AbstractID: 8608 Title: Quick Quality Assurance of Photon Beam Energy...

AbstractID: 8608 Title: Quick Quality Assurance of Photon Beam Energy Using Profiles
Energy wedges have been used to monitor the energy of electron beams. It presents a simple and fast method to check energy shift in electron
beams as compared to traditional water scans. We have investigated fast methods to check energy shifts of photon beams. The energy of a 6 MV
beam from a Clinac 600EX from Varian Medical Systems has been varied by changing the accelerating RF power from the magnetron. Since the
wave-guide is in line with the target, the steering of the beam didn’t need to be adjusted when the energy was varied. The percentage depth dose
measured in a 3D water phantom (SSD 100 cm, 10x10 cm²) showed variations of 1.3% over the range of energies tested. A 7.6 cm height stainless
steel energy wedge was unable to show the energy shift. However the change in flatness of open beam profiles clearly indicates an energy shift
both in water scans and with in air diode array. The flattening filter in the linear accelerator head acts as a build in energy wedge. The variation in
the profiles is more than 5 times larger than the variation in percentage depth dose for the same energy shift at the depth of dose maximum where
the horns from the flattening filter are larger. Flatness monitoring is more than adequate for routine quality assurance of the photon energy.
Although we have already implemented this monitoring method, the work has to be continued for higher energy beams with validations using
Monte Carlo calculations.
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