Dosimetric comparison of intensity-modulated radiosurgery and helical tomotherapy for the treatment of multiple intracranial metastases.

The purpose of this study was to evaluate the dosimetry of single fraction, single-isocenter intensity-modulated radiosurgery (IMRS) plans for multiple intracranial metastases and to compare Helical Tomotherapy (HT). Ten treatment plans with 3-6 brain metastases treated with IMRS were re-planned with HT. The mean number of lesions was 5 and mean PTV 22 cm(3). The prescribed dose was 16-20 Gy. The mean V100% was similar for IMRS and HT, and the mean conformity index was 1.4, mean Paddick confirmity index was 0.7, and mean MDPD was 1.1 for both. The mean gradient index was similar for both. The mean 50% _isodose volume was 179.2 cm(3) for IMRS and 277.0 cm(3) for HT (p=0.01). The mean maximum doses to organs at risk were lower for IMRS except brainstem and right optic nerve. For brain, the integral dose was 5.1 and 6.8 Gy-kg (p<0.001) and mean dose 4.0 and 5.4 Gy (p<0.001) for IMRS and HT, respectively. The mean treatment times were 23 (IMRS) and 41 (HT) minutes. Conformity and homogeneity indices were equivalent and sparing of the organs at risk was clinically acceptable for both IMRS and HT. Though the gradient index was similar for IMRS and HT, the mean 50% isodose volume and integral dose to normal brain were lower for IMRS as was treatment time.