American Association of Physicists in Medicine AAPM Working Group on Standardization of CT Nomenclature and Protocols

American Association of Physicists in Medicine Charge Develop consensus protocols for frequently performed CT examinations, summarizing the basic requirements of the exam and giving several model-specific examples of scan and reconstruction parameters. Develop a set of standardized terms for use on CT scanners

American Association of Physicists in Medicine Membership AAPM –Mike McNitt-Gray, Bob Pizzutiello, Jim Kofler ACR –Mark Armstrong, Penny Butler ASRT –Kevin Reynolds FDA –Thalia Mills

American Association of Physicists in Medicine Manufacturers GE –John Jaeckle Hitachi –Mark Silverman Philips –Mark Olszewski Siemens –Christianne Liedecker Toshiba –Rich Mather MITA –Stephen Vastagh

American Association of Physicists in Medicine Scanner Protocols Peer review process Protocol databases for sites to confirm their approach is reasonable AAPM Working Group on Standardization of CT Nomenclature and Protocols –Protocols to provide “reasonable” benchmarks –Terminology Lexicon

American Association of Physicists in Medicine

Limit who can alter protocols Must not lock out the ability of any single user to modify parameters for a given patient –Patient and exam specifics occasionally require modification of the default settings –We want the user to be able to “think” and adjust default values so that individual exams are optimized Should limit who can change the default scan parameters –Avoids “patient specific” parameters becoming set as generic parameters

American Association of Physicists in Medicine Meaningful Dose Information Standardized, monotonic scanner output (CTDIvol) –Head exam: 16 cm –Body exam: 32 cm Mean and surface DOSE to center of scan range for any patient size (requires knowledge of patient size) AAPM TG 204 Turner et al –Variation in Organ Doses and CTDIvol Normalized Organ Doses from a range of 64-Slice MDCT Scanners: A Monte Carlo Study. Med Phys –Feasibility of Patient Size-Corrected, Scanner-Independent Organ Dose Estimates for Abdominal CT Exams. Med Phys. Accepted pending revision

American Association of Physicists in Medicine Dose at center of scan (mGy) / CTDIvol (mGy) Siemens Flash Siemens Sens 16 GE VCT GE Ultra Abdomen CT

American Association of Physicists in Medicine Meaningful Dose Information Defined DICOM fields exportable to external databases –Exam type/clinical indication info essential for proper DRLs User configurable dose warnings and limits –Stochastic limits linked to diagnostic reference levels –Deterministic (skin, eye lens) limits relatively straightforward –Patient size MUST be taken into account

American Association of Physicists in Medicine AEC challenges: Errors in estimating size X-ray tube Detector Patient (centered) X-ray tube Detector Patient (not centered) X-ray tube Detector Patient (not centered) Distorted CT radiograph influences the mAs calculation!

American Association of Physicists in Medicine L1 L2 L3 L1 L2 L3

American Association of Physicists in Medicine L1 L2 L3 L1 L2 L3

American Association of Physicists in Medicine AP & Lateral Patient Attenuation Water equivalent thickness All manufacturers now how to do this (basis for AEC functionality) AAPM WG/TG/CT Subcommittee to present proposal to DICOM and MITA to add these as DICOM fields

American Association of Physicists in Medicine

2 nd AAPM Summit on CT Dose October 6-7, 2011 Denver, Colorado 2010 program made possible in part by generous contributions from ACR, AAPM, MITA and NIBIB Interdisciplinary Program on Scan Parameter Optimization for Radiologists, Technologists and Physicists