SU‐E‐T‐820: Comparison of VMAT and IMRT for Stereotactic Body Radiation Therapy (SBRT) of the Adrenal Metastases

Abstract

Purpose: This study is to compare volumetric arc therapy (VMAT) with intensity modulated radiotherapy (IMRT) for stereotactic body radiation therapy (SBRT) of the adrenal metastases. Methods: For 13 patients who have completed SBRT with conventional IMRT technique, new VMAT plans were generated. Plans were optimized with the aim to protect organs at risk and spare healthy tissue while enforcing highly conformal target coverage of clinical prescriptions. IMRT and VMAT plans were designed on Pinnacle3 Version 9.0. All treatment plans were delivered on Elektaˈs Synergy machine. Plan quality and treatment efficiency for VMAT vs. conventional IMRT were evaluated. Results: all plans designed for conventional IMRT and VMAT techniques fulfilled the specific dose constraints. Both VMAT and IMRT resulted in equivalent target coverage but VMAT had an improved conformity index (CI=0.83±0.02 for VMAT and 0.81±0.02 for IMRT, p=0.025). Normal tissue sparing was comparable in both treatment techniques. The mean dose of the unilateral kidney was 10.5±4.6Gy for VMAT and 10.8±4.8Gy for IMRT (p=0.11). The VMAT reduced the total MUs per fraction by 13.1% (1192±261MU for VMAT and 1371±224MU for IMRT, p<0.001). The treatment delivery time for VMAT was 185± 18 seconds per fraction, while IMRT plans presented higher values with an average of 572±79 seconds. Conclusions: For equivalent target coverage and comparable normal tissue sparing, VMAT plans presented improvement in conformity index, and VMAT demonstrates significantly reduced treatment time and fewer MUs to achieve comparable dosimetric plans.