Which of the following is NOT a factor in determining isodose distributions in brachytherapy?

In brachytherapy, isodose distribution is influenced by several key factors that directly affect the dose delivery to the target area and surrounding tissues. Understanding these factors is critical in optimizing treatment outcomes.

The delineation of the planning target volume (PTV) is essential because it defines the boundaries within which the dose must be delivered effectively. Accurate delineation ensures that the prescribed dose covers the tumor while minimizing exposure to normal tissues.

The geometry of the implant sources plays a crucial role as well. The arrangement and spacing of the radioactive sources directly influence the spatial distribution of radiation. Different geometries can result in varying degrees of dose escalation to the target and de-escalation to surrounding organs at risk.

The treatment planning system is also a vital component, as it utilizes complex algorithms and calculations to predict and visualize the distribution of doses based on the input parameters, including source characteristics and spatial configurations.

While the timing of radiation delivery is important for overall treatment protocols and patient management, it does not directly impact the formation of isodose distributions during a specific brachytherapy procedure. The actual distribution is determined by factors related to the physical layout of the sources and the characteristics of the target volume, rather than the temporal aspects of when radiation is delivered. Thus, this