Methods for the determination of target skin distances when obstructions block visual measurement

The target to skin distance (TSD) is one of the most common measurements taken for radiation therapy. This value is used for determination of the depth at which the treatment time is calculated. The optical distance indicator (ODI) is most often used to find the TSD. However, the ODI relies on a clear line of sight. The three methods presented can be used when the ODI is obstructed.