Evaluation of beam hardening and photon scatter by brass compensator for IMRT

Shimpei Hashimoto, Katsuyuki Karasawa, Yukio Fujita, Hisayuki Miyashita, Weishan Chang, Toru Kawachi, Tetsurou Katayose, Nao Kobayashi, Etsuo Kunieda, Hidetoshi Saitoh

    Research output: Contribution to journalArticlepeer-review

    4 Citations (Scopus)

    Abstract

    When a brass compensator is set in a treatment beam, beam hardening may take place. This variation of the energy spectrum may affect the accuracy of dose calculation by a treatment planning system and the results of dose measurement of brass compensator intensity modulated radiation therapy (IMRT). In addition, when X-rays pass the compensator, scattered photons are generated within the compensator. Scattered photons may affect the monitor unit (MU) calculation. In this study, to evaluate the variation of dose distribution by the compensator, dose distribution was measured and energy spectrum was simulated using the Monte Carlo method. To investigate the influence of beam hardening for dose measurement using an ionization chamber, the beam quality correction factor was determined. Moreover, to clarify the effect of scattered photons generated within the compensator for the MU calculation, the head scatter factor was measured and energy spectrum analyses were performed. As a result, when X-rays passed the brass compensator, beam hardening occurred and dose distribution was varied. The variation of dose distribution and energy spectrum was larger with decreasing field size. This means that energy spectrum should be reproduced correctly to obtain high accuracy of dose calculation for the compensator IMRT. On the other hand, the influence of beam hardening on kQ was insignificant. Furthermore, scattered photons were generated within the compensator, and scattered photons affect the head scatter factor. These results show that scattered photons must be taken into account for MU calculation for brass compensator IMRT.

    Original languageEnglish
    Pages (from-to)999-1005
    Number of pages7
    JournalJournal of radiation research
    Volume53
    Issue number6
    DOIs
    Publication statusPublished - 2012 Nov

    Keywords

    • Brass compensator IMRT
    • beam hardening
    • dose distribution
    • quality correction factor
    • scatter photon

    ASJC Scopus subject areas

    • Radiation
    • Radiology Nuclear Medicine and imaging
    • Health, Toxicology and Mutagenesis

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