Multisession Stereotactic Radiosurgery for Vestibular Schwannomas: Single-Institution Experience With 383 Cases
Division of Neurological Surgery, Department of Surgery, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand. Neurosurgery
(Impact Factor: 3.62).
05/2011; 69(6):1200-9. DOI: 10.1227/NEU.0b013e318222e451
Single-session stereotactic radiosurgery (SRS) treatment of vestibular schwannomas results in excellent tumor control. It is not known whether functional outcomes can be improved by fractionating the treatment over multiple sessions.
To examine tumor control and complication rates after multisession SRS.
Three hundred eighty-three patients treated with SRS from 1999 to 2007 at Stanford University Medical Center were retrospectively reviewed. Ninety percent were treated with 18 Gy in 3 sessions, targeting a median tumor volume of 1.1 cm3 (range, 0.02-19.8 cm3).
During a median follow-up duration of 3.6 years (range, 1-10 years), 10 tumors required additional treatment, resulting in 3- and 5-year Kaplan-Meier tumor control rates of 99% and 96%, respectively. Five-year tumor control rate was 98% for tumors < 3.4 cm3. Neurofibromatosis type 2-associated tumors were associated with worse tumor control (P = .02). Of the 200 evaluable patients with pre-SRS serviceable hearing (Gardner-Robertson grade 1 and 2), the crude rate of serviceable hearing preservation was 76%. Smaller tumor volume was associated with hearing preservation (P = .001). There was no case of post-SRS facial weakness. Eight patients (2%) developed trigeminal dysfunction, half of which was transient.
Multisession SRS treatment of vestibular schwannomas results in an excellent rate of tumor control. The hearing, trigeminal nerve, and facial nerve function preservation rates reported here are promising.
Available from: Matthew K Steehler
- "Tumor control rate was assessed using two definitions. Interventional tumor control rate was defined as the absence of the need for additional surgical or radiosurgical intervention according to the Stanford update series (Hansasuta et al., 2011). Radiographic tumor control was defined as progression on the follow-up MRI according to a neuroradiologist interpretation. "
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ABSTRACT: Objective: To examine tumor control, hearing preservation, and complication rates after frameless fractionated stereotactic radiosurgery (SRS) in patients with vestibular schwannomas (VS).
Methods: Thirty-seven patients treated with fractionated SRS from 2002 to 2011 were retrospectively analyzed. Ninety-five percent were treated with 25 Gy in five fractions, targeting a median tumor volume of 1.03 cc (range 0.14–7.60).
Results: With a median follow-up of 4.25 years (range, 15 months–9 years), no tumors required an additional treatment resulting in 100% tumor control rate. Radiographic control rate was 91% in 32 patients at a median follow-up of 3 years. Of the 14 patients with serviceable hearing and with audiograms, the hearing preservation rate was 78% at a median follow-up of 18 months. Twenty-six patients with serviceable hearing pretreatment, were evaluated by a phone survey with a hearing preservation rate of 73% at a 5 year median follow-up. There were two cases that developed both new increased trigeminal parasthesias and facial spasms but there were no cases of facial weakness. Patient had 96% of good to excellent satisfaction rate with the treatment at a median follow-up of 5 years.
Conclusion: Frameless fractionated SRS treatment of VS results in good rate of tumor control. Hearing preservation rate and rates of cranial nerve toxicity are comparable to what is reported in the literature. Patients choose this modality because of its non-invasive nature and are generally very satisfied with their long term outcome.
Available from: Dueng-Yuan Hueng
- "Acoustic neuromas can destroy the quality of life through affecting hearing impairment . Therapeutic options for acoustic neuroma have been well-developed including microneurosurgery, Gamma-knife, linear accelerator, proton beam and CyberKnife ® stereotactic radiosurgery    . Bassim et al. conducted a critical review of 56 literature regarding radiation therapy for the treatment of acoustic neuromas . "
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The ABC/2 equation is commonly applied to measure the volume of intracranial hematoma. However, the precision of ABC/2 equation in estimating the tumor volume of acoustic neuromas is less addressed. The study is to evaluate the accuracy of the ABC/2 formula by comparing with planimetry method for estimating the tumor volumes.
Thirty-two patients diagnosed with acoustic neuroma received contrast-enhanced magnetic resonance imaging of brain were recruited. The volume was calculated by the ABC/2 equation and planimetry method (defined as exact volume) at the same time. The 32 patients were divided into three groups by tumor volume to avoid volume-dependent overestimation (<3 ml, 3-6 ml and >6 ml).
The tumor volume by ABC/2 method was highly correlated to that calculated by planimetry method using linear regression analysis (R2=0.985). Pearson correlation coefficient (r=0.993, p<0.001) demonstrates nearly perfect association between two methods.
The ABC/2 formula is an easy method in estimating the tumor volume of acoustic neuromas that is not inferior to planimetry method.
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ABSTRACT: OBJECTIVE: For multisession radiosurgery, no published data relate the volume and dose of cochlear irradiation to quantified risk of hearing loss. We conducted a retrospective, dosimetric study to evaluate the relationship between hearing loss after stereotactic radiosurgery (SRS) and the dose-volume of irradiated cochlea. METHODS: Cochlear dose data were retrospectively collected on consecutive patients who underwent SRS (18 Gy in 3 sessions) for vestibular schwanoma between 1999 and 2005 at Stanford University Hospital. Inclusion criteria included Gardner-Robertson (GR) grade I or II hearing prior to radiosurgical treatment, complete audiograms, and magnetic resonance imaging (MRI) follow-up. A cochlea dose-volume histogram was generated for each of the 94 patients who qualified for this study. RESULTS: GR grade I-II hearing posttreatment was maintained in 74% of patients (70/94). Median time to last follow-up audiogram was 2.4 years (range 0.4-8.9) and to last MRI was 3.6 years (range 0.5-9.4). Each higher level of cochlear irradiation was associated with increased risk of hearing loss. Larger cochlear volume was associated with lower risk of hearing loss. Controlling for differences in cochlear volume among subjects, each additional mm(3) of cochlea receiving 10 to 16 Gy (single session equivalent doses of 6.6-10.1 Gy(3)) significantly increased the odds of hearing loss by approximately 5%. CONCLUSIONS: Larger cochlear volume is associated with lower risk of hearing loss following trisession SRS for vestibular schwannoma. Controlling for this phenomenon, higher radiation dose and larger irradiated cochlear volume are significantly associated with higher risk of hearing loss. This study confirms and quantifies the risk of hearing loss following trisession SRS for vestibular schwannoma.
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