Radiation therapy is a common and effective treatment for various cancers, using high-energy particles or waves to destroy cancer cells. A frequent concern for patients and their families centers on whether radiation remains in the body after treatment and for how long. The presence and duration of radiation in the body depend entirely on the specific type of radiation therapy received.
Understanding Radiation Therapy Modalities
Radiation therapy precisely targets and damages cancer cells, either destroying them or slowing their growth. This therapeutic approach utilizes different methods to deliver radiation. The primary delivery techniques include external beam radiation therapy, internal radiation therapy, and systemic radiation therapy. Each method employs distinct mechanisms to deliver radiation, influencing how it interacts with the body and whether any radioactive material remains afterward.
External Beam Radiation: No Residual Radioactivity
External beam radiation therapy (EBRT) is the most common form of radiation treatment. It involves a machine positioned outside the body that directs high-energy radiation beams toward the tumor. The radiation passes through the body to reach the targeted area. Once the machine is turned off, no radiation remains in the patient’s body, meaning they are not radioactive and pose no risk of radiation exposure to others. This type of treatment affects cells only during the short period of exposure.
Internal and Systemic Radiation: Temporary Radioactivity
Unlike external beam therapy, some forms of radiation treatment involve placing radioactive material directly into the body. Internal radiation therapy, known as brachytherapy, involves placing radioactive sources inside or very close to the tumor. These sources can be temporary, inserted for a set period and then removed, or permanent, where small radioactive seeds are implanted and remain in the body, gradually losing their radioactivity over time. For instance, Iodine-125 seeds, sometimes used for prostate cancer, decay, or lose their energy, at a rate of 50% every 60 days, becoming nearly inert after about 10 months. Palladium-103 seeds decay even quicker, with a half-life of 17 days, becoming inert after approximately 3 months.
Systemic radiation therapy involves administering substances, called radioisotopes, orally or intravenously. These substances travel through the bloodstream to target cancer cells throughout the body. For example, Iodine-131 (I-131) is used for thyroid cancer, and Radium-223 (Ra-223) is used for prostate cancer that has spread to bones. The radioactivity diminishes over time through natural processes, primarily excretion and radioactive decay.
The half-life of a radioactive isotope indicates the time it takes for half of its atoms to decay. For I-131, the physical half-life is about 8 days, but its effective half-life in the body can be much shorter. Most of the administered I-131 is eliminated through bodily fluids, mainly urine, within the first few days, with over 70% excreted within 24 hours and over 95% after 72 hours. Radium-223 has a physical half-life of 11.4 days and is primarily excreted through feces, mostly within the first week.
Patient Safety Guidelines After Treatment
Following internal or systemic radiation therapy, specific safety guidelines are important to minimize potential radiation exposure to others. Patients who receive external beam radiation therapy do not need to follow any special precautions since no radioactive material remains in their body. Those who undergo brachytherapy or systemic radiation will receive tailored instructions from their healthcare team.
For patients treated with systemic radiation, precautions are temporary and vary based on the isotope and dose. Common recommendations for I-131 include maintaining distance from others, particularly pregnant women and young children, often for a week or two. Patients may be advised to sleep alone for a few days, use separate bathrooms, flush toilets multiple times, and wash laundry separately. For Radium-223, precautions typically last about one week and involve careful hygiene, such as flushing the toilet twice after use and wearing disposable gloves when handling bodily fluids.
In brachytherapy with permanent implants, patients might be advised to avoid prolonged close contact with children and pregnant women for a few months. Temporary brachytherapy means the radioactive source is removed after treatment, so patients are no longer radioactive once discharged. Adhering to the specific instructions provided by the medical team is important for ensuring the safety of both the patient and those around them.