Polymer gel dosimeter is a radiation sensitive chemical dosimeter that can measure 3 D dose distribution with high resolution. Due to the increasing complexity of radiotherapy treatment planning and delivery, accurate experimental radiation dosimetry plays an important role in the implementation and quality assurance of new treatment techniques. A polymer gel dosimeter must possess several important characteristics of a dosimeter to be able to measure absorbed dose precisely. two important dosimetric properties of a dosimeter were determined in this study; accuracy and precision. The MAGAT gels were made of 5% gelatin, 6% methacrylic acid and 10 mM tetrakis-hydroxy-methyl-phosphonium chloride (THPC). The irradiation of MAGAT gel was performed by 6-MV photon beam at a dose range 1 to 10 Gy and was imaged by 1.5 T Magnetic Resonance Imaging (MRI). The dose response of MAGAT gel dosimeter was obtained from spin-spin relaxation rate (R2) of MRI signal. The accuracy of MAGAT gel dosimeter has a range within 4% for doses greater than and equal to 3 Gy. The reproducibility of the MAGAT gel dosimeter at one irradiation was less than 1% whilst the long term reproducibility was within 3% over the five month period. For temporal stability, the dose sensitivity of MAGAT gel dosimeter irradiate at 1 to 11 days post-manufacturing decreased over time. While the dose sensitivity imaged at 1 to 9 days post-irradiation increased up to 4 days post-irradiation and subsequently starts decreasing after 4 days till 9 days. From the study of two dosimetric properties, MAGAT gel dosimeter shows a great dose response with a superior dose response. Thus the MAGAT gel dosimeter can be apply as a 3 D radiotherapy dosimeter.
The effect of gel homogeneity on dose response in a low-density polymer gel dosimeter for radiation therapy
