In electron beam therapy, the dose prescription point is typically located at which depth?

In electron beam therapy, the dose prescription point is typically located at the 90% isodose depth. This depth represents where the radiation dose delivered to the tissue is considered appropriate for effective treatment while minimizing damage to surrounding healthy tissues.

Positioning the prescription point at the 90% isodose depth allows for a beneficial balance between adequate dose delivery to the target volume and sparing of critical structures nearby. Generally, electron beams have a rapid dose fall-off beyond a certain depth, meaning that the dose quickly decreases as it penetrates further into the tissue. By prescribing at the 90% level, clinicians ensure that the maximum therapeutic effect is achieved close to the skin surface and within the target area while adequately accounting for the dose variation in the tissue.

This depth is particularly significant because it correlates with the clinical principle of treating to a depth that maximizes the dose delivery to the cancerous tissue while maintaining safety protocols to protect healthy tissues. Therefore, situating the prescription dose at the 90% isodose depth is aligned with established practices in radiation oncology for achieving optimal therapeutic outcomes.