Iranian Journal of Medical Physics
Volume:9 Issue: 3, Summer 2012

Superficial X-ray therapy is one of the most important treatment methods in radiotherapy especially in the treatment of superficial skin lesions (Up to 300 kVp). Quality of the X-ray beam that can be expressed by Half-Value Layer (HVL), are important indices for this type of treatment effective energy of photon and Homogeneity Coefficient (HC). The HC of the superficial X-ray machine at 180 kVp was determined by an experimental method and also by simulation (EGSnrc code) and the results were compared. The exposure after the first (0.5 mmCu) and second (1 mmCu) attenuation layers were measured by Farmer dosimeter for three different field sizes. The HC was derived from these experimental data and was compared with corresponding results acquired by EGSnrc code package. The BEAMnrc code was used to transport photons and electrons at exit level of the applicator, DOSXYZnrc code for calculation of absorbed dose in the phantom, and BEAMDP for drawing the output spectra. Results showed that the mean percentage difference of errors obtained by experimental data and simulation method is 3.3% and the average energy of output spectra in 180 kVp after passing through filters and attenuation layers increases to 15.3% to 25.4%. The maximum percentage difference of errors for the applied methods is higher than analogous devolves elsewhere reports which could be due to setup parameters such as SSD and field size. However, the present method has the advantage of ease of setup and matching with clinical conditions.

The present work describes a study in which, based on patient dose measurements, thermoluminescent dosimeters were used to obtain the diagnostic reference level arising from panoramic radiography. Ten panoramic units and a sample of 15 patients per X-ray unit were studied. Two thermoluminescent dosimeter chips were placed on the skin surface of selected organs. Mean value of two ESDs was taken as the measured representation dose at the point of interest. Mean ESD on parotid glands derived from panoramic radiography was equal to 369.2 µGy. Individual patient's dose value varied from 180.1 to 470.3 µGy. Third quartile of mean absorbed dose distribution arising from a particular examination has been adopted as diagnostic reference level. Based on this definition, local diagnostic reference level arising from panoramic radiography of the greater Khorasan province is equal to 400 µG.

3D reconstruction of an object from its 2D cross-sections (slices) has many applications in different fields of sciences such as medical physics and biomedical engineering. In order to perform 3D reconstruction, at first, desired boundaries at each slice are detected and then using a correspondence between points of successive slices surface of desired object is reconstructed. In this study, Gradient Vector Flow (GVF) was used in order to trace the boundaries at each slice. Then, cubic Bezier Spline curves were used to approximate each of obtained contours and to approximate the corresponding points of different contours at successive slices. The reconstructed surface was a bi-cubic Bezier Spline surface which was smooth with G2 continuity. Our presented method was tested on SPECT data of JASZCZAK phantom and human's left ventricle. The results confirmed that the presented method was accurate, promising, applicable, and effective. Using GVF algorithm to trace boundaries at each slice, and cubic Bezier Spline curves to approximate the obtained rough contours yield to the procedure of reconstruction which was fast and also the final surface was smooth with G2 continuity. So far, some mathematical curves such as spline, cubic spline, and B-spline curves were used to approximate the computed contour during a time consuming procedure. This study presented a 3D reconstruction method based on a combination of GVF algorithm and cubic Bezier Spline curves. There was a good trade-off between speed and accuracy in using cubic Bezier Spline curves which is especially useful for training students.

Non-invasive Fluorescent Reflectance Imaging (FRI) is used for accessing physiological and molecular processes in biological media. The aim of this article is to separate the overlapping emission spectra of quantum dots within tissue-equivalent phantom using SVD, Jacobi SVD, and NMF methods in the FRI mode. In this article, a tissue-like phantom and an optical setup in reflectance mode were developed. The algorithm of multispectral imaging method was then written in Matlab environment. The setup included the diode-pumped solid-state lasers at 479 nm, 533 nm, and 798 nm, achromatic telescopic, mirror, high pass and low pass filters, and EMCCD camera. The FRI images were acquired by a CCD camera using band pass filter centered at 600 nm and high pass max at 615 nm for the first region and high pass filter max at 810 nm for the second region. The SVD and Jacobi SVD algorithms were written in Matlab environment and compared with a Non-negative Matrix Factorization (NMF) and applied to the obtained images. PSNR, SNR, CNR of SVD, and NMF methods were obtained as 39 dB, 30.1 dB, and 0.7 dB, respectively. The results showed that the difference of Jacobi SVD PSNR with PSNR of NMF and modified NMF algorithm was significant (p<0.0001). The statistical results showed that the Jacobi SVD was more accurate than modified NMF. In this study, the Jacobi SVD was introduced as a powerful method for obtaining the unmixed FRI images. An experimental evaluation of the algorithm will be done in the near future

BNCT is an effective method to destroy brain tumoral cells while sparing the healthy tissues. The recommended flux for epithermal neutrons is 109 n/cm2s, which has the most effectiveness on deep-seated tumors. In this paper, it is indicated that using D-T neutron source and optimizing of Beam Shaping Assembly (BSA) leads to treating brain tumors in a reasonable time where all IAEA recommended criteria are met. The proposed BSA based on a D-T neutron generator consists of a neutron multiplier system, moderators, reflector, and collimator. The simulated Snyder head phantom is used to evaluate dose profiles in tissues due to the irradiation of designed beam. Monte Carlo Code, MCNP-4C, was used in order to perform these calculations. The neutron beam associated with the designed and optimized BSA has an adequate epithermal flux at the beam port and neutron and gamma contaminations are removed as much as possible. Moreover, it was showed that increasing J/Φ, as a measure of beam directionality, leads to improvement of beam performance and survival of healthy tissues surrounding the tumor. According to the simulation results, the proposed system based on D-T neutron source, which is suitable for in-hospital installations, satisfies all in-air parameters. Moreover, depth-dose curves investigate proper performance of designed beam in tissues. The results are comparable with the performances of other facilities.

CR-39 detectors are widely used for Radon and progeny measurement in the air. In this paper, using the Monte Carlo simulation, the possibility of using the CR-39 for direct measurement of Radon and progeny in water is investigated. Assuming the random position and angle of alpha particle emitted by Radon and progeny, alpha energy and angular spectrum that arrive at CR-39, the calibration factor, and the suitable depth of chemical etching of CR-39 in air and water was calculated. In this simulation, a range of data were obtained from SRIM2008 software. Calibration factor of CR-39 in water is calculated as 6.6 (kBq.d/m3)/(track/cm2) that is corresponding with EPA standard level of Radon concentration in water (10-11 kBq/m3). With replacing the skin instead of CR-39, the volume affected by Radon and progeny was determined to be 2.51 mm3 for one m2 of skin area. The annual dose conversion factor for Radon and progeny was calculated to be between 8.8-58.8 nSv/(Bq.h/m3). Using the CR-39 for Radon measurement in water can be beneficial. The annual dose conversion factor for Radon and progeny was calculated to be between 8.8-58.8 nSv/ (Bq.h/m3).

Studying motility of biological objects is an important parameter in many biomedical processes. Therefore, automated analyzing methods via microscopic videos are becoming an important step in recent researches. In the proposed method of this article, a hypothesis testing function is defined to separate biological particles from artifact and noise in captured video. Then, a decision about each hypothesis is made in the following steps: selecting primary candidates using stochastic modeling, pruning false candidates using graph theory, and confirming remained particles by Kalman filtering. Performance of the proposed method is evaluated on real videos containing low and high densities of live Listeria particles. The results show that in the first scenario, the proposed and MD algorithms detect 95% and 65% of particles in presence of 2% and 44% false detections, respectively. In the second scenario, the proposed and MD algorithms detect 91% and 55% of particles in presence of 14% and 45% false detections, respectively. In the first scenario, the proposed algorithm detects and tracks particles typically 30% and 31% better than MD. Moreover, its false detected particles and trajectories are 42% and 27% less than MD. In the second scenario, the proposed method detects and tracks particles typically 36% and 38% better than MD, also its false detected particles and trajectories are 31% and 18% less than MD. Consequently, better characterization of particles in proposed algorithm not only does not lead to extracting more false particles and trajectories but also decreases the rate of false characterized particles and trajectories compared with existing algorithms.

During the process photodynamic therapy (PDT), bleaching of photosensitizer induced by irradiation and generation of reactive oxygen species (ROS) can provide some information concerning the efficiency of treatment. Since gold nanoparticles (GNPs) have been highlighted as efficient drug delivery systems, in this study, by utilizing GNPs conjugated with 5 aminolevulinic acid (5-ALA-GNPs), the photobleaching of ALA-induced protoporphyrin IX (PpIX) was estimated on a colon carcinoma tumor model. CT26 tumor models were prepared by subcutaneous injection of 5×105 cells into the right flank of Balb/c inbred mice. To estimate the time required to reach maximum concentration of PpIX in the tumors, the fluorescence signal of PpIX was monitored and PDT was performed by intratumoral injection of 5-ALA-GNPs, GNPs, and 5-ALA in separated groups for 15 min with a cycle of 5 min irradiation and 1 min darkness. The photobleaching rate was calculated from recorded fluorescence signals at the darkness intervals. The maximum fluorescence of PpIX was recorded 3 and 5 hr after injection of 5-ALA and 5-ALA-GNPs, respectively. Despite the low PpIX accumulation in tumors receiving conjugate, the photobleaching rate of PpIX was determined to be higher than 5-ALA. The reduction of the fluorescence signal due to 5-ALA-GNPs clearance was higher than that of 5-ALA. Administration of 5-ALA-GNPs, intensification of ROS generating and the subsequent elevation of photobleaching results in higher treatment efficiency. Also, more rapid clearance of PpIX has an important implication in clinical application of 5-ALA-GNPs that decreases the undesirable effects on healthy tissues.