Palliative Radiation Field Extent for Post-Operative Indwelling Hardware

Abstract

Bone stabilization is indicated following tumor debulking or for the prevention or management of cortical fracture. Instrumentation can take many forms, such as intramedullary rods placed in the long bones of extremities, or extramedullary rods with pinning for spine fusion. Radiation is recommended following surgery with instrumentation whether tumor was debulked or not. However, it is not known how to best design the radiation field, and whether covering part of the implanted hardware could result in comparable tumor control with reduced toxicity. We evaluated the clinical response to palliation based on the extent of hardware coverage. Local failure was assessed by imaging and patient reported pain control. We performed a retrospective review of the patients treated at an academic cancer center and reviewed patients with post-operative indwelling hardware who received adjuvant radiation. The primary endpoints were patient reported pain outcomes and recurrence by imaging. Using dosimetry records from 2015 to 2019, patient records were then reviewed in the electronic medical record for follow up imaging and patient reported pain. Statistical analysis consisted of log rank testing and Kaplan-Meier estimates. A total of 34 patients were identified. Median follow up was 7 months. There were 16 patients treated to the entire extent of the hardware vs 18 to a partial extent of the hardware. There were 10 patients with spinal fusion, 24 patients with extremity fixation. A total of 21 patients had systemic therapy within a month of their last follow up. The rates of freedom from imaging-based recurrences were 83% (entire) and 92% (partial) at 12 months, 83% (entire) and 77% (partial) at 24 months (p = 0.89). Patient reported freedom from pain rates were 83% (entire) and 72% (partial) at both 12 months and 24 months (p = 0.39). Patient reported pain control were 86% (20 Gy/ 5 fx) and 100% (30 Gy/ 10 fx) at 24 months (p = 0.34). There were no statistically significant differences in either patient reported or imaging-based recurrences at 12 and 24 months based off of radiation field extent for indwelling hardware. Overall patients had very good rates of local control at 12 to 24 months. Using partial fields for radiation planning in regards to hardware extent for palliative purposes appears to offer reasonable and similar rates of local control. Further investigation is needed to see if increasing the sample size will result in a statistically significant difference.