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Published in final edited form as: World Neurosurg. 2020 Nov 3;146:e678–e684. doi: 10.1016/j.wneu.2020.10.153

Convexity Meningiomas in Patients with Neurofibromatosis Type 2: Long-Term Outcomes After Gamma Knife Radiosurgery

Henry Ruiz-Garcia 1,2, Daniel M Trifiletti 1,2, Nasser Mohammed 3, Yi-Chieh Hung 3, Zhiyuan Xu 3, Tomas Chytka 4, Roman Liscak 4, Manjul Tripathi 5, David Arsanious 6, Christopher P Cifarelli 6, Marco Perez Caceres 7, David Mathieu 7, Herwin Speckter 8, Gregory P Lekovic 9, Gautam U Mehta 9, Jason P Sheehan 3
PMCID: PMC7988886  NIHMSID: NIHMS1681556  PMID: 33152493

Abstract

BACKGROUND:

Convexity meningiomas are common tumors requiring treatment in patients with neurofibromatosis type 2 (NF2). Although different therapeutic options are described for sporadic convexity meningioma, much less is known about these lesions in patients with NF2 despite their distinct biology and need for multiple treatments. We analyzed the value of Gamma Knife radiosurgery (GKRS) as definitive treatment for convexity meningiomas in patients with NF2.

METHODS:

This international multicenter retrospective study was approved by the International Radiosurgery Research Foundation. Patients with NF2 with at least 1 convexity meningioma and 6-month follow-up after primary GKRS were included.

RESULTS:

Inclusion criteria were met by 18 patients with NF2. A total of 120 convexity meningiomas (median treatment volume, 0.66 cm3 [range, 0.10–21.20 cm3]) were analyzed. Median follow-up after initial GKRS was 15.6 years (range, 0.6–25.5 years). Median age at GKRS was 32.5 years (range, 16–53 years). Median number of meningiomas per patient was 13 (range, 1–27), and median number of convexity lesions receiving GKRS per patient was 3.5 (range, 1–27). One case of tumor progression was reported 24 years after GKRS, leading to actuarial progression-free survival rates of 100% at 2, 5, and 10 years. No malignant transformation or death due to meningioma or radiosurgery was recorded.

CONCLUSIONS:

GKRS is safe and effective as definitive treatment of small to medium-sized convexity meningiomas in patients with NF2. Despite concerns about the particular mutational burden of these tumors, no malignant transformation manifested after treatment. GKRS represents a minimally invasive option that offers long-term tumor control to this specific group of patients.

Keywords: Convexity, Gamma Knife radiosurgery, Meningioma, Neurofibromatosis type 2

INTRODUCTION

Convexity meningiomas are supratentorial tumors that manifest with a sole attachment to the dura mater covering the convexity of the brain hemispheres. These tumors are the most common among idiopathic meningiomas and are effectively managed with either resection or radiosurgery.1–7 In patients with neurofibromatosis type 2 (NF2), meningiomas are the second most common type of tumors, and they may develop in up to 80% of patients by 70 years of age.8,9 Meningiomas of the convexity are also among the most common tumors in patients with NF2, and they represent one of the most common lesions requiring treatment in this group of patients.10–14 In general, the presence of NF2-associated meningiomas is linked to higher intracranial and spinal tumor burden, increased need for multiple surgical interventions, and elevated morbidity and mortality.15 Furthermore, particularities in the genetic profile and natural history of NF2-associated meningiomas have called for evaluation of interventions that have been proven safe and effective in idiopathic meningiomas to determine if they are also valuable in treatment of NF2-associated lesions.12,16–18 As patients with NF2 represent a clinical challenge owing to the predisposition to development of new tumors over their life span and require several therapeutic interventions, minimally invasive options able to minimize patient morbidity while still securing high effectiveness are of uppermost interest in neurosurgical oncology practice.

In this study, we analyzed outcomes from an international multicenter cohort of patients with NF2 with convexity meningiomas treated with Gamma Knife (Elekta AB, Stockholm, Sweden) radiosurgery as definitive treatment. Tumor control and complications associated with Gamma Knife radiosurgery (GKRS) in this specific cohort of patients with a long follow-up were assessed.

MATERIALS AND METHODS

Study Inclusion Criteria and Patient Cohort

This international multicenter retrospective study was performed as a collaborative effort on behalf of the International Radiosurgery Research Foundation. Patient data were collected after institutional review board approval in 7 medical centers that are members of the International Radiosurgery Research Foundation; patient consent was waived in each location. The data were deidentified, pooled, and subsequently analyzed. The STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) statement was followed to guide data reporting.

Eligibility criteria included patients with NF2 with at least 1 convexity meningioma managed with primary GKRS and 6 months of follow-up. Owing to lack of definitive pathology confirmation, radiologic diagnosis of meningioma was deemed adequate for patient inclusion. Radiologic features consistent with meningioma, such as dural-based extra-axial location, contrast enhancement, and intratumoral calcifications, were considered important diagnostic criteria. GKRS was indicated in patients with symptomatic or progressively growing lesions and in patients who desired the treatment and the benefit-to-risk ratio was good. Patient age was not a limiting factor for inclusion. Exclusion criteria included prior meningioma surgical resection or radiation. Other NF2-associated tumors, such as vestibular schwannomas, were not included in the analysis (Figure 1).

Figure 1.

Figure 1.

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Patient selection algorithm. GKRS, Gamma Knife radiosurgery; NF2, neurofibromatosis type 2.

Baseline Clinical and Radiosurgical Variables

Baseline clinical parameters, including age at diagnosis, age at first GKRS, sex, total number of meningiomas, symptoms, and neurological deficits, were recorded. Baseline radiosurgical parameters, including maximum dose, margin dose, and treatment volume, were also recorded directly from the medical records.

Follow-Up and Outcomes

Clinical and radiological follow-up was recorded. Time to tumor progression was defined from the date of the radiosurgical procedure. Volumetric analysis was performed, and tumor progression was defined as an increase of ≥20% over the baseline tumor volume (original volume) before GKRS compared with the last follow-up magnetic resonance imaging. A cutoff value of 20% was selected, as this is consistent with the current brain Response Assessment in Neuro-Oncology (RANO) criteria. Radiation-induced adverse effects and their time to development were recorded. Radiation necrosis was defined on the basis of either tissue pathology or neuro-imaging. Criteria for radiographic diagnosis of radiation necrosis included characteristic enhancement of central necrosis on T1-weighted series and/or high signal intensity indicating the central necrotic tissue surrounded by low signal intensity indicating the solid nonnecrotic peripheral portion on T2-weighted images.19 Need for irradiation, adjuvant chemotherapy, or surgery after GKRS was also recorded. Mortality related to GKRS or associated with the treated meningioma was evaluated. Information about each lesion was collected independently in patients with NF2 presenting with multiple meningiomas.

Radiosurgery Technique

Details of the single fraction Gamma Knife technique employed during the radiosurgical treatment of the included patients have been extensively described by our group.20,21 Briefly, patients were placed in a Leksell Gamma Knife Frame (Elekta AB) under sedation and local anesthesia to obtain thin-slice axial and/or coronal magnetic resonance imaging for treatment planning and delivery. In all cases, a multidisciplinary team of neurosurgeons, radiation oncologists, and radiation physicists was involved in different aspects of the treatment. Different models of Leksell Gamma Knife units (model B, U, 4C, Perfexion, and Icon; Elekta AB) were used depending on the available technology at the medical center and the time of procedure.

Statistical Analysis

Descriptive statistics were performed according to each variable type; numerical variables were described using mean, median, and/or range. Gaussian distribution and homogeneity of variance were tested accordingly when needed. Student t test was performed to compare continuous variables. Given that only 1 case of tumor progression was reported, analysis of predictors of tumor progression via Cox proportional regression was considered not appropriate. The Kaplan-Meier method was used to independently estimate actuarial rates of progression-free survival (PFS). When a patient presented with >1 tumor, each lesion was considered individually for analysis of tumor control or progression. Statistical analysis was performed using IBM SPSS Version 25 (IBM Corporation, Armonk, New York, USA). A 2-tailed P value < 0.05 was required for statistical significance.

RESULTS

Patients and Tumor Characteristics

The final cohort comprised 18 patients with NF2 with a total of 224 meningiomas who presented with 120 convexity-based lesions and received GKRS as primary treatment. This cohort was part of a bigger group of 40 patients with NF2 with a total of 395 meningiomas from all brain locations (Figure 1). Patient demographics and clinical characteristics are described in Table 1. Of 18 patients, 13 were female (72.2%). Female patients presented with almost double of the mean (SD) total number of meningiomas (6.6 [3.3]/14.7 [2.3]) and mean (SD) number of convexity tumors receiving GKRS (4.0 [1.6]/7.7 [2.3]) compared with male patients (P > 0.05).

Table 1.

Characteristics of Patients with Neurofibromatosis Type 2–Associated Convexity Meningiomas Treated with Gamma Knife Radiosurgery

Characteristic Value
Demographics and clinical characteristics
 Number of patients 18
 Sex, M/F 5/13
 Meningiomas according to sex, M/F, mean (SD)* 6.6 (3.3)/14.7 (2.3)
 Treated convexity meningiomas according to sex, M/F, Mean (SD) 4.0 (1.6)/7.7 (2.3)
 Age at diagnosis, years, median (range) 30.5 (16–53)
 Age at GKRS, years, median (range) 32.5 (16–53)
 Number of meningiomas in included patients* 224
 Number of meningiomas receiving GKRS in included patients 176
 Number of convexity meningiomas treated with GKRS 120
 Number of convexity meningiomas treated with GKRS per patient, median, mean (range) 3.5, 6.7 (1–27)
 Number of meningiomas per included patient, median, mean (range) 13, 12.4 (1–27)
Signs or symptoms before GKRS
 Patients with pre-existing neurological deficit due to meningiomas 13 (81.25%)
 Patients with asymptomatic presentation 5/18 (27.8%)
 Patients with headache 8/18 (44.5%)
 Patients with seizures 2/18 (11.1%)
 Patients with gait instability 3/18 (16.7%)
 Patients with visual disturbance 0/18 (0%)
 Patients with motor weakness 7/18 (38.9%)
 Patients with hearing loss 6/18 (33.3%)
 Patients with sensory deficit 0/18 (0%)
 Number of meningiomas per patient, median (range) 13 (1–27)
 Patients with ≤10 meningiomas* 8/18 (44.5%)
 Patients with ≥11 meningiomas* 10/18 (55.5%)
Tumor location and follow-up among total cohort of meningiomas receiving GKRS
 Convexity 120/204 (60%)
 Follow-up after initial GKRS, years, median (range) 15.6 (0.6–25.5)
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M, male; F, female; GKRS, Gamma Knife radiosurgery.

*

Refers to total tumor burden disease.

The median age at diagnosis of the cohort was 30.5 years (range, 16–53 years). Symptoms were present in 81.25% of patients. The most common symptoms were headaches (44.5%), motor weakness (38.9%), and hearing loss (33.3%). Seizures were present in only 2 patients (11.1%). The percent of patients with symptoms reflects the overall cranial tumor burden as well as their associated symptoms in this cohort of patients and not just symptoms associated with convexity meningiomas. The median number of convexity meningiomas treated with GKRS per patient was 3.5 (mean 6.7, range 1–27). Median age at GKRS was 32.5 years (range, 16–53 years).

Radiosurgical Treatment Parameters

The median maximum dose delivered was 24.5 Gy (range, 20–50 Gy), and the median margin dose was 12.0 Gy (range, 12–25 Gy). Median treatment volume for the studied cohort was 0.66 cm3 (range, 0.10–21.2 cm3) (Table 2).

Table 2.

Radiosurgical and Outcomes Details for Patients with Neurofibromatosis Type 2–Associated Convexity Meningiomas Treated with Gamma Knife Radiosurgery

Radiosurgical Parameter/Outcome Value
Treatment volume, cm3, median (range) 0.66 (0.10–21.20)
Maximum dose, Gy, median (range) 24.5 (20–50)
Margin dose, Gy, median (range) 12.0 (12–25)
Tumors with post-GKRS progression 1 (0.8%)
 Central failure 0 (0.0%)
 Marginal failure 1 (0.8%)
Time to progression, years 24
Lesions receiving post-GKRS radiation 0/120 (0%)
Lesions receiving post-GKRS surgery 1/120 (0.8%)
Patients receiving adjuvant chemotherapy 0/18 (0%)
Radiation-induced adverse effects 1/18 (5.5%)
Nature of adverse radiation effect
 Brain edema 1/18 (5.5%)
 Time to adverse radiation effect, months 24
Malignant transformation in treated tumors 0 (0.0%)
Mortality due to meningioma-related causes 0 (0.0%)
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GKRS, Gamma Knife radiosurgery.

Radiologic Tumor Control and PFS

Different parameters related to treatment outcomes are shown on Table 2. Overall tumor control rate was 99.1%. Radiographic tumor PFS was defined as the time interval between the initial GKRS and time to tumor growth either inside or outside of the target volume. Actuarial tumor PFS rates at 5, 10, and 15 years were 100% (Figure 2). Median follow-up time after GKRS was 15.6 years (range, 0.6–25.5 years). Only 1 female patient presented with a treatment failure (marginal) 24 years after the index GKRS, in which a margin dose of 12 Gy had been delivered. The recurrent lesion was managed with surgical resection, and final pathology showed a World Health Organization (WHO) grade I meningioma. The initial volume of the recurrent tumor was 10.7 cm3, which was >91.7% of the other cases. However, it was not possible to analyze the predictive value of this variable, as only 1 case of tumor progression was reported.

Figure 2.

Figure 2.

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Tumor progression-free survival for patients with neurofibromatosis type 2–associated convexity meningiomas treated with Gamma Knife radiosurgery. NF2, neurofibromatosis type 2; GKRS, Gamma Knife radiosurgery; PFS, progression-free survival.

Radiation-Induced Adverse Effects, Malignant Transformation, and Death

GKRS was generally well tolerated in convexity meningiomas. Radiation-induced adverse effects were noted in only 1 patient (0.8%). The patient presented with perilesional edema 24 months after therapy; this was medically managed with steroids. There were no cases of malignant transformation after GKRS. Deaths as a result of intracranial tumor progression or GKRS were not observed.

DISCUSSION

Meningiomas are the second most common tumors in patients with NF2. Given their particular biology and natural history, they represent a challenging clinical scenario. Patients with NF2 presenting with meningiomas have increased intracranial and spinal tumor burden, higher mortality, and higher likelihood of under-going more surgical procedures.15,22 Therefore, it is relevant to revise outcomes specific to NF2-associated meningiomas to validate the appropriateness of current treatment options. This International Radiosurgery Research Foundation–approved international multicenter study provides estimates of long-term outcomes and complications for this specific group of patients presenting with convexity-based meningiomas treated with primary GKRS.

Convexity Meningiomas in Patients with NF2

Convexity meningiomas are a commonly encountered pathology in neurosurgical practice. In sporadic meningiomas, the convexity of the skull has been reported as the most common location for these tumors, accounting for 16.6%–29.3% of cases.1–5 In patients with NF2, meningiomas of the convexity are the most common tumor outside of bilateral vestibular schwannomas. Dirks et al.10 studied the natural history of NF2-associated intracranial tumors; the authors described 13 patients with 139 NF2-associated meningiomas and found that the convexity was the most common location, harboring 44 of 139 lesions. Other series have described similar results, with convexity meningiomas representing approximately 24.4%–44% of the lesions.11–14 Li et al.13 showed that the location pattern of NF2-associated meningiomas varied according to age of the patient population. Convexity meningiomas were the most common in adult patients with NF2, but the skull base was a more common location for these tumors in pediatric patients. The authors also studied clinical features of newly developed tumors, and they found that de novo meningiomas were more likely to appear in the convexity as patients get older. Furthermore, newly developed meningiomas demonstrated faster growth rates than other meningiomas.12,13,22 In our study, 120 of a total of 204 meningiomas receiving GKRS were located in the convexity (60%). Patients with convexity lesions had a median of 13 meningiomas in general (range, 1–27 lesions, regardless of treatment status), and a median of 3.5 convexity meningiomas received GKRS (range, 1–27 lesions). As we included only symptomatic or growing lesions in our analysis, it is evident that convexity meningiomas represent a relevant group among tumors requiring treatment in patients with NF2.

Therapeutic approaches for convexity meningiomas have been described for almost 100 years.23 However, although treatment of sporadic convexity meningiomas has been relatively well studied,3,7,24,25 much less is known about outcomes for this specific group of meningiomas in patients with NF2.

Role of Surgery for NF2-Associated Convexity Meningiomas

Complete resection has been historically considered the goal for convexity meningiomas, and low recurrence rates have been expected, as they are thought to be reasonably easy to resect with modern neurosurgical techniques.1,6,26 Alvernia et al.27 described outcomes from surgery in 100 sporadic convexity lesions with an average tumor size of 3.6 ± 0.4 cm; Simpson grade I resection was achieved in 91 lesions, and only 2 lesions had recurred after a mean follow-up of 7.2 years. Sanai et al.3 presented a series of 141 sporadic convexity meningiomas with a mean tumor volume of 146.3 cm3 (range, 1–512 cm3); Simpson grade 0 or I resection was achieved in 87% of cases. There were no intraoperative complications or deaths, but medical or neurosurgical complications were recorded in 14 patients, accounting for a 10% complication rate. Postoperative complications included deep vein thrombosis and pulmonary embolism requiring treatment, hematoma requiring evacuation, cerebrospinal fluid leak, and operative site infection.3

Despite the fact that patients with NF2 harboring associated meningiomas have greater tumor burden (e.g., intracranial schwannomas, spinal tumors) and tend to undergo a higher number of surgical procedures in their lifetime, only a few studies have reported on the role of surgery in patients with NF2.12,22 Nguyen et al.28 summarized a small series of cases, in which only 2 convexity lesions were described and complete resection was achieved in both of them. Aboukais et al.22 described 34 patients with NF2 presenting with 100 intracranial meningiomas; half of the patients underwent surgery for 25 of these lesions. Recurrence occurred in 5 lesions; 2 of these were WHO grade I (2 of 20 WHO grade I lesions), and 3 were WHO grade II (3 of 5 WHO grade II lesions), which highlights the relevance of the WHO grade in the postoperative progression of NF2-associated meningiomas. Goutagny et al.12 described results of surgery in 56 NF2-associated meningiomas; complete resection was achieved in 43 lesions, and none of the lesions with complete resection recurred in a 51.7-month postoperative follow-up. Overall, although there are limited studies on convexity meningiomas in patients with NF2, the same principles derived from sporadic meningioma surgery seem to apply to NF2-associated meningiomas. Nonetheless, while resection remains an excellent treatment option, its role in patients with NF2-associated convexity meningiomas is not well defined. Tumor size, proximity to major cerebrovascular structures, functional status, history of previous surgeries, and potential need for future treatments should be carefully considered during decision making in this particular group of patients.15,22

GKRS for NF2-Associated Convexity Meningioma

Patients with NF2 typically undergo longitudinal radiologic follow-up. Thus, convexity meningiomas are more likely to be detected when they are still small and are an easy target for radiosurgery.26 Pollock et al.29 found that GKRS provides similar tumor control to Simpson grade I resection in patients with sporadic meningiomas of small or medium size (<35 mm on average) and higher PFS compared with Simpson grade II resection. In general, radiosurgery has been shown to be safe and effective in the management of sporadic meningiomas in different locations.7,30–41

However, there have been some concerns regarding the role of GKRS in the management of NF2-associated meningiomas, as some authors have related stereotactic radiosurgery with higher risk of malignant transformation.28,42,43 Few studies have evaluated the role of stereotactic radiosurgery in patients with NF2. Liu et al.14 reported on the role of GKRS in patients with NF2-associated meningiomas. Their study included 12 patients with 87 meningiomas receiving GKRS. Convexity meningiomas represented 38% of the total number of meningiomas in these patients. Overall, their clinical characteristics were similar to our cohort, with a median age at the time of first GKRS of 31 years, a median total number of 9 meningiomas (range, 4–22 lesions), and a median number of meningiomas treated during first procedure of 3.5. Local control rates at 1, 3, and 5 years were 100%, 98%, and 92% for meningiomas from all brain locations. The authors performed an analysis matching PFS after the use of GKRS in NF2-associated meningiomas and sporadic benign meningiomas and found that the outcomes were comparable. Birckhead et al.44 also reported on the use of GKRS in 15 patients with NF2-associated meningiomas. Convexity lesions represented 23% of the 62 lesions receiving single-fraction stereotactic radiosurgery. Median radiographic follow-up was 103 months, and the 5- and 10-year local controls were 96%. Gao et al.45 reported on the use of GKRS in 35 patients with 99 meningiomas. All tumors received radiosurgery, and the median follow-up time was 96 months. The median tumor volume treated was 6.8 cm3, and local control rates at 1, 3, and 5 years were 100%, 97.1%, and 90%. In this series, convexity meningiomas represented 35.4% of the total number of lesions. Contrary to the concerns arguing against the use of radiosurgery in patients with NF2 owing to the presupposed higher risk of malignant transformation, none of the 248 NF2-associated meningiomas treated in these 3 series developed malignant transformation.

Our series describes 18 patients with 120 meningiomas specifically located in the convexity of the brain. These lesions received 68% of the GKRS procedures in this specific cohort and 60% of the total number of procedures in the global cohort of patients with NF2-associated meningiomas from all brain locations. Despite the relevance that convexity meningiomas have during treatment decision making in patients with NF2, no series exists evaluating the safety and efficacy of GKRS in this particular group of patients. Our study shows that GKRS represents a safe and efficient treatment option for these lesions. Similar to the 3 above-mentioned series on GKRS for patients with NF2, none of the 120 meningiomas receiving GKRS developed malignant transformation. Furthermore, postsurgical pathology confirmed the diagnosis of a benign WHO grade I meningioma in the only case of tumor progression. Similarly, the post-GKRS complication rate in our cohort was very low, as only 1 case of post-GKRS brain edema effectively managed with medical treatment was reported. There were no deaths associated with intracranial tumor progression or GKRS. Taken together, our results suggest that GKRS is a quite effective treatment option and does not appear to be associated with increased risk of malignant transformation as previously believed.

We also report adequate local control after GKRS for convexity meningiomas in patients with NF2. Given that only 1 lesion progressed at 24 years of follow-up, rates of tumor PFS in our series were 100% at 5, 10, and 20 years (Figure 2). Although we believe that this number may represent a spurious result and is related to the small tumor volume of the treated lesions (median 0.66 cm3 [range, 0.10–21.20 cm3]), we still trust that the number reflects the fact that GKRS offers similar tumor control rates in patients presenting with either NF2-associated or sporadic convexity meningiomas. Kondziolka et al.7 reported on 125 patients receiving GKRS for sporadic small or medium convexity meningiomas (<35 mm). With 64 tumors treated in the primary setting, an overall tumor control rate of 92% was achieved. From the 5 lesions that enlarged, 2 were <3 cm3, and 3 had a volume between 3 and 10 cm3. Only 6.2% of patients presented with new morbidity after the procedure, and no radiation-induced tumors were reported. Overall, these results support GKRS as an effective treatment option for either idiopathic or NF2-associated convexity meningiomas.

Study Limitations

This study exhibits the same limitations of any retrospective study. We could not obtain information about WHO grade or specific histology type for analysis, as all patients underwent primary GKRS as definitive treatment. Thus, although radiographic diagnosis of meningiomas is usually correct, and a contemporary series showed the risk of image misdiagnosis was only 2.3%,46 it is still possible that we had treated tumors of different histologies than the presumed WHO grade I meningiomas. It is also possible that we included higher-grade meningiomas, which would have tailored the PFS to a less favorable result. Although a matched pair analysis would have been the optimal approach to compare outcomes of GKRS for idiopathic versus NF2-associated convexity meningiomas, data from Liu et al.,14 Birckhead et al.,44 and Gao et al.45 as well as the data published by Kondziolka et al.7 on GKRS for sporadic convexity meningiomas create solid scientific support to frame our conclusions with a reasonable degree of confidence.

CONCLUSIONS

Convexity meningiomas are common tumors requiring treatment in patients with NF2. While resection can be considered, our results show that GKRS is safe and affords long-term control in small and medium-sized tumors. Thus, GKRS may help limit the need for numerous craniotomies, which may be relevant for preservation of quality of life in this complex group of patients, who usually present with increased morbidity and greater need for multiple interventions over time.

ACKNOWLEDGMENTS

The authors thank the International Radiosurgery Research Federation team for helping to coordinate this study.

Abbreviations and Acronyms

GKRS

Gamma Knife radiosurgery

NF2

Neurofibromatosis type 2

PFS

Progression free survival

RANO

Response Assessment in Neuro-Oncology

STROBE

STrengthening the Reporting of OBservational studies in Epidemiology

WHO

World Health Organization

Footnotes

Conflict of interest statement: Roman Liscak serves a consultant for Elekta AB.

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