External Validation of the Renal Ablation-Specific P-RAC Scoring System to Predict Procedure Complexity or Complications from Percutaneous Renal Ablation

Purpose: The percutaneous renal ablation complexity (P-RAC) score (1) is a renal ablation-specific scoring system reported to predict the complexity of a percutaneous renal ablation (PA), including number of probe insertions, procedure duration, and requirement of adjunctive techniques such as hydrodissection. Yet, it has not yet been tested against an external population of patients or in modalities other than microwave ablation (MWA). The purpose of this study is to validate the ability of the P-RAC score to predict the complexity of PA in an external population that underwent either MWA or cryoablation (CA).

Materials and Methods: Retrospective review of patients who underwent either MWA or CA from 2004-2018. Patient demographics and baseline tumor characteristics were collected. Measures of procedural complexity including number of probe insertions, use of adjunctive techniques such as hydrodissection, and procedure duration were recorded. Correlation coefficients were calculated to assess for correlations between the P-RAC score and the number of probes inserted as well as procedure duration. An ROC curve for the score’s ability to predict the use of adjunctive techniques was generated. Analyses were first done on the population as a whole (MWA+CA). Since the scoring system was developed using MWA patients, a sub-analysis was done on patients who underwent MWA.

Results: 236 patients (M=134; F=102; median age=65 (range:27-90)) met inclusion criteria. 197 patients and 39 patients underwent CA and MWA, respectively. Regarding the number of probes inserted, there was a weak correlation with the P-RAC score for the entire cohort (r=0.36, p< 0.0001) but there was no correlation on sub-analysis of the MWA patients (r=0.15, p=0.38). Regarding procedure duration, there was a very weak correlation with the P-RAC score for the entire cohort (r=0.18, p=0.04) but there was no correlation on sub-analysis of the MWA patients (r=0.09, p=0.76). The area under the ROC curve to predict the use of adjunctive techniques was 0.56 and 0.51 for the entire cohort and MWA ablation patients, respectively.

Conclusion: The P-RAC score is a poor predictor of procedural complexity in this patient population. Additional ablation-specific scoring systems are needed to assist the interventional radiologist in patient selection for PA.

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References: 1. Mansilla AV, Bivins EE, Contreras F, Hernandez MA, Kohler N, Pepe JW. CT-guided microwave ablation of 45 renal tumors: analysis of procedural complexity utilizing a percutaneous renal ablation complexity scoring system. J Vasc Intervent Radiol. 2017;28:222-229.