Best practices defined for proton therapy in mediastinal lymphomas



Proton therapy can help mitigate toxicity in adults with mediastinal lymphomas, but only when this modality offers a clear advantage over intensity-modulated radiotherapy, according to new guidelines from the International Lymphoma Radiation Oncology Group.

Proton therapy reduces radiation dose to organs at risk in certain clinical presentations, such as when the mediastinal target is on both sides of the heart. The advantages 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, according to guideline authors Bouthaina Dabaja, MD, professor and section chief of hematology in the department of radiation oncology at the University of Texas MD Anderson Cancer Center, Houston, and her colleagues.

“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,” Dr. Dabaja and her coauthors said in the guidelines, which were published in the journal Blood (doi: 10.1182/blood-2018-03-837633).

Along with intensity-modulated radiotherapy and 3-dimensional conformal radiotherapy, proton therapy presents “another opportunity” for more conformal dose distribution and better sparing of organs at risk, according to the consensus recommendations. Proton therapy can greatly benefit certain patients with mediastinal disease. These include young female patients to reduce breast dose and risk of a secondary breast cancer, patients at high risk of radiation-related toxicity due to previous treatment, and 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 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 (PSPT) is the least complex delivery technique, it is challenging because beams can conform only to one side of the target; by contrast, the experts said, active mode pencil beam scanning proton therapy (PBSPT) potentially provides better conformity and sparing of organs at risk.

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

However, motion management is “of prime importance” with PBSPT, which is more sensitive to density changes in the beam path as compared to PSPT, they added. Toward that end, physicians should pay close attention to evaluating intrafractional movement, which is frequently tied to the breathing cycle.

The guidelines list a total of 11 authors representing The University of Texas MD Anderson Cancer Center; University of Florida, Jacksonville; University of Pennsylvania, Philadelphia; University of Louisiana, Baton Rouge; Proton Therapy Center Czech, Prague; Motol University Hospital, Czech Republic; St. Thomas and Guy Hospital, London; Institut Curie, Paris; and Rigshospitalet, Copenhagen.

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

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