Nuclear energy powers roughly 37 million medical procedures worldwide each year, spanning everything from heart scans to targeted cancer therapy. The same physics that splits atoms in a power plant produces radioactive isotopes that can light up disease inside the body and, in higher doses, destroy it. These applications fall into three broad categories: diagnostic imaging, targeted treatment, and a newer hybrid approach that does both at once.
How Radioactive Tracers Create Medical Images
Most nuclear medicine procedures work by introducing a small amount of radioactive material into your body, usually through an injection. That material travels through your bloodstream and collects in specific organs or tissues. As it decays, it emits energy that a camera outside your body detects, producing a detailed map of what’s happening inside. The radiation doses are comparable to a CT scan, typically between 0.3 and 20 millisieverts, which is low enough that the diagnostic benefit far outweighs the risk.
One isotope dominates the field. Technetium-99m is used in about 80 percent of all nuclear medicine procedures worldwide. It has a short physical half-life of around six hours, meaning it decays quickly and clears from the body fast. Its primary role in the United States is heart imaging: doctors use it to assess blood flow through the heart muscle in patients with coronary artery disease. Because heart disease is so common and the scans require relatively large amounts of the isotope, cardiac imaging drives the single biggest chunk of demand. Technetium-99m is also the go-to tracer for whole-body bone scans that detect cancer that has spread to the skeleton, and for sentinel node imaging before breast cancer or melanoma surgery.
PET scans use a different isotope, fluorine-18, attached to a modified sugar molecule. Cancer cells burn through glucose faster than normal cells, a quirk of tumor metabolism known as the Warburg effect. When the radioactive sugar enters your bloodstream, cancer cells gobble it up and trap it inside themselves. The trapped tracer emits positrons that the PET scanner converts into a three-dimensional image, pinpointing tumors as small as a few millimeters. Oncologists use PET scans not just to find cancer but to monitor whether treatment is working: a tumor that stops lighting up is responding.
Where Medical Isotopes Come From
Producing these isotopes requires two very different pieces of infrastructure. Molybdenum-99, the parent material that decays into technetium-99m, is made in nuclear reactors. Targets containing uranium-235 are irradiated with neutrons for four to eight days, generating molybdenum-99 through fission. That material is then shipped to hospitals in small devices called generators, where technetium-99m is extracted on-site as needed.
Fluorine-18 and other short-lived isotopes cannot survive a long supply chain. They are produced in particle accelerators called cyclotrons, which bombard targets with high-speed protons. Because fluorine-18 decays within about two hours, cyclotrons are often located at or near the hospitals that use them, and PET doses are prepared the same day they are administered.
Targeted Radiation Therapy for Cancer
The same principle that makes imaging work, radioactive material concentrating in specific tissue, also makes treatment possible. The difference is the type and intensity of radiation. Diagnostic isotopes emit energy that passes through the body and reaches an external camera. Therapeutic isotopes emit particles that travel only a short distance, depositing their energy directly into the surrounding cells and destroying them.
Radioactive iodine therapy for thyroid cancer is the oldest and most established example. Thyroid cells are the body’s main consumers of iodine, actively pulling it from the bloodstream through dedicated transport channels. When a patient swallows a capsule of iodine-131, the radioactive iodine follows the same pathway as regular dietary iodine, concentrating in thyroid tissue. About 90 percent of the cell-killing radiation comes from beta particles that penetrate only a millimeter or two, destroying thyroid cancer cells while largely sparing surrounding structures. Iodine-131 has a physical half-life of eight days, so the radiation fades steadily over the following weeks.
A newer generation of targeted treatments works on a similar logic but goes after different cancers. For advanced prostate cancer, a treatment called lutetium-177 PSMA therapy exploits the fact that prostate cancer cells display a specific protein on their surface at levels far higher than normal tissue. The drug pairs the radioactive isotope lutetium-177 with a molecule designed to latch onto that protein. Once bound, the isotope delivers radiation directly to the cancer cell, damaging its DNA and triggering cell death while sparing healthy tissue. In a major clinical trial known as VISION, patients receiving this therapy had a 60 percent reduction in the risk of disease progression or death compared to standard care alone. The treatment is now FDA-approved for metastatic prostate cancer that has stopped responding to other therapies.
A similar approach targets neuroendocrine tumors, rare cancers that arise in hormone-producing cells of the pancreas and gut. These tumors carry receptors that can be targeted with lutetium-177 attached to a different binding molecule, delivering radiation with the same precision.
Theranostics: Diagnosis and Treatment in One System
One of the most significant developments in nuclear medicine is the concept of theranostics, which pairs a diagnostic isotope and a therapeutic isotope that both home in on the same target. A doctor first scans you with the imaging version to confirm the cancer expresses the right molecular target and to map where it has spread. If the scan lights up, you’re a candidate for the treatment version, which delivers a cell-killing dose of radiation to those same spots.
In prostate cancer, this works by pairing a gallium-68 PET scan (which images the PSMA protein) with lutetium-177 therapy (which irradiates cells carrying that protein). In thyroid cancer, iodine-123 or technetium-99m scans map remaining thyroid tissue, and iodine-131 then destroys it. For neuroendocrine tumors, gallium-68 imaging is paired with lutetium-177 treatment, both targeting the same receptor on tumor cells.
The ideal theranostic pair would use the exact same molecule with just a different isotope swapped in. In practice, diagnostic and therapeutic isotopes often have different physical properties, so the binding molecules may differ slightly. What matters is that both versions target the same structure on the cancer cell, ensuring the scan accurately predicts who will benefit from treatment.
Guiding Surgery With Radioactive Tracers
Nuclear energy also plays a role in the operating room. In sentinel node biopsy, a procedure commonly performed during breast cancer and melanoma surgery, a small amount of radioactive tracer is injected near the tumor before the operation. The tracer flows through the lymphatic system and collects in the first lymph nodes that drain the tumor site. During surgery, the surgeon uses a handheld gamma probe to detect where radioactivity has concentrated, identifying the sentinel nodes precisely. Those nodes are removed and checked for cancer cells. If they are clear, the surgeon can often spare the patient a more extensive lymph node removal, reducing the risk of complications like chronic arm swelling.
This technique turns a radioactive tracer into a real-time GPS for the surgeon, replacing what used to require removing large numbers of lymph nodes just to find the few that mattered. It is now standard practice for staging both breast cancer and melanoma.