International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationSingle Fraction Versus Fractionated Linac-Based Stereotactic Radiotherapy for Vestibular Schwannoma: A Single-Institution Experience
Introduction
Vestibular schwannomas (VSs) are benign tumors arising from the vestibular branch of the eight cranial nerve. They are characterized by a slow growth pattern with an increase in diameter of 1 mm per year. Untreated, they usually lead to loss of hearing function. Different treatment options are available and the choice of treatment depends on the likelihood of maximizing local tumor control while preserving hearing function and minimizing cranial nerve toxicity. Microsurgery has long been the standard treatment approach with immediate removal of tumor and low recurrence rates if tumors can be completely excised. However, a subset of patients are not an ideal candidate for surgical resection because of advanced age, medical comorbidities, or intracanalicular location of the tumor. Technical improvements in linear accelerators have led to the introduction of linac-based radiosurgery for stereotactic fractionated or single dose radiosurgery.
Because these linac-based stereotactic radiotherapy (RT) techniques are relatively new, the data on local control and complications are limited. This analysis reports our experience in 119 patients with VSs, treated with linac-based single-fraction stereotactic radiosurgery (SRS) or fractionated stereotactic radiosurgery (SRT) with a uniform planning technique and mini-multileaf collimator (mMLC) for beam shaping. No maximal tumor diameter cutoff limitations were used to assign patients to either treatment modality. The long-term treatment outcome and radiation-induced side effects are compared between the patient groups treated with SRS vs. SRT.
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Patient characteristics
Between 2000 and 2008, 122 patients with vestibular schwannoma (VS) were treated with linac-based stereotactic RT in our institution. Three patients were lost to long-term follow-up, resulting in 119 assessable patients. Seventy-eight patients were treated by SRS and 41 patients, with 42 VSs, received SRT. One patient was treated for bilateral lesions in a single SRT treatment course. Twenty-seven (23%) patients had undergone prior surgical resection, and 2 patients had undergone Gamma knife
Patient characteristics
Median age of the patients was 59 years (range, 25–88 years) in the SRS group and 57 years (range, 22–84 years) in the SRT group. Mean SRS tumor volume was 1.7 mL (range, 0.1–9.5), significantly smaller than the 6.3 mL mean SRT tumor volume (range, 0.2–18.6; p < 0.0001, t test; Fig. 1). Median follow-up for the entire group was 62 months (range, 6–136 months). At the start of RT, 101 patients presented with normal facial nerve function and were at risk for treatment-induced facial nerve
Discussion
We present a series of linac-based SRS for patients with VS, prospectively assigned to the same SRS protocol, with a currently accepted dose prescription, no tumor diameter limitations, a considerable amount of medium to large VSs and careful toxicity monitoring. On the basis of our experience, we can conclude that our 5-year local tumor control probability of 95% compares well with those reported by other groups. Consistent with previous reports, we did not find a significant difference in
Conclusion
Linac-based stereotactic RT with mMLC used for beam shaping offers adequate tumor control of VSs. Cranial nerve toxicity is mainly observed with larger lesions treated with SRS. We advise continuous registration of cranial nerve toxicity after stereotactic RT for medium to large VSs because optimal treatment strategy is still uncertain.
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2021, Advances in Radiation OncologyCitation Excerpt :Despite significantly higher treatment volumes in the FSRT group (median PTV, 3.95 cm3) than in the SRS group (median PTV, 1.02 cm3) (P < .001), a similar LC rate was found between the 2 groups (97.9% and 98.5%, respectively). In addition, the preservation of functional hearing was similar in both groups, with 85% preservation for SRS versus 79% for FSRT.8 Although higher than the literature data, the rate of TND remained higher in the SRS group (13%) compared with 0% in the FSRT group.
Conflict of interest: none.