50ournal of Neurology, Neurosurgery, and Psychiatry 1992;55:590-593

Stereotactic linac radiosurgery for arteriovenousmalformationsB G Kenny, E R Hitchcock, G Kitchen, A E Dalton, D A Yates, S V Chavda

AbstractStereotactic linear accelerator (linac)radiosurgery has been in operation in theWest Midlands since 1987, the first of itskind in the United Kingdom. Forty twopatients with high-flow cerebral arter-iovenous malformations have been trea-ted, 26 of whom have been followed up.Angiography one year after treatmentshowed that five lesions were obliterated,11 were reduced in size and/or flow rateand 10 were unchanged. Overall resultsshow that nine out of 10 patients reviewedat 24 months had total obliteration. Threepatients had complications; one has fullyrecovered, one died of an unrelated causeat 36 months and the other died fromrecurrent haemorrhage at nine months.Two patients had recurrent non-fatalhaemorrhage within 24 months of treat-ment; both recovered without further def-icit. All patients are fit to work but eightare unemployed. Although the follow upperiod is short, the early results indicate asuccess rate similar to those published byothers using linac radiosurgery.

University ofBirinham, Midland

Centre forNeurosprgery andNeurology,Birmingham, UKDepartment ofNeurosurgeryB G KennyE R HitchockDepartment ofNeuroradiologyD AYatesS V ChavdaWolverhampton RoyalHospital,Wolverhampton, UKRadiotherapyDepartmentG KitchenA E DaltonCorrespondence to:B G Kenny, Midland Centrefor Neurosurgery andNeurology, Holly Lane,Smethwick, BirminghamB67 7JX, UKReceived 25 April 1991and in revised form25 October 1991.Accepted 11 December1991

The annual haemorrhage rate for untreatedarteriovenous malformation (AVMs) is about3%' with a long term mortality of 17-29%2 3

and morbidity of 20-27%.`-3 Clinical attitudesto their management have now become moreaggressive. The best results achieved by micro-surgical excision vary from a mortality of0-9-18'8% and morbidity of 4-6-15-5%.4-These risks, which are highest for large oreloquently situated lesions, encouraged the useof other treatments. These included externalbeam irradiation started by Magnus in 1913,8and which still continues to be used.9 Thepotential of radiotherapy was realised with theangiographic demonstration of obliteration ofsome AVMs'0o accompanied by clinicalimprovement.

In the 1950s Leksell conceived the idea ofusing stereotactically-guided external irradia-tion to produce a predictable irradiation effectat an accurately defined intracranial target.'2After extensive experimentation he developedthe first generation cobalt gamma unit in1968.13 He called the technique "Radiosurg-ery" to emphasise the difference between thisand conventional irradiation techniques. Kjell-berg and Fabrikant developed similar radio-surgical systems based on the Bragg peakprinciple using proton and helium beams'4 "1generated by cyclotrons. The high installation

and running costs of the gamma unit andBragg peak systems led several groups todevelop radiosurgical systems using standardor modified linear accelerators (linac).'"'9Themortality from recurrent haemorrhage follow-ing radiosurgery for AVM with the gammaunit, Bragg peak and linac techniques is1-7-4%, with permanent morbidity of2-5%2024 which compares favourably withsurgery.We describe the method of linac radiosur-

gery for AVMs developed at the MidlandCentre for Neurosurgery and Neurology(MCNN) and Wolverhampton Royal Hospital(WRH), which is the first of its kind in the UK,and includes examples of lesions treated.

Materials and methodsForty two patients, 23 male and 19 female (agerange 7-65 years, mean 34 years) were treated.Patients included acute admissions andspecific referrals for radiosurgery fromother regional and overseas neurosurgicaland neuroradiological specialities. Thepresenting event was an intracerebral, intra-ventricular or subarachnoid haemorrhage in 25patients (60%). Epilepsy was present in 24patients (57%), and the only symptom in 16patients (38%).Twenty four lesions (57%) were situated in

the left hemisphere, 15 (36%) in the right andthree (7%) centrally. Lesions were approximat-ed as spherical targets and ranged from5-75 mm (mean 22 mm) in diameter. Threepatients (7%) previously had one or moreattempts at surgical excision and in fourpatients (10%) embolisation had been attemp-ted. One patient had conventional irradiationmore than five years before treatment withstereotactic radiosurgery.

Patients were admitted for treatment for fiveto seven days. None was treated in the acutepost-haemorrhagic phase and neurological sta-tus was either stable or improving at the time oftreatment. All had routine neurological exam-ination and investigation including CT and, insome instances, MRI. Outpatient follow upwas performed a few weeks after discharge andthereafter at three and six months. Patientswere readmitted at 12 and 24 months forrepeat angiography, CT and/or MRI. Kar-nofsky2" scores were obtained for all admis-sions and follow up reviews.

Stereotactic techniqueOnce informed consent had been obtained theHitchcock stereotactic frame,26 (DP Medical,

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Stereotactic linac radiosurgery for arteriovenous malformations

UK), a light alloy square (wt 700 g/1-5 lb)which works on the isocentric arc principle,was applied to the unshaven head under localanaesthesia and secured rigidly to the skull bythree pins. General anaesthesia was used intwo children aged seven and nine years. Incommon with most commercially availablesystems, geomechanical accuracy of thestereotactic system is < 1 mm. Angiographicand CT targeting of the lesion is carried out inrelation to the stereotactic square and the dataused to calculate the precise target for irradia-tion. Radiotherapy took place at a different site(WRH); the patient wore the square for 24-48hours and was encouraged to mobilise normal-ly. The square was well tolerated and no patienthas failed to complete the treatment protocol.On return from radiotherapy, the square wasremoved.

Angiographic techniqueAngiography was performed with a SiemensAngioskop Digitron 3 under local anaesthesia(IA) via a transfemoral route. Individuallymarked, purpose built, angiographic targetinggrids which can be attached above or below thestereotactic square permit a complete range ofoblique projections including extreme Townesviews. From orthogonal stereoscopic viewswith a 10° separation, the lesion diameterswere noted, the volume calculated, and thegeometric centre of the lesion marked. Magni-fication was eliminated by directly measuringdimensions against the grid graduations. Thefinal target isocentre was calculated graphicallyand confirmed by a simple computer program,thus reducing observer error.

Treatment planning and irradiationThe stereotactic square was fixed to the CTcouch in a head frame adaptor and alignedusing vertical and horizontal laser lights. Byplacing the isocentre of the stereotactic squareto that of the CT computer (IGE 8800),stereotactic and CT coordinates became iden-tical. The radiotherapy planning computerrequires direct scan data in the form of axialand oblique reformats taken in the planes ofproposed irradiation arcs. To conform with theseven arc method used, reformats are taken at0, 30, 60, 90, 120, 150 and 180 degreesaround the isocentre chosen from the angio-gram. The lesion diameter can be measuredagain on the CT image and outlined using thecursor trace facility. An advantage of thismethod of targeting is that it gives an excellentview of surrounding structures and this infor-mation can be used to tailor the dose and shapeto suit the clinical situation. Isodose contourswere calculated and configured to the lesionallowing for adjacent vulnerable structures.The CT arc reformats allowed skull thicknessand depth of lesion to be included directly intodose calculations, and appropriate adjustmentswere made to the arc doses.

Patients were irradiated with multiple non-coplanar arcs of 100 150@ on a Phillips SL75-14 Linear Accelerator which produces a highlyacceptable isodose profile compared with othertechniques.27 Purpose built collimators of

Table Results offollow up

Overall status at 1-2 years (n = 26) No(%)

Obliterated 9 (35%)Reduced 7 (27%)*Unchanged 10 (38%)*Total 26

*Note: 16 of 17 patients in the reduced and unchanged groupshave not yet reached two year review.

10 mm, 12 mm, 15 mm, 17 mm and 20 mmwere used to improve spatial accuracy andprovide a steep edge cutoff; this was 2 mmfrom the 90% to the 50% isodose line using the10 mm collimator. The dose range used was12-5-50 Gy (mean 26-7 Gy); the lower doseswere given to the larger lesions.

ResultsAll results refer to patients followed up for12-24 months (range for all patients is 3-47months) with angiography and CT. Twenty sixpatients have been followed up for 12 monthsand 10 patients for 24 months.The overall results are illustrated in the

table. One year after treatment five lesions(19%) were obliterated, 11 (42%) werereduced in size and/or flow rate on comparableangiography and 10 (38%) showed no change.Four of the five patients who required angio-graphy at 24 months had complete oblitera-tion. Nine of 10 AVMs ranging in diameterfrom 5-40 mm which we have followed up fortwo years have been totally obliterated. Severalexamples of total and partial obliteration areillustrated in the figure (A-H).Although five patients had perilesional low

density change on CT scans only three ofthemhad clinical evidence of oedema. One of thesepatients died of recurrent haemorrhage at ninemonths and another died at 36 months from apulmonary embolus. In both cases the cause ofdeath was confirmed at necropsy. The thirdpatient is asymptomatic without treatment at47 months after treatment. Of the threepatients with recurrent haemorrhage, tworecovered without new neurological deficit. Allpatients returned to their previous occupationsexcept eight who are fit to work but unem-ployed. Karnofsky performance scores,25which had improved significantly by the timeof treatment, revealed no deterioration relatedto radiosurgery afterwards.

DiscussionSurgical excision remains the treatment ofchoice for AVM in accessible sites. The rela-tively large number of dominant hemisphereand central lesions in our series reflects thehigher risks associated with these lesions.Published series of stereotactic radiosurgeryreport obliteration rates of 67-5-86-5% at twoyears.20 Nine of our 10 patients reviewed for 24months or more had complete obliteration oftheir AVM. Eleven AVMs (42%) were reducedin size and/or flow rate at 12 months indicatingthe effect of irradiation. Our results suggest asimilar pattern of overall success to publishedseries.

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Figure A-H: Pre-(A) and post-(B) irradiation angiogram showing complete obliteration ofAVM with filling of normal anterior and middle cerebralvessels as a result of shunt reversal in a patient with a coexisting aneurysm. Two AVMs (C and E) pre-irradiation completely obliterated at two yearfollow up (D and F). Pre-irradiation AVM (G) reduced in size and flow at one yearfollow up antiogram (H).

The risk of recurrent haemorrhage remainsunchanged for two years after radiosurgerywith any of the currently available techniques.The mortality from such events, however, islower than that expected from the naturalhistory ofAVMs,20 presumably due to changesin the vascular endothelium. The patient in ourseries who had a third intraventricular haemor-rhage from a hypothalamic AVM illustrates theincreased risk of mortality from repeatedhaemorrhage.2Temporary or permanent neurological dete-

rioration attributable to irradiation and accom-panied by imaging evidence of low densitychange occur in 2-4% of reported series.20Low density change adjacent to the target areain asymptomatic patients has been reported,28and we observed this in two patients.AVMs may be regarded as having an arterial

feeding, and a venous draining phase, con-stituting the nidus of the lesion.29 The relativeimportance of the components of the nidus interms of radio-obliteration is not clear but maybe critical to the success of treatment. In smallAVMs the entire volume may be targeted andthe obliteration rate is highest in this type oflesion.20 In large lesions (>3 cm diameter),the same argument cannot be applied as therisk of radionecrosis is dose/volume related.t`If late phase films are used, the aprarentvolume of the AVM may be misleading. rarget-ing larger volumes is more hazard'rus and the

treatment of such lesions remains problem-atical. It is possible to totally obliterate largerAVMs by targeting only the nidus,24 butperipheral parts may remain unchanged.283'Another possible solution is to use fractiona-tion. There are considerable stereotactic prob-lems associated with fractionation, however,and the radiobiological rationale of such aregime, which is well established in tumourtherapy, may not apply to AVMs. The volumeirradiated could also be reduced by partialembolisation, a technique which has beensuccessfully combined with surgery.32 In ourseries larger lesions were either treated selec-tively or with small doses.Dose regimes vary between units and tech-

niques, although it is apparent that there is atendency to lower total doses.28 30 Except forour first patient, who received 50 Gy, all otherpatients received 40 Gy or less and the meandose for our series is 26-7 Gy. Only long termfollow up will reveal how successful this doserange proves to be.The reported incidence of epilepsy following

excision of AVMs was 57%33 in one series,75% of whom developed epilepsy within twoyears of operation. As yet, none of our patientshas developed de novo epilepsy or EEGchanges. Reduction in the frequency and/orseverity of seizures has been reported followingradiosurgery34 and several of our patients hadsuch an improvement.

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Stereotactic linac radiosurgery for arteriovenous malformations

A variety of arc arrangements are used bydifferent groups. The most common are multi-ple non-coplanar converging techniques. How-ever, innovative systems involving simultane-ous linac head and couch head rotation havealso been developed.35 These rotation systemsmay produce a more suitable isodose con-

figuration than simpler existing systems. Asyet, not enough clinical data exist to confirmthis.

Because the accuracy of all stereotacticradiosurgical techniques is within that of ster-eotactic targeting instrumentation, there isnothing to choose between the various radio-surgical systems so far as accuracy is con-

cerned. The gamma unit and Bragg peaksystems are expensive to install and run. Thisstudy shows that linac radiosurgery using a

locally available and easily modifiable standardlinear accelerator produces highly acceptableresults.

We thank the radiographers and nurses of the Midland Centrefor Neurosurgery and Neurology, Wolverhampton Royal Hospi-tal, Photographic Department SDGH, and W Mitchell andB Pope for the design and construction of the angiographicgrids.

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