Comparison of intensity-modulated radiosurgery with gamma knife radiosurgery for challenging skull base lesions.

PURPOSE: To quantitatively compare intensity-modulated radiosurgery (IMRS) using 3-mm mini-multileaf collimation with gamma knife radiosurgery (GKRS) plans for irregularly shaped skull base lesions in direct proximity to organs at risk (OAR). METHODS AND MATERIALS: Ten challenging skull base lesions originally treated with GKRS were selected for comparison with IMRS using inverse treatment planning and 3-mm mini-multileaf collimation operating in step-and-shoot delivery mode. The lesions ranged in volume from 1.6 to 32.2 cm(3) and were treated with 9-20 GK isocenters (mean 13.2). The IMRS plans were designed with the intent to, at minimum, match the GKRS plans with regard to OAR sparing and target coverage. For each case, IMRS plans were generated using 9 coplanar, 11 equally spaced noncoplanar, and 11 OAR-avoidant noncoplanar beams; the best of these approaches with respect to target conformality, sparing of OAR, and maintaining coverage was selected for comparison with the original GKRS plan.
RESULTS: Assuming no patient motion or setup error, IMRS provided comparable target coverage and sparing of OAR and an improved conformity index at the prescription isodose contour but sometimes less conformity at lower isodose contours compared with the actual GKRS plan. All IMRS plans produced less target dose heterogeneity and shorter estimated treatment times compared with the GKRS plans.
CONCLUSION: Compared with GKRS for complex skull base lesions, IMRS plans using a 3-mm mini-multileaf collimator achieved comparable or sometimes improved target coverage, conformity, and critical structure sparing with shorter estimated treatment times.