Radionecrosis In The Supratentorium Versus Infratentorium. A Retrospective Review Of 1373 Treated Brain Metastases With Gamma Knife Radiosurgery At Northwestern University.

Keywords: brain metastasis, gamma knife, radiotherapy, radiosurgery, radiation injury

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     Radionecrosis occurs in a small percentage of patients with brain metastases treated with gamma knife radiosurgery. 
     This study was designed to evaluate the rates of radionecrosis between the infratentorial lesions specific to the posterior fossa and supratentorium.
     The authors reviewed the data of 687 patients with brain metastases treated with gamma knife radiosurgery at Northwestern Memorial Hospital from 1998 to 2009.  Patients with fewer than 90 days of follow-up, as defined by days elapsed between date of treatment and latest MRI scan, were excluded.  After exclusion, a total of 403 patients were included.  A total of 1373 treated lesions were subdivided into infra and supratentorial locations.  There were 994 supratentorial lesions and 379 infratentorial lesions. Patients with at least 3-month follow-up imaging were included and diagnosed with radionecrosis according to multiple criteria, including appearance on serial imaging and histology. 
     Mean doses, as well as range, were also analyzed between supra- and infratentorial lesions that developed radionecrosis. A two-proportion z-test was utilized to detect a potential difference between the rates of radionecrosis.
     Out of 1373 total lesions treated with gamma knife, 50 (3.6%) developed radionecrosis. Out of 994 supratentorial lesions treated with gamma knife, 45 (4.5%) developed radionecrosis.  Out of 379 infratentorial lesions treated with gamma knife, 5 (1.3%) developed radionecrosis. (z-score= 2.84 and p-value=0.0046).  Mean doses for supra- and infratentorial lesions were 18Gy and 18Gy respectively.  Supratentorial dose range was 10-22Gy.  Infratentorial dose range was 12-20Gy.
     This is a retrospective study.
     Supratentorial brain metastases may have a higher risk of radionecrosis compared to infratentorial lesions. 
      A prospective, randomized validation is recommended to further evaluate this conclusion.


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