Consensus Contouring Guidelines for Postoperative Completely Resected Cavity Stereotactic Radiosurgery for Brain Metastases

Purpose: To propose contouring guidelines based on consensus contours generated by 10 international experts for cavity stereotactic radiosurgery (SRS), an emerging treatment option after surgical resection of brain metastases. No guidelines for contouring the surgical cavity volume have been previously reported.

Methods and materials: Ten postoperative completely resected cases with varying clinical scenarios and locations within the brain were selected. For each case, 10 experts independently contoured the surgical cavity clinical target volume (CTV). All the contours were analyzed, and agreement was calculated using the simultaneous truth and performance level estimation (STAPLE) with the kappa statistic. A follow-up survey was also completed by each investigator to summarize their contouring rationale for a number of different clinical scenarios. The results from the survey and the consensus STAPLE contours were both summarized to establish contouring guidelines.

Results: A high level of agreement was found between the expert CTV contours (mean sensitivity 0.75, mean specificity 0.98), and the mean kappa was 0.65. The agreement was statistically significant at P<.001 for all cases. From these results and analyses of the survey answers, the recommendations for CTV include fusion of the preoperative magnetic resonance imaging scan to aid in volume delineation; contouring the entire surgical tract regardless of the preoperative location of the tumor; extension of the CTV 5 to 10 mm along the dura overlying the bone flap to account for microscopic disease extension in cases with preoperative dural contact; and a margin of ≤5 mm into the adjacent sinus when preoperative venous sinus contact was present.

Conclusions: Consensus contouring guidelines for postoperative completely resected cavity SRS treatment were established using expert contours and clinical practice. However, in the absence of clinical data supporting these recommendations, these guidelines serve as a baseline for further study and refinement.