患者呼吸模擬ファントムシステムを用いた呼吸同期照射法に対する照射位置の評価(<特集>放射線治療論文特集号)

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Respiratory-gated (RG)radiotherapy is useful for minimizing the irradiated volume of normal tissues resulting from the shifting of internal structures caused by respiratory movement. The present study was conducted to evaluate the treatment field in RG radiotherapy using a phantom system simulating patient respiration. A phantom system consisting of a 3-cm ball-shaped dummy tumor and film placed in a cork lung phantom was used (THK Co., Ltd.). RG radiotherapy was employed in the expiratory phase. The phantom movement distance was set to 2cm, and the gating signals from a respiratory-gating system(AZ-733V, Anzai Medical)were varied. The settings used for irradiation were an X-ray energy of 6 MV(PRIMUS, Toshiba Medical Systems), treatment field of 5cm×7cm, and X-ray dose of 100MU. Images were acquired using an electric portal-imaging device(EPID, OPTIVUE 500), and the X-ray dose distribution was measured by the film method. In images acquired using the EPID, the tumor margins became less clear when the gating signals were increased, and the ITVs were determined to be 3.6cm, 3.7cm, 4.2cm, and 5.1cm at gating rates of 10%, 25%, 50%, and no gate, respectively. With regard to the X-ray dose distribution measured by the film method, the dose profile in the cephalocaudal direction was shifted toward the expiratory phase, and the degree of shift became greater when the gating signals were increased. In addition, the optimal treatment fields in the cephalocaudal direction were determined to be 5.2cm, 5.2cm, 5.6cm, and 7.0cm at gating rates of 10%, 25%, 50%, and no gating, respectively. Although RG radiotherapy is useful for improving the accuracy of radiotherapy, the characteristics of the RG radiotherapy technique and the radiotherapy system must be clearly understood when this method is to be employed in clinical practice. Image-guided radiotherapy (IGRT) is now assuming a central role in radiotherapy, and properly identifying internal margins is an important issue for ensuring optimal treatment. The results of this study confirmed that it is necessary to ensure the optimal treatment field in radiotherapy of the trunk and that it is essential to confirm tumor position on the basis of image evaluation.
社団法人日本放射線技術学会の論文
2006-12-20

患者呼吸模擬ファントムシステムを用いた呼吸同期照射法に対する照射位置の評価(<特集>放射線治療論文特集号)

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