What device is attached to the treatment machine in radiation oncology to define the configuration of the treatment portal?

The collimator is the device used in radiation oncology to define the configuration of the treatment portal. It is essential in shaping the radiation beam to match the exact dimensions of the tumor while minimizing exposure to surrounding healthy tissue. The collimator adjusts the beam's shape and size by using adjustable lead or other materials, ensuring that high doses of radiation are delivered to the target area.

In radiation therapy, precise targeting is crucial not only for maximizing treatment effectiveness against the cancer but also for reducing side effects by sparing normal tissues. This level of control is especially important in complex conformal radiation therapy and intensity-modulated radiation therapy (IMRT) techniques.

While beam modulators can also influence the radiation beam characteristics, they typically work to modify the beam intensity rather than shape it. Monochromators are used in optics to separate light into its individual wavelengths but are not relevant to radiation therapy. Filter devices can reduce the energy of the radiation beam or change its quality, but they do not define the configuration of the treatment portal.