Nuclear Medicine — How Radioactive Isotopes Save Lives
Nuclear medicine uses radioactive isotopes to see inside the body and treat diseases — particularly cancer. Unlike X-rays, which beam radiation through the body from outside, nuclear medicine puts the radiation source inside the patient. The isotopes are attached to biological molecules that naturally accumulate in specific organs or tumours, then their radiation is detected externally to create images or used internally to destroy cancerous cells.
Diagnostic imaging: SPECT
Single Photon Emission Computed Tomography uses gamma-emitting isotopes. The workhorse is Technetium-99m (half-life 6 hours), which emits a single 140 keV gamma ray — energetic enough to escape the body but low enough to be safely detected. Tc-99m can be attached to different carrier molecules to image bones, hearts, kidneys, thyroids, and brains. About 40 million diagnostic procedures use Tc-99m worldwide each year.
The 6-hour half-life is deliberate — long enough to perform the scan, short enough that the patient's radiation exposure is minimal. After 24 hours (4 half-lives), only about 6% of the original activity remains. Our half-life calculator can show this decay in detail.
Diagnostic imaging: PET
Positron Emission Tomography uses isotopes that emit positrons (β⁺ decay). The positron immediately annihilates with a nearby electron, producing two 511 keV gamma rays traveling in exactly opposite directions. Detecting both gammas simultaneously (coincidence detection) pinpoints where the annihilation happened, creating precise 3D images.
Fluorine-18 (half-life 110 minutes) is the most common PET isotope, usually attached to glucose as FDG (fluorodeoxyglucose). Cancer cells consume more glucose than normal cells, so tumours light up on PET scans. This is invaluable for detecting metastases and monitoring treatment response.
Therapy: killing cancer with radiation
Therapeutic nuclear medicine delivers lethal radiation doses directly to tumours while minimising damage to surrounding tissue. Iodine-131 (half-life 8 days) treats thyroid cancer because the thyroid naturally absorbs iodine — the radioactive iodine concentrates there and destroys cancerous thyroid cells with its beta particles. Lutetium-177 targets neuroendocrine tumours. Radium-223 treats bone metastases from prostate cancer — it mimics calcium and accumulates in bone, delivering alpha particles that destroy nearby cancer cells.
The effectiveness of these treatments depends on the isotope's half-life (determines treatment duration), radiation type (alpha, beta, or gamma), and the biological targeting mechanism. Our decay calculator computes activity over time for any isotope, and the dose calculator estimates radiation exposure from these sources.