IRANIAN JOURNAL OF MEDICAL PHYSICS
Year:2011 | Volume:7 | Issue:4 (29)|Papers Count:9

Introduction: The PAGAT polymer gel dosimeter melts at 30oC and even at room temperature during the summer, so it needs to be kept in a cool place such as a refrigerator. To increase the stability of the PAGAT gel, different amounts of agarose were added to the PAGAT gel composition and the PAGATA gel was manufactured. Material and Methods: The PAGATA gel vials were irradiated using a Co-60 machine. Then, the samples were evaluated using a 1.5 T Siemens MRI scanner. The ingredients of the PAGATA normoxic gel dosimeter were 4.5% N-N' methylen-bis-acrylamide, 4.5% acrylamide, 4.5% gelatine, 5 mM tetrakis (THPC), 0.01 mM hydroquinone (HQ), 0.5% agarose and 86% de-ionized water (HPLC). Results: Melting point and sensitivity of the PAGAT gel dosimeter with addition of 0.0, 0.3, 0.5, 1.0, 1.5 and 2.0% of agarose were measured, in which the melting points were increased to 30, 82, 86, 88, 89 and 90oC and their sensitivities found to be 0.113, 0.1059, 0.125, 0.122, 0.115 and 0.2 S-1 Gy-1 respectively.Discussion and Conclusions: Adding agarose increased the sensitivity and background R2 of the evaluated samples. The optimum amount of agarose was found to be 0.5% regarding these parameters and also the melting point of the gel dosimeter. A value of 0.5% agarose was found to be an optimum value considering the increase of sensitivity to 0.125 and melting point to 86°C but at the expense of increasing the background R2 to 4.530.

Introduction: Diabetic retinopathy (DR) is the single largest cause of sight loss and blindness in the working age population of Western countries; it is the most common cause of blindness in adults between 20 and 60 years of age. Early diagnosis of DR is critical for preventing vision loss so early detection of microaneurysms (MAs) as the first signs of DR is important. This paper addresses the automatic detection of MAs in fluorescein angiography fundus images, which plays a key role in computer assisted diagnosis of DR, a serious and frequent eye disease.Material and Methods: The algorithm can be divided into three main steps. The first step or pre-processing was for background normalization and contrast enhancement of the image. The second step aimed at detecting landmarks, i.e., all patterns possibly corresponding to vessels and the optic nerve head, which was achieved using a local radon transform. Then, MAs were extracted, which were used in the final step to automatically classify candidates into real MA and other objects. A database of 120 fluorescein angiography fundus images was used to train and test the algorithm. The algorithm was compared to manually obtained gradings of those images.Results: Sensitivity of diagnosis for DR was 94%, with specificity of 75%, and sensitivity of precise microaneurysm localization was 92%, at an average number of 8 false positives per image.Discussion and Conclusion: Sensitivity and specificity of this algorithm make it one of the best methods in this field. Using local radon transform in this algorithm eliminates the noise sensitivity for microaneurysm detection in retinal image analysis.

Introduction: Ophthalmic plaque radiotherapy using I-125 radioactive seeds in removable episcleral plaques is often used in management of ophthalmic tumors. Radioactive seeds are fixed in a gold bowl-shaped plaque and the plaque is sutured to the scleral surface corresponding to the base of the intraocular tumor. This treatment allows for a localized radiation dose delivery to the tumor with a minimum target dose of 85 Gy. The goal of this study was to develop a Monte Carlo simulation method for treatment planning optimization of the COMS and USC eye plaques. Material and Methods: The MCNP4C code was used to simulate three plaques: COMS-12 mm, COMS-20 mm, and USC #9 with I-125 seeds. Calculation of dose was performed in a spherical water phantom (radius 12 mm) using a 3D matrix with a size of 12 voxels in each dimension. Each voxel contained a sphere of radius 1 mm. Results: Dose profiles were calculated for each plaque. Isodose lines were created in 2 planes normal to the axes of the plaque, at the base of the tumor and at the level of the 85 Gy isodose in a 7 day treatment.Discussion and Conclusion: This study shows that it is necessary to consider the following tumor properties in design or selection of an eye plaque: the diameter of tumor base, its thickness and geometric shape, and the tumor location with respect to normal critical structures. The plaque diameter is selected by considering the tumor diameter. Tumor thickness is considered when selecting the seed parameters such as their number, activity and distribution. Finally, tumor shape and its location control the design of following parameters: the shape and material of the plaque and the need for collimation.

Introduction: Polymer gels are modern dosimeters providing three dimensional dose distributions. These dosimeters can be used in brachytherapy in which the tumor dimension is relatively small and the dose gradient is high. In this study, the ability of the MAGICA polymer gel was investigated for assessing the absolute dose values as well as the dose distribution of low dose rate (LDR) Ir-192 wires in interstitial brachytherapy based in triangular implants of the Paris system.Material and Methods: A suitable phantom was made from Perspex. Glass tubes were used as the external tubes for holding the Ir-192 wires in the phantom. The MAGICA polymer gel was made and placed in the phantom. The phantom and the calibration tubes were irradiated using LDR Ir-192 wires and a Co-60 teletherapy unit respectively. They were subsequently imaged using an MRI scanner. The R2 (=1/T2) maps were extracted from several sequential T2-weighted MRI images. The dose values resulting from the polymer gel measurements at the reference points were compared with those from the common calculation method at the same points. In addition, the isodose curves resulting from gel dosimetry were compared with those from a brachytherapy treatment planning system (Flexiplan). Results: The average of the dose values measured with the gel at the reference points was 62.75% higher than those calculated at the same points. Investigating the isodose curves revealed that the maximum distance to agreement (DTAmax) between the isodoses resulting from the gel and those obtained from the treatment planning system was less than 3 mm at different dose levels.Discussion and Conclusion: Although the MAGICA gel indicates a higher absolute dose value than those calculated commonly, it can give the relative dose values accurately. Therefore, it can be recommended to be used for the assessment of dose distributions for the treatment of tissues as well as quality control of the treatment planning systems.

Introduction: Different dosimetric modalities (e.g., ionization chambers, semiconductors, TLDs, radiographic films) often have some problems determining isodose curves and percentage depth doses in high dose gradient regions. Research has been ongoing to develop portable high resolution dosimetry devices with accurate absolute dosimetry capabilities and easy data analysis. The ‘PRESAGE’ dosimeter is a type of polymer dosimeters with improved characteristics in comparison with older polymer dosimeters. It is solid, insensitive to oxygen, and can be made in different shapes. This work presents the fabrication process for a PRESAGE dosimeter and optimization of its radiation sensitivity.Material and Methods: The PRESAGE gel was formed in two steps. In the first step, Leuco Malachite Green was dissolved in a free radical initiator (carbon tetrachloride; CCl4) and a polyol, referred to as ‘Part B’ was added to the solution. The second step consisted of mixing the Leuco dye, a free radical initiator, and a catalyst with ‘Part B’ (a commercially available polyol), then blending them with Part A in equal proportions, placing the blended materials in an appropriate mold, and incubating at an optimal temperature under a pressure of 60 psi for 18 to 24 hours. After this period, the solution turned solid and was subsequently exposed using a cobalt-60 unit. Finally, the PRESAGE gel was read using a spectrophotometer.Results: The results showed that by changing the percentage of both Leuco dye and CCl4 to 4%, an optimum sensitivity of 0.0144 units/Gy can be reached. Discussion and Conclusion: Our results showed that the response function of the PRESAGE dosimeter is linear between 2.5 to 55 Gy. Using different material percentages to make the PRESAGE gel can result in a sensitivity variation ranging from 0.0099 to 0.0144 units/Gy.

Introduction: Biodistribution study in animal models bearing tumors is one of the most important procedures in evaluation of fractional uptake of radiopharmaceuticals in the tumor and non-tumor organs. The aim of this study was to develop a new software-based method to determine activities that accumulate in the main organs as well as the tumor based on scintigraphy images, thereby obviating the need to kill the animals.Material and Methods: The 99mTc labeled MAb PR81 was injected into 30 BALB/c mice with xenograft breast tumors. Anterior and posterior images of the mice were taken 16 hours post-injection using a two-headed gamma camera. The images were transferred to a PC after converting them into the interfile format. Then the anterior and posterior images of each mouse were conjugated using the designed software. Then the counts were obtained within the regions of interest drawn around each organ and the tumor, considering the calibration and background contribution. Subsequently, the mice were killed and the organs were dissected, weighed and counted individually using a well counter. Finally, the measurements obtained using the two methods were compared.Results: The comparison of the results obtained by the two procedures showed that there was a significant difference between them. However, there was a linear relationship between the counts measured by both methods for the main organs.Discussion and Conclusion: The results showed that although the new method cannot replace the invasive one to estimate the absolute activity of each organ (mainly due to the overlapping of the organs), it can be used to compare the relative activities of tumor and main organs for initial evaluation of the quality of biologic radiophamaceuticals in diagnosing tumors.

Introduction: Transient cavitations induced by low frequency irradiation of ultrasound can be used to treat tumors. Previous studies in in-vitro experiments have shown that induced cavitation by dual or multiple frequencies of ultrasound is greater than induced cavitation by single frequency irradiation. In this study, we compared and evaluated the treatment effects of dual frequency irradiation of ultrasound (1 MHz and 150 kHz) and single frequency irradiation in in-vivo experiments on breast adenocarcinoma tumors.Material and Method: In this study, the tumor-bearing mice were divided into 5 groups: control, sham, treated group for 30 min with 150 kHz frequency in continuous mode, another group with 1 MHz frequency in pulse mode, and treated group with combined dual frequency ultrasound (150 kHz in continuous mode and 1 MHz in 80% pulse mode). To evaluate the effects of ultrasound irradiation on tumor growth delay, the volumes of the tumors were investigated for 30 days. Tumor growth delay parameters including relative volume, inhibition ratio percentage and the required times for the tumor volume to reach to two (T2) and five (T5) times its initial volume were calculated.Results: The results showed that the treated groups with single frequency irradiation of 150 kHz continuous mode and 1 MHz pulse mode and combined dual frequency had statistically significant differences in tumor relative volume percentage during the period of 3 to 24 days after treatment (p<0.05). The percentage of tumor growth inhibition in the treated groups with dual frequency irradiation was significantly greater than the treated groups with single frequency irradiation, especially 3, 9 and 18 days after treatment. There were statistically significant differences between the T2 and T5 times of treated groups with dual frequency ultrasound irradiations compared to single frequency irradiations (p<0.05). The mean survival period for animals in the treated groups with single frequency of 150 kHz and dual frequency ultrasound irradiation were 85% greater than the control group. Discussion and Conclusion: It is concluded that simultaneous dual frequency irradiation is more effective than single frequency irradiation to control the growth of breast adenocarcinoma tumors.

Introduction: Laser tissue soldering is a new technique for repair of various tissues including the skin, liver, articular cartilage and nerves and is a promising alternative to suture. To overcome the problems of thermal damage to surrounding tissues and low laser penetration depth, some exogenous chromophores such as gold nanoshells, a new class of nanoparticles consisting of a dielectric core surrounded by a thin metal shell, are used. The aims of this study were to use two different concentrations of gold nanoshells as the exogenous material for skin tissue soldering and also to examine the effects of laser soldering parameters on the properties of the repaired skin. Material and Methods: Two mixtures of albumin solder and different concentrations of gold nanoshells were prepared. A full thickness incision of 2×20 mm2 was made on the surface and after placing 50 ml of the solder mixture on the incision, an 810 nm diode laser was used to irradiate it at different power densities. The changes of tensile strength, st, due to temperature rise, number of scan (Ns), and scan velocity (Vs) were investigated.Results: The results showed that the tensile strength of the repaired skin increased with increasing irradiance for both gold nanoshell concentrations. In addition, at constant laser irradiance (I), the tensile strength of the repaired incision increased with increasing Ns and decreasing Vs. In our case, this corresponded to st = 1610 g/cm2 at I ~ 60 Wcm-2, T ~ 65oC, Ns = 10 and Vs = 0.2 mms-1.Discussion and Conclusion: Gold nanoshells can be used as an indocyanine green dye (ICG) alterative for laser tissue soldering. Although by increasing the laser power density, the tensile strength of the repaired skin increases, an optimum power density must be considered due to the resulting increase in tissue temperature.