Smaller amounts of spillover radiation to healthy tissue and organs have heightened interest in using protons to treat Hodgkin lymphoma.
In the first-of-its-kind study, prospectively comparing radiation dose to normal tissue for involved-node proton therapy with three-dimensional conformal radiation therapy (3DCRT) and intensity modulated radiation therapy (IMRT) in Hodgkin lymphoma patients, the mean dose of inadvertent proton radiation of healthy tissue was about 50 percent less than the mean dose of spillover radiation from 3DCRT and IMRT.
Radiation oncologists call spillover radiation to healthy areas of the body that occur during photon and proton radiation treatments the “integral dose.”
“With proton therapy reducing the integral dose by 50 percent, we expect that will translate to a reduction in secondary cancers and cardiac disease in years to come,” says Brad Hoppe, M.D., M.P.H, a radiation oncologist at the UF Health Proton Therapy Institute, associate professor in the department of radiation oncology at the University of Florida College of Medicine in Jacksonville, Florida, and author of the study published earlier this year in the International Journal of Radiation Oncology Biology Physics.
“Involved-node proton therapy represents the greatest minimization of inadvertent radiation exposure to non-targeted tissues possible thus far in the longstanding continuing international effort to decrease radiation toxicity while maintaining radiation efficacy in Hodgkin lymphoma,” Dr. Hoppe writes.
About 9,000 Americans are diagnosed with Hodgkin lymphoma every year. Conventional radiation treatments combined with chemotherapy have permitted lymphoma survivors to live for decades, says Dr. Hoppe. “But secondary cancers and cardiac complications brought on by those conventional radiation treatments many years before are the primary causes of death for Hodgkin lymphoma survivors,” he adds.
Of the 15 patients who participated in the three-year study, one patient suffered a relapse of Hodgkin lymphoma and another patient developed a non-Hodgkin lymphoma. Considering those numbers, the relapse-free survival rate was 93 percent and the event-free survival rate was 87 percent, the study reported.
“The radiation dose reduction was substantial and clearly relevant,” says Dr. Hoppe. “And we didn’t see any unexpected number of relapses of Hodgkin lymphoma. Patients tolerated the treatments well. We even had one patient who got pregnant and gave birth during the follow-up period.”
According to Dr. Hoppe, protons have been used very sporadically in conjunction with chemotherapy to treat lymphomas. The focus of proton therapy has been on solid tumors. But the results of this initial study have spurred interest among radiation oncologists at proton centers to develop treatment protocols for lymphomas in conjunction with chemotherapy.
Study participants included 10 adults and five children. “For pediatric patients with Stage 3 Hodgkin lymphoma, we didn’t see much nausea since the dose to the stomach was quite low,” says Dr. Hoppe. “People would expect more nausea would be experienced by pediatric Hodgkin patients treated with 3DCRT or IMRT.”
Dr. Hoppe says he plans to conduct a multicenter study on the use of protons to treat Hodgkin lymphoma patients.