Clinical Investigation
Single Fraction Versus Fractionated Linac-Based Stereotactic Radiotherapy for Vestibular Schwannoma: A Single-Institution Experience

https://doi.org/10.1016/j.ijrobp.2011.04.066Get rights and content

Purpose

To evaluate and compare outcomes for patients with vestibular schwannoma (VS) treated in a single institution with linac-based stereotactic radiosurgery (SRS) or by fractionated stereotactic radiotherapy (SRT).

Methods and Materials

One hundred and nineteen patients (SRS = 78, SRT = 41) were treated. For both SRS and SRT, beam shaping is performed by a mini-multileaf collimator. For SRS, a median single dose of 12.5 Gy (range, 11–14 Gy), prescribed to the 80% isodose line encompassing the target, was applied. Of the 42 SRT treatments, 32 treatments consisted of 10 fractions of 3–4 Gy, and 10 patients received 25 sessions of 2 Gy, prescribed to the 100% with the 95% isodose line encompassing the planning target volume. Mean largest tumor diameter was 16.6 mm in the SRS and 24.6 mm in the SRT group. Local tumor control, cranial nerve toxicity, and preservation of useful hearing were recorded. Any new treatment-induced cranial nerve neuropathy was scored as a complication.

Results

Median follow-up was 62 months (range, 6–136 months), 5 patients progressed, resulting in an overall 5-year local tumor control of 95%. The overall 5-year facial nerve preservation probability was 88% and facial nerve neuropathy was statistically significantly higher after SRS, after prior surgery, for larger tumors, and in Koos Grade ≥3. The overall 5-year trigeminal nerve preservation probability was 96%, not significantly influenced by any of the risk factors. The overall 4-year probability of preservation of useful hearing (Gardner-Robertson score 1 or 2) was 68%, not significantly different between SRS or SRT (59% vs. 82%, p = 0.089, log rank).

Conclusion

Linac-based RT results in good local control and acceptable clinical outcome in small to medium-sized vestibular schwannomas (VSs). Radiosurgery for large VSs (Koos Grade ≥3) remains a challenge because of increased facial nerve neuropathy.

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.

Section snippets

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.

References (19)

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    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.

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Conflict of interest: none.

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