International Journal of Radiation Oncology*Biology*Physics
Clinical investigationStereotactic irradiation for intracranial arteriovenous malformation using stereotactic radiosurgery or hypofractionated stereotactic radiotherapy☆
Introduction
Single-fraction stereotactic radiosurgery (SRS) is an effective treatment for patients with intracranial arteriovenous malformations (AVMs) with a diameter of about ≤2.5 cm. However, AVMs >2.5 cm in mean diameter, or around 10 cm3 in volume, and AVMs in eloquent regions are often not cured, because we cannot give an efficient dose to the AVMs without causing radiation damage to the normal tissue 1, 2.
We have used hypofractionated stereotactic radiotherapy (HSRT) as an alternative treatment for AVMs in eloquent regions or large AVMs. Single-fraction SRS was used as a basic treatment method for AVMs located in noneloquent regions or small ones. Our preliminary results have already been published, suggesting that HSRT was as effective as SRS, with possibly a lower complication rate (3). However, the study included only 27 SRS and 26 HSRT patients (3). The present study was not a randomized study involving SRS and HSRT. The efficacy of HSRT was investigated, taking account the selection bias of the treatment protocol. The appropriateness of our treatment policy of stereotactic irradiation (STI) using both SRS and HSRT is discussed.
Section snippets
Irradiation schedule
Stereotactic irradiation was SRS or HSRT. The hypofractionation schedule in this study was determined using the linear-quadratic formula for late complications without correcting for slow repair (4). The α/β ratio of the normal brain was estimated to be 2.0, which is widely accepted with regard to late radiation effects against brain parenchyma (5). A dose of 35 Gy in four fractions and 28 Gy in four fractions would have the same effect as 18.4 Gy and 14.2 Gy, respectively, in a single exposure
Follow-up
All 72 patients had clinical follow-up after STI (mean, 52 months; median, 48 months; range, 0–138 months). One patient did not appear for follow-up at all but was counted as a patient at risk of complete obliteration and was also used for the analysis of acute complications. One died of an unknown cause after angiographic confirmation of AVM obliteration and was counted as having angiographic obliteration. After angiographic confirmation of no obliteration, 1 patient died of bile duct
Discussion
The primary subject of our study was to examine the appropriateness of our treatment policy compared with previous reports in which SRS alone was used. Particularly for AVMs >2.0–2.5 cm (44% > 2.0 cm and 29% > 2.5 cm in our series) and AVMs in eloquent areas (45% of our series), making a comparison with the previous report is quite important. However, we found that it was quite difficult to compare the results of STI for AVMs among different institutions.
The crude obliteration rates of AVMs
Conclusion
Our treatment policy using SRS and HSRT was effective in producing an obliteration rate and complication rate compatible with those found in previous SRS studies. HSRT may have a wider therapeutic window in the treatment of AVMs ≥2.5 cm or AVMs in eloquent areas, because the selection bias in our treatment decision tree could favorably affect SRS but not HSRT. Some might conclude that the SRS dose in this series (minimal dose range, 12–20 Gy; mean, 19.3), was too high and that HSRT possibly has
Acknowledgements
We appreciate the help of the staff of the Departments of Neurosurgery and Radiology, Hokkaido University Hospital. We also appreciate Drs. Takeshi Nishioka and Rikiya Onimaru, for their help in preparing this paper.
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Partly supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, and Technology of Japan.