Development of depth dose meter for heavy ion particle beams with piled plastic scintillators

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We continued to test the new developed depth dose meter. The dosimeter was exposed to x rays (4,10 and 18 MV) and electron beams (6,9,12 and 15 MeV) from Linac at the Osaka University Hospital, proton beams (65 and 200 MeV) from the cyclotron at RCNP of Osaka University and carbon beam (290MeV/n) from the Heavy Ion of Medical Accerator in Chiba of NIRS to test it. The pressed type of fiberblock without heat is more suitable for sensor than that with heat in respect of shielding the light. We could decrease the background signal in obtaining the image data by utilizing the digital filter. The fitness was good between the depth dose data by ionization chamber and by new dosimeter after compensating Cerenkov light for X ray and electron beam, quenching of light by energetic proton beams. The discrepancy became smaller by compensating the characteristics of emission of light from fiberblock. We could measure the depth dose curve for mono peak beam of carbon. But the discrepancy was large for spread outed carbon beams containing different components of LET.There are much room for improvement. After confirming the high quality of depth dose meter by correcting the difference of light emission by variable particles, we have a plan to make more compact 3D depth dose meter with rotation and rectilinear motion of detector. Such a new designed dosimeter will be useful because of reducing time for measurement of the fundamental dose distribution.