In SSD type treatments, PDD is normalized to what dose?

In SSD (Source-Skin Distance) type treatments, the Percentage Depth Dose (PDD) is commonly normalized to the dose at D-Max, which is the depth at which the dose reaches its maximum value for a specific beam energy. This normalization is critical because D-Max represents the point in tissue where the radiation dose is most concentrated and effectively delivered.

By normalizing the PDD to the dose at D-Max, it allows for a standard reference point to measure the dose distribution as the radiation penetrates deeper into the tissue. The PDD values then express the relative dose at various depths as a percentage of the maximum dose delivered at D-Max, facilitating accurate treatment planning and ensuring that enough radiation is applied to the target while sparing surrounding healthy tissues.

This practice is fundamental in ensuring effective dose delivery during radiation therapy, as it helps dosimetrists and radiation oncologists make informed decisions regarding treatment setups, particularly when adjusting for patient-specific factors, variations in tumor depth, or differing beam energies.