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

Abstract

Purpose: To determine alpha/beta (α/ß) 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 α/ß 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 α/ß values could be determined for the optic chiasma.

Conclusion: Acoustic neuromas with a low α/ß value would show no lesion intrinsic benefit from fractionation. Meningiomas probably benefit from a hypofractionated schedule. The high α/ß 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.

Keywords:

• radiosurgery
• arteriovenous malformations
• meningioma
• acoustic neuroma
• optic chiasma
• alpha/beta values