University of Birmingham > Talks@bham > Molecular and Medical Physics Seminar Series > Radiotherapy with Unflattened Photon Beams

Radiotherapy with Unflattened Photon Beams

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If you have a question about this talk, please contact Dan Kirby.

Preceded by tea, coffee and biscuits in the Poynting coffee lounge at 3.30pm

The flattening filter is usually regarded as an essential part of any linear accelerator, acting to produce a flat beam at a depth of 10cm. Despite their longstanding use in medical linear accelerators, however, there are still a number of unresolved issues regarding their use. The head scatter produced by the flattening filter is still the subject of much research and the spectral changes caused by central axis beam hardening and off-axis softening is still not modelled accurately within most planning systems.

Commissioning data has been measured for a 6MV Elekta Precise linear accelerator with no flattening filter, and a beam model produced for the CMS XiO treatment planning system. The aim has been to study the effects of flattening filter removal on machine operation, beam characterisation and treatment planning.

Benefits of flattening filter removal include increased dose rate (2.1 times for open and 1.8 times for wedged fields), reduced head scatter (by approx. 70%), and lower dose outside of the field edge. Measurements in the patient plane show that leakage radiation from the treatment head is reduced by 60%, significantly lowering whole body radiation doses.

All of these effects are desirable properties for radiotherapy treatment planning as they act to reduce doses to normal tissues whilst simplifying beam calculations. Planning studies show that the beam shape can be used effectively in many conventional planning circumstances where the forward-peaked beam profile acts to even out hotspot values in breast and head & neck regions. Great promise has also been demonstrated for IMRT where plans directly comparable to conventional use can be generated, but with simplified beam modelling and head scatter calculations. Whole body radiation doses are also reduced making the use of IMRT for paediatric cases more acceptable.

This talk is part of the Molecular and Medical Physics Seminar Series series.

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