Abstract

Dose outside the planning target volume (PTV) is defined as “nontarget dose.” In radiation therapy, any “nontarget” dose should be minimized, as it offers no therapeutic benefit. Nontarget dose is delivered by nontarget radiation and can be in-field or out-of-field. “In-field nontarget dose” is that within a primary field border, such as entrance and exit dose along the beam path. “Out-of-field nontarget dose” is not only outside of the PTV but also outside of any primary field edge; dose deposited by leakage, scatter, or secondary radiation, i.e., stray radiation.