Gamma knife surgery for cavernous sinus tumors: Advantage of the 4D dose planning based on microanatomy.

Keywords: meningioma, cavernous sinus, schwannoma, gamma knife, technique

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     Tumors in the Cavernous sinus (CS) involve many vital neurovascular structures and therefore are among the most difficult tumors to achieve cure by surgery. Gamma knife surgery (GKS) has increasingly been in use as a safe and effective treatment for residual, recurrent tumors and those considered to be inoperable. However, its treatment accuracy and clinical results are often called into question due to the complex intracavernous sinus structures and difficulty in identifying their specific locations.
     In this report, we review our follow-up of 120 patients treated by GKS based on our original image sequence and precise treatment planning.
     A total of 120 patients harboring CS tumors (89 pituitary adenomas, 19 meningiomas, 6 cavernous angiomas, 4 abducens nerve, and 2 oculomotor nerve schwannomas) were treated and followed at least 2 years
     . Median prescription dose was 12Gy at 50% isodose line except for pituitary adenomas; non-functioning adenomas:18(12-25)Gy, functioning adenomas:25(15-35)Gy. We preferred to use gadolinium enhanced 3D heavily T2 WI (SISS/FIESTA) for MR imaging sequence, which enabled clear visualization of the intracavernous sinus structures. Tumors and surrounding nerves were localized and treatment plan was constructed to avoid normal vital structures. 80% high isodose coverage within tumors should be also considered.
     The length of follow-up ranged from 24 to 76 months (mean, 36 months). Overall, tumor control rate was 97.5% (pituitary adenomas:97%, meningiomas:100%, cavernous angiomas:100%, schwannomas:100%), and tumor shrinkage rate was 68.3% (pituitary adenomas:64%, meningiomas:79%, cavernous angiomas:100%, schwannomas: 67%). Endoclinological normalization was seen in 39% of the cases with functioning adenomas. There was no pituitary dysfunction in all cases. Complication of cranial nerve was seen in 5% (50% in schwannomas: abducens nerve palsy:5, oculomotor nerve palsy:2, and 2.6% in other tumors ) and most of them (83%) were transient.
     This was a retrospective study.
     Clearly, our follow-up period is not enough to evaluate and further prospective studies are required before GKS is established as a standard of treatment for CS tumors. However, even our short-term follow-up resulted in early-phase tumor shrinkage and less radiation-induced complications. 
     We are convinced that GKS will play a bigger role in the treatment of CS tumors in the future.


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