Gamma probes, handheld gamma cameras and dose calibrators

Sentinel lymph node biopsy replaced full node clearance in breast cancer and melanoma because the surgeon can find the node with a handheld gamma probe: a collimated scintillation or semiconductor detector that counts the technetium-99m nanocolloid injected around the tumour, guiding the incision and confirming when the hot nodes are out. Devicor's Neoprobe (now under Mammotome), Eurorad's Europrobe, Crystal Photonics' CrystalProbe and drop-in probes for robotic surgery from Lightpoint Medical are the main devices; small handheld gamma cameras such as Sentinella and Crystal Cam image the node field, and PET-emitting tracers such as gallium-68 PSMA are detected with high-energy probes in radioguided prostate surgery. Magnetic tracers detected by Endomag's Sentimag (also now part of Mammotome) offer the same localisation without radioactivity. In the radiopharmacy and hot lab, dose calibrators, ionisation well chambers such as Capintec's CRC series (Mirion) and Comecer's, measure the activity of every syringe of diagnostic tracer or therapeutic radioligand against the prescription, and survey meters and contamination monitors protect staff.

The probe technique needs a nuclear medicine department to inject and image the tracer, a supply of technetium-99m from molybdenum generators, and radiation-protection handling of specimens; magnetic and fluorescent alternatives remove the isotope but have their own artefacts. Dose calibrators are inexpensive but require regular constancy, linearity and geometry checks and isotope-specific calibration factors, especially for the new alpha and beta therapy isotopes.