The ACR CT Accreditation Program and the Medical Physicist

The ACR CT Accreditation Program and the Medical Physicist Maynard High, PhD New York Medical College with the most kind assistance of Cynthia McCollough, PhD Mayo Clinic Aim of CT Accreditation • Peer Review and Evaluation of facility, including: – – – – personnel qualifications image quality quality control procedures patient radiation exposure Positive Outcomes of CT Accreditation Process from the Viewpoint of a Satisfied User • Technologist: – involvement in performance evaluation • Technologist, radiologist, and physicist: – increased awareness of patient dose • Patient: – review and possible modification of scan protocols affecting dose and image quality Financials of CT Accreditation • Costs are not insignificant: – ~ $5K for 1 CT site with phantom • Some insurers now require CT accreditation: • Many more insurers will require CT accreditation within a year: CT PROGRAM STATISTICS April 2003 • 200 applications received • 40 facilities accredited • ??% passed on 1st attempt – too early in program for statistics – failures about 50% clinical / 50% phantom The Application Process • Submission of site info and personnel credentials • Acquisition of ACR CT phantom • Submission of CT data and images – clinical images – phantom images – dose measurements Personnel Credentials • Radiologist: – Competence, continuing experience, CME • Technologist: – Competence, CME • Medical Physicist: – Competence, CME Medical Physicist Credentials 1) RECOMMEND ABR certification in 2) Be Familiar with CT 3) Be in accordance with ACR Standard for CME – no specific requirement for CT CME – Diagnostic Radiological Physics or – Radiological Physics PERSONNEL DATA FORM ACR Standard for CME: Medical Physicist • 150 hrs/3 yrs (Category 1,2 and MEP) – this 150 hrs includes the 60 hrs below – Category 2 includes meeting attendance, self-study, teaching, publications,peerreview activities, etc • 60 hrs/3 years (Category 1 or MEP) The Application Process • Submission of site info and personnel credentials • Acquisition of ACR CT phantom • Submission of CT data and images – clinical images – phantom images – dose measurements ACR CT Phantom Information Courtesy of CYNTHIA McCOLLOUGH, PHD • All slides of this format and color scheme were kindly loaned to me for use in this talk by Cynthia McCollough, PhD, Chairperson of the ACR CT Accreditation Physics Subcommittee Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. Physics Subcommittee • • • • • • Cynthia McCollough, Ph.D., Chair Tom Payne, Ph.D. Mike McNitt-Gray, Ph.D. Tom Ruckdeschel, M.S. Jim Brink, M.D. ACR: Pam Wilcox, Penny Butler, Krista Bush, Chris Riha Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. Consensus Opinion re: Accreditation Phantom and Film • • • • • • • Single phantom design must be used No existing phantom had all desirable test objects Solid one-piece construction, 20-cm diameter Test objects must be simple to evaluate Objects and tests must be extendable to spiral Dosimetry will be CTDI100-based in PMMA Assessment of phantom images will be film-based until ACR converts to digital submission process Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. The ACR CT phantom was designed to examine a broad range of scanner parameters  Positioning Accuracy  CT # Accuracy  Slice Width Accuracy  Low Contrast Resolution  High Contrast (Spatial) Resolution  Image Uniformity and Noise  Image Artifacts  Distance Measurement Accuracy  Section Sensitivity Profiles Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. ACR Accreditation Application Tests • • • • • • • • • Image Quality Align light accuracy – high contrast resolution Align table to gantry – low contrast resolution Table/gantry tilt – image uniformity Scout slice localization – noise accuracy – artifact evaluation Table incr. accuracy • CTDI Slice thickness • Patient dose for exams CT# accuracy/linearity Hard-copy display Physicist’s Annual CT Survey (ACR) • • • • • • • • • Align light accuracy Align table to gantry Table/gantry tilt Scout slice localization accuracy Table incr. accuracy Slice thickness CT# accuracy/linearity Video display Hard-copy display • Image Quality – – – – – high contrast resolution low contrast resolution image uniformity noise artifact evaluation • • • • CTDI Patient dose for exams Safety evaluation Required State tests Technologist CT QC (ACR) • • • • • Align light accuracy Slice thickness CT# accuracy Video display Hard-copy display • Image Quality – – – – – high contrast resolution low contrast resolution image uniformity noise artifact evaluation Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. Head Foot 4 20 cm High contrast resolution 3 Uniformity & noise Distance accuracy & SSP 2 Low contrast resolution 1 Alignment CT # Slice width 4 cm Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. Technologist and Phantom Testing • Try to give technologist responsibility for accreditation phantom testing – best done together with physicist – helps technologist better understand the physicist’s annual survey (ACR required) – helps the physicist understand how technologist sets up protocols (useful information for annual survey) Site Scanning Data Form • Site or manufacturer-recommended protocols – Adult Head: Routine head CT for evaluation of patient with headaches to exclude neoplasms – High Resolution Chest: CT exam of the chest for evaluation of diffuse lung disease – Adult Abdomen: Routine oncologic CT survey of the abdomen for detection of possible liver metastases – Pediatric Abdomen: CT examination of pediatric (approx. 5 years old) abdomen for the evaluation of blunt trauma injuries Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. INSTRUCTION MANUAL Instruction Manual • Detailed step by step scan and analysis instructions • Tells which set of scan parameters to use to acquire which phantom images • Data sheet provides cells for measured and calculated data • W/L and location on film grid given for all images to be filmed • Dose measurement and calculation methods Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. Test 1: Phantom and Scanner Alignment • Align Module 1 to lasers • Scan with Hi Res Chest protocol • Prescribe a scan at center of Module 4 ie, 120 mm superior • Scan with Hi Res Chest protocol Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. MODULE 1 Polyethylene ≈ -97 HU “Bone” ≈ +910 HU Water ≈ 0 HU Acrylic ≈ +120 HU Air ≈ -1000 HU Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. High-resolution chest technique Must see all four BBs (in Modules 1 & 4) Longer wire must have same number of lines above and below (±1) Wires are 0.5 mm apart in z-direction WW = 1000 WL = 0 Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. DATA FORM Test 2: CT Number Calibration and Slice Thickness • Align Module 1 to lasers • Scan with Adult Adomen protocol & all kVp’s available • Record all HU and slice thickness • Also scan with 3, 5, 7 mm & hi res chest slice thickness • Record water HU and slice thickness for each scan. Adult abdomen technique Poly CT number measured in 5 materials CT number of water measured at several scan widths and kVps Water “Bone” Acrylic Air WW = 400 WL = 0 Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. Adult abdomen technique Scan width measured at several scan widths 11/2 = 5.5 10/2 = 5 WW = 400 WL = 0 Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. DATA FORM Test 3: Low Contrast Resolution • Scan Module 2 with Abdomen and Head protocols • Record the smallest rod seen Low contrast = 6 HU ± 0.5 HU 25 mm MODULE 2 2 mm 3 mm 6 mm 4 mm 5 mm Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. Adult abdomen and head techniques Record diameter of the smallest set of rods for which all 4 rods can be seen ROI check of absolute contrast using large rod WW = 100 WL = 100 Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. DATA FORM Test 4: Uniformity, Noise, Artifacts, and Distance Accuracy • • • • • Scan Module 3 with Abdomen protocol Record HU & SD in center Record HU at 12, 3, 6, 9 o’clock Examine for artifacts and record Check distance accuracy (optional) MODULE 3 100 mm Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. Adult abdomen and head techniques Measure uniformity and noise Assess for artifacts Measure distance accuracy (optional) WW = 100 WL = 0 Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. DATA FORM Test 5: High Contrast Resolution • Scan Module 4: – Hi Resolution Chest protocol – Abdomen protocol • Record limiting lp/mm Bar patterns: lp/cm MODULE 4 Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. Adult abdomen, adult head and high-resolution chest techniques Record the first highest frequency bar pattern for which the bars and spaces merge WW = 100 WL  1100 Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. CT ART? At soft-tissue window settings these streaks are visible and not of concern WW = 400 WL = 0 Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. DATA FORM The Application Process • Submission of site info and personnel credentials • Acquisition of ACR CT phantom • Submission of CT data and images – clinical images – phantom images – dose measurements Dose Information for ACR Accreditation • Submit calculations of CTDIvol, DLP and Effective Dose using the site’s measured CTDIw and the reported scan acquisition parameters (pitch) – Routine head (cerebrum) – Adult abdomen – Pediatric abdomen (5 y.o) • CDTI phantom acquisition must be filmed Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. CTDI Measurements: Adult Body • 32 cm PMMA • Phantom on table • 12 o’clock & isocenter CTDI Measurements: Pediatric Body • 16 cm PMMA • Phantom on table • 12 o’clock & isocenter CTDI Measurements: Adult Head • 16 cm PMMA • Phantom in head holder • 12 o’clock & isocenter DATA & CALCULATION FORM RADIATION DOSIMETRY FORM Dose Calculator Spreadsheet (Exposure) Section 11 - Radiation Dosimetry ( Adult Body) CTDI Body Phantom (32-cm diameter PMMA Phantom) kVp mA Exposure time per rotation (s) Z axis collimation T (mm)1 # data channels used (N)1 Axial (A): Table Increment (mm) = (I)1 OR Helical (H): Table Speed (mm/rotation) = (I) Active Chamber length (mm) Chamber correction factor Measured 120 240 0.8 3.75 4 Calculated Film Page:Box CTAP ID Number 00019 11.25 100 0.97 T, N, I and Pitch (P) • Some scanners do not display collimation width, T. • Can be determined from P = I / N*T • Conversion table for GE on ACR website. Axial or Helical? • ALL CTDI data must be acquired using a single axial (non-helical) scan • Correction for helical pitch will be made in CTDIvol calculation RADIATION DOSIMETRY FORM Center Measurement 1 (mR) Measurement 2 (mR) Measurement 3 (mR) Average of above 3 measurements (mR) Body CTDI at isocenter in phantom (mGy) 12 o'clock position Measurement 1 (mR) Measurement 2 (mR) Measurement 3 (mR) Average of above 3 measurements (mR) Body CTDI at 12 o'clock position in phantom (mGy) CTDIw (mGy) 401 422 401 408.0 23.0 19.0 197 199 199 198.3 11.2 2:9 CTDIw = 1/3 (CTDIcenter)+2/3 (CDTIedge) RADIATION DOSIMETRY FORM CTDIw (mGy) 19.0 Clinical exam dose estimates (using measured CTDIw and site's Adult Abdomen Protocol from Table 1) CTDIvol (mGy) DLP (mGy-cm) Eff Dose (mSv) =CTDIw*N*T/I =CTDIvol*25 =DLP*0.015 25.4 634.2 9.5 Pitch correction: 19.0 * 4/3 = 25.4 RADIATION DOSIMETRY FORM CTDIw (mGy) 19.0 Clinical exam dose estimates (using measured CTDIw and site's Adult Abdomen Protocol from Table 1) CTDIvol (mGy) DLP (mGy-cm) Eff Dose (mSv) =CTDIw*N*T/I =CTDIvol*25 =DLP*0.015 25.4 634.2 9.5 Dose Length Product = (CTDIvol) * (total length of scan) RADIATION DOSIMETRY FORM CTDIw (mGy) 19.0 Clinical exam dose estimates (using measured CTDIw and site's Adult Abdomen Protocol from Table 1) CTDIvol (mGy) DLP (mGy-cm) Eff Dose (mSv) =CTDIw*N*T/I =CTDIvol*25 =DLP*0.015 25.4 634.2 9.5 ESTIMATED Effective Dose = (DLP) * (Tissue Weighting Factor) Reference Doses • Concept has been shown to lower dose average in other modalities and/or other countries • Represent the upper third or quartile of doses sampled from clinical practice • Do not represent ideal or suggested doses • Identify when dose are unusually high Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. European Guidelines Exam CTDIw Head 60 Chest 30 Abd 35 Pelvis 35 Chest/Abd/Pel DLP 1050 650 800 600 2050 Eff. Dose 2.4 11.1 12.0 11.4 34.5 From European Commission EUR 16262 uropean Guidelines on Quality Criteria for Computed Tomograph Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. • ACR CT Dose Reference Values – Adult Head – Adult Abdomen – Pediatric (5yr old) Abdomen 60 mGy 35 mGy 25 mGy • Currently no pass/fail criteria – ACR will require documentation detailing either site’s justification or corrective action – At renewal (3 yrs), reference doses will become pass/fail • Analysis of ACR data will determine future reference dose values (likely CTDIvol) Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission. Case History #1: Are CT Reference Doses Useful? • • • • • • High posterior fossa CTDIw observed Parameters examined with radiologists New parameters proposed Image quality evaluated New protocol instituted (New CTDIw) < 1/2 (Old CTDIw) ! Case History #1: Are CT Reference Doses Useful? Study type Adult Head Post Fossa Cerebrum mAs 480 240 OLD collimation (mm) 2.5 / 2i 7.5 / 2i CTDIw (cGy) 13.6 4.6 mAs 300 300 NEW collimation (mm) 5.0 / 2i 7.5 / 2i CTDIw (cGy) 6.0 6.0 I have used similar reference dose methodologies to lower CTDI at several sites. ACCREDITATION APPROVAL REPORT The Accreditation Approval (or not) Report • Review report with physicists, radiologists, and technologists • Contains peer review feedback on – clinical images – performance from phantom data – dose • May initiate protocol changes ACCREDITATION APPROVAL REPORT: CLINICAL Case History #2: Accreditation Peer Review • Recommended P>1 for pediatric sinus • Parameters examined with technologists • Retrospective thin slice recons not possible for P>1 : This is common req. • Displayed CTDIw not decreased significantly for P>1. • Conclusion: P<1 clinically justified. ACCREDITATION APPROVAL REPORT: PHANTOM ACCREDITATION APPROVAL REPORT: PHANTOM My Personal Conclusions: Phantom • ACR CT Phantom can be used for all routine CT performance evaluation • Single phantom allows intercomparison of CT units • Not so useful where manufacturer gives specifications for their phantom – acceptance testing – noise, uniformity, low contrast, MTF My Personal Conclusions: Program • ACR CT Accreditation process is very worthwhile for TECHNOLOGIST: – increased involvement in performance evaluation – increased awareness of patient dose and of parameters affecting dose My Personal Conclusions: Program • ACR CT Accreditation process is very worthwhile for RADIOLOGIST: – increased awareness of patient dose and of parameters affecting dose – review and possible modification of scan protocols affecting dose and image quality My Personal Conclusions: Program • ACR CT Accreditation process is very worthwhile for PATIENT: – better image quality – probably lowered dose My Personal Conclusions: Program • ACR CT Accreditation process is very worthwhile for MEDICAL PHYSICIST: – better communication with Radiologist and Technologist – increased interest and knowledge re: multislice CT scanners – more respect and popularity Thank You