الفهرس 
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Abstract
Stereotactic Radiosurgery (SRS) is a distinct discipline that utilizes externally generated ionizing radiation in certain cases to inactivate or eradicate (a) defined target(s) in the head or spine without the need to make an incision. The target is defined by high-resolution stereotactic imaging. To assure quality of patient care the procedure involves a multidisciplinary team consisting of a neurosurgeon, radiation oncologist, and medical physicist.
Stereotactic Radiosurgery (SRS) typically is performed in a single session, using a rigidly attached stereotactic guiding device, other immobilization technology and/or stereotactic image-guidance system, but can be performed in a limited number of sessions, up to a maximum of five. Technologies that are used to perform SRS include linear accelerators, particle beam accelerators, and multisource Cobalt 60 units. In order to enhance precision, various devices may incorporate robotics and real time imaging. Stereotactic radiosurgery can be applied used frame based techniques or frameless radiosurgery. Frameless radiosurgery technique enables the application of hypofractionated SRS.
Stereotactic radiosurgery (SRS) has been approved as an effective treatment for skull base tumors. Radiosurgery can be used as a definitive a primary treatment especially for small to moderately sized lesions particularly if the surgical resection is not feasible, for medically infirm patients, or on patients’ preference. Radiosurgery can be used also as an adjuvant therapy for residual lesions, or as a salvage treatment for recurrent tumors.
The role of SRS in skull base tumors treatment is to control the exponential tumor growth, rather than eradicating the lesion, using highly focused radiation that is conformal to the tumor, sparing surrounding normal tissues.
The aim of this study is to critically analyze the short term outcome of stereotactic radiosurgery treatment of skull base tumors at Alexandria Linac Radiosurgery Center.
This study was conducted on 123 patients with 127 skull base tumors, who underwent SRS treatment, between June 2015 and June 2016, with a minimal follow up period of 2 years, using Linac-based radiosurgery technique at the Alexandria Linac Radiosurgery Center in Egypt.
All patients were subjected to proper pre-treatment assessment including; proper history taking, clinical examination, Proper radiological investigations, hormonal assay if needed, and audiometry for vestibular schwannoma patients.
In the treatment day, for all patients, universal CT/MRI-compatible, F.L. Fisher-LEIBINGER model U, open stereotactic head ring was applied to the patient’s head after infiltration of the pin insertion sites with local anesthesia. Treatment planning in the working station is done which should be conformal to target. Quality assurance process of the treatment machine was done before each treatment session to ensure the accuracy of treatment delivery. Patients then were transferred to the treatment room to have the treatment session. After finishing the treatment session, removal of the stereotactic frame, and proper hemostasis was done at the pin insertion points.
Patients were examined after one month of treatment for any possible complications, then followed clinically and radiologically (and hormonal if needed) at 6 months interval, for a minimum period of 2 years.
123 patients with 127 skull base tumors received SRS treatment. Treated lesions included; 56 meningiomas, 33 vestibular schwannomas, 10 non vestibular schwannomas, 13 pituitary adenomas (5 non-functioning, 7 GH-secreting adenomas, 1 prolactin-secreting adenoma), 5 glomus tumors, 4 craniopharyngiomas, 4 skull base metastases, and 2 lesions of local skull base invasions. Treated patients were 35 males (28.5 %) and 88 females (71.5%). Age at time of SRS treatment ranged between 5 and 68 years (mean of 42.66 ± 14.18 years). Primary SRS was done in 83 lesions (65 %), adjuvant SRS in 33 lesions (26%), and salvage SRS was done in 11 lesions (9 %). 51 skull base tumors (40 %) were on the right side, 54 lesions (42.4 %) were on the left side, and 22 lesions (17.6 %) had central location. Median treatment volume was 3.9 cm3, median marginal isodose was at 80%, and the median number of used isocenters was 1.
In meningioma series, ocular cranial nerves were the most commonly affected cranial nerves. Mean marginal dose 10.20 ± 1.60 Gy (range 4.2 - 14 Gy) at median marginal isodose of 80%. 39 patients (71%) had clinical improvement, 11 patients (20%) had unchanged clinical status, and 5 patients (9%) had worsening of their clinical status, which was related to progressive tumor enlargement in the 5 patients. 2 patients developed post SRS symptomatic radiation necrosis as an adverse radiation effect, which was transient, and responded to steroid therapy. Favorable treatment outcome was related to benign tumor pathology and tumor volume < 10 cm3. 22 lesions (39.3%) had reduced treatment size, 29 lesions (51.8%) had stationary tumor size, and 5 lesions (8.9%) had tumor enlargement. 14 patients (25%) had loss of central tumor contrast enhancement. 3 patients had transient post SRS-perilesional brain edema.
In vestibular schwannoma patients, a marginal dose of 11.20 ± 1.11 Gy (range 8-13 Gy) were used at a median marginal isodose of 80%. Clinical improvement were observed in 15 patients (48.4 %), 15 patients (48.4 %) had stationary clinical course, and 1 patient (3.2 %) had clinical deterioration. 6 patients (19.4 %) developed complications; 3 patients had transient facial neuropathy, 3 patients had transient progression of pre-existing trigeminal neuropathy which improved on steroids and pain therapy, 1 patient had transient symptomatic radiation necrosis which improve on medical treatment. One patient with established grade IV Gardner Robertson scale progressed to grade V. Tumor control rate was 100 % (17 lesions decreases in size, and 14 lesions had stationary size). 5 lesions (15.2 %) showed temporary increased size at a median period of 12 months which lasted for a median period of 8 months with spontaneous tumor regression. Tumor genetic type and treatment volume were statistically significant factors affecting hearing preservation.
10 non-vestibular schwannomas were treated; 9 lesions were trigeminal neurinomas, and 1 lesion was a hypoglossal neurinoma. The mean marginal dose was 11.90 ± 0.32 Gy at a median marginal isodose of 80 %. 8 patients showed clinical improvement and one had unchanged clinical status. 8 lesions (80 %) had decreased tumor size, 2 lesions (20 %) had stationary volume. 8 lesions (80 %) showed loss of central contrast enhancement. None of the patients had post-SRS complications.
13 patients with pituitary adenoma received SRS treatment. 5 patients had non-functioning adenomas, 7 patients had GH-secreting adenomas, and patient had prolactinoma. Study included 6 males and 7 females. SRS were adjuvant in 9 patients, salvage in 2 patients, and primary in 2 patients. The mean marginal dose for non-functioning adenomas and functioning-adenomas were 10.80 ± 2.39 Gy and 20.25 ± 6.88 Gy, respectively. Clinically, 7 patients improved and 6 patients had unchanged clinical status. 10 patients showed reduction size, 2 patients had stationary size, and 1 patient showed tumor progression. Regarding the hormonal outcome, out of 8 patients with functioning adenomas, 7 patients showed endocrinological cure and one patient showed endocrinological improvement rather than cure.
4 patients with craniopharyngiomas received SRS. Adjuvant SRS were used in 3 patients and 1 received salvage SRS. Mean marginal treatment dose was 8.30 ± 2.50 Gy at a median isodose of 80 %. 3 patients showed improvement of headache and visual symptoms. One patient had unchanged clinical status. 3 tumors showed reduction of the solid component, one lesion was stationary, 2 lesions had increased pre-SRS cyst size mandating insertion of Ommaya reservoir. None of the patients developed complications.
5 patients with glomus tumors had SRS treatment; 3 males and 2 females. Primary SRS was used in 1 patient, adjuvant SRS in 2 patients and salvage SRS was used in 2 patients. The mean marginal dose was 13.60 ± 1.82 Gy at a median marginal isodose of 80 %. 4 patients improved clinically and had had stationary clinical condition. 2 patients had post SRS transient cranial neuropathy; 1 patient had trigeminal neuralgia, the other had facial neuropathy. Decreased contrast enhancement occurred in single patient and only one patient had asymptomatic perilesional edema.
4 patients with solitary brain metastases were treated.1male, and 3 females. 3 lesions underwent primary SRS, and 1 lesion had salvage SRS. Breast cancer was the primary source in female patients, and the bronchogenic carcinoma was the source in the male patient. Mean marginal dose was 13.06 ± 5.48 Gy. The median marginal isodose was 80%. 1 patient improved clinically whose tumor regressed in size, 2 patients were stationary clinical state and tumor size, and patient deteriorated and had a treatment failure. Only one patient had decreased central contrast enhancement.
2 patients had local skull base invasion from nearby nasopharyngeal carcinomas. One had primary SRS treatment, the other had adjuvant SRS. Mean marginal dose was 10 Gy at a median marginal isodose of 80 %. One patient improved clinically and had reduction in tumor size. The other patient had worse clinical status, and this was correlated with tumor progression. One patient had central contrast loss. One patient had transient asymptomatic perilesional edema.
from the study, a conclusion was made that SRS is an effective treatment tool for skull base tumors, whether used as primary, adjuvant, or salvage SRS, achieving high rates of tumor control on the short term, yet with limited adverse radiation effects on surrounding normal neural tissues, preserving the functional state of the treated patients. Hormonal control was achieved in most of the treated patients with functioning pituitary adenomas.