Guidance

Bowel cancer screening: guidelines for CTC imaging

Updated 4 October 2024

The Radiology Clinical and Professional Group for the NHS Bowel Cancer Screening Programme (BCSP) developed these guidelines to define standards for the delivery of high-quality colon imaging to support the programme.

People with a screening test kit result that requires further investigation are offered a colonoscopy. A specialist screening practitioner (SSP) assesses their medical fitness to undergo the procedure.

Computed tomography colonoscopy (CTC) is the only alternative diagnostic test available in the programme pathway when colonoscopy is incomplete, or the patient is considered medically unfit for colonoscopy. CTC is the best radiological procedure for identifying colorectal cancer and advanced colonic polyps. The examination requires pre-procedure bowel preparation and peri-procedure colonic insufflation and post procedural care. The use of CTC within screening must comply with this guidance.

CTC may be offered as a diagnostic test for people who meet the criteria for colonoscopy, but who are assessed as medically unfit for the procedure.

CTC techniques and performance should follow the guidance specified by the British Society of Gastrointestinal and Abdominal Radiology (BSGAR).

1. Use of CTC in the NHS BCSP

CTC is used for screening people who are medically unfit for a colonoscopy. These include people:

• with complex, severe co-morbidities
• with medication or mobility needs making the risks or difficulties of colonoscopy unacceptable
• with intolerance to the procedure
• with significant neurological, cardiovascular or respiratory comorbidity, which might compromise the safety of the procedure
• deemed too frail to undergo standard laxative bowel preparation

CTC may also be used following an incomplete colonoscopy, or for people with a history of difficult or incomplete colonoscopy. This could be due to technical difficulties such as looping or an impassable stricture, or other issues faced during the procedure.

Assess patients on an individual basis and review previous endoscopy reports if available.

There is no role for the use of barium enema within the NHS BCSP and it must not be used.

There is no reason for people having CTC as their first screening investigation to have a flexible sigmoidoscopy beforehand because CTC is a whole colon examination.

Do not use intravenous (IV) contrast in CTCs unless the individual has an indication to require staging, or it is indicated to clarify other significant pathology identified on immediate scan review. This means the person will move to the symptomatic service and this is done outside of the screening pathway.

2. Incomplete colonoscopy

For CTC following an incomplete colonoscopy, the patient has already taken bowel cleansing preparation. Make every effort to carry out same day or following day CTC. Give oral contrast for stool tagging in such cases. If formal sedation is used for colonoscopy, consent for subsequent CTC could be invalid. Local policy should be agreed which allows for CTC consent at the time of consent for colonoscopy. An alternative would be to perform the CTC the following day when effects of sedation will have passed. BCSP colonoscopy is commonly performed without sedation, in which case CTC consent will not be affected.

Same day CTC is not indicated if colonoscopy has been sub-optimal due to poor bowel preparation. In these circumstances a discussion with the colonoscopist is required. Re-book the patient for colonoscopy after modifying the bowel preparation to avoid a repeat of the inadequate cleansing.

In cases of a suspected malignant obstructing lesion, a same day CTC is desirable to stage the tumour and to allow assessment of other colonic lesions or other malignancies. You can use IV contrast at this procedure unless contraindicated. The patient is symptomatic and will be handed over to the symptomatic service. Therefore the procedure is outside the screening pathway.

3. Patient selection

The decision to refer a patient for CTC rather than colonoscopy rests with the screening endoscopist, in conjunction with the SSPs and the patient. BCSP radiologists take responsibility for accepting the referrals. All challenging cases should be discussed with the BCSP radiologists.

A local pathway must exist to define the process for patient referral for imaging, showing clear lines of responsibility and a referral timeline.

Where a patient is unlikely to be fit enough for an imaging examination, do not automatically refer them. Instead, there should be a full discussion with them and their carers (including a best interest multi-disciplinary team meeting where appropriate) before making a decision. Record these discussions on the Bowel Cancer Screening System (BCSS) and in the patients’ medical records. In some situations, a decision not to progress with further investigations may be the agreed course of action.

Patient choice is not a reason for undertaking a CTC.

If the patient is referred for CTC following a biopsy or polypectomy, direct communication between the radiologist and endoscopist is required to discuss the timing of the scan and to assess the risk of perforation (depending on details available from the procedure). In many cases you should defer immediate CTC. Consider a low radiation dose scan before insufflation to exclude perforation.

If a patient declines the offer of a colonoscopy then that ends the screening episode. The GP can make a symptomatic referral for CTC if required. Close the person’s screening episode on BCSS. This will automatically return them to routine recall in 2 years’ time if they remain within the eligible age range for screening.

4. Patients unfit for CTC

A CT abdomen/pelvis (or similar alternative) must not be performed if a patient attends for CTC but the radiology team feels that they are medically unfit for the procedure. An unprepared CT abdomen/pelvis does not have an evidence base as a screening test for cancer.

The radiology team must make contact with the screening centre within 1 working day to arrange for the episode to be closed, and discharge the patient back to the GP for symptomatic care. Document on BCSS why they were not fit for the diagnostic test.

5. Referral to another screening centre for CTC

Where CTC is not available within the local service, refer the patient to another radiology service that is quality assured by the Screening Quality Assurance Service (SQAS).

Ensure there is a clearly documented pathway in place to show responsibilities and timescales for the referral. A local service level agreement should be in place for this.

6. Staging

Staging CT scanning of patients with an abnormal finding on colonoscopy or CTC is routine, and should follow the usual staging pathway appropriate for the case. Rapid access or even same day staging is encouraged.

If the colonoscopy has been incomplete secondary to pathology, a combined staging and CTC is required.

7. CTC surveillance

CTC surveillance can be considered for patients where there has been an abnormal finding at previous colonoscopy or CTC that was not treated by excision, but requires follow-up.

8. The BCSP radiology team

A team approach is critical to the success of the CTC service for patients in the NHS BCSP. Every member of the CTC team must undertake training appropriate to their role. This should be defined within each service, with reference to national recommendations.

The local service should support opportunities for role extension where appropriate. This requires discussion at the clinical professional group (CPG) and agreement by SQAS.

8.1 Lead radiologist

Every bowel cancer screening centre must have a lead radiologist in post, who is actively involved in BCSP. They are accountable to the NHS BCSP clinical director for their BCSP activity. The lead radiologist is responsible for the quality of the CTC service for BCSP patients, ensuring that guidance is followed and the service complies with the screening standards and CTC pathway.

If there are 2 or more radiology sites or trusts within a BCSP service, there should only be one lead radiologist.

Each site or trust should have a named person responsible for BCSP CTC. This might be another radiologist, or a senior CTC radiographer or consultant GI radiographer working within the BCSP. Where BCSP CTC is performed at more than one site, the lead radiologist is responsible for ensuring that procedures and protocols are at the required standard (and comply with the screening service quality assurance operating model) across all sites.

The roles and responsibilities of each team member should be clearly stated in the service’s quality management system (QMS). The lead radiologist should notify the programme manager/lead SSP of any new BCSP reporting radiologists (or if any leave the trust, so they can be removed from BCSS).

There should be good communication with the other areas of the screening service, particularly with the screening centre management team (clinical director, programme manager and lead SSP).

Programme/service updates along with patient feedback about CTC should be frequently provided by the screening centre to the lead radiologist, to ensure the effective delivery of the screening pathway and good patient experience. The radiology team should have regular imaging team meetings to discuss the BCSP related imaging service and link closely with the screening centre management team.

The lead radiologist should attend relevant BCSP operational meetings (or send a senior representative to deputise). They should provide the programme board with an overview of the CTC service and discuss any service issues. Oversight of the radiology data available on BCSS is essential. The lead radiologist is responsible for ensuring data is captured in accordance with the radiology minimum dataset (see section 16 below).

The lead radiologist should participate in post investigation colorectal cancer audits, along with assisting with root cause analysis and identify cases for learning/sharing.

The time required to fulfil the role of lead radiologist should be reflected within the individual’s job plan.

8.2 Reporting BCSP radiologists and radiographers

Reporting BCSP radiologists are accountable to the lead radiologist (or the deputy lead in their absence).

BCSP reporters must be approved to report CTC by the lead and be registered on BCSS. The screening centre programme manager can support getting the individual registered on BCSS.

Each BCSP reporter must be registered with a professional body. Practitioners with a certificate of completion of training in radiology (or equivalent) can report CTC within the BCSP.

Each BCSP reporter must have undertaken practical training involving at least 50 endoscopically validated CTC cases, as well as in practical aspects of scan acquisition, dose limitation, consent, scan optimisation, bowel preparation, interpretation methods and the pitfalls and management of complications.

In order to provide a quality service, each radiologist and radiographer reporting BCSP cases should aim for a minimum of 120 CTCs a year (this covers both symptomatic and screening practice).

Training alone cannot guarantee competence. Evidence of ongoing continuing professional development (CPD) must be demonstrated. This should include:

• audit
• attending MDTs
• reviews of BCSP data
• feedback on their reported studies
• attendance at local, regional or national QA events

BCSP reporters must be aware of all QA requirements and reporting guidelines. Reporting of the minimum data set is required (see the minimum dataset for CTC reporting in the BCSP).

8.3 Radiographers

A lead radiographer for the BCSP CTC service should be identified on each site. They should ensure all radiographers working with BCSP patients are trained/assessed to the Society and College of Radiographers (SCoR) endorsed CTC Service Practitioner Framework standards.

All radiographers performing CTC for the BCSP must have undertaken training (and be able to provide evidence of training) in CTC technique, including ongoing assessment of their practice in the form of CPD.

The CTC service should be sufficiently staffed to ensure adequate availability of trained radiographers. Adequate staffing will depend on the size of the symptomatic service. The SCoR framework includes recommendations for service staffing levels.

At least one radiographer in each unit must have attended specialist external training in CTC.

Radiographers should familiarise themselves with the SSP assessment process. Best practice is to attend an SSP clinic on a regular basis to remain up-to-date with the programme. The lead SSP can organise SSP clinics to support ongoing CPD for members of the radiology team.

Patient group directives (PGDs) should be in place for the administration of hyoscine butyl bromide (Buscopan), and IV contrast (for examinations with abnormal findings that require a symptomatic referral). A PGD or standard operating procedure (SOP) should be in place for providing bowel preparation in units where radiographers are involved in this activity.

8.4 Radiology assistants

Radiology assistants are employed in many imaging departments. They are involved with preparing patients for CTC examinations including within the BCSP. They should undertake local training, and be familiar with the screening pathway and how it differs from the symptomatic pathway for radiological procedures.

8.5 Specialist screening practitioners (SSPs)

The SSP takes a full medical history from the patient in clinic and documents all relevant information on the referral. The SSP answers routine queries about the CTC procedure and is the patient’s main point of contact regarding the procedure and the wider screening programme.

SSPs should attend a CTC list during their induction and be familiar with the CTC pathway. If the patient requests it, an SSP should try to be available for their attendance for CTC. It is acknowledged that some SSPs cover a large geography and this is not always possible.

9. Governance and risk management

Documents relating to departmental governance and risk management strategies should be available and understood by all team members.

There should be a process for the identification of BCSP cases to ensure the CTC scan is performed in accordance with this guidance.

There should be an SOP for risk management within the CTC unit, including information on the management of complications, and a procedure for escalation when required. SOPs relevant to provision of the BCSP service should be referenced in local policies, and included in updates when these occur.

Processes should be in place to report adverse incidents (AVIs) and screening incidents. All staff working in the radiology department must be aware of the processes and documentation required. All incidents should be reported internally and escalated to the screening centre at the host trust.

BCSP patients should be treated in a similar way to 2-week cancer referrals, with appropriate processes for reporting priorities in place.

10. CTC appointment and pathway

The local CTC referral process should document the requirement of verifying the suitability of patients for bowel preparation.

An SOP must be in place to describe the process of identifying BCSP cases for appropriate prioritisation, preparation, scan technique and timely reporting by a BCSP accredited reporter.

The date of a confirmed test date following the date of CTC referral should be within 2 weeks to meet the pathway standards (see pathway standard BCSP-S07).

A validated CTC report must be available to view within 7 days of the procedure.

Communication of results from radiology to the SSP must be clear. Referral into the MDT and symptomatic service in the event of an abnormal finding should comply with local SOPs on communication/escalation of significant findings.

11. Patient information

A national patient information leaflet is available along with an easy guide version. You must make the national leaflet available to everyone requiring a BCSP CTC, in a format that is appropriate for them to understand.

The national leaflet does not provide locally-specific information. Local patient information must be developed to meet any additional needs, but it should not replace the national leaflet. Locally developed patient information may include:

• dietary advice
• contact details of the CTC team (for any questions, for example about bowel preparation)
• contact details for patients with diabetes
• information for patients with documented allergies to iodinated radiographic contrast agents
• information relating to the clinic location and facilities

12. Consent

Staff involved in the consent process must have received training and be approved as competent by the trust.

The SSP provides the patient with information about the consent process at the time it is agreed to refer the patient for CTC. Information is both verbal and written and given at the SSP clinic appointment.

Written consent must be signed by the patient before CTC is undertaken. This process forms part of the pre-procedure check list.

The consent form and pre-procedure check list should be dated, include details of the consenter, and state the risks of CTC. The consent process must comply with locally agreed policies. If the patient withdraws consent at any point in the pathway this must be acted upon and documented.

13. Screening test standards

The guidance from BSGAR is the reference document for the technical standards of CTC practice.

The guidance provides information on:

• bowel preparation
• scanner parameters
• techniques during the procedure (including rectal intubation, insufflation, positioning and staging)
• use of IV contrast agent
• post procedural care
• reporting (interpretation methods and the minimum dataset)

14. Patient safety

Resuscitation and monitoring equipment must be available to manage emergency situations, along with appropriately qualified medical and nursing staff.

Radiographers who administer an IV contrast agent or hyoscine must do so in accordance with a locally written PGD.

Colonic perforation is a recognised complication of CTC. It occurs in around 1 in 2,500 examinations, although the rate may be lower in asymptomatic people than those with colorectal symptoms.

An appropriately trained radiographer or radiologist should review the scan images to check for perforation before the patient leaves the scanning area. If a perforation is detected, a radiologist should contact the surgical team to request clinical assessment. While most perforations caused by CTC are asymptomatic, further management is at the discretion of the local surgical team. Record the incident in the patient’s notes and on BCSS, and manage it as an AVI.

An SOP should be in place to cover complications including:

• perforation
• abdominal pain
• blurred vision
• hypostension or vasovagal syncope
• extravasation
• anaphylaxis

15. Audit

Bowel cancer screening centres need to demonstrate safe and effective delivery of CTC within the programme. Appropriate audits to demonstrate this are required. These should be presented at BCSP team meetings and at local, regional or national BCSP audit meetings.

See the audit schedule example below. Some of these are annual audits, some are undertaken in advance of a QA visit, and some on request from the SQAS or the clinical director of the screening centre. Some of the data required for the audits is available on BCSS, and some are available on RIS. In addition, some data will need to be generated locally by radiographers, physics departments, radiologists or the lead radiologist.

The lead radiologist should participate in Post Interval Colorectal Cancer (PICRC) audits.

15.1 Audit schedule example

A. Audit of all BCSP CTCs in last 12 months (annual):

• Report turnaround time
• Reporting radiologist (appropriate BCSP radiologist)
• Minimum dataset present Y/N
• Buscopan Y/N
• IV contrast Y/N
• Adequacy (score good/adequate/poor)
• Findings (C grading from BCSS)
• Follow-up of all abnormal colonic findings from CTC, for example colonoscopy/surgery outcome

B. CTC reporting figures per radiologist for previous year (annual)
C. Radiation dose audit (3 yearly)
D. Patient experience survey (3 yearly)
E. Analysis of previous 3 years’ AVIs
F. 3-year BCSP CTC polyp/cancer detection rates per reporting radiologist

16. Minimum data set for CTC report in the BCSP

16.1 Technique

Buscopan (dose), IV contrast, single/dual/triple position with gastrograffin/omnipaque tagging (dose).

16.2 Quality

Good/adequate/poor bowel preparation and distension.

16.3 Summary codes

The codes are:

• E1: normal, anatomic or post surgical variant
• E2: incidental, unimportant/already known
• E3: new incompletely characterised finding (further investigation according to local protocol)
• E4: potentially important new finding (requires further action)
• E5: significant new finding identified

16.4 Intracolonic findings: suspected/characteristic cancer

Morphology

Categories are:

• minimally elevated < 3mm
• polypoid
• saddle shaped
• obstructing
• annular

16.5 Intracolonic findings: suspected/characteristic polyp

Morphology

Categories are:

• pedunculated (Ip) – stalk between polyp and underlying mucosa
• semi-pedunculated (Isp) – broad-based, base narrower than top but no stalk
• sessile (Is) – no stalk base and top of lesion have same diameter (height at least 2.5mm)
• flat: slightly elevated (IIa) – height less than 2.5mm
• flat: slightly elevated with depressed centre (IIa/c) – height less than 2.5mm

16.6 Summary codes

The codes are:

• Cx: inadequate study

• C1: normal, benign lesion or 1 to 2 polyps less than or equal to 5mm

• C2: 1 to 2 polyps, 6mm to 9mm (low risk)

• C3a: 3 to 4 polyps, 1mm to 9mm (intermediate risk)

• C3b: 1 to 2 polyps, at least one polyp greater than or equal to 10mm (intermediate risk)

• C3c: intermediate stricture (intermediate risk)

• C4a: 5 or more polyps, smaller than 10mm (high risk)

• C4b: 3 or more polyps, at least one polyp greater than or equal to 10mm (high risk)

• C5a: colon mass, characteristic of malignancy

• C5b: no tumour additional to colonoscopy findings

17. Minimum data set for CTC report in the BCSP

17.1 Technique

Buscopan (dose), IV contrast, single/dual/triple position with gastrograffin/omnipaque tagging (dose).

17.2 Quality

Good/adequate/poor bowel preparation and distension.

17.3 Summary codes

• E1: normal, anatomic or post surgical variant
• E2: incidental, unimportant/already known
• E3: new incompletely characterized finding (further investigation according to local protocol)
• E4: potentially important new finding (requires further action)
• E5: significant new finding identified

17.4 Intracolonic findings: suspected/characteristic cancer

Morphology

• minimally elevated < 3mm
• polypoid
• saddle shaped
• obstructing
• annular

17.5 Intracolonic findings: suspected/characteristic polyp.

Morphology

• pedunculated (Ip) – stalk between polyp and underlying mucosa
• semi-pedunculated (Isp) – broad-based, base narrower than top but no stalk
• sessile (Is) – no stalk base and top of lesion have same diameter (height at least 2.5mm)
• flat: slightly elevated (IIa) – height less than 2.5mm
• flat: slightly elevated with depressed centre (IIa/c) – height less than 2.5mm

17.6 Summary codes

• Cx: inadequate study
• C1: normal, benign lesion or 1 to 2 polyps less than or equal to 5mm
• C2: 1 to 2 polyps, 6mm to 9mm (low risk)
• C3a: 3 to 4 polyps, 1mm to 9mm (intermediate risk)
• C3b: 1 to 2 polyps, at least one polyp greater than or equal to 10mm (intermediate risk)
• C3c: intermediate stricture (intermediate risk)
• C4a: 5 or more polyps, smaller than 10mm (high risk)
• C4b: 3 or more polyps, at least one polyp greater than or equal to 10mm (high risk)
• C5a: colon mass, characteristic of malignancy
• C5b: no tumour additional to colonoscopy findings

18. Minimum data set for CTC report in the BCSP sample template

The BCSS investigation dataset will contain the following 8 sections:

1. Investigation Dataset

2. Contrast, Tagging & Drug Information:

• IV Buscopan Administered
  • Dose
• IV Contrast Administered
• Tagging Agent Given
  • Tagging Agent Type
  • Dose
• Additional Bowel Preparation

3. Radiology Information:

• Indication – prepopulated by system
• Examination Quality
  • Poor Examination Quality Reason Drop Down
• Number Of Scan Positions Drop Down
• Early Outcome Drop Down
• Late Outcome Drop Down
• Intracolonic Summary Code Drop Down

4. Failure Information:

• Failure Reasons Drop Down

5. Suspected Polyp Information:

• Location Drop Down
• Polyp Classification Drop Down
• Size Estimate

6. Suspected Colorectal Cancer Information:

• Cancer Type Morphology Drop Down
• Cancer Size
• Cancer Location Drop Down

7. Complication Information:

• Early Complication Drop Down
• Late Complication Drop Down

8. Suspected Findings:

• Benign Location Drop Down
• Benign Diagnosis Drop Down
• Extracolonic Summary Code Drop Down