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Background: To evaluate the dosimetric difference between conventional and three-dimensional conformal Radiotherapy (3D-CRT) using 6 and 18 MV X-ray photons. Materials and Methods: Computed tomography scans of 26 pelvic patients were acquired and transferred to the 3D treatment planning system. For each patient, 8 Conventional plans (3, 4, 5 and 6 Fields) and one 3D-CRT plan were prepared using 6 and 18 MV photon energies. The minimum dose (Dmin), maximum dose (Dmax) and mean dose (Dmean) to target (PTV) and organs at risk (OAR), Integral dose, Homogeneity Index and Conformity Index were compared for each plan. Also, Experimental measurements were performed using farmer ionization chamber on a patient based pelvic phantom. Results: On Average, six-field (6F1) plans, offer minimum dose to critical organs and sufficient dose to prostate. Increasing the beam energy lead to a decrease in Dmean of the bladder and femoral heads, as well as Dmax of PTV. The CI and ID were decreased by 4% and 11% respectively with increasing the energy and the number of beams. Experimental measurements were also in good agreement with calculations. 3D-CRT reduced Dmean of bladder, rectum and femoral heads and also CI and ID were significantly improved by 44.6% and 30.8%, respectively. Conclusion: Increasing the photon energy and number of beams, improve the treatment parameters of bladder, femoral heads and PTV, except the rectum. 3D-CRT offered the most conformity in the delivery doses to the prostate while sparing dose to OARs, uninvolved structures with lower integral dose. Iran. J. Radiat. Res., 2012 10(3‐4): 145‐150

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Background: Some tissues in human body are radiobiologically different from water and these inhomogeneity must be considered in dose calculation in order to achieve an accurate dose delivery. Dose verification in complex radiation therapy techniques, such as intensity‐modulated radiation therapy (IMRT) calls for volumetric, tissue equivalent and energy independent dosimeter. The purpose of this study is to verify a compensator‐based IMRT plan in anthropomorphic inhomogeneous phantom by Dose Volume Histograms (DVH) using polymer gel dosimetry. Materials and Methods: An anthropomorphic pelvic phantom was constructed with places for gel inserts. Two attached cubic inserts for prostate and bladder and a cylindrical insert for rectum. A prostate treatment case was simulated in the phantom and the treatment was delivered by a five field compensator‐based IMRT. Gel dosimeters were scanned by a 1.5 Tesla magnetic resonance imaging (MRI). Results were analyzed by DVH and difference of differential DVH. Results: Results showed for 3D compensator‐based IMRT treatment plan for prostate cancer, there was overall good agreement between calculated dose distributions and the corresponding gel measured especially in planning target volume (PTV) region. Conclusion: Our measurements showed that the used treatment plan configuration has had clinically acceptable accuracy and gel dosimetry can be considered as a useful tool for measuring DVH. It may also be used for quality assurance and compensator‐based IMRT treatment verification.

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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 ⁶⁰Co 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 r²=0.981 and sensitivity of 0.814S^-1Gy^-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.