Purpose: To present the SALT group results using Linac radiosurgery (RS) for AVM in 169 evaluable patients treated from January 1990 thru December 1993.
Methods and materials: Median age was 33 years (range 6-68 years). Irradiation was the only treatment in 55% patients. Other treatment modalities had been used prior to RS in 45%: one or more embolizations in 36%, surgery in 6%, and embolization and surgery in 3% patients. Nidus were supratentorial in 94% patients, infratentorial in 6% patients. Circular 15 MV x-ray minibeams (6-20 mm) were delivered in coronal arcs by a GE-CGR Saturne 43 Linac. Patient set-up included a Betti arm-chair, a Talairach frame. Prescribed peripheral dose was 25 Gy on the 60%-70% isodose (max dose 100%). Arteriographic results were reassessed in December 1997 at 48 to 96 months follow-up.
Results: The overall obliteration rate (OR) was 64% (108/169). AVM volumes ranged from 280 to 19,920 mm(3), median 2460 mm(3). OR was 70% for AVM </= 4200 mm(3) 4200 mm(3) (p 25 mm (p = 0.04). OR was 71%, in the absence of embolization, vs. 54% for previously embolized nidus (p = 0.03). OR was 71% for monocentric RS vs. 54% for multi-isocenters (p 28 Gy vs. 55% for values </= 28 Gy (p 79% vs. 57% for lower values (p 17 Gy, vs. 59% for mLd </= 16 Gy (p 40%, vs. 54% for mLi </= 40% (p 85% vs. 60% for CR </= 84% (NS). For patients treated according to our protocol, i.e., 24-26 Gy on the 60%-70% isodoses, OR was higher (68%) than for other patients (47%) (p = 0.02). After multivariate analysis, absence of previous embolization and mono isocentric-irradiation were independent factors predicting obliteration. Complications were: recurrent hemorrhage, 4 patients (1 patient died); brain necrosis on MRI, 2 patients; subsequent epilepsy, 4 patients; other subsequent neurologic deficits, 3 patients.
Conclusion: Overall OR was 64% (48-96 months follow-up). After monovariate analysis higher ORs were associated with smaller volumes </= 4200 mm(3), smaller nidus size </= 25 mm, absence of prior embolization, monoisocentric RS, higher values for mean and minimum lesion doses and compliance to our protocol. Higher values for the peripheral dose and isodose tended to give better results. Multivariate analysis showed that the absence of prior embolization and monoisocentric irradiation were independent factors predicting successful irradiation.