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Clinical Investigation
Internal validation of the prognostic index for spine metastasis (PRISM) for stratifying survival in patients treated with spinal stereotactic radiosurgery
Garrett Jensen, Chad Tang, Kenneth R. Hess, Andrew J. Bishop, Hubert Y. Pan, Jing Li, James N. Yang, Nizar M. Tannir, Behrang Amini, Claudio Tatsui, Laurence Rhines, Paul D. Brown and Amol J. Ghia

Purpose: We sought to validate the Prognostic Index for Spinal Metastases (PRISM), a scoring system that stratifies patients into subgroups by overall survival.

Methods and materials: The PRISM was previously created from multivariate Cox regression with patients enrolled in prospective single institution trials of stereotactic spine radiosurgery (SSRS) for spinal metastasis. We assess model calibration and discrimination within a validation cohort of patients treated off-trial with SSRS for metastatic disease at the same institution.

Results: The training and validation cohorts consisted of 205 and 249 patients respectively. Similar survival trends were shown in the 4 PRISM. Survival was significantly different between PRISM subgroups (P<0.0001). C-index for the validation cohort was 0.68 after stratification into subgroups.

Conclusions: We internally validated the PRISM with patients treated off-protocol, demonstrating that it can distinguish subgroups by survival, which will be useful for individualizing treatment of spinal metastases and stratifying patients for clinical trials.

Keywords: SSRS, SBRT, metastatic disease, prognostic score

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