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Four-Dimensional Dose Distribution Measurement Using Plastic Scintillator

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m hashimoto

M Hashimoto1*, T Nishio2 , A Haga3 , T Hanada4 , S Kabuki5 , T Kozuka1 , M Oguchi1 , (1) The Cancer Institute Hospital, Koutoh Ward, Tokyo, (2) National Cancer Center, Kashiwa, Chiba,(3) University of Tokyo Hospital, Bunkyo Ward, Tokyo, (4) Keio University Hospital, Shinjuku Ward, Tokyo, (5) Tokai University, Isehara, Kanagawa


SU-E-CAMPUS-T-3 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:To develop the detector for the four-dimensional dose distribution measurement.

Methods:We made the prototype detector for four-dimensional dose distribution measurement using a cylindrical plastic scintillator (5 cm diameter) and a conical reflection grass. The plastic scintillator is used as a phantom. When the plastic scintillator is irradiated, the scintillation light was emitted according to absorbed dose distribution. The conical reflection grass was arranged to surround the plastic scintillator, which project to downstream the projection images of the scintillation light. Then, the projection image was reflected to 45 degree direction by flat reflection grass, and was recorded by camcorder. By reconstructing the three-dimensional dose distribution from the projection image recorded in each frame, we could obtain the four-dimensional dose distribution. First, we tested the characteristic according to the amount of emitted light. Then we compared of the light profile and the dose profile calculated with the radiotherapy treatment planning system.

Results:The dose dependency of the amount of light showed linearity. The pixel detecting smaller amount of light had high sensitivity than the pixel detecting larger amount of light. However the difference of the sensitivity could be corrected from the amount of light detected in each pixel. Both of the depth light profile through the conical reflection grass and the depth dose profile showed the same attenuation in the region deeper than peak depth. In lateral direction, the difference of the both profiles was shown at outside field and penumbra region. We consider that the difference is occurred due to the scatter of the scintillation light in the plastic scintillator block.

Conclusion:It was possible to obtain the amount of light corresponding to the absorbed dose distribution from the prototype detector. Four-dimensional dose distributions can be reconstructed with high accuracy by the correction of the scattered light.

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