The PTV-CTV margin is characterized as?

The characterization of the PTV-CTV margin as non-uniform in all directions reflects the complexities involved in treatment planning and anatomical variations in patients. The Planning Target Volume (PTV) is created by adding a margin around the Clinical Target Volume (CTV) to account for uncertainties such as patient movement, variations in anatomy, and inconsistent positioning during treatment.

Factors like tumor motion during breathing or changes in the patient's anatomy over the treatment course can contribute to this non-uniformity. For example, in areas where the tumor's position may be less predictable, a larger margin may be selected, whereas areas with more stable localization might have a narrower margin. This tailored approach helps ensure that the prescribed dose adequately covers the CTV while minimizing exposure to surrounding healthy tissues.

By recognizing the potential variability in patient anatomy and tumor behavior, the treatment planning process aims to optimize radiation delivery, ensuring efficacy while reducing potential side effects.