american association of physicists in medicine aapm working group on standardization of ct...

American Association of Physicists in Medicine

AAPM Working Group on Standardization of CT Nomenclature

and Protocols


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


Membership

• AAPM– Mike McNitt-Gray, Bob Pizzutiello, Jim Kofler

• ACR– Mark Armstrong, Penny Butler

• ASRT– Kevin Reynolds

• FDA– Thalia Mills


Manufacturers

• GE– John Jaeckle

• Hitachi– Mark Silverman

• Philips– Mark Olszewski

• Siemens– Christianne Liedecker

• Toshiba– Rich Mather

• MITA– Stephen Vastagh


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

http://www.aapm.org/pubs/CTProtocols/


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


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. 2010

– Feasibility of Patient Size-Corrected, Scanner-Independent Organ Dose Estimates for Abdominal CT Exams. Med Phys. Accepted pending revision


Dose at center of scan (mGy) / CTDIvol (mGy)

y = 2.98e-0.0143x

R2 = 0.97

0.0

0.5

1.0

1.5

2.0

2.5

0 20 40 60 80 100

A/P + Lateral (cm)

No

rma

lize

d D

os

e

Siemens 4H

Siemens 3P

GE 4J

GE 3J

All Scanners

Expon. (AllScanners)

Siemens Flash

Siemens Sens 16

GE VCT

GE Ultra

Abdomen CT


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


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!


L1

L2

L3

L1

L2

L3


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


2nd AAPM Summit on CT Dose

October 6-7, 2011Denver, 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

american association of physicists in medicine aapm working group on standardization of ct...

Documents

medicine dose

account slide

medicine aapm

given patient patient

medicine charge

protocols protocols

pending revision slide

patient specific parameters