Dose conformity and falloff in single-lesion intracranial SRS with DCA and VMAT methods.

Background: Intracranial stereotactic radiosurgery (SRS) aims at achieving highly conformal dose distribution and, at the same time, attaining rapid dose falloff outside the treatment target. SRS is performed using different techniques including dynamic conformal arcs (DCA) and volumetric modulated arc therapy (VMAT).

Purpose: In this study, we compare dose conformity and falloff in DCA and VMAT plans for SRS with a single target.

Methods: To compare dose conformity in SRS plans, we employ a novel conformity index , RTOG conformity index ( ), and Riet-Paddick conformity index ( ). In addition, we use indices , , and to evaluate dose falloff. For each of the considered 118 cases of SRS, two plans were created using DCA and VMAT. A two-tailed Student's t-test was used to evaluate the difference between the employed indices for the DCA and VMAT plans.

Results: The studied VMAT plans were characterized by higher dose conformity than the DCA plans. The differences between the conformity indices for the DCA plans and VMAT plans were statistically significant. The DCA plans had a smaller number of monitor units (MUs) and smaller indices R50%, V , and V than the VMAT plans. However, the differences between R50%, V , and V for the DCA and VMAT plans were not statistically significant.

Conclusions: Although the studied VMAT plans had higher dose conformity, they also had larger MUs than the DCA plans. In terms of dose falloff characterized by parameters R50%, V , and V , DCA serves as a reasonable alternative to VMAT in the case of a single brain metastasis.