Catheters for performing therapeutic and diagnostic procedures within a body, including human or animal body cavities or lumens, and methods for use. One or more distancing member of the catheter can be used to position a sensor or a therapeutic device a minimum distance from a wall of a lumen or cavity. The catheter can include means for actively or passively controlling or modulating its position within the lumen or cavity during a procedure. Methods for using the catheter include nonocclusive deployment in the human gastrointestinal tract for phototherapy procedures, delivering electromagnetic radiation substantially homogeneously or in a desired pattern to the interior of a lumen.