Sexual reproductive structures in the green alga Ivanovia triassica

Ivanovia triassica is a new species of calcified Codiaceae from Triassic rocks of the Yukon Stikine Terrane in Canada. The genus was known previously only from the late Paleozoic. Stalked outgrowths of the thalli are interpreted as oogonia and dome-shaped outpocketings as male gametangia. These represent the first sexual reproductive structures observed in Ivanovia. Sectional views of the thalli indicate the species was cyathiform and that the inner and outer cortices of the membranes comprising the thallus were dimorphic.     

IVUS Validation of Patient Coronary Artery Lumen Area Obtained from CT Images

Aims

Accurate computed tomography (CT)-based reconstruction of coronary morphometry (diameters, length, bifurcation angles) is important for construction of patient-specific models to aid diagnosis and therapy. The objective of this study is to validate the accuracy of patient coronary artery lumen area obtained from CT images based on intravascular ultrasound (IVUS).

Methods and Results

Morphometric data of 5 patient CT scans with 11 arteries from IVUS were reconstructed including the lumen cross sectional area (CSA), diameter and length. The volumetric data from CT images were analyzed at sub-pixel accuracy to obtain accurate vessel center lines and CSA. A new center line extraction approach was used where an initial estimated skeleton in discrete value was obtained using a traditional thinning algorithm. The CSA was determined directly without any circular shape assumptions to provide accurate reconstruction of stenosis. The root-mean-square error (RMSE) for CSA and diameter were 16.2% and 9.5% respectively.

Conclusions

The image segmentation and CSA extraction algorithm for reconstruction of coronary arteries proved to be accurate for determination of vessel lumen area. This approach provides fundamental morphometric data for patient-specific models to diagnose and treat coronary artery disease.     

Evaluation of cross-sectional geometry and mass density distributions of humans and laboratory animals using computerized tomography

The purpose of this study was to determine the cross-sectional geometry and mass density distribution of a young porcine subject using the X-ray computerized tomographic (CT) method and to perform a comparative study of anatomical features of this subject and a 3 yr old female child specimen. The cross-sectional CT scans of the porcine subject were obtained at 1 cm intervals. The outlines of each cross section and of selected anatomical components within each section were obtained by standard picture processing techniques. The mass and inertia tensor for each cross section and for each anatomical structure in a section were computed based on the CT numbers. The porcine subject was then sacrificed, frozen, sectioned and photographed. These sectional photographs were then compared with those obtained from the CT method. Tabulated cross-sectional mass and inertia tensor obtained from CT scans of the porcine subject were also used to compare with similar results derived from previously completed CT scans of the 3 yr old female child specimen. In particular, the comparisons were made on the location of the center of gravity and the inertia tensor in the head, neck, head and neck and cervical spine regions. Some immediate applications of this data are inputs to finite element models, lumped parameter biodynamic models, computer simulation of vehicle crash victims, and dummy design.     

Contribution of Underlying Connective Tissue Cells to Taste Buds in Mouse Tongue and Soft Palate

Taste buds, the sensory organs for taste, have been described as arising solely from the surrounding epithelium, which is in distinction from other sensory receptors that are known to originate from neural precursors, i.e., neural ectoderm that includes neural crest (NC). Our previous study suggested a potential contribution of NC derived cells to early immature fungiform taste buds in late embryonic (E18.5) and young postnatal (P1-10) mice. In the present study we demonstrated the contribution of the underlying connective tissue (CT) to mature taste buds in mouse tongue and soft palate. Three independent mouse models were used for fate mapping of NC and NC derived connective tissue cells: (1) P0-Cre/R26-tdTomato (RFP) to label NC, NC derived Schwann cells and derivatives; (2) Dermo1-Cre/RFP to label mesenchymal cells and derivatives; and (3) Vimentin-CreER/mGFP to label Vimentin-expressing CT cells and derivatives upon tamoxifen treatment. Both P0-Cre/RFP and Dermo1-Cre/RFP labeled cells were abundant in mature taste buds in lingual taste papillae and soft palate, but not in the surrounding epithelial cells. Concurrently, labeled cells were extensively distributed in the underlying CT. RFP signals were seen in the majority of taste buds and all three types (I, II, III) of differentiated taste bud cells, with the neuronal-like type III cells labeled at a greater proportion. Further, Vimentin-CreER labeled cells were found in the taste buds of 3-month-old mice whereas Vimentin immunoreactivity was only seen in the CT. Taken together, our data demonstrate a previously unrecognized origin of taste bud cells from the underlying CT, a conceptually new finding in our knowledge of taste bud cell derivation, i.e., from both the surrounding epithelium and the underlying CT that is primarily derived from NC.     

About the inevitable compromise between spatial resolution and accuracy of strain measurement for bone tissue: A 3D zero-strain study

The accurate measurement of local strain is necessary to study bone mechanics and to validate micro computed tomography (µCT) based finite element (FE) models at the tissue scale. Digital volume correlation (DVC) has been used to provide a volumetric estimation of local strain in trabecular bone sample with a reasonable accuracy. However, nothing has been reported so far for µCT based analysis of cortical bone. The goal of this study was to evaluate accuracy and precision of a deformable registration method for prediction of local zero-strains in bovine cortical and trabecular bone samples. The accuracy and precision were analyzed by comparing scans virtually displaced, repeated scans without any repositioning of the sample in the scanner and repeated scans with repositioning of the samples.     

Biological effects and adaptive response from single and repeated computed tomography scans in reticulocytes and bone marrow of C57BL/6 mice

This study investigated the biological effects and adaptive responses induced by single and repeated in vivo computed tomography (CT) scans. We postulated that, through the induction of low-level oxidative stress, repeated low-dose CT scans (20 mGy, 2 days/week, 10 weeks) could protect mice (C57BL/6) from acute effects of high-dose radiation (1 Gy, 2 Gy). The micronucleated reticulocyte (MN-RET) count increased linearly after exposure to single CT scans of doses ranging from 20 to 80 mGy (P = 0.033). Ten weeks of repeated CT scans (total dose 400 mGy) produced a slight reduction in spontaneous MN-RET levels relative to levels in sham CT-scanned mice (P = 0.04). Decreases of nearly 10% in γ-H2AX fluorescence levels were observed in the repeated CT-scanned mice after an in vitro challenge dose of 1 Gy (P = 0.017) and 2 Gy (P = 0.026). Spontaneous apoptosis levels (caspase 3 and 7 activation) were also significantly lower in the repeated CT-scanned mice than the sham CT-scanned mice (P < 0.01). In contrast, mice receiving only a single CT scan showed a 19% elevation in apoptosis (P < 0.02) and a 10% increase in γ-H2AX fluorescence levels after a 2-Gy challenge (P < 0.05) relative to sham CT controls. Overall, repeated CT scans seemed to confer resistance to larger doses in mice, whereas mice exposed to single CT scans exhibited transient genotoxicity, enhanced apoptosis, and characteristics of radiation sensitization.     

Experimental validation of a finite element model of a human cadaveric tibia

Finite element (FE) models of long bones are widely used to analyze implant designs. Experimental validation has been used to examine the accuracy of FE models of cadaveric femurs; however, although convergence tests have been carried out, no FE models of an intact and implanted human cadaveric tibia have been validated using a range of experimental loading conditions. The aim of the current study was to create FE models of a human cadaveric tibia, both intact and implanted with a unicompartmental knee replacement, and to validate the models against results obtained from a comprehensive set of experiments. Seventeen strain rosettes were attached to a human cadaveric tibia. Surface strains and displacements were measured under 17 loading conditions, which consisted of axial, torsional, and bending loads. The tibia was tested both before and after implantation of the knee replacement. FE models were created based on computed tomography (CT) scans of the cadaveric tibia. The models consisted of ten-node tetrahedral elements and used 600 material properties derived from the CT scans. The experiments were simulated on the models and the results compared to experimental results. Experimental strain measurements were highly repeatable and the measured stiffnesses compared well to published results. For the intact tibia under axial loading, the regression line through a plot of strains predicted by the FE model versus experimentally measured strains had a slope of 1.15, an intercept of 5.5 microstrain, and an R(2) value of 0.98. For the implanted tibia, the comparable regression line had a slope of 1.25, an intercept of 12.3 microstrain, and an R(2) value of 0.97. The root mean square errors were 6.0% and 8.8% for the intact and implanted models under axial loads, respectively. The model produced by the current study provides a tool for simulating mechanical test conditions on a human tibia. This has considerable value in reducing the costs of physical testing by pre-selecting the most appropriate test conditions or most favorable prosthetic designs for final mechanical testing. It can also be used to gain insight into the results of physical testing, by allowing the prediction of those variables difficult or impossible to measure directly.     

Paired inspiratory-expiratory chest CT scans to assess for small airways disease in COPD

Background

Gas trapping quantified on chest CT scans has been proposed as a surrogate for small airway disease in COPD. We sought to determine if measurements using paired inspiratory and expiratory CT scans may be better able to separate gas trapping due to emphysema from gas trapping due to small airway disease.

Methods

Smokers with and without COPD from the COPDGene Study underwent inspiratory and expiratory chest CT scans. Emphysema was quantified by the percent of lung with attenuation < −950HU on inspiratory CT. Four gas trapping measures were defined: (1) Exp₋₈₅₆, the percent of lung < −856HU on expiratory imaging; (2) E/I MLA, the ratio of expiratory to inspiratory mean lung attenuation; (3) RVC_856-950, the difference between expiratory and inspiratory lung volumes with attenuation between −856 and −950 HU; and (4) Residuals from the regression of Exp₋₈₅₆ on percent emphysema.

Results

In 8517 subjects with complete data, Exp₋₈₅₆ was highly correlated with emphysema. The measures based on paired inspiratory and expiratory CT scans were less strongly correlated with emphysema. Exp₋₈₅₆, E/I MLA and RVC_856-950 were predictive of spirometry, exercise capacity and quality of life in all subjects and in subjects without emphysema. In subjects with severe emphysema, E/I MLA and RVC_856-950 showed the highest correlations with clinical variables.

Conclusions

Quantitative measures based on paired inspiratory and expiratory chest CT scans can be used as markers of small airway disease in smokers with and without COPD, but this will require that future studies acquire both inspiratory and expiratory CT scans.     

The use of routine thoracoabdominal CT scans in the polytrauma patient to estimate obesity

Objective:

To utilize data from routine CT scans to quantify obesity in polytrauma patients without the need to obtain a height and weight.

Design and Methods:

We utilized a comprehensive database including multidetector CT thoracoabdominal images of all polytrauma patients admitted to a Level 1 trauma center. One thousand one hundred seventy‐four patients were reviewed from 2006 to 2008 and of these, 162 had previous documentation of Body Mass Index (BMI) or height and weight measurements as an outpatient within 6 months of trauma activation and with a truncal girth smaller than the scanning area of the CT machine. Truncal Adiposity Volume (TAV) was calculated from three dimensional reconstructions (3DRs) of the CT scans of the thorax and abdomen obtained in the emergency department.

Results:

Statistical analysis yielded a fairly good correlation between TAV and BMI (correlation coefficient = 0.77; p‐value < 0.0001). The intra‐observer and inter‐observer correlations in measuring TAV were high; 0.99 and 0.98 respectively. A linear regression equation of BMI on TAV was estimated and it had a form: 3DR BMI = 20.81+0.00064×TAV. In conclusion, TAV provides a reproducible means of evaluating obesity in trauma patients from routinely obtained CT scans.

Conclusions:

The TAV eliminates the often problematic task of obtaining a height and weight in a trauma patient and it correlates fairly well with the most commonly used clinical method of quantifying patient adiposity, BMI. This method may provide a more direct measurement of adiposity than does BMI, and holds promise for improving trauma care and research in the obese patient.     

Virtual structural analysis of tibial fracture healing from low-dose clinical CT scans

Quantitative assessment of bone fracture healing remains a significant challenge in orthopaedic trauma research. Accordingly, we developed a new technique for assessing bone healing using virtual mechano-structural analysis of computed tomography (CT) scans. CT scans from 19 fractured human tibiae at 12 weeks after surgery were segmented and prepared for finite element analysis (FEA). Boundary conditions were applied to the models to simulate a torsion test that is commonly used to access the structural integrity of long bones in animal models of fracture healing. The output of each model was the virtual torsional rigidity (VTR) of the healing zone, normalized to the torsional rigidity of each patient’s virtually reconstructed tibia. This provided a structural measure to track the percentage of healing each patient had undergone. Callus morphometric measurements were also collected from the CT scans. Results showed that at 12 weeks post-op, more than 75% of patients achieved a normalized VTR (torsional rigidity relative to uninjured bone) of 85% or above. The predicted intact torsional rigidities compared well with published cadaveric data. Across all patients, callus volume and density were weakly and non-significantly correlated with normalized VTR and time to clinical union. Conversely, normalized VTR was significantly correlated with time to union (R² = 0.383, p = 0.005). This suggests that fracture scoring methods based on the visual appearance of callus may not accurately predict mechanical integrity. The image-based structural analysis presented here may be a useful technique for assessment of bone healing in orthopaedic trauma research.     

An accurate estimation of bone density improves the accuracy of subject-specific finite element models

An experimental-numerical study was performed to investigate the relationships between computed tomography (CT)-density and ash density, and between ash density and apparent density for bone tissue, to evaluate their influence on the accuracy of subject-specific FE models of human bones. Sixty cylindrical bone specimens were examined. CT-densities were computed from CT images while apparent and ash densities were measured experimentally. The CT/ash-density and ash/apparent-density relationships were calculated. Finite element models of eight human femurs were generated considering these relationships to assess their effect on strain prediction accuracy. CT and ash density were linearly correlated (R(2)=0.997) over the whole density range but not equivalent (intercep t <0, slope >1). A constant ash/apparent-density ratio (0.598+/-0.004) was found for cortical bone. A lower ratio, with a larger dispersion, was found for trabecular bone (0.459+/-0.100), but it became less dispersed, and equal to that of cortical tissue, when testing smaller trabecular specimens (0.598+/-0.036). This suggests that an experimental error occurred in apparent-density measurements for large trabecular specimens and a constant ratio can be assumed valid for the whole density range. Introducing the obtained relationships in the FE modelling procedure improved strain prediction accuracy (R(2)=0.95, RMSE=7%). The results suggest that: (i) a correction of the densitometric calibration should be used when evaluating bone ash-density from clinical CT scans, to avoid ash-density underestimation and overestimation for low- and high-density bone tissue, respectively; (ii) the ash/apparent-density ratio can be assumed constant in human femurs and (iii) the correction improves significantly the model accuracy and should be considered in subject-specific bone modelling.     

Clinical indications for the use of computed tomography in children who underwent frequent computed tomography: a near-13-year follow-up retrospective study at a single institution in Japan

Recent studies suggest a causal link of childhood leukemia and brain tumor with repeated computed tomography (CT) scans. The reasons why frequent CT scans are taken in a specific child remain unclear. The present study aimed to clarify the medical reasons why frequent CT examinations in children, and the characteristics of the diseases of those children that required multiple CT scans. A long-term follow-up retrospective study was conducted over a 12.75-year period at a single institution. Radiological reports were investigated that contained the indications for the CT scans. The clinical indications were classified for the examination of children under 16 years of age who underwent more than three CT scans into trauma, tumor, inflammation, and others. This study showed that 8.5% of CT examinations were done three times or more. The numbers of patients by indication were 23.3% for trauma, 5.3% for hydrocephalus, and 2.3% for appendicitis. The frequencies of trauma and inflammation decreased rapidly with an increasing number of CT scans. In particular, hydrocephalus brought high frequency more than ten scans. Regarding the frequencies of clinical indications by age groups, there was a significant difference (p<0.05). The near-13-year follow-up study indicated the main clinical indications for frequent CT scans in children were trauma and hydrocephalus. Multiple follow-up CT scans in children with hydrocephalus would be traded off against the resultant increase in brain tumor risk associated with CT exposure.

     

18F-Fluorodeoxyglucose Positron Emission Tomography in Elderly Patients with an Elevated Erythrocyte Sedimentation Rate of Unknown Origin

Patients with an elevated erythrocyte sedimentation rate (ESR) and non-specific symptoms often pose a diagnostic dilemma. PET/CT visualises infection, inflammation and malignancy, all of which may cause elevated ESR. The objective of this study was to determine the contribution of 18F-fluorodeoxglucose positron emission tomography (PET/CT) in the diagnostic work-up of referred patients with an elevated ESR, in whom initial routine evaluation did not reveal a diagnosis. We conducted a combined retrospective (A) and prospective (B) study in elderly (>50 years) patients with a significantly elevated ESR of≥50 mm/h and non-specific complaints. In study A, 30 patients were included. Malignancy (8 patients), auto-inflammatory disease (8 patients, including 5 with large-vessel vasculitis) and infection (3 patients) were suggested by PET/CT. Two scans showed non-specific abnormalities and 9 scans were normal. Of the 21 abnormal PET/CT results, 12 diagnoses were independently confirmed and two alternative diagnosis were made. Two diagnoses were established in patients with a normal scan. In study B, 58 patients in whom a prior protocolised work-up was non-diagnostic, were included. Of these, 25 PET/CT-scans showed suspected auto-inflammatory disease, particularly large-vessel vasculitis (14 cases). Infection and malignancy was suspected in 5 and 3 cases, respectively. Seven scans demonstrated non-specific abnormalities, 20 were normal. Of the 40 abnormal PET/CT results, 22 diagnoses were confirmed, 3 alternative diagnoses were established. Only one diagnosis was established in the 20 patients with a normal scan. In both studies, the final diagnosis was based on histology, clinical follow-up, response to therapy or additional imaging. In conclusion, PET/CT may be of potential value in the diagnostic work-up of patients with elevated ESR if routine evaluation reveals no diagnosis. In particular, large-vessel vasculitis appears to be a common finding. A normal PET/CT scan in these patients suggests that it is safe to follow a wait-and-see policy.     

Medical diagnostic radiation exposures and risk of gliomas

High-dose ionizing radiation is an established risk factor for glioma, but it remains unknown whether moderate- and low-dose radiation increase glioma risk. In this analysis, we assessed the evidence that self-reported exposures to diagnostic ionizing radiation, including computerized tomography (CT) scans, is associated with increased risk of adult glioma. While no independent association was observed for CT scans alone (3+ scans compared to none P = 0.08 and 1-2 scans compared to none P = 0.68), our findings suggest an increased risk of adult gliomas with cumulative exposure to three or more CT scans to the head and neck region (OR = 1.97, 95% CI: 0.92-4.23) limited to those who reported a family history of cancer: the P value for the interaction between having three or more CT scans and family history of cancer was 0.08. The stratum-specific adjusted OR for those with family history of cancer was more than three times that for the sub-group without family history of cancer. While there is some potential for symptom-related bias, one might expect this to be present for all diagnostic procedures rather than specific to one procedure. The interaction between CT scans and glioma with family history of cancer supports the biological plausibility of our findings, because similar results have been found for breast cancer and radiation. This observational data will increase awareness about potential risks associated with CT scans and the need to minimize the use of unnecessary examinations.     

FDG PET scans as evaluation of clinical response to dendritic cell vaccination in patients with malignant melanoma

Background

Measurements of tumour metabolism by [18F]fluorodeoxyglucose positron emission tomography (FDG-PET) have been successfully applied to monitor tumour response after chemo- and chemo-radiotherapy and may not have the same limitations as other morphological imaging techniques. In this study it is investigated whether FDG-PET might add information on the efficacy of immune therapy.

Materials and methods

In a retrospective analysis data from patients with advanced progressive melanoma, treated with DC vaccinations and evaluated by PET/CT scans at baseline as well as after 6 vaccinations were analysed. If a patient achieved stable disease according to RECIST, additional vaccinations were given. The PET scans were evaluated according to EORTC guidelines.

Results

PET/CT scans from 13 patients were evaluated. According to RECIST 3 patients achieved stable disease and 10 patients progressed. Interestingly, when evaluated by PET scans 2 patients had partial metabolic response and 1 patient had complete metabolic response of the 2 index lesions even though a new lesion appeared simultaneously. Ten patients were seen to have stable or progressive metabolic disease.

Conclusion

By adding PET scans to the CT evaluation of patients treated with DC vaccines, a more detailed picture of the single lesions was found. This seems to improve the clinical evaluation of the treatment. The lack of correlation between the PET and CT scans suggests that some of the increases in target lesions seen in CT scans might be due to oedema or immune-infiltrates and not progression of the disease. Thus, further investigation into the contribution of PET scans to the evaluation of cancer immunotherapy is needed.     

兔VX2肝癌模型制作改良及影像学评价

目的 对兔VX2 肝癌模型制作进行改良,以用于介入治疗学研究,同时探讨瘤灶的CT 表现及CT 在检测瘤灶中的作用.方法 将VX2瘤细胞接种于兔皮下使其成瘤并传代;新西兰兔24只,以改良嵌插法建立移植性肝癌模型,于建模后7、14、21 d分别行超声、CT及血管造影检查,用于检测兔肝VX2 瘤灶,评估瘤灶生长变化;随后处死动物,进行尸解,评估影像检查结果.结果 24只（100%） 动物以改良嵌插法建立移植性肝癌模型全部成功.瘤灶以种植后2周CT显示最清楚和典型,直径1 cm～2 cm 左右,平扫呈低密度或等密度,动脉早期明显强化,门脉期呈低密度,与周围肝组织分界较清楚.肝动脉造影显示肿瘤富血供.而种植后超过3 周的肿瘤大部分发生坏死.结论 嵌插改良法是一种值得推广的建立移植性肝癌模型的方法;在对瘤灶进行影像学评价上应尽量选择CT检查,接种后1 周左右的瘤灶较小而难以观察;2 周左右呈肝动脉源性血供丰富的约1 cm～2 cm的实体瘤,造影征像为肿瘤血管与肿瘤染色;3 周以上瘤灶大多出现明显示坏死;因此对1～2cm大小的兔VX2 肝癌瘤体,最适合行血管造影检查.     

Validation of subject-specific automated p-FE analysis of the proximal femur

Background: The use of subject-specific finite element (FE) models in clinical practice requires a high level of automation and validation. In Yosibash et al. [2007a. Reliable simulations of the human proximal femur by high-order finite element analysis validated by experimental observations. J. Biomechanics 40, 3688–3699] a novel method for generating high-order finite element (p-FE) models from CT scans was presented and validated by experimental observations on two fresh frozen femurs (harvested from a 30 year old male and 21 year old female). Herein, we substantiate the validation process by enlarging the experimental database (54 year old female femur), improving the method and examine its robustness under different CT scan conditions.Approach: A fresh frozen femur of a 54 year old female was scanned under two different environments: in air and immersed in water (dry and wet CT). Thereafter, the proximal femur was quasi-statically loaded in vitro by a 1000 N load. The two QCT scans were manipulated to generate p-FE models that mimic the experimental conditions. We compared p-FE displacements and strains of the wet CT model to the dry CT model and to the experimental results. In addition, the material assignment strategy was reinvestigated. The inhomogeneous Young's modulus was represented in the FE model using two different methods, directly extracted from the CT data and using continuous spatial functions as in Yosibash et al. [2007a. Reliable simulations of the human proximal femur by high-order finite element analysis validated by experimental observations. J. Biomechanics 40, 3688–3699].Results: Excellent agreement between dry and wet FE models was found for both displacements and strains, i.e. the method is insensitive to CT conditions and may be used in vivo. Good agreement was also found between FE results and experimental observations. The spatial functions representing Young's modulus are local and do not influence strains and displacements prediction. Finally, the p-FE results of all three fresh frozen human femurs compare very well to experimental observations exemplifying that the presented method may be in a mature stage to be used in clinical computer-aided decision making.     

EGS_cbct: Simulation of a fan beam CT and RMI phantom for measured HU verification

IntroductionA mathematical 3D model of an existing computed tomography (CT) scanner was created and used in the EGSnrc-based BEAMnrc and egs_cbct Monte Carlo codes. Simulated transmission dose profiles of a RMI-465 phantom were analysed to verify Hounsfield numbers against measured data obtained from the CT scanner.Methods and materialsThe modelled CT unit is based on the design of a Toshiba Aquilion 16 LB CT scanner. As a first step, BEAMnrc simulated the X-ray tube, filters, and secondary collimation to obtain phase space data of the X-ray beam. A bowtie filter was included to create a more uniform beam intensity and to remove the beam hardening effects. In a second step the Interactive Data Language (IDL) code was used to build an EGSPHANT file that contained the RMI phantom which was used in egs_cbct simulations. After simulation a series of profiles were sampled from the detector model and the Feldkamp-Davis-Kress (FDK) algorithm was used to reconstruct transversal images. The results were tested against measured data obtained from CT scans.ResultsThe egs_cbct code can be used for the simulation of a fan beam CT unit. The calculated bowtie filter ensured a uniform flux on the detectors. Good correlation between measured and simulated CT numbers was obtained.ConclusionsIn principle, Monte Carlo codes such as egs_cbct can model a fan beam CT unit. After reconstruction, the images contained Hounsfield values comparable to measured data.     

Improving Intra-Fractional Target Position Accuracy Using a 3D Surface Surrogate for Left Breast Irradiation Using the Respiratory-Gated Deep-Inspiration Breath-Hold Technique

Purpose

To evaluate the use of 3D optical surface imaging as a surrogate for respiratory gated deep-inspiration breath-hold (DIBH) for left breast irradiation.

Material and Methods

Patients with left-sided breast cancer treated with lumpectomy or mastectomy were selected as candidates for DIBH treatment for their external beam radiation therapy. Treatment plans were created on both free breathing (FB) and DIBH computed tomography (CT) simulation scans to determine dosimetric benefits from DIBH. The Real-time Position Management (RPM) system was used to acquire patient''s breathing trace during DIBH CT acquisition and treatment delivery. The reference 3D surface models from FB and DIBH CT scans were generated and transferred to the “AlignRT” system for patient positioning and real-time treatment monitoring. MV Cine images were acquired during treatment for each beam as quality assurance for intra-fractional position verification. The chest wall excursions measured on these images were used to define the actual target position during treatment, and to investigate the accuracy and reproducibility of RPM and AlignRT.

Results

Reduction in heart dose can be achieved using DIBH for left breast/chest wall radiation. RPM was shown to have inferior correlation with the actual target position, as determined by the MV Cine imaging. Therefore, RPM alone may not be an adequate surrogate in defining the breath-hold level. Alternatively, the AlignRT surface imaging demonstrated a superior correlation with the actual target positioning during DIBH. Both the vertical and magnitude real-time deltas (RTDs) reported by AlignRT can be used as the gating parameter, with a recommended threshold of ±3 mm and 5 mm, respectively.

Conclusion

The RPM system alone may not be sufficient for the required level of accuracy in left-sided breast/CW DIBH treatments. The 3D surface imaging can be used to ensure patient setup and monitor inter- and intra- fractional motions. Furthermore, the target position accuracy during DIBH treatment can be improved by AlignRT as a superior surrogate, in addition to the RPM system.