Surface and build-up region dose measurement in head and neck region using radio - photoluminescent glass dosimeter

The use of commercially available radio-photoluminescent glass dosimeter (RPLGD) for radiation measurement has increased in recent years. It has been shown to have superior dosimetric characteristics as compared to other dosimeters. The purpose of this research is to evaluate the suitability of the GD-302M glass dosimeter for surface and build-up region dose measurement in head and neck region. The glass dosimeter was analyzed for its dosimetric properties in photon beam. Then, the study was performed for surface and build-up region dose comparison between EBT3 film and RPLGD in solid water phantom at 0, 2, 3, 5, 10 and 15mm depths of 6 MV beams. In addition, 3D-CRT and VMAT plans for nasopharyngeal carcinoma were transferred to a Rando phantom for verification of build-up region dose at 5 and 10mm depths. The results found that uniformity obtained in this study was within 1.1%. The dose-response was linear with R2 of 0.999. Dose rate, reproducibility, angular and energy dependence were found to be within 3.0%. Moreover, fading effect was less than 3% over 4 weeks. The dose in homogeneous solid water phantom showed good agreement between RPLGD and EBT3 film in build-up region. However, RPLGD showed over response of signal at the surface  due to the thickness of its holder. The verification in Rando phantom illustrated that build-up region doses were higher in TPS calculation compared to RPLGD measurements both in 3DCRT and VMAT. The average dose differences between measurements and calculations were -0.18±1.21% and 2.40±1.49% at 5 mm and 10 mm depth for 3D-CRT, and 4.74±1.12% and 3.44±4.41% at 5 mm and 10 mm depth for VMAT, respectively. In conclusion, RPLGD is less suitable for surface dose measurement but has good potential to be used as an in-vivo dosimeter in build-up dose measurements.