Anterior mediastinal masses caused by lymphoma or leukemia can be difficult to treat because sensitive tissues in the area are vulnerable to damage from radiation therapy. To treat these tumors while sparing healthy tissue, radiation oncologists at The University of Texas MD Anderson Cancer Center use a combination of advanced technologies and new techniques.
In addition to standard systemic treatments for their underlying hematological malignancies, patients with anterior mediastinal masses are treated with a radiation dose of 20–30 Gy delivered in daily fractions over 2–3 weeks. Patients with refractory disease may receive a dose as high as 50 Gy over 5 weeks. Historically, treatment plans for these types of tumors delivered the radiation dose using entirely anterior and posterior radiation fields, such that substantial volumes of heart, lung, and/or breast tissue were exposed to an unavoidable radiation dose. Such treatment put patients at risk for cardiotoxicity, radiation pneumonitis, and the development of secondary tumors in the lungs or breasts.
“Many patients with leukemia or lymphoma are very young with a long lifetime to enjoy the benefits of the most effective treatment or, conversely, to suffer long-term toxic effects associated with treatment,” said Grace Smith, M.D., Ph.D., an assistant professor in the Department of Radiation Oncology. “Other patients may be quite fragile because of the chemotherapy they’ve received. Older patients in particular often are frail at baseline, so they are especially vulnerable to toxicity.”
A symphony of radiation strategies
To avoid the adverse effects from the anterior-posterior delivery of radiation therapy to anterior mediastinal masses in patients with hematological malignancies, Dr. Smith said, “We use a combination of advanced techniques to target the mediastinal tumor with radiation while minimizing toxicity to the neighboring organs.” This combination comprises using the “butterfly technique” for planning and delivering intensity-modulated radiation therapy (IMRT), deep inspiration breath hold to reduce motion, computed tomography (CT) scans before each daily treatment to account for changes in the tumor or patient anatomy, and—for female patients—an inclined board fitted to the couch to reduce the radiation dose to the breasts.
The butterfly technique takes advantage of IMRT’s ability to shape radiation fields. Specifically, a five-beam arrangement creates anterior and posterior radiation fields roughly shaped like a butterfly’s wings. “The key to the butterfly technique is that it ‘squeezes’ the radiation dose anteriorly and posteriorly to optimally target the tumor while avoiding specific critical structures, even individual cardiac chambers and vessels,” Dr. Smith said.
Deep inspiration breath hold, a technique used for radiation therapy to various disease sites, such as the lung or breast (see Reducing Cardiotoxicity in Left Breast Irradiation, OncoLog, September 2014), requires the patient to take in a deep breath and hold it for about 20 seconds during treatment. In patients with anterior mediastinal tumors, deep inspiration breath hold reduces the radiation dose to the lungs by minimizing respiration-related movement and to the heart by displacing the heart inferiorly and posteriorly.
Another standard practice at MD Anderson is for patients with mediastinal tumors to undergo a low-dose CT scan before each treatment session so that the treatment plan can be adjusted to account for changes in the patient’s movement, heartbeat, anatomy, or tumor. For example, Dr. Smith said, “If the tumor is shrinking, then we can further tailor the treatment field.”
The addition of a 15° inclined board to the treatment couch for female patients helps move breast tissue out of the radiation field. “Breast tissue is vulnerable to the effects of radiation, especially in young women,” Dr. Smith said. Studies have shown that, compared with women in the general population, women treated for mediastinal lymphoma with radiation to the chest face a much higher lifetime risk of breast cancer and that this risk is highest for those who underwent radiation therapy at age 30 years or younger.
Some of the techniques used at MD Anderson to treat mediastinal masses have already been widely adopted; others, such as the butterfly technique, are relatively new. “This symphony of radiation techniques has been used for several hundred patients with mediastinal tumors caused by hematological malignancies,” Dr. Smith said. “And we have begun to publish our track record of results.” For example, she said, a study of 150 patients treated at MD Anderson for mediastinal lymphoma showed that the techniques decreased the risk of acute radiation pneumonitis.
Toward broad adoption
Dr. Smith said that she and her colleagues are working on the challenge of disseminating their strategy, which combines new techniques and advanced technologies, to other institutions. But despite the success of the strategy at MD Anderson, Dr. Smith said, several obstacles could delay its wide adoption. “Treatment planning and setup can be very time consuming when these techniques are used,” she said. “Plus, a physician needs to verify the daily CT images to ensure the radiation, which is very conformal and focused, is delivered to the right target in the right way.”
Dr. Smith thinks community oncologists will agree that the benefits of reduced toxic effects for patients with mediastinal tumors from lymphoma or leukemia will outweigh the additional time and cost of the strategy. “Our guiding principle as we develop these techniques is to understand the unique needs of this patient population—they are often curable, but they are vulnerable.”
For more information, contact Dr. Grace Smith at 713-563-2342.
Pinnix CC, Smith GL, Milgrom S, et al. Predictors of radiation pneumonitis in patients receiving intensity modulated radiation therapy for Hodgkin and non-Hodgkin lymphoma. Int J Radiat Oncol Biol Phys. 2015;92:175–182.
Voong KR, McSpadden K, Pinnix CC, et al. Dosimetric advantages of a “butterfly” technique for intensity-modulated radiation therapy for young female patients with mediastinal Hodgkin’s lymphoma. Radiat Oncol. 2014;9:94.
OncoLog, March 2016, Volume 61, Issue 3