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60 Cases with Vestibular Schwannoma (AN)

2019-08-26 11:55

Analysis of Follow up of 60 Cases with Vestibular Schwannoma (Acoustic Neuroma AN) Treated by Gamma system (GK) Radiosurgery

Yu Xiaoping, Yao Jianguo,Ling Tong, Zhang Fuji, Liu Liyu

From Gamma system Center of the First Affiliated Hospital of Jinan University (510630), from gamma system center of Jiangxi medical college

[Outline] Objective: To analyze the factors determining the effectiveness of treatment of AN using gamma system.

Methods: A retrospective review of 60 consecutive patients treated for acoustic neuromas with a follow up of mean over 2 years.

Results: A tumor control rate of 91% was achieved, rate of ineffectiveness was 9%, rate with complication was 22%, and gamma system was a safe and successful method to manage patients with small-sized AN and no signs of brain-stem compression and severe high intracerebral pression.

Conclusion: 1. Outcome of patients with small sized AV treated by gamma system is absolute positive, better effectiveness proportionable for smaller size of AV; 2. Peripheral dose (range 12 to 15 GY) is effective and Trigeminal nerve, facial nerve and acoustic nerve function could be preserved well; 3. Over 40% isodose contour matched to the margin of the tumor and isocentres application made effectiveness better and less complications; 4. The over 2 years follow up make positive outcome of patients more clear

Analysis of Follow up of 60 Cases with Vestibular Schwannoma (Acoustic Neuroma AN) Treated by Gamma system (GK) Radiosurgery

Clinic Materials

Between December 1998 and November 2003, 60 patients with acoustic neuromas were treated in our center with gamma system and followed. The mean follow-up period after radiosurgery was 24 months (range 1 month to 48 months).There were 35 women and 25 men in the group, the mean age at treatment being 48 years (range 24 to 74).13 patients were being treated for residual or recurrent disease who had previously undergone surgery for the acoustic neuroma. There were 3 cases with bilateral tumor, one case complicated with pituitary adenomas and 2 cases complicated with intracranial meningiomas. In this series a mean peripheral dose was 12 Gy (range 9 to 15 GY), a mean center dose was 42GY (range 24 to 60GY), a mean 42.5% (range 30% to 55%) isodose contour is matched to the margin of the tumor, a mean number of isocentres used was 5.5(range 2 to 9), the dose of facial never irradiation did not exceed 12GY. Preoperative diagnosis was based on the following factors: 1.clinical presentations and signs: dizziness, tinnitus, durative reduction in hearing, gait imbalance and unilateral facial numbness or paralysis; 2.Image examination: MRI and CT; 3.pathohistological proof after surgery.


According to the latest CT or MRI image, in all patients, stereotactic radiosurgery was performed with a gamma system (MASEP, CHINA). Performed with use of local anesthesia, the procedure consists of fixing the Masep stereotactic frame to the patient抯 head and acquiring radiological images with the stereotactic localiser in place. Currently our planning is largely based on gadolinium enhanced T1 weighted volumetric 1.5MRI scans, transverse slice scan with 2cm consecutively. The number of isocentres and the dose planning was calculated on Y-Plan software.

Clinic results

Criterion for effectiveness evaluation:

1. Significantly effective: MRI demonstrated volume of tumor significantly decreased and symptoms of patients ameliorated

2. Effective: MRI demonstrated volume of tumors decreased but with tumor center obvious necrosis and symptoms of patients ameliorated

3. Ineffective: MRI demonstrated volume of tumors enlarged or symptoms of patients deteriorated

Of 60 patients, there were 9 (15%) significantly effective cases, 45 effective patients, and 6 ineffective cases.. of 60 patients, 7(12%) experienced transitory facial paralysis,5 (8.3%) experienced facial numbness or hyperaesthesia, 1 (1.7%) patients experienced acute irradiation reaction. Total rates of complication for radiosurgery were 22%. Of 60 patients, 18 (47%) were completely unilateral deaf before radiosurgery and no recovery after radiosurgery, another 13 cases experienced variety hearing loss. Total rate of hearing reduction was 52%. From data of table 2 we could tell that volume of significantly effective cases was small and their follow up time exceeded 2 years. In effective cases, 2 months after radiosurgery non-enhanced image in tumor center( tumor necrosis) could be demonstrated by gadolinium enhanced MRI and symptoms and signs such as dizziness, tinnitus gait imbalance gradually ameliorated.2 to 3 years postoperatively, MRI showed low-density image of tumor but no volume changes. In ineffective cases, volume of tumor is almost 30cm3, volume of three cases were larger than 30cm3, one was 27.2cm3 and one was 26.8cm3. Of ineffective cases, 2 patients underwent transcranial surgery resection, 1 patient experienced shunting operation and 3 patients were given conservation therapy. All of the 6 patients deteriorated because of high intracranial pressure (ICP) and brain-stem compression induced by enlargements of tumor volume. Resection surgery showed tumor necrosis: snuffcolored, soft and little hemorrhage in parenchyma. Pathohistology showed tumor cells components decreased, tumor was filled with collagenous tissue and small vascular occluded with thrombosis. Transitory facial palsy and facial numbnesses ordinarily presented 1 month later postoperatively and they recovered half or a year later. All cases involved in 12 to 14 periphery dose experienced transitory facial palsy and facial numbnesses.

Table 1. Clinical results of recent series of acoustic neuromas treated with either gamma system or microsurgery resection (GK: gamma system, MSR: microsurgery resection)
Our unit
Number of patient
Peripheral dose (GY)
Follow up (months)
Rate of tumor control (%)
Rate of facial paralysis (%)
Rate of hearing reduction (%)
Table 2. AN volume and effectiveness of gamma system therapy for AN
Number of niduses
Significant effective
Table3. Peripheral dose contour and effectiveness of gamma system therapy for AN
Peripheral dose contour
Number of patients
Significant effective
Facial paralysis and numbness


1. From data in table 1, the effectiveness of treatments for ANs using gamma system was definitively positive at lower risk with postoperative complications than microsurgery resection. The paramount factor determining outcome of AN patients treated by gamma system we thought was the size of tumor. According to the data in table 1, the smaller size of tumor the higher rate of significant effectiveness vice versa; especially when the volume of tumor was larger than 30cm3 or bad high ICP and brain-stem compression induced by tumor was presented gamma system radiosurgery could not help to ameliorate these presentations and make tumor necrosis or shrinkage effectively. Of ineffective cases, symptoms and signs of 3 patients with tumor volume larger than 30cm3 deteriorated postoperatively and further therapy is a must for them. So we recommend that gamma system was not alternative for AN when volume of tumor was larger than 30cm3 or high ICP and brain-stem compression induced by tumor had been presented.

2. From data in table1,Of our center cases, periphery dose was 12 to 15 GY except for two older age cases with 9 and 10GY ; compared with the other gamma system center this periphery dose was best for gamma system therapy with good outcome and low risk at complication. So we thought 12 to 15GY of periphery dose are safe and effective and lower than 12GY would be suitable for facial and Trigeminal nerves.

3. From data in table3, different percent of isodose contour matched to the margin of the tumor made outcome very different, over 40% isodose contour matched to the margin of the tumor could achieve better effectiveness than below 40% and less complication. With meticulous targeting, using multiple small isocenters of irradiation, with small caliber Linac to make dose curve more sharp and more uniform dose around target outcome could be better

4. Non-enhanced image in tumor center could be presented on MRI only after radiosurgery therapy 1 to 3 months later, but in data of our center 9 significant effective cases were followed over 2 years with high rate of tumor control and symptomatic amelioration; however none of them showed significant effectiveness in 1 to 3 months. So we thought objective evaluation of gamma system radiosugury for AN was determined also by period of follow up, the longer period of follow up the more powerful conclusion for gamma system. Tumor reaction could be detected after operation 6 months for the first time follow up.

5. Finally we reviewed the tumor reaction after gamma system radiosurgery: tumor began to necroses in its center, developed a cyst and presented non-enhanced image phenomena, then collagen content proliferated and tumor shrinkage was followed by cicatrisation. According to MRI, non-enhanced image presented in1-3 months later after radiosurgery, tumor shrinkage presented in 1.5 to 2 years later after radiosurgery and there were no quantitative relationship in shrinkage procedure. In some lager size tumor, previous high ICP and brain-stem compression deteriorated because of the enlargement of cyst formation so patients need further treatment such as microsurgery resection persistent dehydration therapy. From pathohistological data, AN was a benign and it was prone to develop delayed necrosis after radiosurgery whose mechanism went as follow: primary tumorous reaction ( in high dose center, tumor necrosesed because of cellular necrosis, tumor cell proliferation in low-dose areas was inhibited because of damage to tumor chromosomes and cellar organs) and secondary tumor vascular reaction( in therapy areas, vascular endothelial cell reaction: proliferation, hyaline degeneration, coagulation and final thrombosis.)


In principle, for the small size AN without high ICP and brain-stem compression gamma system radiosurgery was safe and effective, including residual or recurrent disease after microsurgery resection. The smaller size of tumor the higher rate of tumor control. The size of tumor lager than 30cm3 or amount to 30cm3 gamma system for AN must be carefully weighed. With pleasing rate of tumor control and low rate of complications periphery dose 12 to 15GY is safe for patient. With sharp dose gradient and isodose distribution gamma system could achieve pleasing outcome at low rate of complications such as facial numbness and facial paralysis. The longer period of follow up the more objective and reliable evaluation of gamma system for AN. So the factors determining the effectiveness of treatment of AN using gamma system went as follow: size, irradiation dose, dose distribution, and period of follow up.

60 Cases with Vestibular Schwannoma (AN)
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