Beam symmetry and flatness are defined over what percentage of the field?

Beam symmetry and flatness are important parameters in radiation therapy that evaluate the uniformity of the radiation dose delivered across the treatment field. Specifically, these parameters are crucial for ensuring that the radiation is evenly distributed, which helps to optimize treatment effectiveness while minimizing exposure to surrounding healthy tissues.

In this context, beam symmetry refers to how evenly the radiation is distributed across the width of the beam, ensuring that areas on one side of the beam receive a similar dose as those on the opposite side. Flatness, on the other hand, describes how uniform the dose distribution is across the entire field, ensuring that there are no significant peaks or troughs in radiation intensity.

The definition of these parameters is typically based on measuring the radiation dose at various points across the field and ensuring that the variation falls within acceptable limits. Standard practice defines these characteristics over 80% of the field. Evaluating over this percentage allows for a comprehensive assessment of the beam characteristics, ensuring that any dosimetric inconsistencies are identified and corrected before therapeutic use.

By adhering to the 80% definition, clinicians and physicists can assure that the majority of the area where treatment is delivered maintains the required level of dose symmetry and flatness, promoting safer and more effective patient care.