Proton Radiosurgery for Arteriovenous Malformations of Small-to-Intermediate Size

Purpose/Objective(s)

To assess the treatment results of proton radiosurgery for inoperable arteriovenous malformation (AVMs) up to 15 cc in volume.

Materials/Methods

We conducted a retrospective chart review of all patients treated for AVMs with proton radiosurgery in the Loma Linda University Department of Radiation Medicine. Cases that met the following criteria were considered for analysis: no prior radiotherapy, AVM size <  =  15cc. A total of 40 patients were identified who met the inclusion criteria. Of these, 29 patients with complete follow up were identified and were included in this analysis. The primary endpoint of the study was angiographic obliteration at a minimum of three years post-treatment.

Results

The average volume of treated AVMs was 6.4cc (range:1 - 14.7cc). Patients were treated with a single or two fractions of proton radiosurgery to a dose of 25 Gy to isocenter, corresponding to a marginal dose of 20 Gy. The overall angiographic obliteration rate was 69% (20/29). This includes 4 patients who failed their initial course of treatment who were successfully salvaged with a second course of proton radiosurgery. The obliteration rates for AVMs of 0 - 4cc and 4.01 - 15cc were 100% (9/9) and 55% (11/20), respectively. On univariate analysis, a trend toward significance for failure to obliterate was noted for lesions in the basal ganglia/thalamus/midbrain as compared to lesions originating in the cortex. Overall, the treatment was well tolerated. No patient reported new onset or worsening of existing seizure disorder. One patient required prolonged decadron administration for symptomatic edema following treatment. His AVM was, however, successfully obliterated with no long-term sequelae of treatment. Two patients with larger AVMs, including one patient re-treated following failure of her initial radiosurgical treatment, developed persistent weakness with imaging findings suggestive of radiation necrosis.

Conclusions

Proton radiosurgery is a viable treatment options for patients with surgically inaccessible AVMs. In this small retrospective analysis, approximately 70% of AVMs were ultimately obliterated with radiosurgery, including 100% of AVMs <4cc. This rate compares favorably to other published series on radiosurgery for AVMs of this size and was accomplished with an acceptable toxicity profile.