Three-dimensional gel dosimetry for dose volume histogram verification in compensator-based IMRT

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. 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 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. 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

Comparison of conventional and 3D conformal treatments using linac energies for prostate cancer

To evaluate the dosimetric difference between conventional and three-dimensional conformal Radiotherapy [3D-CRT] using 6 and 18 MV X-ray photons. 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 [D[min]], maximum dose [D[max]] and mean dose [D[mean]] 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. 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 D[mean] of the bladder and femoral heads, as well as D[max] 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 D[mean] of bladder, rectum and femoral heads and also CI and ID were significantly improved by 44.6% and 30.8%, respectively. 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