Which material is used as the reference phantom for beam calibration in the AAPM TG51 protocol?

In the AAPM TG51 protocol, water is utilized as the reference phantom for beam calibration due to its tissue-equivalent properties. Water closely mimics the radiation interactions that occur in human tissue, making it an ideal medium for dose measurements in radiation therapy. This resemblance allows for accurate calculations and ensures that the dosimetric data obtained in water can be reliably translated to the patient’s actual treatment scenario.

Using water as a reference phantom enables the determination of the absorbed dose to water under standard conditions, which is critical for ensuring consistency and accuracy in radiation dose delivery. The use of water facilitates the application of ionization chambers that measure the ionization produced by radiation in the water, thereby allowing the dosimetrist to establish calibration factors that are essential for safe and effective treatment planning in clinical settings.