Which device is used to shape the treatment portal in radiation oncology?

The device used to shape the treatment portal in radiation oncology is known as a block. In this context, a block is a tool that is placed in the path of the radiation beam to create custom-shaped treatment fields that conform to the contours of the tumor while sparing surrounding healthy tissues. Blocks are essential for optimizing the dose distribution, minimizing exposure to non-target areas, and enhancing treatment efficacy.

While other devices mentioned have specific uses in radiation therapy, they do not serve the same purpose as a block. For example, a bolus is used to bring the radiation dose closer to the skin surface but does not shape the treatment portal. A bite block is often used in oral or maxillofacial radiotherapy to stabilize the patient's mouth and ensure proper positioning, but it is not involved in shaping the treatment field. CAD (Computer-Aided Design) may refer to software used for planning and visualization in treatment planning but does not physically shape the treatment portal itself. Thus, the block is distinctly suited for the task of creating customized treatment shapes in radiation oncology.