How can the equivalent square field of an irregular field be determined for any dose function?

The equivalent square field of an irregular field can be effectively determined using Clarkson's sector integration method. This method is particularly useful in radiotherapy for converting complex field shapes into equivalent square fields, which simplifies the dosimetry calculations necessary for planning treatment.

Clarkson's method involves integrating the dose distribution across the contours of the irregular field, effectively breaking it down into sectors. Each sector's contribution to the total dose can be calculated based on its distance from the radiation source and the angle subtended by the field edge. By systematically evaluating these sectors, the dose characteristics of the irregular field can be accurately modeled and compared to a standard square field, allowing clinicians to apply established dose functions more reliably.

This approach is preferred in clinical practice due to its accuracy in handling non-uniform field shapes and its ability to account for factors such as the variation in beam profile and patient geometry, ensuring that the radiation dose is delivered optimally to the intended treatment area.