Room: AAPM ePoster Library
Purpose: To investigate the response of a radiophotoluminescent glass dosimeter (RGD: GD-302M) for diagnostic kilovoltage x-ray beams.
Methods: The RGD response for x-ray spectra with different tube voltages was evaluated as a function of Al half-value layer (Al-HVL) in free air and at surface of a water phantom. The Al-HVL and quality index (QI) were used as a beam quality specifier. The QI is specified by the ratio of effective photon energy and tube voltage (kVp). The RGD responses in “free air” and at “the phantom surface” were defined as “the ratio of RGD dose and air kerma (K???)” and “the ratio of RGD dose and entrance skin dose (ESD)”, respectively. The both responses were calculated for x-ray spectra with Al-HVL values of 1.5-10.4 mm and monoenergetic photon beams using the EGSnrc/cavity code. The responses were classified by parameter QIs of 0.4, 0.5 and 0.6. In addition, K??? and ESD were measured by RGD for QI of 0.5. The RGD reading was converted to K??? or ESD using the calculated RGD response. Finally, K??? and ESD measured by RGD were compared with those measured with the ionization chamber.
Results: The RGD responses in free air and at the phantom surface indicated a good correlation with Al-HVL by using parameter QI for the x-ray spectra with different tube voltages. The difference in the response between 10 × 10 and 20 × 20 cm² fields at the surface was less than 2% and almost independent of the field size. In addition, K??? and ESD measured by RGD agreed within 3% and 2%, respectively, with those of the chamber measurement.
Conclusion: The RGD response in free air and at the phantom surface for kilovoltage x-ray beams was a good correlation with Al-HVL by using parameter QI.