Purpose: This study aimed to compare the dose characteristics of the volumetric modulated arc therapy (VMAT) and dynamic conformal arc (DCA) techniques for metastatic brain tumor treatment using various indices to evaluate the quality of the plan and provide insights into the clinical implications of each approach.
Methods: Twelve patients with single metastatic brain tumors treated with VMAT were retrospectively analyzed. For comparison with DCA, identical geometric parameters (excluding multileaf collimators) were applied. Dose coverage, normal tissue sparing, and treatment efficiency were evaluated using indices such as CI_LIM98, CI_ICRU, CI_RTOG, QC_RTOG, CI_SALT, HTCI_SALT, and CI_PADDIC. These indices were statistically assessed to evaluate the differences between VMAT and DCA.
Results: VMAT was superior to DCA in most indices for both small and large planning target volumes (PTVs). DCA plans for large PTVs showed a higher V_12Gy, exceeding 10 mL and failing to meet the recommended criteria (<10 mL). However, DCA required nearly half the monitor units (MUs) of VMAT, resulting in shorter treatment times. All indices, except for QCRTOG, demonstrated significant differences between VMAT and DCA.
Conclusions: Careful consideration is necessary for larger PTVs when deciding a plan because DCA can occasionally result in V_12Gy of a brain minus PTV >10 mL. Conversely, DCA provides the advantage of shorter treatment times because of its lower MU. This study highlights the importance of using a combination of indices to comprehensively assess treatment plan quality.

KeywordsStereotactic radiosurgery, Dynamic conformal arc, Volumetric modulated arc therapy, Conformity index, Treatment planning