Scattered photons produced by beam-modifying filters

Area of Science:

• Medical Physics
• Radiotherapy Physics

Background:

• Beam-modifying filters (wedges, compensators) in x-ray beams can generate scattered photons.
• Understanding the dose contribution of these scattered photons is crucial for accurate radiotherapy.

Purpose of the Study:

• To quantify the dose contribution of scattered photons generated by beam-modifying filters in a 4-MV x-ray beam.
• To assess the impact of these scattered photons on dose accuracy in clinical applications.

Main Methods:

• Measurements of dose contribution from a 1-cm copper filter placed in a 4-MV x-ray beam.
• Dose measurements were taken at 30 cm from the filter, on the beam centerline and at the edges.

Main Results:

• A 1-cm copper filter produced a dose contribution of approximately 6% of the transmitted primary dose on the centerline for a 20x20 cm2 field.
• Dose contribution from scattered photons was about half as much at the beam edges compared to the centerline.

Conclusions:

• Scattered photons from beam-modifying filters represent a small but measurable dose component.
• Minor dose errors in clinical radiotherapy can be avoided by accounting for this scattered photon contribution using simple procedures.