Radiation-Emitting Products
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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?
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.
The table below gives a summary of the action needed under each of the three Scenarios discussed above.
kVp Measurement of W/Ag and W/Rh Beams | ||||
Scenario | kVp Meter | Air Kerma Instrument | Action | Correction Factor |
1 | Certified by manufacturer for W/Ag and W/Rh | Ion chamber calibrated for mammography | Accept measurement | N/A |
2 | Not certified by manufacturer for W/Ag and W/Rh | Ion chamber calibrated for mammography | Apply correction factor to kVp measurements | Obtain from kVp meter manufacturer or develop by comparing engineer’s manufacturer-approved measurements during machine installation with your kVp meter |
3 | Not certified by manufacturer for W/Ag and W/Rh | Solid state probe | Apply correction factor to kVp measurements | Obtain 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.
The table below gives a summary of the action needed under each of the three scenarios discussed above.
HVL Assessments of W/Ag and W/Rh Beams | |||||
Scenario | kVp Meter | Air Kerma Instrument | Action | Correction Factor | |
1 | Integrated solid state instrument (measuring kVp, HVL, and dose) certified by manufacturer for W/Ag and W/Rh | Accept measurement | N/A | ||
2 | Integrated solid state instrument (measuring kVp, HVL, and dose) NOT certified by manufacturer for W/Ag and W/Rh | · Apply correction factor to exposure · Calculate HVL in standard manner · 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 | ||
3 | Not certified by manufacturer for W/Ag and W/Rh | Separate solid state probe | · Apply correction factor to exposure · Calculate HVL in standard manner 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 evaluation 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 involvement optional |
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 Unit | ||
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 Replacement | Check FFDM manufacturer’s QC manual | Follow FFDM manufacturer’s QC manual |
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