Urine can sometimes be radioactive after certain types of cancer therapy because the treatment involves radioactive substances that the body eventually eliminates through urine. This phenomenon is most commonly seen after therapies using radiopharmaceuticals or radioactive isotopes designed to target cancer cells.
In some cancer treatments, especially those involving radiopharmaceuticals, a radioactive drug is administered to the patient. These drugs contain radioactive atoms that emit radiation to kill cancer cells. For example, in peptide receptor radionuclide therapy (PRRT), a radioactive component is attached to a molecule that specifically targets tumor cells, such as neuroendocrine tumors. After the radioactive drug binds to the tumor cells and delivers its radiation, the remaining radioactive material that is not absorbed by the tumor is processed and excreted by the body, primarily through urine. This causes the urine to be temporarily radioactive until the radioactive material is fully cleared from the body.
The radioactivity in urine after therapy is due to the radioactive isotopes used in the treatment. These isotopes emit radiation as they decay, and since the body eliminates them through fluids like urine, stool, sweat, and tears, these bodily excretions can carry radioactivity for a short period after treatment. The level of radioactivity in urine decreases over time as the radioactive material decays and is flushed out of the body.
Radiation therapy that uses external beams, such as X-rays or gamma rays, does not make urine radioactive. Instead, it is the internal use of radioactive drugs—radiopharmaceuticals—that leads to radioactive urine. For example, Lutathera, a PRRT drug used to treat neuroendocrine tumors, contains a radionuclide that emits beta particles to kill cancer cells. After treatment, the radioactive particles that do not remain in the tumor are excreted, causing the urine to be radioactive for a period.
The duration and intensity of urine radioactivity depend on the type of radioactive isotope used, its half-life (the time it takes for half of the radioactive atoms to decay), and how quickly the body clears it. Medical teams provide specific instructions on handling bodily fluids after such treatments to minimize radiation exposure to others. Patients may be advised to flush the toilet twice, wash hands thoroughly, and avoid close contact with others for a short time.
In contrast, radiation therapy targeting cancers such as bladder, prostate, or vaginal cancer typically uses external radiation beams or implants that do not cause the urine itself to become radioactive. However, these treatments can cause side effects like bladder irritation or urinary symptoms but do not make urine radioactive.
In summary, urine becomes radioactive after therapy when radioactive drugs are used internally to treat cancer. The radioactive substances are eventually eliminated through urine, temporarily making it radioactive. This is a normal and expected part of the treatment process, and safety protocols are in place to protect patients and those around them during this time.