Current status of radiosurgery for arteriovenous malformations

Geometric parameter analysis to predetermine optimal radiosurgery technique for the treatment of arteriovenous malformation

PURPOSE

To develop a method of predicting the values of dose distribution parameters of different radiosurgery techniques for treatment of arteriovenous malformation (AVM) based on internal geometric parameters.

METHODS AND MATERIALS

For each of 18 previously treated AVM patients, four treatment plans were created: circular collimator arcs, dynamic conformal arcs, fixed conformal fields, and intensity-modulated radiosurgery. An algorithm was developed to characterize the target and critical structure shape complexity and the position of the critical structures with respect to the target. Multiple regression was employed to establish the correlation between the internal geometric parameters and the dose distribution for different treatment techniques. The results from the model were applied to predict the dosimetric outcomes of different radiosurgery techniques and select the optimal radiosurgery technique for a number of AVM patients.

RESULTS

Several internal geometric parameters showing statistically significant correlation (p < 0.05) with the treatment planning results for each technique were identified. The target volume and the average minimum distance between the target and the critical structures were the most effective predictors for normal tissue dose distribution. The structure overlap volume with the target and the mean distance between the target and the critical structure were the most effective predictors for critical structure dose distribution. The predicted values of dose distribution parameters of different radiosurgery techniques were in close agreement with the original data.

CONCLUSIONS

A statistical model has been described that successfully predicts the values of dose distribution parameters of different radiosurgery techniques and may be used to predetermine the optimal technique on a patient-to-patient basis.

Preservation of hypervascularity in hepatocellular carcinoma after effective proton-beam radiotherapy--CT observation

AIM

The aim of this study was to describe persistence of hypervascularity in proton treated hepatocellular carcinoma at serial follow-up computed tomography (CT).

METHODS

Four patients with unresectable solitary hypervascular hepatocellular carcinoma underwent 55-82 Gy proton-beam irradiation for a period of 15-47 days. Follow-up CT including plain, enhanced and dynamic imaging was performed for a period of 9-36 months.

RESULTS

Good preservation of arterial blood supply while gradual decrease in tumour size was clearly depicted by dynamic CT.

CONCLUSION

We believe that preservation of hypervascularity as judged by enhancement at CT and magnetic resonance imaging, does not necessarily mean that radiotherapy in hypervascular malignant tumours has been unsuccessful.

Significance of factors contributing to surgical complications and to late outcome after elective surgery of cerebral arteriovenous malformations

OBJECTIVES

This study focuses on the relevance of size, eloquence, type of venous drainage, the Spetzler-Martin scale as a whole, and other factors, such as rupture of cerebral arteriovenous malformations (AVMs) for the prediction of neurological deficits in the context of microsurgical AVM removal.

METHODS

One hundred and fifty patients with AVMs, whose data were retrieved from a prospectively employed computerised data bank were included. Seventeen patients (11.3%) underwent preoperative embolisation. According to the Spetzler-Martin scale they were graded as follows: 22.0% grade I, 32.0% grade II, 29.3% grade III, 14.0% grade IV, and 2.7% grade V. Intracerebral haemorrhage was present in 39.0%. The AVMs were <3 cm in 52.00/0, 3-6 cm in 43.3% and >6 cm in 4.7%; 59.3% of the AVMs were eloquently located and 29.3% had deep venous drainage (DVD). Follow up information was assessed 6 months after surgery in all but one patient, who died. The applied statistical test was chi2.

RESULTS

Surgical morbidity was 15.3%. Early new deficits were noted in 39.3%, permanent new deficits in 10.6%, being significant (major) in 7.3%. The occurrence of permanent deficits correlated significantly with size, deep venous drainage, and the Spetzler-Martin scale. There was statistical evidence for a trend in risk of poor surgical outcome across the three categories non-eloquent, "less eloquent" (for example, visual cortex) and "highly eloquent" (brainstem, basal ganglia, or precentral cortex) with the last being associated with the highest risk for permanent neurological compromise.

CONCLUSION

"Eloquence" of the Spetzler-Martin scale should be divided into "highly eloquent" and "less eloquent", which is important for risk analysis of the treatment of asymptomatic and deep seated AVMs and for future trials comparing various treatment modalities. In addition, resection of eloquent AVMs v non-eloquent ones is significantly associated with higher surgical morbidity.

Microsurgical results for small arteriovenous malformations accessible for radiosurgical or embolization treatment

OBJECTIVE

A consecutive series of microsurgically treated small arteriovenous malformations (AVMs), up to 3 cm in diameter, which are theoretically ideal candidates for radiosurgery or embolization, is described. We intended to elucidate the safety and efficacy of the microsurgical removal of AVMs, as compared with the results for radiosurgery and embolization reported in the literature.

METHODS

Sixty-two patients (32 female and 30 male patients) ranging in age from 7 to 72 years (mean age, 33.3 yr) were included in the series. Of these, 46.8% presented with intracerebral hemorrhage and 24.2% presented with seizures. The 62 patients underwent microsurgical removal of their small (<3 cm) cerebral AVMs by the same surgeon. Twenty-six AVMs (41.9%) were assigned Spetzler-Martin Grade I, 24 (38.7%) were assigned Grade II, and 12 (19.4%) were assigned Grade III. Thirty-three AVMs (53.2%) were located in eloquent brain regions. All patients underwent postoperative control angiography and clinical follow-up after 3 and 6 months.

RESULTS

The AVMs were extirpated, as confirmed by angiography, in all except one patient, thereby accounting for a 98.4% success rate per angiographic findings. The rate of immediate new postoperative neurological deficits or worsening of preexisting neurological deficits was 27.4%, and the rate of permanent significant neurological deficits was 3.2% at late follow-up. The rate of permanent significant deficits occurring after the microsurgical removal of small AVMs in eloquent regions was 6.1%. The mortality rate in the reported series was 0%. The surgical morbidity rate was 9.7%.

CONCLUSION

Microsurgery for small AVMs is superior to radiosurgery or interventional neuroradiology because of its high rate of efficacy and low rate of permanent morbidity and because immediate cure of the AVMs can be achieved in the vast majority of patients. The place for radiosurgery in the treatment of small AVMs needs to be more sharply defined after careful assessment of relevant cases by an experienced vascular neurosurgeon.

Conventional radiation therapy of intracranial arteriovenous malformations: long-term results

Conventional radiation therapy has been used in the treatment of arteriovenous malformations (AVM's) for many years, but there are limited data pertaining to specific treatment parameters, long-term results, and complications. Between 1955 and 1985, 15 patients with AVM's deemed inoperable or incompletely obliterated using surgical or endovascular techniques were treated at the University of Western Ontario. There were nine males and six females, aged 15 to 48 years (mean 29 years). Presenting symptoms included hemorrhage in nine patients, seizures in four, and focal neurological deficits in two. There were three infratentorial and 12 supratentorial AVM's, ranging in size from 1.5 to 6.5 cm. Therapy prior to irradiation consisted of incomplete surgical removal in four cases and subtotal embolization in four. One patient received 2000 cGy of irradiation, while 4000 to 5000 cGy were delivered in the remaining patients to fields ranging in size from 4 x 4 to 14 x 14 cm in 15 to 28 fractions. The 15 patients have been followed for 1 1/2 to 21 years since undergoing radiotherapy (mean 8.1 years). Angiography in 12 patients at 1 to 21 years following irradiation demonstrated no significant change in seven patients, a slight reduction in AVM size in two, near-complete obliteration in one, and complete obliteration in two. One patient with an AVM measuring 6.5 cm refused angiography but underwent magnetic resonance imaging at 5 years which showed no evidence of residual AVM. There were four hemorrhages in 122 patient-years of follow-up study, indicating a hemorrhage rate of 3.3% per year. The authors conclude that conventional irradiation is successful in obliterating AVM's in only about 20% of cases.