Elekta Instrument AB Research Articles

Dose-Painting Linear Accelerator Radiosurgery of Glomus Jugulare With Dosimetric Comparison to Gamma Knife.

Objectives In this study, we outline our rationale for delivering a dose of ≥15 Gy in stereotactic radiosurgery (SRS) of glomus jugulare tumor (GJT) while ensuring the avoidance of complications associated with doses >13 Gy to the facial nerve. To avoid such complications, we initially utilized the Gamma Knife Perfexion (GK) system (Elekta Instrument AB, Stockholm, Sweden) at our institution but encountered challenges related to lengthy treatment times and difficulty in sculpting doses to minimize doses to spare the facial nerve. As a potential solution, we propose the use of HyperArc (Varian Medical Systems, Palo Alto, CA), a newly developed automated delivery platform for linear accelerator (LINAC)-based SRS. HyperArc offers the potential for faster treatment and more complex shaping of the radiotherapy dose with multiple arcs and multi-leaf collimators. Methods We retrospectively reviewed nine cases of patients with GJT treated with HyperArc. Patients' demographic and treatment data were collected. Additionally, simulated GK treatment plans were created and compared with HyperArc plans to assess time savings, PTV coverage, and plan quality. Results One male and eight female patients, with a mean age of 63.9 years, were included. Treatments were delivered on average in 29 minutes, achieving 95-100% of the tumor while limiting the facial nerve to <13 Gy. Treatments replanned using our GK system could achieve only 92-99% tumor coverage while respecting facial nerve constraints, with average treatment times of 180 minutes. Comparable plan quality parameters were attained with both modalities. Conclusions The HyperArc system provides a qualitatively satisfactory and rapid treatment delivery of a highly sculpted radiotherapy dose to maximize tumor coverage and minimize facial nerve complications.

The Influence of the Technical Parameters of the SRS Plans on the Dosimetric and Radiobiologic Evaluation

Background: The purpose of this study was to evaluate influence of technical parameters on Stereotactic Radiosurgery (SRS) plans on dosimetric evaluation. Materials and methods: There were considered and selected two patients who had brain tumors and had been treating in Tomsk Regional Oncology Center. All treatment plans were simulated using the Monaco treatment planning system v 5.11 (Elekta Instrument AB, Stockholm) on the Elekta Synergy linac with photon beam nominal energy 6 MV. For study there were created several plans with different technical parameters (number of arcs, increment, gantry angle, collimator angle, couch angle, minimum segment width). Each plan was evaluated by metrics such as Conformal, Homogeneity and Gradient indexes. Results: If we use a large increment value it may create few sectors and which can produce low quality plans, and increase treatment time, otherwise if we use a too small increment value it will give us more sectors and they can increase the quality of the plan. The dose which was measured with higher MSW showed to us better agreement with the calculated dose. Conclusion: It is valuable to carefully select technical parameters. The use of rigid increment value, segment width or increasing number of arcs can make plans have lower quality and to rise time of treatment.

Stereotactic Gamma Knife Radiosurgery for Extracranial Arteriovenous Malformations

Introduction: Head and neck extracranial arteriovenous malformations (AVMs) are rare pathological conditions which pose diagnostic and reconstruction challenges. Stereotactic radiosurgery (SRS) is nowadays an established treatment method for brain AVMs, with high obliteration and low complication rates. Here we describe the first report of head extracranial AVMs successfully treated by Gamma Knife (GK) as a retrospective historical cohort. Methods: Over a 9-year period, 2 cases of extracranial AVMs were treated by GK Perfexion (Elekta Instruments AB, Stockholm, Sweden) at a single institution. A stereotactic frame and multimodal imaging, including digital subtraction angiography (DSA), were used. The prescribed dose was 24 Gy at the 50% isodose line. Results: The first case was of a patient with pulsating tinnitus and left superficial parotido-condylian AVM. Embolization achieved partial obliteration. Tinnitus disappeared during the following 6 months after GK. The second case was a patient with repetitive gingival hemorrhages and right superior maxillary AVM, fed by the right internal maxillary and facial arteries. Embolization achieved partial obliteration with recurrence of symptoms. GK was further performed. DSA confirmed complete obliteration in both patients. Conclusions: Single-fraction GK radiosurgery appears to be safe and effective for extracranial AVMs. We recommend prescribing doses that are comparable to the ones used for brain AVMs (i.e., 24 Gy). A stereotactic frame is an important tool to ensure higher accuracy in the context of these particular locations. However, in selected cases, a mask could be applied either for single fraction purposes (if in a non-mobile location) or for hypofractionation, in case of larger volumes. These findings should be validated in larger cohorts, inclusively in terms of dose prescription.

Development of an IAEA phase-space dataset for the Leksell Gamma Knife® Perfexion™ using multi-threaded Geant4 simulations

This study was conducted to develop a phase-space dataset in the International Atomic Energy Agency (IAEA) format for Monte Carlo (MC) simulations of the Leksell Gamma Knife® (LGK, Elekta Instrument AB, Stockholm, Sweden) Perfexion™ (PFX). An open-source MC code, namely, the Geant4 toolkit with a recently updated multi-threaded mode, was used to maximize the efficiency of the developed IAEA phase-space dataset. The absorbed dose profiles for single shots of the LGK PFX were calculated using the developed dataset and compared with those from radiochromic film measurements and Leksell GammaPlan® version 11.0.3 (LGP, Elekta Instruments) for verification. The mean relative absorbed dose differences in all single shots were less than 3.6% compared with the films and less than 4.0% compared with LGP. The collimator output factors were also calculated for all single shots and compared with the LGP results. The simulated collimator output factor was 0.816 ± 0.003 for a 4-mm shot and 0.903 ± 0.001 for an 8-mm shot in a spherical water phantom. The efficiency of the developed dataset was evaluated by comparing the times required for various simulations. Simulations with the phase-space dataset ran 25, 8.2 and 3.2 times faster than simulations without the phase-space dataset for 4-, 8-, and 16-mm shots, respectively. Using the dataset developed in this study, MC simulations of the LGK PFX can be performed more efficiently for various purposes, such as treatment plan verification and beam quality factor calculations.

Influence of SBRT fractionation on TCP and NTCP estimations for prostate cancer

IntroductionStereotactic body radiation therapy is widely used for the hypofractionated treatment of prostate cancer. The range of total doses used in different clinical trials varies from 33.5 to 50 Gy delivered in 4 or 5 fractions. The choice of an optimal total dose value and fractionation regimen for a particular patient can be carried out using the integral radiobiological criteria, namely tumour control probability (TCP) and normal tissue complication probability (NTCP). In this study, we have investigated the dependence of simulated TCP/NTCP values on total dose in the range of 30–40 Gy delivered in 4 or 5 fractions for patients with low-risk prostate cancer in order to find the optimal total dose value and fractionation regimen. MethodsThe anatomic data (DICOM CT images) of 12 patients with low-risk prostate cancer, who were treated at Tomsk Regional Oncology Centre, were used for the calculation. Dosimetric treatment plans for all patients were simulated using VMAT with 2 arcs in the Monaco treatment planning system v5.10 (Elekta Instrument AB, Stockholm) with a total dose equal to 36.25 Gy. The dosimetric plans were rescaled in the dose range of 30–40 Gy. The TCP and NTCP values were calculated based on differential dose volume histograms using the Niemierko model for both TCP and NTCP, and the Källman-s model for NTCP calculations. The TCP calculation was carried out using the uncertainty of well-known tumour radiobiological parameters values, including α/β value. NTCP was calculated for an anterior rectal wall, which was the most irradiated organ at risk due to its close contact with the planning target volume. ResultsThe TCP and NTCP calculations for VMAT of the prostate cancer have shown that the optimal total dose ranges were equal to 32–34 Gy delivered in 4 fractions or 35–38 Gy delivered in 5 fractions. At doses lower than the optimal ones, the TCP values were lower than 95%, while TCP uncertainties were significant (as low as 80%). This fact might bring unexpectedly poor treatment results. At doses higher than optimal ones, the probability of toxicity to the anterior rectal wall became significant. ConclusionThe optimization of radiation therapy regimen based on TCP/NTCP criteria could help to determine an optimal total dose and a number of fractions for a particular patient depending on patient-specific anatomic features and planned dose distribution.

Dosimetric effects of Onyx embolization on Gamma Knife arteriovenous malformation dose distributions.

OBJECTIVE Patients with arteriovenous malformations (AVMs) treated with Gamma Knife radiosurgery (GKRS) subsequent to embolization suffer from elevated local failure rates and differences in adverse radiation effects. Onyx is a common embolic material for AVMs. Onyx is formulated with tantalum, a high atomic number (Z = 73) element that has been investigated as a source of dosimetric uncertainty contributing to the less favorable clinical results. However, prior studies have not modeled the complicated anatomical and beam geometries characteristic of GKRS. This study investigated the magnitude of dose perturbation that can occur due to Onyx embolization using clinically realistic anatomical and Gamma Knife beam models. METHODS Leksell GammaPlan (LGP) was used to segment the AVM nidus and areas of Onyx from postcontrast stereotactic MRI for 7 patients treated with GKRS postembolization. The resulting contours, skull surface, and clinically selected dose distributions were exported from LGP in DICOM-RT (Digital Imaging and Communications in Medicine-radiotherapy) format. Isocenter locations and dwell times were recorded from the LGP database. Contours were converted into 3D mesh representations using commercial and in-house mesh-editing software. The resulting data were imported into a Monte Carlo (MC) dose calculation engine (Pegasos, Elekta Instruments AB) with a beam geometry for the Gamma Knife Perfexion. The MC-predicted dose distributions were calculated with Onyx assigned manufacturer-reported physical constants (MC-Onyx), and then compared with corresponding distributions in which Onyx was reassigned constants for water (MC-water). Differences in dose metrics were determined, including minimum, maximum, and mean dose to the AVM nidus; selectivity index; and target coverage. Combined differences in dose magnitude and distance to agreement were calculated as 3D Gamma analysis passing rates using tolerance criteria of 0.5%/0.5 mm, 1.0%/1.0 mm, and 3.0%/3.0 mm. RESULTS Overall, the mean percentage differences in dose metrics for MC-Onyx relative to MC-water were as follows; all data are reported as mean (SD): minimum dose to AVM = -0.7% (1.4%), mean dose to AVM = 0.1% (0.2%), maximum dose to AVM = 2.9% (5.0%), selectivity = 0.1% (0.2%), and coverage = -0.0% (0.2%). The mean percentage of voxels passing at each Gamma tolerance were as follows: 99.7% (0.1%) for 3.0%/3.0 mm, 98.2% (0.7%) for 1.0%/1.0 mm, and 52.1% (4.4%) for 0.5%/0.5 mm. CONCLUSIONS Onyx embolization appears to have a detectable effect on the delivered dose distribution. However, the small changes in dose metrics and high Gamma passing rates at 1.0%/1.0 mm tolerance suggest that these changes are unlikely to be clinically significant. Additional sources of delivery and biological uncertainty should be investigated to determine the root cause of the observed less favorable postembolization GKRS outcomes.

Dose-volume predictors of radio-induced complications after radiosurgery for uveal melanoma

Introduction Uveal melanoma (UM) is a life threatening intraocular malignant tumor. Gamma Knife Stereotactic Radiosurgery (GKSRS) is a well-assessed strategy for conservative treatment of UM providing good results for survival, local control and eye preservation. Purpose Our aim is to develop predictive models for radio-induced effects in UM patients treated with exclusive GKSRS. Materials and methods Medical records and 3D dosimetry data of critical structures of 66 patients were retrospectively reviewed. Cox’s proportional hazard model was used to identify clinical and dosimetric variables as independent risk factor for most clinically relevant GKSRS-related complications: radiation vasculopathy(RV), radiation papillopathy (RP) and neovascular glaucoma(NVG), visual acuity(VA) reduction >20% (VA20%) and complete loss of basal VA (VA100%). ROC curve analysis allowed predicting cutoff values of significant variables. Results The 2 years incidences were: RV 10%, RP 12%, NVG 14%, VA20% 59% and VA100% 27%. A clear relationship with D1% to optic nerve (ON) was found for RP and RV. Also, for RV, the prescription isodose-ON distance (PIOND) and the anterior to equator position of the tumor resulted as protective variables. The V20 of posterior segment and tumor thickness were predictive for NVG. Multivariate analyses resulted in two variables predictive model both for VA20% and VA100%, including tumor largest diameter and D1% to ON. A second predictive model, including PIOND, was found for VA100%. Conclusion We found clinical and dosimetric variables to predict the risk of main side effects after GKSRS for UM. These results may provide new dose constraints to critical structures potentially able to reduce toxicities. Disclosure Antonella del Vecchio has a contract as starter-up with Elekta Instrument AB. No other conflict of interest to declare for the other authors.

SU‐F‐J‐203: Retrospective Assessment of Delivered Proton Dose in Prostate Cancer Patients Based On Daily In‐Room CT Imaging

Purpose:Retrospective calculation of the delivered proton dose in prostate cancer patients based on a unique dataset of daily CT images.Methods:Inter‐fractional motion in prostate cancer patients treated at our proton facility is counteracted by water‐filled endorectal ballon and bladder filling protocol. Typical plans (XiO, Elekta Instruments AB, Stockholm) for 74 Gy(RBE) sequential boost treatment in 37 fractions include two series of opposing lateral double‐scattered proton beams covering the respective iCTV. Stability of fiducial markers and anatomy were checked in 12 patients by daily scheduled in‐room control CT (cCT) after immobilization and positioning according to bony anatomy utilizing orthogonal X‐ray. In RayStation 4.6 (RaySearch Laboritories AB, Stockholm), all cCTs are delineated retrospectively and the treatment plans were recalculated on the planning CT and the registered cCTs. All fraction doses were accumulated on the planning CT after deformable registration. Parameters of delivered dose to iCTV (D98%&gt;95%, D2%&lt;107%), bladder (V75Gy&lt;15%, V70Gy&lt;25%, V65Gy&lt;30%), rectum (V70Gy&lt;10%, V50Gy&lt;40%) and femoral heads (V50Gy&lt;5%) are compared to those in the treatment plan. Intra‐therapy variation is represented in DVH bands.Results:No alarming differences were observed between planned and retrospectively accumulated dose: iCTV constraints were met, except for one patient (D98%=94.6% in non‐boosted iCTV). Considered bladder and femoral head values were below the limits. Rectum V70Gy was slightly exceeded (&lt;11.3%) in two patients. First intra‐therapy variability analysis in 4 patients showed no timedependent parameter drift, revealed strongest variability for bladder dose. In some fractions, iCTV coverage (D98%) and rectum V70Gy was missed.Conclusion:Double scattered proton plans are accurately delivered to prostate cancer patients due to fractionation effects and the applied precise positioning and immobilization protocols. As a result of rare interventions after daily 3D imaging of the first 12 patients, in‐room CT frequency for prostate cancer patients was reduced. The presented study supports this decision.The authors acknowledge the German Federal Ministry for Education and Research for funding the High Precision Radiotherapy Group at the OncoRay ‐ National Center for Radiation Research in Oncology (BMBF‐ 03Z1N51).

TU‐G‐BRD‐04: A Round Robin Dosimetry Intercomparison of Gamma Stereotactic Radiosurgery Calibration Protocols

Purpose:The purpose of this multi‐institutional study was to compare two new gamma stereotactic radiosurgery (GSRS) dosimetry protocols to existing calibration methods. The ultimate goal was to guide AAPM Task Group 178 in recommending a standard GSRS dosimetry protocol.Methods:Nine centers (ten GSRS units) participated in the study. Each institution made eight sets of dose rate measurements: six with two different ionization chambers in three different 160mm‐diameter spherical phantoms (ABS plastic, Solid Water and liquid water), and two using the same ionization chambers with a custom in‐air positioning jig. Absolute dose rates were calculated using a newly proposed formalism by the IAEA working group for small and non‐standard radiation fields and with a new air‐kerma based protocol. The new IAEA protocol requires an in‐water ionization chamber calibration and uses previously reported Monte‐Carlo generated factors to account for the material composition of the phantom, the type of ionization chamber, and the unique GSRS beam configuration. Results obtained with the new dose calibration protocols were compared to dose rates determined by the AAPM TG‐21 and TG‐51 protocols, with TG‐21 considered as the standard.Results:Averaged over all institutions, ionization chambers and phantoms, the mean dose rate determined with the new IAEA protocol relative to that determined with TG‐21 in the ABS phantom was 1.000 with a standard deviation of 0.008. For TG‐51, the average ratio was 0.991 with a standard deviation of 0.013, and for the new in‐air formalism it was 1.008 with a standard deviation of 0.012.Conclusion:Average results with both of the new protocols agreed with TG‐21 to within one standard deviation. TG‐51, which does not take into account the unique GSRS beam configuration or phantom material, was not expected to perform as well as the new protocols. The new IAEA protocol showed remarkably good agreement with TG‐21.Conflict of Interests: Paula Petti, Josef Novotny, Gennady Neyman and Steve Goetsch are consultants for Elekta Instrument A/B; Elekta Instrument AB, PTW Freiburg GmbH, Standard Imaging, Inc., and The Phantom Laboratory, Inc. loaned equipment for use in these experiments; The University of Wisconsin Accredited Dosimetry Calibration Laboratory provided calibration services.

Advanced Image Coregistration within the Leksell Workstation for the Planning of Glioma Surgery: Initial Experience

Background Leksell GammaPlan (LGP) and SurgiPlan (ELEKTA Instruments AB, Stockholm, Sweden) may be used effectively for the detailed evaluation of regional neuroanatomy before open neurosurgical procedures. We report our initial experience in the cases of cerebral gliomas. Methods LGP v.8.3 was used before the surgical resection of cerebral gliomas for (1) the delineation of subdural grid electrodes and a detailed evaluation of their position relatively to cortical structures, and (2) for the fusion of structural magnetic resonance imaging and diffusion tensor imaging (DTI) for a detailed visualization of the corticospinal tract (CST) and optic radiation. Results Delineation of the subdural grid within LGP in a patient with seizures caused by left parietal glioma permitted a detailed assessment of the location of electrodes relative to the cortical gyri and sulci and significantly facilitated interpretation of brain mapping before tumor resection. In another patient with parieto-occipital glioma, simultaneous three-dimensional visualization of the tumor, CST, and optic radiation with the use of LGP permitted us to perform tumor resection without postoperative neurologic complications. Finally, incorporation of DTI into SurgiPlan resulted in precise planning of stereotactic biopsy for bilateral thalamic glioma. Conclusion The possibility for detailed evaluation of regional neuroanatomy based on various images within LGP and SurgiPlan may facilitate effective and safe surgical management of intracranial gliomas.

SU-E-T-571: Comparison of Collapsed Cone Convolution with the Traditional Tissue Maximum Ratio Algorithms for Dose Calculation in a Gamma Knife Radiation Treatment Planning System

Purpose: Advanced treatment delivery techniques in radiosurgery require improved treatment planning system (TPS). The aim of this study was to compare the traditional tissue maximum ratio calculation method (TMR) with recently developed by Elekta collapsed cone convolution (CCC) algorithm for dose calculation in Gamma Plan TPS. Methods: The possibility of this study was a consequence of the untraditional approach to the Gamma Knife treatments at Cleveland Clinic using both MR and CT studies for the absolute majority of the treatments. The basis for the plan data were approximately 1000 clinical cases treated on Perfexion Gamma Knife using TMR classic and complete MR/CT studies. Dose characteristics like D95 (dose received by 95% of target), D50 (dose received by 50% of target), minimum dose, maximum dose, average dose, integral dose, average target density, shortest distance to skull surface, and average axial skull radii were calculated for both algorithms and analyzed. The shot time and configuration were fixated according to the original plan made with TMR Classic. Convolution dose calculations were enabled by retrospectively assigning HU/ED conversion table to the available CT study. The comparison was done for different clinical indications. Results: As expected by the inherent approximation of all tissue to water, the TMR algorithm systematically overestimates the actual physical dose delivered compared with CCC method. It was shown that D95 was basically independent, when error bars considered, from the type of the lesion. The CCC/TMR ratios were in the range of 0.92/0.94. It was shown that there were statistically significant correlations for the most of the analyzed dose characteristics. Conclusion: This work indicates the potential for adjusting dose prescriptions with a mathematical factor which could imply a simple transition to use of more advanced and accurate CCC algorithm for calculation of the dose distributions for the Gamma Knife radiosurgery treatments. Elekta Instrument AB have provided means to calculate the data and have been involved in the data analysis.

FLUKA Monte Carlo simulation for the Leksell Gamma Knife Perfexion radiosurgery system: Homogeneous media

The purpose of this work is to investigate the capability of the FLUKA Monte Carlo (MC) code to simulate the Elekta Leksell Gamma Knife Perfexion (LGK-PFX) and reproduce the Treatment Planning System (TPS) Leksell GammaPlan version 8.2 (LGP) dose calculations for the case of a water equivalent phantom target. Thanks to the collaboration with Elekta Instruments AB, the collimation system geometry, the source positions and all the involved material have been simulated in detail. The relative linear dose distribution along the three coordinate axes, for each collimator size, and the Relative Output Factors (ROF) have been investigated. The simulation has been validated comparing simulated linear dose profiles with measurements performed with EBT radiochromic films. The acceptance criterion between experimental data and FLUKA results is based on the gamma index (GI) method. The FLUKA MC calculation for the ROF provided the values of 0.920 for the 8 mm collimators and 0.800 for the 4 mm collimators. These values are in good agreement with the Elekta reference data of 0.924 and 0.805 respectively. The percentage difference between calculated and reference values for the ROF is under 1% and within the FLUKA uncertainty. Also the simulated relative dose profiles show a good agreement with the LGP calculation expressed by means of the gamma index method. This established accuracy proves that FLUKA is a suitable and powerful tool in order to reproduce successfully the LGP calculations for the homogeneous media.

Detection of residual brain arteriovenous malformations after radiosurgery: diagnostic accuracy of contrast-enhanced four-dimensional MR angiography at 3.0 T

To evaluate the diagnostic accuracy of four-dimensional MR angiography (4D-MRA) at 3.0 T for detecting residual arteriovenous malformations (AVMs) after Gamma Knife (Elekta Instrument AB, Stockholm, Sweden) radiosurgery (GKRS). We assessed 36 angiographically confirmed AVMs in 36 patients who had been treated with GKRS. 4D-MRA was performed after GKRS and the time intervals were 39.4 ± 26.0 months [mean ± standard deviation (SD)]. 4D-MRA was obtained at 3.0 T after contrast injection, with a measured voxel size of 1 × 1 × 1 mm and a temporal resolution of 1.1 s (13 patients) or a voxel size of 1 × 1 × 2 mm and a temporal resolution of 0.98 s (23 patients). X-ray angiography was performed as the standard reference within 53 ± 47 days (mean ± SD) after MRA. To determine a residual AVM, the 4D-MRA results were independently reviewed by two readers blinded to the X-ray angiography results. We evaluated diagnostic sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of 4D-MRA for detection of a residual AVM. A residual AVM was identified in 13 patients (13/36, 36%) on X-ray angiography. According to Readers 1 and 2, 4D-MRA had a sensitivity of 79.6% and 64.3%, a specificity of 90.9% and 100%, a PPV of 84.6% and 100% and an NPV of 90% and 81.5%, respectively, and a diagnostic accuracy of 86.1% for Readers 1 and 2, for detecting residual AVMs after GKRS. The diagnostic accuracy of 4D-MRA at 3.0 T seems high, but there is still the possibility of further improving the spatiotemporal resolution of this technique.

Do Carbamazepine, Gabapentin, or Other Anticonvulsants Exert Sufficient Radioprotective Effects to Alter Responses From Trigeminal Neuralgia Radiosurgery?

Laboratory studies have documented radioprotective effects with carbamazepine. We sought to determine whether carbamazepine or other anticonvulsant/neuroleptic drugs would show significant radioprotective effects in patients undergoing high-dose small-volume radiosurgery for trigeminal neuralgia. We conducted a retrospective review of 200 patients undergoing Gamma Knife (Elekta Instrument AB, Stockholm, Sweden) stereotactic radiosurgery for trigeminal neuralgia between February 1995 and May 2008. We selected patients treated with a maximum dose of 80 Gy with 4-mm diameter collimators, with no previous microvascular decompression, and follow-up ≥6 months (median, 24 months; range, 6-153 months). At the time of radiosurgery, 28 patients were taking no anticonvulsants, 62 only carbamazepine, 35 only gabapentin, 21 carbamazepine plus gabapentin, 17 carbamazepine plus other anticonvulsants, and 9 gabapentin plus other anticonvulsants, and 28 were taking other anticonvulsants or combinations. Pain improvement developed post-radiosurgery in 187 of 200 patients (93.5%). Initial complete pain relief developed in 84 of 200 patients (42%). Post-radiosurgery trigeminal neuropathy developed in 27 of 200 patients (13.5%). We could not significantly correlate pain improvement or initial complete pain relief with use of carbamazepine, gabapentin, or use of any anticonvulsants/neuroleptic drugs or other factors in univariate or multivariate analysis. Post-radiosurgery numbness/paresthesias correlated with the use of gabapentin (1 of 36 patients with gabapentin vs. 7 of 28 without, p = 0.017). In multivariate analysis, decreasing age, purely typical pain, and use of gabapentin correlated (p = 0.008, p = 0.005, and p = 0.021) with lower risks of developing post-radiosurgery trigeminal neuropathy. New post-radiosurgery numbness/paresthesias developed in 3% (1 of 36), 5% (4 of 81), and 13% (23 of 187) of patients on gabapentin alone, with age ≤70 years, and Type 1 typical trigeminal neuralgia pain compared with 25% (7 of 28), 20% (23 of 114), and 33% (4 of 12) of patients taking no anticonvulsants, age >70 years, and partly atypical Type 2 trigeminal neuralgia, respectively. The use of carbamazepine or gabapentin at the time of radiosurgery does not decrease the rates of obtaining partial or complete pain relief after radiosurgery, but gabapentin may reduce the risks of developing post-radiosurgery trigeminal neuropathy.

Gamma Knife Radiosurgery for Benign Cavernous Sinus Tumors: Treatment Concept and Outcomes in 120 Cases

Availability of modern computer-aided robotized devices, such as the Automatic Positioning System (APSTM; Elekta Instruments AB, Stockholm, Sweden) and PerfexionTM (Elekta Instruments AB), allowed us to develop the original concept of robotic gamma knife microradiosurgery, which is based on the very precise irradiation of the lesion with regard to conformity and selectivity; intentional avoidance of the excessive irradiation of functionally-important anatomical structures, particularly cranial nerves, located both within and in the vicinity of the target; and delivery of sufficient irradiation energy to the tumor with the intention to attain lesion shrinkage, while keeping the marginal dose sufficiently low for prevention of possible complications. The results of such treatment strategy were evaluated retrospectively in 120 patients with benign cavernous sinus neoplasms (pituitary adenomas, meningiomas, schwannomas, and hemangiomas), who were followed up from 24 to 78 months (mean 47 months) after radiosurgery. Tumor growth control and shrinkage rates were 98% and 68%, respectively. More than 50% volume reduction was noted in 25% of lesions. The most prominent volumetric tumor response was observed in hemangiomas, followed by schwannomas, pituitary adenomas, and meningiomas. Treatment-related complications were marked in 7% of cases, and were mainly related to transient isolated cranial neuropathy appearing within several months after radiosurgery. Major morbidity was limited to one patient (0.8%). Application of microradiosurgical treatment principles provides effective and safe management of benign cavernous sinus tumors and is associated with high probability of lesion shrinkage and minimal risk of complications.

Assessment of variation in Elekta® plastic spherical‐calibration phantom and its impact on the Leksell Gamma Knife® calibration

Traditionally, the dose-rate calibration (output) of the Leksell Gamma Knife (LGK) unit is performed using a 160 mm diameter plastic spherical phantom provided by the vendor of the LGK, Elekta Instrument AB. The purpose of this study was to evaluate variations in the Elekta spherical phantom and to assess its impact and use for the LGK calibration. Altogether, 13 phantoms from six different centers were acquired, 10 of these phantoms were manufactured within the past 10 years and the last 3 approximately 15-20 years ago. To assess variation in phantoms, the diameter and mass densities were measured. To assess the impact on LGK calibration, the output of two models of LGK (LGK Perfexion and LGK 4C) were measured under identical irradiation conditions using all 13 phantoms for each LGK model. The mean measured deviation in diameter from expected nominal 160 mm for 13 phantoms was 0.51 mm (range of 0.09-1.51 mm). The mean measured phantom mass density for 13 phantoms was 1.066 +/- 0.019 g/cm3 (range of 1.046-1.102 g/cm3). The percentage deviation of output for individual phantom from mean of 13 phantom outputs ranged from -0.37% to 0.55% for LGK Perfexion. Similarly, the percentage deviation of output for individual phantom from mean of 13 phantom outputs ranged from -0.72% to 0.47% for LGK 4C. This study demonstrated that small variations in terms of phantom size and mass density of the phantom material do not have a significant impact on dose-rate measurements of the Leksell Gamma Knife. Also, date of manufacture of the phantom did not show up to be a significant factor in this study.

Tumor control and hearing preservation after Gamma Knife radiosurgery for vestibular schwannomas in neurofibromatosis type 2

To analyze the effect of Gamma Knife radiosurgery (GKS) on tumor control and hearing preservation rates in patients with vestibular schwannomas (VS) in a setting of neurofibromatosis type 2 (NF 2), a retrospective study was carried out at a tertiary-level referral Gamma Knife unit. Dose plans, pre- and postoperative radiology, and follow-up clinical records of patients with NF 2 who had undergone GKS for VS using a Leksell Gamma Knife (Elekta Instruments AB, Stockholm, Sweden) model B unit from 1997 to 2008 were reviewed. Thirty patients with 54 VS underwent GKS. The average age of the cohort was 29 years (range 10-56 years). Twenty-four patients had bilateral VS. The commonest clinical presentation was hearing loss and tinnitus. Primary GKS was given to 36 tumors, while 18 tumors received it as an adjunct to surgery. Average tumor size was 3.7 cc (range 0.1-13.3 cc). A median 12 Gy prescription dose (range 10-15 Gy) was administered at the 50% isodose (range 42-50%) to cover on average 91.5% of the tumor. Eighteen patients were available for clinical, 14 patients for radiological, and 5 patients (with useful hearing) for audiometric follow-up at an average of 26.6 months. The tumor control rate was 87.5% in this series (33.3% tumor regression), while hearing preservation was noted in 66.7% of cases. One patient developed worsening of facial function. GKS for VS provides satisfactory tumor control and hearing preservation in patients with NF 2. Long-term follow-up will determine future recommendations.

RADIOSURGERY WITH THE WORLD'S FIRST FULLY ROBOTIZED LEKSELL GAMMA KNIFE PERFEXION IN CLINICAL USE

The world's first Leksell Gamma Knife PerfeXion (Elekta Instrument AB, Stockholm, Sweden) for radiosurgery of the head and neck became operational at Timone University Hospital in Marseille on July 10, 2006. To allow strict evaluation of the capabilities, advantages, disadvantages, and limitations of this new technology, patients were enrolled in a prospective, randomized trial. In 66 working days, between July 10 and December 20, 2006, 363 patients were treated by gamma knife surgery at Timone University Hospital, Marseille. Of these patients, 200 were eligible for the comparative prospective study (inclusion criteria were informed consent obtained, tumor or vascular indication, and no previous radiosurgery or radiotherapy). In accordance with the blinded randomization process, 100 patients were treated with the Leksell Gamma Knife 4C (Elekta Instrument AB) and Gamma Knife 100 (Elekta Instrument AB) with the Leksell Gamma Knife PerfeXion. Dose planning parameters, dosimetry measurements on the patient's body, workflow, patient comfort, quality assurance procedure, and a series of other treatment-related parameters were systematically and prospectively evaluated in both arms of the trial. No technical failure of the treatment procedure was encountered. The new dose-planning system led to the use of composite shots in 39.4% of the patients. The median number of different collimator sizes used was larger with the PerfeXion than with the 4C (2 and 1, respectively). The mean number of isocenters used was lower (10.67 and 13.08, respectively). The median total treatment time was significantly shorter with the PerfeXion (40 and 60 minutes, respectively), but there was no significant difference in the median radiation time (34.02 and 33.40 minutes, respectively). The procedure was performed using only a single run in 98.99% of the PerfeXion cases and in 42% of the 4C cases. Collision risk on the 4C forced us to change the frame gamma angle for at least 1 shot in 24% of the patients and led to treatment in manual mode for at least 1 shot in 21% of the patients. Collision risk requiring technical adaptation did not occur with the PerfeXion. In 1 patient treated with the PerfeXion, the system required a direct collision check. In terms of dose to structures outside the target area, the PerfeXion delivers 8.2 times less to the vertex, 10 times less to the thyroid, 12.9 times less to the sternum, and 15 times less to the gonads. Our prospective study indicates that procedures with the PerfeXion were collision-free, even with very eccentric lesions (e.g., multiple metastases). The duration of the surgical procedure, the amount of time required for nurse, physicist, and physician intervention on the machine, and the duration of the quality assurance procedure were all shown to be dramatically reduced with the PerfeXion gamma knife. Patient protection is greatly improved with the PerfeXion. In our experience, the technological advances of the Leksell Gamma Knife PerfeXion will make a very significant contribution to future progress in head and neck radiosurgery.

THE LEKSELL GAMMA KNIFE PERFEXION AND COMPARISONS WITH ITS PREDECESSORS

The objective of this study is to introduce a new radiosurgical device, the Leksell Gamma Knife Perfexion (Elekta Instruments AB, Stockholm, Sweden). Design and performance characteristics are compared with previous models of the gamma knife in a clinical setting. Performance-related features in the design of the new radiosurgical system are described, and the ability to create complex shapes of isodose volumes even with a single isocenter is demonstrated. The concept of "dynamic shaping" of dose distribution is introduced as a means of decreasing the exposure to structures outside the target. Dose plans for the Leksell Gamma Knife Models B, 4C, and Perfexion have been created for target pathologies to illustrate how the software and hardware of the new radiosurgical system can increase treatment quality, decrease treatment time, and increase patient comfort. Radiation doses to critical organs in the rest of the human body are compared. The automated collimator arrangement in the Perfexion makes it possible to produce more complex treatment volumes than with previous models of the gamma knife. This results from the enhanced ability to shape isodose volumes, even for single isocenters. The collimator arrangement and the patient positioning system also allow shorter patient transit times, reducing unwanted radiation exposure during movement between isocenters. The Perfexion exceeds the capabilities of previous gamma knife models in terms of treatment efficiency, conformity, and radiation protection. These qualities enable treatment of larger target volumes, especially close to eloquent areas. Pathologies previously inaccessible in the head and neck are now treatable due to the increased volume of the radiation cavity.

THE LEKSELL GAMMA KNIFE PERFEXION AND COMPARISONS WITH ITS PREDECESSORS

The objective of this study is to introduce a new radiosurgical device, the Leksell Gamma Knife Perfexion (Elekta Instruments AB, Stockholm, Sweden). Design and performance characteristics are compared with previous models of the gamma knife in a clinical setting. Performance-related features in the design of the new radiosurgical system are described, and the ability to create complex shapes of isodose volumes even with a single isocenter is demonstrated. The concept of "dynamic shaping" of dose distribution is introduced as a means of decreasing the exposure to structures outside the target. Dose plans for the Leksell Gamma Knife Models B, 4C, and Perfexion have been created for target pathologies to illustrate how the software and hardware of the new radiosurgical system can increase treatment quality, decrease treatment time, and increase patient comfort. Radiation doses to critical organs in the rest of the human body are compared. The automated collimator arrangement in the Perfexion makes it possible to produce more complex treatment volumes than with previous models of the gamma knife. This results from the enhanced ability to shape isodose volumes, even for single isocenters. The collimator arrangement and the patient positioning system also allow shorter patient transit times, reducing unwanted radiation exposure during movement between isocenters. The Perfexion exceeds the capabilities of previous gamma knife models in terms of treatment efficiency, conformity, and radiation protection. These qualities enable treatment of larger target volumes, especially close to eloquent areas. Pathologies previously inaccessible in the head and neck are now treatable due to the increased volume of the radiation cavity.