Journal of Radiation Research and Applied Sciences (Dec 2022)

The determination of virtual source position using convergent arcSIN method for scanning-passive scatter beam in carbon ion therapy

  • Hai-Shi Chen,
  • Li Meng,
  • Jia-Ming Wu

Journal volume & issue
Vol. 15, no. 4
p. 100475

Abstract

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Introduction: We developed a convergent arcSIN (cASIN) technique capable of dealing with the virtual source position delivered by different carbon ion energies from the pattern of scanning-passive scatter beam in this study. Materials and methods: A homemade large-format CMOS sensor and Gaf Chromic EBT3 films were used for the virtual source position measurement. The Gaf films were embedded in a self-designed rectangular plastic frame to tight the films and set up on a treatment couch for irradiation in the air with the film perpendicular to the carbon ion beam at the nominal source-axis-distance (SAD) as well as upstream and downstream from the measurement point at SAD. The horizontal carbon ion beam with 5 energies at a machine opening field size was carried out in this study. The virtual source position was determined with a convergent arcSIN method and compared to the way used nowadays with the linear regression by back projecting the FWHM to zero at a SAD distance upstream from the various source-film-distance. Results: The determination of virtual source position using convergent arcSIN method agrees with the method by back projecting the FWHM to zero, and for higher carbon ion energy has an obvious longer distance from the SAD since the more carbon ion beam energy, the less spreading affected by the horizontal and vertical magnetism, therefore, the distance of virtual source positions is decreased from the SAD point with high to low energy. Conclusion: We have developed a technique capable of dealing with the virtual source position with a convergent arcSIN method to avoid any manual measurement mistakes as well as a double-check mistake-proofing in scanning-passive scatter carbon ion beam. The method for investigating the virtual source position in the carbon ion beam in this study can also be used for external electrons and the proton.

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