Development of a Single-Isocenter Planning Strategy for SRS Treatment of Multiple Brain Metastases Using Raystation Treatment Planning System
Abstract
Purpose
To develop and evaluate a clinically practical single-isocenter stereotactic radiosurgery (SRS) planning strategy for patients with multiple brain metastases in RayStation, with the goals of establishing institutional planning guidelines and performing in-house dosimetric validation.
Methods
Nine patients with 3–9 brain metastases (median: 5) were retrospectively selected. Lesion volumes ranged from 0.2–4.3 cm³ (mean: 0.95 cm³). For each patient, three planning techniques based on VMAT for treating multiple metastases with single isocenter were generated and compared: (1) non-coplanar arcs with manual optimization of collimator angles to minimize island blocking effect; (2) non-coplanar multiple arcs per couch position targeting grouped lesions using RayStation “treat” feature; and (3) coplanar arcs treating one lesion at a time using the “treat” feature. All plans were normalized to achieve comparable target coverage. Plan quality was evaluated using conformity index (CI), gradient index (GI), organ-at-risk (OAR) doses, and monitor units per lesion (MU/lesion).
Results
Our preliminary results show that coplanar arc plans achieved excellent conformity and dose fall-off, with CI and GI comparable to those reported for HyperArc-style non-coplanar techniques, and were less planning-intensive. However, these plans required substantially higher MU, resulting in longer treatment delivery time, particularly for patients with more lesions. The grouped-target non-coplanar approach demonstrated consistently favorable CI and GI values, reduced normal brain dose, and significantly lower MU compared to coplanar techniques, while maintaining quicker treatment delivery. Overall, this technique provided the best balance between dosimetric quality and clinical practicality.
Conclusion
Single-isocenter SRS for multiple brain metastases can be effectively achieved using both coplanar and non-coplanar strategies in RayStation. While coplanar techniques offer high-quality dosimetry, their increased treatment times limit practicality for patients with numerous lesions. A non-coplanar grouped-lesion approach represents a robust and efficient planning strategy suitable for routine clinical implementation and institutional standardization.