What component is used in port films to increase film sensitivity?

The use of a metal screen in port films enhances film sensitivity by providing a means to convert the radiation from the x-ray exposure into visible light. This luminescent effect allows the film to capture the image more effectively, thereby increasing the sensitivity of the film to the x-rays being emitted. The metal screen absorbs the x-ray photons and emits light photons that expose the film, making it more responsive than it would be if exposed to x-rays alone. This results in a clearer and more detailed image, crucial for accurate dose distribution assessment and patient treatment planning in radiation therapy.

Other components like a lead shield serve different purposes, such as protecting sensitive areas from unnecessary exposure, while chemical additives, although they can enhance certain properties of film, are not the primary means of increasing sensitivity in port films. The glass film holder is primarily designed for support and protection, rather than affecting film sensitivity.