IRANIAN JOURNAL OF MEDICAL PHYSICS
Year:2010 | Volume:7 | Issue:3 (28)|Papers Count:8

Introduction: This paper addresses a method for automatic detection of blood vessels in color fundus images which utilizes two main tools: image partitioning and local Radon transform.Material and Methods: The input images are firstly divided into overlapping windows and then the Radon transform is applied to each. The maximum of the Radon transform in each window corresponds to the probable available sub-vessel. To verify the detected sub-vessel, the maximum is compared with a predefined threshold. The verified sub-vessels are reconstructed using the Radon transform information. All detected and reconstructed sub-vessels are finally combined to make the final vessel tree.Results: The algorithm’s performance was evaluated numerically by applying it to 40 images of DRIVE database, a standard retinal image database. The vessels were extracted manually by two physicians. This database was used to test and compare the available and proposed algorithms for vessel detection in color fundus images.By comparing the output of the algorithm with the manual results, the two parameters TPR and FPR were calculated for each image and the average of TPRs and FPRs were used to plot the ROC curve.Discussion and Conclusion: Comparison of the ROC curve of this algorithm with other algorithms demonstrated the high achieved accuracy. Beside the high accuracy, the Radon transform which is integral-based makes the algorithm robust against noise.

Introduction: In the present study, the effects of light cure on wound healing of mice’s skin with complete thickness were studied.Materials and Methods: Forty male mice of NMRI race were placed randomly into two groups of examination and control. Under aseptic and unconscious conditions, a circular wound of 6 mm width with complete thickness of skin was made on the back of each mice. The surgery day was established as day zero. Blue light of wavelength 420-500 nm from a light cure instrument was shined onto all the mice from the first day. Over the 3rd, 7th, 10th, 15th and 21st days after curing, four kinds of wound and healthy skins were taken from each mice. The practical procedures of general histology were applied on the samples, then slices of 5 micron thickness were taken from them and finally, they were colored with Hematoxline Eosin. The cell population of wound bed including fibroblast cells, macrophages, neutrophils and endothelia of vessels were studied.Results: The examination group showed significantly increased fibrosis and decreased inflammation (p≤0.05).Conclusion: Halogen blue light (light cure) causes significant early open wound healing of skin with complete thickness.

Introduction: Brachytherapy is the use of small encapsulated radioactive sources in close vicinity of tumors. Various methods are used to obtain the dose distribution around brachytherapy sources. TG-43 is a dosimetry protocol proposed by the AAPM for determining dose distributions around brachytherapy sources. The goal of this study is to update this protocol for presence of bone and air inhomogenities.Material and Methods: To update the dose rate constant parameter of the TG-43 formalism, the MCNP4C simulations were performed in phantoms composed of water-bone and water-air combinations. The values of dose at different distances from the source in both homogeneous and inhomogeneous phantoms were estimated in spherical tally cells of 0.5 mm radius using the F6 tally.Results: The percentages of dose reductions in presence of air and bone inhomogenities for the Cs-137 source were found to be %4 and %10, respectively. Therefore, the updated dose rate constant (L) will also decrease by the same percentages.Discussion and Conclusion: It can be easily concluded that such dose variations are more noticeable when using lower energy sources such as Pd-103 or I-125.

Introduction: This study investigates to what extent the computed dose received by lung tissue in a commercially available treatment planning system (TPS) for 192Ir high-dose-rate breast brachytherapy is accurate in view of tissue in homogeneities and presence of ribs.Materials and Methods: A CT scan of the breast was used to construct a patient-equivalent phantom in the clinical treatment planning system. An implant involving 13 plastic catheters and 383 programmed source dwell positions were simulated using the MCNPX code.Results: The results were compared with the corresponding commercial TPS in the form of isodoses and cumulative dose-volume histogram in breast, lung and ribs. The comparison of Monte Carlo results and TPS calculation showed that the isodoses greater than %62 in the breast that were located rather close to the implant or away from the breast curvature surface and lung boundary were in good agreement. TPS calculations, however, overestimated dose in the lung for lower isodose contours and points that were lying near the breast-air boundary and relatively away from the implant.Discussion and Conclusions: Taking into account the ribs and entering the actual data for breast, rib and lung, revealed an average overestimation of dose in lung in the TPS calculation.

Introduction: Treatment with megavoltage electron beams is ideal for irradiating superficial tumors because of their limited range in tissues. However, for electron treatment of extended areas, such as the chest wall, two or more adjacent fields can be used. Abutment of these fields may lead to significant dose in homogeneities in the junction region. The aim of this study is to offer a new method for generating a homogeneous dose distribution in the junction region between two adjacent fields in electron beam therapy.Materials and Methods: Several approaches have been proposed to solve the problem of ‘hot’ and ‘cold’ spots in the junction region between abutting electron fields. These techniques are based on beam-edge modifying devices or penumbra generators which act to broaden the electron beam penumbra, and thus facilitate field matching. But use of these devices is time consuming and design of the modifications to the applicators are generally applicator dependent. An idea which was originally proposed for matching two adjacent photon fields (with dose inhomogeneity of about %2) is resurrected here. This method is based on the rotation of the gantry such that the adjacent fields have a common edge and the overlap region in treatment volume is eliminated. For this purpose, the effective source to surface distance (SSDeff) for the available electron beam energies (6, 9, 12 and 15 MeV) and applicators (cones) (6×6, 10×10, 15×15, 20×20 and 25×25 cm2) have been determined for a Varian 2100C linear accelerator.Result: Using SSDeff, in respect to beam divergence, one can use the photon beam behavior for electron beams and achieve a uniform dose distribution in adjacent electron fields.Discussion and Conclusion: Compared to beam-edge modifying devices or penumbra generators that are usually time consuming to plan and set up, rotating the gantry to eliminate the overlap region is simple and applicable in the problem of abutting electron fields.

Introduction: Variable resolution x-ray (VRX) CT is a new type of CT that can image objects at various spatial resolutions. In a VRX CT scanner, the spatial resolution increases at the cost of reduction in the field of view (FOV). An important factor that limits the spatial resolution of the VRX CT is the effect of focal spot size. Also, the optimum magnification is different at each incident angle.Material and Methods: To investigate the spatial resolution and the FOV in VRX CT, we used the numerical parameters of an actual VRX CT scanner. The effects of decreasing the focal spot size and optimizing magnification on the spatial resolution and the FOV of the system were studied theoretically.Results: The focal spot size was found to greatly limit the spatial resolution of the VRX CT at the small incident angles. By decreasing the focal spot size, the spatial resolution was comparatively improved. Optimization of the system magnification without decreasing the focal spot size could greatly increase the spatial resolution of the system. After optimization of magnification, the FOV of the system decreased significantly.Discussion and Conclusion: The spatial resolution of the system after optimizing the magnification increased from 7.5 to more than 35 cycles/mm and also the effect of the focal spot no longer limited the spatial resolution at incident angles smaller than 13o. The disadvantage of optimization of magnification was a great decrease in the FOV of the system. The optimization of magnification has the reverse effect on the spatial resolution and the FOV of the system so at each incident angle, according to the importance of spatial resolution or FOV, the system magnification can be set to lead to the desirable condition.

Introduction: Breast conserving radiotherapy is one of the most common procedures performed in any radiation oncology department. A tangential parallel-opposed pair is usually used for this purpose. This technique is performed using 2D or 3D treatment planning systems. The aim of this study was to compare 2D treatment planning with 3D treatment planning in tangential irradiation in breast conserving radiotherapy. In this comparison, homogeneity of isodoses in the breast volume and lung dose were considered.Material and Methods: Twenty patients with breast cancer treated with conservative surgery were included in this study. The patients were CT scanned.Two-dimensional treatment planning with the Alfard 2D TPS was performed for each patient using a single central CT slice. The data used on the Alfard 2D TPS was imported into the Eclipse 3D TPS, on which 3D treatment planning was performed. Cobalt-60 beams were used in all plans.Results: Comparing 2D and 3D treatment planning, homogeneity of isodoses was improved in 3D treatment planning (p<0.02). Volume of lung receiving a dose of>30Gy was increased in 3D treatment planning (p<0.01).Discussion and Conclusion: 3D treatment planning is a more suitable option for patients with breast cancer treated with conservative surgery because of improved dose homogeneity in 3D treatment planning. The results of the treatment can be improved with reduced recurrence probability and skin problems.

Introduction: Clinical application of encapsulated radioactive brachytherapy sources has a major role in cancer treatment. In the present research, the effects of different tissue densities on the dose distribution of a 103Pd brachytherapy source in a spherical phantom of 50 cm radius have been studied.Material and Methods: As is well known, absorbed dose in tissue depends to its density, but this difference is not clear in measurements. Therefore, we applied the MCNP code to evaluate the effect of density on the dose distribution. 103Pd brachytherapy sources are used to treat prostate, breast and other cancers.Results: Absorbed dose has been calculated and presented around a source placed in the center of the phantom for different tissue densities. Also, we derived anisotropy and radial dose functions and compared our Monte Carlo results with experimental results of Rivard and Li et al. for F (1, q) and g(r) in 1.040 g/cm3 tissue.Conclusion: The results of this study show that relative dose variations around the source center are very considerable at different densities, because of the presence of a photoabsorber (Au-Cu alloy) in the source core. Dose variation exceeds %80 at the point (Z=2.4 mm, Y=0 mm). Computed values of anisotropy and radial dose functions are in good agreement with the experimental results of Rivard and Li et al.