Bone Scan — Nuclear Skeletal Imaging

Radionuclide bone scintigraphy relies on intravenous injection of a radioactive tracer, most commonly technetium-99m linked to a bisphosphonate carrier molecule like methylene diphosphonate (Tc-99m MDP). This radiotracer distributes throughout the vascular system and adsorbs onto newly forming crystalline hydroxyapatite in areas of active bone remodelling. Regions experiencing osteoblastic reaction or increased capillary blood flow incorporate proportionally higher concentrations of the radiotracer.

After an interval allowing physiological clearance of unabsorbed tracer through the urinary tract, a gamma camera scans the patient's body to detect emitted radiation. The resulting images reveal skeletal areas with abnormally elevated metabolic turnover as 'hot spots'. While sensitive for detecting osteoblastic bone metastases, bone scans can also highlight non-malignant bone repair processes, including healing traumatic fractures, osteomyelitis, and degenerative osteoarthritis.

The skeletal system is one of the most common sites for solid tumours to spread. Detecting bone involvement early alters the clinical cancer stage and redirects treatment goals from localised therapy toward systemic approaches. Bone scans enable rapid whole-body skeletal evaluation, helping clinical teams identify metastatic lesions before they trigger serious complications like spinal cord compression or bone fractures. Additionally, comparing baseline scans with follow-up imaging provides valuable visual feedback regarding how well systemic cancer therapies are working.

A bone scan does not require tissue sampling. Patients receive an intravenous injection of Tc-99m radiotracer and are asked to drink extra fluids to promote urinary excretion of unbound tracer. Whole-body planar imaging or SPECT/CT (single-photon emission computed tomography combined with conventional CT) is performed two to four hours later to achieve precise anatomical localization.

Bone scans are widely used for staging and surveillance in prostate cancer and breast cancer, both of which exhibit a high predilection for osteoblastic skeletal metastases. They are also utilised in non-small cell lung cancer, renal cell carcinoma, thyroid malignancies, and primary bone tumours like osteosarcoma.

Detecting skeletal metastases typically shifts clinical management toward systemic therapies, such as endocrine treatment, chemotherapy, or immunotherapy. It also prompts the addition of bone-protective therapies like bisphosphonates or denosumab, and directs focused palliative radiotherapy to areas causing severe pain or presenting high fracture risk.