Chamber Position Research Articles

P233] Investigation of the response of cylindrical ionization chamber in non-reference conditions when using high-energy photon beams

Purpose To investigate the response of CC13 cylindrical ionization chamber in non-reference conditions with focus on the penumbra region and the depth of maximum dose when using high-energy photon beams. This chamber is used for beam data measurements and also for pre-treatment quality assurance procedures for dynamic treatments. Methods Measurements and Monte Carlo calculations are performed, employing a Varian iX Linac (6 MV photon beam), at the depths of 15 mm and 100 mm for the field sizes of 20 × 20 mm 2 ; 20×100 mm 2 and 100×100 mm 2 . The Monte Carlo model is developed using the egs-chamber in the EGSnrc package. Conversion factors are calculated relating the absorbed dose to air in the air cavity of the chamber to the absorbed dose to water through using: (a) water volume equal to the air cavity of the chamber, (b) 1×1×1 mm 3 water voxel representing point dose. Corresponding correction factors, C w/chamber and C w,point/chamber , are determined to quantify the variations in the conversion factors. Results Agreement within 3.5%/0.5 mm is obtained between the measurements and calculations. The correction factors for a chamber position at the central axis of the beam and at the center of the field penumbra are between 0.98 and 1.02 for all field sizes and depths examined. The largest corrections are seen for off-axis positions 3 mm beyond the penumbra center where C w,point/chamber varies between 0.54 and 0.71 for the depth of 100 mm and 0.45 and 0.58 for the depth of 15 mm indicating an overestimation of the absorbed dose to water when using the CC13 chamber. C w,point/chamber factors up to 1.27 are obtained in regions close to the penumbra inside the 20×20 mm 2 and 20×100 mm 2 fields indicating an underestimation of the absorbed dose to water. The maximum variation of the C w/chamber factors is between 0.70 and 1.06 for the 20×20 mm 2 field at the depth of 15 mm. Conclusions Uncorrected chamber response of the CC13 chamber, or similar, results in under or overestimation of the absorbed dose to water at positions inside or outside of the beam close to the penumbra for small as well as large field sizes.

Analysis of ion beam teletherapy patient-specific quality assurance

The objective of this study was to evaluate the procedures for patient-specific quality assurance measurements using modulated scanned and energy stacked beams for proton and carbon ion teletherapy. Delivery records from 1734 portal measurements were analyzed using a 3-point pass criteria: more than 22 of 24 chambers in a water phantom (WP) had to have a measured dose difference from the planned portal doses less than or equal to 3%, or the distance from the measurement point location to a point location in the plan having the same dose had to be less than or equal to 3 mm (distance to agreement [DTA]), and the mean dose deviation of all chambers had to be less than 3%. Stratification of results showed some associations between measurement parameters and pass rates. For proton portals, pass rates were high at all measurement depths, but for carbon ion portals, pass rates decreased as a function of increasing measurement depth. Pass rates of both proton and carbon ion portals with 1 WP were slightly lower than those with a second WP. The total pass rates were 97.7% and 91.9% for proton and carbon ion patient portals, respectively. In general, the measured doses exhibited good agreement with the treatment planning system (TPS) calculated doses. When the chamber position was deeper than 150 mm in carbon ion beams, a lower pass rate was observed, which may have been caused by ion chamber array setup uncertainty (lateral and depth) in highly modulated portals or incorrect modeling of scatter by the TPS. These deviations need further investigation.

The Differences of Nitrous Oxide (N₂O) Emissions as Crop Presence and Location of Gas Sampling Chambers in Upland

Nitrous oxide is one of the main sources of greenhouse gases and its concentration has increased from 273 ppb in 1,750 to 315 ppb in 2005. Specially, nitrogen fertilizer used in agricultural soils is considered as an important source of atmospheric N2O emission. This study was conducted to estimate the difference of nitrous oxide emission as chamber position on furrow and ridge and crop existence in gas sampling chamber on upland. Four treatments used in this experiment were ① no-fertilizer without crop in chamber on ridge, ② fertilizer application without crop in chamber on ridge, ③ fertilizer application with crop in chamber on ridge, ④ fertilizer application without crop in chamber on ridge and furrow. Nitrous oxide emission at fertilizer application with crop in chamber on ridge were the highest while were the lowest at no-fertilizer without crop in chamber on ridge. There was no significant difference of nitrous oxide emission by chamber position, but total emission by crop existence in chamber was significant difference. Therefore, in order to estimate greenhouse gases emission using chamber method in upland, it should be considered in correlation with crop existence in chamber and characteristic changes like as the soil moisture, microbial flora by crop growth stage.

Numerical analysis of factors influencing explosion suppression of a vacuum chamber

Vacuum chambers can effectively suppress gas explosion without relying on any explosion suppression material. The effect of explosion suppression by a vacuum chamber is correlated with the negative pressure of the vacuum chamber and flame front position when the diaphragm breaks. Accurate control of the experimental conditions of explosion suppression is challenging, and the use of experimental methods alone for analyzing their interrelation is difficult. This study analyzed considerable experimental data on explosion suppression by a vacuum chamber, investigated factors that influenced the explosion suppression, and evaluated parameters of the explosion suppression by using the ΔP-I principle. This study established a BP neural network optimized by a genetic algorithm, and discovered the non-linear relations among all parameters. The trained neural network was used to analyze the influence of vacuum degree and flame front position on explosion suppression when the diaphragm breaks. The results demonstrated that a good explosion suppression was achieved when a vacuum degree of P0was > 0.06 MPa and the optimal position of the flame front index S was 0 m. Explosion suppression of the vacuum chamber can be predicted by a fitting curve I = 5.61e (-P0/0.028) + 1.70, which was obtained using the trained neural network and S = 0.86 m.

Effects of lubricating oil on the performance of a semi-hermetic twin screw refrigeration compressor

Lubricating oil is often employed in a twin-screw refrigeration compressor for lubricating bearings, sealing leakage paths, cooling refrigerant gas and regulating capacity. In this paper, the effect of lubricating oil on the performance of a semi-hermetic twin-screw refrigeration compressor is investigated. A mathematical model is established and a comprehensive experimental investigation is performed for this purpose. The model is validated using experimental data and then used to investigate the effect on compressor performance of lubricating oil supplied to the suction and discharge end bearings, and returned to the suction pipe. The results show that the compressor performance is reduced as the compensation oil injection flow rate increases in the suction pipe. However, as the compensation oil injection position moves from the suction pipe to a proper compression chamber position, the compressor efficiencies increase as the oil flow rate increases. The results also show that the compressor performance decreases as the oil flow rate increases at the suction end bearing. But the effect on the compressor performance of the lubricating oil supplied to the discharge end bearing depends on the oil temperature. Low temperature oil supplied to the discharge end bearing increases the compressor performance, while high temperature oil lowers the compressor performance. These analyses provide useful information for optimizing lubricating oil distribution to maximize energy efficiency in semi-hermetic twin screw refrigeration compressors.

The impact of x-ray tube stabilization on localized radiation dose in axial CT scans: initial results in CTDI phantoms

Rise, fall, and stabilization of the x-ray tube output occur immediately before and after data acquisition on some computed tomography (CT) scanners and are believed to contribute additional dose to anatomy facing the x-ray tube when it powers on or off. In this study, we characterized the dose penalty caused by additional radiation exposure during the rise, stabilization, and/or fall time (referred to as overscanning). A 32 cm CT dose-index (CTDI) phantom was scanned on three CT scanners: GE Healthcare LightSpeed VCT, GE Healthcare Discovery CT750 HD, and Siemens Somatom Definition Flash. Radiation exposure was detected for various x-ray tube start acquisition angles using a 10 cm pencil ionization chamber placed in the peripheral chamber hole at the phantom’s 12 o’clock position. Scan rotation time, ionization chamber location, phantom diameter, and phantom centering were varied to quantify their effects on the dose penalty caused by overscanning. For 1 s single, axial rotations, CTDI at the 12 o’clock chamber position (CTDI100, 12:00) was 6.1%, 4.0%, and 4.4% higher when the start angle of the x-ray tube was aligned at the top of the gantry (12 o’clock) versus when the start angle was aligned at 9 o’clock for the Siemens Flash, GE CT750 HD, and GE VCT scanner, respectively. For the scanners’ fastest rotation times (0.285 s for the Siemens and 0.4 s for both GE scanners), the dose penalties increased to 22.3%, 10.7%, and 10.5%, respectively, suggesting a trade-off between rotation speed and the dose penalty from overscanning. In general, overscanning was shown to have a greater radiation dose impact for larger diameter phantoms, shorter rotation times, and to peripheral phantom locations. Future research is necessary to determine an appropriate method for incorporating the localized dose penalty from overscanning into standard dose metrics, as well as to assess the impact on organ dose.

SU‐E‐J‐07: IGRT Gently: Evaluating Imaging Dose in Phantoms of Different Sizes

Purpose:IGRT imaging procedures have emerged as a common method of patient position verification in radiotherapy, though imaging dose is generally neglected in the treatment plan. Consequently, evaluating and optimizing the dose from these procedures is worthwhile. This process is especially important for children, who are more radiosensitive than adults. The aim of this work was to gain some understanding of the relative doses involved with various XVI‐preset parameters for an “adult” and “child” phantom set, with the hopes that imaging dose for a child can be reduced.Methods:32 and 16cm CTDI‐phantoms were used as surrogates for adult and child torsos, respectively. Dose was measured in the central and peripheral chamber positions of the phantoms. CBCT scans were made for both phantoms using Elekta's Chest‐preset to establish a dose baseline. The child‐phantom was then scanned using the Elekta Head and Neck (HN) preset. A modified HN‐preset (named Peds Abd‐pelvis) was also created with a doubled mAs to maintain a reduction in dose to the child‐phantom (relative to the baseline), while providing clinically‐usable image quality.Results:The baseline dose to the child‐phantom from the Chest‐preset was 310% that of the adult‐phantom for the center chamber position and 150% at the periphery. An average dose reduction of 97% was obtained in the childphantom by switching from the Chest‐preset to the HN‐preset, while the Peds Abd‐pelvis‐preset similarly reduced the dose by an average of 92%.Conclusion:XVI‐preset parameters significantly affect dose, and should be optimized to reduce dose, while ensuring clinically‐usable image quality. Using a modified imaging preset (Peds Abd‐pelvis‐preset) greatly reduced the dose to the child‐phantom compared to the dose for the Chest‐preset for both the child and adult‐phantoms. This outcome provides support for the development of child‐specific protocols for IGRT imaging in pediatric patients.

Investigation on temperature separation and flow behaviour in vortex chamber

In the previous researches, it is known that the swirl flow in circular pipe causes the temperature separation. Recently, it is shown that the temperature separation occurs in a vortex chamber when compressed air are pumped into this device from the periphery. Especially, in a cavity installed in the periphery of the chamber, the highest temperature was observed. Therefore, it is expected that this device can be used as a heat source in the engineering field. In recent researches, the mechanism of temperature separation in vortex chamber has been investigated by some researchers. However, there are few researches for the effect of diameter and volume of vortex chamber, height of central rod and position of cavity on the temperature separation. Further, no detailed physical explanation has been made for the temperature separation phenomena in the vortex chamber. In the present study, the effects of chamber configuration and position of the cavity on temperature separation in the vortex chamber were investigated experimentally.

Development of a passive liquid valve (PLV) utilizing a pressure equilibrium phenomenon on the centrifugal microfluidic platform.

In this paper, we propose an easy-to-implement passive liquid valve (PLV) for the microfluidic compact-disc (CD). This valve can be implemented by introducing venting chambers to control the air flow of the source and destination chambers. The PLV mechanism is based on equalizing the main forces acting on the microfluidic CD (i.e., the centrifugal and capillary forces) to control the burst frequency of the source chamber liquid. For a better understanding of the physics behind the proposed PLV, an analytical model is described. Moreover, three parameters that control the effectiveness of the proposed valve, i.e., the liquid height, liquid density, and venting chamber position with respect to the CD center, are tested experimentally. To demonstrate the ability of the proposed PLV valve, microfluidic liquid switching and liquid metering are performed. In addition, a Bradford assay is performed to measure the protein concentration and evaluated in comparison to the benchtop procedure. The result shows that the proposed valve can be implemented in any microfluidic process that requires simplicity and accuracy. Moreover, the developed valve increases the flexibility of the centrifugal CD platform for passive control of the liquid flow without the need for an external force or trigger.

Automated long-term monitoring of parallel microfluidic operations applying a machine vision-assisted positioning method.

As microfluidics has been applied extensively in many cell and biochemical applications, monitoring the related processes is an important requirement. In this work, we design and fabricate a high-throughput microfluidic device which contains 32 microchambers to perform automated parallel microfluidic operations and monitoring on an automated stage of a microscope. Images are captured at multiple spots on the device during the operations for monitoring samples in microchambers in parallel; yet the device positions may vary at different time points throughout operations as the device moves back and forth on a motorized microscopic stage. Here, we report an image-based positioning strategy to realign the chamber position before every recording of microscopic image. We fabricate alignment marks at defined locations next to the chambers in the microfluidic device as reference positions. We also develop image processing algorithms to recognize the chamber positions in real-time, followed by realigning the chambers to their preset positions in the captured images. We perform experiments to validate and characterize the device functionality and the automated realignment operation. Together, this microfluidic realignment strategy can be a platform technology to achieve precise positioning of multiple chambers for general microfluidic applications requiring long-term parallel monitoring of cell and biochemical activities.

Optimum patient orientation for pelvic and hip radiography: A randomised trial

PurposeTo investigate the effect of patient orientation on the radiation dose and image quality (IQ) for digital (DR) and computed radiography (CR) examinations of the pelvis. MethodsA randomised study was conducted using DR and CR X-ray equipment. The standard patient orientation of head towards (HT) the two outer Automatic Exposure Device (AED) chambers was compared with a group of patients with their head away (HA) from the two outer AED chambers. Collection of mAs, source-to-skin distance and kVp data facilitated the calculation of entrance surface dose (ESD) and effective dose (ED) which were compared between groups. Each image was graded independently by three observers. IQ data were analysed for inter-observer variability and statistical differences. ResultsFor DR pelvis examinations switching orientation (HT to HA) reduced the mean ESD and ED by 31% (P < 0.001), respectively. For CR examinations the dose reduction was greater between the two orientations (38%; P = 0.009). Examinations of the hips allowed dose reductions of around 50% when switching between orientations. For DR examinations minor reductions in IQ were seen and favoured the HT orientation (P = 0.03). For CR examinations there were no statistical differences in IQ between orientations. ConclusionSwitching patient orientation relative to the AED chambers can help optimise radiation dose. In order to facilitate this chamber position should be clearly marked on all equipment and patient orientation should be a consideration when tailoring individual examinations. For DR minor changes in IQ are a consequence of changing orientation and should be factored into the decision making.

The CFD Simulation of Tray Dryer Design for Kenaf Core Drying

Tray dryer is the most extensively use for kenaf core drying because of its simple and economic design. The product is spread out on trays at an acceptable thickness so that the product can be dried uniformly. Most tray dryers use hot air stream where water is vaporized from the product and removed by air stream. In a tray dryer, more products can be loaded as the trays are arranged at different levels. The drawback of this dryer is non-uniformity in the desired moisture content of end product. The key to the successful operation of the tray dryer is uniform airflow distribution over the trays. Therefore, the good design of the drying chamber configuration in a tray dryer is necessary to obtain optimum performance. This research is to design the uniform airflow distribution throughout the drying chamber using CFD simulation for kenaf core drying. Several configurations of drying chamber and trays position was designed and simulated to determine the tray dryer which can produce better airflow distribution. It was found that the design B gives a more uniform airflow distribution compared to others design. The good design of kenaf core dryer should be able to produce uniform drying at high drying capacity and shorter drying time.

Poly(p-phenylene benzobisoxazole) 고성능 섬유의 자외선 저항성 향상을 위한 표면처리 기술 연구

A UV testing chamber was designed and prepared for testing the UV-resistance of poly(p-phenylene benzobisoxazole) (PBO) fibers. The optimum conditions for the test were established by measuring UV irradiation at a chamber position using various kinds of UV sources and different irradiation times. Expectedly, PBO fibers (Zylon<TEX>$^{(R)}$</TEX>) showed significant degradation under UV irradiation by exhibiting a decrease in the tensile strength and elongation of up to 37% and 18%, respectively. Selected UV-absorbing and -stabilizing agents were successfully coated onto the fibers using water-borne polyurethane. It was found that triazine-type UV absorbing agents were more effective than benzophenone- or benzotriazole-type agents in reducing the degradation of PBO fibers under UV irradiation.

SU-E-T-83: Validation and Testing of Performance of a Novel Phantom Specially Designed for Volumetric Modulated Arc Therapy MU/dose Verification

Purpose: To validate and performance test a novel phantom for Volumetric Modulated Arc Therapy MU/dose verification. Methods: A cylindrical phantom was designed using a 2 litter beverage plastic bottle, having useful length of 20.7cm and average diameter is 9.9cm. A hollow plastic tube, having a stopper in the middle, was inserted along the long axis of the bottle and cemented at both end for a reproducible chamber position. A 0.125cc Semiflex chamber (PTW, Germany) was inserted through the central tube. Reproducibility of the set up was ensured. Axial CT cuts were accrued for 2mm separation. Total 33 VMAT plans were generated on Elekta (Norcross, GA) Monaco V 3.1.01 treatment planning system (TPS) and tested using this phantom. Cone Beam CT or portal images were used for reproducing the phantom position, Phantom was repositioned using 3 dimensional or six dimensional (Hexapod couch) couch movement as per the availability. Results: For dose calculation, chamber volume was contoured and 4 individual points were considered along chamber length. MU/dose were calculated against average point dose and volumetric dose. MU verification was done by calculating % variation of TPS calculated and LINAC measured dose. Mean point dose and volumetric dose variations were 1.05±1.077 % and 1.02±1.22% respectively. Conclusion: We present a novel indigenous phantom for VMAT quality assurance. Imaging verification was essential for reproducibility of the phantom positioning. 6D couch movement was marginally better than 3D movement and does not produce a dosimetrically significant variation. This in-house made phantom cost about 9 USD and gives a very good accuracy for MU/ dose verification. Exactrac (Brainlab) system, using a ±45° X-ray images could not detect the phantom as well as chamber position properly; giving an average longitudinal shift of 11.4 cm.

TU‐G‐103‐07: Quantifying the Dose Distribution of OBI CBCT Using Monte Carlo Simulations with a Measurement‐Based Source Model

Purpose: To test the feasibility of using a measurement‐based source model in Monte Carlo simulations to calculate in‐phantom 3D dose distributions, with the application to kV‐CBCT dose quantification on a Varian OBI platform. Methods: A 3‐part nested CTDI phantom was used in this investigation. It contains 7 tracks in the x‐y plane that can be probed. The central reference point of the phantom was aligned at machine isocenter, and using standard head and pelvis CBCT protocols, point dose measurements were made at various 3D locations with a 0.6cc thimble ionization chamber by moving the phantom along the z‐direction and changing the ionization chamber position among the tracks under repetitive scans. We have generated a measurement‐based source model for the OBI system and incorporated it with the Monte Carlo software MCNPX to model each CBCT protocol under examination. The in‐phantom CBCT dose (mGy per particle) was simulated at all 3D measurement locations and converted to absolute dose (mGy) by normalizing with the ratio between measured and Monte Carlo simulated dose at the reference center. The calculated results were compared with the physical measurement and their discrepancies were assessed quantitatively. Results: Agreement was observed between Monte Carlo simulation results and in‐phantom measurements for both the OBI CBCT head and pelvis protocols. For the head protocol, the average agreement was 3.40% with a maximum and minimum disagreement of 5.72% and 1.61%, respectively. For the pelvis protocol, the average agreement was 3.18% with a maximum and minimum disagreement of 4.29% and 1.87%, respectively. Conclusion: We have demonstrated the accuracy of a measurement‐based OBI source model to reproduce an array of measured point doses in phantom when using the CBCT mode of operation. These results serve as the basis for using this source model to investigate OBI dosimetry with anthropomorphic phantoms and patient specific models. (a) Dr. McNitt‐Gray: Institutional research agreement, Siemens AG;Recipient research support Siemens AG; Consultant, Flaherty Sensabaugh Bonasso PLLC; Consultant, Fulbright and Jaworski, LLC; (b) Dr. Dan Ruan: Recipient research support AACR; Recipient research support TRDRP; (c) K McMillan: Research partially supported by a grant from Siemens AG; Research partially supported by a grant from AACR; Research partially supported by a grant from TRDRP

Options for radiation dose optimisation in pelvic digital radiography: A phantom study

PurposeTo investigate the effects of phantom orientation and AEC chamber selection on radiation dose and image quality (IQ) for digital radiography (DR) examinations of the pelvis. MethodsA phantom study was conducted using a DR detector, utilising all AEC chamber combinations. Current recommended orientation (Cr-AEC) was with the outer AEC chambers cranially orientated. mAs (given), source-to-skin distance and kVp data facilitated entrance surface dose and effective dose calculations. Six anatomical areas were blindly graded by two observers (3-point scale) for IQ. Statistical differences in radiation dose were determined using the paired Student’s t-test. IQ data was analysed for inter-observer variability (ICC) and statistical differences (Wilcoxon test). ResultsSwitching phantom orientation (caudally orientated outer AEC chambers: Ca-AEC) reduced mean radiation dose by 36.8%, (p<0.001). A minor reduction in median IQ (15.5 vs. 15) was seen (p<0.001). One Ca-AEC orientated image (1.6%) had all anatomical areas graded ‘inadequate’ by at least one observer; all other images were considered ‘adequate’ for all areas. In the Ca-AEC orientation, at least a 44% dose reduction was achievable (p<0.001) when only the outer AEC chambers were used. In the Cr-AEC orientation, at least 11% dose reduction was achieved (p<0.001); here the central chamber was used alone, or in combination. IQ scores fell, but remained ‘adequate’. ConclusionSwitching pelvic orientation relative to AEC chamber position can optimise radiation dose during pelvic radiography. AEC chamber position should be clearly marked on equipment to facilitate this. AEC selection should be an active process.

TU-A-BRB-11: A New Method for the Measurement of Reference Dosimetric Quantities in Electron Beams

Purpose: To present and confirm the accuracy of a new method to extract data for reference dosimetry in electron beams from depth‐ionization measurements. Methods: Depth‐ionization curves are measured in water using NRC reference ion chambers and several plane‐parallel chambers in 4 to 18 MeV electron beams from the Elekta Precise clinical linear accelerator. To extract useful information from depth‐ionization results, the accuracy of setting the chamber position must be established. For this purpose, differences in the depth at which the chamber's ionization reading falls to 50% of its maximum value are used to derive EPOM values relative to those of reference chambers which have been previously established (Lacroix et al., Med. Phys. 37 (2010) 4331). After validation of positioning accuracy, relative ion chamber perturbation factors are determined using the ratio of readings to those of reference ion chambers as a function of mean electron energy, which changes smoothly with depth.Results:Repeatable results for EPOM at the 0.1 mm level indicate little uncertainty from positioning. Different chambers of the same type give EPOM results that differ by less than 0.2 mm, suggesting insignificant chamber‐to‐chamber variability. Values of EPOM at I50 determined for 4 to 18 MeV beams do not exhibit significant variation with beam energy. For well‐behaved chambers, relative perturbation factors at the same mean electron energy are consistent regardless of the incident beam energy. Relative perturbation factors for the same chambers repeated using a different reference chamber after several days are unchanged within 0.3%. Relative perturbation factors for the NACP and Roos chambers agree with published data. Conclusions: These measurements show promising results for the determination of reference dosimetry data from depth‐ionization curves. Ultimately, these relative measurements will be compared against the NRC primary standard calorimeter to get absolute perturbation factors that will prove valuable for updated dosimetry protocols.

A convolution model for obtaining the response of an ionization chamber in static non standard fields

This work contains an alternative methodology for obtaining correction factors for ionization chamber (IC) dosimetry of small fields and composite fields such as IMRT. The method is based on the convolution/superposition (C/S) of an IC response function (RF) with the dose distribution in a certain plane which includes chamber position. This method is an alternative to the full Monte Carlo (MC) approach that has been used previously by many authors for the same objective. The readout of an IC at a point inside a phantom irradiated by a certain beam can be obtained as the convolution of the dose spatial distribution caused by the beam and the IC two-dimensional RF. The proposed methodology has been applied successfully to predict the response of a PTW 30013 IC when measuring different nonreference fields, namely: output factors of 6 MV small fields, beam profiles of cobalt 60 narrow fields and 6 MV radiosurgery segments. The two-dimensional RF of a PTW 30013 IC was obtained by MC simulation of the absorbed dose to cavity air when the IC was scanned by a 0.6 × 0.6 mm(2) cross section parallel pencil beam at low depth in a water phantom. For each of the cases studied, the results of the IC direct measurement were compared with the corresponding obtained by the C/S method. For all of the cases studied, the agreement between the IC direct measurement and the IC calculated response was excellent (better than 1.5%). This method could be implemented in TPS in order to calculate dosimetry correction factors when an experimental IMRT treatment verification with in-phantom ionization chamber is performed. The miss-response of the IC due to the nonreference conditions could be quickly corrected by this method rather than employing MC derived correction factors. This method can be considered as an alternative to the plan-class associated correction factors proposed recently as part of an IAEA work group on nonstandard field dosimetry.

Heart Dissection in Larval, Juvenile and Adult Zebrafish, &lt;em&gt;Danio rerio&lt;/em&gt;

Zebrafish have become a beneficial and practical model organism for the study of embryonic heart development, however, work examining post-embryonic through adult cardiac development has been limited. Examining the changing morphology of the maturing and aging heart are restricted by the lack of techniques available for staging and isolating juvenile and adult hearts. In order to analyze heart development over the fish's lifespan, we dissect zebrafish hearts at numerous stages and photograph them for further analysis. The morphological features of the heart can easily be quantified and individual hearts can be further analyzed by a host of standard methods. Zebrafish grow at variable rates and maturation correlates better with fish size than age, thus, post-fixation, we photograph and measure fish length as a gauge of fish maturation. This protocol explains two distinct, size dependent dissection techniques for zebrafish, ranging from larvae 3.5 mm standard length (SL) with hearts of 100 μm ventricle length (VL), to adults, with SL of 30 mm and VL 1mm or larger. Larval and adult fish have quite distinct body and organ morphology. Larvae are not only significantly smaller, they have less pigment and each organ is visually very difficult to identify. For this reason, we use distinct dissection techniques. We used pre-dissection fixation procedures, as we discovered that hearts dissected directly after euthanization have a more variable morphology, with very loose and balloon like atria compared with hearts removed following fixation. The fish fixed prior to dissection, retain in vivo morphology and chamber position (data not shown). In addition, for demonstration purposes, we take advantage of the heart (myocardial) specific GFP transgenic Tg(myl7:GFP)(twu34), which allows us to visualize the entire heart and is particularly useful at early stages in development when the cardiac morphology is less distinct from surrounding tissues. Dissection of the heart makes further analysis of the cell and molecular biology underlying heart development and maturation using in situ hybridization, immunohistochemistry, RNA extraction or other analytical methods easier in post-embryonic zebrafish. This protocol will provide a valuable technique for the study of cardiac development maturation and aging.

Two-dimensional trajectory analysis of the diatom Navicula sp. using a micro chamber

We describe a trajectory analysis of diatom cell locomotion by combining a micro chamber and two-dimensional position coordinate analysis. By shutting cells in a micro chamber, continuous microscopic observation of Navicula sp. cells was possible. The trajectory of each cell was visualized once every second by using position coordinate analysis although time resolution of previous papers were range of minutes. Our data revealed frequent change of movement direction. Furthermore, the correlation between the distances moved, the velocity, and the acceleration of the cells was discussed in detail.