10x10 Cm2 Research Articles

Harnessing the Power of Machine Learning for Accurate and Efficient Linear Accelerator Beam Data Commissioning

Linear accelerator (linac) commissioning is a fundamental process in the safe introduction of new linacs into the clinical workflow of any radiation oncology department. Commissioning data is vital not only for verification of proper linac operation, but also for the continuing quality assurance process and as input to the treatment planning software. Current commissioning of a new linac is a highly reparative and time-consuming task performed under time pressure but with great need for high precision. The process lacks in clear operational standards and no validation tools are commercially available. In this study, we propose a fast and robust linac beam data commissioning method to significantly save time and manpower in the process of linac commissioning. Routine linac commissioning/annual beam data, including percentage depth dose (PDD) and depth dose profile (DDP) at various beam energies and field sizes, were extracted from three medical linear accelerators at our institution. The datasets were split into training and testing data. For each beam energy, we formulated the PDD or DDP as an output of least square optimization problem, which is solved by a multivariate linear regression model with an input of a few point data measurements at a different field size. Using data augmentation technique, we use 1000 sets of data to train the linear regression model. PDD and DDP were predicted using models trained with and without Ridge Regularization and a few measured sampling points. The predicted PDD and DDP were evaluated using percentage relative error (pRE). Both PDD and DDP were accurately predicted at different beam energies and field sizes. The pRE for predictions of field sizes of 4×4 cm2 and 30×30 cm2 based on 10x10 cm2 beam data was less than 0.8% for both 6 MV and 15 MV beams. Three data points sampled along the PDD was needed to obtain this accuracy; no further increase in accuracy was found with increased number of sample points. For model trained without Ridge Regularization, the pRE was reduced by up to 50%. For model training with Ridge Regularization, data augmentation showed only marginal improvement on pRE. We propose a fast and accurate machine learning-based method to generate linac commissioning beam data for routine radiation therapy. With this method, beam data related to PDD and DDP can be accurately generated using only a few measured sampling points. We envision that this approach will significantly simplify the tedious linac commissioning procedure, save time and manpower, while increasing the safety and precision of the commissioning process.

New thick silicon carbide detectors: Response to 14 MeV neutrons and comparison with single-crystal diamonds

Abstract In this work we present the response of a new large volume 4H Silicon Carbide (SiC) detector to 14 MeV neutrons. The device has an active thickness of 100 μ m (obtained by epitaxial growing) and an active area of 25 mm2. Tests were conducted at the ENEA-Frascati Neutron Generator facility by using 14.1 MeV neutrons. The SiC detector performance was compared to that of Single-Crystal Diamond (SCD) detectors. The SiC response function was successfully measured and revealed a very complex structure due to the presence in the detector of both Silicon and Carbon atoms. Nevertheless, the flexibility in the SiC manufacturing and the new achievements in terms of relatively large areas (up 1x1 cm2) and a wide range of thicknesses makes them an interesting alternative to diamond detectors in environments where limited space and high neutron fluxes are an issue, i.e. modern neutron cameras or in-vessel tokamak measurements for the new generation fusion machines such as ITER. The absence of instabilities during neutron irradiation and the capability to withstand high neutron fluences and to follow the neutron yield suggest a straightforward use of these detectors as a neutron diagnostics.

An Assessment of Dosimetric Characteristics of Inline 2.5 Mega Voltage Unflattened Imaging X-Ray Beam.

Purpose:The aim of this work is to study the dosimetric parameters of newly introduced 2.5 MV imaging x-ray beam used as inline imaging to do setup verification of the patient undergoing radiation therapy. As this x-ray beam is in megavoltage range but comprises of a lower energy spectrum. It is essential to study the pros and cons of 2.5 MV imaging x-ray beam for clinical use.Methods:The mean energy was calculated using the NIST XCOM table through MAC. Profile analysis was done using RFA to understand the percentage depth dose, degree of unflatteness, symmetry, penumbra and out of field dose. Dose to skin for the 2.5 MV x-ray beam was analysed for field sizes 10x10 cm2, 20x20 cm2, 30x30 cm2. Leakage measurements for treatment head and at the patient plane were done using IEC 819/98 protocol. Finally, the spatial resolution and contrast were analyzed with and without patient scatter medium. Results:The MAC at 15 cm off-axis was found to be lower than that at the CAX. Similarly, there was a decrease in mean energy from 0.47 MV to 0.37 MV at 15 cm off-axis. The reduction of mean energy towards off-axis is lower than the other high energy MV x-ray beams. The tuned absolute dose of 1 cGy/MU is consistent and within < ±1 %. The relative output factors were found to be in correlation with Co-60. The beam quality of 2.5 MV x-ray beam was found to be 0.4771. The profile parameters like the degree of unflatness of the 2.5 x-ray beam were studied at 85 %, 90 %, 95 % lateral distances, and the penumbra at different depth and field sizes are higher than the 6 MV treatment beam. In addition, out of field dose also drastically increases to a maximum of up to 30 % laterally at 5cm at deeper depths. The skin dose increases from 48.51 % to 88.15 % from 6 MV to 2.5 MV x-ray beam for the field size 10x10 cm2. Also, the skin dose increases from 88.15 % to 91.78 % from the field size 10x10 cm2 to 30x30 cm2. Although the measured leakage radiation for 2.5 MV x-ray beam at the patient plane and other than patient planes are with the tolerance limit, an increase in exposure towards gantry side compared to other areas around treatment head and the patient plane may lead to more skin dose to head and chest while imaging pelvis region. The MLC transmission of 2.5 MV x-ray beam such as inter, intra and edge effect are 0.40 %, 0.37 % and 11% respectively. The spatial resolution of 2.0, 1.25 and 0.9 LP/mm was observed for KV, 2.5MV, and 6 MV x-ray beams. The spatial resolution and contrast of 2.5 MV x-ray beam are superior to 6 MV x-ray beam and inferior to KV x-rays. Conclusions:The 2.5 MV x-ray imaging beam is analysed in view of beam characteristics and radiation safety to understand the above-studied concepts while using this imaging beam in a clinical situation. In future, if 2.5MV x-ray beam is used for treatment purpose with increased dose rate, the above-studied notions can be incorporated prior to implementation.

Testing of 5x5 cm2 Solid Oxide Fuel Cell in Direct Methane

The 5x5 cm2 planar tape cast solid oxide fuel cell (SOFC) having LSM cathode, YSZ electrolyte and 2% Ni-6% CeO2 impregnated La0.20Sr0.25Ca0.45TiO3 (LSCTA-) anode tested in H2 and CH4 fuel for 12 hours at 800 °C. The maximum power density, 242 mW cm-2 (526 mA cm-2) has been observed in H2. The corresponding impedance spectra shows 0.82 and 0.17 ohm cm2 ohmic and total polarization resistance respectively. In CH4, the maximum power density, 207 mW cm-2 (384 mA cm-2) and the corresponding ohmic and total polarization resistance 0.86 and 0.16 ohm cm2 is been observed, respectively. The cell has also been tested in mixed fuel gas (CH4+N2+CO2) environment for next 10 hours at 800 °C. The product gas has been analysed using online gas chromatography during cell operation. The study of the effect of coke deposition has also been carried out using the thermo gravimetric analyser (TGA) and the results are analysed.

Investigation of silver nanoparticles on titanium surface created by ion implantation technology.

Objectives: Using dental Ti implants has become a well-accepted and used method for replacing missing dentition. It has become evident that in many cases peri-implant inflammation develops. The objective was to create and evaluate the antibacterial effect of silver nanoparticle (Ag-NP) coated Ti surfaces that can help to prevent such processes if applied on the surface of dental implants.Methods: Annealing I, Ag ion implantation by the beam of an Electron Cyclotron Resonance Ion Source (ECRIS), Ag Physical Vapor Deposition (PVD), Annealing II procedures were used, respectively, to create a safely anchored Ag-NP layer on 1x1 cm2 Grade 2 titanium samples. The antibacterial effect was evaluated by culturing Staphylococcus aureus (ATCC 29213) on the surfaces of the samples for 8 hours, and comparing the results to that of glass as control and of pure titanium samples. Alamar Blue assay was carried out to check cytotoxicity.Results: It was proved that silver nanoparticles were present on the treated surfaces. The average diameter of the particles was 58 nm, with a 25 nm deviation and Gaussian distribution, the the filling factor was 25%. Antibacterial evaluation revealed that the nanoparticle covered samples had an antibacterial effect of 64.6% that was statistically significant. Tests also proved that the nanoparticles are safely anchored to the titanium surface and are not cytotoxic.Conclusion: Creating a silver nanoparticle layer can be an option to add antibacterial features to the implant surface and to help in the prevention of peri-implant inflammatory processes. Recent studies demonstrated that silver nanoparticles can induce pathology in mammal cells, thus safe fixation of the particles is essential to prevent them from getting into the circulation.

Factors influencing the electron dose calculation in Eclipse eMC

This study aims to evaluate the factors influencing electron dose calculation in Eclipse electron Monte Carlo (eMC) on virtual phantoms. Each parameter of accuracy, calculation grid size, random number generator seed, number of particle histories, smoothing method and smoothing level in Eclipse eMC was varied while other parameters were fixed in default value. Gamma analysis was used to evaluate dose distribution accuracy. The reference dose distributions were set as the best option values. The 1% accuracy, 1 mm calculation grid size, 2100000000 random generator seed number, 0 number of particle histories, 3D Gaussian smoothing method and strong smoothing level with 2%/2mm criteria were defined as the best option values. The 6 and 18 MeV energy, the sizes of 6x6 cm2 and 10x10 cm2 applicator were used. The overall results showed the gamma passing rate higher than 90% except when higher accuracy than 2%, 5 mm calculation grid size, no smoothing/low smoothing level and changed the number of particle histories other than 0 were applied. This study shows that the accuracy, calculation grid size, smoothing method, smoothing level and number of particle histories parameters are significantly impact to dose distribution and the first two factors are also affect to calculation time.

Short communication: Morphological characteristics of flower and fruit in several rambutan (Nephelium lappaceum) cultivars in Serang City, Banten, Indonesia

Abstract. Windarsih G, Efendi M. 2019. Morphological characteristics of flower and fruit in several rambutan (Nephelium lappaceum L.) cultivars in Serang City, Banten, Indonesia. Biodiversitas 20: 1442-1449. Indonesia is one of the centers of diversity of rambutan in the world with 22 species. Compared to other species, Nephelium lappaceum L. is mostly cultivated species. This study aimed to identify the generative morphological variation in several rambutan cultivars in the area of Serang City, Banten Province. The plant materials used were five cultivars of rambutan, Parakan, Rapiah, Aceh, Sinyonya, wild type, and male trees. In each plant, three bunches of inflorescence were taken, and then the flowers from each bunch were observed when the flowering phase was open (blooming). In addition, 3-5 fruit bunches were taken per plant, and then 3-5 fruits per bunch were observed. Based on the results obtained, it can be concluded that there is monoecious plants of rambutan (Aceh, Rapiah, wild type), and dioecious plant (male tree). In a monoecious plant, it produces the hermaphrodite flowers, whereas, in a dioecious plant, it just produces the male flowers. In the hermaphrodite flower, it is composed of pedicel, tepal, stamen, and pistil, while the male flower does not have pistil. The Aceh cultivar has the longest average fruit bunch (22.90 cm), Rapiah has highest number of fruit per bunch (15.86 fruits), Parakan has highest spine density (11.64 strands per 1x1 cm2) and longest spine (13.2 mm), Rapiah has a shortest average spine (3.4 mm) with a stiff texture, Rapiah and Aceh have a thickest of fruit rind (3.3 mm). Aceh has the largest size and weight of fruit with the fruit length 4.62 cm, fruit diameter 3.83 cm, fruit weight 37.42 g, weight of fruit rind 17.51 g, weight of aryl 17.94 g, and thickness of aryl 7.7 mm. From a dendrogram analysis, the five cultivars had a similarity distance coefficient from 40% to 69%. Parakan and Sinyonya had highest similarity distance (69%), while Aceh was separated from other cultivars with a similarity distance 40%.

Komunitas dan Preferensi Habitat Gastropoda pada Kedalaman Berbeda di Zona Litoral Danau Singkarak Provinsi Sumatera Barat

This research was conducted in Lake Singkarak from February to March 2016, using purposive sampling method in three locations namely Tanjung Mutiara, Malalo and Paninggahan, at a depth of 0.5 m, 1 m and 1.5 m in each location. Samples were collected using 30x30 cm2 surber net. The result showed four gastropod species from family of Thiaridae, namely Melanoides granifera, Melanoides tuberculata, Brotia costula and Thiara scabra. Average population density of gastropod in Lake Singkarak was 399.75 ind / m2. The population density at depths ranging from 271.11 to 568.89 ind/m2, the highest population density is showed at a depth of 1.5 m and the lowest at a depth of 0.5 m. Melanoides tuberculata shows highest density at all depths. M. granifera prefers habitats with a depth of 1.5 m, M. tuberculata prefers a depth of 1 m, T. scabra prefers a depth up to 1.5 m and B. Costula prefer habitat with a depth of 0.5 m. Condition of Lake Singkarak shows as favorable and suitable habitat for gastropod’s life.

Assessment the Photo-neutron Contamination of IMRT and 3D-Conformal Techniques Using Thermo-luminescent Dosimeter (TLD)

The aim of the study is to evaluate the dependence of photo-neutron production on field size, depth in phantom and distance from isocenter and also to calculate the equivalent neutron doses for PTV and OARs of IMRT and 3DCRT techniques using TLD (600/700).The Linac Siemens Oncor installed at Nasser Institute, Cairo, Egypt. TLDs, Neutron Monitor, Ionization chamber were provided by NIS, the duration of the study was from November 2017 to July 2018. 5 prostate cancer cases were selected treated with high energy beam (15MV) Linear accelerator using 3DCRT and IMRT treatment plans. The OARs were bladder, rectum and femur. Once the plans were completed, there were copied from the planning system onto the RW3 slab phantom in which pairs of TLD chips (600/700) were placed at the exact site of PTV and OARs. The results showed that: The measured photo-neutron decreases from 0.2 mSv/Gy to 0.09 mSv/Gy as increases field sizes from 2x2 cm2 to 20x20 cm2. The measured photo-neutron was maximum at dmax =0.15 mSv/Gy and decreases gradually as increases the depth in phantom reaches to 0.07 mSv/Gy at 10cm depth in phantom. The measured photo-neutron decreases from 1.5 mSv/Gy to 0.02 mSv/Gy when measured at isocenter and at 100cm along the patient couch. Using 3DCRT for PTV and OARs were ranging from 0.027 to 0.39 mSv per photon Gy and for IMRT were 0.135 to 2.34 mSv per photon Gy. In conclusion the photo-neutron production is decreases as increases field size and distance from isocenter along patient couch while increases with depth in phantom up to dmax and decreases gradually as increases depth in phantom. IMRT requires longer beam-on time than 3DCRT leading to worse OARs sparing and increase the production of photo-neutrons than 3DCRT.

Evaluation of Plasticizer Addition in Composite Edible Coating on Quality of Fresh-Cut Mangoes during Storage

A composite edible coating made from carrageenan - beeswax with two plasticizers was used to cover fresh-cut mangoes. The purpose of this research was to develop edible film with plasticizer treatment and investigate the effect of an edible coating on quality changes in fresh-cut mangoes during refrigerated storage. The film-forming solution was poured onto an acrylic plate 20x20 cm2 and dried at 50 °C for 24 hours in a cabinet dryer. Coated and uncoated mangoes were placed into styrofoam then over-wrapped with cling wrap and stored at 6°C for 6 days. Edible films containing two plasticizers had a higher thickness, water vapor transmission rate (WVTR), and solubility than the single plasticizer film. It was found that edible coatings could preserve a fresh-cut mango quality by reducing weight loss, delaying an increase in total soluble solids, maintaining pH, total acidity and growth of microorganisms. It also indicated no difference in sensory perception between the coated and the uncoated fresh-cut mangoes.

Physical and Dosimetric Aspect of Euromechanics Add-on Multileaf Collimator on Varian Clinac 2100 C/D

Background: Before treatment planning and dose delivery, quality assurance of multi-leaf collimator (MLC) has an important role in intensity-modulated radiation therapy (IMRT) due to the creation of multiple segments from optimization process.Objective: The purpose of this study is to assess the quality control of MLC leaves using EBT3 Gafchromic films.Material and Methods: Leaf Position accuracy and leaf gap reproducibility were checked with Garden fence test. The garden fence test consists of 5 thin bands A) 0.2 Cm width spaced at 2 Cm intervals and B) 1 Cm width spaced at 1 Cm intervals. Each leaf accuracy was analyzed with measuring the full-width half-maximum (FWHM). Maximum and average leaf transmission were measured with gafchromic EBT3 films from Ashland for both 6 MV and 18 MV beams.Results: Leaf positions were found to be in a range between 1.78 – 2.53 mm, instead of nominal 2 mm for the test A and between 9.09 – 10.36 mm, instead of nominal 10 mm for the test B. The Average radiation transmission of the MLC was noted 1.79% and 1.98% of the open 10x10 Cm2 field at isocenter for 6 MV and 18 MV beams, respectively. Maximum radiation transmission was noted 4.1% and 4.4% for 6 MV and 18 MV beams, respectively.Conclusion: In this study, application of gafchromic EBT3 films for the quality assurance of Euromechanics multileaf collimator was studied. Our results showed that the average leaf leakage and positional accuracy of this type of MLC were in the acceptance level based on the Protocols.

Physical and Dosimetric Aspect of Euromechanics Add-on Multileaf Collimator on Varian Clinac 2100 C/D

Before treatment planning and dose delivery, quality assurance of multi-leaf collimator (MLC) has an important role in intensity-modulated radiation therapy (IMRT) due to the creation of multiple segments from optimization process. The purpose of this study is to assess the quality control of MLC leaves using EBT3 Gafchromic films. Leaf Position accuracy and leaf gap reproducibility were checked with Garden fence test. The garden fence test consists of 5 thin bands A) 0.2 Cm width spaced at 2 Cm intervals and B) 1 Cm width spaced at 1 Cm intervals. Each leaf accuracy was analyzed with measuring the full-width half-maximum (FWHM). Maximum and average leaf transmission were measured with gafchromic EBT3 films from Ashland for both 6 MV and 18 MV beams. Leaf positions were found to be in a range between 1.78 - 2.53 mm, instead of nominal 2 mm for the test A and between 9.09 - 10.36 mm, instead of nominal 10 mm for the test B. The Average radiation transmission of the MLC was noted 1.79% and 1.98% of the open 10x10 Cm2 field at isocenter for 6 MV and 18 MV beams, respectively. Maximum radiation transmission was noted 4.1% and 4.4% for 6 MV and 18 MV beams, respectively. In this study, application of gafchromic EBT3 films for the quality assurance of Euromechanics multileaf collimator was studied. Our results showed that the average leaf leakage and positional accuracy of this type of MLC were in the acceptance level based on the Protocols.

Analysis of Effect of Change Source to Surface Distance (SSD) and the Field Size to Distribution Dose Using Monte Carlo Method-EGSnrc

Research was conducted to analyze the effect of changes in the distance radiation source to the surface it is called the medium Source to Surface Distance (SSD) and wide exposure field (Field Size) on the distribution of the dose in linear air Accelerator (LINAC) using Monte Carlo - EGSnrc. Monte Carlo simulation is used for modeling and simulation head linac at BEAMnrc. Virtual model of the linac is made based on the data characteristics of the aircraft Linac Varian Clinac iX then its output obtained information characteristic photon beam using BEAMDP, while modeling and simulation phantom done on DOSXYZnrc with the size of the phantom is (40x40x40) cm3 , with the material in the form of water, using a beam of photons 6 MV, testing variation SSD at 80 cm, 90 cm, 100.1 cm, 110 cm, 120 cm and variation field size is (6x6) cm2, (10x10) cm2, (20x20) cm2 to obtain disribution of dosage form of curves Percentage Depth dose (PDD) and Profile dose. The results showed that the smaller distance radiation source to the surface of the medium (SSD) and the greater the broad field (field size), then increasing the dose distribution is obtained. In the SSD and Field Size variation, the radiation dose will continue to rise significantly from the surface of the medium 0 cm to a depth of maximum dose (Dmax), then the dose began to decline after passing the depth Dmax.

Grid Monte Carlo Simulation of a Medical Linear Accelerator

A full grid simulation of the head of an Elekta Synergy Platform medical linear accelerator is performed using the Geant4 Monte Carlo platform. The simulation includes all components of the accelerator head and a homogeneous water phantom. Results in terms of depth doses and lateral dose profiles are presented for 6 MV photon beam with the 10x10 cm2 reference field size at 100 cm distance from the source. Overall, a good agreement with the measured dose data is achieved with a precision better than 0.93% and 2.63% for the depth dose profile and lateral dose profiles respectively.

Grid Monte Carlo Simulation of a Medical Linear Accelerator

A full grid simulation of the head of an Elekta Synergy Platform medical linear accelerator is performed using the Geant4 Monte Carlo platform. The simulation includes all components of the accelerator head and a homogeneous water phantom. Results in terms of depth doses and lateral dose profiles are presented for 6 MV photon beam with the 10x10 cm2 reference field size at 100 cm distance from the source. Overall, a good agreement with the measured dose data is achieved with a precision better than 0.93% and 2.63% for the depth dose profile and lateral dose profiles respectively.

13 Response to high energy photons of the redesigned PTW T31022 PinPoint 3D ion chamber

Introduction The aim of this study was to investigate the dosimetric performances of the new PTW T31022 PinPoint 3D which replaces the PTW T31016 PinPoint 3D. Methods Experimental data were collected using a Varian TrueBeam linear accelerator (Varian Medical Systems, Palo Alto) at nominal energies of 6 and 10 MV with (WFF) and without a flattening filter (FFF) (6WFF, 10WFF and 6FFF, 10FFF, respectively). Measurements of absolute and relative dosimetry were undertaken. Ion collection efficiency associated with Jaffe plots for different dose per pulse, polarity effect, beam profiles, depth dose curves (PDD) and output factors associated to small field output correction factors were investigated. Results The T31022 Jaffe plots were found to be more linear than those of the T31016. The use of the two-voltage technique is sufficient for clinical practice and is consistent with the accuracy of the Jaffe plots technique. Less polarity effect was found for T31022 compared to T31016. The polarity correction factor of the T31022 was dependent on the field size, although it was at a lesser extent than for the T31016. The largest deviation of polarity factors was obtained for the largest field size and for WFF beams. From 3x3 cm2 to 40x40 cm2 field sizes, excellent agreement was found between T31022 output ratios corrected from polarity and T31010 Semiflex results, exhibiting maximum deviations of 0.2% for all energies. Without polarity correction maximum deviations are also relatively low reaching 0.7%, −0.4%, 0.7% and −0.4% for 6WFF, 6FFF, 10WFF and 10FFF respectively. The use of the chamber in small fields ( ⩽ 1x1 cm2) leads to an underestimation of output factors but presents lower field output correction factors than its predecessor. PDD curves present good agreement but discrepancies around 2% were observed for the largest field size and have been identified as a polarity dependence. This effect was moreover emphasized by keeping the electrometer at a distance less than 5 m from the water phantom. Conclusions The T31022 PinPoint 3D ion chamber is an improvement over its predecessor, the T31016, in terms of polarity, ion recombination and in small field dosimetry. The T31022 polarity correction factor has to be considered when measuring output factors and PDD for large field size.

Study to Fabricate the Large Scale Buckypaper Based on Carbon Nanotubes

Carbon nanotubes (CNTs) have attracted great attention because of their unique structural, electrical, mechanical and thermal properties. Then CNTs have potential application as electrode for batteries and supercapacitors, especially binder-free electrodes. The major challenge is to fabricate the large scale electrode with the uniform thickness, electrical property. The large scale CNTs buckypaper can be fabricated via vacuum filtration technique. The characteristics of CNT dispersion and buckypaper depend on variety of factor such as sonication power, sonication time, dispersant…. In this study, we investigate the multiwall carbon nanotubes (MW CNTs) in Isopropanol (IPA) solvent with different sonication conditions, membrane filter size for paper with areal density of 3 mg/cm2 with different sizes such as 4, 10, 20 cm in diameter and large scale of 30x30 cm2. It is observed that the dispersion of CNTs are good and the thickness, conductivity are uniform over whole sample for above sizes. We also can get the highest conductivity of buckypaper was 3.9x103 S/m in 30 mins. It is found that the higher sonication power and higher sonication time are better for buckypaper.

Dry spots dynamics in shear-driven thin liquid films under intensive local heating

Development of the modern microelectronic equipment requires the effective cooling solutions because it is necessary to remove high heat fluxes of up to 1 kW/cm2 and higher from the local hot spots of the processor. Thin and ultra-thin (less than 10 μm in thickness) liquid films, moving under the action of a forced gas flow in a mini-channel, are promising for the use in the temperature control systems of the modern semiconductor devices. Here we report results of systematic experimental studies of the flow and rupture of a water film, shear-driven in the channel, under intense heating from a local heat source with size of 1x1 cm2. To carry out high-speed visualization of the process, the FASTCAM SA1.1 CCD camera is used (with the speed of up to 100 000 frames per second). The camera is equipped with an optical system of high spatial resolution (2.5 μm per 1 pixel of the camera sensor). With the help of high-speed imaging, it was found that the maximum intensity of heat removal from the heater is achieved in the mode, when the film flow continuity is broken. The heater is covered with dry spots having typical size on the order of 10-100 μm and typical lifetime on the order of 0.1-1 ms. At that, the number of dry spots that exist simultaneously on 1 cm2 of the heater surface can reach several hundred. During 1 s up to 1 million dry spots appear and disappear at the area of the heater.

ANALISIS NILAI PERCENTAGE DEPTH DOSE(PDD) TERHADAP VARIASI KEDALAMAN TARGET DAN LUAS LAPANGAN PENYINARAN MENGGUNAKAN PESAWAT LINAC-CX

Percentage Depth Dose (PDD) value measurement is done by varying the target depth and field size. The study was carried out with variations in target depth of 0 cm to 30 cm with 1 cm intervals and fields size ranging from (5x5) cm2 to (39x39) cm2 with intervals (2x2) cm2. PDD is a comparison of the radiation dose at a depth to the radiation dose at the maximum depth normalized by percentage. This study was also conducted to determine the value of radiation doses received by phantoms from the PDD measurement value. This research used 2 photon energy beam that is 6 MV and 10 MV. This study uses water phantom as a substitute for patients with radiation source technique Source Surface Distance (SSD). PDD measurements were performed using a chamber ionization detector. The results obtained showed that the number of radiation doses received by fantom increased to the maximum depth (zmax). After passing zmaks, the radiation dose received by the phantom has decreased. Likewise along with the increase in the amount of radiation field, the value of radiation doses received by phantoms will also increase.

Surface Dose Measurements on an Indigenously Made Inhomogeneous Female Pelvic Phantom Using Metal-Oxide-Semiconductor-Field-Effect-Transistor Based Dosimetric System

Introduction: Megavoltage X-ray beams are used to treat cervix cancer due to their skin-sparing effect. Preferably, the radiation surface doses should be negligible; however, it increases due to electron contamination produced by various field parameters. Therefore, it is essential to provide proper knowledge about the effect of different field parameters on radiation doses. This study sought to find out the effect of various physical parameters on the surface doses. Materials and Methods: The effects of field size, source-to-surface distance, and open or acrylic block tray fields on surface doses were determined. Metal-Oxide-Semiconductor-Field-Effect-Transistor based dosimetric system was used for dose measurements for 6 MV photon beam. The directly measured radiation surface doses on pelvic phantom were compared to surface dose values computed by treatment planning system in the similar field parameters. Results: The measured results for the percentage depth dose (PDD0) in field size of 10x10 cm2 were 13.32%, 12.95% and 13.87% for open field and 36.87%, 36.31% and 35.88% for acrylic block tray field. In addition, the computed doses were 7.83%, 7.73% and 7.65% for open field and 16.33%, 16.12% and 15.88% for acrylic block tray field at 80 cm, 100 cm, and 120 cm SSDs, respectively. Conclusion: The surface dose increases along with the size of the field and decreases with increasing SSD. The surface doses in acrylic block tray fields were significantly higher than the open ones. The treatment planning system computed a lesser radiation doses in same field parameters.