A. Kessel1, J. F. Burlile1, W. O. Tobin2,3, G. Goyal4, M. V. Shah5, N. Bennani5, R. L. Rouse5, S. C. Lester1, J. P. Abeykoon5, R. S. Go2, and W. Breen1; 1Department of Radiation Oncology, Mayo Clinic, Rochester, MN, 2Department of Neurology, Mayo Clinic, Rochester, MN, 3Center for Multiple Sclerosis and Autoimmune Neurology, Mayo Clinic, Rochester, MN, 4University of Alabama, Birmingham, AL, 5Division of Hematology, Department of Medicine, Mayo Clinic, Rochester, MN
Purpose/Objective(s): The primary objective of this study was to evaluate local disease control after external beam radiation therapy (EBRT) for Erdheim Chester disease (ECD). Radiation is effective at low doses for Langerhans cell histiocytosis, but data in ECD are limited. We hypothesized that EBRT could provide high rates of local control in ECD, with higher doses providing more durable local control. Materials/
Methods: This is a single institution retrospective review of patients with a clinical diagnosis of ECD who were treated with EBRT. We recorded the anatomic site of disease as well as dose of radiation utilized at each site, and determined local lesion control. Recurrence was assessed via imaging based on treatment location. Results: Eight patients with ECD who underwent radiation treatment were identified, with a median follow-up of 7.1 years (range, 0.5-16.6). The median age at time of first radiation treatment was 47 years (range, 29-67). Most patients were female (6/8). There were 20 distinct sites of disease treated. Bone was the most commonly treated site (57%), followed by the brain (24%).The median radiation dose was 18 Gy (range, 10-45 Gy) and median number of fractions was 6 (range 5-25). In disease sites treated with 11 Gy or less, 7 out of 8 sites developed in-field recurrence among the 2 out of 3 patients at a median time of 62.6 months (range, 2.6 - 98.8 months). In this subgroup, local recurrences occurred in bone (7) and brain (1). One patient treated with 16 Gy to a brain lesion experienced worsening clinical neurologic symptoms concerning for clinical disease progression 30.0 months post treatment. In disease sites treated with 18 Gy or more, recurrence was noted in 1 out of 11 sites in 5 total patients. Notably the patient who progressed was treated with 19.8 Gy in 11 fractions to the cerebellum, but it was unclear if progression was in-field or marginal. Concurrent systemic therapy was given during treatment of two distinct sites treated with 18 Gy or more. These therapies were nivolumab and binimetinib plus encorafenib, respectively. Median followup for patients receiving less than 18 Gy was 13.5 years, compared to 3.5 years for those receiving = 18 Gy. Although retrospective review of adverse events for these patients is limited, there were no identified grade 3+ toxicities from radiation. Conclusion: EBRT to involved disease sites may be beneficial for local control in ECD, though conclusions are limited by patient numbers and follow-up duration. Unlike Langerhans cell histiocytosis which can typically be controlled with 10 Gy, it appears that doses of 20 Gy or higher may be needed for durable local control in ECD.
