Search

Background and Purpose: The purpose was to present the successive steps of dosimetric planning and the different means used to allow the choice of the best solution among several planning projects considering the anatomical and clinical features of arteriovenous malformation. Method. Four successive steps were: A study of these factors for 5 different plannings of a clinical case using different isocenters is presented and the results are discussed., Conclusion: For complex arteriovenous malformations several hours are often necessary to permit physicians/radiotherapists to elaborate planning which is often a compromise among several solutions.

Background and Purpose: Between 20 to 50% of cerebral arteriovenous malformations treated with radiosurgery (RS) fail to obliterate 2 to 5 years after irradiation. Patients are not protected against the risks leading to treatment. Two therapeutic options can be used to eradicate the persisting nidus: micro-surgery and a second irradiation. Our group has reirradiated 39 such patients., Material: From 1989 to 2000, 39 patients have been reirradiated (14 females and 25 males; median age 31 years). There were more left lesions: 59% than right (35%) and 5% on midline. The most frequent locations were: temporal 12 cases; parietal 8 cases; frontal 7 cases; thalamus 7 cases. The predominant first symptoms were hemorrhage (68.5%) and seizure (15.8%). Prior RS, 21/39 patients had embolization (53.8%) and 3 surgery. Method. Treatment has been performed with the same system for the first and the second radiosurgery for 37 patients. Planification and dosimetry improved during that period. The level of dose was similar for the 2 RS. MRI has been used as a non invasive follow-up tool., Results: Only 28 patients were evaluable because 7/39 patients had the second radiosurgery in 1999 or in 2000 and data were lacking at the time of writing for 4 patients. Obliteration rate was 17/28 (60.7%). Nine patients bled between the two radiosurgery procedures., Complications: 4 new regressive deficits occurred after the second radiosurgery. The rate of parenchymal changes were higher, after the second radiosurgery. Except one patient who died of a non-related affection 2 years after obliteration of his cerebral arteriovenous malformation, thus 38/39 patients were alive., Conclusion: This series was small compared to the potential number of candidates suffering from failure of the first radiosurgery, but the results are promising.

The aim of this paper is to analyze retrospectively the reasons for the failure in cerebral arteriovenous malformations radiosurgery. Several factors are evoked and discussed mainly: inaccurate target, intentional partial irradiation, repermeabilization of a previously embolized cerebral arteriovenous malformation. The results suggest the necessity of a complete irradiation of the nidus. The strategy of partial volume irradiation should be avoided, even if it necessitates lowering of the doses in large cerebral arteriovenous malformations. Accuracy in the target determination is required and a complete stereoangiography is necessary.

Purpose: To study dosimetric implications of our group dose prescription methodology on a series of 408 cerebral arteriovenous malformations., Material: and method. Between January 1990 and July 1998, 408 patients with cerebral arteriovenous malformations that had never been irradiated before, were treated radiosurgically in a single fraction at Tenon Hospital. 223 patients were treated with a single isocentre and 185 with multiple isocenters. Dosimetric characteristics have been studied as a function of the global quality index of planning, defined our group as the standard deviation of the differential dose volume histogram calculated in the lesion., Results: One percent correlation obtained between some dosimetric data and the global quality index of planning allowed to modelize by linear equations the connection between this quality index and minimum isodose in the lesion, mean doses and isodoses in the underdosed part of the lesion and in the complete lesion. This was done for mono isocentric cases and multi isocentric cases., Conclusion: Before the choice of the therapeutic dose and prescription isodose, it is therefore possible from the global quality index of planning to foresee isodoses modelized by the defined equations. So, the radiotherapist can compensate using the prescription since conformity is not perfect and thus attenuate healthy tissues overdosage.

Background and Purpose: After a review of the main radiosurgical published series, to evaluate our own series of 705 patients with cerebral arteriovenous malformations treated by radiosurgery alone or in combination with embolization or surgery., Patients: and method. From January 1984 to December 1998, 705 patients were treated by a multidisciplinary team including neurosurgeons, neuroradiologists, radiophysicians and radiotherapists. Age of revelation of the cerebral arteriovenous malformations ranged between birth to 73 years (mean 27, median 25). Age at time of radiosurgery ranged between 7 and 75 years (mean 33, median 31). There were 410 males for 295 females (sex- ratio 1.4). Symptoms of revelation were hemorrhage for 59%, seizures for 23%, headaches for 14% and progressive deficits for 4%. Discovery of cerebral arteriovenous malformation was fortuitous in 4% of cases. Repartition following Spetzler's grading was 12% in grade I, 36% in grade II, 40% in grade III, 12% in grade IV and 0% in grade V. Maximal size ranged between 4 and 60 mm (mean 23, median 20). Volume ranged between 0.2 and 24.3 cc (mean 3.8, median 2.8). Majority of cerebral arteriovenous malformations were large size (42% with size higher than 25 mm) and large volume (54% higher than 10 cc. 54% of patients had treatment prior radiosurgery: 38% had embolization, 10% were operated, 4% were treated by radiosurgery (reirradiation) and 3% were operated and embolized., Results: Overall complete obliteration rate was 55%. The obliteration rate was correlated with size (77% for cAVMs lower than 15 mm, 62% for cerebral arteriovenous malformations between 15 and 25 mm, and 44% for cerebral arteriovenous malformations higher than 25 mm), with volume (94% for cerebral arteriovenous malformations lower than 1 cc, 64% between 1 and 4 cc, 48% between 4 and 10 cc, and 62% for cerebral arteriovenous malformations higher than 10 cc), dose at reference isodose, minimal dose, morphological parameters (presence of dural components, arteriolovenous fistula, plexiform angioarchitecture, arterial steal, arterial recruitment, deep exclusive drainage, venous plicature, venous confluence, venous ectasia, venous reflux), sectional topography and good recovery of the target. Embolization was a confusion factor not associated with obliteration rate. After multivariate analysis, only Dmin and complete coverage of the cerebral arteriovenous malformations were correlated with obliteration rate. Delay of obliteration was significantly correlated after multivariate analysis with Dmin, complete coverage, arteriolovenulary angioarchitecture (positive correlation) and venous ectasia (negative correlation)., Conclusion: Overall complete obliteration rate is unreliable data to assess efficacy of radiosurgical method in the tretment of cerebral arteriovenous malformations. The obliteration rate must be interpretated after stratification on several morphological and dosimetric parameters.

We present a review of current technological progress enabling improvement in the quality of stereotactic irradiations: imaging fusion; individual adaptation of dosimetric planning to the shape of the target thanks to several collimation systems, spatial modulation of the beam with the use of multileaf microcollimators, beam intensity modulation, robotisation of the materials, owing to hardware and software developments.

Between May 1986 and March 1987, 46 small and medium sized cerebral arteriovenous malformations (AVM) were treated by radiosurgery in Paris. The stereotaxic coordinates of the lesions were determined according to the method of J. Talairach and the total radiation dose was delivered on spherical or ovoid target volumes with minibeams of 18 MV photons, using the technique developed by Osvaldo Betti. A review of the cases was undertaken in december 89. Twenty-one patients had previously been treated by embolization and/or surgery (46.6%). During the 25 to 40 months follow-up there were only 2 recurrences of bleeding (4.3). Control arteriography was performed in 38 cases (38/46 = 82.6%). There were thirteen cases of total disappearance of the AVM (13/36 = 34.2%), 17 incomplete obliterations (44.7%) and 9 (23%) arteriographies failed to show any radiological improvement. Eight patients had no arteriographic follow-up: 2 of them experienced a recurrence of bleeding and died before the planned arteriography, 1 was lost to follow-up and 5 patients refused control arteriography. A multidisciplinary team is needed to study the shape, the volume, the hemodynamic features of the AVM and the dosimetry in order to attain the best definition of the target volume and of the dose distribution. It seems that when the target volume included the nidus and the venous collector, follow-up arteriography results were satisfactory. Even though the optimum dose is yet to be determined, our results imply that a dose distribution allowing for 25 grays at the periphery of the AVM (isodose 70%) seems sufficient provided that the target volume is included within the 25.00 Gy isodose curve.