Gamma Knife to the surgical resection bed for intracranial metastases: do tumor diameter and treatment volume matter?

Keywords: brain metastasis, resection, gamma knife, outcome, radiosurgery

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     Stereotactic radiosurgery (SRS) is an emerging alternative to whole brain irradiation (WBI) after resection of intracranial metastases. 
     However, the literature disagrees about the prognostic significance of pre-operative largest tumor diameter and SRS treatment volume with respect to local failure rate and need for salvage WBI. We sought to clarify these factors.
     Thirty patients had imaging follow-up and were included in this study. Twenty-six patients (87%) had no prior history of intracranial surgery or radiation. One patient underwent re-resection prior to GK. Three patients received WBI after a prior resection, recurred locally, and went on to re-resection and GK.
     We retrospectively reviewed the SRS experience for intracranial metastases at Pennsylvania Hospital from 2006-2010. Of 435 total patients, 34 received Gamma Knife (GK) to the resection bed after removal of a single lesion. 
     The most common primary tumors were non-small cell lung (50%), melanoma (23%), and breast (20%). The median pre-operative tumor diameter was 2.75 cm (range 0.8-5.5). A median dose of 16 Gy (range 13-21) was prescribed to the 50% isodose line to a median volume of 11.1 cm3 (range 2.5-34.7). Twenty patients (67%) received GK to the resection bed alone, while 10 (33%) were simultaneously treated for 1-2 synchronous metastases. With a median follow-up of 13.9 months, patients survived a median 14.5 months from GK. Local treatment failure occurred in 7 cases (23%) and distant intracranial failure in 21 (70%). Thirteen patients (43%) underwent salvage WBI at a median of 5.2 months (range 1.5-26.6) after GK. Five of 13 patients (38%) with a pre-operative tumor diameter > 3 cm failed locally, versus 2 of 17 (12%) with a diameter ? 3 cm (p = 0.19). Diameter did not predict for subsequent salvage WBI (p = 0.72). SRS treatment volume, analyzed as a continuous variable and as > or ? 11 cm3, did not predict for local failure or salvage WBI.
     This was a retrospective study.
     SRS to the resection bed spares many patients WBI and delays it for others. 
     Our experience supports the view that pre-operative tumor diameter > 3 cm may predict for local failure. SRS treatment volume did not impact local failure or salvage WBI.


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