Guidance

Breast screening: Testing biopsy systems guidance

Published 7 March 2024

Applies to England

1. Introduction and guiding principles

It is important that needle placement is accurate when carrying out breast biopsies and localisations under x-ray guidance. For biopsies, inaccurate needle placement could lead to the wrong part of the breast being sampled. For localisations, it could lead to the wrong part of the breast being excised during surgery.

A service will typically use several different types of needles for biopsies and localisations. Vertical and lateral approaches may be required, and some procedures may be carried out in stereotactic, tomosynthesis or contrast enhanced modes. Attachments to existing mammography units or dedicated prone biopsy tables may be used.  As a consequence, there may be a large number of combinations of needle, set-up and mode of operation that are used clinically.

In developing a robust and effective quality assurance programme, the choice of combinations tested, and frequency of testing must be carefully balanced against the time taken to carry out the tests. When making these choices, consideration should be given to the following:

• recommendations from x-ray biopsy system supplier for calibration and testing
• availability of any test/calibration test needles and/or targets provided by the supplier
• how frequently biopsies and localisations are carried out using the equipment
• how often each type of clinical needle is used
• if stereotactic, tomosynthesis and/or contrast enhanced modes are used, and if so, how often
• if vertical and lateral approaches are used for each needle type, and if so, how often
• if biopsies and localisations are carried out with the gantry angled
• if any of the needles require special mountings that have potential for being set up incorrectly (such as for vacuum assisted biopsies)
• any other variables that could give rise to errors such as the throw of the biopsy gun, needle gauge or mechanism of attaching the calibration test needle
• which combinations are considered most critical
• whether the programmed settings are editable by the user

When developing a quality assurance system, advice should be sought from both the medical physics expert (MPE) and the supplier of the x-ray biopsy system.

Mammographic quality assurance (QA) and quality control (QC) are the responsibility of all mammographers in the service and are monitored closely by radiography managers and other staff with delegated responsibility. More details can be found in NHS BSP guidance for mammographers. The breast screening service should designate members of staff who are trained and competent in the operation and testing of the biopsy system as QA radiographers.

This document focuses on needle testing required within the NHS breast screening programme (NHS BSP) but additional tests on the x-ray biopsy system may be required as indicated by the supplier and other published guidance.

1.1 Equipment required

• x-ray biopsy system and biopsy paddles
• supplier’s test tool, incorporating metal pointers or radiopaque objects to use as targets
• supplier’s calibration test needle or pointer (a fine needle used for aspirations could be used if no test needle is provided)
• an open sample of each type of needle, marker and localisation device that are programmed into the x-ray unit, securely sheathed for safety where appropriate
• multi-use biopsy needle firing mechanisms for example biopsy gun
• supplier- approved needle guides, holders, and mountings for every type of needle, mode and approach tested
• spacers (widgets), if used

All test equipment must give an accurate, reproducible position for the needle without adding to the uncertainty of the measurement.

The same consumables (unless damaged) must be used at each test session to ensure consistency.

2. Testing at commissioning

Biopsies and localisations carried out in different imaging modes and approaches may be calibrated separately by the supplier of the x-ray biopsy system. During commissioning of the x-ray unit, the full set of calibrations and/or tests recommended by the supplier must be carried out to confirm the accuracy of the target spatial coordinates in each of the modes and approaches available on the unit. This may involve using test/calibration needles and phantoms provided by the supplier. They could be carried out before the clinical needles have been set up if agreed by all parties involved.

When a new x-ray biopsy system is installed, all the needle types that are to be used must be programmed into the unit by the x-ray biopsy system supplier’s application specialist with input from clinical staff. The programmed settings should account for all the modes, approaches and biopsy gun throws that might be used, taking care where there are multiple gauges or lengths of the same needle type and considering when the post-fire position may be different from that of the pre-fire position. Decisions will be required around the choice of localisation point, for example, if this should be at the middle of the cutting edge of a biopsy notch, tip of the needle for localisation, or middle of the needle bevel for marker clips.

It may be useful to make sure the most commonly used needle settings are most prominently visible at the top of the programmed list. Naming of programmes should be agreed with clinical staff and must avoid any ambiguity. These naming conventions should be consistent across x-ray units within the same organisation. A record of all the programmed settings should be made and kept separately from the x-ray biopsy unit, in case of software back-up failures.

During commissioning, the accuracy of needle positioning must also be confirmed for every setting that has been programmed into the x-ray unit. This can be demonstrated most effectively by the application specialist with the local QA radiographer and a member of the medical physics team in attendance. However, in some circumstances, attendance by medical physics may not be necessary. For example, duplication of needle settings from an established system or where training records demonstrate the QA radiographer is both confident and competent in needle set up. The breast screening service and the MPE must be satisfied that all needles have been correctly programmed into the unit and have been tested. Safety margins must also be checked according to the supplier’s recommendations.

Commissioning is a good opportunity to discuss and agree a routine QC programme for the users, considering advice from the x-ray biopsy system supplier, advice from the MPE, and the clinical requirements. Testing at commissioning and sign off by the service and MPE should be documented. During commissioning, the testing should also be developed into work instructions for routine testing, in discussion with the local QA radiographer. A set of test equipment should be assembled at this stage. These work instructions should be regularly reviewed and updated as required and in line with current professional guidance.

3. Training

The procedures required to set up and perform the different needle tests are often complex, requiring many steps, each of which is crucial to obtaining the right result. It is therefore essential to have in place a robust programme of training, assessment of competency and maintenance of competency for all staff involved. Evidence of this should be clearly documented. A balance must be struck between ensuring sufficient staff numbers are trained and competent to carry out the tests, whilst ensuring that each member of staff has sufficient opportunity to perform them in order to maintain their competency. Consideration should be given to identifying “super users” who can cascade training to all staff involved in biopsy testing.

Testing at commissioning can form part of local staff training. It is an opportunity for users to familiarise themselves with all the tests including those that confirm the accuracy of the target spatial coordinates.

When developing a training programme for biopsy and localisation QC testing, particular attention should be given to the following:

• correct use and application of test phantoms
• setting up of different needle mountings and holders
• selection and deployment of the correct needles and needle guides
• correct use of the x-ray biopsy system software interface, including targeting and selection of programmed needles
• checking safety margins
• documenting test results
• checking results against tolerances and escalating when appropriate (see section 6)

This list is not exhaustive.

Additional training needs must be considered when introducing new consumables such as vacuum biopsy devices and new needle types.

4. Routine user QA programme

Development of a routine user QA programme should be guided by the principles set out in the introductory section

It is considered good practice for the local QA team and the medical physics service to continue to liaise over the QA programme following commissioning. During a routine medical physics survey, there may be insufficient time to set up and perform tests for all needle and device combinations. Medical physics staff may also find it difficult to maintain sufficient competence in setting up all the different combinations without assistance from the local QA team. Instead, it may be more useful for medical physics to witness the tests performed by the local QA team on an annual basis. This provides good opportunities for discussing any problems with the QA programme, identifying any changes that may have occurred, and reviewing test methodology and results. It helps to foster collaborative working which is likely to reduce risks and improve the quality of service.

All equipment should be checked at each testing session for any signs of wear or damage. In particular, all test needles should be checked to ensure they are not bent and, if necessary, should be replaced by a new one of the same type. The detector should also be checked for signs of needle damage as this can be an indication of inaccurate targeting.

4.1 Tests to confirm the accuracy of the target spatial coordinates

Tests that confirm the accuracy of the target spatial coordinates in every mode and approach will be necessary on a routine basis unless particular modes or approaches are never used. Tests should use the supplier’s calibration test needles and phantoms and follow the supplier’s recommendations, where these are available. In the absence of supplier’s test objects and/or recommendations, advice should be sought from the MPE.

Frequency: As recommended by the x-ray biopsy system supplier or, if not specified by the supplier, before each biopsy/localisation session

Tolerances: 

Suspension levels as recommended by the x-ray biopsy system supplier or, if not specified by the supplier:

Greater than 1mm misalignment in the X, Y and Z directions

If results are out of tolerance, the set up must first be checked and the test repeated.  If results are still out of tolerance, corrective action must be taken before the system is used clinically. This may result in contacting the system supplier.

4.2 Tests to confirm clinical needle accuracy

These tests make sure that the physical set-up for each clinical needle matches the settings programmed into the x-ray unit to maintain accurate targeting. As outlined in the introductory section, the choice of combinations tested, and frequency of testing should be given careful consideration.

When developing testing procedures, methods must allow for an assessment of the difference between the targeted coordinates and the physical target location. One method of achieving this is to allow for a manual movement of the needle such that it is aligned with the physical target. This allows the displayed target coordinates to be used as a measurement of accuracy. Note that on some systems when you use the ‘fine jog’ motion, the target coordinate at the biopsy attachment control module (BCM) changes.

For clinical needles, the error in targeting accuracy should be recorded in millimetres in X, Y and Z dimensions rather than a simple pass or fail.

If tests confirming the accuracy of the target spatial coordinates have already been carried out according to the previous section: 4.1 in all modes (stereotactic, tomosynthesis and/or contrast enhanced), then it is unlikely to be necessary to test the thrown clinical needle position in all of these modes. The mode that is most frequently used could be selected for routine testing. An exception might be if clinical needles use different mountings for the different modes, in which case testing in each mode should be considered.

If tests confirming the accuracy of the target spatial coordinates have already been carried out according to the previous section: 4.1 in all approaches (vertical, left/right lateral), then it may only be necessary to test the thrown clinical needle position in different approaches if different mountings are used. Depending on the set up used, needle tests may result in error codes relating to safety margins on the x-ray biopsy unit which should not be overridden. Care should be taken not to damage the breast table or other parts of the assembly. Damage to phantoms or needles used for calibration could cause problems with equipment performance. Note that requirements for testing in vertical or lateral approaches will be different for prone biopsy tables.

The clinical needles settings that are used most frequently should be prioritised for testing. If a combination is rarely used, it may be sufficient to only test before use. If there are different programmed selections for the same needle with different throws, then each throw may need to be tested. 

When multiple needles, modes and approaches are used, the service should consider a rolling schedule that tests each combination on rotation within a specified time period - for example, all needles tested within 1 month. This should be guided by the principles set out in the introductory section. Needles can be grouped together to make more efficient use of time, but care should be taken to ensure that each programmed needle setting is tested even if needles appear to be similar, as this might mean that the needle length or position of the cutting edge is different. In all cases, advice on testing schedules and frequency should be sought from the MPE.

Frequency: Weekly to monthly, or before each biopsy/localisation session if less frequent

Tolerances: 

Suspension levels as recommend by the x-ray biopsy system supplier or, if not specified by the supplier:

Tolerances to be set locally depending on needle type and approach.

Greater than 3mm may be typical in the direction of needle throw

Greater than 2mm may be typical in the 2-remaining directions 

If results are out of tolerance, the set up must first be checked and the test repeated.  If results are still out of tolerance, corrective action must be taken before the system is used clinically. This may involve contacting the system supplier. Remedial levels are not appropriate in this context.

Suppliers may suggest other tests involving the biopsy system, for example checking needle holder accuracy or checking the automatic exposure control (AEC) with different thicknesses of polymethylmethacrylate (PMMA) in biopsy mode. These tests are out of the scope of this document. AEC tests may be performed by the medical physics service in biopsy mode.

5. Tests following service visits

There must be robust handover procedures in place for any visits by service engineers and application specialists. The handover procedures should identify whether any adjustments have been made that might affect targeting accuracy or if there have been any changes to the programmed needle settings. Scenarios where tests of the biopsy system may be required include software, workstation or monitor upgrades, and instances where software back-ups have been restored.

If any such adjustments or changes are indicated, appropriate tests will be required prior to carrying out any clinical biopsy or localisation procedure to confirm the accuracy of the target spatial coordinates, and/or to make sure that the physical set-up for each clinical needle matches the settings programmed into the x-ray unit. Advice on the tests to be carried out should be sought from the MPE.

There should be no need to perform tests of the biopsy system following routine planned preventative maintenance or physics surveys, or following interventions such as recalibration of AECs, unless software has been restored or any relevant changes are explicitly indicated.

6. New consumables and housekeeping

When new needle types or devices such as vacuum biopsy systems are being introduced, there must be cooperation between the application specialists for both the x-ray biopsy system and the needle or device supplier to understand clinical requirements. Any new needle or device parameters should preferably be entered on the x-ray biopsy system by the supplier’s application specialist, who can make sure this is done accurately and robustly. Some suppliers prohibit the user from entering or amending parameters on the x-ray biopsy system, thus making errors much less likely.

Documented evidence of the changes made must be kept by the breast screening service and on the application specialist’s records.

Where the needle or device parameters have to be entered or amended by the users, this should be carried out by 2 experienced mammographers who have been trained in the process. There must be documented evidence including details of the exact changes made, who made the changes, and who witnessed and authorised the changes. 

Irrespective of who made the changes, once a new needle or device has been entered, the accuracy of needle positioning must be confirmed as described in the 2. commissioning section and clearly documented.

Needles and devices undergo rigorous QC testing by their suppliers to provide consistency. Once set up correctly on the x-ray biopsy system, there should be negligible variation within or between batches removing the need to test a needle or device from every new batch. Care should be taken to confirm the specification of needle matches that expected, particularly when the supplier changes.

It is useful to maintain good housekeeping of the programmed needles to make sure that only those in clinical use and available within the department are retained. Where they are no longer in use, the details should be made inaccessible on the drop-down menu of the x-ray biopsy system by deleting or retiring them. This will minimise the risk of incorrect needle selection and reduce errors.

7. Examples

Example 1:

A breast screening service carries out biopsies and localisations on 2 x-ray units. Unit 1 is enabled for tomosynthesis and stereotactic biopsies/localisations. Unit 2 is enabled only for stereotactic biopsies/localisations. The service uses a range of needles for localisations, markers, core biopsies and vacuum assisted biopsies. A vertical approach is used most frequently, though a lateral approach may be used occasionally for vacuum assisted biopsies. Needle settings have been programmed to reflect the different options and are the same on each unit.

• Regime for checking target spatial coordinate accuracy:

Weekly tests are carried out using the supplier’s calibration test needle and pin phantom as follows:

Unit	Stereotaxis			Tomosynthesis
	Vert	L Lat	R Lat	Vert	L Lat	R Lat
Unit 1: tomo and stereo biopsy	Yes	Yes	Yes	Yes	Yes	Yes
Unit 2: stereo biopsy only	Yes	Yes	Yes	No	No	No

• Regime for checking clinical needle accuracy:

For each clinical procedure the type of needle to be used, the approach, and (for Unit 1) the mode (stereotaxis or tomosynthesis), are known before the clinical procedure is undertaken. Tests are carried out using the predetermined needle, approach, and mode immediately before the clinical procedure. The only aspect that might change once a procedure has started is the mode used for Unit 1 (stereotaxis or tomosynthesis). If there is any doubt about which mode will be used, both are tested. The weekly calibration test checks localisation accuracy in both stereotaxis and tomosynthesis modes, so testing both modes with the clinical needle is not strictly necessary.

Example 2:

A breast screening service uses a wide range of needles for different procedures in a variety of approaches. Only 1 x-ray unit is used within this department for biopsies and localisations.

• Regime for checking target spatial coordinate accuracy:

Calibration test needle tested in each approach (vertical and lateral arm) every day that the system is used.

• Regime for checking clinical needle accuracy:

Monthly rolling programme of testing all needles in the vertical and lateral approach.

If a new needle is introduced, this should be added to the needle schedule as appropriate.

Daily	Week 1	Week 2	Week 3	Week 4
Calibration test needle	Needle A - 16cm	Needle B - 9cm	Wire A - 9cm	Needle C - 9cm
	Needle A - 10cm	Needle B - 11cm	Wire B - 11cm	Needle C - 11cm