Room: Exhibit Hall | Forum 8
Purpose: To calculate the absorbed dose-to-water conversion factor (CF) for direct surface dose measurements using a commercial nanoDot optically stimulated luminescent detector (OSLD) in kilovoltage x-ray beams.
Methods: Thirty-nine fluence spectra of kilovoltage x-ray beams were calculated for Al-HVL values ranging from 1.4 to 8.5 mm (effective energy range of 25 to 57 keV) and tube voltages of 50 to 137.6 kVp using the SpekCalc program. Using these spectra, the water dose and nanoDot dose at the surface in a water phantom were calculated with the EGSnrc/cavity Monte Carlo code. The CFs for the beam qualities of the 39 x-ray fluence spectra were obtained from the ratio of both doses (water dose/nanoDot dose at the water surface) in the range from 10 Ã— 10 to 40 Ã— 40 cmÂ² field at a source-to-surface distance of 100 cm. In addition, the CFs were calculated for the 10 monoenergy photon beams of 25 to 55 keV (Al-HVL in the range of 1.5 to 8 mm).
Results: The CFs at a 20 Ã— 20 cm2 field were at 0.297 to 0.415 for Al-HVL in the range of 1.4 to 8.5 mm, respectively. The CFs linearly increased as Al-HVL increased. The difference in CFs between 10 Ã— 10 and 40 Ã— 40 cmÂ² field was up to 2% for Al-HVL of 8.5 mm. Similarly, the CFs for the monoenergy photon beams were at 0.289 to 0.376 in the energy range of 25 to 55 keV, respectively. The CFs quadratically increased as Al-HVL increased. The difference in the CFs between x-ray fluence spectra and the monoenergy photon beams was up to 11% for Al-HVL of 6 mm.
Conclusion: Using CFs calculated in this study, it made it possible to directly evaluate the entrance surface dose using a nanoDot detector for kilovoltage x-ray beams.