Fractionated radiation therapy for vestibular schwannoma

Fluorescent Detection of Vestibular Schwannoma Using Intravenous Sodium Fluorescein In Vivo

BACKGROUND

Vestibular schwannoma (VS) are intracranial tumors caused by merlin deficiency. Sodium fluorescein (SF) is a fluorescent compound that accumulates in various intracranial tumors, causing tumors to emit green fluorescence after blue light excitation.

HYPOTHESIS

Intravenous SF preferentially deposits in VS, helping surgeons differentiate tumor from surrounding tissue.

METHODS

Merlin-deficient Schwann cells were grafted onto cochleovestibular nerves of immunodeficient rats. Rats were randomized to receive SF (7.5 mg/kg; n = 5) or saline (n = 3). Tissues were harvested at 1 hour and photographed in white and blue light. Sixteen surgeons identified and marked the tumor-tissue interfaces on images. Fluorescence was measured on tissue specimens using the IVIS imaging system and on tissue cross-sections obtained with confocal microscopy. Western blot was performed to measure levels of organic anion transporting polypeptide (OATP), a drug transporter specific for SF.

RESULTS

Under blue light, tumors from SF rats demonstrated bright green fluorescence under direct visualization, higher fluorescence measurements on tissue specimens (p < 0.001), and more SF deposition on tissue cross-sections (p < 0.001), when compared with surrounding tissues and placebo rats. Surgeons were better able to distinguish the tumor-tissue interfaces in SF rats. Furthermore, the expression level of OATP1C1 was significantly higher in tumors than in surrounding tissues (p < 0.0001).

CONCLUSION

In a xenograft model of VS, intravenous SF preferentially deposits in tumors, compared with normal surrounding tissue. Under blue light, tumors emit an intense green fluorescence that can help surgeons differentiate tumor from critical structures nearby, which may improve clinical outcomes in complicated VS surgery.

Outcomes of stereotactic radiosurgery for large vestibular schwannomas: a systematic review and meta-analysis

Background

Large vestibular schwannomas (VS) pose a treatment challenge for both microsurgery (MS) and stereotactic radiosurgery (SRS). Technical developments have allowed for safer irradiation of large tumors. It remains unclear if SRS can achieve appropriate tumor control and acceptable cranial nerve toxicities. In this study, we assess outcomes of irradiation for large VS.

Methods

PubMed MEDLINE, EMBASE, Web of Science, and Cochrane were searched for all the studies assessing SRS outcome in large VS. Primary endpoints included clinical and radiographic tumor control, need for salvage surgery, serviceable hearing, cranial nerve V and VII impairment, presence of hydrocephalus requiring shunting, and presence of vertigo/dizziness.

Results

Twenty-two studies were identified that met selection criteria for analysis from an initial pool of 1272 reports. They were evaluated according to treatment protocol: 1) single-dose SRS (13 studies, 483 patients), 2) combination of MS and SRS (7 studies, 182 patients), and 3) fractionated SRS (3 studies, 82 patients). Tumor control was achieved in 89%, 94%, and 91% of patients, respectively. Odds ratios (ORs) of post- over pretreatment serviceable hearing were 0.42 (P < .01), 0.47 (P = .05), and 0.60 (P = .22); for facial nerve impairment, these ORs were 1.08 (P = .69), 3.45 (P = .28), and 0.87 (P = .71), respectively.

Conclusions

The management of large VS remains challenging. All treatment modalities resulted in high tumor control rates and worsening of pretreatment hearing. None, however, caused significant facial nerve impairment, suggesting that management strategies incorporating focal irradiation can be successful.

Tumor Microenvironment-Regulated and Reported Nanoparticles for Overcoming the Self-Confinement of Multiple Photodynamic Therapy

The efficiency of photodynamic therapy (PDT) highly depends on the tumor oxygenation state. However, PDT itself can not only cause oxygen depletion but also prevent oxygen supply in tumors. Such self-confinement effect significantly limits the efficacy of PDT, especially fractionated PDT (fPDT). Herein, we proposed a multifunctional nanoparticle system having a four-pronged pipelined therapeutic scheme to address this issue. It performed in situ oxygen supply and tumor microenvironment modulation together to effectively maintain tumor oxygenation even after multiple PDT fractions. It also introduced a new photosensitizer that not only was highly efficient in producing ROS but also could visually report tumor oxygenation state in a real-time fashion. All these functions were integrated into a single nanoparticulate system to obtain pipeline-style teamwork, which was then applied for the fPDT on a mice tumor model, and achieved significantly better tumor oxygenation even after multiple PDT fractions, ending up with a better tumor inhibition efficiency.

Usefulness of High Resolution T2-Weighted Images in the Evaluation and Surveillance of Vestibular Schwannomas? Is Gadolinium Needed?

OBJECTIVES

First aim of study was to compare the diagnostic accuracy of high resolution T2-WI (HRT2-WI) and gadolinium-enhanced T1-weighted image (Gd T1-WI) sequences in quantitative evaluation of vestibular schwannomas (VS). The second one was to determine through qualitative evaluation when Gd-injection should be recommended.

METHODS

Two observers in consensus retrospectively reviewed 137 magnetic resonance imaging (MRI) scans of patients with histological diagnosis of VS (33 women, 26 men), 116 with both HRT2-WI and Gd T1-WI. The examinations were subdivided in: surveillance (10), pretreatment (30), posttreatment (43), and posttreatment follow-up (33) studies. Quantitative evaluation was based on size measurement of the lesion. Structural details of the lesion, facial nerve course, and involvement of the fundus of the internal auditory canal were assessed for the qualitative evaluation in both sequences.

RESULTS

No statistically significant changes were demonstrated between size measurement in the HRT2-WI and Gd T1-WI (p = 0.329). Sensitivity, specificity, and accuracy of HRT2-WI in the detection of lesional size were 90.4, 98.9, 92.5%, respectively. HRT2-WI was worse for characterization of structural details in pretreatment, posttreatment, and posttreatment follow-up examinations. HRT2-WI showed better or equal capability for all the groups in the demonstration of the facial nerve course. In the evaluation of the involvement of the fundus of the internal auditory canal, HRT2-WI showed worse results or had a complementary role for the posttreatment and posttreatment follow-up groups, while in the other groups was considered mainly equal or complementary. Only in the surveillance group, HRT2-WI was never worse for all the criteria.

CONCLUSION

Results for quantitative evaluation were similar in both the sequences. Gadolinium injection can be avoided only in surveillance studies.

Local experience with radiosurgery for vestibular schwannomas and recommendations for management

INTRODUCTION

There are many treatment options for vestibular schwannomas (VSs), including radiosurgery. Previous studies have shown good outcomes for smaller tumours. We report the results of a seven-year cohort of patients with VS who were treated at our centre using a linear accelerator-based stereotactic radiosurgery system.

METHODS

We retrospectively reviewed the case notes and magnetic resonance (MR) images of patients with VS treated with radiosurgery. Treatment was administered as either a single 13 Gy session or 25 Gy in five sessions. At our centre, only larger or higher Koos grade VSs, were routinely treated with hypofractionated radiosurgery. Tumour response and hearing were assessed using RECIST criteria and Gardner-Robertson scale, respectively. Other toxicities were assessed using physical examination and history-taking. Freedom from radiological progression was estimated with the Kaplan-Meier method.

RESULTS

46 patients received single-fraction radiosurgery and 31 received hypofractionated radiosurgery. Median follow-up duration was 40.6 months. 29 patients had prior surgery to remove the tumour (median size 1.68 cm3). One patient who had symptomatic increase in tumour size (> 20% in largest diameter) was treated conservatively and subsequently showed stable disease on MR imaging. Progression-free survival was 98.7%. Another patient had symptomatic oedema requiring ventriculoperitoneal shunt insertion. 11 patients had serviceable hearing before radiotherapy and 72.7% of them retained useful hearing (20.1 dB mean decline in pure tone average). Facial and trigeminal nerve functions and sense of equilibrium were preserved in > 90% of patients.

CONCLUSION

Radiosurgery is effective and safe for small VSs or as an adjunct therapy after microsurgery.

Stereotactic radiotherapy in three weekly fractions for the management of vestibular schwannomas

PURPOSE

This study evaluates the rates of tumor control, hearing preservation and cranial nerve toxicity with the use of CyberKnife stereotactic radiotherapy consisting of 2100 cGy to the 80% isodose line delivered in three weekly fractions to treat vestibular schwannomas.

MATERIALS AND METHODS

Retrospective chart review of vestibular schwannoma patients treated with CyberKnife stereotactic radiotherapy or undergoing watchful waiting between 2006 and 2017 was performed. For inclusion, patients receiving CyberKnife stereotactic radiotherapy must have had pretreatment magnetic resonance imaging and audiography, and 2 follow-up magnetic resonance imaging and audiograms. Watchful waiting patients must have had a minimum of 2 magnetic resonance imaging and 2 audiograms.

RESULTS

Forty patients met inclusion criteria. Twenty-two underwent CyberKnife stereotactic radiotherapy. Eighteen remain in watchful waiting. Crude tumor control was 86.4% at mean radiographic follow-up of 52.3 months. Kaplan-Meier progression-free survival was 76.9% at 5 years. Kaplan-Meier survival from radiographic growth was 61.5% at 5 years. Kaplan-Meier hearing preservation was 17.5% at 5 years. All patients undergoing watchful waiting presenting with serviceable hearing maintained serviceable hearing. Serviceable hearing among CyberKnife stereotactic radiotherapy patients was 42.9% prior to treatment and 14.2% through mean follow-up of 53.7 months. One patient experienced trigeminal nerve toxicity 45 months after SRT. 95.5% of CyberKnife stereotactic radiotherapy patients were complication-free.

CONCLUSIONS

Our fractionation regimen provides tumor control consistent with current literature. Hearing outcomes, however, should be discussed with patients prior to CyberKnife stereotactic radiotherapy.

Adaptive Hybrid Surgery: Paradigm Shift for Patient-centered Neurosurgery

The surgical management of cerebral and skull base lesions has evolved greatly in the last few decades. Still, a complete resection of lesions abutting critical neurovascular structures carries significant morbidity. Stereotactic radiosurgery (SRS) has emerged as an increasingly accepted treatment option. Minimally invasive, SRS results in excellent tumor control and low complication rates in patients with moderate-size tumors. The management of large cerebral and skull base tumors remains a formidable challenge. In such large tumors, radical surgical extirpation offers a significantly higher risk of neurological deficit, and SRS alone cannot be used because of the elevated incidence of radiation-induced complications known to be associated with large-volume tumors. With increasing treatment volumes, SRS-associated tumor control rates decrease and complication rates increase. Planned subtotal resection (STR) with adjuvant SRS (adaptive hybrid surgery [AHS]) has gained increasing interest in recent years as a multimodal approach. In AHS, a planned STR (aimed at decreasing surgical morbidity) followed by SRS to a preplanned residual tumor aids in harnessing advantages offered by both approaches. Although intuitive and reasonable, this paradigm shift from maximal resection at all cost has not been adopted widely. Combining open microsurgery with SRS requires a good understanding of both surgical and SRS modalities and their respective safety-efficacy features. We present a review and discussion on AHS as a modern, multidisciplinary treatment approach. Available data and views are discussed for vestibular schwannoma (VS) as a sample tumor. Other indications for AHS are mentioned in brief.

Planned Subtotal Resection of Vestibular Schwannoma Differs from the Ideal Radiosurgical Target Defined by Adaptive Hybrid Surgery

OBJECTIVE

To retrospectively compare ideal radiosurgical target volumes defined by a manual method (surgeon) to those determined by Adaptive Hybrid Surgery (AHS) operative planning software in 7 patients with vestibular schwannoma (VS).

METHODS

Four attending surgeons (3 neurosurgeons and 1 ear, nose, and throat surgeon) manually contoured planned residual tumors volumes for 7 consecutive patients with VS. Next, the AHS software determined the ideal radiosurgical target volumes based on a specified radiotherapy plan. Our primary measure was the difference between the average planned residual tumor volumes and the ideal radiosurgical target volumes defined by AHS (dRV_AHS-planned).

RESULTS

We included 7 consecutive patients with VS in this study. The planned residual tumor volumes were smaller than the ideal radiosurgical target volumes defined by AHS (1.6 vs. 4.5 cm³, P = 0.004). On average, the actual post-operative residual tumor volumes were smaller than the ideal radiosurgical target volumes defined by AHS (2.2 cm³ vs. 4.5 cm³; P = 0.02). The average difference between the ideal radiosurgical target volume defined by AHS and the planned residual tumor volume (dRV_AHS-planned) was 2.9 ± 1.7 cm³, and we observed a trend toward larger dRV_AHS-planned in patients who lost serviceable facial nerve function compared with patients who maintained serviceable facial nerve function (4.7 cm³ vs. 1.9 cm³; P = 0.06).

CONCLUSIONS

Planned subtotal resection of VS diverges from the ideal radiosurgical target defined by AHS, but whether that influences clinical outcomes is unclear.

Long-term beneficial outcome of fractionated stereotactic radiotherapy for smaller and larger vestibular schwannomas

Background and purpose

Fractionated stereotactic radiotherapy (FSRT) is an alternative treatment for large vestibular schwannomas (VS), if patients are not fit for or refuse surgery. In this study, we compared long-term clinical and radiological outcome in both small–medium sized and larger tumours.

Material and methods

A retrospective study was performed of patients with sporadic VS who underwent primarily conventional FSRT. In total, 50 consecutive patients were divided into two groups by volume. Clinical and volumetric parameters were analysed.

Results

In all, 41 patients (82%) had large tumours affecting the 4thventricle (modified Koos stage 4). Definitive expansion of VS occurred in eight out of 50 patients (16%). After 7·2 years (median) the overall freedom from clinical failure was 100% in smaller and 92% in larger schwannomas (arbitrarily sized >7·4 cc). Useful hearing was preserved in only 35% of the patients. The facial nerve remained intact in all cases, while new deficit of the trigeminal nerve occurred in 20% of the cases. Of the larger tumours 20% needed a cerebrospinal fluid (CSF) shunt.

Conclusions

FSRT is a treatment in its own right as it is highly effective in both smaller and larger VS without causing permanent disabling complications. The outcome is beneficial also in larger tumours that affect the 4thventricle.

Vestibular Schwannomas Treated with Cyberknife®: Clinical Outcomes

Purpose

Fractionated stereotactic radiotherapy (FSR) is a recognized treatment for vestibular schwannomas (VS). This study's aim is to present clinical outcomes and local control (LC) results for patients with VS treated with FSR using the Cyberknife® (CK) in 2 French cancer centers.

Methods

Patients treated with FSR for VS between 2007 and 2012 were retrospectively analyzed. Local control was determined using follow-up MRI. The hearing preservation (HP) rate was determined by analyzing pretreatment and posttreatment audiograms.

Results

Forty patients were treated for VS with the CK in both centers. The mean maximal VS dimension was 18.3 mm (range 3–30). The median follow-up was 36 months and the LC was 97% at 3 years of follow-up and 89% after 5 years. The HP rate was 83% and no facial nerve impairment was reported.

Conclusions

Our results in terms of LC and HP rate are congruent with similar studies that use the CK to treat VS. It appears that the CK is safe and efficient in VS management even for large lesions. Further studies with larger cohorts are warranted.

Perfusion magnetic resonance imaging provides additional information as compared to anatomical imaging for decision-making in vestibular schwannoma

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DSC/ASL-MRI can be acquired in growing VS with sufficient image quality.

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In most patients DSC and ASL techniques provide similar qualitative scores.

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These techniques can be of importance in future decision-making.

Objective

The added value of perfusion MRI for decision-making in vestibular schwannoma (VS) patients is unknown. MRI offers two perfusion methods: the first employing contrast agent (dynamic susceptibility contrast (DSC)-MRI) that provides information on cerebral blood volume (CBV) and cerebral blood flow (CBF), the second by magnetic labeling of blood (arterial spin labeling (ASL)-MRI), providing CBF-images. The goal of the current study is to investigate whether DSC and ASL perfusion MRI provides complimentary information to current anatomical imaging in treatment selection process of VS.

Methods

Nine patients with growing VS with extrameatal diameter >9 mm were included (>2 mm/year and 20% volume expansion/year) and one patient with 23 mm extrameatal VS without growth. DSC and ASL perfusion MRI were obtained on 3 T MRI. Perfusion in VS was scored as hyperintense, hypointense or isointense compared to the contralateral region.

Results

Seven patients showed hyperintense signal on DSC and ASL sequences. Three patients showed iso- or hypointense signal on at least one perfusion map (1 patient hypointense on both DSC-MRI and ASL; 1 patient isointense on DSC-CBF; 1 patient isointense on ASL). All patients showed enhancement on post-contrast T1 anatomical scan.

Conclusion

Perfusion MR provides additional information compared to anatomical imaging for decision-making in VS.

Fractionated stereotactic radiotherapy of benign skull-base tumors: a dosimetric comparison of volumetric modulated arc therapy with Rapidarc® versus non-coplanar dynamic arcs

Background

Benign tumors of the skull base are a challenge when delivering radiotherapy. An appropriate choice of radiation technique may significantly improve the patient’s outcomes. Our study aimed to compare the dosimetric results of fractionated stereotactic radiotherapy between non-coplanar dynamic arcs and coplanar volumetric modulated arctherapy (Rapidarc®).

Methods

Thirteen patients treated with Novalis TX® were analysed: six vestibular schwannomas, four pituitary adenomas and three meningioma. Two treatment plans were created for each case: dynamic arcs (4–5 non coplanar arcs) and Rapidarc® (2 coplanar arcs). All tumors were >3 cm and accessible to both techniques. Patients had a stereotactic facemask (Brainlab) and were daily repositioned by Exactrac®. GTV and CTV were contoured according to tumor type. A 1-mm margin was added to the CTV to obtain PTV. Radiation doses were 52.2–54 Gy, using 1.8 Gy per fraction. Treatment time was faster with Rapidarc®.

Results

The mean PTV V95 % was 98.8 for Rapidarc® and 95.9 % for DA (p = 0.09). Homogeneity index was better with Rapidarc®: 0.06 vs. 0.09 (p = 0.01). Higher conformity index values were obtained with Rapidarc®: 75.2 vs. 67.9 % (p = 0.04). The volume of healthy brain that received a high dose (V90 %) was 0.7 % using Rapidarc® vs. 1.4 % with dynamic arcs (p = 0.05). Rapidarc® and dynamic arcs gave, respectively, a mean D40 % of 10.5 vs. 18.1 Gy (p = 0.005) for the hippocampus and a Dmean of 25.4 vs. 35.3 Gy (p = 0.008) for the ipsilateral cochlea. Low-dose delivery with Rapidarc® and dynamic arcs were, respectively, 184 vs. 166 cm³ for V20 Gy (p = 0.14) and 1265 vs. 1056 cm³ for V5 Gy (p = 0.67).

Conclusions

Fractionated stereotactic radiotherapy using Rapidarc® for large benign tumors of the skull base provided target volume coverage that was at least equal to that of dynamics arcs, with better conformity and homogeneity and faster treatment time. Rapidarc® also offered better sparing of the ipsilateral cochlea and hippocampus. Low-dose delivery were similar between both techniques.