A Method to Improve the Safety and Tolerability of External Beam Radiation Therapy for Heterotopic Ossification Prophylaxis

Abstract

Heterotopic ossification is a debilitating form of dystrophic calcification that occurs in 50-90% of patients with traumatic acetabular fractures. Radiation therapy in the peri-operative period is a proven intervention to reduce the incidence of heterotopic ossification. However, as many of the patients requiring radiation have suffered polytrauma and/or are clinically unstable, the treatment of these patients can be logistically challenging, uncomfortable for the patient and, at times, clinically unsafe. In this study, we describe the development and characterization of a clinical protocol in which the diagnostic images obtained on patients requiring radiation therapy for HO prophylaxis can be used for radiation treatment planning. This protocol allows for individualized patient treatment plans to be generated and transferred to the record and verify system prior to the patient being brought to the department for therapy. Using this method, these often times critically ill patients can be treated with improved efficiency and safety. We retrospectively identified 10 patients treated in 2015 in our department after traumatic hip fracture for heterotopic ossification prophylaxis who had undergone CT simulation for treatment planning. The diagnostic CT scans of the patients obtained by orthopedic surgery immediately post operatively to examine hardware placement were imported into the MIMvista system and corrected for orientation and then adjusted to a neutral pelvis alignment. These scans were then imported into the Pinnacle treatment planning system and plans were designed to treat the affected hip to 7.5 Gy in 1 fraction per institutional standard for HO prophylaxis. In order to determine the safety of this protocol, the treatment plans were then transferred without alteration onto the CT data set obtained at the time of CT simulation, and the dose distributions were compared. There were limited differences in the dose distributions in the plans generated on the diagnostic scans and dose distributions after transfer to the CT simulation data sets. The maximum point dose was within 1% (range -1% to 1%), and the volumes receiving 7.5 Gy and 7.0 Gy were within 25% (range, -25% to 20%) and 6% (range -3% to 6%) respectively. Additionally, the treatment plans after transfer to the CT simulation data sets were each reviewed by four physicians in the department not involved in the replanning portion of the study, and 100% of the plans were felt to be appropriate for treatment. This study demonstrates that diagnostic imaging scans can reasonably be used to plan patients requiring radiation for heterotopic ossification prophylaxis. As a result, patients can be treated efficiently, potentially reducing the time they will spend in the department and improving patient safety.