Method for simultaneous selection of treatment isocenters and margins for polymetastatic extracranial stereotactic ablative radiotherapy.

Abstract

BackgroundStereotactic ablative radiotherapy (SABR) represents a new era of treatment for polymetastatic extracranial disease but introduces unique challenges in isocenter selection and margin optimization to balance treatment efficiency and normal tissue sparing.PurposeDevelop an end-to-end method to simultaneously cluster M tumor targets and optimize isocenter number (N) and position to minimize the additional margins required to maintain target coverage as tumor-to-isocenter distance increases.MethodsK-means clustering identified candidate isocenters ranging from one to one per target. Margins required for 95% coverage probability were determined based on tumor-to-isocenter distance, accounting for translational (5 mm) and rotational (1°, 2°, 3°) uncertainties modeled as three-dimensional normal distributions. K-means total margin volume was compared versus isotropic 5- and 10-mm margins and benchmarked against a derivative-free hybrid optimization method. The method was evaluated on 20 clinical lung cases with 2-21 targets per patient, target-to-target distances of 3.8-32.4 cm, and volumes of 0.07-41.05 cm3.ResultsThe total margin volume determined by k-means showed no significant differences (p = 0.94) relative to the hybrid optimization method, with median differences of 0.03% (0.01 cm3), 0.14% (0.06 cm3), and 0.19% (0.15 cm3) for 1°, 2°, and 3° rotational uncertainties, respectively. Significant (p ConclusionK-means clustering offers an efficient method for selecting the number and locations of isocenters to reduce the total margin volume in multi-target extracranial SABR.