Transducer array with shape that contours to a subject's body and method of determining shape and placement of transducer arrays

A transducer apparatus for delivering tumor treating fields to a subject's body, the transducer apparatus including: a substrate and an array of electrodes disposed on the substrate, the array configured to be positioned over the subject's body with a face of the array facing the subject's body; wherein, when viewed from a direction perpendicular to the face of the array, the substrate has at least one concave edge forming at least a portion of a boundary of the array, the at least one concave edge defines an opening between two opposing sides of the substrate, no electrodes are present in the opening, and the substrate has a substantially C-shaped, U-shaped, rounded V-shaped, or annular shaped surface.