Introduction: Gamma knife radiosurgery is known to be a safe and effective treatment modality for local control and progression-free status of brain metastases. However, little research has been conducted on the predictors for the treatment of metastases with cystic components.
Methods: Our institution’s database of 71 patients with cystic brain metastases treated with GKS from 2006 to 2010 was used for patient selection. Out of 56 patients with lung cancer, 20 (59%) were randomly selected; all breast (n = 9, 36%) and colorectal (n = 5, 15%) cancer patients were included, for a total of 34 patients and 52 lesions. We classified 16 lesions as deep and 36 lesions as superficial. Volumetric analysis was done on tumours using treatment date and the latest MRI (or before salvage therapy, if applicable) to measure both the cystic and solid components of all GKS-treated metastases and to calculate growth rate. Clinical data and dosimetry parameters were also reviewed to analyze factors that led to changes in cystic and/or overall tumour volume.
Results: Pre-treatment, metastatic lesions from the lung had larger cystic components (by volume) than colorectal metastasis (p=0.039), and significantly larger cystic/total ratios than breast metastases(p=0.023). Post-treatment, a trend of >25% improvement in both cystic and solid components of tumours was seen in lung metastases (p=0.291). Metastatic brain tumours of colorectal origin demonstrated the best treatment response of the cystic component, higher than metastases from the breast (p = 0.007), but not the lung. Superficial tumours not only had greater cystic volumes pre-GKS than deep tumours (non-significantly), but also had higher post-treatment cystic volumes (p=0.041). Of the nine lesions that required surgical resection, eight were superficial.
Conclusions: Our results indicate that primary cancer pathology and brain lesion depth are prognosticators of the response of cystic and solid components of metastastic tumours to GKS treatment.
Patient Care: The prognostic factors identified can help physicians predict the response of a patient with cystic brain metastases to treatment with Gamma Knife radiosurgery.
Learning Objectives: By the end of this session, the audience will be able to 1) understand that Gamma Knife radiosurgery is an effective treatment for cystic brain metastases, without prior aspiration 2) appreciate the possible prognostic factors for GKS treatment response and 3) identify the need for further research in this field.