Guidelines for proton therapy in mediastinal lymphomas


Photo from Penn Medicine

Treatment room at the Roberts Proton Therapy Center at the University of Pennsylvania.

Proton therapy can help mitigate toxicity in adults with mediastinal lymphomas, but the treatment should only be used in patients expected to derive the most benefit, according to new guidelines from the International Lymphoma Radiation Oncology Group.

The guidelines note that proton therapy reduces the radiation dose to organs at risk in certain clinical presentations, such as when the mediastinal target is on both sides of the heart.

However, the advantages of proton therapy are not always clear in other situations, such as when the target spans the right side of the heart or when the target is above the heart with no axillary involvement.

“The limited availability of proton therapy calls for case selection based on a clear understanding of which cases will derive most benefit from proton therapy as compared to advanced photon techniques,” said guideline author Bouthaina Dabaja, MD, of the University of Texas MD Anderson Cancer Center in Houston, and her colleagues.

The group’s guidelines were published in Blood.

The guidelines note that proton therapy—like intensity-modulated radiotherapy and 3-dimensional conformal radiotherapy—presents an opportunity for more conformal dose distribution and better sparing of organs at risk.

Proton therapy can greatly benefit certain patients with mediastinal disease, including:

  • Young female patients in whom proton therapy would reduce the breast dose and decrease the risk of secondary breast cancer
  • Patients at high risk of radiation-related toxicity due to previous treatment
  • Patients with disease spanning below the origin of the left main stem coronary artery that is anterior to, posterior to, or on the left side of the heart.

“The relation of disease to organs at risk determines the situations in which proton therapy is most beneficial,” the experts said in the guidelines.

However, the consideration of proton therapy needs to factor in the complexities of proton therapy planning, the need to manage uncertainties, and the “evolving nature of the technology,” which includes the development of pencil beam scanning.

While passive scattering proton therapy is the least complex delivery technique, it is challenging because beams can conform only to one side of the target. In contrast, active mode pencil beam scanning proton therapy potentially provides better conformality and sparing of organs at risk.

“Because treatment involves delivery of individual controlled spots, inhomogenous doses can be created deliberately,” the guideline authors said.

However, “motion management is of prime importance” with pencil beam scanning proton therapy, which is more sensitive to density changes in the beam path than is passive scattering proton therapy.

To that end, physicians should pay close attention to evaluating intrafractional movement, which is frequently tied to the breathing cycle.

Dr. Dabaja and her coauthors reported no funding or conflicts of interest.

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