What type of radiation detector is commonly used for radiation therapy beam calibration?

The selection of Farmer-type ionization chambers as a commonly used radiation detector for radiation therapy beam calibration is based on their sensitivity and accuracy in measuring ionizing radiation. These ionization chambers are designed to provide precise dose measurements in various radiation fields, making them ideal for calibrating linear accelerators and ensuring the correct dose is delivered to patients during treatment.

Farmer-type ionization chambers have a specific design that optimizes their performance in clinical settings. They have a relatively large volume that allows for averaging the dose over a wide area, mitigating the effects of any inhomogeneities in the radiation field. Additionally, their construction with suitable materials minimizes the uncertainty associated with energy dependence and provides reliable measurements across a range of energies commonly used in radiation therapy.

In contrast, other detectors mentioned, such as Geiger-Muller counters, are better suited for detecting low levels of radiation in various environments but are not ideal for the precise calibration required in radiation therapy. Sodium Iodide detectors are typically used in nuclear medicine for detecting gamma radiation, while photographic film badges are more oriented towards monitoring personnel exposure rather than accurate beam calibration in therapy.