Intensity-modulated radiosurgery with rapidarc for multiple brain metastases and comparison with static approach

Rotational RapidArc (RA) and static intensity-modulated radiosurgery (IMRS) have been used for brain radiosurgery. This study compares the 2 techniques from beam delivery parameters and dosimetry aspects for multiple brain metastases. Twelve patients with 2-12 brain lesions treated with IMRS were replanned using RA. For each patient, an optimal 2-arc RA plan from several trials was chosen for comparison with IMRS. Homogeneity, conformity, and gradient indexes have been calculated. The mean dose to normal brain and maximal dose to other critical organs were evaluated. It was found that monitor unit (MU) reduction by RA is more pronounced for cases with larger number of brain lesions. The MU-ratio of RA and IMRS is reduced from 104% to 39% when lesions increase from 2 to 12. The dose homogeneities are comparable in both techniques and the conformity and gradient indexes and critical organ doses are higher in RA. Treatment time is greatly reduced by RA in intracranial radiosurgery, because RA uses fewer MUs, fewer beams, and fewer couch angles.