Local recurrence patterns following post-operative stereotactic radiosurgery to resected brain metastases: a quantitative analysis to guide target delineation

Publication date: Available online 26 April 2018
Source:Practical Radiation Oncology
Author(s): Chengcheng Gui, Joseph Moore, Jimm Grimm, Lawrence Kleinberg, Todd McNutt, Colette Shen, Linda Chen, Chetan Bettegowda, Michael Lim, Kristin J. Redmond
PurposeIn the treatment of resected metastatic brain disease, the recent phase 3 NCCTG N107C/CEC.3 trial surprisingly found that the local control rate of whole-brain radiotherapy was better than that of stereotactic radiosurgery (SRS). To optimize target delineation, we perform a quantitative analysis of local failures following post-operative SRS.MethodsPatients with brain metastases treated with surgery and SRS to the cavity were evaluated. Local failure was defined by pathologic confirmation or MRI evidence of progression leading to further overlapping radiotherapy. T1 post-gadolinium MRIs taken pre-operatively and at recurrence were co-registered to the simulation CT. Three volumes were compared: (1) pre-operative tumors, (2) resection cavities originally contoured as clinical target volumes for SRS, and (3) recurrent tumors. Overlap volume histograms (OVH) quantified proximity of the three volumes to the meninges.ResultsIn the cohort of 173 patients, 18 patients experienced local failure in 19 resection cavities. The original SRS target volume overlapped with a median of 69.6% of the recurrent tumor. Including the entire pre-operative tumor increased overlap with the recurrent tumor to a median of 76.8%. Recurrent tumors were closer to the meninges than corresponding pre-operative tumors (p=0.03), but a median 8.2mm expansion of the target volume from the meninges was needed to increase overlap with the recurrent tumor to 90%. Increases in overlap with the recurrent tumor were achieved most efficiently by uniformly expanding the contoured cavity; a median 2.8mm expansion covered 90% of the recurrent tumor.ConclusionOur quantitative analysis of recurrence patterns suggests that a larger 3mm uniform expansion of the SRS target volume substantially increases coverage of the volume later occupied by recurrent tumor and may provide improved local control, whereas including the pre-operative tumor extent in the target volume or expanding the target volume from the meninges provides little benefit.



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