bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐J‐106: Dose Adaptation with a Virtual 6D Couch for Frameless Brain Radiosurgery Via a Dedicated Gamma‐Ray Device
Authors: Cheung J , Braunstein S , Sneed P , McDermott M , Theodosopoulos P , Ma L 
Published: July 2016

Purpose:The couch for Gamma Knife Radiosurgery (GKSRS) is limited to translational movements. With frameless designs, patient positional rotations may become an important factor. Therefore, we investigated the effect of rotations for GKSRS and the ability to correct for these rotations with simple couch translations.Methods:Seven previously treated GKSRS patients with different disease types (tumor volumes 0.01–12cc) were selected for this study. The planning MRI images were processed in order to digitally rotate the stereotactic frame (Leksell G‐frame) to ±1, ±2, ±3, ±5, and ±10‐degrees in the transverse plane from the nominal position. These images were imported back into the clinical planning system (LGP 10.2) and dose from the original treatment plan was calculated with these rotational errors. Translation corrections for each shot based on the rotation transform matrix were applied to the plan and coverage and Paddick conformity index (PCI) were evaluated for the uncorrected and corrected plans.Results:The rotational errors resulted in large decreases in plan coverage, with some small tumors being missed completely with rotations of ±3‐degrees or more. The rotated plans resulted in an average (range) decreased coverage of 8% (0–33%), 28% (0–87%), 43% (0–100%), 57% (0–100%), and 72% (5–100%) for ±1, ±2, ±3, ±5, and ±10‐degrees, respectively. For the corrected plans, the average (range) decrease in coverage was only 1% (0–4%), even for the rotations of ±10‐degrees. The PCI differences improved as well, with the rotated plans resulting in decreased PCI of 2% (0–11%), 13% (0–32%), 22% (0–50%), 31% (1–56%), 42% (4–67%) for ±1, ±2, ±3, ±5, and ±10‐degrees, respectively, which improved to 1% for all of the corrected plans with a range from 5% decrease to 13% increase in PCI.Conclusion:The applications of simple 3D couch translations were successful in recovering rotation uncertainties up to ±10‐degrees for frameless GKSRS.
SU‐F‐J‐107: Online Adaptive VMAT Planning Based On Deformed Dose
Authors: Qiu R , Vassil A , Godley A 
Published: July 2016

Purpose:Prostate treatment with volumetric‐modulated arc therapy (VMAT) in conjunction with small PTV margins, allows the dose to the rectum and bladder to be minimized, at the potential cost of prostate coverage. Coverage can be restored by online adaptive planning. Here, the deformed planning dose is used as the goal for adaptive plan optimization.Methods:9 prostate patients with CT‐on‐Rails (CTOR) imaging were replanned using Monaco (Elekta AB, Stockholm, Sweden) with 2 VMAT arcs, and 70 Gy to 95% of the PTV. A variable margin of 4–6 mm was used. The planning CT was deformably registered to each CTOR, the resulting deformation field was then applied to morph the structures and dose to the CTORs, using ADMIRE (Elekta AB, Stockholm Sweden). The deformed dose, edited contours and CTOR were imported into Monaco, and the dose referred as a guide for plan optimization. The original treatment plan was also copied to the CTOR, keeping the center of the prostate as the isocenter, to mimic the current repositioning based therapy.Results:The deformed dose guided optimization maintained the prostate coverage and the sparing of OAR. The shifted plan was unable to do both. The mean percentage volume covered by 100% isodose line increased from 96.11±2.04 to 99.74±0.10 for prostate, and 83.48±2.63 to 94.61±0.34 for PTV by adapting the deformed dose guided optimization. PTV coverage is of some interest, as there still needs to be some margin for intra‐fraction motion. Besides, the resulting lower inter‐fraction dose variation of optimized plan implied a better dose delivery consistency.Conclusion:Using the planned dose, deformed to the daily CTOR provided a successful goal for adaptive optimization, allowing reduced margins, increased OAR sparing, and maintained prostate coverage.Godley receives research grant from Elekta.
SU‐F‐J‐109: Generate Synthetic CT From Cone Beam CT for CBCT‐Based Dose Calculation
Authors: Wang H , Barbee D , Wang W , Pennell R , Hu K , Osterman K 
Published: July 2016

Purpose:The use of CBCT for dose calculation is limited by its HU inaccuracy from increased scatter. This study presents a method to generate synthetic CT images from CBCT data by a probabilistic classification that may be robust to CBCT noise. The feasibility of using the synthetic CT for dose calculation is evaluated in IMRT for unilateral H&N cancer.Methods:In the training phase, a fuzzy c‐means classification was performed on HU vectors (CBCT, CT) of planning CT and registered day‐1 CBCT image pair. Using the resulting centroid CBCT and CT values for five classified “tissue” types, a synthetic CT for a daily CBCT was created by classifying each CBCT voxel to obtain its probability belonging to each tissue class, then assigning a CT HU with a probability‐weighted summation of the classes’ CT centroids. Two synthetic CTs from a CBCT were generated: s‐CT using the centroids from classification of individual patient CBCT/CT data; s2‐CT using the same centroids for all patients to investigate the applicability of group‐based centroids. IMRT dose calculations for five patients were performed on the synthetic CTs and compared with CT‐planning doses by dose‐volume statistics.Results:DVH curves of PTVs and critical organs calculated on s‐CT and s2‐CT agree with those from planning‐CT within 3%, while doses calculated with heterogeneity off or on raw CBCT show DVH differences up to 15%. The differences in PTV D95% and spinal cord max are 0.6±0.6% and 0.6±0.3% for s‐CT, and 1.6±1.7% and 1.9±1.7% for s2‐CT. Gamma analysis (2%/2mm) shows 97.5±1.6% and 97.6±1.6% pass rates for using s‐CTs and s2‐CTs compared with CT‐based doses, respectively.Conclusion:CBCT‐synthesized CTs using individual or group‐based centroids resulted in dose calculations that are comparable to CT‐planning dose for unilateral H&N cancer. The method may provide a tool for accurate dose calculation based on daily CBCT.
SU‐F‐J‐113: Multi‐Atlas Based Automatic Organ Segmentation for Lung Radiotherapy Planning
Authors: Kim J , Han J , Ailawadi S , Baker J , Hsia A , Xu Z , Ryu S 
Published: July 2016

Purpose:Normal organ segmentation is one time‐consuming and labor‐intensive step for lung radiotherapy treatment planning. The aim of this study is to evaluate the performance of a multi‐atlas based segmentation approach for automatic organs at risk (OAR) delineation.Methods:Fifteen Lung stereotactic body radiation therapy patients were randomly selected. Planning CT images and OAR contours of the heart ‐ HT, aorta ‐ AO, vena cava ‐ VC, pulmonary trunk ‐ PT, and esophagus – ES were exported and used as reference and atlas sets. For automatic organ delineation for a given target CT, 1) all atlas sets were deformably warped to the target CT, 2) the deformed sets were accumulated and normalized to produce organ probability density (OPD) maps, and 3) the OPD maps were converted to contours via image thresholding. Optimal threshold for each organ was empirically determined by comparing the auto‐segmented contours against their respective reference contours. The delineated results were evaluated by measuring contour similarity metrics: DICE, mean distance (MD), and true detection rate (TD), where DICE=(intersection volume/sum of two volumes) and TD = {1.0 ‐ (false positive + false negative)/2.0}. Diffeomorphic Demons algorithm was employed for CT‐CT deformable image registrations.Results:Optimal thresholds were determined to be 0.53 for HT, 0.38 for AO, 0.28 for PT, 0.43 for VC, and 0.31 for ES. The mean similarity metrics (DICE[%], MD[mm], TD[%]) were (88, 3.2, 89) for HT, (79, 3.2, 82) for AO, (75, 2.7, 77) for PT, (68, 3.4, 73) for VC, and (51,2.7, 60) for ES.Conclusion:The investigated multi‐atlas based approach produced reliable segmentations for the organs with large and relatively clear boundaries (HT and AO). However, the detection of small and narrow organs with diffused boundaries (ES) were challenging. Sophisticated atlas selection and multi‐atlas fusion algorithms may further improve the quality of segmentations.
SU‐F‐J‐118: On‐Treatment 4D CT Reconstruction From Planning 4D CT Using Linear Amplitude Scaling
Authors: Park S , Jung J , Kim J , Yeo I , Yi B 
Published: July 2016

Purpose:To reconstruct on‐treatment 4D CT images from planning 4D CT images by adapting deformation vector field (DVF) of the planning CT to the on‐treatment condition, while the adaptation is based on the scaling of two amplitudes that are motion characteristics at the times of treatment and planning CT acquisition, respectively.Methods:An anthropomorphic digital phantom (XCAT) was used to generate 4D image sets with 1‐cm and 2‐cm tumor motions simulating conditions of planning CT and treatment, respectively. DVFs were acquired from the planning CT image set. The DRR images were acquired simulating setup kV images from the two CT image sets. On the DRR images, tumor positions and their motion amplitudes were quantified. The DVFs were scaled linearly by the amplitude ratio between the treatment and the planning CT times, assuming the elasticity of lung. The scaled DVFs were used to resample the planning 4D CT images generating on‐treatment 4D CT images. The on‐treatment 4D CT images thus acquired were compared with the reference on‐treatment images (2‐cm motion).Results:The resampled images showed good agreement within 1 mm residual errors with the reference images. The normalized cross correlation was 0.995.Conclusion:A linear model of amplitude scaling was developed to reconstruct on‐treatment 4D CT images from planning 4D CT images using the setup KV images acquired during treatment. The model was validated on a digital phantom. For the model to fully work, a further research needs to be followed, that aims at utilizing a phase‐specific CT image set that is geometrically identical between pretreatment and treatment conditions.
SU‐F‐J‐119: Pilot Study On the Location‐Based Lung Motion Assessment
Authors: Lee TK , Ewald A 
Published: July 2016

Purpose:In most of lung treatment cases with various radiotherapy beam modalities, 4DCT images are obtained in order to define ITV. ITV is defined with the signal from motion monitoring system, e.g. RPM. However, the signal is not consistent with tumor motion because it varies with location, its size, age, gender, etc. In the present study, the location‐based motion assessment is presented.Methods:4DCT images of 70 patients were reviewed: 28‐left‐lung and 42‐right‐lung patients; 36‐female and 34‐male patients; the age range of 51.2–89.9; tumor‐size range of 0.75–9.50cm with 25% of these adherent to bony‐anatomy. Philips Big‐Bore Simulation CT and RPM systems were used. The study was performed as follows. First, RPM signal and tumor motion in superior‐inferior direction was compared. Second, the tumor size and its motion amplitude in all directions were measured at multiple locations. Third, the average tumor motion was calculated to assess general motion amplitudes at various locations.Results:RPM amplitude is not consistent with lung tumor motion amplitude. The tumors of similar sizes at similar location present various motion amplitude up to 1.1cm difference, but in average, the standard deviation was <0.5cm. Almost regardless of tumor sizes, the tumor motion was greatest at lower lobe location (>=1.0cm), and the smallest at upper lobe location and when adherent to bony‐anatomy (<=0.5cm).Conclusion:The tumor size affects the motion amplitude less than does the tumor location. However, as the study results indicate that tumor motion has noticeable variation and so further study with more patient cases is needed. Also, for the same patient, the RPM signal presents instability of breathing, and clinically the patient with the instability of RPM breathing of <=10% is selected for respiratory‐gated radiotherapy and ∼25% of patients under current study was treated. Patient‐specific motion‐uncertainty margins are considered to be added following further study.
SU‐F‐J‐124: Reduction in Dosimetric Impact of Motion Using VMAT Compared to IMRT in Hypofractionated Prostate Cancer Patients
Authors: Ravindranath B , Xiong J , Happersett L , Mageras G , Zhang P , Hunt M 
Published: July 2016

Purpose:To quantify and compare the dosimetric impact of motion management correction strategies during VMAT and IMRT for hypofractionated prostate treatment.Methods:Two arc VMAT and 9 field IMRT plans were generated for two prostate cancer patients undergoing hypofractionated radiotherapy (7.5Gy × 5 and 8Gy × 5). 212 motion traces were retrospectively extracted from treatment records of prostate cancer patients with implanted Calypso beacons. Dose to the CTV and normal tissues was reconstructed for each trace and plan taking into account the actual treatment delivery time. Following motion correction scenarios were simulated: (1) VMAT plan – (a) No correction, (b) correction between arcs, (c) correction every 20 degrees of gantry rotation and (2) IMRT plan ‐ (a) No correction,(b) correction between fields. Two mm action threshold for position correction was assumed. The 5–95% confidence interval (CI) range was extracted from the family of DVHs for each correction scenario.Results:Treatment duration for 8Gy plan (VMAT vs IMRT) was 3 vs 12 mins and for 7.5Gy plan was 3 vs 9 mins. In the absence of correction, the VMAT 5–−95% CI dose spread was, on average, less than the IMRT dose spread by 2% for CTVD95, 9% for rectalwall (RW) D1cc and 9% for bladderwall (BW) D53. Further, VMAT b/w arcs correction strategy reduced the spread about the planned value compared to IMRT b/w fields correction by: 1% for CTVD95, 2.6% for RW1cc and 2% for BWD53. VMAT 20 degree strategy led to greater reduction in dose spread compared to IMRT by: 2% for CTVD95, 4.5% for RW1cc and 6.7% for BWD53.Conclusion:In the absence of a correction strategy, the limited motion during VMAT's shorter delivery times translates into less motion‐induced dosimetric degradation than IMRT. Performing limited periodic motion correction during VMAT can yield excellent conformity to planned values that is superior to IMRT.This work was partially supported by Varian Medical Systems
SU‐F‐J‐134: Evaluation of Deformation Field Accuracy Using Regional Rigid Registrations with Variable Size
Authors: Ahunbay E , Li X 
Published: July 2016

Purpose:How to quickly assess the uncertainty in the Deformation Field (DF) generated from Deformable Image Registration (DIR) over the imaged anatomy is a major issue. Here we introduce a method to determine the DF uncertainty using local rigid registrations of varying box size.Methods:A series of 6‐degree rigid registrations are performed with a cubic ROI centered on the voxel of the interest. The size of the registration box is varied from a large value, e.g. 30mm to 3mm. The translation vector obtained from the registration of the largest box is assumed to be most reliable and the reliability of the registrations with smaller regions is assumed to be good as long as the variation in the translation vector, as the box size is reduced, is less than the reduction amount in the box size at each step. In this way a smallest reliable box (SRB) size is determined. A distance uncertainty (DU) is calculated for each voxel based on (1) half size of SRB and (2) the magnitude difference between the SRB translation vector to the voxel's DF. This DU is compared to other DIR reliability measures such as Jacobian determinant and root mean square.Results:The DU for selected voxels was found to agree with those expected from various organ types. For example, mean DU from the voxels in rectum and bladder was 8.4 and 8.9mm respectively, while the DU of the mean femoral head was 2.2mm. 88% of voxels with small DU (<3mm) resulted in reliable Jacobian determinant range (0.5–2), while DU>5mm voxels had 69% of voxels in this range.Conclusion:A method to assess DIR reliability is introduced. The method's ability to provide uncertainty information in terms of distance could be an advantage over other measures such as Jacobian or intensity difference.
SU‐F‐J‐137: Intrafractional Change of the Relationship Between Internal Fiducials and External Breathing Signal in Pancreatic Cancer Stereotactic Body Radiation Therapy
Authors: Pettersson N , Murphy J , Simpson D , Cervino L 
Published: July 2016

Purpose:The use of respiratory gating for management of breathing motion during stereotactic body radiation therapy (SBRT) relies on a consistent relationship between the breathing signal and the actual position of the internal target. This relationship was investigated in patients treated for pancreatic cancer.Methods:Four patients with pancreatic cancer undergoing SBRT that had implanted fiducials in the tumor were included in this study. Treatment plans were generated based on the exhale phases (30–70%) from the pre‐treatment 4DCT. The margin between the internal target volume (ITV) and the planning target volume was three mm. After patient setup using cone‐beam CT, simultaneous fluoroscopic imaging and breathing motion monitoring were used during at least three breathing cycles to verify the fiducial position and to optimize the gating window. After treatment, fluoroscopic images were acquired for verification purposes and exported for retrospective analyses. Fiducial positions were determined using a template‐matching algorithm. For each dataset, we established a linear relationship between the fiducial position and the anterior‐posterior (AP) breathing signal. The relationships before and after treatment were compared and the dose distribution impact evaluated.Results:Seven pre‐ and post‐treatment fluoroscopic pairs were available for fiducial position analyses in the superior‐inferior (SI) and left‐right (LR) directions, and five in the AP direction. Time between image acquisitions was typically six to eight minutes. An average absolute change of 1.2±0.7 mm (range: 0.1–1.7) of the SI fiducial position relative to the external signal was found. Corresponding numbers for the LR and AP fiducial positions were 0.9±1.0 mm (range: 0.2–3.0) and 0.5±0.4 mm (range: 0.2–1.2), respectively. The dose distribution impact was small in both the ITV and organs‐at‐risk.Conclusion:The relationship change between fiducial position and external breathing signal has been observed to be about 1 mm in four pancreas SBRT patients, leading to small dose distribution impact.Pettersson and Cervino are funded by a Varian Medical Systems grant.
SU‐F‐J‐140: Using Handheld Stereo Depth Cameras to Extend Medical Imaging for Radiation Therapy Planning
Authors: Jenkins C , Xing L , Yu S 
Published: July 2016

Purpose:A correct body contour is essential for the accuracy of dose calculation in radiation therapy. While modern medical imaging technologies provide highly accurate representations of body contours, there are times when a patient's anatomy cannot be fully captured or there is a lack of easy access to CT/MRI scanning. Recently, handheld cameras have emerged that are capable of performing three dimensional (3D) scans of patient surface anatomy. By combining 3D camera and medical imaging data, the patient's surface contour can be fully captured.Methods:A proof‐of‐concept system matches a patient surface model, created using a handheld stereo depth camera (DC), to the available areas of a body contour segmented from a CT scan. The matched surface contour is then converted to a DICOM structure and added to the CT dataset to provide additional contour information. In order to evaluate the system, a 3D model of a patient was created by segmenting the body contour with a treatment planning system (TPS) and fabricated with a 3D printer. A DC and associated software were used to create a 3D scan of the printed phantom. The surface created by the camera was then registered to a CT model that had been cropped to simulate missing scan data. The aligned surface was then imported into the TPS and compared with the originally segmented contour.Results:The RMS error for the alignment between the camera and cropped CT models was 2.26 mm. Mean distance between the aligned camera surface and ground truth model was −1.23 +/−2.47 mm. Maximum deviations were < 1 cm and occurred in areas of high concavity or where anatomy was close to the couch.Conclusion:The proof‐of‐concept study shows an accurate, easy and affordable method to extend medical imaging for radiation therapy planning using 3D cameras without additional radiation.Intel provided the camera hardware used in this study.
SU‐F‐J‐143: Initial Assessment of Image Quality of An Integrated MR‐Linac System with ACR Phantom
Authors: Wang J , Yung J , Kadbi M , Ding Y , Fuller C , Ibbott G 
Published: July 2016

Purpose/Objective(s):To assess the image quality of an integrated MR‐Linac system and compare with other MRI systems that are primarily used for diagnostic purposes.Materials/Methods:An ACR MRI quality control (QC) phantom was used to evaluate the image quality of a fully integrated 1.5T MRI‐Linac system recently installed at our institution. This system has a new split magnet design which gives the magnetic field strength of 1.5T. All images were acquired with a set of phased‐array surface coils which are designed to have minimal attention of radiation beam. The anterior coil rests on a coil holder which keeps the anterior coil's position consistent for QA purposes. The posterior coil is imbedded in the patient couch. Multiple sets of T1, T2/PD images were acquired using the protocols as prescribed by the ACR on three different dates, ranging 3 months apart.Results:The geometric distortion are within 0.5 mm in the axial scans and within 1mm in the saggital (z‐direction) scans. Slice thickness accuracy, image uniformity, ghosting ratio, high contrast detectability are comparable to other 1.5T diagnostic MRI scanners. The low‐contrast object detectability are lower comparatively, which is a result of using the body array coil. Additionally, the beam's‐eye‐view images (oblique coronal and saggital images) have minimal geometric distortion at all linac gantry angles tested. No observable changes or drift in image quality is found from images acquired 3 month apart.Conclusion:Despite the use of a body array surface coil, the image quality is comparable to that of an 1.5T MRI scanner and is of sufficient quality to pass the ACR MRI accreditation program. The geometric distortion of the MRI system of the integrated MR‐Linac is within 1mm for an object size similar to the ACR phantom, sufficient for radiation therapy treatment purpose.The authors received corporate sponsored research grants from Elekta which is the vendor for the MR‐Linac evaluated in this study.