bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐I‐101: A Parallel Implementation for Fast Deformable Image Registration of Large Data Sets
Authors: Zhang L , Zhang Y , Mohan R , Dong L
Published: July 2008

Purpose: One major obstacle for using deformable image registration for online or near real‐time applications is its high computational cost. The goal of this study is to implement a practical parallel computing technique for image intensity‐based deformable registration of relatively large data sets. Method and Materials: Taking advantage of the locality characteristic of the deformed images, deformable image registration can be parallelized by dividing the entire volume into smaller sub‐volumes. We implemented a parallel solution with the single‐program‐multiple‐data (SPMD) programming model in a cluster. The cluster is composed of one lead computer and 12 nodes. To ensure continuity at boundaries of sub‐volumes, we added an overlapping volume, which became a computational overhead. We proposed two techniques to reduce the overlapping volume by applying pre‐registration during the coarse levels of a multi‐resolution approach, and by handling the boundary condition carefully when applying the smoothing filter during registration. The baseline data for comparison was the deformation result from one CPU. Results were compared in three difficult cases with large deformation and large data set. The scalability was also analyzed. Results: 8‐1 nodes appears to be enough to handle each case. Four overlapping slices combined with pre‐registration at coarse level were able to get the correct deformation field at the boundary of each sub‐volumes even in the presence of relatively large deformations. Computing times were 20.5s, 44.4s, and 76.5s for a prostate case (matrix size: 294*237*62), a head & neck case (361*414*87), and a breast case (465*371*157), respectively. The same data sets required 54.5s, 150.2s, and 331.6s to compute on a single CPU, respectively. Conclusion: We have implemented an effective parallel solution for deformable image registration which can handle large data sets in a short time.
SU‐GG‐I‐102: Evaluation of Nine Similarity Metrics for Intensity‐Based CT‐To‐CBCT Prostate Registrations
Authors: Kim J , Hammoud R , Chetty I , Pradhan D , Movsas B
Published: July 2008

Purpose: The prostate can be localized automatically on daily cone‐beam CT (CBCT) images by means of intensity‐based 3D/3D image registrations. The goal of this study is to evaluate nine different similarity metrics for the best localization accuracy. Method and Materials: Seven prostate patients were retrospectively selected with natural prostate calcifications, which resulted in a dataset of 220 CBCT and 7 simulation CT (SimCT) images. On each SimCT image, a region of interest (ROI) was defined by expanding the treatment planning prostate structure by 6 mm and subtracting the rectum with 10 mm expansion. The expansions were chosen empirically. Then, all CBCT images were registered to the corresponding SimCT images by maximizing the similarity within the defined ROI. Downhill simplex method was employed for optimization with full 6D rigid‐body transformation. The pixel values corresponding to bone and air were also excluded from similarity calculations. After each registration, the calcification mismatch was recorded as a measure of prostate localization error. The registrations were repeated for each similarity metric. The nine similarity metrics investigated were: normalized cross‐correlation (NCC), entropy of difference (EOD), mutual information (MI), correlation ratio (CR), sum of absolute difference (SAD), sum of squared difference (SSD), gradient correlation (GC), gradient difference (GD), and pattern intensity (PI). Results: The absolute error means (±standard deviations) were 2.1(±1.6) mm for GD and GC, 2.6(±2.8) mm for PI, 3.9(±4.3) mm for NCC, and 6.4 (±8.0) mm for MI. The others showed over 10 mm mean errors. The directional errors of GD were −0.1(±0.5) mm, 0.1(±1.4) mm, and −0.2(±2.1) mm in the left‐right, anterior‐posterior, and superior/inferior directions respectively. Conclusion: Among the investigated similarity metrics, registrations using GD and GC showed the most accurate prostate localizations on daily CBCT images.
SU‐GG‐I‐108: Applications of High Definition Volume Rendering in Radiotherapy: Investigation of Radiotherapy Treatment Using Accurate Three and Four Dimensional Volume Rendering
Authors: Wolfgang J , Lee J , Chen Y , Chen G
Published: July 2008

Current tools used to construct and analyze radiotherapy treatment plans involves the reduction of a volumetric CT/MRI/PET datasets into a series of 2D planes used by the physician and physicist to define treatment volumes and describe final radiation dose distributions. While convenient for the user, such reduction of what is naturally a highly connected, complex three‐dimensional volume, introduces significant loss of relevant anatomic detail, important for the final analysis of any treatment. Through the use of accurate, highly interactive volume rendering of the patient anatomy, target delineation, radiotherapy port selection and final dosimetric analysis can be significantly enhanced. Such appreciation of the true anatomical map underlying the artificial construction of 2D radiotherapy contours improves the clinical understanding of any given treatment plan, and may lead to improved modeling of treatment outcome. A new, high definition volume rendering engine produced by Fovia, Inc. allows for the creation of accurate three and four dimensional images from dicom data sets. This rendering engine has been adapted for the purposes of radiotherapy treatment planning and analysis, incorporating target volume definition in three and four dimensions, the projection of the planned radiotherapy treatment ports through the volume and fusion of the dose distribution map to the true anatomical rendering. The inherent four‐dimensional capability of this volume rendering engine allows for incorporation of change detection as viewed over the treatment cycle. Further, follow‐up scan data may be incorporated to develop long term 3D models for local control, helping to illustrate disease growth patterns associated with observed recurrences. Several case studies including CNS, cardiac and lung treatment sites will serve to further illustrate the advantages of regular use of anatomic volume rendering in radiotherapy.
SU‐GG‐I‐119: A Novel Tensor Decomposition Algorithm for Assessment of Glioma White Matter Infiltration During Radiotherapy Treatment Planning
Authors: Jena R , Price S , Gillard J
Published: July 2008

Purpose: We have previously demonstrated that diffusion tensor MR imaging (DT‐MRI) can be used as a tool for the assessment of glioma white matter infiltration. The technique demonstrates improved sensitivity and specificity compared to standard MR image sequences, but feature extraction from standard DT‐MRI displays is a laborious process. We present a novel algorithm based on tensor decomposition techniques to facilitate the rapid identification of white matter tract infiltration. Our aim was to produce a real‐time interactive version of this tool for use at the time of radiotherapy treatment planning. Method and Materials: Post operative DT‐MRI was performed in six patients with Glioblastoma prior to radiotherapy treatment planning. A graphical user interface was written in Object Pascal which enabled the user to navigate through the DT‐MRI data set in 3D. For each voxel in the data set, the diffusion tensor is characterised by plotting the magnitude of the isotopic (p) and anisotropic (q) components of water diffusion on orthogonal axes. Using these plots of p‐q space it is possible to produce a tissue signature for each voxel which allows the user to rapidly distinguish between normal and potentially infiltrated white matter. Results: When compared to standard fractional anisotropy displays, the p‐q space navigation tool provides a rapid visual assessment of white matter integrity. The tool can be run alongside the planning workstation at the time of contouring. Conclusion: The p‐q space navigation tool provides a feasible technique for the assessment of white matter infiltration at the time of radiotherapy treatment planning. Further development of the tool to include co‐registration with the planning CT data and export of region of interest data is under way. Conflict of Interest: Research sponsored by Siemens Oncology Care Systems USA.
SU‐GG‐I‐125: Treatment Responses Monitored by Estimated Returning‐To‐Origin Probability for Clinical High Diffusion Image
Authors: Chu A , Knisely J , Fulbright R , Constable R , Nath R
Published: July 2008

Background and Purpose: The usefulness of diffusion magnetic resonance imaging (MRI) to monitor treatment response has been recognized. For more specific information like extra‐/intracellular space, and water exchange, an extensive diffusion encoding with high diffusion weighting is required. However the intrinsic low signal‐to‐noise with eddy‐current contamination prohibits the high diffusion weighting imaging from becoming a useful clinical tool in spite of its great clinical potentials. We proposed a novel expression to represent high diffusion encoded image based on q‐space analysis for clinical purpose. Our q‐space analysis is to approximate the probability theory of ensemble averaged water molecules “returning” to their original spot at the beginning diffusion observation for a given diffusion time. Method and Materials: The 14‐minute MRI sequence employed a high‐diffusion encoding with 9 b‐values ranging as: 1∼ 4×103 sec/mm2, and a re‐focused diffusion gradient waveform is to balance eddy‐current effect, and the diffusion gradient is set in 6 directions for uniformly sampling in 3 dimensions to provide the information for returning‐to‐origin (RTO) probability as well as diffusion tensor imaging (DTI). In q‐space, the 9‐point diffusion encoding values from each voxel are interpolated before spatial domain conversion. The fractional anisotropy (FA) map is derived from the Eigenvalue of a given DTI. The giloblastoma patient's image is presented in this study. Results and Conclusion: A better signal‐to‐noise RTO map demonstrates its superior image quality than any diffusion images derived from the conventional apparent diffusion coefficient (ADC) analysis because the q‐space analysis uses the integration over q‐space instead of differentiating used in ADC analysis. The RTO also highlights the slower water diffusion along white matter as FA map, and it also shows the slow diffusion in fiber‐deteriorated part in GBM tumor location that FA map cannot. The slow diffusion helps to identify the high‐grade glioma due to its higher cellularity.
SU‐GG‐I‐126: Method for Determining Apparent Diffusion Coefficient (ADC) Values for Cerebral Lesions From Diffusion Weighted Magnetic Resonance Imaging (DWMRI) Examinations
Authors: McDaniels T , Ewell L
Published: July 2008

Purpose: This work involves analyzing Apparent Diffusion Coefficient (ADC) values for cerebral lesions from Diffusion Weighted Magnetic Resonance Imaging (DWMRI) examinations. The methodology presented permits transferring lesion geometry from treatment plan images to sequential DWMRI images for intensity measurement and subsequent ADC determination. Uncertainty in ADC calculation was correlated with image intensity. Method and Materials: DWMRI images were taken for several patients at specific intervals during treatment. Location of lesions were defined by the treatment plan contours and transferred to DWMRI images by use of a geometric algorithm. ADC values were calculated by a least squares line fit to DW intensities at varied b‐values. ADC values for the entire volume of each lesion were calculated by a weighted sum of individual DWMRI slice values. Initially, the weighting was based on the individual slice volume compared to the total volume as determined by the number of lesion voxels in each slice. Results: Greater uncertainty in ADC values were obtained for baseline b‐values (b=0) where the average image intensity was lower. The baseline intensity values were included in the weighting factor for determining the whole volume ADC value, with lower weighting given to individual slices with higher uncertainty. Conclusion: ADC values were determined for cerebral lesions outlined on treatment plan contours and transferred to DWMRI images. Corrections for variation between images and size of individual slice geometries allowed for the calculation of ADC value for whole lesion volumes. Low intensity in the baseline scans was correlated with greater uncertainty in resulting ADC values. For average intensities less than 1000, the uncertainty was more than 10% of the absolute ADC value. When the average intensity was higher than 4000, the ADC uncertainty was less than 5%.
SU‐GG‐I‐129: Temporal Variations of Hemodynamic Responses of BOLD FMRI at 3T: Spin Echo Vs. Gradient Echo
Authors: Yeh M , Wei Y , Wei P , Kuan W , Liu H
Published: July 2008

Purpose: Because of its superior sensitivity, gradient‐echo (GE)‐BOLD signal is currently the most widely used contrast for fMRI. However, several works have suggested that the spin‐echo (SE)‐BOLD can improved spatial localization of neural activity due to its greater weighting to smaller vessels. We hypothesized that the temporal variations of measured hemodynamic responses (HR), a basic factor of temporal resolution of fMRI, directly related to spatial accuracy of the methods. Therefore this study compared GE‐ to SE‐BOLD in time course and onset time variations of the HR. Method and Materials: Five normal volunteers participated in this study at a 3.0T MRI scanner. The paradigm consisted of 30 trials each with 1‐s visual stimulation and 15‐s fixation. Both the GE and SE experiments used echo‐planar readouts with TR/TE/FA= 1000ms/35ms/64 and TR/TE=1000ms/72ms, respectively. Eight slices with 5‐mm thickness were acquired to cover visual areas. For each activated voxel, the time series were extracted and averaged randomly across 30, 20 and 10 trials, from which the onset times and CNRs were determined with curve fitting to a gamma variate function. Results: Variance of the onset time decreased with CNR increased. At the same CNR levels, we observed significantly smaller onset variances for SE compared to GE. Decreased sensitivities were noted for the SE when comparing the number of activated voxels with the GE results. The mean time courses showed earlier onset for the SE response as compared to the GE. Discussion: We observed earlier onset times with smaller within‐region variances in the SE‐ than in the GE‐BOLD. Since the SE technique gives more weighting to the extravascular contributions around small vessels, we suggest that it could more accurately detect the onset time related to neuronal events. When comparing at the same CNR levels, the smaller latency variations of the SE measurement demonstrated its superior spatiotemporal natures.
SU‐GG‐J‐36: Application of Gafchromic XR‐RV2 Film for Small Animal Irradiation Dosimetry
Authors: Weng X , Yan Y , Ratanatharathorn V
Published: July 2008

Purpose: To assess the accuracy of self‐developing Gafchromic XR‐RV2 film for the dosimetry of small animal kilovoltage x‐ray irradiation. Method and Materials: Two kilovoltage x‐ray beams (100kVp and 150kVp) for small animal irradiation from a Faxitron machine were employed in this study. The doses of a point at the center of a round field with diameter of 20cm in a 30×30×10 cm3 solid water phantom at a depth of 1cm were measured via Gafchromic XR‐RV2 films and a Farmer ion chamber. The films, cut into small samples (3.5×1.5cm2 in size), were from the same batch to remove the variability between batches. Two film calibration curves were established for the two beams. The films were scanned with an Epson V700 flat‐bed scanner 24 hours after exposure and analyzed with FilmQA software. The doses of the same point for a round field with diameter of 1cm were also measured. Results: The Gafchromic XR‐RV2 film calibration curves were found to be weak dependent of beam energy (<8% difference of the pixel values between 100kVp and 150kVp). The agreement of measured doses for big field between Gafchromic XR‐RV2 films and Framer chamber were within 5% (−4.0% to 5.0%). While for small field irradiation, large difference (up to 75%) of measured doses was observed, which indicates that Farmer chamber underestimated the point dose due to field size is not big enough to cover chamber body. Conclusion: The Gafchromic XR‐RV2 film can provide acceptable accuracy of dose measurements for kilovoltage x‐ray irradiation and it is more accurate than Farmer ion chamber for small field irradiation that are often used in small animal treatments. The combination of Gafchromic XR‐RV2 film with flat‐bed scanner represents a low‐cost and viable dosimetry tool for small animal irradiation.
SU‐GG‐J‐39: Assessment of Early Vascular Response to Anti‐Angiogenic Therapy in a Murine Model Using Acoustic Radiation‐Mediated Multimodal Optical Spectroscopy
Authors: Yan K , Wachsberger P , Liu Y , Marrero N , Hu Y , Yu Y
Published: July 2008

Purpose: To investigate the efficacy of using acoustic radiation force (ARF) combined with optical spectroscopy to assess early effects of anti‐angiogenic therapy on changes in oxy‐hemoglobin saturation in a human glioblastoma xenograft model. Method and Materials: Pilot experiments were carried out with nude mice bearing human U87 glioblastoma xenografts. Acoustic field intensities were generated using a focused transducer operating below the FDA diagnostic ultrasound limits. During each experiment, ultrasound was administered for 5‐second bursts, with 55‐second relaxation periods between bursts and a total of five bursts per data collection per tumor position. A broadband light source was used for tissue illumination; diffuse reflectance spectra were collected from the tumor using an optical probe and a room‐temperature spectrometer. Baseline measurements were taken on Day‐0 before injecting a VEGF blocker drug to the mice. After drug administration, multimodal ARF‐optical measurements were taken each day at the same locations of each tumor for 4 consecutive days (Day1–4). Results: Preliminary results revealed that the mean values of the spectroscopic signals reflecting oxy‐ vs. deoxy‐hemoglobin concentrations increased over a period of 4 days, which suggest an increase in oxygen level over time during treatment with the VEGF blocker in the tumor tissue. On Day‐2, post‐ischemic reactive hyperemia was highly significant, a phenomenon previously observed in normal vasculature only, which suggests that the drug effects on blood vessel normalization were most significant at this treatment time‐point. On Day‐4, the multimodal ARF‐optical signal starts to display the behavior of flow stasis in benign vessels, which corresponds to the expected schedule of the drug on vessel normalization. Conclusion: This is the first pilot study to demonstrate the feasibility of using multimodal imaging to monitor and assess early changes of blood vessel normalization due to anti‐angiogenic therapy. Ongoing experiments are being carried out for further mechanistic investigation.
SU‐GG‐J‐43: Breast Tumor Volume Change Estimation in Whole Breast Automated Ultrasound by Image Based Registration and Initial Segmentation
Authors: Narayanasamy G , LeCarpentier G , Carson P , Roubidoux M , Yang Z , Fowlkes J , Schott A
Published: July 2008

Purpose: To estimate the change in breast tumor volume during treatment using 3D whole breast ultrasound (US) with segmentation of only the initial study. Image volume based registration (IVBaR) of the initial study to a subsequent study provides a transform which, when applied to the segmented tumor volume, gives the estimated subsequent volume. Method and Materials: Nine patients undergoing neoadjuvant chemotherapy participated in 3D US scans using a GE Logiq 9. For each subject, the whole breast was scanned before, at mid‐treatment and after a chemotherapy regimen of 115 +/−14 days. After acquisition, a senior breast imaging radiologist outlined a 3D tumor region in each image volume. Resultant volume changes (ΔV) were calculated. For the automated analysis, the original pre‐treatment image volume was warped to the post‐treatment image volume. The resultant transformation was applied to the segmented pre‐treatment volume to determine an “automated” post‐treatment volume and ΔV for comparison with manual segmentation. In the follow‐up reader study, comparisons were made of tumor volumes marked by 4 readers on unregistered and registered image volume pairs. Results: Preliminary results of the analyzable seven cases showed a mean ΔV of 50% ± 24% versus −43% ± 24%, measured by the expert radiologist and semi‐automated method, respectively. The mean fractional difference between %ΔV measures was −0.14 ± 0.08. Conclusion: Results to date suggest that tumor volume tracking is possible using a semi‐automated US registration method, given the reasonable (14%) correspondence with volume change by expert segmentation. Since tumor volume estimation is difficult and time consuming, successful IVBaR could aid in detection and estimation of tumor changes in response to neoadjuvant chemotherapy. Potential future usage also exists in breast cancer screening and diagnosis.
SU‐GG‐J‐46: CINE‐Magnetic Resonance Image Assessment of Intra‐Fraction Prostate Motion
Authors: Hsi Wen C , Vargas Carlos , Saito Anneyuko I , Dempsey James F , Flampouri Stella , Li Zuofeng , Palta Jatinder
Published: July 2008

Purpose: To measure the intra‐fraction prostate motion with CINE magnetic resonance imaging (MRI) for patients in supine or prone position and with or without rectal balloon. Method and Materials: The prostate motion within four‐minute time interval was investigated for seven patients using 17 series of CINE MRI. For each series, four sets of images were sequentially taken for each patient in supine/prone position and with/without rectal balloon. Saline water was injected into rectum for scans without rectal balloon. In each set of images, 100 sagittal images of 1.0 cm slice thickness in the prostate region were acquired sequentially with b‐FFE (balanced Fast Field Echo) sequence. The b‐FFE sequence reduces the scan time to 2.4 second. For each series, contours for prostate, rectum, bladder, abdominal wall etc. were manually on the first image and then copied to next 99 images using auto deformation tool. And, a movie loop of 100 images with contours was made to inspect the fidelity and quality of images and contours. The magnitude of the relative movement of the center of mass (COM) of prostate was automatically computed from prostate contours. Recorded data was further reduced to a mean and standard deviation over a time interval of 30 seconds to smooth periodical motion induced by breathing for prone position. Results: Larger movement was observed on the superior side of prostate with the interior edge as its rotation pivot point. For prone position, the magnitudes of the relative movement at the time of 4 minutes are 2.1 mm +/− 1.9mm and 1.7 mm +/− 1.1 mm for without and with rectal balloon respectively. For supine position, the magnitudes are 1.5 mm +/− 1.4mm and 1.3 mm +/1.2 mm for without and with rectal balloon respectively. Conclusion: The COM movement is a good surrogate for the intra‐fraction prostate motion.
SU‐GG‐J‐48: Clinical Implementation of Varian On‐Board Imaging System
Authors: Zeng  , McGowan T , Larsen T , Tsao J , Bruce L , Moran N , Nielsen M , Islam M , MacPherson M
Published: July 2008

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‐GG‐J‐63: CT Artifacts of High‐Density Materials in Proton Radiation Therapy
Authors: Li H , Sahoo N , Dong L , Gillin M , Mohan R , Zhu X
Published: July 2008

Method and Materials: A GE Lightspeed 16‐slice CT scanner was used to obtain images for this work. CT image artifacts introduced by HDM including bone, aluminum, titanium and steel inserts in cylindrical acrylic phantoms with diameters of 16 and 32 cm and water phantoms with different shapes (rectangular and oval shaped) and sizes, were evaluated. The proton ranges in terms of water equivalent thickness (WET) of 50 mm radiating from the surface of each high‐density implant in all directions were calculated from the CT images. The calculated WETs for the artifact‐contaminated images were compared with the corresponding artifact‐free images for the homogenous phantom. A modified scaling method for high‐density artifact correction was implemented and applied to CT images containing HDM artifacts. The WETs after correction were compared with the WET values of before correction, and with the expected values. Results: Presence of HDM generates radiating streak artifacts in CT images, depending on the shape and size of the phantoms carrying these objects. The most extended and severe artifact was observed for the sharp edge, rectangular phantom with large elongation. For a 1‐inch diameter steel insert placed in this phantom, the associated proton range error could be up to 18 mm or 36%. The HDM artifact correction technique could reduce the range error to 2.4 mm or 4.8%. Conclusion: Realistic phantoms with smooth surface shape and proper size should be used to study the HDM artifacts in CT images. High‐density materials artifact reduction techniques could effectively reduce the range uncertainty but would not eliminate it.
SU‐GG‐J‐66: Delivered Dose Assessment with Beam's‐Eye‐View Imaging During Radiotherapy
Authors: Berbeco R , Hacker F , Zatwarnicki C , Park S , Ionascu T , O'Farrell D , Mamon H
Published: July 2008

Purpose: During conventional radiotherapy the location of the patients' anatomy, particularly the tumor, while the treatment beam is on is of primary importance. This becomes especially relevant in treatment sites where large intra‐fraction motion has been observed (upper abdomen and thorax). We have already demonstrated a method for monitoring the target during irradiation with beam's‐eye‐view (BEV) imaging. In this work we use the intra‐fraction data to retrospectively calculate the delivered dose. This can be done in between each fraction and the cumulative treatment dose updated daily. If discrepancies are seen between planned and delivered, the treatment may be altered such that the delivered distribution converges with the plan. Method and Materials: The radiotherapy target is visualized daily during radiotherapy by collecting the exit radiation with an electronic portal‐imaging device (EPID). In between each fraction, the location of the target in the treatment images is compared with the reference position from simulation. The in‐treatment target positions are introduced in the treatment planning software as sub‐fields representing equal fractions of the original fields' monitor units. The dose distributions from each of the sub‐fields are summed to calculate the dose delivered each day. This distribution is updated daily to provide the cumulative delivered dose distribution. Results: The dose‐volume histograms (DVH) for the planned and delivered distributions have been calculated for several patients. Delivered doses to target and critical structures are generated for each fraction and cumulatively. Conclusion: The delivered dose can be calculated using the information contained in BEV images acquired during irradiation. By calculating the dose actually delivered to the target, we can assess our treatment procedures as well as more accurately report clinical results. Conflict of Interest: This work was partially supported by Varian Medical Systems, Inc.
SU‐GG‐J‐72: Development of Megavoltage Cone Beam Image Guided Radiation Therapy (IGRT) for Mini‐Multileaf Collimator (mMLC) Based IMRT and Radiosurgery Applications
Authors: Gupta N , Kong X , Shukla H , Bose S , Weldon M , Mayr N , Lo S , Wang J , Li K , Zhang H
Published: July 2008

Purpose: The purpose of this work was to investigate the technical feasibility of using the widely deployed Megavoltage Cone Beam CT (MVCBCT) for 3D IGRT applications with mMLC based treatment delivery. Method and Materials: In most clinical applications of MVCBCT IGRT, the largest possible field of view (FOV) is sought for evaluating adjacent organs‐at‐risk. However, an add‐on mMLC with maximum field size of 10cm×12cm is preferred for precise small‐field hypofractionated treatments. mMLC based treatments utilizing 2.5mm leaf widths are usually performed for SRS, SRT and SBRT applications, where the higher accuracy of 3D IGRT localization is also warranted. Current clinical systems do not allow restricting the field size of CBCT acquisition in the X direction. Performing imaging with the mMLC mounted and the field size opened to ∼27cm results in major truncation artifacts rendering the images unusable, as well as the irradiation of the mMLC electronics during image acquisition, which is undesirable. The current study was conducted with MVision™ and Moduleaf™ mMLC (Siemens Medical Systems), using anthropomorphic head and neck, and chest phantoms. A custom cerrobend aperture block was fabricated to shield the mMLC from radiation damage during imaging with the X Jaw open. The clinically used reconstruction algorithm was set to only reconstruct a smaller field of view corresponding to the clinically useful restricted treatment field size, although the data acquisition field size was set to the required 27.4 cm in the X direction. Results: With the changes described above, we were able to accomplish high quality images with the mMLC. The image quality was better than images obtained for the full field acquisition in the clinical mode for the same phantoms. Conclusion: We believe this to be the first study demonstrating high quality 3D IGRT through a small mMLC collimator designed for SRT.
SU‐GG‐J‐73: Dose Distribution Improvements for Prostate Cancer Patients Using Hybrid Image Guidance Systems
Authors: Rong Y , Tolakanahalli R , Tome W , Paliwal B
Published: July 2008

Purpose: Daily setup variations may compromise the precision of dose delivery, tumor control and normal tissue avoidance. This study analyzed the setup variations predicted by kilo‐voltage Cone Beam CT (CBCT) combined with 3D Ultrasound image guidance. The overall integrity of prostate dose distribution was considered to define an offset threshold above which image guidance becomes crucial for dose delivery. Method and Materials: Initial immobilization was performed using three‐point in‐room lasers. The residual positional errors were assessed using CBCT from Varian Trilogy™ and Ultrasound guidance by Sonarray™ system. Superposition of offset vectors on the initial prostate plans enabled detailed evaluation of resultant changes in dosimetric and biological aspects for target and organs at risk. On‐line CBCT images were used for calculation. Dose volume histograms (DVH), Gamma Index (GI), equivalent uniform dose (EUD) and tumor control probability (TCP) were calculated. Other indices such as mean total dose (mTd) and maximal total dose (MTD) for normal structures were also considered in defining the threshold. Results and Conclusion: After initial laser alignment, the mean vector of residual displacements over all prostate patients is 6.2mm with a 5.0mm standard deviation. The decrease in EUD for defined tumor volumes was up to 66% when the largest offset was applied and 10% in the composite plan which incorporated overall offset histories. Results show that if patient's offsets were smaller than the applied PTV margin (5mm), unappreciable changes in dose coverage and tumor control were revealed. However, if offsets were larger than the PTV margin, tumor control and normal tissue sparing can be significantly compromised if proper couch shifts are not made under the imaging guidance system. In this situation, special attention is needed especially on organs at risk and even the adaptive radiotherapy might be necessary.
SU‐GG‐J‐74: Dose Guided Patient Setup Improvement for Head‐And‐Neck Cancer IMRT Using Cone‐Beam CT
Authors: Chen Y , Paskalev K , Price R , Feigenberg S , Ma C
Published: July 2008

Purpose: Accurate dose delivery for H&N IMRT is often compromised by changes in patient anatomy and setup. Verification of setup parameters that have a significant impact on dose delivery presents difficult QA problems. In this work a method was developed to monitor the dose delivery using daily cone beam CT. Method and Materials: A virtual simulation procedure was developed to assure the region of interest is inside the field of view of cone beam CT. The treatment isocenter was placed accordingly for collision‐free patient imaging and treatment. The prescribed isodose surface and other levels of interest in the approved IMRT plan were extracted as auxiliary structures for reference. Patient setup correction was based on vertebral body matching first. Subsequently skin matching between cone beam CT and reference CT was checked. An action level based on phantom studies was established for patient external surface mismatch. Results: Patient external surfaces with beam intersections were acquired by planning on the region of interest for imaging, critical for calculating the delivered dose. The isodose surface shift due to mismatch of external surfaces could be estimated based on the beam path length, and this could affect the correction of patient setup. Repositioning of patient setup was required when an over 2 cm mismatch of external surfaces in any part of beam intersection was observed, which would result in an over 3% change in dose to PTV and critical structures. Conclusion: Planning on the imaging volume is a key step to optimize the clinical workflow for geometric and dosimetric verification using cone beam CT. Displaying planned isodose surfaces is useful for patient setup correction. By imaging the patient's external surface we can monitor the delivery of the planned dose distribution and decide when re‐planning is necessary.
SU‐GG‐J‐77: Dosimetry of a Novel MicroCT/RT System for Small Animal Conformal Radiotherapy
Authors: Rodriguez M , Zhou H , Graves E , Keall P , Van den Haak F , Xu J
Published: July 2008

Purpose: To measure the absorbed dose to the surface of water at the isocenter of a custom microCT system for small animal conformal radiotherapy. Percentage depth dose curves and backscatter factors for field sizes smaller than 2 cm were also investigated. Method and Materials: The dose rate at the surface of water at the isocenter (35.4 cm) of the GE microCT was measured using the in‐air method proposed in the AAPM protocol TG‐61. The half value layer (HVL) of the X‐ray beam was measured using an ion chamber and calculated using Monte Carlo simulation. Ion chamber measurements were taken using 6 cm field size diameter. PDD curves and dose rate for field diameters of 2, 1, 0.5 and 0.1 cm were investigated using Gafchromic EBT film. Backscatter factors were calculated via Monte Carlo simulation. Results: The HVL of the beam was measured as 5.6 mmAl suggesting average photon energy of 46 keV. The dose rate at the surface of water at the isocenter of the microCT is . The beam is attenuated to 50% at 3 cm depth in water for 1 cm field size and at 2.4 cm depth for 0.1 cm field size. The calculated backscatter factors for field sizes larger than 1 cm agree with those tabulated in AAPM protocol TG‐61 within 1%, and for field sizes smaller than 1 cm agree with those extrapolated from TG‐61 tables within 3%. Conclusion: The dose rate at the isocenter of the microCT is high enough to deliver therapeutic radiation doses to mice in reasonable irradiation times. The beam has enough penetration power to irradiate tumors inside mouse bodies. This microCT is therefore capable of performing 3‐D conformal radiotherapy in mice using radiation fields as small as 1 mm in diameter.
SU‐GG‐J‐78: Dynamic Internal/external Correlation Updates for Effective Gated Treatment with Reduced Internal Imaging
Authors: Wu H , Zhao Q , Berbeco R , Shirato H , Nishioka S , Jiang S
Published: July 2008

Purpose: The effectiveness of gated radiotherapy dependents on the precise localization of tumor positions in real‐time during the treatment. Two widely used gating approaches are internal gating and external gating. Internal gating is accurate but invasive and radiation dose to the patients is a big concern. External gating is non‐invasive but less accurate. We have proposed a new gating approach to combine the advantages and minimize the disadvantages of internal and external gating. Method and Materials: In our new approach, the external signal is acquired at high frequency while the internal signal is acquired at very low frequency. Algorithms are designed to decide the optimal x‐ray imaging time and update the internal/external correlation in real‐time, which will be used to derive the internal tumor position. A simulation system has been implemented to evaluate hybrid gating using the synchronized internal/external signals acquired during patient treatment. Results: Two dynamic correlation updating algorithms are introduced: based on amplitude and a piecewise linear model. Two assessment metrics, gating duty cycle and target coverage, have been defined to quantitatively evaluate the simulation results. The influences of different clinical scenarios for hybrid gating, including the gating window size, x‐ray imaging frequency, and the timing for internal signal acquisition, has been investigated. Our results demonstrated that dynamically updating the internal/external correlation in or around the gating window will improve the target coverage (by ∼14%) with relatively diminished duty cycle (by ∼10%). Conclusion: The developed hybrid gating technique has higher accuracy than external gating at a cost of much lower x‐ray imaging dose than internal gating. This improvement will benefit patients with mobile tumors, especially greater for early stage lung cancers, for which the tumors are less attached or freely floating in the lung with more movement.
SU‐GG‐J‐85: Evaluation of Electromagnetic Beacon Localization Correlation with KV‐KV Matching for Prostate Treatments
Authors: Ogunleye T , Rossi P , Elder E
Published: July 2008

Purpose: To evaluate the correlation between an electromagnetic treatment positioning system and an orthogonal kV image localization system for the alignment of prostate patients for radiotherapy. Method and Materials: Two systems, taking advantage of the same three implanted fiducial markers, have been used to localize the target volume for radiotherapy of the prostate. These markers are radio‐opaque, unique frequency transponders placed in the patient's prostate designed and built by Calypso Medical Systems. The Calypso 4D Localization System employs an electromagnetic array that excites the transponders triangulates their position from their received signal. The second system, the Varian On Board Imager (OBI), acquires orthogonal kV radiographs visualizing the fiducials and performs a match with isocentric digital reconstructed radiographs. For each treatment session, external skin marks and room lasers were used to orient the patient on the treatment couch with the linac isocenter. The Calypso system was then set to localize and track, although no patient alignment motion was performed. OBI localization was carried out. Lateral, longitudinal and vertical offsets to align the transponders were recorded for the following: Calypso prior to OBI shift, OBI, and Calypso after OBI shift. Results: Analysis of the lateral, longitudinal, vertical axes and vector of patient positioning through 141 sessions showed that on average Calypso and OBI differed by a magnitude of 0.65, 1.1 and 1.5mm respectively with an average vector magnitude of 2.1mm. Conclusion: Our evaluation shows that the Calypso system can provide at least the same level of confidence in localization for prostate patients without the need for daily orthogonal x‐ray imaging. While the kV imaging system provides a subjective localization prior to treatment, the electromagnetic system presents an objective alignment prior, during and after treatment.
SU‐GG‐J‐89: Evaluation of the Internal Target Tracking Algorithms in a Commercial Research Fluoroscopic Toolkit
Authors: Santoro J , Mageras G , Yorke E , Amols H , Goodman K , Mostafavi H , Sloutsky A
Published: July 2008

Purpose: A means of tracking internal target or structure motion in x‐ray images is important for monitoring motion at treatment. We evaluate the accuracy and robustness of several tracking algorithms in a commercial research toolkit with patient images. Method and Materials: Anterior/posterior view fluoroscopic images (10/s) over several respiratory cycles in the thorax or abdomen are acquired with a gantry‐mounted kV imaging system immediately after radiation treatment. We compare three tracking algorithms available in the research toolkit with manual tracking: single implanted fiducial or surgical clip, diaphragm, and markerless tracking of tumor in lung. The latter mode provides separation of moving features from stationary features in the images, for improved extraction of motion signals. For each algorithm, the position of the object in the superior‐inferior direction is compared to the manually determined one in each image in the sequence. We also determine the mean and variance discrepancy between algorithm and manual tracking. Intra‐observer variability is determined from repeated manual tracking of a subset of fluoro sequences. The percentage of images in which discrepancy is <5mm is taken as a measure of algorithm robustness. Results: The mean and standard deviation of the algorithm‐manual difference were: Single Marker μ=0.53 mm, σ=0.92 mm, Diaphragm μ=0.88 mm, σ=1.4 mm, and markerless μ=2.06 mm, σ=1.68 mm. This compares with an intra‐observer variability mean of ⩽ 1 mm, 2 mm, and 3.5 mm respectively. The discrepancy between algorithmic and manual tracking exceeding the robustness threshold occurred 0%, 2%, and 3% of the time of the three algorithms respectively. Conclusion: For the algorithms examined, the toolkit agreement with manual tracking is consistent with or less than intra‐observer variation. Future plans are to evaluate the toolkit's performance with multiple fiducials in close proximity, and at other gantry orientations.
SU‐GG‐J‐92: Feasibility Study of Hadamard Multiplexing Radiography Based On Carbon Nanotube Field Emission Multi‐Pixel X‐Ray Technology
Authors: Zhang J , Peng R , Yang G , Chang S , Lu J , Zhou O
Published: July 2008

Purpose: Current CT scanners perform CT scans by rotating a single beam x‐ray source around an object and collect multiple projection images sequentially, one at a time. The serial approach demands fast gantry rotation and high x‐ray peak power which in turn limits the CT scanning speed. To overcome those limitations, novel CT scanners with multiple x‐ray sources have been proposed and developed, such as the Dynamic Spatial Reconstructor (DSR) from Mayo Clinic and the dual source CT from Siemens. Our approach is based on the carbon nanotube field emission multi‐pixel x‐ray technology and Hadamard multiplexing principle. Method and Materials: For the proposed stationary multiplexing CT scanner, multiple x‐ray sources are spatially distributed along the CT scanning path. It completely eliminates the need for gantry rotation during CT scans. Furthermore, since the x‐ray radiation can be readily modulated to form different waveforms due to its field emission mechanism, the CT scanning procedure can be multiplexed based on Hadamard multiplexing principle which has been widely used in analytical instruments and communication areas to improve data throughput. Results: Without considering noise effects, Hadamard multiplexing method can increase the imaging speed by a factor of (N+1)/2 where N is the number of projection images, without increasing the x‐ray peak power. This becomes significant when N is large (∼1000). Experimentally, even with the presence of noises, we have successfully demonstrated that significant gain in terms of imaging speed for Hadamard multiplexing can be achieved using our prototype multi‐pixel x‐ray imaging system. Conclusion: We show the feasibility of Hadamard multiplexing radiography that enables simultaneous collection of multiple x‐ray images. The combination of the multi‐pixel x‐ray technology and multiplexing principle has the potential to lead to a new generation of stationary multiplexing CT scanners that have drastically increased data throughput and reduced x‐ray peak power.
SU‐GG‐J‐95: Feasibility to Use Daily Cone‐Beam‐CT to Determine Dose‐Surface Histogram of Oral Mucosa in Radiotherapy of H&N Cancer
Authors: Li S , Kuritzky N , Micaily B , Miyamoto C
Published: July 2008

Purpose: to develop a novel approach for estimating dose delivered to the oral mucosa — dose‐surface histogram (DSH)‐ to facilitate assessment of radiation induced mucositis from radiotherapy for head and neck (H&N) cancer. Method and Materials: Mucositis, Xerostomia, and dental caries are common oral complications from radiotherapy. We hypothesized that an improved method for describing dose distribution to oral mucosa and parotid glands would better enable prediction of these dose‐limiting effects. Due to large uncertainties related to mobility of oral tongue and month, we used daily CBCT to delineate the oral cavity and the gum, which were then expanded by 1‐mm. The shell of the expended 1‐mm should represent the mucosal layer. A dose‐surface‐histogram (DSH) was then calculated from the difference between the DVHs for the oral cavity from the 1‐mm expansion. In addition, the daily CBCT would also allow us to calculate the DVHs to the parotid glands that could be displaced and shrunken during the course of treatment. Results: We have successfully applied this method to two patients currently receiving IMRT for H&N cancer. The absolute mucosal surface area receiving a high dose (>80% of prescription dose) is significantly different from the volume within the oral cavity. Conclusion: DSH for oral mucosa is achievable using daily CBCT images. The dose distribution to the mucosa may provide us with a more robust predictor of radiation‐induced mucositis and Xerostomia.