Subtraction Fusion With Prior Images Helps Identify Additional Brain Metastases for Repeat Radiosurgery

John C. Flickinger, MD1, Hideyuki Kano, MD, PhD2, Josef Novotny3, Yoshio Arai4, Jagdish Bhatnagar5, Ajay Niranjan, MCh2, L Dade Lunsford6, Douglas Kondziolka, MSc, MD2

1Department of Radiation Oncology, University of Pittsburgh 2Department of Neurological Surgery, University of Pittsburgh 3Prague, Czech Republic 4Dept. of Radiation Oncology, U. of Pittsburgh School of Medicine 5Pittsburgh, United States 6Dept. of Neurological Surgery, U. of Pittsburgh School of Medicine

Keywords: brain metastasis, brain tumor, gamma knife, radiosurgery, Imaging

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     Identification of all brain metastases present on planning stereotactic images is necessary to optimize control of brain metastases and limit the need for additional radiosurgery or radiotherapy to the brain.
     We hypothesized that subtraction fusion of new minus old high-resolution stereotactic contrast enhanced magnetic resonance (MR) images of brain metastasis patients for radiosurgery planning would improve detection of small brain metastases.
     We studied 75 patients with 1-6 (median = 1) prior brain metastasis radiosurgery procedures to 1-55 metastases (median = 4) at the time of subsequent radiosurgery to 1-26 metastases (median= 4).
     Prior high-resolution stereotactic contrast enhanced MR images were co-registered with new images to identify and outline all prior radiosurgery treatment volumes. All new brain metastases were outlined after review by at least one attending Neurosurgeon, one attending Radiation Oncologist and one Medical Physicist. Subtraction-fusion (new minus latest prior) images were constructed and reviewed to see if additional brain metastases could be identified. Two patients had two prior courses of whole-brain (WB) radiotherapy (XRT), 21 patients had one. 51 had none and one had partial brain XRT. The median interval since the latest prior radiosurgery imaging was 6 months (range: 2-29).
     Without the subtraction-fusion imaging 0-29 (median=3) new metastases were identified (3 patients had radiosurgery only to retreat metastases). After review of the subtraction-fusion (new-old) MR-images 16/75 (21 %) of patients had 1-5 additional brain metastases identified, measuring 3-176 cu-mm (median, 15 cu-mm, n=23). Stepwise linear-regression correlated increasing numbers of additional brain metastases identified by subtraction fusion with the total number of new and previously identified brain metastases (p=0.001) and prior WB-XRT (p=0.017). Logistic regression correlated an increasing rate of detecting any additional metastases by subtraction fusion with the number of previously identified brain metastases (p=0.029).
     This was a retrospective review.
     Subtraction-fusion of new minus prior contrast-enhanced high-resolution MR images appears to help identify additional brain metastases for radiosurgery planning, particularly with in patients with greater numbers of brain metastases.
     The findings of this study show that subtraction imaging can affect dose planning.


Project Roles:

J. Flickinger (), H. Kano (), J. Novotny (), Y. Arai (), J. Bhatnagar (), A. Niranjan (), L. Lunsford (), D. Kondziolka ()