution should be taken when attempting to use a VMI dataset at 120 keV for radiation therapy treatment planning with a standard 120 kVp CT-density curve. While the datasets produce similar HU values for lower density materials, high-density materials such as bone may show greater differences, potentially leading to errors in dose calculation.