A New Scoring Tool to Estimate Post-Treatment Ambulatory Status after Radiotherapy of Metastatic Spinal Cord Compression

Purpose/Objective(s) To improve treatment personalization of patients irradiated for metastatic spinal cord compression (MSCC), a score predicting post-treatment ambulatory status after radiotherapy (RT) alone (without surgery) was presented in 2008. Since then, upfront decompressive surgery has become more popular, which may decrease the predictive value of this score. A new scoring tool may be helpful. Materials/Methods Data of 283 patients treated with RT alone for MSCC in three prospective trials since 2010 were re-evaluated. Dose-fractionation of RT and 12 factors were analyzed including age (<=67 vs >67 years), gender, tumor type (breast ca. vs prostate ca. vs myeloma/lymphoma vs lung ca. vs others), interval from tumor diagnosis to MSCC (<=6 vs >6 months), number of affected vertebrae (1-2 vs >=3), further bone lesions (no vs yes), visceral metastases (no vs yes), time developing motor deficits (<=7 vs >7 days), pre-RT ambulatory status (ambulatory without aid vs ambulatory with aid vs not ambulatory), performance score (ECOG-PS 1-2 vs 3-4), sensory deficits (no vs yes), and sphincter dysfunction (no vs yes). For each factor that achieved significance in the multivariate analysis (logistic regression model) after backward regression modelling, scoring points were calculated by dividing the post-RT ambulatory rates (in %) by 10. The scoring points of these factors were added for each patient. The new score was compared to the previous tool for prediction (positive predictive value, PPV) of ambulatory and non-ambulatory status after RT. Results In the multivariate analysis, primary tumor type (p=0.010), sensory deficits (p=0.002), sphincter dysfunction (p=0.017), pre-RT ambulatory status (p<0.001) and ECOG-PS (p<0.001) were significant; a trend was found for the time developing motor deficits (p=0.054). Five of these factors were included in the score and available for 278 patients. ECOG-PS was not included, since ambulatory status and ECOG-PS were confounding variables. For internal validation, bootstrapping with 1000 replications was used. Corrected C-statistic accounting for overfitting was 0.91, which demonstrated good predictive performance of the model. Based on post-RT ambulatory rates, three prognostic groups (25-29, 30-38 and 39-45 points) were designed with ambulatory rates of 11% (5/44), 64% (49/77) and 97% (152/157), respectively. Rates of local control of MSCC were 100%, 82% and 94% at 1 year, and 100%, 82% and 87% at 2 years. Survival rates were 20%, 21% and 55% at 1 year, and 13%, 12% and 39% at 2 years. PPVs of the new score to predict ambulatory and non-ambulatory status were 97% and 89% vs 98% and 79% when using the previous score. Conclusion The new score appeared more precise than the previous one in predicting non-ambulatory status after RT. Depending on survival prognosis, patients with <=38 points likely benefit from upfront surgery. Since patients of the 39-45 points group had very high rates of post-RT ambulatory status and local control, they may not require surgery.