Fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT) for small acoustic neuromas

Eight patients with acoustic neuromas were treated using a novel method developed at our institution for delivering fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT). We present treatment parameters, dosimetry analysis, and preliminary clinical outcome. The method incorporates high-precision invasive fixation, obliquely-oriented tomotherapy arcs, and reduced dimension pencil beams. The delivered dose distributions for the 8 patients treated from April 1999 to May 2001 were assessed for dose conformality, homogeneity, and doses to organs at risk. Total doses prescribed were 54 Gy in daily doses of 1.8 Gy. Results show that the median planning target volume (gross tumor volume plus a safety margin of 2 mm) was 2.48 cm3 (1.64 to 16.86 cm3) and that the median conformality and homogeneity indices were 1.69 (1.56 to 2.16) and 1.12 (1.09 to 1.19), respectively. The respective average mean and maximum doses to the brain stem were 12.67 Gy and 53.86 Gy. The treatment parameters for the novel FS-IMRT method developed here document excellent dose conformality and normal tissue sparing. Preliminary short-term follow-up (mean 17, median 18.5 months) revealed a 100% local control and hearing preservation rate. No new persistent impairment of facial and trigeminal nerve was observed. Our current follow-up experience indicates a reasonable potential for achieving outcomes comparable to established stereotactic radiotherapy techniques.