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Comparison of Relative Dosimetric Response of KCl:Eu2+ Between Proton and Photon Irradiation: Implications for LET Independence

J Setianegara*, T Mazur, B Maraghechi, A Darafsheh, D Yang, T Zhao, H Li, Washington University School of Medicine, St. Louis, MO

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To investigate if the modest Z of reusable KCl:Eu2+ storage phosphor dosimeter will result in a more water-like response in a proton spread-out Bragg peak (SOBP) field and if KCl:Eu2+ is less susceptible to linear energy transfer (LET) effects.
Methods: Cylindrical KCl:Eu2+ dosimeters with dimensions of 6 mm diameter and 1 mm thickness were fabricated in-house. The dosimeters were irradiated using both a Mevion S250 passive scattering proton therapy system and a Varian linear accelerator. Photon irradiations are generally believed to be free from LET effects. Dosimetric readouts were performed using a laboratory optical reader after irradiations. The dosimeters were modelled using their fundamental dosimetric quantities including mass stopping powers in detector and water for a given proton beam, and mass energy absorption coefficients and massing stopping powers in detector and water for a given photon beam.
Results: The detected PSL signal strength of the dosimeter in the proton field had been calculated accurately to a maximum discrepancy of 2% using its dosimetric quantities along with its measured signal strength in a photon field at the same dose-to-water. This discrepancy might be attributed to an under-response due to LET effects. However, comparisons of depth-dose measurements in an SOBP field with a parallel-plate ionization chamber showed no clear evidence of LET effects. Furthermore, range measurements agreed with ionization chamber measurements to within 1 mm. KCl:Eu2+ showed linear response over a large dynamic range from 0 to 60 Gy and a strong radiation hardness for at least 200 Gy, which may explain why it is almost free-from LET.
Conclusions: KCl:Eu2+’s relatively low atomic number of 18 and near LET independence make it suited for quantitative proton dosimetry. Any potential measurement artifacts encountered in complex irradiation conditions should be able to be corrected for using its fundamental dosimetric quantities.

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Keywords

Dosimetry, Protons

Taxonomy

TH- Radiation Dose Measurement Devices: Development (new technology and techniques)

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