Abstract: A tool is provided for use in acquiring a treatment portal on the skin surface of a patient undergoing radiation therapy or the like. The portal acquisition tool includes a template portion having a cut-out pattern for marking the treatment portal on the skin and a handle portion which both facilitates use of the template and includes ruled markings for taking measurements. Additionally, the handle portion is provided with transverse lines for assisting the therapist in altering the source-to-skin distance during the administration of electron energy and an opaque backing which serves as a screen for reflecting the optical distance indicator projected by the linear accelerator.