2188 - Hypofractionated Four-Fraction SRS Regimen for Pituitary Adenomas and Meningiomas Abutting or Overlapping the Optic Apparatus: Clinical Outcomes and Proposed Optic Abutment Grading
Presenter(s)
C. Reynolds1, C. K. Cramer2, J. D. Bourland3, M. T. Munley2, M. Ehrig4, S. Tatter5, A. Laxton6, K. H. Belanger1, R. L. Calafiore7, P. J. Young2, C. Kittel8, M. D. Chan2, and J. White6; 1Atrium Health Wake Forest Baptist, Winston-Salem, NC, 2Department of Radiation Oncology, Wake Forest University School of Medicine, Winston-Salem, NC, 3Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, NC, 4Atrum Health Wake Forest Baptist, Winston-Salem, NC, 5Wake Forest University School of Medicine, Winston-Salem, NC, United States, 6Department of Neurosurgery, Wake Forest University School of Medicine, Winston-Salem, NC, 7Atrium Health Wake Forest Baptist, Winston, NC, 8Atrium Health Wake Forest Baptist, Win, NC
Purpose/Objective(s): Peri-optic pituitary adenomas and skull base meningiomas pose a challenge: durable tumor control while avoiding optic or chiasm injury. Conventionally fractionated radiotherapy has been preferred for lesions near the optic apparatus due to fractionation sensitivity, but hypofractionated regimens are increasingly used for lower integral brain dose and reduced cognitive toxicity. A large series identified 20 Gy in 4 fractions as the lowest effective BED regimen with >10-year control. Single-institution experience evaluates intermediate-term outcomes using Gamma Knife dose falloff with this regimen to spare optic structures without compromising control. Because published “peri-optic” series define proximity inconsistently and often underrepresent true contact/overlap, we applied a geometric Optic Abutment Grade (OAG) to standardize optic involvement and support geometry-based toxicity modeling.
Materials/Methods: Retrospective review of patients with pituitary adenomas or meningiomas treated with 20 Gy in 4 fractions for tumors abutting or overlapping the optics/chiasm. Variables included demographics, histology, prior surgery, and follow-up. Local control was assessed using RANO criteria. Toxicity, including visual outcomes consistent with radiation-induced optic neuropathy (RON), was scored with CTCAE v5.0. Tumor–optic relationships were categorized using OAG: OAG 0 (=3 mm), OAG 1 (>1–<3 mm), OAG 2 (0–1 mm, no overlap), OAG 3 (=2 mm overlap), OAG 4 (>2 mm or >10% optic volume overlap). Dosimetry was extracted from the planning system; institutional guidelines limited optic point dose to 4 Gy/fraction. Cox modeling evaluated associations between OAG, tumor type, and visual toxicity controlling for age, sex, and prior surgery. Univariable logistic regression assessed OAG–toxicity associations; multivariable Cox modeling was limited by sparse CTCAE =2 events.
Results: 143 patients, 4 with two treated tumors (pituitary adenomas: 59 [40.1%]; meningiomas: 88 [59.9%]) were included. Mean age was 63.1 years (SD 13.5); 62.9% were female. Local control at last follow-up was 98.6% with median follow-up of 26.3 months. Any-grade CTCAE toxicity occurred in 39/147 (26.5%) tumors, and 19/147 (13.0%) had CTCAE =2 toxicity, including 9/147 (6.1%) visual events (grade 1: 1/147 [0.6%], grade 2: 8/147 [6.0%], grade 3: 1/147 [0.6%]); all grade 1–2 visual toxicities resolved. Median time to toxicity was 0 months (IQR 0–4.9), typically during treatment. OAG was neither predictive of visual toxicity on univariable logistic regression nor significantly associated with time to toxicity on Cox or log-rank analyses.
Conclusion: 20 Gy in 4-fraction regimen achieved high local control with low rates of clinically significant visual toxicity for tumors abutting or overlapping the optic apparatus. The Optic Abutment Grade (OAG) provides a reproducible framework to standardize tumor–optic geometry and support cross-study comparisons and future optic risk modeling.