Treatment outcomes after Gamma Knife stereotactic radiosurgery for intracranial chordoma and chondrosarcoma: a single institution experience

Summary: To investigate the clinical outcomes of patients with intracranial chordoma and chondrosarcoma undergoing Gamma Knife stereotactic radiosurgery (GKSRS) and examine if there is a predictor value for treatment failure with various GKSRS treatment planning metrics. This study was a retrospective review of patients who underwent GKSRS for chordoma or chondrosarcoma from August 2010 to July 2017. The 2yr,5yr and 12yr progression free survival (PFS) were analyzed. In cases of treatment failure, the predictive value of different clinical parameters and various GKSRS treatment planning metrics (e.g., Paddick Conformity Index (PCI), Gradient Index (GI), selectivity, D99%, tumor volume, target coverage) were examined. Treatment failure was defined as increased tumor size after GKSRS treatment. In-field failure was defined as recurrence or increased tumor size within the 80% isodose line. Marginal failure was defined as recurrence or increased tumor size within 1 cm of the treated volume. Distant failure was defined as recurrence or increased tumor size at an intracranial location > 1 cm from the treated volume. Seventeen patients were included in this study, pathology confirmed ten chordoma and seven chondrosarcoma patients. One chordoma patient was censored, as several GKSRS metrics were missing. At 5-year follow-up, the PFS was significantly higher in the chondrosarcoma group than the chordoma group, 85.7% vs 33.3% (log-rank p=0.0425). Therapy failure in male patients trended to be higher compared to females, although non-significant (p=0.0984). GI 2.85 (p=0.0425). Using ROC, prescription dose (AUC: 0.833) is a potential predictor of in-field failure. Selectivity (AUC: 0.75) and PCI (AUC: 0.714) were potential predictors of marginal failure. On Cox hazard regression chordoma histology was correlated with treatment failure (HR: 6.23) and female patients had a lesser risk of treatment failure (HR: -8.43). The outcomes after GKSRS treatment were significantly more favorable in patients with chondrosarcoma, of female gender, and those treated with a planning GI>2.85, the former of which has been previously observed in other studies. GKSRS treatment planning metrics such as selectivity, PCI, and prescription dose are suggested as potential predictors for different types of treatment failure. This is the first study in the literature to our knowledge that explores the relationship between these GK planning metrics and treatment failure. This study shows that we could further explore the predictive value of GK treatment planning metrics for treatment failure with more studies with larger patient cohorts. Joseph A. Adedigba (he/him/his), MD (Presenting Author) - Medical University of South Carolina; Sean Roles, MS (Co-Author) - Medical University of South Carolina; Guillermo Rangel Rivera, MD (Co-Author) - Medical University of South Carolina; osagie s. Igiebor (he/him/his), n/a (Co-Author) - Medical university of south carolina; Charlotte Rivers, MD (Co-Author) - Medical University of South Carolina