Author: John T Barrett, Mehnaz Haque, Chulhaeng Huh, Shands James, Thomas B. Lavin, Anobel Maghsoodpour, Farshad Mostafaei, Austin Sanders 👨🔬
Affiliation: Department of Radiation Oncology, Augusta University, Department of Radiation Oncology, Medical College of Georgia, Augusta University, Georgia Radiation Therapy Center, Wellstar-MCG Health, Department of Radiation Oncology, Doctors Hospital of Augusta, Department of Radiology and Imaging, Augusta University 🌍
Purpose: This study assesses Philips’ O-MAR effectiveness in adjusting AVHU values of common anatomical materials affected by various high-density metal artifacts at varying distances.
Methods: Lung, adipose, tissue, and bone inserts (reference materials) were individually CT scanned without O-MAR at multiple positions within Accuray’s Cheese Phantom using a Philips Big Bore CT. Next, each reference material was scanned again at the same position with a high-density metal (either aluminum, titanium, or stainless steel) nearby while applying O-MAR. All scans were performed using the site’s clinical pelvis protocol, with dose modulation disabled, and standard technique factors for an average-sized patient were implemented. Then, Eclipse TPS was used to select a 10x10 mm2 region of interest at each reference material’s center to obtain AVHU values for all scans. AVHU difference values (AVHU with O-MAR minus AVHU without O-MAR) were analyzed since AVHU percent difference values are skewed for materials with AVHUs equal to or close to zero, such as tissue.
Results: “AVHU difference values” versus “distance to high-density metal” was plotted for each reference material. O-MAR corrected CT scans are 3-9 AVHUs higher than CT scans without O-MAR for lung at farther distances to all high-density metals. Also, O-MAR corrected CT scans are 1-9 AVHUs higher for adipose across all distances to titanium or stainless steel. The largest AVHU deviation occurs when O-MAR corrected CT scans are 8-25 AVHUs lower for bone at closer distances to stainless steel. Notably, tissue AVHUs deviate the least across all distances to any high-density metal.
Conclusion: O-MAR effectively reduces distortion of CT scans but faces challenges in precisely adjusting AVHUs. Materials close to the center of the HU curve, such as tissue (AVHU = 0), experience minimal AVHU deviation due to metal artifacts.