Improving the Efficiency of Single-Isocenter Multiple Metastases Stereotactic Radiosurgery Treatment.

PURPOSE

Multiple brain metastases can be treated efficiently with stereotactic radiosurgery (SRS) using a single-isocenter dynamic conformal arc (SIDCA) technique. Currently, plans are manually optimized, which may lead to unnecessary table angles and arcs being used. This study aimed to evaluate an automatic 4π optimization SIDCA algorithm for treatment efficiency and plan quality.

METHODS AND MATERIALS

Automatic 4π-optimized SIDCA plans were created and compared with the manually optimized clinical plans for 54 patients who underwent single-fraction SRS for 2 to 10 metastases. The number of table angles and number of arcs were compared with a paired test using a Bonferroni-corrected significance level of < .05/4 = .0125. The reduction in treatment time was estimated from the difference in the number of table angles and arcs. Plan quality was assessed through the volume-averaged inverse Paddick Conformity Index (CI) and Gradient Index (GI) and the volume of normal brain surrounding each metastasis receiving 12 Gy (local V12 Gy). For a 5-patient subset, the automatic plans were manually adjusted further. CI and GI were assessed for noninferiority using a 1-sided test with the noninferiority limit equal to the 95% interobserver reproducibility limit from a separate planning study (corrected significance level < .05/[4 - 1] = .017).

RESULTS

The automatic plans significantly improved treatment efficiency with a mean reduction in the number of table angles and arcs of -0.5 ± 0.1 and -1.3 ± 0.2, respectively (±SE; both < .001). Estimated treatment time saving was -2.7 ± 0.5 minutes, 14% of the total treatment time. The volume-averaged CI and GI were noninferior to the clinical plans (both < .001), although there was a small systematic shift in CI of 0.07 ± 0.01. The resulting difference in local V12 Gy, 0.25 ± 0.04 cm, was not clinically significant. Minor manual adjustment of the automatic plans removed these slight differences while preserving the improved treatment efficiency.

CONCLUSIONS

Automatic 4π optimization can generate SIDCA SRS plans with improved treatment efficiency and noninferior plan quality.