What is the first step in the geometric reconstruction of source positions in brachytherapy?

The first step in the geometric reconstruction of source positions in brachytherapy involves obtaining two orthogonal radiographs using the isocentric method. This approach is crucial as it enables accurate spatial localization of the radioactive sources within the patient’s anatomy. By capturing two orthogonal views, the dosimetrist can determine the precise coordinates of the sources in three-dimensional space.

This technique enhances the accuracy of the source positioning by allowing for triangulation; the intersection of the two orthogonal radiographs helps delineate the exact location of the brachytherapy seeds within the target area, improving treatment planning and delivery. It serves as a foundational step before more complex imaging or analysis techniques are applied, ensuring that subsequent calculations and adjustments are based on accurately represented source positions.

Utilizing a single radiograph, while simpler, does not provide the necessary spatial information to adequately reconstruct three-dimensional coordinates, which is vital for successful treatment. Similarly, performing 3D imaging techniques or analyzing tumor dimensions might occur later in the process but does not constitute the initial step in source localization. Thus, acquiring two orthogonal radiographs is essential for forming a reliable geometric framework in brachytherapy.