SI Direction Research Articles

WE‐AB‐209‐08: Novel Beam‐Specific Adaptive Margins for Reducing Organ‐At‐Risk Doses

Purpose:Current practice of using 3D margins in radiotherapy with high‐energy photon beams provides larger‐than‐required target coverage. According to the photon depth‐dose curve, target displacements in beam direction result in minute changes in dose delivered. We exploit this behavior by generating margins on a per‐beam basis which simultaneously account for the relative distance of the target and adjacent organs‐at‐risk (OARs).Methods:For each beam, we consider only geometrical uncertainties of the target location perpendicular to beam direction. By weighting voxels based on its proximity to an OAR, we generate adaptive margins that yield similar overall target coverage probability and reduced OAR dose‐burden, at the expense of increased target volume. Three IMRT plans, using 3D margins and 2D per‐beam margins with and without adaptation, were generated for five prostate patients with a prescription dose Dpres of 78Gy in 2Gy fractions using identical optimisation constraints. Systematic uncertainties of 1.1, 1.1, 1.5mm in the LR, SI, and AP directions, respectively, and 0.9, 1.1, 1.0mm for the random uncertainties, were assumed. A verification tool was employed to simulate the effects of systematic and random errors using a population size of 50,000. The fraction of the population that satisfies or violates a given DVH constraint was used for comparison.Results:We observe similar target coverage across all plans, with at least 97.5% of the population meeting the D98%>95%Dpres constraint. When looking at the probability of the population receiving D5<70Gy for the rectum, we observed median absolute increases of 23.61% (range, 2.15%–27.85%) and 6.97% (range, 0.65%–17.76%) using per‐beam margins with and without adaptation, respectively, relative to using 3D margins.Conclusion:We observed sufficient and similar target coverage using per‐beam margins. By adapting each per‐beam margin away from an OAR, we can further reduce OAR dose without significantly lowering target coverage probability by irradiating more less‐important tissues.This work is supported by Cancer Research UK under Programme C33589/A19908. Research at ICR is also supported by Cancer Research UK under Programme C33589/A19727 and NHS funding to the NIHR Biomedical Research Centre at RMH and ICR.

SU‐F‐I‐11: Software Development for 4D‐CBCT Research of Real‐Time‐Image Gated Spot Scanning Proton Therapy

Purpose:To acquire correct information for inside the body in patient positioning of Real‐time‐image Gated spot scanning Proton Therapy (RGPT), utilization of tomographic image at exhale phase of patient respiration obtained from 4‐dimensional Cone beam CT (4D‐CBCT) has been desired. We developed software named “Image Analysis Platform” for 4D‐CBCT researches which has technique to segment projection‐images based on 3D marker position in the body. The 3D marker position can be obtained by using two axes CBCT system at Hokkaido University Hospital Proton Therapy Center. Performance verification of the software was implemented.Methods:The software calculates 3D marker position retrospectively by using matching positions on pair projection‐images obtained by two axes fluoroscopy mode of CBCT system. Log data of 3D marker tracking are outputted after the tracking. By linking the Log data and gantry‐angle file of projection‐image, all projection‐images are equally segmented to spatial five‐phases according to marker 3D position of SI direction and saved to specified phase folder. Segmented projection‐images are used for CBCT reconstruction of each phase. As performance verification of the software, test of segmented projection‐images was implemented for sample CT phantom (Catphan) image acquired by two axes fluoroscopy mode of CBCT. Dummy marker was added on the images. Motion of the marker was modeled to move in 3D space. Motion type of marker is sin4 wave function has amplitude 10.0 mm/5.0 mm/0 mm, cycle 4 s/4 s/0 s for SI/AP/RL direction.Results:The marker was tracked within 0.58 mm accuracy in 3D for all images, and it was confirmed that all projection‐images were segmented and saved to each phase folder correctly.Conclusion:We developed software for 4D‐CBCT research which can segment projection‐image based on 3D marker position. It will be helpful to create high quality of 4D‐CBCT reconstruction image for RGPT.

Evaluation of the setup margins for cone beam computed tomography–guided cranial radiosurgery: A phantom study

The aim of this study is to evaluate the setup margins from the clinical target volume (CTV) to planning target volume (PTV) for cranial stereotactic radiosurgery (SRS) treatments guided by cone beam computed tomography (CBCT). We designed an end-to-end (E2E) test using a skull phantom with an embedded 6mm tungsten ball (target). A noncoplanar plan was computed (E2E plan) to irradiate the target. The CBCT-guided positioning of the skull phantom on the linac was performed. Megavoltage portal images were acquired after 15 independent deliveries of the E2E plan. The displacement 2-dimensional (2D) vector between the centers of the square field and the ball target on each portal image was used to quantify the isocenter accuracy. Geometrical margins on each patient׳s direction (left-right or LR, anterior-posterior or AP, superior-inferior or SI) were calculated. Dosimetric validation of the margins was performed in 5 real SRS cases: 3-dimesional (3D) isocenter deviations were mimicked, and changes in CTV dose coverage and organs-at-risk (OARs) dosage were analyzed. The CTV-PTV margins of 1.1mm in LR direction, and 0.7mm in AP and SI directions were derived from the E2E tests. The dosimetric analysis revealed that a 1-mm uniform margin was sufficient to ensure the CTV dose coverage, without compromising the OAR dose tolerances. The effect of isocenter uncertainty has been estimated to be 1mm in our CBCT-guided SRS approach.

Coulomb heating behavior of fast light diclusters channeled into Si (110) direction

Coulomb heating behavior of fast light diclusters channeled into Si (110) direction

Evaluating deviations in prostatectomy patients treated with IMRT

AimTo evaluate the deviations in prostatectomy patients treated with IMRT in order to calculate appropriate margins to create the PTV. BackgroundDefining inappropriate margins can lead to underdosing in target volumes and also overdosing in healthy tissues, increasing morbidity. Material and methods223 CBCT images used for alignment with the CT planning scan based on bony anatomy were analyzed in 12 patients treated with IMRT following prostatectomy. Shifts of CBCT images were recorded in three directions to calculate the required margin to create PTV. Results and discussionThe mean and standard deviation (SD) values in millimetres were −0.05±1.35 in the LR direction, −0.03±0.65 in the SI direction and −0.02±2.05 the AP direction. The systematic error measured in the LR, SI and AP direction were 1.35mm, 0.65mm, and 2.05mm with a random error of 2.07mm; 1.45mm and 3.16mm, resulting in a PTV margin of 4.82mm; 2.64mm, and 7.33mm, respectively. ConclusionWith IGRT we suggest a margin of 5mm, 3mm and 8mm in the LR, SI and AP direction, respectively, to PTV1 and PTV2. Therefore, this study supports an anisotropic margin expansion to the PTV being the largest expansion in the AP direction and lower in SI.

Channeling energy loss and dechanneling of He along axial and planar directions of Si

In the present work, the energy loss and the dechanneling of He ions in the energy of 1.5MeV and 2MeV along the 〈100〉 and 〈110〉 axial directions as well as the {100} and {110} planar directions of Si were studied by the simulation of the channeling Rutherford backscattering spectra. The simulation was done based on the considerations that a fraction of the aligned beam enters the sample as a random component due to the ions scattering from the surface, and the dechanneling starts at the greater penetration depths, xDech. It was presumed that the dechanneling process follows a simple exponential law with a parameter λ which is proportional to the half-thickness. The Levenberg–Marquardt algorithm was used to set the best parameters of energy loss ratio, xDech and λ. The experimental results are well reproduced by this simulation. Differences between various axial and planar channels in the Si crystal and their influence on the energy loss ratio and dechanneling of He ions are described. Moreover, the energy dependence of energy loss ratio and dechanneling of He ions were investigated. It is shown that the dechanneling behavior of ions depends on the energy and energy loss of the ions along a channel. The channeled to random energy loss increases by decreasing ions energy.

Coverage‐based treatment planning to accommodate delineation uncertainties in prostate cancer treatment

To compare two coverage-based planning (CP) techniques with fixed margin-based (FM) planning for high-risk prostate cancer treatments, with the exclusive consideration of the dosimetric impact of delineation uncertainties of target structures and normal tissues. In this work, 19-patient data sets were involved. To estimate structure dose for each delineated contour under the influence of interobserver contour variability and CT image quality limitations, 1000 alternative structures were simulated by an average-surface-of-standard-deviation model, which utilized the patient-specific information of delineated structure and CT image contrast. An IMRT plan with zero planning-target-volume (PTV) margin on the delineated prostate and seminal vesicles [clinical-target-volume (CTV prostate) and CTVSV] was created and dose degradation due to contour variability was quantified by the dosimetric consequences of 1000 alternative structures. When D98 failed to achieve a 95% coverage probability objective D98,95 ≥ 78 Gy (CTV prostate) or D98,95 ≥ 66 Gy (CTVSV), replanning was performed using three planning techniques: (1) FM (PTV prostate margin = 4,5,6 mm and PTVSV margin = 4,5,7 mm for RL, PA, and SI directions, respectively), (2) CPOM which optimized uniform PTV margins for CTV prostate and CTVSV to meet the D98,95 objectives, and (3) CPCOP which directly optimized coverage-based objectives for all the structures. These plans were intercompared by computing percentile dose-volume histograms and tumor-control probability/normal tissue complication probability (TCP/NTCP) distributions. Inherent contour variability resulted in unacceptable CTV coverage for the zero-PTV-margin plans for all patients. For plans designed to accommodate contour variability, 18/19 CP plans were most favored by achieving desirable D98,95 and TCP/NTCP values. The average improvement of probability of complication free control was 9.3% for CPCOP plans and 3.4% for CPOM plans. When the delineation uncertainties need to be considered for prostate patients, CP techniques can produce more desirable plans than FM plans for most patients. The relative advantages between CPCOP and CPOM techniques are patient specific.

The Schottky barrier modulation at PtSi/Si interface by strain and structural deformation

We show, using density functional theory (DFT) calculations, that the Schottky barrier height (SBH) at the PtSi/Si interface can be lowered by uniaxial strain applied not only on Si but also on PtSi. The strain was applied to the (001) direction of Si and PtSi, which is normal for the interface. The SBH of the hole is lowered by 0.08 eV under 2% of tensile strain on Si and by 0.09 eV under 4 % of compressive strain on PtSi. Because the SBH at PtSi/Si contact is approximately 0.2 eV, this amount of reduction can significantly lower the resistance of the PtSi/Si contact; thus applying uniaxial strain on both PtSi and Si possibly enhances the performance of Schottky barrier field effect transistors. Theoretical models of SB formation and conventional structure model are evaluated. It is found that Pt penetration into Si stabilizes the interface and lowers the SBH by approximately 0.1 eV from the bulk-terminated interface model, which implies that conventionally used bulk-terminated interface models have significant errors. Among the theoretical models of SB formation, the model of strong Fermi level pining adequately explains the electron transfer phenomena and SBH, but it has limited ability to explain SBH changes induced by changes of interface structure.

SU‐E‐J‐33: Comparison Between Soft Tissue Alignment and Bony Alignment for Pancreatic Cancer Radiotherapy

PurposeAn IGRT modality for pancreatic cancer treatment with dose escalation at our institution is in‐room daily CT imaging. The purpose of this study is to assess the difference between soft tissue alignment and bony alignment for pancreatic tumor localization.MethodsEighteen patients with pancreatic tumors who underwent IMRT treatment with an inspiration breath‐hold technique between July 2012 and February 2015 are included in this study. Prior to each treatment, a CT scan was acquired. The CT image guidance started with auto‐alignment to either the bony anatomy (vertebral bodies) or fiducials (for the six patients with the stent in/near the tumor) and then, when necessary, manual adjustments were made based on soft tissue alignment using clinical software (CT‐Assisted Targeting system). The difference between soft tissue alignment and bony/fiducial alignment was evaluated.ResultsOf all 380 treatments, manual adjustment was made in 225 treatments, ranging from 11% (3 treatments out of 28) to 96% (27 treatments out of 28) per patient. The mean of the difference between soft tissue alignment and bony/fiducial alignment per patient ranged from −3.6 to 0.3 mm, −1.5 to 2.8 mm, and −3.3 to 3.4 mm in the AP, SI, and RL directions, respectively. The maximum difference over all treatments was −9.5, −14.6, and −14.6 mm in the AP, SI, and RL directions, respectively.ConclusionAbout 60% of the time, manual adjustment based on soft tissue alignment was required. The extent of manual adjustment was usually small but varied significantly from patient to patient. The ultimate goal of the IGRT modality using daily CT imaging is not to fully cover the target but to spare organs‐at‐risk as much as possible to avoid them moving into higher dose gradients than accepted in the treatment plan. To this end, manual adjustment based on soft tissue alignment is critically important.

TU‐CD‐BRA‐06: 3D Reconstruction From 2D CineMRI Orthogonal Slices: A Feasibility Study

Purpose:The ideal image guidance strategy to acquire complete spatio‐temporal information for the patients during therapy. MRI‐Linacs come close to this ideal, but there are spatial and temporal trade‐offs. Several authors have proposed simultaneous orthogonal images as a guidance strategy for MRI‐Linac. In order to estimate the missing 3D information from the 2D orthogonal images we present a feasibility study on the reconstruction of a 3D volume directly from 2D orthogonal CineMRI slices for MRI‐guided treatment.Methods:A 4DCT XCAT lung tumor phantom was generated in two respiratory phases (i.e. exhale and inhale) with 3cm diaphragm motion. We simulated the cine acquisition by extracting sagittal and coronal orthogonal slices from the inhale XCAT phantom. Then, we performed DIR between the selected slices at the inhale phase with the corresponding ones at exhale. An interpolation of the derived motion field was performed in the RL, AP and SI directions, thus obtaining a 3D motion field that was used to warp the exhale phase and obtain a 3D estimation of the inhale phase (i.e. estimated_inhale volume). As validation we compared the estimated_inhale volume with the inhale phase (i.e. ground truth). We also applied the method on one CineMRI lung patient image set, where inter‐leaved sagittal/coronal cineMRI images were available.Results:The estimated_inhale volume resulted comparable with the ground truth. The distance between landmarks identified in the two respiratory phases was quantified as 24.8±7.2mm for exhale/estimated _inhale, vs.21.9±9.8mm for exhale/inhale. Tumor motion between exhale and estimated_inhale was 28.3mm, consistent with the measured diaphragm motion (i.e. 30mm). The patient results confirmed that the estimated_inhale volume compensated for organ motion (i.e. diaphragm distance between inhale and estimated_inhale was within 4.7±2.4mm).Conclusion:The method provided a framework for the volumetric reconstruction from 2D orthogonal slices. The application to a patient case showed the capability to account for organ motion.

SU‐E‐T‐729: The Dosimetric Impact of Moving Small Size Lung Tumor Using Helical Tomotherapy

Purpose:Respiration during radiotherapy irradiation causes dose delivery uncertainty to the lung tumor. This phantom study was designed to investigate the dosimetric impact of tumor motion during respiration with TomoTherapy treatment.Methods:Dynamic thorax phantom (CIRS. Inc, Norfolk, VA), was used to mimic small size lung tumors (1, 2, and 3cm in diameter) motion during respiration. CT images of tumors under static condition were imported into TomoTherapy Hi‐Art system. Plans were calculated with different jaw sizes for each size of tumor. Dose measurement was performed under both static and respiratory simulation produced by dynamic thorax phantom. Our respiratory simulation setting was chosen due to more compatible with clinical breathing cycle pattern including 1cm amplitude movement in SI direction, 4s breathing period and cos6 breathing pattern. Two‐dimensional dose of DQA plans were measured by EBT3 films. The point dose was measured in the center of each tumor using A1SL ion chamber.Results:The point dose of 1 cm motion tumor was 9% higher than plan dose, and decreased variation by increasing jaw size. The point dose of 1 cm and 2 cm motion tumors were greater than static tumors, but the results of 3 cm tumor were in contrast. Dose coverage was improved by increasing tumor size and jaw size. The width of 50% dose level of motion tumors on horizontal 2D dose profile were similar with widths of static tumor, but dose distribution shifted toward inferior direction. The widths of 60% dose level of motion tumors were smaller than widths of static tumor and difference decreased by increasing tumor and jaw size.Conclusion:Small size motion tumor has greater dose difference than bigger tumors. Large jaw size leads to more penumbra but provides better dose coverage. Larger margin was suggested at the longitudinal superior direction to compensate the dose distribution deviation during respiration.

SU‐E‐J‐26: A Novel Technique for Markerless Self‐Sorted 4D‐CBCT Using Patient Motion Modeling: A Feasibility Study

Purpose:To develop an automatic markerless 4D‐CBCT projection sorting technique by using a patient respiratory motion model extracted from the planning 4D‐CT images.Methods:Each phase of onboard 4D‐CBCT is considered as a deformation of one phase of the prior planning 4D‐CT. The deformation field map (DFM) is represented as a linear combination of three major deformation patterns extracted from the planning 4D‐CT using principle component analysis (PCA). The coefficients of the PCA deformation patterns are solved by matching the digitally reconstructed radiograph (DRR) of the deformed volume to the onboard projection acquired. The PCA coefficients are solved for each single projection, and are used for phase sorting. Projections at the peaks of the Z direction coefficient are sorted as phase 1 and other projections are assigned into 10 phase bins by dividing phases equally between peaks. The 4D digital extended‐cardiac‐torso (XCAT) phantom was used to evaluate the proposed technique. Three scenarios were simulated, with different tumor motion amplitude (3cm to 2cm), tumor spatial shift (8mm SI), and tumor body motion phase shift (2 phases) from prior to on‐board images. Projections were simulated over 180 degree scan‐angle for the 4D‐XCAT. The percentage of accurately binned projections across entire dataset was calculated to represent the phase sorting accuracy.Results:With a changed tumor motion amplitude from 3cm to 2cm, markerless phase sorting accuracy was 100%. With a tumor phase shift of 2 phases w.r.t. body motion, the phase sorting accuracy was 100%. With a tumor spatial shift of 8mm in SI direction, phase sorting accuracy was 86.1%.Conclusion:The XCAT phantom simulation results demonstrated that it is feasible to use prior knowledge and motion modeling technique to achieve markerless 4D‐CBCT phase sorting.National Institutes of Health Grant No. R01‐CA184173 Varian Medical System

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.

TH-CD-204-01: FEATURED PRESENTATION and BEST IN PHYSICS (JOINT IMAGING-THERAPY): Novel SG-KS-4D-MRI Sequence Reduces 4D Rebinning Artifacts and Improves GTV Contouring Consistency for Pancreatic Cancer Patients

Purpose: Dynamic magnetic resonance imaging (MRI) has been used to characterize tumor motion but real time acquisition has been limited to 2-dimensions. Methods have been developed to reconstruct four-dimensional MRI (4D-MRI) based on time-stamped 2D images or 2D K-space data. These methods suffer from anisotropic resolution and rebinning artifacts. We have developed a self-gating based K-space sorted 4D-MRI (SG-KS-4D-MRI) method to overcome these limitations and in this study apply it to monitoring organ motion of pancreatic cancer patients. Methods: Ten patients were imaged using 4D-CT, cine 2D-MRI and the SG-KS-4D-MRI method, which is a spoiled gradient recalled echo (GRE) sequence with 3D radial-sampling K-space projections and 1D projection-based self-gating. Tumor volumes were drawn at the end of exhalation phases in the 4D-MRI and 4D-CT, and mapped to the other phases using deformable registration. The tumor volumes and motion trajectories were compared. Results: An isotropic resolution of 1.6 mm was achieved in the SG-KS-4D-MRI images, which showed superior soft tissue contrast to 4D-CT and appeared to be free of rebinning artifacts. SG-KS-4D-MRI was able to detect out-of-plane tumor motion and showed good correlation with 4D-CT and cine 2D-MRI in superior-inferior direction with a correlation coefficient of 0.91±0.06 and 0.93±0.03, respectively. The average standard deviation of GTV (GTV_σ) calculated from ten breathing phases were 0.81 cc and 1.02 cc for SG-KS-4D-MRI and 4D-CT (p=0.004) respectively. Conclusion: A novel SG-KS-4D-MRI acquisition method capable of reconstructing rebinning-artifact-free high resolution 4D-MRI images was used to quantify pancreas tumor motion. The resultant pancreatic tumor motion trajectories better agreed with 2D-cine-MRI and 4D-CT in the SI direction than the other 2 directions due to smaller motions in those directions. The pancreatic tumor volumes derived using SG-KS-4D-MRI were significantly more consistent than those from the 4D-CT.This work is supported in part by NIH grant 1R03CA173273-01. This study is supported in part by NIH 1R03CA173273

TH-AB-303-09: Gated Prostate Radiotherapy: Accuracy and Dosimetric Results From First Clinical Study with Kilovoltage Intrafraction Monitoring

Purpose: The purpose of this study is to investigate the localisation accuracy and dosimetric impact of a new real-time IGRT system, kilovoltage intrafraction monitoring (KIM), in a gated prostate cancer radiotherapy clinical trial. Methods: KIM uses kV fluoroscopy to monitor, in real-time, the 3D position of radio-opaque markers implanted into the prostate target. The real-time target position is used to guide the treatment: if the prostate moves outside the tolerance (displacement exceeding 3mm for 5 seconds) the beam is paused and the patient is repositioned. Localisation accuracy is calculated offline by comparing using triangulation when markers are visible in both kV and MV images (ground truth) with the KIM determined positions. Dosimetric accuracy is calculated for fractions with gating events by comparing reconstructed delivered dose (with or without simulated gating events) against planned doses. Results: Seven patients have been recruited to the KIM study, with 4 patients completed treatment. Localisation accuracy of KIM from the 126 fractions to date is 0.1±0.5, 0.3±0.3, and −0.5±0.4 mm in the LR, SI and AP directions, respectively. Prostate gating and couch shift correction was applied in 15 fractions, which reduced the mean prostate position error from 3.9±1.4 mm (simulated no gating) to 2.0±1.2 mm. Delivered target doses (PTV D95%) were closer to planned with gating −1.4% compared to simulated no gating 3.2%. Delivered OAR doses were also closer to planned with gating compared to simulated no gating, mean (range) differences were respectively: rectum V65% −3.5 (−9.4, 5.7) & −5.0 (−11.2,18.7); and bladder V65% 3.2 (−0.9, 25.3) & 4.7 (−1.0, 30.5). Conclusion: KIM gating for prostate radiotherapy has been clinically implemented with sub-millimeter accuracy and improved agreement between the planned and delivered dose distributions. The KIM technology has wide-scale applicability as it is implemented on a standard linear accelerator with little modification. Varian Collaborative Research Agreement; Cancer Australia; NHMRC Australia

TH‐AB‐BRB‐12: A Novel 2D Expansion Technique Based On Beam Geometry for Generating Margins

Purpose:Current practice of using 3D margins in radiotherapy with high‐energy photon beams provides larger‐than‐required target coverage. Negligible dose changes for small CTV displacements in the beam direction allow for the design of 2D‐based CTV‐PTV margins. We investigate the impact of a novel 2D margin concept for prostate radiotherapy treatments.Methods:Our implementation of 2D margins follows van Herk's (2000) margin recipe by considering only geometrical uncertainties perpendicular to the incident beam direction. The union of all beam‐angle‐dependent expansions defines our PTV. Five prostate radiotherapy plans were generated using IMRT inverse planning following clinical protocols with a prescription of 74Gy in 37 fractions. Systematic uncertainties of 1.1, 1.1, 1.5mm in the LR, SI, and AP directions, respectively, and 0.9, 1.1, 1.0mm for the random uncertainties, were used. A verification tool was used to simulate the effects of systematic and random errors, using a population of 10,000 identical geometries. The fraction of the population that satisfies or violates a certain dose or volume constraint was used for comparison.Results:The median observed PTV volume reduction between the 3D and 2D margins is 7.85% (range, 7.14–8.29%). Using the verification tool, all CTVs had close to 100% of the population satisfying D98% > 95% of the prescribed dose. When applying the verification tool to analyse the rectal doses delivered, a median relative reduction of 1.05% (range, 0.66–6.17%) of the population was observed for D2% above 70Gy; similarly for D2% above 74Gy, a median relative reduction of 31.7% (range, 13.3–52.6%) was observed.Conclusion:We are able to ascertain sufficient dose coverage using our 2D margin concept for planning whilst lowering dose to nearby structures, though the amount of sparing depends largely on the patients’ anatomy. With the coverage observed using our novel technique, we believe additional room exists for sparing dose to target‐adjacent OARs.Research at The Institute of Cancer Research is supported by Cancer Research UK under Programme C33589/A19727. We acknowledge NHS funding to the NIHR Biomedical Research Centre at The Royal Marsden and The Institute of Cancer Research.

TU-AB-303-06: Does Online Adaptive Radiation Therapy Mean Zero Margin for Intermediate-Risk Prostate Cancer? An Intra-Fractional Seminal Vesicles Motion Analysis

Purpose: To provide benchmark for seminal vesicles (SVs) margin selection to account for intra-fractional motion; and to investigate the effectiveness of two motion surrogates in predicting intra-fractional SV underdosage. Methods: 9 prostate SBRT patients were studied; each has five pairs of pre-treatment and post-treatment cone-beam CTs (CBCTs). Each pair of CBCTs was registered based on fiducial markers in the prostate. To provide “ground truth” for coverage evaluation, all pre-treatment SVs were expanded with isotropic margin of 1,2,3,5 and 8mm, and their overlap with post-treatment SVs were used to quantify intra-fractional coverage. Two commonly used motion surrogates, the center-of-mass (COM) and the border of contour (the most distal points in SI/AP/LR directions) were evaluated using Receiver-Operating Characteristic (ROC) analyses for predicting SV underdosage due to intra-fractional motion. Action threshold of determining underdosage for each surrogate was calculated by selecting the optimal balancing between sensitivity and specificity. For comparison, margin for each surrogate was also calculated based on traditional margin recipe. Results: 90% post-treatment SV coverage can be achieved in 47%, 82%, 91%, 98% and 98% fractions for 1,2,3,5 and 8mm margins. 3mm margin ensured the 90% intra-fractional SV coverage in 90% fractions when prostate was aligned. The ROC analysis indicated the AUC for COM and border were 0.88 and 0.72. The underdosage threshold was 2.9mm for COM and 4.1mm for border. The Van Herk’s margin recipe recommended 0.5, 0 and 1.8mm margin in LR, AP and SI direction based on COM and for border, the corresponding margin was 2.1, 4.5 and 3mm. Conclusion: 3mm isotropic margin is the minimum required to mitigate the intra-fractional SV motion when prostate is aligned. ROC analysis reveals that both COM and border are acceptable predictors for SV underdosage with 2.9mm and 4.1mm action threshold. Traditional margin calculation is less reliable for this application. This work is partially supported a master research grant from Varian Medical Systems.

SU‐F‐BRB‐01: How Effective Is Abdominal Compression at Reducing Lung Motion? An Analysis Using Deformable Image Registration Within Different Sub‐Regions of the Lung

Purpose:To investigate the effectiveness of employing abdominal compression (AC) in reducing motion for the target region and sub‐regions of the lung as part of the planning process for radiation therapy.Methods:Fourteen patients with early lung cancer were scanned with 4DCT and it was determined that target motion exceeded our institutional limit of > 8 mm motion and received a repeat 4DCT with AC. For each 4DCT, deformable image registration (DIR) was used to map the max inhale to the max exhale phase to determine the deformation vector fields (DVF). DIR was performed with Morphons and Demons algorithms. The mean DVF was used to represent that sub‐region for each patient. The magnitudes of the mean DVF were quantified for the target and 12 sub‐regions in the AP, LR SI directions. The sub‐regions were contoured on each lung as (add prefix R or L for lung): Upper‐Anterior (UA), Upper‐Posterior (UP), Mid‐Anterior (MA), Mid‐Posterior (MP), Lower‐Anterior (LA) and Lower‐Posterior (LP).Results:The min/max SI motion for the target on the uncompressed 4DCT was 8mm/24.5 mm. The magnitude of decrease in SI was greatest in the RLP region (3.7±4.0mm) followed by target region (3.3±2.2mm) and finally the LLP region (3.0±3.5mm). The magnitude of decrease in 3D vector followed the same trend; RLP (3.5±2.2mm) then GTV (3.5±2.6mm) then LLP (2.7±3.8mm). 79% of the cases had a SI decrease of >12.5%, 43% had a SI decrease of >25% and 21% had a SI decrease of >50% as compared to the motion on the uncompressed 4DCT.Conclusion:AC is useful in reducing motion with the largest decreases observed in the lower posterior regions of the lungs. However, it should be noted that AC will not greatly decrease motion for all cases as 21% of cases did not reduce SI motion more than 12.5% of initial motion.

Adaptive motion mapping in pancreatic SBRT patients using Fourier transforms

Background and purposeRecent studies suggest that 4DCT is unable to accurately measure respiratory-induced pancreatic tumor motion. In this work, we assessed the daily motion of pancreatic tumors treated with SBRT, and developed adaptive strategies to predict and account for this motion. Materials and methodsThe daily motion trajectory of pancreatic tumors during CBCT acquisition was calculated using a model which reconstructs the instantaneous 3D position in each 2D CBCT projection image. We developed a metric (termed “Spectral Coherence,” SC) based on the Fourier frequency spectrum of motion in the SI direction, and analyzed the ability of SC to predict motion-based errors and classify patients according to motion characteristics. ResultsThe amplitude of daily motion exceeded the predictions of pre-treatment 4DCT imaging by an average of 3.0mm, 2.3mm, and 3.5mm in the AP/LR/SI directions. SC was correlated with daily motion differences and tumor dose coverage. In a simulated adaptive protocol, target margins were adjusted based on SC, resulting in significant increases in mean target D95, D99, and minimum dose. ConclusionOur Fourier-based approach differentiates between consistent and inconsistent motion characteristics of respiration and correlates with daily motion deviations from pre-treatment 4DCT. The feasibility of an SC-based adaptive protocol was demonstrated, and this patient-specific respiratory information was used to improve target dosimetry by expanding coverage in inconsistent breathers while shrinking treatment volumes in consistent breathers.

보아의 K-Pop 넘버원 댄스 핵심동작의 생체역학적 분석

Abstract The purpose of this study was to investigate biomechanical factors on key motions in K-Pop dance(BoA’sNo.1). A professional choreographer who was BoA’s K-Pop No. 1 dance participated in this study. ROMs(range of motion) of shoulder and elbow joints in AP direction were greater than other joints. Those of trunk and pelvis inML direction were the greatest of other directions. The velocity of CoG in SI direction was greater than other directions, and also max angular velocities of shoulder, elbow, knee, and hip joints in AP direction were the greatestof all directions. But ROM and angular velocity of ankle joint were very small. Max rotational powers of shoulderand knee joints were larger than other joints. Key Words ： Biomechanics, BoA’s NO.1 dance, K-Pop dance, Moment, Power * 이 논문은 2014년 제52회 한국체육학회 학술발표회에 포스터로 발표한 내용을 수정, 보완하였음을 밝힙니다.본 연구는 문화체육관광부 및 한국콘텐츠진흥원의 2014년도 문화기술연구개발지원의 연구결과로 수행됐음. * Corresponding Author : Young-Kwan Jang(Kangwon Univ.) Tel: +82-33-570-6585 email : ykjang@kangwon.ac.krReceived January 22, 2015 Revised February 10, 2015 Accepted February 12, 2015