Characterizing a PTW microDiamond detector in kilovoltage radiation beams

• Published in: Medical physics (Lancaster) 2020-09, Vol.47 (9), p.4553-4562
• Main Authors: Khan, Ahtesham Ullah, Culberson, Wesley S., DeWerd, Larry A.
• Format: Article
• Language: English
• Subjects: Calibration; Diamond; diamond dosimetry; energy dependence; kilovoltage x‐ray beams; Monte Carlo Method; Photons; radiation dosimetry; Radiometry; solid‐state detectors; X-Rays
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1002/mp.14330

Purpose The aim of this work was to characterize the dosimetric properties of the PTW microDiamond (60019) single crystal synthetic diamond detector (DD) in kilovoltage x‐ray beams. The following characteristics were addressed in this study: required preirradiation dose, dose‐rate linearity, energy dependence, and percent depth dose response of the DD. Methods UWADCL x‐ray beams, characterized by NIST‐traceable ionization chambers, were used in this study. Preirradiation dose required by the DD, in order to stabilize the detector’s response to within 0.1%, was quantitated. Dose‐rate dependence was also investigated using the UW250‐M and UW50‐M beams, where the dose rate was varied by changing the tube current. Nk and ND,w calibration coefficients for all the available M series beams at UWADCL were obtained to determine the energy dependence of the DD, Diode E, Diode P, and P11 parallel‐plate ionization chamber. A custom‐built water tank was utilized to measure the percent depth dose (PDD) response of the DD, Diode E, Diode P, and P11 chamber in UW250‐M, UW100‐M, and UW50‐M beams. The measured PDD response of the detectors was compared with the simulated PDD data using EGSnrc Monte Carlo code. Results A 1.5 Gy dose‐to‐water or air‐kerma was found to be sufficient for the given DD’s response to stabilize to within 0.1% in all of the beams used in this study. The dose‐rate dependence parameter, Δ, was found to be 1.00 ± 0.02 and 1.016 ± 0.05 for the UW250‐M and UW50‐M beams, respectively. Relative to the 60 Co calibration coefficients, the DD was found to under‐respond relative to calculated absorbed dose to water response and over‐respond relative to the calculated air‐kerma response in the M‐series beams. Agreement of 1.5% was found between the measured PDD values and Monte Carlo simulated PDD values for UW250‐M, UW100‐M, and UW50‐M beams. Conclusions In order to stabilize the response, the DD needs a preirradiation dose, which is unique to every DD. A linear relationship between detector response and dose rate was found within the evaluated uncertainty. An energy dependence of the DD was studied, which is more pronounced in the low‐energy beams and can be partially attributed to the metal contact material around the sensitive volume of the DD. Overall, the DD was found to be suitable for kilovoltage x‐ray dosimetry.