What method is generally used to assess photon beam flatness?

The method commonly used to assess photon beam flatness is through film measurement. This technique involves using radiographic film, which is sensitive to ionizing radiation, to visualize the distribution of dose delivered by the radiation beam. When the film is exposed to the photon beam, the film darkens in proportion to the amount of radiation it receives. By comparing the density of the developed film across the irradiated area, dosimetrists can evaluate the beam's flatness. A flat photon beam indicates an even distribution of dose across a treatment area, which is crucial for effective radiation therapy.

Film measurement provides a high spatial resolution and allows for clear visualization of any variations in beam intensity. It is particularly useful because the resulting film can be quantitatively analyzed using densitometry techniques, offering precise data on flatness across the beam profile.

Other methods mentioned, while useful for different aspects of beam quality assurance or measurement, do not specifically focus on assessing beam flatness in the way film measurement does.