Increasing crop field size does not consistently exacerbate insect pest problems.

Increasing diversity on farms can enhance many key ecosystem services to and from agriculture, and natural control of arthropod pests is often presumed to be among them. The expectation that increasing the size of monocultural crop plantings exacerbates the impact of pests is common throughout the agroecological literature. However, the theoretical basis for this expectation is uncertain; mechanistic mathematical models suggest instead that increasing field size can have positive, negative, neutral, or even nonlinear effects on arthropod pest densities. Here, we report a broad survey of crop field-size effects: across 14 pest species, 5 crops, and 20,000 field years of observations, we quantify the impact of field size on pest densities, pesticide applications, and crop yield. We find no evidence that larger fields cause consistently worse pest impacts. The most common outcome (9 of 14 species) was for pest severity to be independent of field size; larger fields resulted in less severe pest problems for four species, and only one species exhibited the expected trend of larger fields worsening pest severity. Importantly, pest responses to field size strongly correlated with their responses to the fraction of the surrounding landscape planted to the focal crop, suggesting that shared ecological processes produce parallel responses to crop simplification across spatial scales. We conclude that the idea that larger field sizes consistently disrupt natural pest control services is without foundation in either the theoretical or empirical record.

Support for an area-heterogeneity tradeoff for biodiversity in croplands.

Rapid expansion of the human population poses a challenge for wildlife conservation in agricultural landscapes. One proposal for addressing this challenge is to increase biodiversity in such landscapes by increasing crop diversity. However, studies report both positive and negative effects of crop diversity on biodiversity. One possible explanation, derived from the "area-heterogeneity tradeoff hypothesis," is that the effect of crop diversity on biodiversity depends on a tradeoff between increasing the number of crop types in a landscape and decreasing the amount of each single crop type. This should cause positive effects of increasing crop diversity at low to intermediate crop diversity and negative effects at intermediate to high crop diversity. We also propose two factors that could change the point at which the effect of increasing crop diversity shifts from positive to negative. First, we predicted that this shift would occur at a lower crop diversity when the surrounding landscape contains less semi-natural habitat and at a higher crop diversity when the landscape contains more semi-natural habitat. This should increase the likelihood of detecting negative effects of crop diversity when semi-natural cover is low and positive effects when it is high. Second, we predicted that the shift from a positive to negative effect would occur at a lower crop diversity when it is measured locally than when it is measured at greater distances from the site, making detection of negative crop diversity effects more likely when measurements are at local extents. We tested these predictions using data on the biodiversity of herbaceous plants, butterflies, syrphid flies, woody plants, bees, carabid beetles, spiders, and birds at 221 crop field edges in Eastern Ontario, Canada. We found support for an area-crop diversity tradeoff. Semi-natural cover and measurement extent influenced the biodiversity-crop diversity relationship, with positive effects when semi-natural cover was high and negative effects when semi-natural cover was low and when crop diversity was measured at local extents. The results suggest that policies/guidelines designed to increase crop diversity will not benefit biodiversity in the landscapes where conservation action is most urgently needed, that is, in landscapes with high agricultural use and low semi-natural cover.

Radiation dose evaluation to organs in neonatal patients by field size during potable X-ray examination in incubators: A Monte Carlo simulation study.

BACKGROUND: Neonatal patients located in incubators are exposed to as many as 159 radiographs until discharge. To reduce the dose exposed to the patient, factors that may cause unnecessary exposure to the patient were judged. When conducting portable X-rays of neonatal patients located in an incubator, it is not easy to determine the exact field size because collimation light is exposed on the acrylic plate, an incubator canopy, and the resulting shadow is reflected on the patient's body. OBJECTIVE: This study aims to measure the organ dose exposed to the patient according to the field size when a portable radiograph is given to a neonatal patient in a neonatal intensive care unit (NICU) incubator. METHODS: To identify the absorbed organ dose depending on the radiation field size during portable X-ray examination of neonatal patient, a Monte Carlo N-Particle (MCNP) simulation, a SpeckCalc program, and a neonatal phantom from the ICRP 89 are applied for the calculation. According to the minimal field size (MinFS) standards of the European Commission (EC), the smaller field size is intended to measure tightly from the top of the lung apices to the bottom of the genitals; a larger field size is also calculated by adding 6 cm in width and length. RESULTS: Compared to the hospital C condition from the previous study, the larger and smaller field sizes are decreased by an average of 45% and 67%, respectively. Study results also show a 42% reduction in smaller field size compared to the larger field size. CONCLUSION: When taking chest and abdomen radiographic images of neonatal patients in incubators, appropriate field sizes are required to prevent inappropriate dose absorption for non-thoracic organs.

Economics of field size and shape for autonomous crop machines.

Field size and shape constrain spatial and temporal management of agriculture with implications for farm profitability, field biodiversity and environmental performance. Large, conventional equipment struggles to farm small, irregularly shaped fields efficiently. The study hypothesized that autonomous crop machines would make it possible to farm small, non-rectangular fields profitably, thereby preserving field biodiversity and other environmental benefits. Using the experience of the Hands Free Hectare (HFH) demonstration project, this study developed algorithms to estimate field times (h/ha) and field efficiency (%) subject to field size and shape in grain-oil-seed farms of the United Kingdom using four different equipment sets. Results show that field size and shape had a substantial impact on technical and economic performance of all equipment sets, but autonomous machines were able to farm small 1 ha rectangular and non-rectangular fields profitably. Small fields with equipment of all sizes and types required more time, but for HFH equipment sets field size and shape had least impact. Solutions of HFH linear programming model show that autonomous machines decreased wheat production cost by €15/ton to €29/ton and €24/ton to €46/ton for small rectangular and non-rectangular fields respectively, but larger 112 kW and 221 kW equipment with human operators was not profitable for small fields. Sensitivity testing shows that the farms using autonomous machines adapted easily and profitably to scenarios with increasing wage rates and reduced labour availability, whilst farms with conventional equipment struggled. Technical and economic feasibility in small fields imply that autonomous machines could facilitate biodiversity and improve environmental performance. Supplementary Information: The online version contains supplementary material available at 10.1007/s11119-023-10016-w.

Determination of inflection points of CyberKnife dose profiles within acceptability criteria of deviations in measurements.

AIM: The aim of this study was to determine the Inflection Points (IPs) of flattening filter free (FFF) CyberKnife dose profiles for cone-based streotactic radiotherapy. In addition, dosimetric field sizes were determined. BACKGROUND: The increased need for treatment in the early stages of cancer necessitated the treatment of smaller tumors. However, efforts in that direction required the modeling accuracy of the beam. Removal of the flattening filter (FF) from the path of x-ray beam has provided the solution to those efforts, but required a different normalization approach for the beam to ensure the delivery of the dose accurately. As a solution, researchers proposed a normalization factor based on IPs. MATERIALS AND METHODS: Measurements using microDiamond (PTW 60019), Diode SRS (PTW 60018) and Monte Carlo (MC) calculations of dose profiles were completed at SAD 80 cm and 5 cm depth for 15-60 mm cones. Performance analysis of detectors with respect to MC calculation was carried out. Gamma evaluation method was used to determine achievable acceptability criteria for FFF CyberKnife beams. RESULTS: Acceptability within (3%-0.5 mm) was found to be anachievable criterion for all dose profile measurements of the cone beams used in this study. To determine the IP, the first and second derivatives of the dose profile were determined via the cubic spline interpolation technique. CONCLUSION: Derivatives of the interpolated profiles showed that locations of IPs and 50% isodose points coincide.

Estimating the global distribution of field size using crowdsourcing.

There is an increasing evidence that smallholder farms contribute substantially to food production globally, yet spatially explicit data on agricultural field sizes are currently lacking. Automated field size delineation using remote sensing or the estimation of average farm size at subnational level using census data are two approaches that have been used. However, both have limitations, for example, automatic field size delineation using remote sensing has not yet been implemented at a global scale while the spatial resolution is very coarse when using census data. This paper demonstrates a unique approach to quantifying and mapping agricultural field size globally using crowdsourcing. A campaign was run in June 2017, where participants were asked to visually interpret very high resolution satellite imagery from Google Maps and Bing using the Geo-Wiki application. During the campaign, participants collected field size data for 130 K unique locations around the globe. Using this sample, we have produced the most accurate global field size map to date and estimated the percentage of different field sizes, ranging from very small to very large, in agricultural areas at global, continental, and national levels. The results show that smallholder farms occupy up to 40% of agricultural areas globally, which means that, potentially, there are many more smallholder farms in comparison with the two different current global estimates of 12% and 24%. The global field size map and the crowdsourced data set are openly available and can be used for integrated assessment modeling, comparative studies of agricultural dynamics across different contexts, for training and validation of remote sensing field size delineation, and potential contributions to the Sustainable Development Goal of Ending hunger, achieve food security and improved nutrition and promote sustainable agriculture.

A second-order orientation-contrast stimulus for population-receptive-field-based retinotopic mapping.

Visual field or retinotopic mapping is one of the most frequently used paradigms in fMRI. It uses activity evoked by position-varying high luminance contrast visual patterns presented throughout the visual field for determining the spatial organization of cortical visual areas. While the advantage of using high luminance contrast is that it tends to drive a wide range of neural populations - thus resulting in high signal-to-noise BOLD responses - this may also be a limitation, especially for approaches that attempt to squeeze more information out of the BOLD response, such as population receptive field (pRF) mapping. In that case, more selective stimulation of a subset of neurons - despite reduced signals - could result in better characterization of pRF properties. Here, we used a second-order stimulus based on local differences in orientation texture - to which we refer as orientation contrast - to perform retinotopic mapping. Participants in our experiment viewed arrays of Gabor patches composed of a foreground (a bar) and a background. These could only be distinguished on the basis of a difference in patch orientation. In our analyses, we compare the pRF properties obtained using this new orientation contrast-based retinotopy (OCR) to those obtained using classic luminance contrast-based retinotopy (LCR). Specifically, in higher order cortical visual areas such as LO, our novel approach resulted in non-trivial reductions in estimated population receptive field size of around 30%. A set of control experiments confirms that the most plausible cause for this reduction is that OCR mainly drives neurons sensitive to orientation contrast. We discuss how OCR - by limiting receptive field scatter and reducing BOLD displacement - may result in more accurate pRF localization as well. Estimation of neuronal properties is crucial for interpreting cortical function. Therefore, we conclude that using our approach, it is possible to selectively target particular neuronal populations, opening the way to use pRF modeling to dissect the response properties of more clearly-defined neuronal populations in different visual areas.

Landscape configurational heterogeneity by small-scale agriculture, not crop diversity, maintains pollinators and plant reproduction in western Europe.

Agricultural intensification is one of the main causes for the current biodiversity crisis. While reversing habitat loss on agricultural land is challenging, increasing the farmland configurational heterogeneity (higher field border density) and farmland compositional heterogeneity (higher crop diversity) has been proposed to counteract some habitat loss. Here, we tested whether increased farmland configurational and compositional heterogeneity promote wild pollinators and plant reproduction in 229 landscapes located in four major western European agricultural regions. High-field border density consistently increased wild bee abundance and seed set of radish (Raphanus sativus), probably through enhanced connectivity. In particular, we demonstrate the importance of crop-crop borders for pollinator movement as an additional experiment showed higher transfer of a pollen analogue along crop-crop borders than across fields or along semi-natural crop borders. By contrast, high crop diversity reduced bee abundance, probably due to an increase of crop types with particularly intensive management. This highlights the importance of crop identity when higher crop diversity is promoted. Our results show that small-scale agricultural systems can boost pollinators and plant reproduction. Agri-environmental policies should therefore aim to halt and reverse the current trend of increasing field sizes and to reduce the amount of crop types with particularly intensive management.

Accuracy evaluation of distance inverse square law in determining virtual electron source location in Siemens Primus linac.

AIM: The aim of this study is to evaluate the accuracy of the inverse square law (ISL) method for determining location of virtual electron source (SVir) in Siemens Primus linac. BACKGROUND: So far, different experimental methods have presented for determining virtual and effective electron source location such as Full Width at Half Maximum (FWHM), Multiple Coulomb Scattering (MCS), and Multi Pinhole Camera (MPC) and Inverse Square Law (ISL) methods. Among these methods, Inverse Square Law is the most common used method. MATERIALS AND METHODS: Firstly, Siemens Primus linac was simulated using MCNPX Monte Carlo code. Then, by using dose profiles obtained from the Monte Carlo simulations, the location of SVir was calculated for 5, 7, 8, 10, 12 and 14 MeV electron energies and 10 cm × 10 cm, 15 cm × 15 cm, 20 cm × 20 cm and 25 cm × 25 cm field sizes. Additionally, the location of SVir was obtained by the ISL method for the mentioned electron energies and field sizes. Finally, the values obtained by the ISL method were compared to the values resulted from Monte Carlo simulation. RESULTS: The findings indicate that the calculated SVir values depend on beam energy and field size. For a specific energy, with increase of field size, the distance of SVir increases for most cases. Furthermore, for a special applicator, with increase of electron energy, the distance of SVir increases for most cases. The variation of SVir values versus change of field size in a certain energy is more than the variation of SVir values versus change of electron energy in a certain field size. CONCLUSION: According to the results, it is concluded that the ISL method can be considered as a good method for calculation of SVir location in higher electron energies (14 MeV).

Reducing radiation-related morbidity in the treatment of nasopharyngeal carcinoma.

While radiation therapy is the mainstay of treatment for nasopharyngeal carcinoma, the anatomic location of the nasopharynx in close proximity to radiation-sensitive organs such as the salivary glands, optic nerves and chiasm, cochlea, brainstem and temporal lobes presents a special challenge. Technological approaches to reducing the morbidity of nasopharyngeal cancer irradiation have been historically successful with the evolution from 2D techniques to increasingly conformal forms of radiation therapy. This report reviews normal tissue dose constraints and major considerations in target delineation for patients with nasopharyngeal cancer in the intensity-modulated radiation therapy era. Furthermore, this report discusses more contemporary approaches to toxicity reduction such as the judicious reduction or omission of radiation to low-risk regions and the potential role of particle beam therapy.

Mapping global cropland and field size.

A new 1 km global IIASA-IFPRI cropland percentage map for the baseline year 2005 has been developed which integrates a number of individual cropland maps at global to regional to national scales. The individual map products include existing global land cover maps such as GlobCover 2005 and MODIS v.5, regional maps such as AFRICOVER and national maps from mapping agencies and other organizations. The different products are ranked at the national level using crowdsourced data from Geo-Wiki to create a map that reflects the likelihood of cropland. Calibration with national and subnational crop statistics was then undertaken to distribute the cropland within each country and subnational unit. The new IIASA-IFPRI cropland product has been validated using very high-resolution satellite imagery via Geo-Wiki and has an overall accuracy of 82.4%. It has also been compared with the EarthStat cropland product and shows a lower root mean square error on an independent data set collected from Geo-Wiki. The first ever global field size map was produced at the same resolution as the IIASA-IFPRI cropland map based on interpolation of field size data collected via a Geo-Wiki crowdsourcing campaign. A validation exercise of the global field size map revealed satisfactory agreement with control data, particularly given the relatively modest size of the field size data set used to create the map. Both are critical inputs to global agricultural monitoring in the frame of GEOGLAM and will serve the global land modelling and integrated assessment community, in particular for improving land use models that require baseline cropland information. These products are freely available for downloading from the http://cropland.geo-wiki.org website.

Secondary cancer risk assessments following the proton therapy of lung cancer as the functions of field characteristics and patient age.

INTRODUCTION: Radiation-induced secondary cancers relevant to proton therapy are still a main concern among cancer survivors. This study aims to determine the effects of age at exposure and treatment field size on radiation-induced secondary tumors following the proton therapy of lung cancer within out of field organs through the Monte Carlo (MC) simulation approach. MATERIAL AND METHODS: A full MC model of ICRP-110 male phantom was simulated to calculate the absorbed dose corresponding to secondary radiations within distant organs from the tumor volume. Then, the risks of secondary malignancies were estimated by employing the recommended risk model by the Committee of Biological Effects of Ionizing Radiation (BEIR) for different treatment field sizes and various patient ages at exposure. RESULTS: The results revealed that by increasing the patient age from 25 to 45 years, lifetime attributable risk (LAR) values were decreased. Maximum and minimum mortality rates were obtained for the liver and thyroid at the fixed age of 25 years, respectively. Calculated risk values for most near organs to the tumor were higher than those for distant organs. Changing the aperture size from 5 × 5 cm2 to 8 × 10 cm2 resulted in LAR increments with maximum variations of 12.5% for the stomach and a rough variation of 1.12 times in LAR for all exposure ages. CONCLUSION: Our work on whole-body phantom addresses the impact of age at exposure and aperture size on LAR during the proton therapy of lung cancer. To minimize secondary cancer risks relevant to proton therapy of lung cancer, extra attention should be considered.

Development of metasurface based hyperthermia lens applicator for heating of cancerous tissues.

Numerous designs and methods have been examined to improve penetration depth (PD), but there is a need for research to explore the potential increase in PD through uniform heating, a compact applicator, and low input power. This paper presents metasurface based hyperthermia lens applicator with water bolus for uniform heating of cancerous tissues. The proposed applicator consists of a stacked spiral antenna and a spiral-shaped frequency selective surface as a superstrate. The spiral antenna and superstrate are optimized on a low cost FR4 substrate having a size of 32 × 32 × 3.27mm3 and 10 × 10 × 1.6mm3 (size of the unit cell), respectively. The proposed applicator is simulated with heterogeneous phantom (skin, fat, and muscle layers) and with the Gustav voxel model with and without a water bolus layer. The number of unit cells in the superstrate is optimized to direct the maximum energy toward the tumor location. The performance study of the applicator is carried out in terms of specific absorption rate, PD, and effective field size. Further, thermal analysis is carried out with 1.9 W of input power at the antenna port, and the highest 44.7 °C temperature rise is obtained. The cancerous tissue's (tumor) surrounding temperature is between 41 and 45 °C, which is adequate for efficient hyperthermia treatment. Finally, the proposed metasurface hyperthermia lens applicator is fabricated and experimentally validated in a mimicked phantom's presence. Supplementary Information: The online version contains supplementary material available at 10.1007/s13534-023-00300-z.

Dosimetric effects of small field size, dose grid size, and variable split-arc methods on gamma pass rates in radiation therapy.

This study investigates the influence of calculation accuracy in peripheral low-dose regions on the gamma pass rate (GPR), utilizing the Acuros XB (AXB) algorithm and ArcCHECK™ measurement. The effects of varying small field sizes, dose grid sizes, and split-arc techniques on GPR were analyzed. Various small field sizes were employed. Thirty-two single-arc plans with dose grid sizes of 2 mm and 1 mm and prescribed doses of 2, 5, 10, and 20 Gy were calculated using the AXB algorithm. In total, 128 GPR plans were examined. These plans were categorized into three sub-fields (3SF), four sub-fields (4SF), and six sub-fields (6SF). The GPR results deteriorated with smaller target sizes and a 2 mm dose grid size in a single arc. A similar degradation in GPR was observed with smaller target sizes and a 1 mm dose grid size. However, the 1 mm dose grid size generally resulted in better GPR compared with the 2 mm dose grid size for the same target sizes. The GPR improved with finer split angles and a 2 mm dose grid size in the split-arc method. However, no statistically significant improvement was observed with finer split angles and a 1 mm dose grid size. This study demonstrates that coarser dose grid sizes result in lower GPRs in peripheral low-dose regions as calculated by AXB with ArcCHECK™ measurement. To enhance GPR, employing split-arc methods and finer dose grid sizes could be beneficial.

Dosimetric Evaluation of Semiflex Three-dimensional Chamber under Unflatten Beam in Comparison among Different Detectors.

Purpose: The goal of this study is to investigate the dosimetric properties of a Semiflex three-dimensional (3D) chamber in an unflatten beam and compare its data from a small to a large field flattening filter-free (FFF) beam with different radiation detectors. Methods: The sensitivity, linearity, reproducibility, dose rate dependency, and energy dependence of a Semiflex 3D detector in flattening filter and filter-free beam were fully investigated. The minimum radiation observed field widths for all detectors were calculated using lateral electronic charged particle equilibrium to investigate dosimetric characteristics such as percentage depth doses (PDDs), profiles, and output factors (OPFs) for Semiflex 3D detector under 6FFF Beam. The Semiflex 3D measured data were compared to that of other detectors employed in this study. Results: The ion chamber has a dosage linearity deviation of +1.2% for <10 MU, a dose-rate dependency deviation of +0.5%, and significantly poorer sensitivity due to its small volume. There is a difference in field sizes between manufacturer specs and derived field sizes. The measured PDD, profiles, and OPFs of the Semiflex 3D chamber were within 1% of each other for all square field sizes set under linac for the 6FFF beam. Conclusion: It was discovered to be an appropriate detector for relative dose measurements for 6 FFF beams with higher dose rates for field sizes more than or equal to 3 cm × 3 cm.

The role of the visual field size in artificial vision.

Objective. Artificial vision has been and still is the subject of intense research. The ultimate goal is to help blind people in their daily life. Approaches to artificial vision, including visual prostheses and optogenetics, have strongly focused on restoring high visual acuity for object recognition and reading. Consequently, clinical trials were primarily focused on these parameters.Approach. Alternatively, enlarging the visual field (VF) size could significantly improve artificial vision.Main results. I propose that approaches towards artificial vision address the challenge of creating this rudimental form of sight within a large VF.Significance. Enlarging the VF size will enable users to improve their mobility and perform visually-driven search tasks. Eventually, it could make artificial vision more efficient, comfortable and acceptable from the user's point of view.

On the field size definition and field output factors in small field dosimetry.

BACKGROUND: There is a major conceptual difference between small-field and large field dosimetry that is, different definition of the field size. The dosimetry protocol IAEA TRS-483 recommends the use of the field size defined by measured dose profiles (full-width half maximum, FWHM) that is significantly different from conventional field size definition by the geometric field opening of MLC/Jaw at the isocenter. The application of the effective field size concept, Sclin , was introduced by Cranmer-Sargison et al. (DOI:10.1016/j.radonc.2013.10.002) as a reporting mechanism for field output factors of rectangular fields. The study by Das et al. (DOI:10.1002/mp.15624) indicated the limitations of obtaining the field size by experimentally measuring FWHM, for example, the measured FWHM is smaller than beam geometric size, which is contradictory to what is expected as a result of partial occlusion of the primary photon source by the collimating devices. Cranmer-Sargison et al. and Das et al suggested that additional investigations are needed to evaluate its limitations. PURPOSE: This study investigates the validity of the field size definition by FWHM and by MLC/Jaw opening and finds the pros and cons between these two methods to resolve the controversial issue. METHODS: The FWHM can be obtained by measuring or calculating dose profiles. Using Monte Carlo simulations this study compares the field size obtained by FWHM and by field geometric field opening. The EGSnrc system is used to simulate 6 MV beam to generate square and rectangular fields from 5-30 mm with every possible permutation (keeping one jaw fixed and varying other jaw from 5 to 30 mm). The calculated FWHM and output factors are compared with measurements obtained by a microSilicon detector. RESULTS: The results show that field width (FWHM) derived from MC calculations generally agrees with machine geometric field width within 0.5 mm for square or rectangular fields with a minimum field width of ≥8 mm. For the extremely small fields with a minimum field width of 5 mm the discrepancies are up to 1.6 mm. The field width (FWHM) obtained by measuring dose profiles are unreliable for small fields due to the measurement uncertainties for an extremely small field. The effect of partial occlusion of the primary photon source by the jaws on the beam axis is clearly observed in the calculated dose profiles. For the extremely small field width of 5 mm, Monte Carlo predicted up to 10% exchange factor differences which are confirmed by the measurements. CONCLUSION: The field size defined by the geometric opening of the beam-defining system, is still valid for small fields. The field size defined by geometric opening is independent of measurement uncertainties, independent of machine design, and highly reproducible. It is feasible to accurately tabulate the output factors as a function of geometric field opening thus eliminating user and detector choice for FWHM measurements. The field output factor of a small rectangular field cannot be related to an equivalent field size without considering the exchange factor due to partial occlusion of the photon source.

Pelvic radiation dose measurement for trauma patients in multifield radiographic examinations: A phantom-based TLD dosimetry study.

Background and Aims: Trauma patients often suffer from multiple injuries and require undergoing various radiography which is referred to as multifield radiographic examinations. Protective measures may be ignored for these examinations due to stressful emergency situations or patients' conditions. This study was conducted to evaluate the scattered doses received by the pelvis during different common multifield radiographic examinations with an emphasis on field size adjustment. Methods: A whole-body phantom, PBU-50, resembling the body mass, was used to carry out the common examinations for trauma patients (extremities, skull, chest, abdomen, pelvis, femur, and lumbar radiography), using a Pars Pad X-ray machine. To measure the primary entrance skin doses, three calibrated GR 200 thermoluminescence dosimeter (TLD) chips were placed in the central X-ray beam of scanned organs. Three TLDs were also placed on the pelvis symphysis pubis to measure the scattered dose received by the pelvis due to each carried-out radiography for standard and clinically used field sizes. A Harshaw 3500 TLD Reader was used to read the chips. TLD readouts (nano-Coulomb) were converted to dose (milli Gray [mGy]) using the predefined calibration curve. Results: The scattered doses to the pelvis due to scanning a single organ differed from 0.80 to 1.70, and 0.82 to 4.09 mGy for standard and clinically used field sizes, respectively. The scattered doses to the pelvis in multifield examinations varied from 0.80 to 8.43 and 0.82 to 13.6 mGy for standard and clinically used field sizes, respectively, depending on the number of scanned organs and their distances from the pelvis. Conclusions: Multiple and repeated radiographs combined with insufficient protective measures can increase the patient's dose. The findings indicate that the scattered doses received by the pelvis can exceed the reference values in multifield radiography, especially if the radiation field is not restricted properly to the scanned organ.

Estimation of Total Platelet Count From Peripheral Blood Smear Needs a Correction Factor.

Background Despite many advances in platelet counting by cell counters, the problem of falsely low or falsely high total platelet counts (TPC) is common. Many laboratories estimate platelet count on the peripheral smear to cross-check the platelet counts. However, due to the lack of a standard calculation method, discrepant results are obtained from different laboratories leading to confusion among clinicians. We aimed to formulate a standard estimation method for platelet count on peripheral smear. Methodology In the first step (in 100 blood samples), we determined the ratio of the TPC obtained by the automated cell counter and the total number of platelets per oil immersion field (filed size: 0.22 mm) of the corresponding blood smears. The mean of the ratios thus obtained was designated as the "multiplication factor" to be used for visual platelet count estimation on the peripheral blood smear. In the subsequent step, validation of the same was done on another 100 samples. TPC on the peripheral smears of these samples was estimated using the above "multiplication factor" and compared with the corresponding TPC obtained on the automated cell counter. Results The "multiplication factor" obtained was 9.4 x 103 in the first set of 100 blood samples. It was used to estimate the platelet value of the second set of 100 blood samples. Conclusions We found an excellent agreement between the platelet counts obtained by automated cell counters and the estimation method. We suggest the multiplication factor 9.4 x 103 may be used with correction for microscopic field size to estimate platelet count on peripheral smears. This method is, however, not so reliable for very low platelet counts.

Technical Note: Field size analysis of patient-specific quality assurance in scanned carbon ion radiotherapy.

PURPOSE: To evaluate the dose difference between measurement and double Gaussian beam model prediction according to the field size and correct the measurements in patient-specific quality assurance (QA). METHODS: The field size dependence of the dose was evaluated with volumes of 20 × 20 × 80 mm3 , 40 × 40 × 80 mm3 , 60 × 60 × 80 mm3 , and 80 × 80 × 80 mm3 of 1 Gy uniform dose at three depths. Additional two 80 × 80 × 80 mm3 volumes of nonuniform fields were created: one high-dose field was given 1 Gy at the central 40 × 40 mm2 and 0.5 Gy in its surrounding, and the other low-dose field was given 0.5 Gy in the middle and 1 Gy at the periphery. The dose in the center of the spread-out Bragg peak (SOBP) was measured in a water phantom and compared with the treatment planning system (TPS) predication. A field factor based on the two-dimensional (2D) dose distribution was proposed to estimate the field size. The field factor was first evaluated against the dose difference in the square fields, and then used to analyze and correct the patient-specific QA results. RESULTS: TPS overestimated dose for fields smaller than 80 × 80 mm2 . A practically positive correlation was observed between the measured dose and the field factor. In the patient-specific QA, measured doses were lower than the TPS predication as they were calculated a relatively small field factor. The corrected dose differences were no longer field factor dependent. CONCLUSIONS: Using the proposed field factor, we have shown that all the measurements with a large dose deviation were due to the small-sized field. It is clinically relevant to take into consideration the field size in the QA analysis as long as the double Gaussian beam model being used for the dose calculation. Correction to the measurement can be made based on the field factor.