Theoretical and empirical investigations of KCl:Eu{sup 2+} for nearly water-equivalent radiotherapy dosimetry

• Published in: Medical physics (Lancaster) Vol. 37; no. 1
• Main Authors: Zheng Yuanshui, Han Zhaohui, Driewer, Joseph P., Low, Daniel A., Li, H. Harold
• Format: Journal Article
• Language: English
• Published: United States 15-01-2010
• Subjects: ATOMIC NUMBER; BARIUM FLUORIDES; DOPED MATERIALS; DOSE EQUIVALENTS; DOSEMETERS; DOSIMETRY; ENERGY DEPENDENCE; EUROPIUM; EUROPIUM IONS; IONIZATION CHAMBERS; IRRADIATION; MATERIALS SCIENCE; MONTE CARLO METHOD; PHANTOMS; PHASE SPACE; POTASSIUM CHLORIDES; RADIATION DOSES; RADIATION PROTECTION AND DOSIMETRY; RADIOTHERAPY; SENSITIVITY; TWO-DIMENSIONAL CALCULATIONS
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.3271338

Purpose: The low effective atomic number, reusability, and other computed radiography-related advantages make europium doped potassium chloride (KCl:Eu{sup 2+}) a promising dosimetry material. The purpose of this study is to model KCl:Eu{sup 2+} point dosimeters with a Monte Carlo (MC) method and, using this model, to investigate the dose responses of two-dimensional (2D) KCl:Eu{sup 2+} storage phosphor films (SPFs). Methods: KCl:Eu{sup 2+} point dosimeters were irradiated using a 6 MV beam at four depths (5-20 cm) for each of five square field sizes (5x5-25x25 cm{sup 2}). The dose measured by KCl:Eu{sup 2+} was compared to that measured by an ionization chamber to obtain the magnitude of energy dependent dose measurement artifact. The measurements were simulated using DOSXYZnrc with phase space files generated by BEAMnrcMP. Simulations were also performed for KCl:Eu{sup 2+} films with thicknesses ranging from 1 {mu}m to 1 mm. The work function of the prototype KCl:Eu{sup 2+} material was determined by comparing the sensitivity of a 150 {mu}m thick KCl:Eu{sup 2+} film to a commercial BaFBr{sub 0.85}I{sub 0.15}:Eu{sup 2+}-based SPF with a known work function. The work function was then used to estimate the sensitivity of a 1 {mu}m thick KCl:Eu{sup 2+} film. Results: The simulated dose responses of prototype KCl:Eu{sup 2+} point dosimeters agree well with measurement data acquired by irradiating the dosimeters in the 6 MV beam with varying field size and depth. Furthermore, simulations with films demonstrate that an ultrathin KCl:Eu{sup 2+} film with thickness of the order of 1 {mu}m would have nearly water-equivalent dose response. The simulation results can be understood using classic cavity theories. Finally, preliminary experiments and theoretical calculations show that ultrathin KCl:Eu{sup 2+} film could provide excellent signal in a 1 cGy dose-to-water irradiation. Conclusions: In conclusion, the authors demonstrate that KCl:Eu{sup 2+}-based dosimeters can be accurately modeled by a MC method and that 2D KCl:Eu{sup 2+} films of the order of 1 {mu}m thick would have minimal energy dependence. The data support the future research and development of a KCl:Eu{sup 2+} storage phosphor-based system for quantitative, high-resolution multidimensional radiation therapy dosimetry.