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Stereotactic body-radiation therapy (SBRT) has gained acceptance in treating lung cancer. Localization of a
thoracic lesion is challenging as tumors can move significantly with breathing. Some SBRT systems compensate
for tumor motion with the intrafraction tracking of targets by two stereo fluoroscopy cameras. However, many
lung tumors lack a fluoroscopic signature and cannot be directly tracked. Small radiopaque fiducial markers,
acting as fluoroscopically visible surrogates, are instead implanted nearby. The spacing and configuration of
the fiducial markers is important to the success of the therapy as SBRT systems impose constraints on the
geometry of a fiducial-marker constellation. It is difficult even for experienced physicians mentally assess the
validity of a constellation a priori. To address this challenge, we present the first automated planning system
for bronchoscopic fiducial-marker placement. Fiducial-marker planning is posed as a constrained combinatoric
optimization problem. Constraints include requiring access from a navigable airway, having sufficient separation
in the fluoroscopic imaging planes to resolve each individual marker, and avoidance of major blood vessels.
Automated fiducial-marker planning takes approximately fifteen seconds, fitting within the clinical workflow.
The resulting locations are integrated into a virtual bronchoscopic planning system, which provides guidance to
each location during the implantation procedure. To date, we have retrospectively planned over 50 targets for
treatment, and have implanted markers according to the automated plan in one patient who then underwent
SBRT treatment. To our knowledge, this approach is the first to address automated bronchoscopic fiducialmarker
planning for SBRT.
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