CyberKnife multisession stereotactic radiosurgery and hypofractionated stereotactic radiotherapy for perioptic XXXX : intermediate-term results and radiobiological considerations.

@entity1 @entity1653 @entity5 @entity227
Single fraction radiosurgery is conventionally precluded for lesions lying <2-3  mm of the anterior visual pathway because of the radiosensitivity of the optic nerve. We analyzed a series of 64 @entity1 with "perioptic" @entity1653 treated by CyberKnife multisession radiosurgery and hypofractionated stereotactic radiotherapy (hSRT). Between July 2007-May 2010, @entity1 were treated using conventional multisession Cyberknife schemes (2-5 fractions) and results were retrospectively analyzed. A radiobiological model was then developed to estimate the best @entity5 ( @entity5 )/ normal tissue complication probability (NTCP) for these lesions. Resulting dose/fraction schemes were applied to @entity1 treated between May 2010 and July 2014. Data were prospectively collected Twenty-five @entity1 were included in the retrospective part of the study. Median @entity5 volume was 4.95  cc; median dose was 23.0  Gy and median number of fraction was 5 (range 2-5). No @entity1 had @entity227 at mean follow-up of 60        12  months. Tumor control was achieved in all cases. Thirty-nine @entity1 were treated according the radiobiology model and results prospectively analyzed. Median @entity5 volume was 7.5  cc, median dose 25.0  Gy and mean number of fraction 5 (range 3-15). No @entity1 had @entity227 progression at mean follow-up of 17        10  months. Conventional multisession CyberKnife treatments (2-5 fractions) provided satisfactory results. Nonetheless, our estimation of @entity5 suggests the use of higher doses to grant long-term disease control. To achieve higher equivalent doses without significantly increasing the NTCP, we suggest the use of a greater number of fractions, moving to hSRT, in @entity5 in which the encasement of optic nerves is presumed.
