(P 111) DOES DOSE MATTER? POSTOPERATIVE RADIATION DOSE AND OUTCOMES FOLLOWING FIXATION OF METASTATIC EXTREMITY BONE LESIONS

Objective: Pathologic and impending fractures are debilitating complications of bone metastases. Standard care involves surgical stabilization followed by post-operative radiation therapy (PORT), but optimal dosing and efficacy remain unclear. This study identified factors associated with local progression, hardware failure, and interventional survival (IS-time from surgery to death) in patients undergoing surgery and PORT for extremity fractures due to metastases.

Methods: A retrospective review was conducted of patients treated with surgery and PORT between 2000–2025. Data included demographics, tumor characteristics, and treatment details. Outcomes assessed were local progression-free survival (LPFS), IS (time from surgery to death), and hardware failure-free survival (HFFS), analyzed with Kaplan-Meier and Cox models. A subset analysis examined radioresistant (RR) tumors (RCC/sarcoma).

Results: 171 patients (190 sites) were included. Median age was 61 years; median follow-up was 34.1 months. Tumor types were adenocarcinoma (29%), RCC (19%), hematologic (15%), sarcoma (6%), squamous (3%), and others (28%). Patient, tumor, treatment characteristics, and outcomes for the non-RR and RR groups are summarized in Table 1. RR patients more often had visceral metastases (74% vs. 54%, p=0.0008). Two-year LPFS was lower in RR vs. non-RR tumors (78% vs. 94%, p=0.02).
On MVA, OS was worse with KPS < 80 (p=0.0004; HR 2.0) and better with multiple myeloma (p=0.01; HR 0.49). HFFS was worse with pathologic fractures (p=0.002; HR 9.8) and better in upper extremity metastases (p=0.02; HR 0.15). LPFS improved with bisphosphonates (p=0.03; HR 0.06) but worsened in RR tumors (p=0.0006; HR 7.8) and with 8 Gy x1 fraction (p=0.01; HR 11.0). IS was worse without systemic therapy (p < 0.0001; HR 3.5), with PORT < 20 Gy (p=0.046; HR 1.7), and improved with RCC histology (p=0.01; HR 0.6).
In RR patients, reduced IS was linked to lack of systemic therapy (p=0.002; HR 3.8) and KPS < 80 (p=0.04; HR 2.0). PORT < 20 Gy trended toward decreased IS (p=0.05; HR 2.8).

Conclusion: Performance status, histology, systemic therapy, PORT dose, and bisphosphonates influenced outcomes. PORT < 20 Gy was linked to reduced IS, and 8 Gy x1 fraction to higher local progression, underscoring the need for individualized, multidisciplinary management in this high-risk population.

Table 1: Patient, Tumor, Treatment Characteristics, and Outcomes