Dosimetric Comparison of Volumetric-Modulated Arc Therapy and Dynamic Conformal Arc Therapy in Threefraction Single-isocenter Stereotactic Radiosurgery for Multiple Brain Metastases

OBJECTIVE The objective of the study was to compare single-isocenter volumetric-modulated arc therapy (VMAT) and dynamic conformal arc therapy (DCAT) techniques in patients who received multifraction stereotactic radiosurgery (SRS) for multiple brain metastases. METHODS Twenty-one patients who were treated with a radiation dose of 27 Gy in three fractions were replanned. Both VMAT and DCAT plans with single isocenter were obtained for each patient. Plan quality indices, cumulative monitor unit (MU) values, maximum dose for organs at risk, and mean dose, V19.6_Gy, and V23.1_Gy for healthy brain tissue were compared. RESULTS The conformity index (p=0.0002), gradient index (p=0.003), maximum dose for brainstem (p=0.016) and mean dose (p=0.00007), V19.6_Gy (p=0.00006), and V23.1_Gy (p=0.00006) values for healthy brain tissue were significantly superior in the VMAT technique, compared to DCAT technique. In addition, a trend toward significance for achieving lower maximum dose value to the optic nerves and/or pathway was observed with VMAT (p=0.073). DCAT provided significantly lower MU values (3097.44 vs. 1479.09; p=0.00006). CONCLUSION VMAT was able to provide better target conformity and lower risk of brain radionecrosis at least dosimetrically in multifraction SRS for patients with multiple brain metastases. DCAT may be chosen in patients with relatively poor performance status or low tolerance to long-lasting radiotherapy sessions.