If a lesion at a shallow depth requires the 90% isodose line at 3 cm, what is the suitable electron energy for treatment?

To treat a lesion at a shallow depth of 3 cm with a 90% isodose line, it is essential to select the appropriate electron energy, as the penetration depth of electrons is closely related to their energy.

Electrons deposit their maximum dose at a point known as the surface dose, with a significant dose falloff occurring beyond their range in tissue. Typically, the range of electrons in tissue can be approximately estimated using the formula that relates electron energy to depth: higher energy electrons travel deeper into tissue.

For a target depth of 3 cm, 12 MeV electrons are suitable because they have a range that adequately covers that depth while maintaining a 90% isodose line. Higher energy electron beams like 12 MeV provide a good balance between delivering sufficient dose to the tumor while sparing the surrounding healthy tissue, as they taper off sharply beyond their range.

While the other energy levels might also yield some dose at that depth, they may either not penetrate adequately or might deliver a dose profile that does not conform to the requirements of limiting the dose to normal tissues. Thus, the choice of 12 MeV matches the requirement for a 90% isodose line effectively at that specified depth, making it the most