Dual optimization in single-isocenter radiosurgery for multiple brain metastases: a dosimetric planning study.

BACKGROUND: This study evaluated a dual-optimization strategy for single-isocenter multiple-target stereotactic radiosurgery (SIMT-SRS) in patients with multiple brain metastases, combining target-anchored isocenter placement with individualized dose prescription for each planning target volume (PTV). METHODS: Three volumetric modulated arc therapy-based SIMT-SRS planning techniques were compared in 22 patients harboring 5-10 brain metastases: geometric center isocenter with composite dose prescription (GCI-Comp), target-anchored isocenter with composite dose prescription (TAI-Comp), and target-anchored isocenter with individual dose prescription (TAI-Ind). Dosimetric parameters for PTVs and organs at risk (OARs) were extracted and compared using the Friedman test followed by Bonferroni-corrected post hoc analyses. RESULTS: All three techniques achieved equivalent target coverage (V95% > 99%, p = 0.202), plan quality (QRTOG, p = 0.385), and conformity (CIPaddick, p = 0.546). Compared to GCI-Comp and TAI-Comp, TAI-Ind produced significantly higher intratumoral dose escalation (PTV-Dmax: 2025.60 vs. 2113.80 vs. 2241.34 cGy, p < 0.001) while achieving a significantly steeper dose gradient (R50%: 13.43 vs. 12.07 vs. 10.31; GIPaddick: 12.91 vs. 12.10 vs. 9.41; both p < 0.001). TAI-Ind also resulted in the lowest normal brain dose exposure (V12Gy: 35.53 cm3; D50%: 322.36 cGy) and significantly reduced maximum doses to the hippocampus, brainstem, spinal canal, and bilateral cochleae (all p < 0.001). These dosimetric advantages were achieved at the expense of requiring a higher number of monitor units (6013.84 vs. 6494.89 vs. 7268.92, p < 0.001). CONCLUSIONS: The TAI-Ind dual-optimization strategy provided greater intratumoral dose escalation and more favorable OARs sparing compared with the composite-prescription techniques, without compromising target coverage. This approach represents a promising strategy for SIMT-SRS planning in patients with multiple brain metastases, warranting further clinical validation.