In the Paris system of volume implant, the source points in the central plane form which geometric shape?

In the Paris system of volume implant brachytherapy, the arrangement of source points in the central plane is designed to optimize dose distribution within the target volume while minimizing exposure to surrounding healthy tissues. This is accomplished by strategically placing source points in a way that allows for uniform coverage of the treatment area.

The correct geometric shape formed by the source points in the central plane is equilateral triangles. This arrangement allows for effective overlapping of the radiation dose distribution from each source point, ensuring that the prescribed dose is delivered to the target while also achieving a steep dose fall-off outside the treatment area. The use of equilateral triangles in this system is significant because it helps in maximizing the dose homogeneity within the treatment volume and minimizes the unwanted dose to adjacent healthy tissues.

The specific design and spacing of this triangular arrangement also aid in achieving the desired therapeutic ratio in brachytherapy, highlighting its importance in treatment planning and execution.