Fractionated stereotactic radiotherapy for acoustic neuromas

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Purpose/Objective: When compared to radiosurgery, fractionated stereotactic radiotherapy (FSR) offers escalation of tumor dose (Gy) and potential sparing of facial and auditory functions in the treatment of acoustic neuromas. Materials/Methods: Over 380 patients (pts) have received FSR for AN. Two hundred forty-one consecutive pts (130 M and 111 F) (median age 52.5 years; mean 53.6 ±0.8; range 18.6–86.5) have had follow up greater than 1 year (median 2.0; mean 2.3 ±0.1; range 1.0–8.6) and comprise this report. For simulation pts had non-invasive, repeat fixation mask fitting, spiral CT (2 mm slice thickness) and MRI image fusion. Pts received FSR via multiple non-coplanar arcs via circular or micro-multileaf collimation. Differential collimation and beam weighting achieved conformality. The prescribed isodose was 80%. To achieve precision of the positioning of the pt, the digitally reconstructed radiograph (DRR) allowed representation of the isocenter in AP and lateral views. Prior to each fraction the actual AP and lateral radiographs provided by the dedicated 6 MeV linear accelerator allowed comparison with the DRR for verification of position. Fractionation of dose (Gy) increased for larger AN. For AN < 3.0 cm diameter (mean volume 1.5 ±0.1 cc), ≥ 3.0 but < 4.0 cm diameter (10.0 ±0.9 cc) and ≥ 4.0 cm diameter (23.0 ±1.7 cc) doses of 25 Gy in 5 consecutive daily fractions of 5 Gy (211 pts) vs. 30 Gy in 10 fractions of 3 Gy (27 pts) vs. 40 Gy in 20 fractions of 2 Gy (3 pts) were given. Results: The percentage decreases in size were 14 ±1 (range 0–100; 95% CI 9–15), 13 ±2 (range 0–38; 95% CI 5.9–20.2) and 6 ±3 (range 0–11; 95%CI 2.2–10.0) for the 25, 30 and 40 Gy regimens, respectively. One hundred twenty-nine pts had audiograms both before and after the FSR. Prior to FSR 46 pts had Gardner-Robinson (GR) score of 1. After FSR the scores for these pts were 1 (16 pts), 2 (20 pts), 3 (7 pts) and 5 (3 pts). For the 40 pts who had GR score of 2 prior to FSR, the scores after FSR were 1 (5 pts), 2 (28 pts), 3 (5 pts) and 4 (2 pts). GR scores were unchanged in 66 pts, improved in 12 pts and worsened in 51. The actuarial probability of preservation of useful hearing (GR score 1 or 2) was 76%. Before vs. after FSR the speech reception threshold (dB) was 38.0 ±3.5 vs. 50.3 ±3.2 (p < 0.05), the speech discrimination (%) was 78.1 ±2.4 vs. 61.3 ±3.1 and the pure tone average (dB) was 44.8 ±3.0 vs. 59.4 ±2.9. After FSR two pts had transient facial hypesthesia. No pt had facial weakness, no pt had tumor growth and no pt had surgery. Conclusions: FSR provides control of AN with preservation of normal function. Longer follow up is required to determine the durability of these observations.