Technical considerations in the use of prophylactic radiation therapy to prevent heterotopic bone formation

The UCLA Department of Radiation Oncology radiated 97 hips at high risk for heterotopic bone (HTB) formation from 1980 through 1988. Adequate follow-up (minimum of 2 months, median, 10 months) is available in 92 hips (82 patients). These hips were treated with a variety of doses, fractionation schedules, and shielding techniques as treatment evolved over time. There was a total of 49 hips with porous coated ingrowth prostheses. These were all shielded with custom blocks. There were no untoward complications in this subgroup. Only 6 of the 92 hips evaluable developed clinically significant HTB. Five of these 6 failures can be attributed to initiating treatment after postoperative day (POD) 5 or block malposition. Of the 78 hips that initiated radiation therapy before POD 6 (with proper shielding), only 1 (1.3%) developed clinically significant HTB. Radiation therapy is very effective at preventing HTB formation following hip surgery when treatment is initiated within 4 days of surgery. To assure an optimal outcome, close attention to the technical aspects treatment is critical.