Progress in Medical Physics (한국의학물리학회지:의학물리)

Korean Society of Medical Physics (한국의학물리학회)
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Development of a Beam Source Modeling Approach to Calculate Head Scatter Factors for a 6 MV Unflattened Photon Beam

  • Park, So-Yeon (Department of Radiation Oncology, Veterans Health Service Medical Center) ;
  • Choi, Noorie (Department of Radiation Oncology, Veterans Health Service Medical Center) ;
  • Jang, Na Young (Department of Radiation Oncology, Veterans Health Service Medical Center)
  • Received : 2021.11.30
  • Accepted : 2021.12.14
  • Published : 2021.12.31
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Abstract

Purpose: This study aimed to investigate the accuracy of head scatter factor (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.

Keywords

Acknowledgement

This study was supported by a VHS Medical Center Research Grant, Republic of Korea (grant number: VHSMC 21021).

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