Clinical impact of magnetic resonance imaging on Gamma Knife surgery for brain metastases

Abstract

Stereotactic radiosurgery is beneficial for patients with a limited number of small brain metastases. Increased numbers of brain metastases, not infrequently at unreachable locations, are identified using thin-section magnetic resonance (MR) imaging on the day of Gamma Knife surgery (GKS). To improve patient selection and design better treatment strategies, a retrospective study was conducted to determine factors that may contribute to detecting additional brain metastases on the day of GKS. A total of 100 patients with brain metastases who underwent GKS between October 2003 and May 2006 at the University of California Davis Medical Center were included in the present study. Patients were categorized by age, sex, Karnofsky Performance Scale score, status of systemic disease, histological characteristics of the primary tumor, and whether they received previous whole-brain radiotherapy (WBRT). The number of lesions identified by diagnostic MR imaging at referral, by thin-section double-contrast MR imaging on the day of GKS, and the actual lesions treated by GKS were recorded. The diagnostic MR images were categorized in terms of section thickness and time interval before GKS. The characteristics of this patient population match well with the general GKS practice. Fifty-six had been treated with WBRT. On average, patients presented with 2.2 +/- 1.7 lesions, a number based on their original diagnostic MR imaging, had 3.6 +/- 3.4 lesions identified on the thin-section treatment MR imaging (p < 0.05), and underwent treatment of 3.1 +/- 2.6 lesions on the day of GKS. Significantly, treatment was compromised in 21 patients, in whom not all additional lesions could be treated with the initial headframe placement. Analysis shows that a significantly greater number of lesions were detected using thin-section MR imaging on the day of GKS in patients who had undergone thick-section diagnostic MR imaging, did not receive WBRT, and had progressive systemic disease. To optimize treatment planning and minimize additional treatment, the number of metastases needs to be determined accurately before frame placement, ideally by performing thin-section MR imaging, as used on the day of GKS.