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KMID : 1164220190310010043
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Journal of Korean Society for Radiotherapeutic Technology
2019 Volume.31 No. 1 p.43 ~ p.49
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Comparison of Doses of Single Scan PBS and Layered Rescanning PBS Using Moving Phantom in Proton Therapy
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Kim Kyeong-Tae
Kim Sun-Young
Kim Dae-Woong
Kim Jae-Won
Park Ji-Yeon
Jeon Sang-Min
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Abstract
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Purpose : We apply the Layered Rescanning PBS designed to complement the Pencil Beam Scanning(PBS), which is vulnerable to moving organs with the Moving Phantom, and compare the homogeneity with the single scan PBS.
Methods and materials : Matrix X (IBA, Belgium) and Moving Phantom (standard imaging, USA) were used. A dose of 200 cGy was measured in the AP direction on a hypothetical tumor 10x10x5 cm. The plan type was planned as 4 kinds of sinlge scan PBS, rescan number 4, 8, 12 times. Were measured three times for each types. During the measurement, the respiratory cycle of the Moving Phantom was generally set to 4 seconds per cycle, and the movement radius in the S-I direction was set to 2 cm. In addition, beam on time was measured.
Results : The mean values of Dmax in the PTV were 246.47±18.8 cGy, 223.43±8.92 cGy, and 222.47±7.7 cGy, 213.9±6.11 cGy and the mean values of Dmin were 165.53±4.32 cGy, 173.13±11.94 cGy, 184.13±8.04 cGy, 182.67±4.38 cGy and the mean values of Dmean 192.77±6.98 cGy, 196.7±4.01 cGy, 198.17±4.96 cGy, 195.77±3.15 cGy respectively. As the number of rescanning increased, the Homogeneity Index converged to 1. The beam on time was measured as 2:15, 3:15, 4:30, 5:37 on average. In the measurement process, in the low dose layer of the MU, the problem was found that it was not rescanned as many times as the set number of rescan.
Conclusions : In the treatment of tumors with long-term movements, the application of layered rescanning PBS showed a more uniform dose distribution than single scan PBS. And as the number of rescan increase, the distribution of homogeneity is uniform. Compared with single scan plan and 12 rescan plan, HI value was improved by 0.32. Further studies are expected to be applicable to patients who can not be treated with respiratory synchronous radiation therapy.
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KEYWORD
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Proton therapy, PBS, Layered Rescanning, Moving Phantom
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