Background: Since 1984 MRI gel DOSIMETRY has been introduced as a potential technique for 3D DOSIMETRY. Most of the studies have measured R1 (1/T1) or R2 (1/T2) properties of the gel depending on the gel type. We have studied image intensity change in the Fricke gel by different MRI protocols. Materials and Methods: Gel Dosimeters contain 0.4 mM ferrous sulphate, 1 mM NaCl, 50 mM H2SO4 and 1% by weight agarose in distilled water. Prepared gels were poured in Plastic tube phantom and irradiated to a beam of Co-60 gamma rays. Imaging was performed by a 0.5T MRI system in the head coil with SE and GRE techniques.Results: Our results showed that linear response exists between the variations of image intensity with absorbed dose (1-15 Gy). Optimal imaging parameters should be defined locally according to the type of MRI scanner and exact composition of the gel. Gradient echo (GRE) imaging technique also have been studied in comparison with classic spin echo (SE) imaging technique which will be discussed in detail. Conclusions: Linearity of absorbed dose with intensity exists up to 15 Gy and can be used for MRI gel DOSIMETRY. Reduction of imaging time is achievable in image intensity technique so that it’s possible to image the gel in less than 20 minutes, which is critical to over-come the adverse ion-diffusion properties of the Fricke gel. Iran

Introduction: Despite the fact that the clinical implementation of polymer gel DOSIMETRY has been facilitated after the introduction of normoxic gels, there are still complications in its clinical routine use that are under investigation. In the current work, the feasibility of using a normoxic polymer gel dosimeter named MAGICA has been investigated for use in our clinical brachytherapy applications at Imam Hospital and the deviations between the results obtained from two different calibration methods were investigated. Materials and Methods: The gel fabrication was performed at Novin Medical Radiation Institute and 4 Perspex walled phantoms designed especially for brachytherapy irradiations were filled with the same gel, together with 15 plastic calibration test tubes. The test tubes were irradiated with a range of known doses using a cobalt-60 teletherapy unit and the phantoms were irradiated with two brachytherapy remote-after-loaders using Cs137 and Co60 brachytherapy sources according to the treatment planning data. Imaging was performed with a Multi-spin-echo protocol using a Siemens 1.5T MRI machine. Image processing was performed in MATLAB environment to extract R2 maps of the dose distributions. Gel fabrication, irradiation and imaging were performed at three different centers, so the dosimeters and test tubes were transferred from one center to another under non-uniform conditions. R2 values of the first dosimeter which was irradiated with a single cesium source were extracted from different distances from the source along a horizontal profile and correlated to the dose values at the same distances in treatment planning data. This was used as the second calibration method to extract the absolute measured values of the other three dosimeters. Diagrams of the absorbed dose versus distance were plotted for each dosimeter and the results obtained from the two calibration methods were compared. Results: Results of the measured values that were calibrated with the test tubes show a 3 to 6 Gy dose difference in plateaus and more than 2 mm distance to agreement gap in steep dose gradients. However, the results of using the second calibration method show at most a 0.36 Gy dose difference in plateaus and less than 2 mm distance to agreement gap in steep dose gradients. Discussion and Conclusion: As the gel fabrication, irradiation and imaging conditions were the same for all the gel dosimeters and the calibration tubes, the unexpected deviations between the results of the two calibration methods deserves more investigations. It seems plausible to attribute this deviation to the difference in the size of calibration test tubes and original dosimeters. From a practical point of view, as the origin of this effect has not yet been investigated, it would be best to use a calibration phantom with the same size and characteristics as the original dosimeters.

Introduction: Estimation of activity accumulated in tumor and organs is very important in predicting the response of radiopharmaceuticals treatment. In this study, we synthesized 177Lu-trastuzumab-iron oxide nanoparticles as a double radiopharmaceutical agent for treatment and better estimation of organs activity in a new way by MRI imaging.Methods: 177Lu-trastuzumab-iron oxide nanoparticles was synthesized and all the quality control tests such as labeling yield, nanoparticle size determination, stability in buffer and blood serum up to 4 days, immunoreactivity and biodistribution in normal mice was determined. In mice bearing tumor, liver and tumor activities were calculated in three methods: SPECT, MRI imaging and organs extraction were compared with each other.Results: The good results of quality control tests (labeling yield: 61±2%, mean nanoparticle hydrodynamic size ~ 41±15, stability in buffer: 86±5%, stability in blood serum: 80±3%, immunoreactivity: 80±2%) indicated that 177Lu-trastuzumab-iron oxide nanoparticles could be used as a double radiopharmaceutical agent in mice bearing tumor. Results showed that 177Lu-trastuzumab-iron oxide nanoparticles with MRI imaging had the ability to measure organs activities more accurate than SPECT imaging.Conclusion: Co-conjugating radiopharmaceutical to MRI contrast agents such as iron oxide nanoparticles may be a good way for better DOSIMETRY in nuclear medicine treatment.

Introduction: The purpose of this work was to study the ability of MRI normoxic polymer gel DOSIMETRY for evaluating the dose distribution in HDR brachytherapy of esophagial cancer at Imam Reza brachytherapy center (Mashhad, Iran). Materials and Methods: Initially, 2liters of normoxic gel (MAGIC) was fabricated and then poured into 12 calibration test tubes and placed in a perspex walled phantom. The gel phantom was irradiated with a brachytherapy remote-afterloader unit using a cobalt-60 brachytherapy source and the test tubes were irradiated with a range of known doses with a cobalt-60 teletherapy unit. Imaging was performed with a multi-spin-echo protocol and a T2 quantitative technique using a Siemens 1.5 T MRI machine. The MRI images were transferred to a computer and then image processing was performed in the MATLAB environment to extract R2 maps of the irradiated area. Results: In this study and at the reference point, the dose deviation between the gel DOSIMETRY and the calculated data was 4.5%. The distance to agreement (DTA) for dose profiles was 2.7 mm. Also, dose sensitivity of the MAGIC gel dosimeter was 0.693 S-1Gy-1 (R2=0.9376). Conclusion: In this work, the data obtained from TPS calculations were found in very good agreement with the measured results provided by gel DOSIMETRY. It was evaluated using a comparison of isodoses and dose at the reference point, and dose profile verification. It is also concluded that the gel DOSIMETRY systems have proven to be a useful tool for DOSIMETRY in clinical radiotherapy applications.

Introduction: Computed tomography (CT) has numerous applications in clinical procedures but its main problem is its high radiation dose to the patients compared to other imaging modalities using x-ray. CT delivers approximately high doses to the nearby tissues due to the scattering effect, fan beam (beam divergence) and limited collimator efficiency. The radiation dose from multi-slice scanners is greater than the single-slice scanners and since multi-slice scanners increasingly employ a wide beam, 100 mm ion chambers currently used in measuring the CTDI100, are not capable of accurately measuring the total dose profile of the slice width. Therefore, the CT dose is underestimated by using them. The purpose of this study is to measure the Computed Tomography Dose Index (CTDI) of a GE multi-slice CT scanner (64-slice) using polymer gel DOSIMETRY based on MRI imaging (MRPD). CTDI is the sum of point doses along the central axis and estimates the average patient dose during CT scanning.Materials and Methods: For measuring CTDI, after designing and fabricating the phantom and preparing the MAGIC gel, MRI imaging using a 1.5 T Siemens MRI scanner was performed with the imaging parameters of ST=2 mm, NEX=1, TE=20-640 ms and TR=2000 ms. CTDI was measured with a 100 mm ion chamber (CTDI100) and also the MAGIC gel with MRPD method for 10 mm and 40 mm CT scan nominal widths.Results: Following the measurement of the CTDI100 for 10 mm and 40 mm nominal slice widths of the multi-slice scanner using both ion chamber and MAGIC gel, the results showed that the ion chamber underestimates CTDI100 by 28.71% and 14.03% compared to gel for 10 mm and 40 mm respectively.Discussion and Conclusion: It was concluded from this study that gel dosimeters have the capability to measure CTDI in wide beams of multi-slice CT scanners whereas 100 mm standard ion chamber due to its limited length is not reliable even for a 10 mm beam width. In addition, due to the 3 dimensional nature of gel DOSIMETRY, by using a MAGIC polymer gel, it is possible to obtain a lot of important information from the mentioned profiles such as the actual slice thickness and z-axis geometric efficiency. In addition to the stated parameters, the percentages of the total and partial homogeneities in the slice plane can be obtained only from gel DOSIMETRY. The results of this study show that MAGIC polymer gel DOSIMETRY based on MRI can be used as a supplementary method to using conventional ion chamber DOSIMETRY especially in measurements for slice widths greater than 2 mm.

Introduction: 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. Materials and Methods: 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. Results: 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 were observed. Discussion and Conclusion: 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. At 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.

Radiotherapy has been the modality for treating cancer patients worldwide for more than 100 years. Radiation dose to patients is delivered through different techniques using high-energy photon beams generated by the linear accelerators. Radiotherapy techniques are developing at a speed never seen before. For continuous improvement, safe and effective radiotherapy delivery requires implementing adapted quality assurance (QA) programs and integral quality management (QM) systems. A key step in any QA program is the DOSIMETRY audit. It provides an effective tool to improve the accuracy of patients’ treatments. In the global panorama, DOSIMETRY audit programs are conducted by various institutions. Still, the largest of them is the International Atomic Energy Agency (IAEA) in Vienna, Austria, the Imaging and Radiation Oncology Core (IROC-H) Houston QA Center in the USA, and EQUAL (European Quality Laboratory) Laboratory in the framework of the ESTRO (European Society for Therapeutic Radiology and Oncology) ESTRO – EQUAL Laboratory in Villejuif Cedex, France.