Question

In beam modelling with Pinnacle RTPS, What is the role of the flattening filter? What is the advantage of flattening filter free and what is the main restriction.

Answer 1

In beam modelling with Pinnacle RTPS, the system's Dose calculation is based on a model-based system working on first principles and not a correction-based system. One of the main components of this beam modelling is the modelling of incident energy fluence as a 2D array which is perturbed by the Flattening filter. Here, in the Infield region, the flattening filter changes the fluence of the beam as a function of off-axis distance and also changes the beam energy as a function of off-axis distance.

The flattening filter basically aims to attenuate the forward peaked photon output from the target into a flatter beam. Here the desired flatness refers to a profile measured at 10cm depth with a field of 40 X 40 cm^2.

Restrictions :

1. The Flattening filter has to be sufficiently thick so that a large proportion of transmitted electrons could incident on the flattening filter to act as an additional source of photons.

2.It should usually be made of copper with varying thickness due to the good conductivity of the material.