[Electron beam dosimetry in heterogenous phantoms using a MAGIC normoxic polymer gel

Nowadays radiosensitive polymer gels are used as a reliable dosimetry tool for verification of 3D dose distributions. Special characteristics of these dosimeters have made them useful for verification of complex dose distributions in clinical situations. The aim of this work was to evaluate the capability of a normoxic polymer gel to determine electron dose distributions in different slab phantoms in presence of small heterogeneities. Different cylindrical phantoms consisting gel were used under slab phantoms during each irradiation. MR images of irradiated gel phantoms were obtained to determine their R2 relaxation maps. 1D and 2D lateral dose profiles were acquired at depths of 1 cm for an 8 MeV beam and 1 and 4 cm for the 15 MeV energy, and then compared with the lateral dose profiles measured using a diode detector. In addition, 3D dose distributions around these heterogeneities for the same energies and depths were measured using a gel dosimeter. Dose resolution for MR gel images at the range of 0-10 Gy was less than 1.55 Gy. Mean dose difference and distance to agreement [DTA] for dose profiles were 2.6% and 2.2 mm, respectively. The results of the MAGIC-type polymer gel for bone heterogeneity at 8 MeV showed a reduction in dose of approximately 50% and 30% and 10% at depths 1 and 4 cm at 15 Mev. However, for air heterogeneity increases in dose of approximately 50% at depth 1 cm under the heterogeneity at 8 MeV and 20% and 45% respectively at 15 MeV. However, for air heterogeneity increae in dose of approximately 50% at depth 1 cm under the heterogeneity at 8 MeV and 20% and 45% respectively at 15 MeV were observed. Generally, electron beam distributions are significantly altered in the presence of tissue inhomogeneities such as bone and air cavities, this being related to mass stopping and mass scattering powers of heterogeneous materials. A the same time, hot and cold scatter lobes under heterogeneity regions due to scatter edge effects were also seen. However, these effects [increased dose, reduced dose, hot and cold spots] at deeper depths, are compensated with the contributions of scattered electrons. Our study showed that normoxic polymer gels are reliable detectors for determination of electron dose distributions due to their characteristics such as tissue equivalence, energy independence, and 2D and 3D dose visualization capabilities

[Dosimetric comparison of various radiotherapeutic treatment plans using cobalt-60 and linac for prostate cancer]

This study was designed to evaluate dosimetric parameters such as rectal dose, bladder dose, integral dose [ID], homogeneity index [HI] and conformity index [CI] in various treatment plans for prostate cancer. Pelvic computed tomography [CT] scans of 27 patients were acquired and transferred to the RTDosePLAN treatment planning system. For each patient, 8 conventional plans [3, 4, 5 and 6 fields] were planned for the cobalt-60 photon energy. Subsequently, the same plans were performed for 6 MY and 18 MY photon energies. By increasing the energy of the beam relative to the cobalt-60 energy, the D[mean] values for rectum and bladder were reduced from 3% to 4% and 4% to 6%, respectively, the dose received by the whole of the bladder volume decreased by 26% for 6 MV and by 58% for 18 MV. Increasing the photon beam energy decreased CI to 7% and 10% ID was decreased by l0% and 20% and D[max] was decreased by 3% and 4% respectively. A six-field treatment plan in comparison to the other plans offers the minimum dose to critical organs and sufficient dose to the prostate. Increasing the photon energy improves the treatment parameters of the bladder and the PTV