Manufacturer Specific Considerations for CT Accreditation…amos3.aapm.org/abstracts/pdf/67-17537-44971-585.pdf · Toshiba Aquilion 32 or 64 slice CT Scanners The maximum number of

Manufacturer Specific Considerations for CT

AccreditationMelissa C. Martin, M.S., FAAPM, FACR

AAPM Spring Clinical Meeting March 20, 2012 Dallas, TX

Phantom Submission

Slide provided by Doug Pfeiffer

Phantom Submission


Phantom Submission


Phantom Site Scanning Form -Page 1


Phantom Site Scanning Data Form - Page 2


Phantom Images


Phantom Images


Phantom Images


Phantom Scoring


CT # Accuracy


Contrast-Noise Ratio


Contrast-Noise Ratio


CT # Uniformity


Dosimetry

Table 1 - Common MistakesFor mA row – entering mAs, effective mAs or mAs/sliceHelp site understand difference between these

And that they are not all equivalentmA ≠ mAsmAs ≠ eff. mAsmAs≠ mAs/slice

DosimetrySiemens – eff. mAs (effective mAs)

Philips – mAs/Slice (similar definition to eff. mAs)

Toshiba and GE use mA, time , Pitch as separate values

PitchtimerotmAmAsEff _*_. = timerot

PitchmAsEffmA_

*_.=

PitchtimerotmAslicemAs _*/ = timerot

PitchSlicemAsmA_

*)/(=

Dosimetry

Common Mistakes include:Reporting mAs or eff. mAs or mAs/slice in Table

1Then using mAs or eff. mAs when performing CTDI measurements

Example: 200 eff. mAs, pitch .9, rot. time = 0.5 secIn this case, mA = 360 Should perform CTDI measurement with 180 mAsSpreadsheet will use pitch 0.9 and correct for values of effective mAs

Dosimetry

Common Mistakes include:If site does this incorrectly, spreadsheet will have

incorrect valuesIf they perform acquisition with 200 mAsAnd then use N,T and I such that a pitch of 0.9 results, then CTDIvol reported will be too high

If Pitch < 1, CTDIvol reported will be too highIf Pitch > 1, CTDIvol reported will be too low

DosimetryCommon Mistakes - Reporting collimation incorrectly

Admittedly this can be confusing for some scannersExample: Siemens Sensation 64

Scanner user interface says 64 x 0.6 mmScanner uses z-flying focal spot, which double samples on z-axis of anode to obtain 2X images. Actual beam width is N=32, T = 0.6 mmFor Pitch 1.0, table travel will be 19.2 mm/rotationSite sometimes list N=64, T=0.6mm, I= 38.4mm (-> Pitch 1)In spreadsheet, this yields CTDIvol that is half what it should be

Dosimetry

Common Mistakes - Reporting collimation incorrectlyConsult ACR CT Accreditation website for FAQs and clarificationshttp://www.acr.org/accreditation/computed/ct_faq.aspx

Dosimetry


Dosimetry


Dosimetry


Dosimetry


Dose Levels


Dosimetry


Dosimetry


Dosimetry


Pass/Fail Criteria


Phantom Deficiencies









Toshiba CT Scanners

Aquilion Scanners (32, 64 or 320)

Slide provided by Erin Angel, Toshiba Medical Systems

Toshiba Aquilion 32 or 64 slice CT Scanners

The maximum number of axial images able to be acquired simultaneously in a single rotation (Nmax) is 4.The minimum rotation time for a full 360rotation can be found in the product data sheet or via loading any helical protocol and choosing the lowest available 360 rotation time (note: grayed-out times are not available).


Toshiba Aquilion 32 or 64 slice CT Scanners

Slice thicknesses available in helical mode include:0.5mm, 1.0mm, 2.0mm, 3.0mm, 5.0mm, 7.0mm,

and 10.0mm.Slice thicknesses available in axial mode include:

0.5mm, 1.0mm, 2.0mm, 3.0mm, 4.0mm, 6.0mm, 8.0mm, 12mm (16mm, 24mm, and 32mm are also available for non-clinical applications).

Available beam energies* are80 kVp, 100 kVp, 120 kVp, and 135 kVp


Toshiba Aquilion 16 slice CT Scanners

The maximum number of axial images able to be acquired simultaneously in a single rotation (Nmax) is 4.The minimum rotation time for a full 360rotation can be found in the product data sheet or via loading any helical protocol and choosing the lowest available 360 rotation time (note: grayed-out times are not available).


Toshiba Aquilion 16 slice CT Scanners

Slice thicknesses available in helical mode include:0.5mm, 1.0mm, 2.0mm, 3.0mm, 5.0mm, 7.0mm,

and 10.0mm.Slice thicknesses available in axial mode include:

0.5mm, 1.0mm, 2.0mm, 3.0mm, 4.0mm, 6.0mm, 8.0mm, 12mm (16mm, 24mm, and 32mm are also available for non-clinical applications).

Available beam energies* are80 kVp, 100 kVp, 120 kVp, and 135 kVp


Toshiba Scanners - Location of Technical Parameters

Toshiba Scanners - Scan Detail Tab



Scan Details for Axial Scanning


Recon Details Tab

IEC Pitch Value and Table Speed

Always use the IEC definition of pitch when reporting to ACR

IEC pitch can be calculated either by:Dividing the helical pitch (HP) by the number of

detector channels being used (N)Clicking on the HP button on the Scan Details tab to find the IEC pitch value (ex: PF 0.828). The IEC pitch value is called “Pitch Factor” on your Aquilion scanner, also denoted PF.


IEC Pitch Value and Table Speed


IEC Pitch Values and Table Speed

Detailed PitchRow Helical Pitch (HP) IEC Pitch Factor16 11 0.688 32 21 0.656 64 41 0.641



Standard PitchRow Helical Pitch (HP) IEC Pitch Factor16 15 0.9375 32 27 0.84375 64 53 0.828

Fast PitchRowHelical Pitch (HP)IEC Pitch Factor (PF)16231.437532451.4062564951.484



Fast PitchRow Helical Pitch (HP) IEC Pitch Factor16 23 1.4375 32 45 1.40625 64 95 1.484

ACR Tips for Toshiba CT’s

Have the scanner calibrated for air and water, at all relevant kVps, prior to testing Make sure you scan the ACR phantom with the small (S) Scan FOV for the image quality tests. Scanning a small size phantom with a large size FOV can lead to CT number and uniformity errors.For best results be sure the phantom is properly centered, utilizing the lasers and a level.Slide provided by Erin Angel, Toshiba Medical Systems

ACR Tips for Toshiba CT’s

Have your “Average Clinical Parameters” chart filled out in advance and be certain to scan the phantom with the corresponding parameters. Before proceeding with phantom image quality testing, ensure your protocols are optimized for dose while obtaining adequate image quality and that radiation doses do not exceed ACR guidelines.For proper landmarking, note where the center of the slice will be when you prescribe a scan in axial or helical mode


Finding the Center Slice LocationAxial Mode: If a scan is prescribed, for example,

from 24mm to 26mm in 4 x 0.5mm axial mode, the center slice location will be as follows:


Helical Mode: If a scan is prescribed, for example, from 24mm to 26mm in 4 x 0.5mm helical mode, the center slice location will be as follows (note:

this is different from axial mode):


Objectives

CONCLUSIONSFor all scanners, make sure that the facility has had service perform preventive maintenance recently.

Review the protocols used with the technologist prior to performing phantom scans and dosimetry.

Contact the vendor help desk for further clarification on a particular scanner.

If at all possible, burn the CD’s for ACR Submission prior to leaving the facility. Do not depend on staff at the facility to correctly burn the CD’s.

Contact Information:

Melissa C. Martin, M.S., FACR, FAAPMTherapy Physics Inc.879 West 190th St., Ste 400Gardena, CA 90248

e-mail: [email protected]: www.TherapyPhysics.com

Phone: 310-612-8127

Documents

Manufacturer Specific Considerations for CT Accreditation…amos3.aapm.org/abstracts/pdf/67-17537-44971-585.pdf · Toshiba Aquilion 32 or 64 slice CT Scanners The maximum number of