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Cochlea Dose Tolerance for Acoustic Neuroma Patients Treated with CyberKnife Stereotactic Radiosurgery


A Rashid

A Rashid*, D Pang, S Karam, Georgetown University Hospital, Washington, DC

SU-E-T-272 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:

In this study, a predictive model was generated to estimate the probability of hearing loss as a result of acoustic neuroma radiosurgey in five fractions, since we have not seen any other published cochlea dose response model for five fractions
Methods:
Cyberknife stereotactic radiosurgey at the Medstar Georgetown University Hospital was used in the treatment of 44 acoustic neuroma patients from 2003 to 2012. Toxicity was scored using Common Toxicity Criteria for Adverse Events (CTCAE) 3.0. Grade 1 toxicity was experienced by 2 patients; Grade 2 by 3 patients; and Grade 3 by 2 patients.

The maximum cochlea doses and grade of the complications from cochlea were imported into the DVH Evaluator where the probit dose response model was fitted using the maximum likelihood algorithm. The model fitting parameters were optimized to provide the best fit to the observed complication data for hearing loss in one ear for acoustic Neuroma patients.

Results:

The two standard maximum point dose tolerance limits for cochlea in five fractions are Timmerman's 27.5Gy limit and the TG-101 25Gy limit. From this dataset for Grade 3 complications the predicted risk level of these dose tolerance limits are 13.3% and 7.9%, respectively. For Grade 2 or higher events, the 5%, 10%, and 25% risk levels were estimated to be 11.4, 18.4, and 30.0Gy, respectively. For Grade 3 events, the 5%, 10%, and 25% risk levels were estimated to be 23.1, 26.1, and 31.2Gy.
Conclusion:
NTCP using cochlea maximum doses can be used to estimate the rate of hearing risk analysis from acoustic Neuroma Radiosurgery. More clinical data and further study will lead to refinement of the dose tolerance estimates.

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