Abstract
Background: It has been shown that as the target volume of a given lesion treated by radiosurgery increases, there is a geometric increase in the amount of normal brain tissue that receives a significant radiotherapy dose. In order to limit toxicity to normal brain tissue as target volume increases, the dose prescribed to the target volume is lowered, decreasing the theoretical probability of local control. The purpose of this paper was to retrospectively review target volumes greater than 13.5 cc (corresponding to a spherical diameter of greater than 3 cm) in order to assess the local control as well as the complications associated with treating larger target volumes. Methods: The charts of 34 patients with target volumes greater than or equal to 13.5 cc who received treatment by Leksell γ-knife stereotactic radiosurgery (GK) for primary brain tumor or metastasis were reviewed retrospectively. These 34 patients were divided into three main groups based on histological subtype. These patients were treated between March 1994 and July 1996. Clinical and radiologic imaging follow-up data were correlated with radiosurgery volumes and doses. Results: At the time of the last follow-up done in August 1998, three patients had been lost to follow-up, 11 patients were still alive, and 20 patients had died. Eighteen of the patients who died and four of the patients still alive had failed locally. The median follow-up of the survivors was 31 months. Range of follow-up including patients who died was 0.5–48 months. Fifteen patients with primary high-grade gliomas (PHG) with a mean treatment dose of 14.5 Gy to the 45–50% isodose line (ISD) had a local control of 33% and an overall survival of 53% at 1 year after GK treatment. Nine patients with brain metastasis (Met) with a mean treatment dose of 15 Gy to the 45–50% ISD had a local control of 29% and an overall survival of 17% one year after GK treatment. Ten patients with meningiomas or schwannomas (M/S) with a lower mean dose of 12.8 Gy had a local control of 83% and 63% and overall survival of 90% and 72% at 1 and 2 years after GK treatment, respectively, with the median progression-free survival (PFS) and median overall survival (OS) not yet reached at the time of analysis. There was a 26% incidence of necrosis noted on radiologic imaging and an 8.5% incidence of related clinical symptomatology. Conclusions: Although we would prefer not to treat lesions greater than 4 cm in effective diameter (33 cc in volume) unless necessary, the incidence of related clinical symptomatology is not prohibitive based on the data from our patient population. In addition, patients with primary high-grade gliomas may benefit from higher doses, whereas for patients with meningiomas a lower dose may suffice. Patients with large metastasis do poorly and may not benefit from radiosurgery regardless of dose. Therefore, a critical limiting factor to be considered in treating “large” lesions with radiosurgery is not only volume, but also local control and eventual survival, which are dependent in large part on histology and individual patient prognostic factors.