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KMID : 1038720210320040137
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Progress in Medical Physics
2021 Volume.32 No. 4 p.137 ~ p.144
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Development of a Beam Source Modeling Approach to Calculate Head Scatter Factors for a 6 MV Unflattened Photon Beam
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Park So-Yeon
Choi Noo-Rie
Jang Na-Young
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Abstract
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Purpose: T his s tudy a imed t o i nvestigate t he a ccuracy o f h ead s catter f actor ( Sc) by applying a developed multi-leaf collimator (MLC) scatter source model for an unflattened photon beam.
Methods: Sets of Sc values were measured for various jaw-defined square and rectangular fields and MLC-defined square fields for developing dual-source model (DSM) and MLC scatter model. A 6 MV unflattened photon beam has been used. Measurements were performed using a 0.125 cm3 cylindrical ionization chamber and a mini phantom. Then, the parameters of both models have been optimized, and Sc has been calculated. The DSM and MLC scatter models have been verified by comparing the calculated values to the three Sc set measurement values of the jaw-defined field and the two Sc set measurement values of MLC-defined fields used in the existing modeling, respectively.
Results: For jaw-defined fields, the calculated Sc using the DSM was consistent with the measured Sc value. This demonstrates that the DSM was properly optimized and modeled for the measured values. For the MLC-defined fields, the accuracy between the calculated and measured Sc values with the addition of the MLC scatter source appeared to be high, but the only use of the DSM resulted in a significantly bigger differences.
Conclusions: Both the DSM and MLC models could also be applied to an unflattened beam. When considering scattered radiation from the MLC by adding an MLC scatter source model, it showed a higher degree of agreement with the actual measured Sc value than when using only DSM in the same way as in previous studies.
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KEYWORD
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Head scatter factor, Unflattened photon beam, Multi-leaf collimator, Dual-source model
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