Milestones in stereotactic radiosurgery for the central nervous system

The current status and shortcomings of stereotactic radiosurgery

Background

Stereotactic radiosurgery (SRS) is a common treatment for intracranial lesions. This work explores the state of SRS treatment delivery to characterize current treatment accuracy based on treatment parameters.

Methods

NCI clinical trials involving SRS rely on an end-to-end treatment delivery on a patient surrogate (credentialing phantom) from the Imaging and Radiation Oncology Core (IROC) to test their treatment accuracy. The results of 1072 SRS phantom irradiations between 2012 and 2020 were retrospectively analyzed. Univariate analysis and random forest models were used to associate irradiation conditions with phantom performance. The following categories were evaluated in terms of how they predicted outcomes: year of irradiation, TPS algorithm, machine model, energy, and delivered field size.

Results

Overall, only 84.6% of irradiations have met the IROC/NCI acceptability criteria. Pass rate has remained constant over time, while dose calculation accuracy has slightly improved. Dose calculation algorithm (P < .001), collimator (P = .024), and field size (P < .001) were statistically significant predictors of pass/fail. Specifically, pencil beam algorithms and cone collimators were more likely to be associated with failing phantom results. Random forest modeling identified the size of the field as the most important factor for passing or failing followed by algorithm.

Conclusion

Constant throughout this retrospective study, approximately 15% of institutions fail to meet IROC/NCI standards for SRS treatment. In current clinical practice, this is particularly associated with smaller fields that yielded less accurate results. There is ongoing need to improve small field dosimetry, beam modeling, and QA to ensure high treatment quality, patient safety, and optimal clinical trials.

The evolution of stereotactic radiosurgery in neurosurgical practice

INTRODUCTION

Stereotactic radiosurgery (SRS) was born in an attempt to treat complex intracranial pathologies in a fashion whereby open surgery would create unnecessary or excessive risk. To create this innovation, it was necessary to harness advances in other fields such as engineering, physics, radiology, and computer science.

METHODS

We review the history of SRS to provide context to today's current state, as well as guide future advancement in the field.

RESULTS

Since time of Lars Leksell, the young Swedish neurosurgeon who pioneered the development of the SRS, the collegial and essential partnership between neurosurgeons, radiation oncologists and physicists has given rise to radiosurgery as a prominent and successful tool in neurosurgical practice.

CONCLUSION

We examine how neurosurgeons have helped foster the SRS evolution and how this evolution has impacted neurosurgical practice as well as that of radiation oncology and neuro-oncology.

Multiplatform Radiosurgery for Intracranial Meningiomas and Dose to the Dural Tail

Introduction

Meningiomas are extra-axial central nervous system tumors. Complete resection is often curative with macroscopically complete removal of the tumor, excision of its dural attachment, and any abnormal bone. Radiosurgery is also an option for high-risk patients or in patients with surgically residual disease. Dural tail is a typical radiological sign on contrast-enhanced MRI; it can contain tumor cells or be a reaction due to vascular congestion and edema. Radiosurgical planning treatment varies regarding the identification and coverage of the dural tail. This study aimed to retrospectively analyze a series of 143 patients with WHO Grade I meningiomas treated with different radiosurgical platforms, and dosing parameters focused on planning and dose delivery to the dural tail.

Methods

From February 2011 to July 2020, 143 patients with histologically confirmed or radiologically assumed WHO Grade I meningiomas were treated using rotating gamma-ray Infini™ (Gamma [MASEP Medical Science Technology Development Co., Shenzhen, China]), TomoTherapy® (Tomo [Accuray Inc., Sunnyvale, CA]), and CyberKnife® (CK [Accuray Inc.]). All plans were retrospectively reviewed to establish the maximum distance (MaxDis) from the prescription dose to the end of the dural tail and the minimum dose at the dural tail (MinDoseT) at this point. We also established the midpoint distance (MPDis) from the prescription dose to MaxDis and the dose at this point (MPDose). Plans were further distinguished when the physician intended to cover the dural tail versus when not. Patients and tumor response were assessed by imaging and clinical and phone call evaluations.

Results

Of the 143 patients, 81 were treated using Gamma, 34 using Tomo, and 28 using CK. Eighty patients were eligible for follow-up, of whom 58 (72.5%) had an unmistakable dural tail sign. Median follow-up was 1,118 days (range 189-3,496), mean age was 54.5 (range 19-90), and 61 were women, and 19 were men. Overall tumor volume was 6.5 cc (range 0.2-59); mean tumor volumes by different platforms were 2.4, 9.45, and 8 cc; dose prescribed and mean tumor coverage were 14 Gy and 92%, 14.5 Gy and 95%, and 14 Gy and 95.75% with Gamma, Tomo, and CK, respectively. The dural tail was drawn and planned with an attempt to treat in 18 patients (31%); the mean MaxDis, MinDoseT, MPDis, and MPDose were 9.0 mm, 2 Gy, 4.5 mm, and 10.6 Gy, respectively. At last follow-up, tumor control was achieved in 96% of patients for the whole series, and there were no statistical variations regarding tumor volume, dose, conformality, or control when stereotactic radiosurgery was used to cover the dural tail versus when it was not (p=0.105). One patient experienced a Grade 4 Radiation Therapy Oncology Group toxicity as an adverse radiation effect that required surgery, and 11 (7.6%) experienced a Grade 1 toxicity.

Conclusions

This is our preliminary report regarding the efficacy of radiosurgery for meningiomas using diverse platforms at three years of follow-up; the results regarding tumor control are in accordance with the published literature as of this writing. A conscious pursuit of the dural tail with the prescription dose has not proven to provide better tumor control than not doing so - even small areas of the tumor uncovered by the prescription dose did not alter tumor control at current follow-up. The doses delivered to these uncovered areas are quite significant; further follow-up is necessary to validate these findings.

Gamma Knife Radiosurgery in Patients with Crooke Cell Adenoma

BACKGROUND

Crooke cell adenoma is a very rare subtype of pituitary neoplasm that is known to be clinically aggressive. These tumors can secrete adrenocorticotropic hormone or may be endocrinologically silent. We evaluated the effect of Gamma Knife radiosurgery (GKRS) on endocrine remission and tumor control.

MATERIALS AND METHODS

This study comprised 5 patients (2 men, 3 women; median age at GKRS, 55 years [range, 21-65 years]) with pathology-confirmed Crooke cell adenoma treated with GKRS at the Gamma Knife Center of the University of Virginia. The median time interval between transsphenoidal resection and GKRS was 5.8 months. The median margin dose was 25 Gy (range, 18-25 Gy). Median treated adenoma volume was 3.12 mL. Median follow-up was 107 months (range, 44-122 months).

RESULTS

Tumor control was achieved in all patients. Three patients achieved endocrine remission at the last follow-up. The median time interval to cortisol normalization when off of anti-hormone secreting medication was 12 months (range, 6-24 months). Newly developed or worsening endocrinopathy occurred in 3 patients at 6, 15, and 18 months, respectively. Cranial nerve III neuropathy developed in 1 patient. Two patients required bilateral adrenalectomy at 44 months and 50 months, respectively, following GKRS.

CONCLUSIONS

GKRS appears to be a safe and reasonably effective treatment option for Crooke cell adenoma. Multicenter studies with larger numbers of patients are needed to verify these findings.

Factors Associated with Treatment Failure and Radiosurgery-Related Edema in WHO Grade 1 and 2 Meningioma Patients Receiving Gamma Knife Radiosurgery

BACKGROUND

Before the advent of radiosurgery, neurosurgical treatment of meningiomas typically involved gross total resection of the mass whenever surgery was deemed possible. Over the past 4 decades, though, Gamma Knife radiosurgery (GKRS) has proved to be an effective, minimally invasive means to control the growth of these tumors. However, the variables associated with treatment failure (regrowth or clinical progression) after GKRS and GKRS-related complications, such as cerebral edema, are less well understood.

METHODS

We retrospectively collected data between 2009 and 2018 for patients who underwent GKRS for meningiomas. After data collection, we performed univariate and multivariable modeling of the factors that predict treatment failure and cerebral edema after GKRS. Hazard ratios (HR) and P values were determined for these variables.

RESULTS

Fifty-two patients were included our analysis. The majority of patients were female (38/52,73%), and nearly all patients presented with a suspected or confirmed World Health Organization grade 1 meningioma (48/52, 92%). The median tumor volume was 3.49 cc (range, 0.22-20.11 cc). Evidence of meningioma progression after treatment developed in 5 patients (10%), with a median time to continued tumor growth of 5.9 months (range, 2.7-18.3 months). In multivariable analysis, patients in whom treatment failed were more likely to be male (HR = 8.42, P = 0.045) and to present with larger tumor volumes (HR = 1.27, P = 0.011). In addition, 5 patients (10%) experienced treatment-related cerebral edema. On univariate analysis, patients who experienced cerebral edema were more likely present with larger tumors (HR = 1.16, P = 0.028).

CONCLUSIONS

Increasing meningioma size and male gender predispose to meningioma progression after treatment with GKRS. Increasing tumor size also predicts the development of postradiosurgery cerebral edema.

Current and novel practice of stereotactic radiosurgery

Stereotactic radiosurgery emerged as a neurosurgical discipline in order to utilize energy for the manipulation of brain or nerve tissue, with the goal of minimal access and safe and effective care of a spectrum of neurosurgical disorders. Perhaps no other branch of neurosurgery has been so disruptive across the entire discipline of brain tumor care, treatment of vascular disorders, and management of functional problems. Radiosurgery is mainstream, supported by thousands of peer-reviewed outcomes reports. This article reviews current practice with a focus on challenges, emerging trends, and areas of investigation.