Hodgkin Lymphoma Treatment with Proton Therapy

Hodgkin lymphoma is a cancer of the lymph nodes that predominantly affects children and young adults. Every year in the United States approximately 8,000 new cases are diagnosed and cure rates following standard therapy, including chemotherapy followed by radiotherapy, can reach 90 percent. It typically presents with a painless mass (usually in the lower neck), but might also be associated with fevers, night sweats, or unexplained weight loss.

Proton therapy may have a role in reducing risk of second cancers or heart disease in survivors of Hodgkin lymphoma.

Due to the excellent outcomes for patients with Hodgkin lymphoma and the young age that it typically presents, the major focus for researchers have been in identifying treatment related toxicities and finding ways of reducing them. Specifically, the Childhood Cancer Survivor Study identified Hodgkin lymphoma survivors as one of the highest risk groups of developing severe or life threatening chronic health conditions with the highest risk of developing a subsequent cancer or heart disease. In fact, the two leading causes of death more than 15 years after completing treatment in Hodgkin lymphoma survivors is from second cancers or heart disease. These increased risks in second cancers and heart disease are likely due to the late effects from chemotherapy (specifically bleomycin and adriamycin) as well as from radiotherapy.

Groups have begun to look at ways to reduce these treatment related complications by finding safer chemotherapy regimens, reducing the dose of radiotherapy, and shrinking the radiation treatment field. Early reports have confirmed that these changes translate into fewer complications late in life.

Hodgkin lymphoma survivors and treatment toxicities have been an important part of the research effort for over two decades at the University of Florida. Importantly, we have identified increased risks of developing secondary cancers, pulmonary complications, and cardiac disease (including valvular disease and coronary artery disease) in this group of patients. As a result, we have modified our treatment regimen to reflect what we have learned and now treat with smaller radiation fields and lower radiation doses. Our next objective has been to explore whether proton therapy might further reduce the side effects of treatment compared with conventional radiotherapy.

Proton Therapy for Hodgkin Lymphoma

Currently the Radiation Oncology group at the University of Florida has one of the few active proton therapy centers in the country and has actively been looking into ways of applying this technology to different disease sites. Protons have a unique ability to stop at specified depths in tissue, without penetrating deeper. This important property allows irradiation to be delivered to areas at risk of disease, while further minimizing the amount of normal tissue irradiated. This reduction in normal tissue irradiated should translate into fewer long term side effects.

Studies at the University of Florida Proton Therapy Institute show that proton therapy can reduce the amount of a Hodgkin lymphoma patient’s body exposed to harmful radiation by 50 percent.

Recently, our group looked back and reported on several patients with Hodgkin lymphoma that were treated with conventional X-ray radiation and compared their radiation treatment plan with a proton therapy plan. Compared with conventional X-ray therapy, protons reduced the amount of the patient’s body exposed to harmful radiation by 50 percent. Below is an example of what we found.

Figure A shows an axial CT scan slice through the heart (red) of a patient with Hodgkin lymphoma involving the mediastinum. The dark blue line represents the target area for the radiation. The green line represent the volume receiving 95 percent of the total prescribed dose of radiation, while the light blue line reflects the volume of the body receiving 10 percent of the total prescribed radiation dose. You can see in this picture with conventional radiation (left), the X-rays go all the way through the body and therefore treat much more of the heart and breasts than truly need to be treated. The proton plan (right) demonstrates the ability of protons to stop, and thus avoid treating unnecessarily through the heart and breasts. With the proton plan we were able to reduce the mean dose to the heart by more than 50 percent and the mean dose to the breast by 70 percent. We feel this should translate to fewer cardiac problems and a lower risk of developing breast cancer in the future.

Figure A

Hodgkin Lymphoma Proton Therapy Protocol

Due to the reduction of normal tissue exposed to radiation with proton therapy we have developed the first Hodgkin lymphoma protocol using proton therapy for patients with involvement of the mediastinum. We anticipate that proton therapy will be associated with fewer early and late toxicities because of the reduction of normal tissue exposed to radiation. Hodgkin Lymphoma Protocol