A Comprehensive Review Of Magnetic Resonance Imaging Changes Following Radiosurgery To 500 Intracerebral Metastases

McHugh Brian1, Jonathan Knisely2, Veronica Chiang3

1Yale New Haven Hospital 2Manhasset, United States 3New Haven, United States

Keywords: Imaging, brain metastasis, gamma knife, outcome, magnetic resonance imaging

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     Radiosurgical treatment with or without whole brain radiation therapy (WBRT) is well known to result in durable control of intracranial metastatic lesions over the average expected 6-8 month survival period of this patient group.   As systemic therapy becomes more individualized and successful, many patients are surviving longer.  
     A longitudinal quantitative analysis of the response of brain metastases to radiosurgery over time has never been done.
     Follow-up magnetic resonance (MR) imaging of 500 metastatic lesions in 225 patients treated using Gamma Knife stereotactic radiosurgery from Jan 2004 to Dec 2008 were studied.  
     By our standard protocol, all patients underwent follow-up imaging at 1.5, 3, 6, 9, and 12 months following radiosurgery and then every 3 to 6 months after this. Lesion volume based on gadolinium-enhanced MRI was calculated for every lesion at the time of treatment and on every follow-up scan obtained. Change in lesion size at each time interval was then correlated with radiosurgical treatment dose, tumor histopathology, use of WBRT, systemic chemotherapeutic or immunotherapy, lesion location and subsequent imaging changes
     Our analysis demonstrates that the largest decrease in tumor volume following radiosurgery occurs in the first six weeks with 80% of lesions decreasing in size.   Tumors decrease on average 44% by 6 weeks. By 12 to 18 weeks after radiosurgery, however, while 87% of lesions are still smaller than at the time of radiosurgery, the average decrease in lesion size is only 28% i.e. some treated lesions have increased in size again compared with their 6 week volume.  Subanalysis reveals a tendency for breast and lung cancer lesions to demonstrate this enlargement. At 24 weeks, 100% of lesions are smaller than at the time of treatment and the enlargement seen at the 12-18 week scans is shown to be transient.   The majority of lesions then remain stable until time of patient death. In the 40% of patients who survive beyond 9 months, subanalysis by tumor type reveals that the lesions demonstrating regrowth after 36 weeks of follow-up are predominantly colo-rectal cancers and melanomas.  We report additional sub-analysis of the predictive effects of radiosurgical treatment dose, use of WBRT, systemic chemotherapeutic or immunotherapy, lesion location on radiosurgical response.
     This is a retrospective study.
     The quantitative response of intracerebral metastases to radiosurgical treatment appears be highly variable.
     The quantitative response also seems to be affected by histopathological type.


Project Roles:

M. Brian (), J. Knisely (), V. Chiang ()