bluuebunny/crossref_metadata_2025_split huggingface dataset:
Loss of radiobiological effect of imaging dose in image guided radiotherapy due to prolonged imaging‐to‐treatment times
Authors: Flynn Ryan T. 
Published: June 2010

Purpose: Increased use of cone beam CT guidance in image guided radiotherapy has prompted the inclusion of the imaging dose in treatment plans, thus using imaging beams to treat tumors. Sublethal radiation damage repair during , the time between imaging and treatment, could reduce the effectiveness of the imaging dose, resulting in tumor underdosage. The theoretical magnitude of this effect was quantified using radiobiological modeling.Methods: The therapeutic effective dose (TED), which, if delivered using only therapeutic beams, would result in the same tumor cell survival as for both the imaging and therapeutic beams, was derived using the generalized linear‐quadratic model. The correction factor by which therapeutic dose can be scaled to compensate for sublethal damage repair was also derived. TED and are dependent on , sublethal damage repair half‐time , imaging dose and dose rate , therapeutic dose and dose rate , and . TED and were calculated as a function of , and each parameter was varied independently while holding the remaining parameters at their reference values. The reference values were based on prostate cancer cells and were , , , , , , and . Estimates of the expected values of TED and , and , were calculated using and distributions from a few thousand prostate treatment fractions.Results: For a typical value of 5.0 min and all other parameters set to their reference values, TED was 0.5% lower than the prescription dose . For and all other parameters at reference conditions, TED dropped by 5% relative to when was 20% and by 2% relative to when or . varied more with than when , varying by up to 1% over and by less than 0.1% over . Under the reference conditions, was lower than by 0.5%. For the extreme and all other parameters at their reference values, setting resulted in dropping below by 2.5% and setting resulted in dropping below by 4%. For tumors with a of 16 min or greater and of 11 Gy, dropped below by 0.2% or less.Conclusions: For prostate tumors receiving a reasonable percentage of 5% of their total dose from imaging beams, the theoretical drop in relative to was 0.5%. This loss could be accounted for during treatment planning by scaling the therapeutic dose by the expected sublethal damage repair factor . For nonprostate tumors with values of 11 Gy, the theoretical drop in relative to the reference TED was low at 0.2%.
Ion recombination for ionization chamber dosimetry in a helical tomotherapy unit
Authors: Palmans H. , Thomas R. A. S. , Duane S. , Sterpin E. , Vynckier S. 
Published: June 2010

PurposeIon recombination for ionization chambers in pulsed high‐energy photon beams is a well‐studied phenomenon. Despite this, the correction for ion recombination is often determined inaccurately due to the inappropriate combination of using a high polarizing voltage and the simple two‐voltage method. An additional complication arises in new treatment modalities such as IMRT and tomotherapy, where the dosimetry of a superposition of many constituting fields becomes more relevant than of single static fields. For these treatment modalities, the irradiation of the ion chamber geometry can be instantaneously inhomogeneous and time dependent.MethodsThis article presents a study of ion recombination in ionization chambers used for dosimetry in a helical tomotherapy beam. Models are presented for studying the recombination correction factors in a continuous beam, in pulsed large and small fields, and in helical fields. Measurements using Exradin A1SL, NE2571, and NE2611 type chambers and Monte Carlo simulations usingPENELOPE are performed in support of these models.ResultsInitial recombination and charge multiplication are found to be the same in and in the pulsed high‐energy photon beam for the chambers and operating voltages used in this study. Applying the two‐voltage technique for the A1SL chamber at its recommended operating voltage of 300 V leads to an overestimation of the recombination. Operating at a voltage of 100 V yields larger but more accurate values for the recombination correction. The recombination correction measured for this chamber in the TomoTherapy HiArt unit is lower than the 1% applied in the routine dosimetry for this treatment unit. For a helical dose delivery with a small slice width, lateral electron scatter in the cavity makes that the recombination is smaller than for an open beam delivering the same total dose. In a Farmer type chamber, a helical delivery with a 1 cm slice field results in a time and spatially integrated volume recombination of 55% of that with a 2.5 cm slice field. The relative recombination corrections for different slice widths and different field offsets with respect to the chamber center obtained from the developed models are in good agreement with experimental data.ConclusionsBecause of the presence of charge multiplication, it is more accurate to determine the recombination correction at lower operating voltages than are often applied using the two‐voltage method. Models and experiments for partial irradiation conditions of the ion chamber show that resulting recombination corrections are reduced compared to those for an open field. A model for helical dose deliveries results in recombination corrections that get lower with smaller slice widths. This model could be adapted to any IMRT delivery where the ion chamber is instantaneously partial and/or inhomogeneously irradiated, and could provide a practical procedure to calculate the recombination for complex deliveries for which it is difficult to be measured.
Quantitative imaging in breast tomosynthesis and CT: Comparison of detection and estimation task performance
Authors: Richard Samuel , Samei Ehsan 
Published: June 2010

PurposeThis work investigates a framework for modeling volumetric breast imaging to compare detection and estimation task performance and optimize quantitative breast imaging.MethodsVolumetric reconstructions of a breast phantom, which incorporated electronic, quantum, and anatomical noise with embedded spherical lesions, were simulated over a range of acquisition angles varying from 4° to 204° with a constant total acquisition dose of 1.5 mGy. A maximum likelihood estimator was derived in terms of the noise power spectrum, which yielded figures of merit for quantitative imaging performance in terms of accuracy and precision. These metrics were computed for estimation of lesion area, volume, and location. Estimation task performance was optimized as a function of acquisition angle and compared to the performance of a more conventional lesion detection task.ResultsResults revealed tradeoffs between electronic, quantum, and anatomical noise. The detection of a 4 mm sphere was optimal at an acquisition angle of 84°, where reconstructed images using a smaller acquisition angle exhibited increased anatomical noise and reconstructed images using a larger acquisition angle exhibited increased quantum and electronic noise. For all estimation tasks, accuracy was found to be fairly constant as a function acquisition angle indicating adequate system calibration, whereas a more significant dependence on acquisition angle was observed for precision performance. Precision for the 2D area estimation task was optimal at , while precision of the 3D volume estimation task was optimal at larger angles . Precision for the localization task showed orientation dependence where localization was significantly inferior in the depth direction. Overall, precision for localization was optimal at larger angles (i.e., ) compared to the size estimation tasks. Results suggested that for quantitative imaging tasks, the acquisition angle should be larger than currently used in conventional breast tomosynthesis for lesion detection.ConclusionsAnalysis of quantitative imaging performance using Fourier‐based metrics highlights the difference between estimation and detection task in volumetric breast imaging and provides a meaningful framework for optimizing the performance of breast imaging systems for quantitative imaging applications.
A time‐domain wavelet‐based approach for fluorescence diffuse optical tomography
Authors: Ducros Nicolas , Da Silva Anabela , Dinten Jean‐Marc , Seelamantula Chandra Sekhar , Unser Michael , Peyrin Françoise 
Published: June 2010

PurposeIn the context of fluorescence diffuse optical tomography, determining the optimal way to exploit the time‐resolved information has been receiving much attention and differentfeatures of the time‐resolved signals have been introduced. In this article, the authors revisit and generalize the notion of feature, considering the projection of the measurements onto some basis functions. This leads the authors to propose a novel approach based on the wavelet transform of the measurements.MethodsA comparative study between the reconstructions obtained from the proposed wavelet‐based approach and the reconstructions obtained from the reference temporal moments is provided. An inhomogeneous cubic medium is considered. Reconstructions are performed from synthetic measurements assuming Poisson noise statistics. In order to provide fairly comparable reconstructions, the reconstruction scheme is associated with a particular procedure for selecting the regularization parameter.ResultsIn the noise‐free case, the reconstruction quality is shown to be mainly driven by the number of selected features. In the presence of noise, however, the reconstruction quality depends on the type of the features. In this case, the wavelet approach is shown to outperform the moment approach. While the optimal time‐resolved reconstruction quality, which is obtained considering the whole set of time samples, is recovered using only eight wavelet functions, it cannot be attained using moments. It is finally observed that the time‐resolved information is of limited utility, in terms of reconstruction, when the maximum number of detected photons is lower than .ConclusionsThe wavelet approach allows for better exploiting the time‐resolved information, especially when the number of detected photons is low. However, when the number of detected photons decreases below a certain threshold, the time‐resolved information itself is shown to be of limited utility.
Patient‐specific motion artifacts in 4DCT
Authors: Watkins W. Tyler , Li Ruijiang , Lewis John , Park Justin C. , Sandhu Ajay , Jiang Steve B. , Song William Y. 
Published: June 2010

PurposeFour‐dimensional computed tomography (4DCT) has enhanced images of the thorax and upper abdomen during respiration, but intraphase residual motion artifacts will persist in cine‐mode scanning. In this study, the source and magnitude of projection artifacts due to intraphase target motion is investigated.MethodsA theoretical model of geometric uncertainty due to partial projection artifacts in cine‐mode 4DCT was derived based on ideal periodic motion. Predicted artifacts were compared to measured errors with a rigid lung phantom attached to a programmable motion platform. Ideal periodic motion and actual patient breathing patterns were used as input for phantom motion. Reconstructed target dimensions were measured along the direction of motion and compared to the actual, known dimensions.ResultsArtifacts due to intraphase residual motion in cine‐mode 4DCT range from a few mm up to a few cm on a given scanner, and can be predicted based on target motion and CT gantry rotation time. Errors in ITV and GTV dimensions were accurately characterized by the theoretical uncertainty at all phases when sinusoidal motion was considered, and in 96% of 300 measurements when patient breathing patterns were used as motion input. When peak‐to‐peak motion of 1.5 cm is combined with a breathing period of 4 s and gantry rotation time of 1 s, errors due to partial projection artifacts can be greater than 1 cm near midventilation and are a few mm in the inhale and exhale phases. Incorporation of such uncertainty into margin design should be considered in addition to other uncertainties.ConclusionsArtifacts due to intraphase residual motion exist in 4DCT, even for ideal breathing motions (e.g., sine waves). It was determined that these motion artifacts depend on patient‐specific tumor motion and CT gantry rotation speed. Thus, if the patient‐specific motion parameters are known (i.e., amplitude and period), a patient‐specific margin can and should be designed to compensate for this uncertainty.
Clinical application of Varian OBI CBCT system and dose reduction techniques in breast cancer patients setup
Authors: Ueltzhöffer Stefan , Zygmanski Piotr , Hesser Jürgen , Högele Wolfgang , Wong Julia , Bellon Jennifer R. , Lyatskaya Yulia 
Published: June 2010

PurposeTo characterize the standard modes of Varian on board imaging (OBI) v1.4 system and identify techniques to further optimize imaging parameters, in particular, for breast treatment setup.MethodsA male anthropomorphic torso phantom was used for image quality assessment and a simpler thorax phantom for dose measurements. Both phantoms had artificial breasts attached. Doses were measured with an ion chamber in seven locations in the thorax and the breast. Evaluation of image quality was performed in terms of contrast‐to‐noise ratio (CNR) and in combination with the dose‐to‐contrast‐to‐noise (CNRD) parameter. The effect of kVp and mAs on the image quality, dose, and CNRD parameter was analyzed. In addition, image geometry with noncentral isocenter location with start and stop imaging angles adjusted for greater sparing of the contralateral breast was evaluated in terms of image quality and dose.ResultsThe measurements showed doses between 0.02 and 1.6 cGy for the three full‐fan modes and 0.6–3.2 cGy for half‐fan modes. This is a reduction of over 80% and 30%–50% compared to OBI v.1.3 modes for full‐fan and half‐fan modes, respectively. The CNRD is the highest for both low dose modes (low dose thorax and low dose head). Optimal ranges for an averaged sized thorax are tube voltages not higher than 100 kVp and current‐time products between 100 and 400 mAs . For the contralateral breast and lung, a dose less than 0.03 cGy per scan was measured for the optimized image geometry with the noncentral isocenter location.ConclusionsThe OBI v1.4 system allows for imaging with a larger variety of imaging parameters compared to previous OBI v1.3 systems. The largest doses (up to 4 cGy) were measured in a phantom when OBI v1.4 system was used for imaging with half‐fan modes. Using full‐fan modes resulted in the doses less than 1.6 cGy. Further decrease in dose may be achieved by reducing mAs while preserving acceptable image quality. Organ specific sparing (e.g., contralateral breast) may be achieved by proper selection of the start and stop angles. For thorax imaging, the use of Low Dose Thorax mode is recommended.
Allergen and endotoxin exposure in a companion animal hospital
Authors: Samadi Sadegh , Heederik Dick J J , Krop Esmeralda J M , Jamshidifard Ali-Reza , Willemse Ton , Wouters Inge M 
Published: June 2010

BackgroundExposure to allergens, both in general and occupational environments, is known to result in sensitisation and exacerbation of allergic diseases, while endotoxin exposure might protect against allergic diseases. This may be important for veterinarians and co-workers. However, exposure levels are mostly unknown.ObjectiveWe investigated the allergen and endotoxin exposure levels of veterinary medicine students and workers in a companion animal hospital.MethodsAirborne and surface dust was collected using various sampling methods at different locations. Allergen levels in extracts were measured with sandwich ELISAs and/or the multiplex array for indoor allergens (MARIA). Endotoxin was determined by limulus amebocyte lysate (LAL) assay.ResultsFel d 1 (Felis domesticus), Can f 1 (Canus familiaris) and endotoxin were detected in all except stationary samples. The geometric mean (GM) level of personal inhalable dust samples for Fel d 1 was 0.3 ng/m3(range: below lower limit of detection (<LOD) to 9.4), for Can f 1 3.6 ng/m3(<LOD to 73.3) and for endotoxin 4.4 EU/m3(<LOD to 75). Exposure levels differed significantly between job titles, with highest allergen exposure for student assistants in the intensive care unit (Fel d 1, GM 1.5 ng/m3; Can f 1, GM 18.5 ng/m3), and highest endotoxin exposure for students (GM 10.1 EU/m3). Exposure levels in dust captured by diverse sampling methods correlated with each other (p<0.05).ConclusionAllergen exposure likely occurs during veterinary practice, with relatively low endotoxin levels. Future research should investigate dose–response relationship between airborne allergen exposure and health effects.
Geographical and historical determinants of microsatellite variation in Eucalyptus pilularis
Authors: Shepherd Mervyn , Sexton Timothy R. , Thomas Dane , Henson Michael , Henry Robert J. 
Published: June 2010

Geographically distributed genetic variation is expected in species that have wide latitudinal and habitat ranges, like Eucalyptus pilularis Sm. Coastal and inland ecotypes of this tall forest tree have been distinguished in genecological studies, but patterns of regionally distributed quantitative variation are weak. At the coarsest level, variation of 12 microsatellite markers divided a rangewide sample of 424 E. pilularis trees into two zones: the region to the south of Sydney forming one zone and regions to the north forming another. Genetic structuring did not correspond with ecotypes but rather with a biogeographic division, suggesting an imprint of historical isolation. Typical and uniform levels of genetic diversity (He= 0.78 ± 0.02 (mean ± SE)) were found across 10 geographic regions. Genetic structuring by regions (PhiRT = 3%), by localities within regions (PhiPT = 2%), between coastal and inland provenances (PhiPT = 2%), or due to isolation by distance was subtle. These observations, along with the lack of evidence for bottlenecks, suggested genetic cohesion within zones due to gene flow and historically large population sizes. The low levels of diversity and poor growth performance of the Fraser Island ecotype were better explained by recent colonization and adaptation than by genetic isolation, since there was no evidence of inbreeding.
Spatial distributions of species in an old-growth temperate forest, northeastern China
Authors: Wang Xugao , Ye Ji , Li Buhang , Zhang Jian , Lin Fei , Hao Zhanqing 
Published: June 2010

Studying spatial distributions of species can provide important insights into processes and mechanisms that maintain species richness. We used the relative neighborhood density Ω based on the average density of conspecific species in circular neighborhoods around each species to quantify spatial distributions of species with ≥10 individuals in a fully mapped 25 ha temperate plot at Changbaishan, northeastern China. Our results show that spatial aggregation is a dominant pattern of species in the Changbaishan temperate forests. However, the percentage of significantly aggregated species decreases with spatial scale, especially for rare species. Rare species are more aggregated than intermediate and common species. The aggregation intensity declines with increasing size class (diameter at breast height), i.e., species become more regularly spaced as species grow, which is consistent with the predictions of self-thinning and Janzen–Connell spacing effects. Species functional traits (canopy layer, seed dispersal ability, shade tolerant, etc) also havea significant effect on the spatial distributions of species. Our results partially conform to the prediction that better dispersal reduces aggregation. Consequently, dispersal limitation, self-thinning, Janzen–Connell spacing effects, and habitat heterogeneity may primarily contribute to spatial distributions of species in the temperate forests.
Habitat preferences of an arboreal forage lichen in a Sierra Nevada old-growth mixed-conifer forest
Authors: Rambo Thomas R. 
Published: June 2010

The arboreal forage lichen Bryoria fremontii (Tuck.) Brodo & D.Hawksw. appears sensitive to conditions of prolonged hydration in wet forests of British Columbia. I estimated the abundance of this lichen in mixed-conifer forest canopy in the contrasting Mediterranean climate of the southern Sierra Nevada in relationship to the vertical gradient of vapor pressure deficit. Abundance was estimated by biomass in 5 m strata from the ground to the tops of 50 trees. Transplants of Bryoria thalli were installed in 18 fir trees for 1 year to assess their growth relative to distance from perennial streams. VPD generally increased with height, being significantly greater at 45 m than 5 m. Bryoria biomass averaged across tree heights was estimated as 15.9, 0.60, 0.15, 0.25, and 0.19 g·m–1in red fir (Abies magnifica A.Murray), white fir (Abies concolor (Gordon & Glend.) Hildebr. var. lowiana (Gordon) Lemmon), incense cedar (Calocedrus decurrens (Torr.) Florin), Jeffrey pine (Pinus jeffreyi Balf.), and sugar pine (Pinus lambertiana Douglas), respectively. Transplant growth was significantly greater in trees <25 m from water (11.4%) than in trees >25 m from water (9.7%). Bryoria had strong positive associations with red fir, proximity to streams, and decreasing VPD. The sensitivity of Bryoria to prolonged hydration does not appear to be important in this climate characterized by extended summer dryness.
Advantages of long-term measurement of fine root demographics with a minirhizotron at two balsam fir sites
Authors: Krasowski M.J. , Lavigne M.B. , Olesinski J. , Bernier P.Y. 
Published: June 2010

We used 15 site-years of minirhizotron observations (1998–2006 at one site; 1998–2000 and 2004–2006 at second site) from two mature balsam fir ( Abies balsamea (L.) Mill.) sites to quantify interannual variability in fine root demography and assess the accuracy of estimates from early years of observation. Annual production varied fourfold at Forêt Montmorency (FM) (5.8–26.5 roots·100 cm–2) and twofold at Green River (GR) (7.2–14.2 roots·100 cm–2). Annual mortality varied more than 30-fold at the two sites (FM: 0.7–23.2 roots·100 cm–2; GR: 0.3–10.9 roots·100 cm–2), year-end standing crops varied two- to eight-fold (FM: 3.6–28.4 roots·100 cm–2; GR 8.5–18.6 roots·100 cm–2), and median life-span of annual cohorts varied from 180 to 540 days at FM and from 350 to 577 days at GR. This variation illustrates that root demography estimates from short-term studies may differ widely from long-term means. Annual mortality and standing crops were lowest in the first year of observation and tended to increase for two or more years at both sites, whereas these trends were not observed for annual production. Our results indicate that minirhizotron tubes must be in place for more than 2 years to accurately estimate fine root demography at balsam fir sites.