For a patient treated with a single field of a 16 MeV electron beam, what is the depth of the 90% isodose line along the central axis?

The depth of the 90% isodose line for electron beams is significantly influenced by both the energy of the beam and the characteristics of the tissue it penetrates. For a 16 MeV electron beam, the penetration capability is quite substantial compared to lower energy beams.

Typically, the depth of the 90% isodose line for a specific energy can be approximated using clinical data or established dose distribution characteristics. Generally, higher energy electron beams, like the 16 MeV, have a 90% isodose line that falls at a depth ranging from approximately 3 cm to 5 cm in tissue. For this energy level, empirical data and clinical practices suggest that the depth of the 90% isodose line is around 4 cm.

Understanding that the 90% isodose line represents the depth at which 90% of the prescribed dose is delivered is critical for proper treatment planning. Since the 16 MeV beam is used to target tumors that may be located at a moderate depth beneath the surface, recognizing this specific depth helps ensure that the treatment is both effective and minimizes exposure to surrounding healthy tissue.

Therefore, the depth of the 90% isodose line being identified at