Dosimetry with a clinical linac adapted to FLASH electron beams
| Autor: | Kirpal Kohli, Yingli Zhao, Stanislaw Szpala, Andrew I. Minchinton, Alastair H. Kyle, V Huang, Tania Karan |
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| Jazyk: | angličtina |
| Rok vydání: | 2021 |
| Předmět: |
Materials science
Film Dosimetry ultra‐high dose rate Electrons Electron FLASH Linear particle accelerator 030218 nuclear medicine & medical imaging 03 medical and health sciences Flash (photography) 0302 clinical medicine Optics ionization chamber Dosimetry Radiation Oncology Physics Humans Radiology Nuclear Medicine and imaging Radiometry Instrumentation Reproducibility gafchromic film Radiation business.industry Reproducibility of Results 030220 oncology & carcinogenesis Ionization chamber Cathode ray Particle Accelerators business Beam (structure) |
| Zdroj: | Journal of Applied Clinical Medical Physics |
| ISSN: | 1526-9914 |
| Popis: | Purpose To assess dosimetric properties and identify required updates to commonly used protocols (including use of film and ionization chamber) pertaining to a clinical linac configured into FLASH (ultra‐high dose rate) electron mode. Methods An 18MV photon beam of a Varian iX linac was converted to FLASH electron beam by replacing the target and the flattening filter with an electron scattering foil. The dose was prescribed by entering the MUs through the console. Fundamental beam properties, including energy, dose rate, dose reproducibility, field size, and dose rate dependence on the SAD, were examined in preparation for radiobiological experiments. Gafchromic EBT‐XD film was evaluated for usability in measurements at ultra‐high dose rates by comparing the measured dose to the inverse square model. Selected previously reported models of chamber efficiencies were fitted to measurements in a broad range of dose rates. Results The performance of the modified linac was found adequate for FLASH radiobiological experiments. With exception of the increase in the dose per MU on increase in the repetition rate, all fundamental beam properties proved to be in line with expectations developed with conventional linacs. The field size followed the theorem of similar triangles. The highest average dose rate (2 × 104 Gy/s) was found next to the internal monitor chamber, with the field size of FWHM = 1.5 cm. Independence of the dose readings on the dose rate (up to 2 × 104 Gy/s) was demonstrated for the EBT‐XD film. A model of recombination in an ionization chamber was identified that provided good agreement with the measured chamber efficiencies for the average dose rates up to at least 2 × 103 Gy/s. Conclusion Dosimetric measurements were performed to characterize a linac converted to FLASH dose rates. Gafchromic EBT‐XD film and dose rate‐corrected cc13 ionization chamber were demonstrated usable at FLASH dose rates. |
| Databáze: | OpenAIRE |
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