Lymphomas are the new targets for protons. Primarily preferred for treating solid mass tumors, protons are now being viewed as a prudent type of radiation for treating Hodgkin and non-Hodgkin lymphomas.
About 9,000 Americans are diagnosed with Hodgkin lymphoma every year. And more than 65,ooo Americans are diagnosed with non-Hodgkin lymphoma annually.
According to Brad Hoppe, M.D., M.P.H, a radiation oncologist at the University of Florida College of Medicine in Jacksonville, Florida, the combination of chemotherapy and conventional radiation has dramatically increased survivorship for lymphoma patients. “People go on to live for decades,” he says. “And then we see late complications from their treatment, such as secondary cancers and cardiac complications that end their lives.”
Those complications are primarily the consequence of unintended radiation reaching healthy tissue during the time the lymphoma was treated with photons many years before. “Consequently, some oncologists feel the risks of long-term side effects of conventional radiation outweigh the benefits in improving the cure rate with radiation,” Dr. Hoppe says.
Since protons release the bulk of their radiation energy at the specific site of cancerous cells, there is a dramatic reduction in spillover radiation going to unintended areas of the body, what radiation oncologists call the “integral dose.”
“So, the integral dose,” Dr. Hoppe adds, “is the dose we don’t want to be delivering at all. To the breast tissue. To the heart, the lungs and thyroid. With protons, we believe the lower integral dose will lead to lower risk of secondary cancers and cardiac toxicities — which are the primary causes of death for Hodgkin lymphoma survivors.”
Until recently, the use of protons to treat lymphomas hadn’t been seriously explored. “With lymphomas, the conventional radiation doses utilized are quite low,” he says. “Twenty to 30 gray for Hodgkin lymphoma. And 30 to 36 gray for non-Hodgkin. That’s generally a lot lower dose than would cause any short-term toxicities. People thought, ‘If it’s a low dose of radiation, who really cares?’ ”
But over time, clinicians have come to understand the long-term harm photon treatments can generate, especially in low-dose treatments like lymphomas, Dr. Hoppe says.
“With lymphomas, our [radiation treatment] fields are huge because of the distribution of the disease,” says Dr. Hoppe. “The typical Hodgkin field goes from the top of the neck down to the diaphragm. And while we are using low-radiation doses, they are still going to healthy tissue along that treatment path.”
Reimbursement by health insurers remains a challenge. “What an insurer really wants is clinical results that show the superiority of proton therapy over other photon radiation modalities,” Dr. Hoppe says. “They want data right away. But the real benefit of protons isn’t going to manifest itself for 10, 20 or 30 years.”
Dr. Hoppe and an associate at UF Health Proton Therapy Institute, Dr. Julie Bradley, are working to identify biomarkers that may indicate very early signs of cardiac disease caused by unintended radiation, rather than waiting decades. “Our work to quantify early damage is very much in its infancy,” he cautions.