Development of new devices measuring dose distributions in a tissue equivalent material and incident electron energies for therapeutic electron beams

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1. A new type of beam-energy monitor has been developed to check the energies of electron beams from radiotherapy accelerators. The monitor consists of a pair of scintillating fibers and photodiode read-out circuits that measure the energy depencence of electron transmission through a wedge-shaped absorber. A linear energy response and 1% accuracy for energy constancy measurements were attained with the monitor. The monitor having advantages of simple mechanical and electronic constructions, small size and low cost is suitable for practical use as a portable device.2. A new type of depth-dose measuring device has been developed for electron beam therapy. The device employs plastic scintillating fiber detectors inserted in a plastic (PMMA) phantom in line along an incident electron beam. Output photons from a fiber, the number of which is proportional to absorbed dose at each depth of the phantom, were converted to an electric signal with a photodiode. Each signal from the photodiode was transmitted to a personal computer through a multi-channel AD converter and processed to draw a depth-dose curve on the computer display. A depth-dose curve could be obtained in a measuring time of 5 sec for each incident electron beam with an energy range between 4 and 21 MeV.The mean electron energies estimated using the curves and a depth-scaling factor for PMMA were consistent with those obtained by conventional depth-dose measurements using an ion chamber and a water phantom. The newly developed device, being simple and not time consuming, is suitable for routine use as a quality assurance tool for therapeutic electron beams.