Teaching pack: Imaging

Anatomic imaging (CT, MRI, ultrasound) shows shape and size. Functional and molecular imaging (PET, SPECT) shows biology: glucose uptake, receptor expression, immune cell presence. The frontier is target-specific PET that predicts whether a targeted drug will work, and imaging that reads out treatment response within days rather than months.

• AI in radiology: Software that reads scans alongside radiologists, catching cancers earlier and predicting who is at risk.
• Aidoc CARE (clinical radiology foundation model): Aidoc CARE is a single foundation model behind many FDA-cleared triage alerts in emergency radiology.
• CAIX PET (89Zr-girentuximab): CAIX PET is a scan using an antibody against a protein almost unique to clear-cell kidney cancer, to tell cancer from benign kidney lumps without a biopsy.
• CT (computed tomography): A CT scan is a fast 3D X-ray that shows the size and shape of tumours and whether they have spread.
• CT-FM (whole-body CT foundation model): A model pretrained on 148,000 CT scans to segment organs and triage findings.
• FAPI PET: FAPI PET is a PET scan that lights up the scaffolding around almost any solid tumour, including cancers the standard sugar scan misses.
• FDG PET: FDG PET is the standard PET scan. A radioactive sugar shows which tissues are burning glucose fast, which most cancers do.
• Fluorescence-guided surgery: Injecting a dye that makes tumour glow so the surgeon can see exactly where to cut.
• HER2 PET: HER2 PET is a PET scan using radiolabelled trastuzumab or smaller HER2 binders to map HER2 across all metastases at once.
• Imaging core labs and central review: Independent radiologists who re-read every scan in a trial the same way, so response rates mean the same thing across hospitals.

• Molecular imaging roadmap: FDG → PSMA → FAP → antigen and immune PET · PET and FDG (historic)
• Molecular imaging roadmap: FDG → PSMA → FAP → antigen and immune PET · Receptor PET: SSTR and PSMA (historic)
• Molecular imaging roadmap: FDG → PSMA → FAP → antigen and immune PET · Stromal PET and total-body scanners (current)
• Molecular imaging roadmap: FDG → PSMA → FAP → antigen and immune PET · Drug-target and immune PET (emerging)
• Molecular imaging roadmap: FDG → PSMA → FAP → antigen and immune PET · Speculative (speculative)

• VISION (phase 3, n=831): Overall survival: 15.3 months vs 11.3 months, HR 0.62
• RATHL (phase 3, n=1,214): Progression-free survival at 3 years (PET2-negative): 85.7% vs 84.4%
• NLST & NELSON (low-dose CT screening) (phase 3, n=53,454): NLST: relative reduction in lung cancer mortality: 20%
• GHSG HD21 (phase 3, n=1,500): Progression-free survival at 4 years: 94.3% vs 90.9%, HR 0.66
• MSLT-II (phase 3, n=1,939): Melanoma-specific survival at 3 years: 86% vs 86%
• PRECISION (phase 3, n=500): Detection of clinically significant cancer: 38% vs 26%

1. Does the TROP2 level measured on a biopsy tell you whether Trodelvy will work?
   Answer

   Not reliably. ASCENT showed benefit regardless of TROP2 IHC, so no companion diagnostic is required; expression is heterogeneous and archival tissue may not reflect current status. TROP2 PET tracers are being developed to map expression across the body and over time.
2. What is theranostics and what is the best-known example?
   Answer

   Using the same targeting molecule for a diagnostic scan and a treatment: PSMA PET shows where prostate cancer is, and 177Lu-PSMA-617 (Pluvicto) delivers radiation to the same target.
3. What did the VISION trial show?
   Answer

   177Lu-PSMA-617 plus standard care improved overall survival (15.3 vs 11.3 months, HR 0.62) in PSMA-positive metastatic castration-resistant prostate cancer after ARPI and taxane.
4. What is the difference between a CT scan and a PET scan?
   Answer

   CT is a fast 3D X-ray showing size and shape; PET shows biology by tracking where a radioactive tracer accumulates (for example glucose uptake with FDG or a specific protein such as PSMA). PET/CT combines both.
5. What does a FAPI PET scan see that an FDG scan often misses?
   Answer

   The activated fibroblasts (FAP) in tumour stroma, present in more than 90% of epithelial cancers, giving high contrast in pancreatic, gastric, HCC, and peritoneal disease where FDG is weak; it is not yet approved.
6. How could a TROP2 PET scan change how ADCs are used?
   Answer

   It would map antigen expression across all lesions and over time, potentially selecting patients, choosing between TROP2 ADCs, and detecting antigen loss at progression to guide a switch to a different target, as PSMA PET does for Pluvicto. First-in-human tracers exist; no outcome data yet.