Radiation-Emitting Products

Most non-invasive kVp meters are only calibrated for Mo/Mo and Mo/Rh beams and therefore give inaccurate kVp readings when used with FFDM units that only have W/Ag or W/Rh target/filter combinations. How should I compensate for this error when doing surveys and MEEs on such units?

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The kVp value needs to be measured under one target/filter combination for which the kVp meter is calibrated (e.g., Mo/Mo, Mo/Rh, etc.). However, if the mammography unit has only a W/Ag or W/Rh target/filter combination, the measurement results must be appropriately corrected. FDA believes that the issue of inaccurate non-invasive kVp measuring instruments is one that ultimately is best resolved by the kVp instrument manufacturers and the medical physicists. Until this matter is resolved, FDA has the following suggestions for the equipment scenarios listed below:

kVp Measurements

Scenario 1.  If you are using a kVp meter that has been manufacturer-certified for W/Ag and W/Rh beams and a mammography-calibrated ion chamber, you may accept the measurement results and record them in the medical physicist survey or mammography equipment evaluation (MEE;

Scenario 2. If your kVp meter has not been manufacturer-certified for W/Ag and W/Rh beams and you are using a mammography-calibrated ion chamber, you should include a correction factor in your kVp measurements. This correction factor may be obtained from the kVp meter manufacturer, or by working with the mammography unit’s service engineer (by comparing the engineer’s manufacturer-approved measurements during machine installation with your non-invasive meter results). You may also use this correction factor when performing MEEs or surveys using this kVp meter/ion chamber combination on other FFDM units by the same manufacturer that also have W/Ag or W/Rh target filter combinations.

Scenario 3. If your kVp meter has not been manufacturer-certified for W/Ag and W/Rh beams and you are using a separate solid-state probe, then you should follow Scenario 2 for kVp Measurements.

Scenario

kVp Meter

Air Kerma Instrument

Action

Correction Factor

1Certified by manufacturer for W/Ag and W/RhIon chamber calibrated for mammographyAccept measurementN/A
2Not certified by manufacturer for W/Ag and W/RhIon chamber calibrated for mammographyApply correction factor to kVp measurementsObtain from kVp meter manufacturer or develop by comparing engineer’s manufacturer-approved measurements during machine installation with your kVp meter
3Not certified by manufacturer for W/Ag and W/RhSolid state probeApply correction factor to kVp measurementsObtain from kVp meter manufacturer or develop by comparing engineer’s manufacturer-approved measurements during machine installation with your kVp meter

 HVL Assessments 

 Scenario 1. If you are using an integrated solid state instrument (one that automatically measures kVp, HVL, and dose) and the instrument is manufacturer-certified for W/Ag and W/Rh, you may accept the measurement results and record them in the medical physicist survey or MEE.    

Scenario 2. If you are using an integrated solid state instrument that is not manufacturer-certified for W/Ag or W/Rh, you should determine the HVL using exposure measurements in the standard manner. You may then use this HVL value with the appropriate dose conversion table that is provided in the FFDM manufacturer’s QC manual to estimate the dose. Determine from the manufacturer of the dosimetry device if the exposure readings need to be corrected as aluminum is added to the beam. If so, then apply the correction factors applicable to each reading. It may be necessary to determine a typical correction factor by intercomparison with a mammography-calibrated ion chamber; this factor may then be used in the future. If the estimated dose is above 2.7 milligray (270 mrad), you should determine the actual HVL with a mammography-calibrated ion chamber and then use the actual HVL value to estimate the dose using the same conversion table provided in the QC manual. 

Scenario 3. If your kVp meter has not been manufacturer-certified for W/Ag and W/Rh beams and you are using a separate solid-state probe, you should follow Scenario 2 for HVL Assessments. 

Scenario

kVp Meter/Air Kerma Instrument

Action

Correction Factor

1Integrated solid state instrument (measuring kVp, HVL, and dose) certified by manufacturer for W/Ag and W/RhAccept measurementN/A 
2Integrated solid state instrument (measuring kVp, HVL, and dose) NOT certified by manufacturer for W/Ag and W/Rh
  1. Apply correction factor to exposure
  2. Calculate HVL in standard manner
  3. Use corrected kVp with estimated HVL from dose table (in FFDM manufacturer’s QC manual) to see estimated dose (see scenario 2 for more info
Obtain from kVp meter manufacturer or develop by comparing engineer’s manufacturer-approved measurements during machine installation with your kVp meter 
3Not certified by manufacturer for W/Ag and W/Rh and Separate solid state probe
  1. Apply correction factor to exposure
  2. Calculate HVL in standard manner
  3. Use corrected kVp with estimated HVL from dose table (in FFDM manufacturer’s QC manual) to see estimated dose (see scenario 2 for more info)
Obtain from kVp meter manufacturer or develop by comparing engineer’s manufacturer-approved measurements during machine installation with your kVp meter

Modification to the table in Quality Assurance/Equipment/Annual Physics Survey, Quality Assurance/Equipment/Mammography Equipment Evaluations, and Quality Assurance/Equipment/Use of Test Results

For any adjustment, change, or repair not listed in the table below, or if the facility is unsure as to whether the adjustment, change, or repair qualifies as a major repair, the facility should consult its medical physicist to determine the proper extent of his or her involvement in evaluating the item.

 

Item

Major Repair

Medical Physicist Involvement

Automatic Exposure Control  

AEC Replacement

Y

MP conducts evaluation in person

Thickness compensation internal* adjustment

N

MP oversight

AEC sensor replacement

Y

MP conducts evaluation in person

AEC circuit board replacement

Y

MP conducts evalution in person

Density control - internal* adjustment

N

MP oversight

Bucky (New to Facility) Replacement  

AEC sensor also replaced

Y

MP conducts evaluation in person

AEC sensor not replaced

N

MP oversight

FFDM detector also replaced

Y

MP conducts evaluation in person

FFDM detector not replaced

N

MP oversight

Cassette Replacement  

Same screen speed

N

MP oversight

Faster screen speed

N

MP oversight

Slower screen speed where the dose increase may exceed 3.0 mGy for the standard breast

Y

MP conducts evaluation in person

Collimator  

Replacement

Y

MP conducts evaluation in person

Reassembly with blade replacement

Y

MP conducts evaluation in person

Adjustment

N

MP oversight

Compression Device 

Pressure adjustment

N

MP oversight

Thickness scale accuracy adjustment but only if it affects AEC performance

N

MP oversight

Repair of auto decompression

N

MP involvement optional

Compression Paddle

  

Paddle (new to facility) replacement

N

MP oversight

Deflection adjustment

N

MP oversight

Adjustment due to extension beyond allowable limit, or visibility on images

N

MP oversight

Darkroom  

Repair of light leaks

N

MP involvement optional

Safe light change

N

MP involvement optional

Film Type/Speed Change

N

MP oversight

Processor  

Chemistry type change

N

MP involvement optional

Fixer/Developer replacement

N

MP involvement optional

Installation

Y

MP conducts evaluation in person

Reassembly

Y

MP conducts evaluation in person

Replenishment rate adjustment

N

MP involvement optional

Roller replacement

N

MP involvement optional

X-ray  

kVp, mA or time internal* adjustments

N

MP oversight

High voltage generator replacement

Y

MP conducts evaluation in person

X-ray tube replacement

Y

MP conducts evaluation in person

Filter replacement

Y

MP conducts evaluation in person

Installation

Y

MP conducts evaluation in person

Reassembly

Y

MP conducts evaluation in person

Manufacturer's software modifications (see approved alternative standard)

Y

MP conducts evaluation in person

FFDM detector replacement or repair

Y

MP conducts evaluation in person

FFDM Display (monitor)/Printer ReplacementCheck FFDM manufacturer's QC manualFollow FFDM manufacturer's QC manual

 

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Page Last Updated: 08/13/2014
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