Postoperative Cavity Stereotactic Radiosurgery for Brain Metastases

Abstract

During the past decade, tumor bed stereotactic radiosurgery (SRS) after surgical resection has been increasingly utilized in the management of brain metastases. SRS has risen as an alternative to adjuvant whole brain radiation therapy (WBRT), which has been shown in several studies to be associated with increased neurotoxicity. Multiple recent articles have shown favorable local control rates compared to those of WBRT. Specifically, improvements in local control can be achieved by adding a 2 mm margin around the resection cavity. Risk factors that have been established as increasing the risk of local recurrence after resection include: subtotal resection, larger treatment volume, lower margin dose, and a long delay between surgery and SRS (>3 weeks). Moreover, consensus among experts in the field have established the importance of (a) fusion of the pre-operative magnetic resonance imaging scan to aid in volume delineation (b) contouring the entire surgical tract and (c) expanding the target to include possible microscopic disease that may extend to meningeal or venous sinus territory. These strategies can minimize the risks of symptomatic radiation-induced injury and leptomeningeal dissemination after postoperative SRS. Emerging data has arisen suggesting that multifraction postoperative SRS, or alternatively, preoperative SRS could provide decreased rates of radiation necrosis and leptomeningeal disease. Future prospective randomized clinical trials comparing outcomes between these techniques are necessary in order to improve outcomes in these patients.

Efficacy and Tolerance of Post-operative Hypo-Fractionated Stereotactic Radiotherapy in a Large Series of Patients With Brain Metastases

“…Our delineation practices are in line with these guidelines. Improvements in local control can be achieved by adding a 2 mm margin around the resection cavity (33). The choice of 1 mm to define PTV is arguable.…”

Current multidisciplinary management of brain metastases

“…This is important because SF‐SRS requires dose reductions to treat larger target volumes (>3 cm) to minimize toxicity. Retrospective studies suggest that HF‐SRS provides excellent control of large BMs (>2 cm) and resection cavities with a low radionecrosis rate . Further insight will be gained when the results of the ongoing phase 3 cooperative group trial (clinicaltrials.gov identifier NCT04114981) comparing SF‐SRS versus fractionated SRS (3‐5 sessions) for resected BM are released.…”

“…Retrospective studies suggest that HF-SRS provides excellent control of large BMs (>2 cm) and resection cavities with a low radionecrosis rate. 72,73 Further insight will be gained when the results of the ongoing phase 3 cooperative group trial (clinicaltrials.gov identifier NCT04114981) comparing SF-SRS versus fractionated SRS (3-5 sessions) for resected BM are released. Currently, we typically use HF-SRS for lesions that are >3 cm in size and/or when normal tissue constraints cannot be met using SF-SRS.…”

The Relationship Between Tumor Volume and Timing of Post-resection Stereotactic Radiosurgery to Maximize Local Control: A Critical Review

“…The Radiation Therapy Oncology Group (RTOG) has yet to provide exact guidelines regarding the optimal timing of postoperative SRS. However, a recent review recommends that based on current evidence, performing SRS within 2-3 weeks after surgery is the best option to allow the patient to recover surgically, without excessively delaying postoperative treatment [31]. This is based on recent evidence from Iorio-Morin et al that a significant risk factor for decreased LC is a delay of greater than three weeks before surgery, and Patel et al, who found no significant cavity shrinkage after 2-3 weeks and concluded that SRS within 2-3 weeks is most appropriate [30,32].…”

“…Based on the current evidence showing the unpredictability of the exact pattern of change in resection cavity size over time, we can conclude that obtaining a planning MRI as close in time to treatment as possible should be prioritized [21,25,31]. This was supported by Ahmed et al’s findings that more patients became eligible for SRS with increasing follow-up time due to cavity shrinkage; Jarvis et al’s results showing unpredictable rates of cavity volume increase or decrease during follow up; and the numerous other studies showing continuous cavity-volume decrease after surgery [18-20].…”