What is the consequence of using standard PDD tables for exit dose calculations?

Using standard Percent Depth Dose (PDD) tables for exit dose calculations often leads to an underestimation of the actual dose received at the exit surface of a patient. This is primarily because these tables are generally designed for calculating doses at various depths within the tissue but do not account adequately for the additional factors influencing exit dose.

When radiation passes through tissue, it interacts with the medium, depositing energy as it goes, which is accurately represented by the PDD values calculated for specific depths. However, the exit dose calculations must account for other factors such as backscatter and the dose buildup past a defined depth. Standard PDD tables may not fully consider the backscatter contributions that occur at the exit point, leading to the assumption that dose distribution remains uniform and consistent.

In clinical situations, the presence of backscatter, particularly when the radiation exits the body, can increase the dose received at the exit point. Standard tables do not incorporate this variability since they are based on certain depths and do not integrate adjustments for backscatter or the actual material properties of tissue at the exit surface. Consequently, relying solely on standard PDD tables can result in a dose estimation that is lower than what is actually delivered to the exit surface, leading to inadequate treatment planning and potentially