For a 15 MeV electron beam treatment, what field size should be used for a lesion with a width of 5 cm?

In radiation therapy, especially with electron beams, the field size is an important factor in ensuring adequate coverage of the treatment area while minimizing exposure to surrounding tissues. Electrons have a limited penetration depth, and their dose distribution characteristics necessitate that the field size be appropriately selected to cover the entire target lesion.

For a lesion with a width of 5 cm, choosing a field size that closely matches or slightly exceeds the width of the lesion is essential. The rationale for selecting a cone with a width of 6 cm is that it provides a buffer zone around the lesion, ensuring that the entire area of the target receives sufficient radiation dose. This is particularly important for electron beams, as they deposit their dose at a depth determined by their energy levels and can exhibit dose fall-off at the periphery. By using a 6 cm field size, the treatment plan accounts for this fall-off, enhancing the probability of fully treating the lesion while also considering the variability in positioning and the need for full coverage.

Using a 6 cm cone also takes into account any potential inaccuracies in positioning the treatment area and allows for a slight margin around the lesion, which is a standard practice in radiation oncology to ensure that the tumor is adequately treated and to minimize the risk of missing any