Manufacturer Specific Considerations for CT Accreditation Melissa C. Martin, M.S., FAAPM, FACR

Manufacturer Specific

Considerations for CT

Accreditation

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

AAPM Spring Clinical Meeting

March 20, 2012 Dallas, TX

Phantom Submission

Slide provided by Doug Pfeiffer





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 Mistakes

For mA row – entering mAs, effective mAs or mAs/slice

Help site understand difference between these

And that they are not all equivalent mA ≠ mAs mAs ≠ eff. mAs mAs ≠ mAs/slice

Dosimetry

Siemens – eff. mAs (effective mAs)

Eff .

_ mAs

= mA * rot _ time

Pitch mA

=

Eff .

_ mAs * Pitch rot _ time

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

= mA * rot _

Pitch time mA

=

( mAs / Slice rot _

) * time

Pitch

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

Dosimetry

Common Mistakes include:

Reporting mAs or eff. mAs or mAs/slice in Table

1

Then using mAs or eff. mAs when performing

CTDI measurements

Example: 200 eff. mAs, pitch .9, rot. time = 0.5 sec

In this case, mA = 360

Should perform CTDI measurement with 180 mAs

Spreadsheet 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 values

If they perform acquisition with 200 mAs

And 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 high

If Pitch > 1, CTDIvol reported will be too low

Dosimetry

Common Mistakes - Reporting collimation incorrectly

Admittedly this can be confusing for some scanners

Example: Siemens Sensation 64

Scanner user interface says 64 x 0.6 mm

Scanner uses z-flying focal spot, which double samples on zaxis of anode to obtain 2X images.

Actual beam width is N=32, T = 0.6 mm

For Pitch 1.0, table travel will be 19.2 mm/rotation

Site 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 incorrectly

Consult ACR CT Accreditation website for FAQs and clarifications http://www.acr.org/accreditation/computed/ct_faq.asp

x

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 360 rotation 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 * are

80 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 360 rotation 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 * are

80 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 Pitch

Row Helical Pitch (HP) IEC Pitch Factor

16 11

32

0.688

21 0.656

64 41 0.641



Standard Pitch


16 15

32

0.9375

27 0.84375

64 53 0.828

Fast PitchRowHelical Pitch (HP)IEC Pitch Factor

(PF)16231.437532451.4062564951.484



Fast Pitch


16 23

32

1.4375

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

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 Location

Axial 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

CONCLUSIONS

For 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,

FAAPM

Therapy Physics Inc.

879 West 190th St., Ste 400

Gardena, CA 90248 e-mail:

Melissa@TherapyPhysics.com

website: www.TherapyPhysics.com

Phone: 310-612-8127

Manufacturer Specific Considerations for CT Accreditation Melissa C. Martin, M.S., FAAPM, FACR

Manufacturer Specific

Considerations for CT

Accreditation

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Manufacturer Specific Considerations for CT Accreditation Melissa C. Martin, M.S., FAAPM, FACR