Frameless Hypofractionated Stereotactic Radiosurgery Treatment To Tumors Within 2 Mm Of The Optic Apparatus.

e12549 Background: Conventional tx options for benign or malignant tumors w/in 2 mm of the optic apparatus include 25-28 conventional RT txs given over 5 wks, surgery to pull the tumor further than 2 mm from the optic apparatus followed by a 1 fx of stereotactic radiosurgery (SRS), 1 fx SRS alone, a clinical trial, or close observation. A retrospective study from Stanford University Medical Center has shown promise for effective treatment of perioptic lesions with hypofractionated SRS, showing high rates of tumor control and visual function retention. This prospective study is intended to build upon the Stanford study, increase the body of knowledge, and advance evidence-based tx options. Methods: The Rx dose: 25 Gy delivered in 5 sessions (5 Gy x 5 fx). The planning target volume (PTV) consists of the perioptic lesion with no margin. The plans are constructed so that 95% of the PTV receives ≥ 95% of the prescribed dose. The critical structures that are contoured in all cases are both eyes, brainstem, optic chiasm, and both optic nerves. Dose constrains that apply: 10 Gy to eyes, 20 Gy to brainstem, 25 Gy to optic chiasm, and 25 Gy to optic nerves. Variables to be analyzed: local tumor control rate and the acute adverse and delayed effects of this tx regimen on the optic apparatus. Results: Currently 6 pts (2 pts with adenomas and 4 with meningiomas have undergone hypofractionated frameless SRS using an image-guided 6 MV linear accelerator. All 6 pts received 25 Gy in 5 fx. The critical structure dose constrains were met per protocol. Mean fu: 7 mos. Mean LOS: 14 mos. There have been no Grade 3-5 adverse events. All 6 pts were clinically and radiologically stable at their 30 day fu post-SRS. Local control: 100%. No pts have experienced a decline in visual function. 1 pt had an unrelated dx of high-risk prostate cancer that unfortunately metastasized to his bone, liver and pancreas. This pt died 8.25 mos post SRS for an orbital meningioma. Conclusions: This data suggests that 5 fx SRS for control of perioptic tumor is a promising tx. This prospective study is ongoing. Centers should consider adding patients to this study Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Central Illinois Neuro Health Sciences