ABSTRACT
Background: in this study a series of basic dosimetric properties of a low-density [LD] gel dosimeter are investigated. The dose response is studied regarding to linearity, sensitivity, dose-rate and energy dependence as well as lung tissue equivalence
Materials and Methods: the LD gel was made by mixing the polymer gel with expanded polystyrene spheres. Energy dependence was studied at two different energies: 1.25 MeV and 6 MV photon beams which were produced by [60]Co and Linac machines. Investigation of dose rate dependence was performed in the low, medium, and high absorbed dose regions. Also reproducibility of dose response was studied in three sets of LD gel with identical preparation, irradiation and imaging procedure at three different days. Moreover the linearity and sensitivity were investigated up to 30Gy
Results: the results showed that the dose response was reproducible. The gel response was found linear up to 22Gy with r[2]=0.981 and sensitivity of 0.814S[-1]Gy[-1]. In the measured ranges, the dose response of LD gel was independent of beam energy within less than +/-0.02 and dose rate had no effect on the gel response. LD gel was nearly lung tissue equivalent with mass density 0.37 to 0.4g/cm3 and relative electron density 0.41
Conclusion: MAGAT LD gel dosimeter appears to be a promising dosimeter in all aspects of dosimetric properties evaluated in this study. In addition, its high linearity together with no dose rate dependence in different level of absorbed doses makes it a suitable dosimeter to measure 3D-dose distributions inside a non-homogeneous media
ABSTRACT
In this study the basic radiation properties of N-isopropylacrylamaide polymer gel dosimeter were determined together with verification of its soft tissue equivalency. The NIPAM gel was prepared and irradiated approximately 2 h after manufacturing. The magnetic resonance [MR] images were made 24 h after irradiation. The nuclear magnetic resonance [NMR] response [R2] of the dosimeters was analyzed for conditions of varying dose, batch, dose rate, time post-irradiation and energy. In order to verify tissue equivalence of NIPAM dosimeter, several parameters such as physical density, effective atomic number, relative electron density, CT [Computed Tomography] number and also elemental composition were determined and compared with those for soft tissue. The response of the gel was found to be stable 24 hours after irradiation. The results showed that the dose response of the NIPAM polymer gel is reproducible in same and different batches of chemical and the gel response was linear up to 26 Gy with r2=0.995. In the measured range, the dose response of the NIPAM gel is independent of beam energy within less than +/- 0.02 and the dose rate had no effect on the gel response. This polymer gel has been found to be tissue equivalent. NIPAM gel dosimeter appears to be a promising dosimeter in all aspects of dosimetric properties which were assessed in this study, in addition to the advantage of reduced toxicity which it has over other polymer gels