01Purpose and principlesWhat the assessment is for and the core concepts behind it.
Cancer imaging begins with the management decision. Ultrasound offers real-time assessment and guidance without ionising radiation; CT provides rapid cross-sectional staging of chest, abdomen and pelvis; MRI gives high soft-tissue contrast for brain, spine, pelvis, liver and local surgical planes; PET-CT demonstrates metabolically active disease in selected tumours and questions. The best test depends on tumour biology, anatomical site and whether the result will alter biopsy, curative treatment or symptom control.
Baseline imaging should use an agreed technique before treatment so later change is comparable. Response may be complete, partial, stable or progressive under formal criteria, but size is only one dimension. Necrosis, metabolic activity, marrow disease and non-measurable lesions need different approaches. Radiotherapy and immunotherapy can create inflammation; surgery changes anatomy; antiangiogenic therapy can change enhancement before size.
Safety includes justification of radiation and contrast, pregnancy assessment where relevant, kidney and allergy review, device compatibility and a plan for incidental findings. Urgent symptoms override scheduled imaging. A patient with new neurological deficit, dyspnoea or sepsis needs targeted acute assessment even if surveillance imaging is booked next month.
Key points
- Imaging answers a defined question: detect a lesion, characterise local anatomy, stage spread, guide biopsy, plan treatment, assess complications or measure response.
- Ultrasound, CT, MRI, PET-CT, plain radiography and nuclear medicine have complementary strengths; no modality is a universal gold standard for all cancers.
- Use the tumour-specific first-line staging pathway and image enough anatomy to change management without repeating recent adequate studies.
- A suspicious imaging finding is not always malignant; infection, inflammation, treatment change and benign lesions can mimic cancer or progression.
- Compare response with a documented baseline using consistent technique and recognised disease-specific criteria, not impressionistic size language alone.
- Immunotherapy can cause atypical response and inflammatory appearances; clinical deterioration still requires urgent assessment rather than assuming pseudoprogression.
- Contrast, radiation, pregnancy, renal function, implanted devices and claustrophobia affect modality selection and preparation.
- Urgent imaging for cord compression, obstruction, haemorrhage, thrombosis or treatment toxicity is separate from routine restaging intervals.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
MRI or site-specific cross-sectional imaging may define fascial planes, neurovascular involvement and resectability better than a general staging scan.
CT or selected PET-CT maps nodal and distant disease when the result changes curative field, surgery or systemic treatment.
Clearly defined lesions reproducibly measurable on serial studies can anchor formal response assessment, while diffuse or tiny disease may be non-measurable.
Inflammation, radiation change, postoperative collection or immune activation may increase size or uptake without viable progression.
New cord, brain, airway, vascular, bowel or urinary compromise requires same-day targeted imaging and acute specialist action.
03Method and interpretationA systematic approach to the test and its findings.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Contrast-enhanced CTFirst step - Why
- Stage thoracic, abdominal and pelvic anatomy rapidly and assess many acute complications.
- Interpretation and limitations
- Review contrast suitability and compare with prior studies; small marrow, brain or pelvic lesions may require another modality.
- 02
MRI with tailored sequences - Why
- Characterise high-contrast soft-tissue anatomy and marrow, brain, liver or pelvic disease.
- Interpretation and limitations
- Protocol selection matters; assess implant safety, motion and gadolinium context, and do not delay emergency CT when MRI is unavailable.
- 03
Ultrasound - Why
- Characterise superficial, hepatobiliary, pelvic or thyroid lesions and guide sampling.
- Interpretation and limitations
- Operator and acoustic-window limits apply; a concerning deep or complex lesion often needs cross-sectional staging.
- 04
FDG PET-CT or tumour-specific nuclear imaging - Why
- Map biologically active disease in selected staging and response pathways.
- Interpretation and limitations
- Physiological uptake, infection, inflammation and recent treatment can create false positives; low-avidity tumours can be falsely negative.
- 05
Formal response assessment - Why
- Compare disease burden with baseline under recognised criteria.
- Interpretation and limitations
- Use consistent lesions, technique and timing, document non-target and new disease, and involve radiology when apparent progression conflicts with clinical course.
04Clinical next stepsHow the result changes management or prompts escalation.
01SelectMatch modality to the decisionFirst stepCancer is suspected or confirmed and imaging is required.+
- 1State whether the question is diagnosis, local staging, distant staging, biopsy access, emergency complication or treatment response.
- 2Use the tumour-specific recommended modality and review recent images to avoid duplication, radiation and delay.
- 3PreferredEscalationPrepare for contrast, pregnancy, renal, allergy, device and access needs, and escalate if the preferred study is unsafe or unavailable.
02MeasureCreate and compare a baselineSystemic or radiotherapy treatment is planned and response will influence continuation.+
- 1Acquire appropriate baseline imaging close enough to treatment to represent current disease and identify reproducible target lesions.
- 2Repeat at the protocol-defined clinical interval using comparable technique, while adding urgent imaging for new symptoms.
- 3Classify response using the recognised tumour and treatment criteria, describing uncertainty, non-target disease and suspected treatment effect.
03ResolveInvestigate apparent progressionImaging worsens but timing, symptoms or treatment mechanism creates uncertainty.+
- 1Assess clinical trajectory, treatment type, inflammatory markers and the exact radiological pattern rather than applying a pseudoprogression label automatically.
- 2AlternativeDiscuss targeted biopsy, short-interval imaging or alternative modality when the distinction would change treatment and the patient is stable.
- 3Treat acute deterioration and organ compromise immediately; confirmation strategies must not delay necessary rescue or infection therapy.
05Risks, monitoring and follow-upComplications, safety checks and further assessment.
- Maintain accessible baseline images and reports, including target lesions and modality, for every subsequent response comparison.
- Track cumulative contrast reactions, renal function and relevant radiation exposure when repeated studies are considered.
- Review incidental findings according to risk and ensure a named clinician owns any recommended follow-up.
- Escalate unexpected new symptoms between scheduled scans rather than advancing routine restaging without clinical assessment.
- At MDT, record whether imaging establishes, suggests or cannot exclude progression so uncertainty is visible in the treatment decision.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Question before modality
Naming the decision prevents habitual CT, unfocused PET requests and scans that cannot alter care.
Uptake is not malignancy
Inflammation, infection, muscle activity and physiological organs can be PET-avid, requiring anatomical and temporal correlation.
Size is not all biology
Cystic change, necrosis, marrow response and metabolic alteration may occur without a simple reduction in longest diameter.
Pseudoprogression is uncommon
It is a possibility in selected immunotherapy contexts, not a safe default explanation for every worsening scan.
Incidental findings need ownership
A recommendation buried in a report can create harm when neither oncology nor primary care knows who must act.
07Common pitfallsFrequent interpretation and management errors.
- 01
Ordering imaging without a management question.
- 02
Calling PET uptake diagnostic of cancer.
- 03
Comparing scans with different technique casually.
- 04
Ignoring non-measurable or new disease.
- 05
Assuming all early immunotherapy worsening is pseudoprogression.
- 06
Delaying emergency imaging until scheduled restaging.
- 07
Leaving incidental follow-up unassigned in clinical practice.