Radiation Therapy Prophylaxis for Heterotopic Ossification in Non-Hip Sites

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