A New Measure for the Gamma Knife Radiosurgery Response: The Slope and Plot of Tumor Volume Changes First Evaluated for Non-small-cell Lung Carcinoma Brain Metastases

Douglas Kondziolka, MSc, MD1, Aditya K Iyer, BS, MSc2, Agam D Patel3, John C. Flickinger, MD4, Hideyuki Kano, MD, PhD1, Ajay Niranjan, MCh1, L. Dade Lunsford, MD1

1Department of Neurological Surgery, University of Pittsburgh 2University of Pittsburgh 3University of Pittsburgh School of Medicine 4Department of Radiation Oncology, University of Pittsburgh

Keywords: gamma knife, lung cancer, brain metastasis, outcome, Imaging

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     Reporting simple tumor volume changes (smaller, no change, larger) after radiosurgery has been used for decades but is inadequate to define the radiobiologic effect. We hypothesized that the slope and appearance of the volumetric response plot would define the radiobiologic effect for specific lesions, radiosurgical techniques, and/or devices. 
     We tested this concept using brain metastases from non-small cell lung cancer (NSCLC).
     100 patients with lung cancer were studied.
     Serial post-radiosurgery MRI images were evaluated in 100 patients who underwent Gamma knife radiosurgery between 2006 and 2010 for brain metastases from NSCLC. Patients received between 16 and 20 Gy to the tumor margin. The largest tumor (>1cc) was selected for each patient and its volume measured over time using available software. Patients were imaged from 0.4 months to 42.4 months following radiosurgery (mean, 9 months).
     The overall treated tumor control rate was 87%. Eighteen percent of patients had transient tumor enlargement and 9% had sustained tumor growth. Overall, 60% of patients had gradual tumor regression. The reduction in tumor volume occurred most rapidly in the first three months following Gamma knife radiosurgery (mean treated tumor reduction = 45%) followed by a less steep decline in size over the subsequent two years (mean reduction = 32% after 3 months). At each interval the reduction was as follows: 3 months=45%, 6 months=47%, 9 months =55%; 12 months=64%, 15 months=66%, 18 months=75%, 21 months= 81%, 24 months=77%.
     This was a retrospective analysis.
     The tumor volume response after Gamma knife radiosurgery is dynamic; the reduction in tumor volume is most pronounced in the three month interval after radiosurgery.
     The slope and appearance of the response curve will facilitate comparisons with other tumor types, radiosurgical techniques or technologies. Shifts of the curve to the left or right will indicate poorer or improved radiosurgery response profiles.


Project Roles:

D. Kondziolka (), A. Iyer (), A. Patel (), J. Flickinger (), H. Kano (), A. Niranjan (), L. Lunsford ()