RL Direction Research Articles

Effect of Microstructures on the Shear Strength of Larix kaempferi

Shear strength is important for the application of Larix kaempferi (Lamb) Carr. The structural difference between earlywood and latewood of Larix kaempferi affects its mechanical properties, especially shear strength. The microstructures of earlywood and latewood in Larix kaempferi, however, are different. In this study, we investigated the shear strength and shear failure mode in the RL direction of 40 Larix kaempferi specimens. The results demonstrated that the initial crack appears in any location of a growth ring, whereas shear failure is concentrated in earlywood, as well as the junction between earlywood and latewood. The destruction of earlywood is the tear destruction, whereas when the destruction happened in the junction of earlywood and latewood, one to three earlywood cells usually adhered to latewood. At the cell wall level, the shear failure of earlywood was mostly observed in the direction of the microfibril angle (MFA). When the crack occurs in latewood, the destruction of latewood also occurs in the intercellular layer and preserves the complete morphology of tracheids. When destruction occurs in the wood ray, the ray cells detach intact from the tracheids. The failure mode is determined by the microstructure of earlywood and latewood. Our research suggests that the density, cell wall thickness, and MFA have significant differences between earlywood and latewood. The earlywood was found to have an MFA of 25.4°, a cell wall thickness of 6.36 µm, and a density of 0.39 g/cm3. The MFA, cell wall thickness, and density of latewood density were 17.60°, 12.37 µm, and 0.78 g/cm3, respectively. However, there was no significant difference found in the crystallinity between the earlywood (43.97%) and latewood (42.79%). The correlation between the microstructures and shear strength showed that earlywood with a thin cell wall, large MFA, and low density had poor shear performance, while the latewood with a thicker tracheid, smaller MFA, and higher density had better shear performance. Therefore, when shear failure occurred, it occurred in earlywood. We thus deduced that the MFA, cell wall thickness, and density of earlywood synergically affect the shear strength in the RL direction of L. kaempferi.

Accuracy of an MR-only workflow for prostate radiotherapy using semi-automatically burned-in fiducial markers

BackgroundThe benefit of MR-only workflow compared to current CT-based workflow for prostate radiotherapy is reduction of systematic errors in the radiotherapy chain by 2–3 mm. Nowadays, MRI is used for target delineation while CT is needed for position verification. In MR-only workflows, MRI based synthetic CT (sCT) replaces CT. Intraprostatic fiducial markers (FMs) are used as a surrogate for the position of the prostate improving targeting. However, FMs are not visible on sCT. Therefore, a semi-automatic method for burning-in FMs on sCT was developed. Accuracy of MR-only workflow using semi-automatically burned-in FMs was assessed and compared to CT/MR workflow.MethodsThirty-one prostate cancer patients receiving radiotherapy, underwent an additional MR sequence (mDIXON) to create an sCT for MR-only workflow simulation. Three sources of accuracy in the CT/MR- and MR-only workflow were investigated. To compare image registrations for target delineation, the inter-observer error (IOE) of FM-based CT-to-MR image registrations and soft-tissue-based MR-to-MR image registrations were determined on twenty patients. Secondly, the inter-observer variation of the resulting FM positions was determined on twenty patients. Thirdly, on 26 patients CBCTs were retrospectively registered on sCT with burned-in FMs and compared to CT-CBCT registrations.ResultsImage registration for target delineation shows a three times smaller IOE for MR-only workflow compared to CT/MR workflow. All observers agreed in correctly identifying all FMs for 18 out of 20 patients (90%). The IOE in CC direction of the center of mass (COM) position of the markers was within the CT slice thickness (2.5 mm), the IOE in AP and RL direction were below 1.0 mm and 1.5 mm, respectively. Registrations for IGRT position verification in MR-only workflow compared to CT/MR workflow were equivalent in RL-, CC- and AP-direction, except for a significant difference for random error in rotation.ConclusionsMR-only workflow using sCT with burned-in FMs is an improvement compared to the current CT/MR workflow, with a three times smaller inter observer error in CT-MR registration and comparable CBCT registration results between CT and sCT reference scans.Trial registry Medical Research Involving Human Subjects Act (WMO) does apply to this study and was approved by the Medical Ethics review Committee of the Academic Medical Center. Registration number: NL65414.018.18. Date of registration: 21–08-2018.

Comparison of methods for determining shear modulus of wood

In this study, the relatively new picture frame method applied to wood is compared with three established shear test methods, namely the experimental modal analysis, the square plate twist method and the torsion test. For the investigations, the wood species European beech (Fagus sylvatica L.) and spruce (Picea abies L. Karst.) were used and the shear tests were conducted in LR and RL direction. The results show comparable shear moduli for beech and spruce in the range of 931–1289 Nmm−2 and 495–842 Nmm−2, respectively. In contrast to the theory of linear elastic orthotropic materials, significant differences in the results of the picture frame method between LR and RL direction were observed for spruce.

The impact of the offset distance between the planning target volume and isocenter on irradiation time in TomoTherapy: A phantom study

PurposeThe influence of the offset distance from treatment target to gantry isocenter (GIC) on the dosimetric parameter and irradiation time was investigated using TomoTherapy MethodsThe reference position was defined as the centers of both the I’mRT phantom and planning target volume (PTV) with a spherical of 4 cm diameter aligned with the GIC. The dose calculations were performed in two offset methods with 2 and 12 Gy/fr, Method 1. The PTV was moved from 0.0 to 12.5 cm along the RL direction and −5.0 to 5.0 cm along the AP direction (PTV offset), Method 2. The phantom was moved from 0.0 to −7.5 cm along the RL direction and −5.0 to 5.0 cm along the AP direction (Phantom offset). The maximum, minimum and mean doses, homogeneity index, conformity index, irradiation time, and monitor unit were compared. ResultsThe irradiation times increased with increasing PTV offset. The increases in the irradiation time were 54.4% and 40.8% at PTV offsets of 12.5 cm along the RL direction for 2 and 12 Gy/fr, while the increases were 20.1% and 15.0% at a PTV offset of 5.0 cm along the AP direction. An increased irradiation time was not observed for the phantom offset. The offset didn’t affect the other parameters. ConclusionsThe PTV location offset of ≥5 cm from the GIC along the RL and AP axes increased the irradiation time; therefore, the PTV should be aligned with the GIC as much as possible to reduce the irradiation time on TomoTherapy.

Comparison of Fiducial Marker Implantation and Soft Tissue Registration Using Cone Beam CT in Image-Guided Radiation Therapy of the Prostate

With the advent of Cone Beam CT (CBCT) in Image Guided Radiation Therapy (IGRT) of prostate cancer, daily registration can now be achieved with aligning patient position based on their soft tissue (ST) as opposed to surgically-inserted radio-opaque fiducial markers (FM). There are a limited number of studies directly comparing the differences in registration based on CBCT FM versus CBCT ST, despite differing standards of practice with the use of FM in IGRT of prostate cancers. There is disagreement in the literature whether CBCT ST offers an equivalent means of patient registration. For this study, we retrospectively collected the radiation treatment plan and daily CBCT imaging for 25 patients treated for prostate cancer at our center from 2014-2015. All patients had 3 FM implanted in the apex, mid and base of prostate under ultrasound guidance, pre-simulation. Three radiation therapists (each >2 years of experience in the use of CBCT ST and FM registration) performed registration of CBCT scans, uniformly spread over the treatment, to the reference CT based on both FM and ST using a stand-alone XVI (X-ray Volume Imaging) system by Elekta™ (Crawley, UK). Shifts in the RL, SI, and AP direction were calculated for each of the 5 fractions for each patient. Average shifts across patients were calculated and the results between the FM- and ST-based matching were compared using a Bland and Altman analysis. In a sample set of 5 patients, average shifts in the RL, SI, and AP directions were 2.5, 2.5, and 4.2 mm with CBCT FM, and 2.6, 1.4, and 4.0 mm with CBCT ST. A Bland and Altman comparison between CBCT FM versus CBCT ST resulted in a 95% confidence intervals of -2.4 to 1.6mm for RL, -1.9 to 4.4mm for SI, and -2.1 to 3.5mm for AP. The percentage of shifts in agreement between ±3mm was 98% for RL, 88% for SI, and 94% for AP, while the percentage of shifts in agreement between ±5mm was 98% for RL, 98% for SI, and 100% for AP. Our experience with CBCT ST has shown that it is comparable to CBCT FM alignment, in a center with radiation therapists experienced in aligning based on CBCT ST.

TU‐F‐CAMPUS‐J‐04: Setup Uncertainties in the Mediastinum Area for IMRT Treatment of Lymphoma Patients

Purpose:Despite daily image guidance setup uncertainties can be high when treating large areas of the body. The aim of this study was to measure local uncertainties inside the PTV for patients receiving IMRT to the mediastinum region.Methods:Eleven lymphoma patients that received radiotherapy (breath‐hold) to the mediastinum were included in this study. The treated region could range all the way from the neck to the diaphragm. Each patient had a CT scan with a CT‐on‐rails system prior to every treatment. The entire PTV region was matched to the planning CT using automatic rigid registration. The PTV was then split into 5 regions: neck, supraclavicular, superior mediastinum, upper heart, lower heart. Additional auto‐registrations for each of the 5 local PTV regions were performed. The residual local setup errors were calculated as the difference between the final global PTV position and the individual final local PTV positions for the AP, SI and RL directions. For each patient 4 CT scans were analyzed (1 per week of treatment).Results:The residual mean group error (M) and standard deviation of the inter‐patient (or systematic) error (Σ) were lowest in the RL direction of the superior mediastinum (0.0mm and 0.5mm) and highest in the RL direction of the lower heart (3.5mm and 2.9mm). The standard deviation of the inter‐fraction (or random) error (σ) was lowest in the RL direction of the superior mediastinum (0.5mm) and highest in the SI direction of the lower heart (3.9mm) The directionality of local uncertainties is important; a superior residual error in the lower heart for example keeps it in the global PTV.Conclusion:There is a complex relationship between breath‐holding and positioning uncertainties that needs further investigation. Residual setup uncertainties can be significant even under daily CT image guidance when treating large regions of the body.

SU‐C‐18A‐04: 3D Markerless Registration of Lung Based On Coherent Point Drift: Application in Image Guided Radiotherapy

Purpose:This study evaluated a new probabilistic non‐rigid registration method called coherent point drift for real time 3D markerless registration of the lung motion during radiotherapy.Method:4DCT image datasets Dir‐lab (www.dir‐lab.com) have been used for creating 3D boundary element model of the lungs. For the first step, the 3D surface of the lungs in respiration phases T0 and T50 were segmented and divided into a finite number of linear triangular elements. Each triangle is a two dimensional object which has three vertices (each vertex has three degree of freedom). One of the main features of the lungs motion is velocity coherence so the vertices that creating the mesh of the lungs should also have features and degree of freedom of lung structure. This means that the vertices close to each other tend to move coherently. In the next step, we implemented a probabilistic non‐rigid registration method called coherent point drift to calculate nonlinear displacement of vertices between different expiratory phases.Results:The method has been applied to images of 10‐patients in Dir‐lab dataset. The normal distribution of vertices to the origin for each expiratory stage were calculated. The results shows that the maximum error of registration between different expiratory phases is less than 0.4 mm (0.38 SI, 0.33 mm AP, 0.29 mm RL direction). This method is a reliable method for calculating the vector of displacement, and the degrees of freedom (DOFs) of lung structure in radiotherapy.Conclusions:We evaluated a new 3D registration method for distribution set of vertices inside lungs mesh. In this technique, lungs motion considering velocity coherence are inserted as a penalty in regularization function. The results indicate that high registration accuracy is achievable with CPD. This method is helpful for calculating of displacement vector and analyzing possible physiological and anatomical changes during treatment.

Measuring uncertainty in dose delivered to the cochlea due to setup error during external beam treatment of patients with cancer of the head and neck

To use Cone Beam CT scans obtained just prior to treatments of head and neck cancer patients to measure the setup error and cumulative dose uncertainty of the cochlea. Data from 10 head and neck patients with 10 planning CTs and 52 Cone Beam CTs taken at time of treatment were used in this study. Patients were treated with conventional fractionation using an IMRT dose painting technique, most with 33 fractions. Weekly radiographic imaging was used to correct the patient setup. The authors used rigid registration of the planning CT and Cone Beam CT scans to find the translational and rotational setup errors, and the spatial setup errors of the cochlea. The planning CT was rotated and translated such that the cochlea positions match those seen in the cone beam scans, cochlea doses were recalculated and fractional doses accumulated. Uncertainties in the positions and cumulative doses of the cochlea were calculated with and without setup adjustments from radiographic imaging. The mean setup error of the cochlea was 0.04 ± 0.33 or 0.06 ± 0.43 cm for RL, 0.09 ± 0.27 or 0.07 ± 0.48 cm for AP, and 0.00 ± 0.21 or -0.24 ± 0.45 cm for SI with and without radiographic imaging, respectively. Setup with radiographic imaging reduced the standard deviation of the setup error by roughly 1-2 mm. The uncertainty of the cochlea dose depends on the treatment plan and the relative positions of the cochlea and target volumes. Combining results for the left and right cochlea, the authors found the accumulated uncertainty of the cochlea dose per fraction was 4.82 (0.39-16.8) cGy, or 10.1 (0.8-32.4) cGy, with and without radiographic imaging, respectively; the percentage uncertainties relative to the planned doses were 4.32% (0.28%-9.06%) and 10.2% (0.7%-63.6%), respectively. Patient setup error introduces uncertainty in the position of the cochlea during radiation treatment. With the assistance of radiographic imaging during setup, the standard deviation of setup error reduced by 31%, 42%, and 54% in RL, AP, and SI direction, respectively, and consequently, the uncertainty of the mean dose to cochlea reduced more than 50%. The authors estimate that the effects of these uncertainties on the probability of hearing loss for an individual patient could be as large as 10%.

Appropriate patient instructions can reduce prostate motion

BackgroundInterfraction prostate motion must be compensated by increased safety margins. If filling status of rectum and bladder is constant, motion should be reduced. We attempted to reduce interfraction motion errors by proper patient instruction.MethodIn 38 patients pairs of radio-opaque fiducial markers were implanted prior to definitive radiotherapy. Patients were positioned either according to skin marks or infrared body marker. We measured prostate displacement, i.e. pelvic bones versus intraprostatic marker position, via ExacTrac (two orthogonal radiographies) in 1252 fractions. Systematic and random setup and displacement errors were determined and safety margins estimated.ResultsIn our study interfraction prostate displacement is < 1 mm in RL direction, and < 2 mm in AP and SI direction. Systematic errors are slightly below random errors (< 1.5 mm). Positioning according skin marks results in higher inaccuracies of ±1.5 – 2 mm in RL and ±2 – 2.5 mm in AP/SI direction.ConclusionsIn case of appropriate patient instructions (constant organ filling) the positioning via bone fusion requires CTV-PTV margins of 2 mm in RL, 4 mm in AP, and 5 mm in SI direction. Studies without any description of patient instruction found much higher margins of > 1 cm in AP and SI direction.

Set-up errors in radiotherapy for oesophageal cancers – Is electronic portal imaging or conebeam more accurate?

PurposeTo compare kV computed tomography (CBCT) with electronic portal imaging (EPI) and evaluate set-up variations in the anterior–posterior (AP), right–left (LR) and cranio-caudal (CC) directions and rotational variations: pitch, roll, and yaw, for oesophageal cancer patients treated with radical radiotherapy. Methods and materialsTwenty patients with locally advanced oesophageal cancer treated with chemoradiation were consented for this prospective ethics approved protocol. Patients were positioned using skin marks/tattoos, kV-CBCT scans (XVI) and EPI’s were performed prior to treatment and registered to the planning CT scans and digitally reconstructed radiographs, respectively. XVI data was used to adjust patient setups before treatment delivery. A total of 122 EPI pairs and 207 CBCT scans were analysed. The systematic and random errors were calculated. ResultsThe systematic and random errors (mm) for XVI were 1.3, 1.7, 1.4 and 2.6, 3.9, 2.0 in RL, CC and AP direction, respectively, with EPI of similar magnitude. There was no correlation between the 2 modalities of imaging as 31.7% of all image pairs were discordant >3mm and 12.5% >5mm. XVI identified rotations >3° in 44 images. ConclusionsEPI results in different position correction for verification of radiotherapy in oesophageal malignancies when compared with CBCT. CBCT verification offers adequate 3D volumetric image quality to improve the accuracy of treatment delivery for oesophageal malignancies in radiotherapy and should be used for image guidance.

The Effectiveness of Rectal Balloon and Orthogonal Imaging for Proton Therapy of Prostate Cancer

The Effectiveness of Rectal Balloon and Orthogonal Imaging for Proton Therapy of Prostate Cancer

SU‐GG‐J‐88: Evaluation of Patient Setup Accuracy for Targeted Marrow Irradiation with Image‐Guided Helical Tomotherapy

Purpose: Targeted marrow irradiation (TMI) using intensity‐modulated fields could allow dose escalation while limiting radiation toxicities to critical organs for patients who traditionally would receive total body irradiation. In this study, we evaluated patient setup uncertainties and the efficacy of our image‐guided setup techniques for TMI treatments based on helical tomotherapy megavoltage CT image registrations. Method and materials: We analyzed image registrations from 206 treatment fractions for 26 TMI patients. Prior to each treatment fraction, two MVCT scans were performed encompassing the head &amp; neck region and the pelvic region, respectively. image registrations were performed for each scan. The two image registrations were averaged to correct patient setup errors. Results: In the head &amp; neck region, the mean and standard deviation (SD) of setup corrections was 3.5±6.4 mm in the RL direction, −2.4±5.3 mm in the SI direction, −0.7±5.8 mm in the AP direction, and 0±1.2° in roll. In the pelvic region, it was 1.5±7.7 mm in the RL direction, −3.7±5.6 mm in the SI direction, 2.1±5.7 mm in the AP direction, and 0±1.1° in roll. After the two registrations were averaged, it was 2.5±6.6 mm in the RL direction, −3.1±5.1 mm in the SI direction, 0.7±5.1 mm in the AP direction, and 0±0.8° in roll. The residual setup errors in the head &amp; neck region had mean and SD of 1.0±2.5 mm in the RL direction, 0.7±1.9 mm in the SI direction, −1.4±2.7 mm in the AP direction, and 0±0.8° in roll. Conclusion: The two‐scan technique ensured that the superior and inferior portions of the patient bony structure were properly set up in most cases. In cases when the residual setup errors were significant, the superior and inferior segments should be treated separately with separate setup corrections to ensure adequate target volume coverage.

SU‐GG‐J‐48: Clinical Implementation of Varian On‐Board Imaging System

Purpose: Two Varian on‐board imaging (OBI) systems have been installed and commissioned in our clinic. Over recent months, a daily QA procedure was developed to monitor system's performance and a clinical study was implemented to transition electronic portal image (EPI) guided to OBI guided prostate treatments. Method and Materials: A Penta‐Guide phantom (QUASAR™) is used for daily QA. The functions of match and couch auto motion in the OBI kilo‐voltage (kV) and OBI‐CBCT systems are tested. For the clinical study, to be finished in April, 2008, 14 prostate (78Gy/39) patients have been recruited. CBCT soft tissue‐based (ST) match and couch shift are performed twice a week and kV‐orthogonal fudical marker (FM) match and shift are executed 3 times a week for each patient before treatment. EPI FM match, our standard image guided procedure is used to verify the OBI match and couch motion. The differences are recorded. Results: Daily QA data over 5 months show that the coincidence between EPI and OBI after couch motion is 0.1±0.5mm, −0.2±0.6mm and −1.3±0.6mm (2σ) in RL, SI and AP direction, respectively. The AP mean was caused by the systematic couch motion error. For the clinical study, the preliminary data from the first 8 patients have been analyzed. The differences between OBI‐kV FM match and EPI FM match are −0.1±1.6mm, −0.4±1.8mm and −1.2±2.6mm (2σ) in RL, SI and AP direction, respectively. The differences between OBI‐CBCT ST match and EPI‐FM match are −0.9±4.1mm, −0.8±5.0mm and −1.6±5.1mm (2σ) in RL, SI and AP direction respectively. The AP mean is largely due to the systematic treatment couch motion error. Conclusion: The daily QA is comprehensive to capture systematic errors; OBI‐kV FM and EPI FM match agree within 3 mm in all three directions and CBCT‐ST match demonstrates larger variations of 5mm compared with EPI‐FM in three directions.

SU-FF-J-82: Characterization of Parotid Gland Movement and Deformation During IMRT Treatment

Purpose: To quantify the pattern of internal parotid gland movement and shape variations in patients undergoing IMRT.Methods & Materials: Eleven head & neck patients' treatment planning CTs and repeat in‐room CTs were acquired for this analysis. In‐room treatment CTs were first registered to the reference planning CT by a rigid registration. The purpose of this bony registration was to remove un‐interested daily setup errors so that the study was focused on soft tissue changes. A deformable image registration was then carried out for the region of interest to obtain the voxel‐by‐voxel displacement map of the parotid glands. We developed a metric, referred here as the shift profile, to quantify internal positional changes of the parotid. The shift profile was basically a displacement profile along the direction of interest for all points in a plane perpendicular to the direction. The shift profile can be used to quantify the rate of volume shrinkage or expansion as well as the location and time‐trend of these volumetric internal changes. Results: About 82% of the patients show clear shrinkage along right‐left direction (RL) for both parotids, and about 35% of the patients show either clear shrinkage or clear expansion along superior‐inferior (SI) and anterior‐posterior (AP) directions, respectively. The magnitude of the shift along SI and AP direction was much smaller than along the RL direction. Moreover, the shrinkage toward the center was found to be linear with the elapsed time in the first 3–4 weeks and became relative stable thereafter. Conclusions: We've found some interesting patterns to describe parotid gland variations during IMRT treatment, which shows the potential for organ specific modeling and prediction of anatomic changes.

844 POSTER Is lodine allergy a contraindication to prostate brachytherapy using lodine125?

A computed tomography (ct) scanner on Rails has been installed in a linear accelerator room at Morristown Memorial Hospital since 2000. The ct-on-Rails has been used for the localization of patient position during radiation delivery for prostate, lung and liver cancer patients. The image management system, the Siemens Syngo system, is the primary software employed in the registration of the planning ct and the treatment ct images. This study compares the two image fusion methods available in the system: Landmark Registration and Visual Alignment. Shifts in 6 ct scans with Rando phantom were deduced from Landmark Registration (automatic algorithm) and from Visual Alignment (manual registration), and compared with the shifts directly measured on the phantom. For Visual Alignment, the isocenter shifts deduced from the fused images generally agreed well with the directly measured shifts on the Rando phantom, with average absolute error of 0.9 mm in anterior-posterior (ap) direction, 1.0 mm in right-left (rl) direction, and 2.0 mm in superior-inferior (si) direction. The image fusion algorithm was confirmed to be accurate. Some scans with Landmark Registration gave erroneous ap shifts when the anterior radio-opaque marker (bb) registration was of in the ap direction. Visual Alignment was more robust than Landmark Registration in these clinical situations.

842 POSTER Postoperative radiotherapy for prostate cancer — evaluation of target motion and treatment technique (intensity modulated versus three-dimensional conformal radiotherapy)

A computed tomography (ct) scanner on Rails has been installed in a linear accelerator room at Morristown Memorial Hospital since 2000. The ct-on-Rails has been used for the localization of patient position during radiation delivery for prostate, lung and liver cancer patients. The image management system, the Siemens Syngo system, is the primary software employed in the registration of the planning ct and the treatment ct images. This study compares the two image fusion methods available in the system: Landmark Registration and Visual Alignment. Shifts in 6 ct scans with Rando phantom were deduced from Landmark Registration (automatic algorithm) and from Visual Alignment (manual registration), and compared with the shifts directly measured on the phantom. For Visual Alignment, the isocenter shifts deduced from the fused images generally agreed well with the directly measured shifts on the Rando phantom, with average absolute error of 0.9 mm in anterior-posterior (ap) direction, 1.0 mm in right-left (rl) direction, and 2.0 mm in superior-inferior (si) direction. The image fusion algorithm was confirmed to be accurate. Some scans with Landmark Registration gave erroneous ap shifts when the anterior radio-opaque marker (bb) registration was of in the ap direction. Visual Alignment was more robust than Landmark Registration in these clinical situations.

A comparison of two image fusion techniques in ct-on-rails localization of radiation delivery

A computed tomography ( ct) scanner on Rails has been installed in a linear accelerator room at Morristown Memorial Hospital since 2000. The ct-on-Rails has been used for the localization of patient position during radiation delivery for prostate, lung and liver cancer patients. The image management system, the Siemens Syngo system, is the primary software employed in the registration of the planning ct and the treatment ct images. This study compares the two image fusion methods available in the system: Landmark Registration and Visual Alignment. Shifts in 6 ct scans with Rando phantom were deduced from Landmark Registration (automatic algorithm) and from Visual Alignment (manual registration), and compared with the shifts directly measured on the phantom. For Visual Alignment, the isocenter shifts deduced from the fused images generally agreed well with the directly measured shifts on the Rando phantom, with average absolute error of 0.9 mm in anterior-posterior ( ap) direction, 1.0 mm in right-left ( rl) direction, and 2.0 mm in superior-inferior ( si) direction. The image fusion algorithm was confirmed to be accurate. Some scans with Landmark Registration gave erroneous ap shifts when the anterior radio-opaque marker ( bb) registration was of in the ap direction. Visual Alignment was more robust than Landmark Registration in these clinical situations.

Fracture toughness of wet and dry Pinus radiata

were determined using a three-point bend test and a compact-shear specimen test respectively. The fracture toughness across the grain (LT and LR) in mode 1 was ten times greater than in other directions for both wet and dry specimens. The mode 1 fracture toughness of wet wood was lower than dry wood in every orientation except TR. The mode 2 fracture toughness for dry wood was found for all directions except the longitudinal ones (LT and LR). In the longitudinal direction, mode 2 fracture did not occur, as the wood failed in compression before its shear limits were reached. In wet wood, pure mode 2 fracture occurred only in the RL direction. In other directions, the fracture did not originate from the notch tip, or the wood fractured in a mixed mode.

New splitting method for wood fracture characterization

A testing procedure with a new and simple specimen shape is presented which is appropriate to characterize fracturing of inhomogeneous and complex materials like wood. With this, the fracture energy of spruce wood is determined in the TL and RL direction. The “size effect”, i.e. influences of specimen dimensions on KIC and Gf (specific fracture energy) are investigated. Stress and deformation distribution in the newly developed specimens are analysed with FE methods. The measured load-displacement curves are approximated by bilinear softening diagrams and FE analysis. Based on these results, it is tried to interpret typical deviations from LEFM's behaviour by mechanisms like microcracking, crack branching or crack tip bridging.

直立時重心動揺の冗長性

Normal stabilogram were examined in 38 subjects, 38 males and 7 females, aged 30 to 62 years, standing erect in Romberg's posture with eyes open and with eyes closed. From analog data of body sways in both lateral (RL) and anterior-posterior (AP) directions, digital data of 51.2 sec duration with a sampling time 50 msec were obtained in each case. Each serial partial statokinesigram of 5 or 10 msec duration was displayed on rectangular coordinates, the origin of which was fixed at the mean value of each location of the center of gravity during 51.2 sec with the use of a microcomputer (NEC PC 9801). The slow deviation with a period of about 50 sec or with 0.02 Hz, of body sway in the RL or AP direction was not infrequently observed when the eyes were open. However, it was eliminated or negligible when the eyes closed. When such a slow deviation of body sway appeared, larger values of standard deviation and maximal range of body sway occurred in spite of the short length of the trace of the center of gravity.The incidence of slow deviation of body sway decreased in the RL direction and increased in the AP direction with the age of the test subjects. The origin of such a slow deviation is considered to be a redundancy of human standing ability, because it appeared only in stable and safe standing in normal subjects with eyes open.