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

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]: 2.84.6 Gy) for meningiomas, 2.4 Gy (95 CL: 0.83.9 Gy) for acoustic neuroma, and 14.7 Gy (95 CL: 3.825.7 Gy) for arteriovenous malformations were determined. The respective alpha/beta values using the Tucker method were 3.3 Gy (95CL: 2.26.8 Gy), 1.77 Gy (95CL: 1.33.0 Gy) and-57 Gy (95CL:-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. © 2010 Informa UK Ltd.Articl

Long-term results of stereotactic proton beam radiotherapy for acoustic neuromas

Background and purpose: A retrospective study evaluating the role of hypofractionated stereotactic proton beam therapy for acoustic neuromas. Materials and methods: The data of 51 patients treated with hypofractionation (3 fractions) and followed up for a minimum of 2 years, were analyzed. Mean dose prescribed to ICRU reference point (isocenter) was 26 cobalt gray equivalent (CGyE) in 3 fractions. Mean minimum tumor dose was 21.4 CGyE/3. Cranial nerve functions were evaluated clinically. Serial MR Scans were used to evaluate local control. Results: With a mean clinical and radiological follow-up of 72 and 60 months respectively, the 5-year results showed a 98% local control, with a hearing preservation of 42%, a facial nerve preservation of 90.5% and a trigeminal nerve preservation of 93%. Conclusion: For those patients harboring large acoustic neuromas that are inoperable, hypofractionated stereotactic proton beam offers long-term control with minimal side-effects. © 2008 Elsevier Ireland Ltd. All rights reserved.Articl

Stereotactic proton beam therapy for intracranial arteriovenous malformations

Purpose: To investigate hypofractionated stereotactic proton therapy of predominantly large intracranial arteriovenous malformations (AVMs) by analyzing retrospectively the results from a cohort of patients. Methods and Materials: Since 1993, a total of 85 patients with vascular lesions have been treated. Of those, 64 patients fulfilled the criteria of having an arteriovenous malformation and sufficient follow-up. The AVMs were grouped by volume: <14 cc (26 patients) and <14 cc (38 patients). Treatment was delivered with a fixed horizontal 200 MeV proton beam under stereotactic conditions, using a stereophotogrammetric positioning system. The majority of patients were hypofractionated (2 or 3 fractions), and the proton doses are presented as single-fraction equivalent cobalt Gray equivalent doses (SFEcGyE). The overall mean minimum target volume dose was 17.37 SFEcGyE, ranging from 10.38-22.05 SFEcGyE. Results: Analysis by volume group showed obliteration in 67% for volumes <14 cc and 43% for volumes <14 cc. Grade IV acute complications were observed in 3% of patients. Transient delayed effects were seen in 15 patients (23%), becoming permanent in 3 patients. One patient also developed a cyst 8 years after therapy. Conclusions: Stereotactic proton beam therapy applied in a hypofractionated schedule allows for the safe treatment of large AVMs, with acceptable results. It is an alternative to other treatment strategies for large AVMs. AVMs are likely not static entities, but probably undergo vascular remodeling. Factors influencing angiogenesis could play a new role in a form of adjuvant therapy to improve on the radiosurgical results. © 2005 Elsevier Inc.Articl