(P131) The Role of Radiation Therapy in the Management of Neurogenic Heterotopic Ossification

Elizabeth C. Ester, MD, Ian S. Gallaher, MD, Daniel A. Jones, MD, Joseph G. Lynch, CMD; Department of Radiation Oncology, Minneapolis Veterans Affairs Medical Center; Department of Radiation Oncology, University of Minnesota Medical Center

Background: Patients who sustain brain and spinal cord injuries are at risk for developing neurogenic heterotopic ossification (NHO), the formation of bone in extraskeletal soft tissue. The pathogenesis of NHO is unclear but may be a combination of local inflammation, prostaglandins, and growth factors stimulating the differentiation of soft tissue mesenchymal progenitor cells into osteoblasts. NHO most commonly affects the hip and elbow joints and ranges from asymptomatic to clinically significant restriction in range of motion resulting in functional deficits. Prevention and management of NHO includes pharmacologic interventions, surgical resection, and radiation therapy (RT). Radiation for NHO is controversial, and the effectiveness of a single 700-cGy fraction, as used in heterotopic ossification (HO) prophylaxis, has been questioned. The purpose of this study was to review the experience and to report the outcome of eight consecutively irradiated joints in four patients with NHO at the Minneapolis Veterans Affairs Medical Center between July and September 2013.

Materials and Methods: The management of eight consecutively treated joints in patients with clinically significant NHO was reviewed. One patient had an anoxic brain injury, and the remaining patients had thoracic spinal cord injury (SCI) ranging from T4–T8. Patients were irradiated with 800 cGy in a single fraction to the area of visible ossification. Patients were followed with physical examination and imaging to determine efficacy of therapy. Toxicity was evaluated and reported according to Common Terminology Criteria for Adverse Events version 4.0 (CTCAE v4.0).

Results: Sites irradiated included six hips and two elbows. The mean age was 34 years, and median follow-up was 11 weeks. Three hip joints were treated with surgical resection followed by RT and indomethacin at 25 mg tid for 6 weeks. One hip joint, previously treated with surgical resection and RT, had NHO recurrence within 2 months of therapy and was retreated. Radiation was delivered between 24 and 60 hours of surgery. All three patients with treated hip joints achieved improvement in joint range of motion and functionality. Three hip joints and two elbow joints were treated with RT and etidronate without surgical resection. All joints initially demonstrated improvement in range of motion after RT. One patient subsequently experienced progression, clinically and radiographically, 2 months following treatment. Overall treatment efficacy was 87.5%. Acute toxicity was minimal and limited to grade 2 dermatitis in a single patient.

Conclusion: While this cohort of patients is small, outcomes suggest that a single fraction of 800 cGy, in addition to pharmacologic prophylaxis, may be a reasonable regimen to study in patients with NHO. Follow-up is short, and long-term efficacy and toxicity are unknown. The risk of secondary malignancy is small, as reported by others.