Radiosurgical Planning of Meningiomas: Compromises with Conformity

Pituitary adenomas

Pituitary adenomas produce a complex collection of disorders. Some are incidental findings. Some distort local anatomical structures which can lead to disorders of vision or hormone production. Some produce excesses of hormones which can be either life threatening or clinically distressing. The management requires the expertise of a variety of experts who plan together. No single treatment is universally successful in controlling these conditions. Medical, biochemical, surgical and radiosurgical management can all have parts to play. Coordinate co-operation between specialists will provide patients with the best available treatment.

Meningiomas

Meningiomas arise in various locations. Convexity tumors are relatively simple to remove. Skull base tumors and tumors adjacent to the major cerebral veins and venous sinuses can be very difficult to extirpate. Attempts at radical resection can lead to serious morbidity. The combination of bulk reduction using microsurgery followed by GKNS gives greatly improved survival and very low morbidity. With smaller tumors, GKNS may be used as the primary treatment. Increasing numbers of asymptomatic meningiomas are demonstrated either as an unexpected finding or as a residual or recurrent tumor after surgery. In all of these situations, GKNS gives a better result than observation or reoperation.

A Retrospective Analysis of the Role of Single-Session Gamma Knife Stereotactic Radiosurgery in Sporadic Vestibular Schwannomas with Tumor Volumes Greater Than 10 cm3: Is It Worth Stretching the Boundaries?

OBJECTIVE

To evaluate the role of single-session Gamma Knife stereotactic radiosurgery (GK-SRS) in the treatment of vestibular schwannomas (VSs) with volumes of greater 10 cm3.

METHODS

A retrospective analysis was performed of 103 patients treated with single-session GK-SRS between 1993 and 2011 with a mean follow-up of 6.2 years ± 4.4 SD. Treatment, clinical and outcome details were recorded and assessed.

RESULTS

Eighty-one (78.6%) patients achieved radiological control with slow progression in a further 5 (4.9%) patients, who did not require further treatment. Linear measurements did not correlate well with volume, which can predict outcome following treatment more precisely. 2.9% of patients developed a new facial paresis, 5.8% trigeminal numbness and 2.9% facial pain. In all, 26 (25.2%) patients who were tested preserved some level of hearing following treatment.

CONCLUSIONS

The overall radiological control rate in this study was 78.6%, while tumor volumes less than 20 cm3 can be safely treated with single-stage GK-SRS with an expected control rate of 83.2% without unacceptable morbidity rates. GK-SRS can be utilized as a first-line treatment option in patients with large-volume VSs especially in whom surgery is unattractive.

Analysis of the results of recurrent intracranial meningiomas treated with re-radiosurgery

OBJECTS

Meningioma is the most common intracranial neoplasm, comprising approximately 30% of all primary intracranial tumors (Claus et al., 2005) [1]. Treatment options include observation, microsurgical resection, stereotactic radiosurgery (SRS), and whole brain radiation therapy (WBRT). Gamma knife radiosurgery (GKRS) is a very effective treatment for intracranial meningiomas; previous studies showed the tumor control rate at 5-10 years of follow-up as 84.3%-100% in all cases (Feigl et al., 2005; Linskey et al., 2005; Malik et al., 2005; Aichholzer et al., 2000; Hakim et al., 1998; Chang and Adler 1997; Lunsford, 1994; Ganz et al., 1993) [2-9]. Many studies have discussed issues like optimal dose, conformal configurations, and adverse effects to improve the treatment result with GKRS (Malik et al., 2005; Kenai et al., 2005; Rowe et al., 2004; Shrieve et al., 2004) [4,10-12]. There are some cases in which the radiosurgery result is unfavorable and perhaps further treatment is needed. In these cases, re-radiosurgery can be an option. However, there have not been comprehensive studies discussing the issues of re-radiosurgery. Therefore, we analyzed the result of re-radiosurgery for recurrent meningiomas and their impact on clinical outcomes.

METHODS

From 1995 to 2015, we retrospectively reviewed 1163 patients who underwent GKRS for intracranial meningioma at the Asan Medical Center. Patients with multiple meningiomas or a follow-up with a period of less than a year were excluded from this study. Finally, 865 patients were enrolled in this study. Clinical symptoms and brain magnetic resonance imaging (MRI) scans were assessed by neurosurgeons. When tumor size increased together with newly developed neurologic symptoms, further management, such as microsurgical resection or SRS, was considered. Histologic analysis of the resected tumors was performed by neuropathologists. Clinical data, including patient's sex, age, and tumor locations were recorded. Treatment data included tumor volume, tumor grade, radiation dose, and presence of edema. Final outcome data including follow-up period, time to progression, interval between first and second radiosurgery courses and interval between microsurgery and radiosurgery were obtained.

RESULTS

Among 865 patients, tumor recurrence was found in 63 patients (7.28%). Seven patients showed transient tumor growth after GKRS. These patients have been under close observation without any further treatments. Fifty-six patients (6.47%) showed permanent tumor growth on follow-up MRI. Thirty-three patients from this group underwent repeated radiosurgery owing to tumor growth, resulting in a re-irradiation rate of 3.82% at our radiosurgery center. The other 23 patients were treated using methods other than re-radiosurgery. Among the 33 patients, 25 underwent microsurgical resection prior to their initial course of GKRS, and the other 8 were treated with re-radiosurgery only. An analysis was performed to determine factors that may have a role in treatment results. Of the many variables, tumor grade (p=0.004, Fisher's exact test) was the only significant factor for progression-free survival (PFS). Thirteen patients with unbiopsied or benign meningioma showed stable tumor size, while there was tumor growth in 8 patients. Among high-grade meningioma patients, 3 and 9 showed stable disease and tumor growth, respectively. As a result of re-radiosurgery, 11 out of 17 patients showed tumor growth and needed further treatments; this involved a third GKRS for 4 patients, microsurgical resection for 6 patients, and cyber knife radiosurgery (CKRS) for 1 patient. Four patients from this group were also treated with WBRT.

CONCLUSION

We analyzed the results of re-radiosurgery for recurrent meningiomas and observed that World Health Organization (WHO) grade II and III was significantly associated with a lower PFS rate compared with low-grade meningiomas (p=0.004). Conversely, patients with benign meningioma or unbiopsied tumors had much better results. Hence, re-radiosurgery is recommended for patients with unknown or benign meningiomas if their first GKRS result is unsatisfactory. However, re-radiosurgery should be considered carefully for recurrent high-grade tumors. Owing to the small number of recurrent meningioma patients treated with re-radiosurgery, further studies are required to delineate the role of this treatment.

The cavernous sinus meningiomas' dilemma: Surgery or stereotactic radiosurgery?

Despite the advances in techniques and technologies, the management of cavernous sinus (CS) meningiomas still remains a challenge for both neurosurgeons and radiation oncologists. On the other hand, the improvement of the anatomical knowledge and the microsurgical techniques together with diffusion of radiosurgery are currently changing the treatment strategy, opening new perspectives to the patients which are suffering from such lesions. The authors reviewed here the literature data. A multidisciplinary treatment algorithm is also proposed.

The relation between various conformity indices and the influence of the target coverage difference in prescription isodose surface on these values in intracranial stereotactic radiosurgery

OBJECTIVE

The purpose of this study was to describe the relation between various frequently used conformity indices (CIs) and to examine the influence of the target coverage (TC) difference in prescription isodose surface (IDS) on these CI values in dynamic conformal arc (DCA) plans.

METHOD

73 plans for simple-shaped brain metastases that were previously characterised for dose distribution with regard to the effect of the target volume (TV) and the depth from the skin surface were reviewed. Three different-definition CI values for each TV were calculated at the 80% IDS, and at D99, D95, D90 and D85, considering the interplanner variability in the TC values for the prescription IDS.

RESULTS

The CI used as the Radiation Therapy Oncology Group criterion showed nearly perfect values at D90. The CI defined in the BrainSCAN (BrainLAB AG, Feldkirchen, Germany) treatment planning system (CI(BS)) denoted lower (superior) values as the TC of the reference IDS decreased. Nakamura's CI (NCI) had lower variability but demonstrated lower (superior) values at D95. NCI showed the most stringent (higher) values at an 80% IDS, but the differences between the plans were less distinct with NCI.

CONCLUSION

The TC difference in IDS chosen for dose prescription or evaluation significantly led to CI value variability in a definition-dependent manner, even when NCI was applied. Definition of the reference IDS at a specific TC value according to clinical situation would reduce the CI value variability to a minimum and would make the CI(BS) sufficient for the objective metric with a perfect value of 1.

Characterisation of dose distribution in linear accelerator-based intracranial stereotactic radiosurgery with the dynamic conformal arc technique: consideration of the optimal method for dose prescription and evaluation

OBJECTIVES

The purpose of this study was to characterise dose distribution in linear accelerator-based intracranial stereotactic radiosurgery using the dynamic conformal arc technique, and to validate the pertinence of dose prescription to the specific percentage isodose surface (IDS).

METHODS

73 plans for brain metastases were reviewed and replanned with a uniform method for target definition and treatment planning.

RESULTS

In all cases except 1 the dose prescription to the 80% IDS satisfied the criteria of the standardised prescription IDS as previously proposed. However, both of the planning target volume (PTV) coverage values for the 80% and 90% IDSs and the PTV D99 and D95 (IDS receiving at least 99% or 95% of the PTV) were inconsistent and significantly increased as a function of the PTV size. The 80% IDS for a PTV of more than 5 cm(3) achieved adequate PTV coverage without a leaf margin. The dose conformity for 80% IDS gradually worsened as the PTV increased, whereas that for the PTV D99 or D95 improved as a function of the PTV size. The addition of a leaf margin attained 100% PTV coverage for 80% IDS, while leading to a poorer dose conformity.

CONCLUSION

The dose prescription to the specific percentage IDS does not necessarily guarantee consistent target coverage, D99 and D95, and desirable dose conformity in proportion to the target volume. The dose prescription and evaluation at the specific target coverage would therefore be preferable as an objective method in order to report the "marginal dose" and to clearly compare the planning parameters with those from other modalities.

Long-term outcomes of stereotactic radiosurgery for treatment of cavernous sinus meningiomas

PURPOSE

Patients with cavernous sinus meningiomas (CSM) have an elevated risk of surgical morbidity and mortality. Recurrence is often observed after partial resection. Stereotactic radiosurgery (SRS), either alone or combined with surgery, represents an important advance in CSM management, but long-term results are lacking.

METHODS AND MATERIALS

A total of 88 CSM patients, treated from January 1991 to December 2005, were retrospectively reviewed. The mean follow-up was 86.8 months (range, 17.1-179.4 months). Among the patients, 22 were followed for more than 10 years. There was a female predominance (84.1%). The age varied from 16 to 90 years (mean, 51.6). In all, 47 patients (53.4%) received SRS alone, and 41 patients (46.6%) had undergone surgery before SRS. A dose of 14 Gy was prescribed to isodose curves from 50% to 90%. In 25 patients (28.4%), as a result of the proximity to organs at risk, the prescribed dose did not completely cover the target.

RESULTS

After SRS, 65 (73.8%) patients presented with tumor volume reduction; 14 (15.9%) remained stable, and 9 (10.2%) had tumor progression. The progression-free survival was 92.5% at 5 years, and 82.5% at 10 years. Age, sex, maximal diameter of the treated tumor, previous surgery, and complete target coverage did not show significant associations with prognosis. Among the 88 treated patients, 17 experienced morbidity that was related to SRS, and 6 of these patients spontaneously recovered.

CONCLUSIONS

SRS is an effective and safe treatment for CSM, feasible either in the primary or the postsurgical setting. Incomplete coverage of the target did not worsen outcomes. More than 80% of the patients remained free of disease progression during long-term follow-up.

The use of stereotactic radiosurgery in the management of meningiomas

This is a systematic review of a consecutive series of 309 meningiomas treated with gamma knife stereotactic radiosurgery between 1994 and 2000. There was an extreme selection bias towards lesions unfavourable for surgery, determined by the patients referred for treatment: 70% of tumours involved the skull base, 47% specifically the cavernous sinus: 15% of patients had multiple meningiomatosis or type 2 neurofibromatosis. Tumour histology was the main determinant of growth control (p < 0.001), the 5-year actuarial control rates being 87% for typical meningiomas, 49% for atypical tumours and 0% for malignant lesions. Complications from radiosurgery were rare, occurring in 3% of tumours, and were most frequently trigeminal and eye movement disturbances treating cavernous sinus meningiomas. Given the problems inherent in managing these tumours, radiosurgery is a valuable strategy and adjuvant treatment for these meningiomas.

Prediction of intracranial edema after radiosurgery of meningiomas

OBJECT

This study was focused on the development of models with which to predict the occurrence of intracranial edema after Gamma Knife surgery (GKS) of meningiomas, based on clinical and imaging data collected in a large group of patients.

METHODS

Data in 368 patients with 381 meningiomas treated using the Leksell Gamma Knife unit were analyzed. Follow up of more than 24 months was available in 331 patients (90%); this time period ranged from 24 to 120 months (median 51 months). The actuarial tumor control rate was 97.9% at 5 years. Perilesional edema after GKS was radiologically confirmed in 51 patients (15.4%) and 32 of them (9.7%) were symptomatic; symptoms were temporary in 23 (6.9%) and permanent in nine (2.7%). Ten different factors were proposed as potential predictors for the occurrence of the intracranial edema after GKS: patient's sex, patient's age, previous surgery, edema before GKS treatment, lobulated margin of meningioma, heterogeneous appearance of the tumor, tumor volume, tumor location, maximum dose to the tumor, and dose to the tumor margin. To identify factors having influence on edema occurrence, univariate and multivariate statistical analyses were performed. There was a significant difference in the incidence of edema for different patient age groups and a significantly higher incidence of edema occurrence in patients in whom no surgical procedure was performed before GKS, those with edema present before GKS, those with a tumor volume larger than 10 cm3, those in whom the tumor was located in the anterior fossa, those in whom the maximum dose to the tumor was higher than 30 Gy, and for different tumor margin doses. A binary logistic regression multifactorial prediction model was used to identify the following significant factors to predict of edema occurrence after GKS: previous surgery, edema before the treatment, tumor volume, tumor location, and tumor margin dose.

CONCLUSIONS

Based on these models estimates of the occurrence of edema after the GKS can be made, and consequently treatment parameters can be adjusted to reduce the occurrence of edema. These results may provide grounds for additional patient care such as more frequent follow up or possibly administration of steroids.

Gamma Knife surgery for benign meningioma

Object

Meningioma is the most frequent benign tumor treated with Gamma Knife surgery (GKS); however, the assessment of its efficacy and safety in slow-growing tumors is an ongoing process, requiring analysis of long-term results.

Methods

Three hundred sixty-eight patients harboring 400 meningiomas treated between 1992 and 1999 at Na Homolce Hospital were evaluated. The median patient age was 57 years (range 18–84 years). The median tumor volume was 4.4 cm3 (range 0.11–44.9 cm3). The median tumor margin dose to the 50% isodose line was 12.55 Gy (range 6.5–24 Gy). Descriptive analysis was performed in 331 patients (90%); 325 patients had a follow-up longer than 24 months (median 60 months), and six patients were included because of posttreatment complications. The volume of treated tumors decreased in 248 cases (69.7%), remained the same in 99 (27.8%), and increased in nine (2.5%). The actuarial tumor control rate was 97.9% at 5 years post-GKS. Perilesional edema after radiosurgery was confirmed on neuroim-aging in 51 patients (15.4%). The temporary and permanent morbidity rates after radiosurgery were 10.2 and 5.7%, respectively.

Results

A significantly higher incidence of tumor volume increase was observed in men compared with women and in tumors treated with a margin dose lower than 12 Gy. Significant risk factors for edema included an age greater than 60 years, no previous surgery, perilesional edema before radiosurgery, a tumor volume greater than 10 cm3, a tumor location in the anterior fossa, and a margin dose greater than 16 Gy.

Conclusions

Stereotactic radiosurgery is a safe method of treatment for meningiomas. A minimum margin dose of 12 to 16 Gy seems to represent the therapeutic window for benign meningiomas with a high tumor control rate in a mid-term follow-up period.

Meningioma

Total excision is an appropriate treatment option for patients with benign meningiomas that are resectable with minimal morbidity. It is particularly appropriate for patients with significant mass effect causing symptoms. Fractionated conformal radiotherapy is an appropriate primary treatment option for patients with benign meningiomas of all sizes and all sites. It is particularly appropriate and preferred for optic nerve sheath meningiomas, for which there are few alternatives. Planned subtotal resection is appropriate if decompression is expected to relieve acute symptoms. After subtotal resection, it is appropriate to offer single-fraction radiosurgery or multifraction radiotherapy, depending on the size, location, and extent of residual tumor, so as to achieve progression-free survival and cause-specific survival rates comparable to those of other approaches.