AbstractID: 8233 Title: A new physical compensation technique for intensity modulated
radiation therapy
A new method of generating physical compensation filters for intensity modulated
radiation therapy (IMRT) is being investigated. The compensation filter is based on a reshapeable material, which can be deformed under pressure. A 2D piston array can be
used to repeatedly shape the attenuating material. Automation of this process will make it
possible to manufacture patient specific physical modulators on a routine basis. The
material is a mixture of tungsten powder and a silicon based binder. The linear
attenuation coefficient of the material was measured to be 0.409 cm-1. The maximum
thickness of the physical compensator is 10.2 cm, which allows a transmission of 1.6%
for 6 MV x-ray beam. The material was shaped into the desired compensator by using a
16x16 steel piston array. Each piston has a cross-section of 6.37x6.37 mm2 and projects
to a 1.0x1.0 cm2 area at the isocenter. Ion chamber and verification films were used to
verify the entrance dose for a 6 MV x-ray beam. The measured absolute and relative
doses were compared with the calculated dose. The agreement is within 3%. The 20%80% penumbra of the compensator was measured to be 5.5-10 mm. A 3x3 automatic
prototype was built and the modulator generated was tested using a 6 MV beam. The
results show the potential that a physical modulator formed by a piston array on the basis
of a deformable attenuation material can provide intensity modulation for IMRT
compatible with those provided by commercial MLC techniques.