Proceedings of the 52nd Annual ASTRO Meeting S559

(46.7%). The difference between the rates of HO in the two groups was 29%; There is a significant difference between HO for-mation rate of the two BMI groups, p \ 0.0001 at a = 0.05.

Conclusions: Our data show there is a higher incidence of HO amongst Class III obese patients after open reduction and internalfixation of traumatic acetabular fractures followed by prophylactic radiation therapy ± Indomethacin. This information can be ap-plied clinically by discussing the risks and benefits of radiation therapy with Class III obese patients undergoing operative repair ofacetabular fractures.

Author Disclosure: J. Ma, None; W.F. Mourad, None; Z. Zhang, None; R.A. Shourbaji, None; G. Dieck, None; G. Russell, None;R. Jennelle, None; M.C. Baird, None; S. Vijayakumar, None; S. Packianathan, None.

2794 Prophylactic Radiation Therapy is Safe and Effective Treatment for the Prevention of Recurrent

Heterotopic Ossification in Elbow and Knee Joints

M. V. Mishra1, L. Austin2, J. Parvizi2, M. Ramsey2, T. N. Showalter1

1Department of Radiation Oncology, Jefferson Medical College of Thomas Jefferson University, Philadelphia, PA, 2RothmanInstitute, Jefferson Medical College of Thomas Jefferson University, Philadelphia, PA

Purpose/Objective(s): Prophylactic radiation therapy (RT) is an established adjuvant therapy for heterotopic ossification (HO) ofthe hip when delivered in the immediate pre- or post-operative setting. Its role in prevention of recurrence after excision of HO issupported by randomized trials for HO of the hip, but there is scant evidence to support a similar approach in non-hip joints. In thecurrent study, we evaluate radiologic and functional outcomes after prophylactic radiation therapy (RT) for prevention of HO of theknee and upper extremity [elbow and metacarpophalangeal (MCP) joints].

Materials/Methods: With IRB approval, patients treated at our institution with prophylactic RT for non-hip HO from 1998-2009were identified. Records were reviewed, including pre- and post-operative records, operative reports, and radiography. The primaryobjectives were to determine the safety and rate of treatment failure, as defined by need for further surgical intervention.

Results: A total of 30 patients received prophylactic RT for HO of the elbow (n = 21), MCP joint (n = 1), and knee (n = 8). 29 of the30 patients were treated within 24-48 hours post-operatively and 1 patient was treated within 24 hours pre-operatively. Based oninstitutional policy, only patients considered to be at high risk of recurrence were selected to receive prophylactic RT. The medianpatient age was 47 years (range, 15-78 years). Patients were treated to a dose of 7 Gy in one fraction, with 2 parallel opposed fields(anterior-posterior and posterior-anterior). Median field size was 9.0 cm wide (range, 7.2-18.1 cm) by 12.0 cm long (range, 9.6-19.7cm) for the elbow and 13.75 cm wide (range, 8.0-34.7 cm) by 12.35 cm long (range, 8.5-16.4 cm) for the knee. Complicationsfollowing treatment included: 2 patients with post-operative wound infections, 1 patient with a ruptured triceps tendon, and 1 pa-tient with a fracture within the treatment field. Follow-up information was available for 26/30 patients, with a median follow-uptime of 16 months (range, 2-143 months). Recurrent HO, requiring surgical re-excision, developed in 10.5% (n = 2) of patients whowere followed for upper extremity HO (n = 19). For patients followed after RT for HO of the knee (n = 7), there were no recurrencesof HO that required further intervention.

Conclusions: This represents the largest reported series to evaluate the safety and efficacy of prophylactic RT for prevention of HOfor non-hip joints. In this group of patients at high risk for developing further HO, prophylactic RT appears to be a safe adjunct tosurgery and is effective in prevention of HO recurrence. Results are similar to published reports of HO of the hip and support the useof surgical excision and perioperative, prophylactic RT for HO of non-hip joints.

Author Disclosure: M.V. Mishra, None; L. Austin, None; J. Parvizi, None; M. Ramsey, None; T.N. Showalter, None.

2795 Timing of Radiation for Non-Abdominal Desmoid Tumors: The Emory Experience

V. L. Robertson1, A. T. Deyrup2, D. K. Monson3, S. V. Oskouei3, J. Landry1, K. Godette1

1Department of Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, GA, 2Department of Pathology,Emory University, Atlanta, GA, 3Department of Orthopedics, Emory University, Atlanta, GA

Purpose/Objective(s): Desmoid tumors are associated with a high rate of local recurrence after resection alone, and postoperativeradiation for margin positivity can provide similar local control rates to complete surgical resection, both around 75%. Our objec-tive was to determine if preoperative radiation (pre-op RT) can provide better local control rates than surgical excision alone, post-operative radiation (post-op RT), or definitive radiation.

Materials/Methods: From January 1990 to December 2008, 90 patients with desmoid tumors were treated at Emory Universitywith surgical excision and/or radiation. We performed a retrospective review of all charts for follow-up, recurrence, and tumorcharacteristics, including pathologic diagnosis, size, margins, and site of disease. We also recorded treatment side effects usingCommon Terminology Criteria for Adverse Events grading.

Results: Forty-seven patients were treated with surgery alone, 6 with definitive radiation, 10 with post-op RT, and 27 with pre-opRT. The mean follow-up time was 41 months. The average time to recur was 32 months. There were 12 recurrences after surgeryalone, 1 after definitive radiation, 2 after post-op RT, and 2 after pre-op RT. There were patients who had recurrences requiringradiation as a part of their subsequent treatment; 2 prior to definitive radiation, 3 prior to post-op RT, and 11 prior to pre-opRT. The rate of close/positive margins was 31.9% with surgery alone, 40% in the post-op RT group, and 33.3% with pre-opRT. Of the 9 patients with close/positive margins after pre-op RT, 4 of them were treated at the time of recurrence and had positivemargins at their prior excision. The local control was 73.3% for surgery alone, 83.3% for definitive radiation, 80% for post-op RT,and 92.6% for pre-op RT. The Fisher’s Exact one-sided test comparing local control following surgery versus pre-op RT was sta-tistically significant (p = 0.041), and the two-sided test showed a trend towards significance (p = 0.065). There were 3 surgicalcomplications with surgery alone, one of which was a wound infection/dehiscence. There were 2 minor acute effects and 2 minorlate effects with definitive radiation; 3 minor acute effects with post-op RT; and 9 minor acute effects and 1 late effect (pulmonaryfibrosis) with pre-op RT.