What is a prerequisite for calculating isodose distributions in brachytherapy?

Calculating isodose distributions in brachytherapy requires a detailed understanding of the geometry of the implant sources relative to the target volume. This is because isodose distributions are created based on the spatial arrangement of the radiation sources and how they deliver dose to the surrounding tissues. Accurate modeling of the sources—such as their positions, orientations, and the distances from the tumor—enables the dosimetrist to predict how the radiation will distribute throughout the tumor and surrounding structures.

Understanding the spatial geometry is crucial for ensuring the tumor receives an adequate dose while minimizing exposure to adjacent healthy tissues. This involves using mathematical formulas and software to model radiation dose delivery based on the specific placement of the brachytherapy sources. Hence, knowing the exact geometry of the implant sources is essential for accurate isodose calculation and effective treatment planning in brachytherapy.