When most people hear “radiation” as a method of treating cancer, they think of external beam radiation therapy, which comes from a machine that aims radiation at the cancer.
However, new, targeted therapies, called radiopharmaceutical therapy — or RPT — can remove the machine from the equation and use radioactive atoms delivered through an infusion to bind to certain cancer cells, killing them.
Dr. Michael Morris is medical director for Advanced Molecular Imaging and Therapy in Glen Burnie, Maryland. He’s also the vice president and scientific program chair for the Mid-Eastern Chapter of Society of Nuclear Medicine and Molecular Imaging, or SNMMI.
He said external beam radiation therapy has proved to be very effective in killing cancer, although with some side effects.
“It’s targeted from the outside of the patient, but just to a specific area, and everything within that area receives a universal dose of radioactivity,” Morris said. “In order to get to the area of interest, the radiation has to pass through the body before getting there, so there is some radiation delivered to the surrounding tissues as well.”
The resulting side effects of radiation, depending on the area of the body treated, can include loss of taste, skin changes, hair loss, diarrhea and sexual problems.
Similar to the way in which targeted drug therapies zoom in on specific mutations in cancer cells, providing a less widespread effect than chemotherapy, RPT isn’t limited by the area of the beam coming from a machine.
With RPT, drugs deliver radiation therapy directly and specifically to cancer cells to reduce the risk of side effects while allowing tiny deposits of cancer cells to be killed throughout the body.
“There’s no machine,” Morris said. “It allows you to deliver the treatment to wherever it is within the body, which is different compared to external beam radiation, which can only target a certain area or region.”
After a patient is diagnosed with cancer, Morris said doctors can use imaging — often in a PET/CT scan — to determine whether a patient may benefit from RPT.
For instance, doctors can use a radioactive tracer to target and destroy PSMA, which is a protein on the outside of prostate cancer cells.
“Any cancer that expresses the PSMA target will receive the treatment, no matter where it is in the body, because that target is on the cancer cell itself,” Morris said. “So, whether it’s in bone, lymph nodes, liver, or in the pelvis, it’s going to be treated.”
Delivering radiation directly to cells isn’t new. Radioactive iodine has been used to treat thyroid cancer since the 1940s.
“So, we’ve been using that treatment for 80 years in that particular area,” Morris said. “And thyroid cancer was one of the first cancers that we can actually cure in medicine, in large part because of RPT therapy, as an adjunct after definitive surgery to take care of other areas of disease, which are called micro-metastases that may be present but can’t be seen at the time of surgery.”
RPT is also currently being used in prostate cancer, Morris said, adding that research continues to find other cancers that will respond well to the therapy.
“We have two clinical trials here, for instance, that are looking at lung cancer indications.”
In addition, Morris said with RPT he can track the success of the radioactive treatment.
“After the treatment, we can confirm that by imaging the treatment itself inside the patient’s tumors, and we can also see how any treatment that’s not bound to the tumors is leaving the body and being excreted,” he said. “We can actually quantify, that is measure, the amount of radioactivity that we delivered to the tumors and to the healthy tissues.”
“That’s why we call this area of nuclear medicine ‘theranostics,'” Morris said, “because there is both a therapeutic aspect and a diagnostic aspect.”
