Geometric and dosimetric effects of an automated clustering and plan optimization pipeline for multiple brain metastasis radiosurgery.

backgroundTreating multiple brain metastases simultaneously with single-isocenter multi-target (SIMT) stereotactic radiosurgery (SRS) can streamline treatment planning and delivery. However, it can also result in targets at large distances from the isocenter, increasing sensitivity to rotational setup errors and requiring wider collimator leaves. Grouping the targets and treating each group with its own plan retains the practical benefits of SIMT SRS while mitigating the concerns of targets at large distances off-isocenter. PURPOSE: This work presents a prototype of a newly integrated treatment planning pipeline that automatically clusters targets into groups and subsequently optimizes a plan for each group simultaneously. Treatment scenarios featuring varying numbers of isocenters were compared.

methodsTwenty-nine treatment courses for patients receiving SRS for 3-15 brain metastases were retrospectively analyzed. Multiple treatment scenarios were prepared for each patient-course by grouping targets into 1-5 isocenters using k-means clustering. PTV margins were added using two methods, one with a magnitude that varied with distance to the isocenter, and a second with a constant 1-mm magnitude. A non-clinical, command-line version of the Brainlab Elements Multiple Brain Mets SRS software was used to optimize plans within each scenario simultaneously. Cumulative doses were analyzed in terms of geometric values (target distances to isocenter, total PTV volume), dosimetric values (volume of normal brain (brain-GTVs) receiving 5, 8, 10, 12, and 18 Gy (V

resultsAs the number of isocenters increased, distances from the targets to the isocenters decreased, and the proportion of targets within a given distance increased. For example, 36%, 77%, 94%, 99%, and 100% of targets were within 4 cm of the isocenter for 1-5 isocenters, respectively. For the variable margin method, the total PTV volume relative to the single-isocenter scenario had a median decrease of 17.5, 24.3, 31.6, and 37.8% for 2-5 isocenters, respectively. Similarly, the relative change in the normal brain dose metrics decreased with increasing number of isocenters (e.g. V

conclusionThe SIMT SRS treatment planning pipeline presented here features automatic grouping of targets followed by automatic dose optimization of up to five isocenters. By quantifying the geometric, dosimetric, and logistical effects of adding isocenters, this pipeline can empower clinicians to make resource-conscious treatment decisions optimal for each patient.