Defining the Interval between the Development of New Lesion on Follow Up Study and 1st Gamma Knife Radiosurgery without Whole-Brain Radiation Therapy in the Management of Brain Metastases

Abstract

The aim of this retrospective study is to define the interval between the development of new lesion on follow up study and 1st gamma knife radiosurgery (GKS) without whole brain radiation therapy (WBRT) in the management of brain metastases. Between May 1992 and January 2006, 378 patients (207 males and 174 females) with brain metastases were treated with radiosurgery at the Yonsei University Medical Center. Reviewing the follow up study was available in 357 (81.7%) cases, and new lesions were found in 83 (23.2%) cases. We classified the development of new lesions after 1st GKS as missed, invisible, true new and undetermined lesions；missed lesions are those which were visible on MRI at the time of 1st GKS retrospectively, but omitted；invisible lesions, too small to be visualized on MRI at the time of 1st GKS, may be less than 1mm in size at that time and will be new lesions, visible on MRI within 4months after 1st GKS；true new lesions, newly metastasized to brain after GKS, developed 8 months after 1st GKS； undetermined lesions, new lesions developed 5 to 7 months after 1st GKS. There were 12 patients (18.18%) of missed lesions, and the number of those lesions was 17；10 patients (15.15%) of invisible, and the number, 51；25 patients (37.88%) of undetermined, and the number, 166；19 patients (28.79%) of true new lesions, and the number, 100. The incidence of new lesion development was high between 5th and 7th months after GKS, and after that, it decreased suddenly. And that low incidence was even after 7th months. GKS without adjuvant WBRT showed good effect, however, strict MRI follow up at 4 and 7months after GKS is necessary to detect and treat the invisible and missed lesions.