Analytical Consideration of Surface Dose and Kerma for Megavoltage Photon Beams in Clinical Radiation Therapy

Birgani, Mohammad Javad Tahmasebi,Behrooz, Mohammad Ali,Razmjoo, Sasan,Zabihzadeh, Mansour,Fatahiasl, Jafar,Maskni, Reza,Abdalvand, Neda,Asgarian, Zeynab,Shamsi, Azin Asian Pacific Journal of Cancer Prevention 2016 Asian Pacific journal of cancer prevention Vol.17 No.1

Background: In radiation therapy, estimation of surface doses is clinically important. This study aimed to obtain an analytical relationship to determine the skin surface dose, kerma and the depth of maximum dose, with energies of 6 and 18 megavoltage (MV). Materials and Methods: To obtain the dose on the surface of skin, using the relationship between dose and kerma and solving differential equations governing the two quantities, a general relationship of dose changes relative to the depth was obtained. By dosimetry all the standard square fields of $5cm{\times}5cm$ to $40cm{\times}40cm$, an equation similar to response to differential equations of the dose and kerma were fitted on the measurements for any field size and energy. Applying two conditions: a) equality of the area under dose distribution and kerma changes in versus depth in 6 and 18 MV, b) equality of the kerma and dose at $x=d_{max}$ and using these results, coefficients of the obtained analytical relationship were determined. By putting the depth of zero in the relation, amount of PDD and kerma on the surface of the skin, could be obtained. Results: Using the MATLAB software, an exponential binomial function with R-Square >0.9953 was determined for any field size and depth in two energy modes 6 and 18MV, the surface PDD and kerma was obtained and both of them increase due to the increase of the field, but they reduce due to increased energy and from the obtained relation, depth of maximum dose can be determined. Conclusions: Using this analytical formula, one can find the skin surface dose, kerma and thickness of the buildup region.

Breast Radiotherapy with Mixed Energy Photons; a Model for Optimal Beam Weighting

Birgani, Mohammadjavad Tahmasebi,Fatahiasl, Jafar,Hosseini, Seyed Mohammad,Bagheri, Ali,Behrooz, Mohammad Ali,Zabiehzadeh, Mansour,meskani, Reza,Gomari, Maryam Talaei Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.17

Utilization of high energy photons (>10MV) with an optimal weight using a mixed energy technique is a practical way to generate a homogenous dose distribution while maintaining adequate target coverage in intact breast radiotherapy. This study represents a model for estimation of this optimal weight for day to day clinical usage. For this purpose, treatment planning computed tomography scans of thirty-three consecutive early stage breast cancer patients following breast conservation surgery were analyzed. After delineation of the breast clinical target volume (CTV) and placing opposed wedge paired isocenteric tangential portals, dosimeteric calculations were conducted and dose volume histograms (DVHs) were generated, first with pure 6MV photons and then these calculations were repeated ten times with incorporating 18MV photons (ten percent increase in weight per step) in each individual patient. For each calculation two indexes including maximum dose in the breast CTV ($D_{max}$) and the volume of CTV which covered with 95% Isodose line ($V_{CTV,95%IDL}$) were measured according to the DVH data and then normalized values were plotted in a graph. The optimal weight of 18MV photons was defined as the intersection point of $D_{max}$ and $V_{CTV,95%IDL}$ graphs. For creating a model to predict this optimal weight multiple linear regression analysis was used based on some of the breast and tangential field parameters. The best fitting model for prediction of 18MV photons optimal weight in breast radiotherapy using mixed energy technique, incorporated chest wall separation plus central lung distance (Adjusted R2=0.776). In conclusion, this study represents a model for the estimation of optimal beam weighting in breast radiotherapy using mixed photon energy technique for routine day to day clinical usage.

Symmetric hole stress concentration in a hybrid composite lamina subjected to matrix plasticity

Pezhman Taghipour Birgani,Mohammad Shishesaz 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.7

In this paper, hole stress concentrations in long fibers and their surrounding matrix bays is examined in a hybrid composite lamina. It is assumed that all fibers lie in one direction while loaded by a force p at infinity in the direction of fibers. The width of the lamina is considered to be finite and bears a hole as a defect. Due to the presence of excessive shear stress in the matrix bays bounding the hole, a yielded zone of size 2a o is developed around the hole. Shear lag model (SLM) is used to drive the displacement and stress fields. The resulting equations are solved analytically based on boundary and continuity conditions. It is shown that the shape and size of the hole, as well as length of the plastic zone, have considerable effect on stress concentrations within the lamina. Compared to a lamina with a single type fiber, a hybridized model shows lower stress concentrations in High modulus (HM) fibers bounding the hole as opposed to those of Low modulus fibers (LM) subjected to the same condition. Moreover, hole shape and size, ratio of extensional stiffness of LM to HM fibers, and size of the plastic zone seem to have considerable effect on shear and normal stresses in the matrix and fibers, respectively.

Determination of an Effective Wedge Angle by Combination of Two Arbitrary Universal Wedge Fields in Radiation Therapy of Cancer Patients with Megavoltage Photon Beams

Shamsi, Azin,Birgani, Mohammad Javad Tahmasebi,Behrooz, Mohammad Ali,Arvandi, Sholeh,Fatahiasl, Jafar,Maskny, Reza,Abdalvand, Neda Asian Pacific Journal of Cancer Prevention 2016 Asian Pacific journal of cancer prevention Vol.17 No.1

Background: Wedge filters are commonly used in radiation oncology for eliminating hot spots and creating a uniform dose distribution in optimizing isodose curves in the target volume for clinical aspects. These are some limited standard physical wedges ($15^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$),or creating an arbitrary wedge angle, like motorized wedge or dynamic wedge,${\ldots}$ The new formulation is presented by the combination of wedge fields for determining an arbitrary effective wedge angles. The isodose curves also are derived for these wedges. Materials and Methods: we performed the dosimetry of Varian Clinac 2100C/D with Scanditronix Wellhofer water blue phantom, CU500E, OmniPro - Accept software and 0.13cc ionization chamber for 6Mv photon beam in depth of 10cm (reference depth) for universal physical wedges ($15^{\circ}$, $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$) and reference field $10.10cm^2$. By combining the isodose curve standard wedge fields with compatible weighting dose for each field, the effective isodose curve is calculated for any wedge angle. Results: The relation between a given effective wedge angle and the weighting of each combining wedge fields was derived. A good agreement was found between the measured and calculated wedge angles and the maximum deviation did not exceed $3^{\circ}$. The difference between the measured and calculated data decreased when the combined wedge angles were closer. The results are in agreement with the motorized single wedge appliance in the literature. Conclusions: This technique showed that the effective wedge angle that is obtained from this method is adequate for clinical applications and the motorized wedge formalism is a special case of this consideration.

Dosimetric Characteristics of 6 MV Modified Beams by Physical Wedges of a Siemens Linear Accelerator

Zabihzadeh, Mansour,Birgani, Mohammad Javad Tahmasebi,Hoseini-Ghahfarokhi, Mojtaba,Arvandi, Sholeh,Hoseini, Seyed Mohammad,Fadaei, Mahbube Asian Pacific Journal of Cancer Prevention 2016 Asian Pacific journal of cancer prevention Vol.17 No.4

Physical wedges still can be used as missing tissue compensators or filters to alter the shape of isodose curves in a target volume to reach an optimal radiotherapy plan without creating a hotspot. The aim of this study was to investigate the dosimetric properties of physical wedges filters such as off-axis photon fluence, photon spectrum, output factor and half value layer. The photon beam quality of a 6 MV Primus Siemens modified by 150 and 450 physical wedges was studied with BEAMnrc Monte Carlo (MC) code. The calculated present depth dose and dose profile curves for open and wedged photon beam were in good agreement with the measurements. Increase of wedge angle increased the beam hardening and this effect was more pronounced at the heal region. Using such an accurate MC model to determine of wedge factors and implementation of it as a calculation algorithm in the future treatment planning systems is recommended.

Gene Expression Biodosimetry: Quantitative Assessment of Radiation Dose with Total Body Exposure of Rats

Saberi, Alihossein,Khodamoradi, Ehsan,Birgani, Mohammad Javad Tahmasebi,Makvandi, Manoochehr Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.18

Background: Accurate dose assessment and correct identification of irradiated from non-irradiated people are goals of biological dosimetry in radiation accidents. Objectives: Changes in the FDXR and the RAD51 gene expression (GE) levels were here analyzed in response to total body exposure (TBE) to a 6 MV x-ray beam in rats. We determined the accuracy for absolute quantification of GE to predict the dose at 24 hours. Materials and Methods: For this in vivo experimental study, using simple randomized sampling, peripheral blood samples were collected from a total of 20 Wistar rats at 24 hours following exposure of total body to 6 MV X-ray beam energy with doses (0.2, 0.5, 2 and 4 Gy) for TBE in Linac Varian 2100C/D (Varian, USA) in Golestan Hospital, in Ahvaz, Iran. Also, 9 rats was irradiated with a 6MV X-ray beam at doses of 1, 2, 3 Gy in 6MV energy as a validation group. A sham group was also included. After RNA extraction and DNA synthesis, GE changes were measured by the QRT-PCR technique and an absolute quantification strategy by taqman methodology in peripheral blood from rats. ROC analysis was used to distinguish irradiated from non-irradiated samples (qualitative dose assessment) at a dose of 2 Gy. Results: The best fits for mean of responses were polynomial equations with a R2 of 0.98 and 0.90 (for FDXR and RAD51 dose response curves, respectively). Dose response of the FDXR gene produced a better mean dose estimation of irradiated "validation" samples compared to the RAD51 gene at doses of 1, 2 and 3 Gy. FDXR gene expression separated the irradiated rats from controls with a sensitivity, specificity and accuracy of 87.5%, 83.5% and 81.3%, respectively, 24 hours after dose of 2 Gy. These values were significantly (p<0.05) higher than the 75%, 75% and 75%, respectively, obtained using gene expression of RAD51 analysis at a dose of 2 Gy. Conclusions: Collectively, these data suggest that absolute quantification by gel purified quantitative RT-PCR can be used to measure the mRNA copies for GE biodosimetry studies at comparable accuracy to similar methods. In the case of TBE with 6MV energy, FDXR gene expression analysis is more precise than that with RAD51 for quantitative and qualitative dose assessment.

Oral colonization by Candida species and associated factors in HIV-infected patients in Ahvaz, southwest Iran

Elham Aboualigalehdari,Maryam Tahmasebi Birgani,Mahnaz Fatahinia,Mehran Hosseinzadeh 한국역학회 2020 Epidemiology and Health Vol.42 No.-

OBJECTIVES: Oropharyngeal candidiasis is one of the most common opportunistic fungal infections among human immunodeficiency virus (HIV)-infected individuals. The most common cause is Candida albicans, followed by non-albicans Candida. This study aimed to identify colonized Candida species in HIV-infected patients from Ahvaz, Iran. Additionally, the relationships between immunity-related factors, lifestyle, and colonization of Candida spp. were studied. METHODS: Oral swabs were taken from 201 HIV-positive patients referred for consultations at the Behavioral Modification Center. Oral Candida colonization was detected using culture-based and molecular assays. Data were assessed by descriptive statistics and analyzed to investigate the correlation between Candida colonization and various factors, including the CD4+ cell count and viral load. RESULTS: It was found that 43.8% of patients were positive for Candida. The most common species was C. albicans (48.0%), followed by non-albicans Candida isolates, including C. dubliniensis, C. glabrata, C. tropicalis, C. parapsilosis, C. guilliermondii, C. kefyr, and C. krusei. Colonization of Candida spp. in patients was associated with a CD4 count ≤200 cells/mm3 (odds ratio [OR], 4.62; p<0.05), history of shared injections (OR, 6.96; p<0.001), and sex (OR, 3.59; p<0.05). CONCLUSIONS: The results of this study showed that C. albicans was the dominant pathogen. The risk factors for colonization of Candida spp. were a CD4 count ≤ 200/mm3, a history of shared injections, and sex. Other factors with potential relationships include viral load, age, and opportunistic infections, but further investigations are needed.

A comparative removal of two dyes from aqueous solution using modified oak waste residues: Process optimization using response surface methodology

Samira Samarbaf,Yaser Tahmasebi Birgani,Mohsen Yazdani,Ali Akbar Babaei 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.73 No.-

In this study, optimization of adsorptive removal of two cationic (methylene blue (MB)) and anionic (acidred 73 (AR 73)) dyes with modified oak waste (MOW) adsorbent was carried out using response surfacemethodology (RSM). The input variables included initial solution pH (2–10), contact time (20–200 min),adsorbent dosage (0.5–2.5 g/L) and initial dyes concentrations (10–90 mg/L). Furthermore, the surfaces ofthe adsorbent were modified with different modifiers tofind the most efficient adsorbent. The obtainedresults of comparative studies on dyes adsorption confirm that sodium hydroxide, compared to othermodifiers, has the highest ability to activate the surfaces of the oak waste (OW) to remove dyes from thesolution. Using NaOH, the removal efficiency of MB and that of AR 73 were obtained to be 96% and 29%,respectively. In addition, results of the optimization study showed that RSM could significantly predictthe experimental data of dyes removal with a high correlation coefficient (0.991 for MB and 0.993 for AR73). The optimum experimental conditions for dyes removal were pH of 6.2, 160 min contact time, 2.0 g/Ladsorbent dosage and 70 mg/L initial dye concentrations. Under this condition, the removal efficiency forMB and AR 73 reached 85.36% and 41.27%, respectively. Ultimately, from thefindings of this study, it isobserved that MOW can be used as an efficient and cost-effective adsorbent for the removal of dyes fromthe contaminated aqueous solution.

Alkali modified oak waste residues as a cost-effective adsorbent for enhanced removal of cadmium from water: Isotherm, kinetic, thermodynamic and artificial neural network modeling

Afshin Takdastan,Samira Samarbaf,Yaser Tahmasebi Birgani,Nadali Alavi,Ali Akbar Babaei 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.78 No.-

Heavy metals are kind of toxic substances which are abundant in all municipal, agricultural, industrialand treated wastewaters. In this research, a comparative study was carried out for adsorptive removal ofCd2+ from aqueous solution using raw oak waste and NaOH-activated oak waste at different experimentalconditions namely, pH of solution (2–8), contact time (5–240 min), adsorbent dosages (0.1–10 g/L) andinitial Cd2+ concentrations (25–100 mg/L). In addition, the experimental data of Cd2+ adsorption werefitted with different isotherm and kinetic models to determine the most appropriate model. Artificialneural network (ANN) model was also used tofind the effect of each individual parameter on Cd2+adsorptive removal. Based on the results of batch experiments, adsorbent dosages and initial Cd2+concentrations had direct and indirect relationships with Cd2+ removal, respectively. Furthermore,among all applied isotherm and kinetic models, Langmuir isotherm model and Avrami fractional-orderkinetic models could best-fitted with the experimental data of Cd2+ removal. The results ofthermodynamic studies revealed that the adsorption of Cd2+ onto the surfaces of oak waste adsorbentsis exothermic and spontaneous. Finally, according to thefindings of ANN studies, this approach couldmodel the role of each parameter on Cd2+ removal with high coefficient of correlation (>0.99). Accordingly, pH of solution and temperature had the highest and lowest influence on removal of Cd2+from solution, respectively. The results implied that oak waste can be selected as a promising andenvironmentally friendly adsorbent for the effective remediation of water bodies containing heavymetals.

Tissue Specific Expression Levels of Apoptosis Involved Genes Have Correlations with Codon and Amino Acid Usage

Mohammadreza Hajjari,Iman Sadeghi,Abbas Salavaty,Habib Nasiri,Maryam Tahmasebi Birgani 한국유전체학회 2016 Genomics & informatics Vol.14 No.4

Different mechanisms, including transcriptional and post transcriptional processes, regulate tissue specific expression of genes. In this study, we report differences in gene/protein compositional features between apoptosis involved genes selectively expressed in human tissues. We found some correlations between codon/amino acid usage and tissue specific expression level of genes. The findings can be significant for understanding the translational selection on these features. The selection may play an important role in the differentiation of human tissues and can be considered for future studies in diagnosis of some diseases such as cancer.