Assessment of the α/β ratios for arteriovenous malformations, meningiomas, acoustic neuromas, and the optic chiasma

Purpose: To determine alpha/beta (alpha/beta) values of arteriovenous malformations (AVM), meningiomas, acoustic neuromas (AN), and the optic chiasma using clinical data. Methods and materials: Data of dose/fractionation schedules form the literature, iso-effective for a specific clinical outcome, were analysed using the Fraction Equivalent plot (FE) method and the Tucker method. Established safe dose/fractionation schedules for the optic chiasma were used to determine its alpha/beta value. Results: With the FE plot method, an alpha/beta value of 3.76 Gray (Gy) (95% confidence level [CL]: 2.8-4.6 Gy) for meningiomas, 2.4 Gy (95% CL: 0.8-3.9 Gy) for acoustic neuroma, and 14.7 Gy (95% CL: 3.8-25.7 Gy) for arteriovenous malformations were determined. The respective alpha/beta values using the Tucker method were 3.3 Gy (95% CL: 2.2-6.8 Gy), 1.77 Gy (95% CL: 1.3-3.0 Gy) and -57 Gy (95% CL: -79.6 to -35.2 Gy). No meaningful alpha/beta values could be determined for the optic chiasma. Conclusion: Acoustic neuromas with a low alpha/beta value would show no lesion intrinsic benefit from fractionation. Meningiomas probably benefit from a hypofractionated schedule. The high alpha/beta value for AVM can be explained but needs further research. Fractionation versus radiosurgery can be considered when the primary objective is to avoid normal tissue damage.