Clinical investigation
Stereotactic irradiation for intracranial arteriovenous malformation using stereotactic radiosurgery or hypofractionated stereotactic radiotherapy

Parts of this paper were presented at the ISRS 2003 in Kyoto, Japan.
https://doi.org/10.1016/j.ijrobp.2004.04.041Get rights and content

Abstract

Purpose

To investigate the appropriateness of the treatment policy of stereotactic irradiation using both hypofractionated stereotactic radiotherapy (HSRT) and stereotactic radiosurgery (SRS) for arteriovenous malformations (AVMs) located in an eloquent region or for large AVMs and using SRS alone for the other AVMs.

Methods and materials

Included in this study were 75 AVMs in 72 patients, with a mean follow-up of 52 months. Of the 75 AVMs, 33 were located in eloquent regions or were >2.5 cm in maximal diameter and were given 25–35 Gy (mean, 32.4 Gy) in four daily fractions at a single isocenter if the patient agreed to prolonged wearing of the stereotactic frame for 5 days. The other 42 AVMs were treated with SRS at a dose of 15–25 Gy (mean, 24.1 Gy) at the isocenter. The 75 AVMs were classified according to the Spetzler-Martin grading system; 21, 23, 28, 2, and 1 AVM were Grade I, II, III, IV, V, and VI, respectively.

Results

The overall actuarial rate of obliteration was 43% (95% confidence interval [CI], 30–56%) at 3 years, 72% (95% CI, 58–86%) at 5 years, and 78% (95% CI, 63–93%) at 6 years. The actuarial obliteration rate at 5 years was 79% for the 42 AVMs <2.0 cm and 66% for the 33 AVMs >2 cm. The 5- and 6-year actuarial obliteration rate was 61% (95% CI, 39–83%) and 71% (95% CI, 47–95%), respectively, after HSRT and 81% (95% CI, 66–96%) and 81% (95% CI, 66–96%), respectively, after SRS; the difference was not statistically significant. Radiation-induced necrosis was observed in 4 subjects in the SRS group and 1 subject in the HSRT group. Cyst formation occurred in 3 patients in the SRS group and no patient in the HSRT group. A permanent symptomatic complication was observed in 3 cases (4.2%), and 1 of the 3 was fatal. All 3 patients were in the SRS group. The annual intracranial hemorrhage rate was 5.5–5.6% for all patients.

Conclusion

Our treatment policy using SRS and HSRT was as effective as the policy involving SRS alone. The HSRT schedule was suggested to have a lower frequency of radiation necrosis and cyst formation than the high-dose SRS schedule. The benefit of HSRT compared with lower dose SRS has not yet been determined.

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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