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Gated Radiotherapy Using Internal Ducial Markers

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Next, we talk about gated radiotherapy using internal ducial markers. Multiple internal ducial markers (normally three to ve numbers) are implanted in or around the tumor site to track the tumor motion in real-time during treatment cycles in order to identify breathing phase and displacement such that the optimal gate can be designed Seppenwoolde et al. (2002); Shirato et al. (2000); Shimizu et al. (2001); Kitamura et al. (2002, 2003, 2002);
Shimizu et al. (2000); Shirato et al. (2003). The individual markers are tracked in all three directions using imaging techniques such as conventional cone beam CT kV projection images.
The tumor location is determined by averaging the marker coordinates in the SI, AP and Lateral directions independently. The markers are gold plated and 2mm in diameter.
Pre-treatment simulations are performed on the patient using digitally reconstructed radiographs
DRRs Russako et al. (2005) that are computed from the planning CT data. This is done to test whether the patient can handle the invasive procedure of marker implantation; to delineate the tumor and surrounding anatomical structures; perform simulations on the generated DRRs over multiple breathing cycles using identical treatment setup geometry at end-of-inhale phase and end-of-exhale phase to design an optimal treatment plan that delivers tumoricidal dose while avoiding normal tissue toxicity. The gating location and size are determined by comparing the marker position during the

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