Radiation exposure of normal temporal bone structures during stereotactically guided gamma knife surgery for XXXX .

@entity1 @entity5513 @entity1844 @entity39 @entity5 @entity425 @entity392 @entity1296 @entity393 @entity2346
OBJECT: The dosimetry of radiation exposure of healthy inner, middle, and external ear structures that leads to @entity393 , @entity392 , @entity425 , @entity1296 , vertigo, and imbalance after gamma knife surgery (GKS) for @entity5513 ( @entity5513 ) is unknown. The authors quantified the dose of radiation received by these structures after GKS for VS to assess the likelihood that these doses contributed to postradiosurgery complications. METHODS: A retrospective study was performed using a prospectively acquired database of a consecutive series of 54 @entity1 with VS who were treated with GKS during a 3.5-year period at an "open unit" gamma knife center. Point doses were measured for 18 healthy temporal bone structures in each @entity1 , with the anatomical position of each sampling point confirmed by a fellowship-trained neurootologist. These values were compared against single-dose equivalents for the 5-year tolerance dose for a 5% risk of complications and the 5-year tolerance dose for a 50% risk of complications, which were calculated using known 2-Gy/fraction thresholds for chronic @entity2346 , @entity1844 , and osseous @entity39 , as well as the @entity5 margin dose and typical @entity5 margin prescription doses for @entity1 in whom hearing preservation was attempted. External and middle ear doses were uniformly low. The intratemporal facial nerve is susceptible to unintentionally high radiation exposure at the fundus of the internal auditory canal, with higher than @entity5 margin doses detected in 26% of cases. In the cochlea, the basal turn near the modiolus and its inferior portion are most susceptible, with doses greater than 12 Gy detected in 10.8 and 14.8% of cases. In the vestibular labyrinth, the ampulated ends of the lateral and posterior semicircular canals are most susceptible, with doses greater than 12 Gy detected in 7.4 and 5.1% of cases. CONCLUSIONS: Doses delivered to middle and external ear structures are unlikely to contribute to post-GKS complications, but unexpectedly high doses may be delivered to sensitive areas of the intratemporal facial nerve and inner ear. Unintentional delivery of high doses to the stria vascularis, the sensory neuroepithelium of the inner ear organs and/or their ganglia, may play a role in the development of post-GKS @entity392 , @entity393 , @entity1296 , vertigo, and imbalance. Minimizing treatment complications post-GKS for VS requires precise dose planning conformality with the three-dimensional surface of the @entity5 .
