Radiation Therapy Prophylaxis for Heterotopic Ossification in Non-Hip Sites

Background: Radiation therapy prophylaxis for heterotopic ossification is well-established for the hip, either pre or post-operatively. There is limited data for this treatment in non-hip sites. We report our institution’s experience. Methods: From October 2004 to August 2015, a total of 39 non-hip sites in 38 patients were treated with prophylactic radiation therapy for heterotopic ossification at our institution. An IRB approved retrospective review was performed. There were 15 patients who received treatments to the elbow, 13 to the knee (1 bilateral for a total of 14 knees), and 10 to other sites (leg stump (2), pubic symphysis (2), femur (1), foot (1), humerus stump (1), abdominal wall (1), shoulder (1), thigh (1)). All but 1 patient were treated with a single fraction treatment with 700 or 800 cGy. One patient received 2000 cGy in 10 fractions to the abdominal wall for heterotopic ossification extending from the xiphoid process. Results: Fifteen patients underwent treatment to the elbow with a median follow-up of 5 months (0 - 99). Median age for this group was 50 years (37 - 69). Nine (60.0%) patients had evidence of heterotopic ossification prior to surgery. All (100%) of the elbow patients were free from recurrence at last follow-up. There were no acute or late toxicities noted. For treatment to the knee, there were 4 (28.6%) recurrences, all in cases where there were pre-operative heterotopic ossification. There were two other recurrences in the non-hip, elbow or knee sites: one patient who received radiation therapy to the abdominal wall and one patient who underwent treatment to the thigh. Conclusions: Prophylactic radiation therapy with 700 cGy or 800 cGy in 1 fraction either before or after surgery remains a safe and effective treatment for both hip and most non-hip sites. Fractionated treatment may be used for larger treatment fields, however experience is limited.