Radiopharmaceutical Therapy (RPT)

What is radiopharmaceutical therapy?

Certain cancers may be treated with radioactive medicines that spread throughout the body via the bloodstream. These treatments may be delivered by swallowing pills or receiving fluids in the vein (intravenous). Radiopharmaceutical therapy (RPT) is a type of treatment like chemotherapy or immunotherapy because the medicine travels through the entire body and gathers in and treats certain cancers. Importantly, there are different types of radioactive medicines for different types of cancers.

Radiopharmaceutical therapies are often given after the patient has an imaging test to confirm they would benefit from the treatment. The decision to treat with RPT is made by you and a group of doctors that may include radiation oncologists, nuclear medicine physicians, medical oncologists, surgeons, and endocrinologists

When are radiopharmaceuticals used to treat cancer?

RPT is one of several treatment options for patients with certain types of cancers and it is important for doctors to have a discussion with patients about the benefits and risks of each. Currently, there are radiopharmaceutical medicines that can be used to treat patients with:

• very advanced cancers associated with bone pain,
• advanced prostate cancers and
• neuroendocrine tumors.

Two medicines that have been used for many years include radioactive iodine (I-131) and radium (Ra-223), which naturally accumulate where the cancer is located. Radioactive iodine capsules are given by mouth to treat some types of thyroid cancer. Radium is injected into a vein to treat pain caused by cancer that has spread to the bones.

Newer types of radiopharmaceutical therapies are attracted to certain molecules on cancer cells no matter where they are in the body. For example, many prostate cancer cells have increased amounts of a molecule called prostate specific membrane antigen (PSMA) on their surface, and there is a radiopharmaceutical medication that recognizes this PSMA molecule and uses it to deliver treatment directly to those cancer cells. Another radioactive medicine can recognize molecules that are present on the surface of neuroendocrine tumors, the somatostatin receptor (SSTR), and can be used to treat patients with these types of tumors.

What is the process of receiving radiopharmaceutical therapy?

The process of receiving RPT depends on the type of treatment. In most cases, you will see a doctor who specializes in RPT. This evaluation may include blood tests and imaging. Before starting these treatments, your doctors will review any special precautions you need to follow while you are on treatment.

Most patients receive outpatient treatment and can come independently to treatment. Some types of treatment require a single visit, but most RPT requires several treatment visits every few weeks or months. For treatments that require several visits, your doctor will ask you to have blood work for monitoring in between treatments.

After each treatment, you are sent home with radiation safety instructions. It is very important for you and your household members to follow these instructions, as some of the radiation will leave your body through fluids, including your urine, sweat, and stool. You may require follow-up visits in the future which can consist of blood tests or imaging tests.

What type of side effects can occur?

RPT side effects depend on the type of medicine that is used and the amount that you are given each treatment. For example, while PSMA is present on the surface of prostate cancer cells in large amounts, it is also present on salivary (spit) glands and the kidneys. This means that the medicine specific to PSMA will also accumulate in the salivary glands and kidneys, and may cause related side effects (e.g. dry mouth, decreased kidney function)

In addition, because the medicines move through the blood, and blood cells are very sensitive to radiation, these medicines can also damage these types of cells and increase risks of infection, bleeding, and feeling tired. Clinicians watch for these side-effects and know how to manage them.

How might radiopharmaceutical therapy change in the future?

RPT are cutting-edge medications with many developments happening for many types of cancer. As RPT evolves, it’s possible that we will have medicines made for different cancers. We will also learn more about how RPT can help other cancer treatments. These potential medicines and combinations will need to be researched in clinical trials before they can become available for general clinical use in patients.

Questions?

Do you have questions about radiopharmaceutical therapy? Are you wondering if this type of treatment might be an option for you? If so, talk with your radiation doctor or medical oncology (chemotherapy) doctor. They can help you to learn more about this treatment.