Measurement of backscattered dose at metallic interfaces using high energy electron beams

BackgroundThe amount of backscattered electrons depends on the thickness of the backscattering metal. The electron backscatter increases with the increase in thickness of the metal until a saturation level is reached and thereafter no change in scatter enhancement is noticed.AimElectron backscatter effects at metallic interfaces were analysed in this study. High energy electron beams ranging from 6 to 20 MeV were used.Materials/MethodsMeasurements were carried out with a PTW thin-window parallel plate ionization chamber and an RDM-1F electrometer. Thin sheets of aluminium, copper and lead were used as inhomogeneities. The chamber was positioned below the inhomogeneities with the gantry maintained under the couch.ResultsThe electron backscatter factor (EBSF) increases with increase in energy for aluminium, copper and lead. With low atomic number materials EBSF increases with increase in scatterer thickness and for lead it attains saturation within a few millimetres.ConclusionsThe information from this study could be useful in predicting the increase in dose at the metal-tissue interface due to electron backscatter

Dosimetric verification of brain and head and neck intensity-modulated radiation therapy treatment using EDR2 films and 2D ion chamber array matrix

Background: The evaluation of the agreement between measured and calculated dose plays an essential role in the quality assurance (QA) procedures of intensity-modulated radiation therapy (IMRT). Aim: The purpose of this study is to compare performances of the two dosimetric systems (EDR2 and I\u2032matriXX) in the verification of the dose distributions calculated by the TPS for brain and head and neck dynamic IMRT cases. Materials and Methods: The comparison of cumulative fluence by using Kodak extended dose rate (EDR2) and I\u2032matriXX detectors has been done for the evaluation of 10 brain, 10 head and neck IMRT cases treated with 6 MV beams. The parameter used to assess the quality of dose calculation is the gamma-index (g -index) method. The acceptance limits for g calculation we have used are 3% and 3 mm respectively for dose agreement and distance to agreement parameters. Statistical analyses were performed by using the paired, two-tailed Student t-test, and P< 0.01 is kept as a threshold for the significance level. Results: The qualitative dose distribution comparison was performed using composite dose distribution in the measurement plane and profiles along various axes for TPS vs. EDR2 film and TPS Vs I\u2032matriXX. The quantitative analysis between the calculated and measured dose distribution was evaluated using DTA and g-index. The percentage of pixels matching with the set DTA and g values are comparable for both with EDR2 film and I\u2032matriXX array detectors. Statistically there was no significant variation observed between EDR2 film and I\u2032matriXX in terms of the mean percentage of pixel passing g for brain cases (98.77 \ub1 1.03 vs 97.62 \ub1 1.66, P = 0.0218) and for head and neck cases (97.39 \ub1 2.13 vs 97.17 \ub1 1.52%, P = 0.7404). Conclusion: Due to simplicity and fast evaluation process of array detectors, it can be routinely used in busy departments without compromising the measurement accuracy

Absolute dose determination in high-energy electron beams: Comparison of IAEA dosimetry protocols

In this study, absorbed doses were measured and compared for high-energy electrons (6, 9, 12, 16, and 20 MeV) using International Atomic Energy Agency (IAEA), Technical Reports Series No. 277 (TRS), TRS 381, and TRS 398 dosimetry protocols. Absolute dose measurements were carried out using FC65-G Farmer chamber and Nordic Association of Clinical Physicists (NACP) parallel plate chamber with DOSE1 electrometer in WP1-D water phantom for reference field size of 15 × 15 cm2 at 100 cm source-to-surface distance. The results show that the difference between TRS 398 and TRS 381 was about 0.24% to 1.3% depending upon the energy, and the maximum difference between TRS 398 and TRS 277 was 1.5%. The use of cylindrical chamber in electron beam gives the maximum dose difference between the TRS 398 and TRS 277 in the order of 1.4% for energies above 10 MeV (R50 > 4 g/cm2). It was observed that the accuracy of dose estimation was better with the protocols based on the water calibration procedures, as no conversion quantities are involved for conversion of dose from air to water. The cross-calibration procedure of parallel plate chamber with high-energy electron beams is recommended as it avoids pwall correction factor entering into the determination of kQ,Qo

Studies of Heat Transfer for Water-Diesel Two-Phase System in a Spiral Heat Exchanger

In the present study, the main objective is to evolve a correlation to predict liquid-liquid two-phase heat transfer coefficients in a spiral plate heat exchanger. Experimental studies were conducted in a spiral plate heat exchanger using the liquid-liquid two-phase system of water-diesel in different volume fractions and flow rates as the cold fluid. Experiments were conducted by varying the volumetric flow rate and temperature, keeping the volumetric flow rate of hot fluid constant. The two-phase heat transfer coefficients were correlated with Reynolds number, Prandtl number and volume fraction in the form Nu = a (Re)b (Pr)c (ψ)d. The data obtained from fresh experiments were compared with the predictions of the obtained correlation. The predicted coefficients showed a spread of ± 12 % in the laminar range, indicating the potential use for practical applications

PARTICLE SWARM OPTIMIZATION TECHNIQUE FOR RULE BASE OPTIMIZATION OF FLC FOR LOW SPEED ACC VEHICLE

ABSTRACT Adaptive Cruise Control is used in vehicles for giving support to the drivers and to circumvent rear end collision. Due to the presence of nonlinearity in the vehicle (system), it is difficult to design an exact mathematical model of the system. Heuristic based fuzzy logic controller with optimized rule base, which does not require accurate mathematical modelling is proposed here which uses the knowledge of the designer for developing the rule base. The performance metrics in terms of better control and response time of the controller depends upon how well the rule base is formulated. More the number of rules in the rule base, higher the search time and increase in the total response time of the system but better will be the control. On the other hand, if the rules are less, then the search time will reduce which in turn decreases the total time of response of the system but control will be poor. In order to obtain an optimized control, the rule base is optimized using Particle Swarm Optimization technique. The result had shown a better performance

Variation of beam characteristics between three different wedges from a dual-energy accelerator

The use of megavoltage X-ray sources of radiation, with their skin-sparing qualities in radiation therapy, has been proved useful in relieving patient discomfort and allowing higher tumor doses to be given with fewer restrictions due to radiation effects in the skin. The purpose of this study was to compare the dosimetric characteristics of a physical and enhanced dynamic wedge from a dual-energy (6 and 18 MV) linear accelerator such as surfaces doses with different source to surface distances (SSD), half value layer (HVL) in water and peripheral doses for both available energies. At short SSD such as 85 cm, higher surface doses are produced by the lower wedges by the short wedge-to-skin distance. For physical wedged field, at heel edge side HVL value was high (17 cm) compared with the measured that of EDW (15.1 cm). It was noticed that, the HVL variation across the beam was significantly higher for 6 MV X-rays than for 18 MV X-rays. The lower wedge has the maximum variation of peripheral dose compared to other wedges. The three wedge systems discussed in this work possess vastly different dosimetric characteristics. These differences will have a direct impact on the choice of the wedge system to be used for a particular treatment. Complete knowledge of the dosimetric characterisitics, including the surface and peripheral doses, is crucial in proper choice of particular wedge systems in clinical use

Design and Analysis of a Wind Turbine Blade with Dimples to Enhance the Efficiency through CFD with ANSYS R16.0

In the global scenario, wind turbines and their aerodynamics are always subjected to constant research for increasing their efficiency which converts the abundant wind energy into usable electrical energy. In this research, an attempt is made to increase the efficiency through the changes in surface topology of wind turbines through computational fluid dynamics. Dimples on the other hand are very efficient in reducing air drag as is it evident from the reduction of drag and increase in lift in golf balls. The predominant factors influencing the efficiency of the wind turbines are lift and drag which are to be maximized and minimized respectively. In this research, surface of turbine blades are integrated with dimples of various sizes and arrangements and are analyzed using computational fluid dynamics to obtain an optimum combination. The analysis result shows that there is an increase in power with about 15% increase in efficiency. Hence, integration of dimples on the surface of wind turbine blades has helped in increasing the overall efficiency of the wind turbine