Benefits of inverse planning as applied to Gamma Knife radiosurgery

An inverse treatment planning system for Gamma Knife radiosurgery has been developed using nonlinear programming techniques. For each patient, the user provides a set of treatment goals such as the minimum isodose line that must surround the entire treatment volume and the maximum number of shots of radiation. After the treatment goals have been defined, the system optimizes the size, the weight, and the location of the shots of radiation. The results from eight patient cases have been analyzed using the conformity index, the homogeneity index, and DVH comparisons. In all cases, the inverse-planning system produced a dose distribution that was more conformal than the corresponding plan developed by the neurosurgeon. Treatment plans using 5-8 shots of radiation can typically be optimized in less than 15 minutes on a Sparc Ultra-10 with a 330 MHz processor.