bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐DD‐A4‐02: A Novel Optical Imager Towards Breast Cancer Diagnosis
Authors: Ge J , Jayachandran B , Zhu B , Regalado S , Godavarty A
Published: July 2006

Purpose: To design and develop a portable optical imager for early‐stage breast cancer diagnostics, providing great depth information, enhanced data acquisition rates, and minimal patient discomfort. Method and Materials: A unique measurement geometry of simultaneous multiple point source illumination was implemented in the design and development of the hand‐held based optical probe. Simultaneous multiple point detection was carried out using an intensified charge‐coupled camera (ICCD) that can be operated in the continuous wave and frequency domain measurement approaches. The hand‐held based imaging probe has been coupled to the ICCD detection system and the performance characteristics (in terms of measurement accuracy and precision) of the imager is characterized through initial phantom studies under homogeneous conditions. Results: Preliminary simulated studies using simultaneous multiple point illumination measurement geometry over the universally used single point illumination geometry demonstrated an increase in the detected signal strength as well as total interrogated tissue volumes. An optimal number of source and detector fibers used to develop the probe head, minimized the dead volume and improved the data acquisition times. Conclusion: A novel fluorescence‐enhanced imaging system was developed using a hand‐held probe and an ICCD camera, enabling the flexible and rapid imaging of any given tissue volume. Further work involves phantom based experimental studies towards 3D optical imaging and tomographic analysis. The final goal is to translate the current laboratory‐based techniques into routine clinical use.
SU‐DD‐A4‐05: Characterization of X‐Ray Scatter and Glandular Dose in Digital Tomosynthesis for Breast Imaging Using Monte Carlo Simulations
Authors: Sechopoulos I , Suryanarayanan S , Vedantham S , Karellas A
Published: July 2006

Purpose: To study the characteristics of x‐ray scatter and glandular dose in digital tomosynthesis for breast imaging. Method and Materials: Monte Carlo simulations of x‐ray transport in breast tomosynthesis were performed using the Geant4 package [Agostinelli et al, Nucl Instrum Meth A 506: 250–303, 2003]. Scatter‐to‐primary ratio (SPR) maps, maximum SPR, scatter point spread functions (PSF) and glandular dose to the breast were computed at several projection angles while varying compressed breast size, thickness, glandularity and x‐ray spectrum. For validation, the SPR and scatter PSF for the planar mammography view (0 degrees) for various setups were compared with published values [Boone et al, Med Phys 27(10): 2408‐16, 2000 and 27(8): 1818–1831, 2000]. Results: SPR maps and PSF show variations with increasing projection angle, with apparent asymmetry appearing at projection angles beyond 10 degrees. When the projection angle is increased from 0 to 21 ‐degrees, while the breast thickness encountered by the central ray increases by 7.1%, the maximum SPR for a semi‐circular 10 cm radius breast increases by 10.1% and 18.8 % for breast thicknesses of 2 cm and 8 cm, respectively. Dose deposition shows a decrease, varying by 3.8–7.6% for the same thicknesses and projection angles. Conclusion: Since the use of an anti‐scatter grid is not easy to implement in tomosynthesis imaging, the development of software‐based post‐acquisition scatter reduction is important, which requires a good understanding of the scatter effects. This work characterizes the scatter signal present in tomosynthesis images and shows that x‐ray scatter affects each projection angle differently and therefore each projection must be corrected separately, using appropriate prior knowledge. Decreased glandular dose with increasing projection angle must be taken into account when planning a tomosynthesis clinical protocol. Research supported in part by: NIH‐NIBIB Grant RO1‐ EB002123 and the Georgia Cancer Coalition.
SU‐EE‐A1‐02: Analysis of Photon Beam Data From Multiple Institutions: An Argument for Reference Data
Authors: Li S , Medin P , Pillai S , Solberg T
Published: July 2006

Purpose: Beam data requirements to support sophisticated treatment planning and delivery techniques are increasingly rigorous. Small field photon measurements are particularly challenging for many centers and practitioners. The purpose of this work is to compare measured beam data characteristics from identical linear accelerators contributed by multiple institutions. Methods and Materials: Measured beam data from 43 “identical” 6 MV linear accelerators were collected from 43 different institutions. A common treatment planning system was used by all participating institutions, standardizing the data collected and simplifying the analysis. Beam data consisted of percent depth dose (PDD), crossbeam profiles and relative scatter factors (SF) as a function of field size. Beam data for field sizes less than 1 × 1 cm2 were contributed by the majority of institutions. A dose‐to‐monitor unit conversion factor was also obtained. All data were normalized in a consistent manner for direct comparison. Data were analyzed using a commercial analysis package. Mean, standard deviation, minimum and maximum deviation were calculated for the PDD data. A one‐population t‐test was applied to PDD, scatter factors and dose‐to‐MU factors to identify statistically significant differences. Results: PDD data for a 10×10 cm2 field size were remarkably consistent among institutions, with 1σ variation of less than 1% at all depths beyond dmax. In contrast, significant variation was observed in small field PDD data; at 0.6×0.6 cm2, the PDD at 10 cm fell outside the 95% confidence level at 63.2% of institutions. Measurement of small field output factors proved to be equally variable. Several significant outliers were noted in dose‐to‐monitor unit conversion factors. Conclusions: Significant differences exist in beam data collected by multiple institutions for identical linear accelerators. Uniform procedures are needed to increase the quality and consistency of measured beam data. Use of a reference set of beam data may help to eliminate fundamental errors.
SU‐EE‐A1‐03: A Novel Three‐Dimensional Radiochromic Film Phantom for Use with Stereotactic Radiosurgery Units
Authors: Griffin S , DeWerd L
Published: July 2006

Purpose: To create a three‐dimensional (3D) film dosimeter capable of simultaneously measuring the entire relative dose distribution of the volume fields of an Elekta Gamma Knife (GK) unit.

Methods and Materials: A spherical head phantom was constructed out of Virtual Water™ (VW™). This phantom was constructed with a bored hole allowing the insertion of a stack of film 2.5cm in thickness and 5cm in diameter. The hole is fitted with two unique fiducial rods that prevent both rotation and inversion of the film. Radiochromic film with a thickness of 105 microns is used, allowing approximately 240 layers of film to be inserted into the phantom. One layer of film is assumed to be water/tissue equivalent; however, the water/tissue equivalency of a thick stack of film has not been determined. Monte Carlo MCNP5 methods were used to determine the water/tissue equivalency of a thick stack of radiochromic film. Results: Using MCNP5 simulations, the water/tissue equivalency of a stack of film 2.5cm thick was determined. For a simplified model of the film phantom, the dose distribution in the active layer of the pieces of film was found to be within −1.7% of the dose distribution in similar layers of VW™, demonstrating that a stack of radiochromic film may be used as 3D dosimeter. Conclusion: Using a stack of film as a 3D dosimeter limits the resolution of the determination of the relative dose distribution only by the resolution of the scanner and by the thickness of the film layers. This allows resolutions of 50×50×105 microns3 to be achieved. Most 3D dosimeters require advanced imaging equipment to read out the data but a 3D film dosimeter allows any institution which has a flat bed scanner to obtain 3D dose distribution information.
SU‐EE‐A1‐04: Verifying Internal Target Volume Using Cone‐Beam CT for Stereotactic Body Radiotherapy Treatment
Authors: Wang Z , Yin F , Yoo S , Wu Q , Willett C , Marks L
Published: July 2006

Purpose: The internal target volume (ITV) could be determined using 4D CT simulation images and be verified in the treatment room using on‐board cone‐beam CT (CBCT) since the CBCT projection images are acquired over approximately 10 breathing cycles. This study used a 4D dynamic phantom to verify the accuracy of this technique and also to develop a procedure for using CBCT to clinically verify ITV in stereotactic body radiotherapy (SBRT) treatment. Method and Materials: A CIRS 4D dynamic phantom, with a target ball and precisely controlled motion, was imaged using a 4D CT scanner. A Varian RPM system was used for respiratory gating. Ten 3‐D image sets were generated corresponding to 10 breathing phases. The ITV was determined based on the phase images. To assess concordance, on‐board CBCT images of the target ball were compared with the 4D‐CT defined ITV. SBRT patient with tumor targets located in the thorax and upper abdomen were similarly scanned using phase gating 4D CT. The ITVs were compared between simulation CT and CBCT scans to identify localization error. Results: The dynamic phantom motion was 20mm along the inferior‐superior direction, 5mm along the anterior‐posterior direction, and 2mm along the left‐right direction with a cycle time of 4 seconds. The concordance of the CBCT and ITV matching was within 1 mm. For the lung SBRT patient, the target volume based on the CT images without respiratory gating was 0.7 cc. The ITV was 2 cc. The ITV matches well with the CBCT images. The localization errors between free‐breathing CT and CBCT were 2 mm to the right, 1 mm to the anterior, and 2 mm to the superior. Conclusion: CBCT provides an accurate assessment of the ITV for targets affected by respiratory motion.
SU‐EE‐A1‐05: Determination of Beam Margins for SRT/IMRT of Small Lung Cancers Based On Monte Carlo Simulations
Authors: Jin L , Ma C , Li J , Wang L
Published: July 2006

Purpose: This work investigates the beam margins used in treatment planning for stereotactic radiotherapy (SRT) and intensity‐modulated radiotherapy (IMRT) of small lung lesions based on Monte Carlo (MC) simulations. Method and Materials: Ninety SRT/IMRT treatment plans generated in a commercial treatment planning system were recalculated using MC simulations with different combinations of beam margin (0 to 18 mm), lung density (0.1 to 0.5 g/cm3) and planning target volume (PTV) (10 to 50 cc) based on the patient geometries built from CT images. Each plan was normalized at D95, of the dose‐volume histogram (DVH) so that the comparison between different plans could be made quantitatively in terms of minimum dose (D99) and maximum dose (D1) in the PTV. The relationship between the beam margin and lung density/tumor size was fitted into modeled functions. The beam margin needed for a particular plan with certain lung density and PTV size can be determined based on the clinical acceptance criteria based on maximum/minimum doses and other normal tissue constraints. Results: The maximum and minimum doses were found to vary with beam margins, the volumes of PTV and lung densities. The relationships between them have been quantitatively generalized into functions from the simulation data. It was found that the maximum dose decreased with increasing beam margin while the minimum dose increased with beam margin when the beam margin was less than 1.5 cm. The trends were reversed with the increasing PTV volume. Conclusion: The generalized formulas for maximum and minimum doses can be used for the estimation of the minimal beam margin required in SRT/IMRT for adequate dose coverage for small lung tumors.
SU‐EE‐A2‐03: Evaluation of Auto‐Segmentation Tools for the Target Definition for the Treatment of Lung Cancer
Authors: Xiao Y , Werner‐Wasik M , Curran W , Galvin J
Published: July 2006

Purpose: With the advent of more sophisticated image devices in the treatment room, image guided radiotherapy (IGRT) and adaptive radiotherapy (ART) have become distinct possibilities. IGRT and ART techniques in their various stages have been implemented in clinics. One of the ART techniques using the daily acquired CT images involves re‐planning due to the target shape variation during the treatment. Lung cancer volumes of some cases are observed to undergo significant changes where re‐planning is a necessity. To be able to define target efficiently can help the treatment flow significantly. This study evaluates various auto or semi‐auto contouring tools either commercially available or under development for their accuracy and ease of use. Method and Materials: Three methods are included in the study. Two are commercially available (Focal,CMS): auto threshold (of gray level); and auto Segmentation where gray level, the edges and prior shape information are used. The third method is the ITK‐SNAP program that uses a powerful level set(snake) segmentation algorithm to segment anatomical structures in three dimensions. Results: Ten image sets from helical and cone beam CTs are included in the study. The acceptable contours are defined as those with distance to agreement to those drawn by radiation oncologists less than 3 mm. For target volume surrounded by normal lung, the percentage slices of contours that do not need manual adjustment are 41–62%, 23–39%, 62–78% for threshold, auto‐segmentation and SNAP respectively. For cone beam CT, these numbers are approximately 10% lower. SNAP can also be used for target volume with no clear boundary, although the percentage success is much lower. Conclusion: More sophisticated auto‐segmentation tools need to be available routinely with more flexibility for users to adjust algorithm parameters in order for them to be useful for routine clinical ART purposes.
SU‐EE‐A2‐04: A Method of Online MLC Aperture Adjustment for Treatment of Patients with Set Up Variations
Authors: Islam M , Heaton R , Cho Y , Norrlinger B
Published: July 2006

Purpose: To investigate MLC aperture adjustments to compensate patient setup variations, replacing couch shift methods for precision treatment delivery. Method and Materials: Patient setup variations can be described by 3‐D translational shifts. A scheme of adjusting MLC apertures to compensate for translational displacements of the patient has been developed. Patient shift information, such as provided by commercial image matching software, establishes the aperture shift vector. The projection of this vector into and orthogonal to the BEV plane was used to determine the displacement vector and divergence for the aperture. Modified beam apertures were generated and MLC leaf positions were determined through a polynomial interpolation.

Dosimetric plan comparisons were made within Pinnacle 7.6c. Static field and segmented IMRT patient plans were investigated for pelvic as well as head and neck sites. Arbitrary shift vectors ranging from 3 mm up to 30 mm have been investigated. Non‐integral MLC leaf width shifts parallel to the leaf bank face to characterize leaf width effects. Results: Conformal plans show dose variations from the original plan of up to 3% in the pelvis for shifts of up to 30 mm. Dose coverage of the PTV was maintained except in the superior‐inferior direction, where coverage in the last 3 mm of target fell as low as 92% of the prescribed dose. Results for prostate and oropharynx IMRT plans showed little increase in maximum critical structure doses, and small increases in mean doses. DVH's for IMRT plans confirmed minimal impact on critical structure doses. Conclusion: An alternative method of on‐line adaptive treatment delivery has been explored which eliminates the need to adjust the patient position. This can potentially increase treatment accuracy and efficiency through minimizing patient disturbances and reducing the time between imaging and treatment.
SU‐EE‐A2‐06: Benefit of 3D Image‐Guided Stereotactic Localization in the Hypofractionated Treatment of Lung Cancer
Authors: Wang L , Feigenberg S , Paskalev K , Chen L , Ma C
Published: July 2006

Purpose: To investigated the benefit of image‐guided stereotactic localization for lung cancer patients treated with hypofractionated radiotherapy. Materials & Methods: A stereotactic body localizer (SBL) was used for patient immobilization, image registration among multi‐phase CT simulation, and image‐guided stereotactic localization. The simulation scans consist of 3 sets of CT images taken during free breathing and 2 breath‐holding scans (at maximum inhalation and exhalation). Target delineation was performed on all 3 sets of images and the combination of the targets forms a composite gross‐target volume (GTV). Treatment planning was performed on the planning‐target volume (PTV) using 3 mm margin to account for the presumed reliability of the CT localization. Prior to each treatment, a localization CT scan using a CT‐on‐rails was obtained. Couch shifts were made based on the changes of the stereotactic coordinates of three pre‐selected bony landmarks. In this retrospective treatment dose verification, we performed image fusion between the simulation CT scan and each pre‐treatment CT scan to obtain the same target and critical structure information. The same treatment plans were re‐loaded onto each pre‐treatment CT scan with their respective stereotactic coordinate system. The changes in dose distributions were assessed by dose‐volume histograms of the PTV and the critical structures before and after isocenter corrections which were prompted by image guided stereotactic localization. We compared D95, D99, and V95 for the PTV and GTV, and V20and V30 for the ipsilateral lung. Results: Our retrospective study for 10 patients with 40 dose reconstructions showed that the average D95, D99, and V95 of the PTVs are 92.1%, 88.1%, and 95.8% of the planned values before isocenter corrections. With the corrections, these values are all improved to 100% of the planned values. Conclusions: 3D image guidance is crucial for stereotactic radiotherapy of lung tumors when small margins are used.
SU‐EE‐A3‐01: A Novel Filtering Approach for Local PET Verification of Proton Radiotherapy
Authors: Parodi K , Bortfeld T , Craft D , Mostagir M , Knopf A
Published: July 2006

Purpose: Proton radiotherapy activates positron emitters in tissue, which can be imaged with PET. However, the resulting PET image is not directly proportional to the delivered dose. We are investigating the spatial relationship between the dose distribution and its PET image without reverting to Monte Carlo methods. The first goal is to validate the proton range in the patient, and ultimately to reconstruct the spatial distribution of the actually delivered dose from its PET image. Method and Materials: The relationship between the proton dose and its PET image can be described mathematically as a convolution (filtering). We derive the convolution kernel analytically. This filter is unique for a given activation channel, independent of beam energy and specific absorber. The straightforward application of the method to determine the PET signal by locally filtering the planned dose distribution was validated through comparisons with Monte Carlo calculations and measured PET data in homogeneous and inhomogeneous media. The challenging inversion of the relationship, determining the dose from the PET signal, was initially explored for a simplified mono‐energetic case in a homogeneous absorber. Results: Activity depth profiles obtained with the convolution approach agreed with measured and Monte Carlo data within 1 mm in depth. In terms of absolute intensity, the agreement was within 1.5% between filtered and simulated profiles and 10% between filtered and measured data in the distal region. Attempts to recover the dose distribution from its PET image through a de‐convolution yielded promising results for idealized data but were strongly noise dependent. Conclusion: We have derived the spatial relationship between dose and positron activation and demonstrated the possibility to obtain the PET image measured after proton treatment by locally filtering the planned dose distribution. The inverse approach, i.e., direct dose quantification from the measured PET, seems possible but is very sensitive to noise.
SU‐EE‐A3‐02: The Potential of FDG‐PET in Delineating the Lumpectomy Cavity for Partial Breast Irradiation Patients
Authors: Thorndyke B , Jarvis L , Horst K , Xing L
Published: July 2006

Purpose: To investigate the potential of FDG‐PET imaging for delineating the surgical cavity in post‐operative partial breast irradiation patients. Method and Materials: A DCIS breast cancer patient was imaged with a GE Discovery ST PET‐CT scanner approximately 2 weeks post lumpectomy. Following the treatment planning CT, a single‐bed (15 cm) FDG‐PET scan was dynamically acquired in 5‐sec intervals over 15 mins. The raw PET data was combined to form bins ranging from 30 sec to 15 min. These data were reconstructed by the GE scanner through an iterative OSEM algorithm, and hardware fused to the treatment planning CT. The value of PET in visualizing the lumpectomy cavity border was investigated through visual comparisons of fused PET‐CT images, the evolution of PET intensity for various breast points, and signal‐to‐noise measurements across the lesion. Results: The PET image showed clear signal enhancement near the lumpectomy cavity. This enhancement formed a ring in each axial slice, matching the locations of surgical clips. Enhancement was also apparent where the cavity border was difficult to evaluate by CT density or clips alone. The ring presented a significantly higher SUV than other breast tissue (2.2 vs. <1.4), while the region inside the ring had a lower SUV than the (presumably benign) glandular tissue in the same breast (1.2 vs. 1.4). The SUV values were transient below 5 min, but remained stable thereafter. Conclusion: FDG‐PET may provide useful information for delineating lumpectomy cavity borders by elucidating regions of enhanced radiotracer uptake due to inflammation. The hypointense PET volume enclosed by the high activity ring may represent fluid and non‐viable tissue stemming from post‐surgical changes, explaining its lower FDG uptake and further supporting the suggestion that the ring corresponds to the cavity border itself. On current hardware, five‐minute scans were required to achieve stable SUVs.
SU‐EE‐A3‐03: A Biomechanical Lung Deformation Model Based On MR Grid‐Tagging Using Hyperpolarized 3He
Authors: Sheng K , Cai J , Altes T , Brookeman J , Larner J , Read P
Published: July 2006

Purpose: Deformable image registration is critical for advancements of lung tumor radiation. Commonly used mathematical deformable registrations do not provide actual biomechanical trajectories of anatomical motion. Therefore, we developed a biomechanical registration model (BRM) based on hyperpolarized 3He MRI grid‐tagging to automatically segment structures and generate BRM encoded cine CT images. Method and materials: Normal volunteers underwent hyperpolarized 3He MR imaging on a 1.5T whole‐body MR scanner. Grid‐tagging was achieved by applying sinc‐modulated RF pulses with a composite flip angle of 90° prior to the acquisition of the images followed immediately by a multi‐slice FLASH‐based acquisition at full inspiration and exhalation. For each slice, a displacement vector was computed for each grid element. The complete lung motion was based on spatial and temporal interpolation of the displacement vectors. The motion and deformation of anatomical structures were obtained using the interpolated vector field through various phases. The displacement vectors were registered to a coronal CT image to generate a set BRM encoded cine CT images. Results: Tagging signals were well preserved and sufficient for quantitatively resolving the tag motion. From the displacement vector map, the lower lobes exhibit the greatest motion magnitude especially in the craniocaudal direction. The motion of the structures driven by the displacement map is continuous and smooth. No substantial artifacts in the BRM generated dynamic Ct images were observed. Conclusions and Discussion: BRM provides an independent measure of lung motion and deformation. Compared to pure‐mathematically constructed registrations, BRM relies on fewer assumptions and avoids errors induced by image matching processes. BRM encoded dynamic images are useful to cross‐validate deformable registration by other imaging modalities and algorithms. We plan to explore the potential of this methodology for auto segmentation and treatment planning.
SU‐EE‐A3‐04: Deformable Registration for In Vivo Imaging and Pathology Correlation
Authors: Brock K , Ahmed S , Moseley J , Moulton C , Guind M , Haider M , Gallinger S , Dawson L
Published: July 2006

Purpose: To describe a deformable registration infrastructure to resolve the geometric discrepancies between in vivo imaging studies and histology from resected tumor specimens to reduce uncertainties in tumor definition. Method and Materials: An IRB approved prospective study investigating the correlation between in‐vivo CT and MR imaging, ex‐vivo specimen imaging and pathologic sections from colorectal cancer liver metastases treated by resection was developed to better define gross and clinical tumor volume. Triphasic liver CT scans, PET‐CT scans and MR scans were obtained in 6 patients within 4 weeks prior to liver resection. On the day of surgery, the fresh liver hepatectomy specimen was imaged using MR. The specimen was fixed and reimaged with MR prior to pathological evaluation. Axial sectioning was done at the time of pathological evaluation, with photos of each liver slice digitized. Histological evaluation was performed on the sections representing the largest tumor. Gross tumor was identified on all images sequences. Gross tumor, microscopic tumor and vascular changes of interest were also identified on the gross and histological pathological specimens. A finite element model‐based deformable modeling algorithm, MORFEUS, was used to resolve the geometric discrepancies due to changes in the position of the liver between each imaging sequence and session through a guided surface projection and finite element analysis. Results: Deformable registration can be used to facilitate comparison of imaging to pathological specimens. In the liver, substantial specimen shrinkage and deformation were seen necessitating deformable image registration. The accuracy of MORFEUS to relate the pathology‐histology to the in vivo imaging was within the slice thickness (5 mm) of the pathology sectioning, determined via identified vessel bifurcations in the liver. Conclusion: An accurate deformable modeling infrastructure has been established to relate the geometric position of the liver and excised liver specimen on different imaging modalities and histology.
SU‐EE‐A3‐05: Accuracy Testing of Deformable Registration Using Dosimetric End‐Points
Authors: Langen K , Meeks S , Limaye A , Zeidan O , Kupelian P , Manon R , Olivera G , Ruchala K , Haimerl J , Lu W
Published: July 2006

Purpose: To develop a dose‐based evaluation method to assess deformable image registration accuracy Method and Materials: An algorithm developed for deformable registration of MVCT to kVCT images was evaluated. The algorithm allows the generation of automatic contours on MVCT images by transferring the kVCT contours using the deformation map. The automatically generated MVCT contours can thus be used to test the deformation algorithm by comparing these contours with manual contours. Instead of a geographic contour comparison, dosimetric endpoints were evaluated after the dose distribution was calculated in the MVCT images. Three dosimetric endpoints (Dmax, Dmean, and Dose to the hottest 2 cc (Dmax (2cc)) were compared for spinal cord contours. The evaluation of geometric end‐points is directly related to the clinical information that needs to be evaluated if daily images are used for adaptive radiation therapy. A total of 93 daily megavoltage CT (MVCT) images from three patients treated for cancers in the head and neck region were evaluated. Results: Averaged over all images the calculated Dmax differed between the automatic and manual contours by 1.1 % with a standard deviation of 3.5 %. The respective values for Dmean and Dmax(2cc) are 0.1 ± 2.5 % and 1.8 ± 2.4 %. Maximum deviations between the dosimetric endpoints were 12 % for Dmax, 8% for Dmean, and 13 % for Dmax(2cc). Conclusions: Using deformable image registration, dosimetric end‐points can be generated from automatic contours in the spinal cord region that differ from manual contours by 1–2 % on average with a standard deviation of 2.5 to 3.5 %. In the spinal cord region the developed deformable image registration appears to provide sufficient accuracy to support clinical decisions. Conflict of interest: Research supported by the vendor that is commercializing the algorithm. Several co‐authors are vendor employees.
SU‐EE‐A3‐06: Deformable Image Registration in Cone‐Beam CT Images for Image‐Guided Adaptive Radiotherapy
Authors: Zhang L , Dong L , Zhu X , Garden A , Ahamad A , Ang K , Mohan R
Published: July 2006

Purpose: With the availability of on‐board imaging devices capable of constructing cone‐beam CT (CBCT) images, it is expected that there will be great interest in using volumetric CBCT for image‐guided adaptive radiotherapy. In order to fully utilize CBCT, automatic segmentation on CBCT images is one of key steps toward this goal. The purpose of this study is to implement a robust deformable image registration for auto‐segmentation. Method and Materials: In four head and neck cancer patients, we used our previously developed, image intensity‐based deformable image registration algorithm to register the planning CT with the 3–5 daily CBCT in three scenarios. First, the daily CBCT was directly used without modification. Second, we applied a generic look‐up‐table transformation to map the CBCT image intensity to the conventional CT intensity using the measured electron density calibration curves for both the conventional and CBCT scanners. In the third scenario, we proposed a wavelet‐based dynamic window/level histogram matching algorithm to map the CT number from CBCT image to the conventional CT image. Then the deformable image registration was performed in the modified CBCT images to map the anatomical structures from the planning CT to the corresponding CBCT images. Results: Without pre‐processing, we found that the CT numbers in CBCT images were inconsistent, especially in soft tissue regions and in patients with large body circumferences. The deformable image registration using the window/level histogram matching method performed the best with good consistency in delineating soft tissue structures. The algorithm is also computationally efficient. Conclusion: We implemented a wavelet‐based window/level histogram matching algorithm to pre‐process the CBCT to allow for more robust deformable image registration of with the reference planning CT. This implementation allows for volumetric CBCT‐guided adaptive radiotherapy.
SU‐EE‐A4‐01: CT Number Accuracy of Lung Nodules: Effect of Patient Body Size and Lung Size
Authors: Goodsitt M , Chan H , Way T , Larson S , Christodoulou E
Published: July 2006

Purpose: To investigate the effects of patient body size and lung size on the CT numbers of lung nodules measured with multi‐detector CT scanners and whether improved accuracy can be obtained with a dual‐energy technique. Method and Materials: Simulated lung nodules consisting of 9.5‐mm diameter spheres containing 50mg/cc and 100mg/cc CaCO3 in a water‐equivalent resin were scanned in two simulated thorax section phantoms with a GE VCT scanner. One phantom (A) represented the middle of the chest. It had large simulated lung regions and simulated ribs, heart and spine. The other (B) represented the upper chest. It had a much wider aspect ratio, smaller simulated lung regions, and simulated ribs, scapula, heart, and spine. Fat rings were added to the phantoms to simulate larger patients. Images were acquired on a GE VCT scanner with high‐resolution techniques (0.53:1 pitch, 0.625‐mm slice thickness and interval) at 80, 120 and 140kVp. Scans were repeated 3 times for reproducibility and analyzed using an automated technique. Results: Body size had a significant effect on the measured mean CT‐numbers of the nodules. For phantom‐A, adding fat rings decreased the overall average CT‐numbers of the 50mg/cc nodules at 120kVp by 15HU and those of the 100mg/cc nodules by 21HU. Corresponding reductions in phantom‐B were 9HU and 13HU. The dual‐energy approach (CT#80kVp‐CT#140kVp) reduces the variability, with a maximum difference of 4HU for all conditions. Lung size had a minimal effect with a maximum difference (nodule CT# phantom A ‐ nodule CT# phantom B) of 4.5 HU. Conclusion: Even with modern multi‐detector CT scanners, beam hardening and x‐ray scatter errors due to body size can result in underestimates of the true CT numbers of lung nodules. A dual‐energy approach compensates for these errors and should be considered especially if it can be implemented using a rapid kVp switching technique.
SU‐EE‐A4‐03: Spatial Resolution‐Matched Comparison Between Fan‐Beam and Cone‐Beam X‐Ray CT Images
Authors: Lasio G , Williamson J , Du W , Fatyga M
Published: July 2006

Purpose: Cone Beam CT (CBCT) kilovoltage imaging devices are increasingly available for daily imaging in radiotherapy departments. Flat‐panel based CBCT scanners present a distinctive set of artifacts due mostly to increased scatter, longer data acquisition time and reduced detector quantum efficiency as compared to helical Fan Beam CT (FBCT) systems. Our purpose is to characterize image quality from FBCT and CBCT scanners based on noise, contrast and dose, using FBCT as a benchmark. Method and Materials: we acquired phantom and clinical patient images with a CBCT Varian On‐Board Imager as well as with a FBCT Picker PQ5000 single‐row helical scanner. The CBCT scanner was equipped with antiscatter grid and bowtie filter. By comparing CBCT and FBCT images of a high contrast resolution insert, the CBCT reconstruction voxel size and filter were adjusted until the spatial resolution of the FBCT and CBCT images was approximately matched. Dose was measured with standard CTDI and Farmer chambers. Noise, contrast and SNR were evaluated and compared. Results: CBCT images of both phantom and patient were relatively free of streaking and cupping artifacts, indicating that the grid had successfully attenuated most of the scatter. Low contrast detectability threshold is similar for the two modalities, when CBCT dose is about twice as large as FBCT. Noise and non‐uniformities are more prevalent in patient CBCT images, but pelvic soft tissue structures are well discernible. For patient and phantom images Dose×SNR2 is about 4 times lower for FBCT than in CBCT, which is about 1.5–2 times larger than expected, given the measured grid transmission and detector quantum efficiency. Conclusion: In this study, resolution‐matched CBCT and FBCT images could exhibit similar SNRs and contrast‐to‐noise ratios through a combination of increased imaging dose and reduced spatial resolution.
SU‐EE‐A4‐04: Phase and Amplitude Binning for 4D‐CT Imaging
Authors: Abdelnour F , Nehmeh S , Pan T , Humm J , Vernon P , Schoder H , Rosenzweig K , Mageras G , Yorke E , Larson S , Erdi Y
Published: July 2006

We compare the consistency and accuracy of two image binning approaches used in 4D‐CT imaging. In 4D‐CT the images and respiratory motion are correlated via RPM Respiratory Gating system (Varian, Palo Alto, CA). In phase binning (PB), RPM assigns each breathing cycle 2π radians, within which the images are grouped. Alternately, the images are assigned bins according to the signal's amplitude (AB). To quantitate both approaches, we used NEMA NU2‐2001 IEC phantom oscillating at random frequencies and amplitudes, simulating patients breathing. 4D‐CT images were obtained using 4‐slice GE Lightspeed CT operating in cine mode. We define consistency error as ability to correctly bin over breathing cycles in the same FOV. Average consistency error in PB ranged from 18%±20% to 30%±35%, while in AB the error ranged from 11%±14% to 20%±24%. For 28mm sphere, PB images were hardly consistent, with error of 43%±47%, while AB images for the same sphere resulted in error of only 18%±22%. In PB, while not all breathing cycles covered all phases, nearly all bins contained sphere slices. AB was more accurate, revealing empty bins where no sphere slices existed. As a proof of principle, we present examples of two NSCLC patients' 4D‐CT lung images binned by both approaches. While AB can lead to gaps in the images, depending on patients' breathing pattern, PB exhibits no gaps but suffers visible artifacts due to misbinning, yielding images that covered a relatively large amplitude range. AB was more consistent, though often resulting in gaps corresponding to CT slices where no data existed due to patients' breathing. We conclude AB is more accurate than PB, which should be factored into treatment planning and diagnosis.

Work supported by GE Healthcare Technologies and Varian Medical Systems.
SU‐EE‐A4‐05: Effects of Cone‐Beam CT Noise and Cupping Artifacts On Deformable Image Registration
Authors: Murphy M , Lu L , Crimaldi A , Cuttino L , Shield C , Keall P , Siebers J , Williamson J
Published: July 2006

Purpose: Image‐guided adaptive radiotherapy proposes to use sequential CT studies to track anatomical change during treatment via deformable image registration. These CT studies can be acquired with either conventional fan‐beam CT systems or more novel cone‐beam CT techniques. However, cone‐beam CT images can have higher noise levels and more imaging artifacts than fan‐beam CT, which might impact registration accuracy. We have investigated the effect of these image quality differences on the deformable registration of fan‐beam and simulated cone‐beam CTs. Method and Materials: Our study used two fan‐beam CT studies of a prostate patient, taken ten days apart. A deformable image registration process was used to register the two studies and then transfer treatment planning contours from one CT to the other. The accuracy of the automatically‐transferred contours (and thus of the deformable registration process) was assessed by comparing them to manual contours, with the differences evaluated with respect to inter‐observer variability in the manual contours. Then one of the fan‐beam CTs was modified to include higher noise and cupping artifacts characteristic of cone‐beam CT and the tests were repeated. Changes in registration accuracy were detected by monitoring changes in the automatically‐transferred contours. Results: We found that the additional noise and the cupping artifact caused no appreciable loss of registration accuracy at magnitudes up to and exceeding what would normally be found in an actual cone‐beam CT. Conclusions: We conclude that deficiencies in cone‐beam CT quality that might reduce manual contouring accuracy do not necessarily reduce image registration and automatic contouring accuracy.
SU‐FF‐I‐01: Determination of Subjective Similarity for Pairs of Lesions On Mammograms: Comparison of Ranking Scores in 2AFC Versus Absolute Ratings for Masses and Microcalcifications
Authors: Muramatsu C , Li Q , Schmidt RA , Suzuki K , Shiraishi J , Newstead GM , Doi K
Published: July 2006

Purpose: We previously obtained the subjective similarity ratings for pairs of lesions on mammograms for quantitative evaluation of similar images. Our purpose in this study was to investigate whether the absolute similarity ratings can be determined reliably by comparison with ranking scores obtained in a 2‐alternative forced‐choice (2AFC) method. Method and Materials: We selected 8 pairs of masses and 8 pairs of clustered microcalcifications based on radiologists' average similarity ratings; similarity ratings for the two sets of 8 pairs were approximately evenly distributed. In the first study, each pair was compared one by one to all other 7 pairs in each group of masses and microcalcifications. In the second study, we combined four pairs of masses and four pairs of microcalcifications to compare the similarity of a pair of masses with that of microcalcifications. Seven radiologists and 3 senior residents were asked to choose one pair that was more similar than another pair with the 2AFC method. The cases were presented in randomized order. The number of times that a pair was selected as more similar was counted as the subjective ranking score. The average scores were compared with the average similarity ratings determined previously. Results: The average ranking scores from the first study were highly correlated (0.93 and 0.98 for masses and calcifications, respectively) with absolute similarity ratings. When mass pairs were compared with calcification pairs, the correlations between ranking scores and absolute ratings were also very high (0.92 and 0.96). In both studies, observers were very consistent in selecting more similar pairs. Conclusion: The result indicates that absolute similarity ratings determined previously are reliable and useful for selection of similar images. The concept of similarity is robust and meaningful even when mass pairs are compared with microcalcification pairs.
SU‐FF‐I‐02: Entrance Exposures During On‐Board KV Imaging
Authors: Kress A T , Santanam L , Klein E
Published: July 2006

Purpose: To estimate entrance exposure levels during on‐board kV imaging (Version 1.2) on Trilogy (Varian Medical Systems). Methods and Materials: The patient was simulated by phantom using 40 cm and 20 cm of 40 × 40cm2 water equivalent slabs. Exposure measurements were acquired for 80 and 90 cm source‐to‐surface distances using a 150 cc Fluke ionization chamber (96020C) and an Innovision 3050A dosimeter. The measurements were performed for various preset techniques that are commonly used in the clinic such as AP pelvis, Lat Pelvis, AP head, AP thorax, and AP extremity. Exposure rate levels were also measured during pulsed fluoroscopy with the automatic background control option activated. For comparison purposes, the exposure levels on a conventional simulator were also measured. Results: The entrance exposure levels on the on‐board imager vary between 0.13 mSv for an extremity technique to 4.9 mSv for a lateral pelvis technique and were comparable to the conventional simulator measurements. On‐board imaging pulsed fluoroscopy exposure levels were higher than those measured using the continuous fluoroscopy technique on the conventional simulator. Conclusions: Though the exposure and exposure rates are relatively low and inconsequential to the overall course of prescribed therapy, it is important to document exposures received. This documentation is essential for imaging protocols that may exceed normal imaging and localization exposure levels.
SU‐FF‐I‐05: Hounsfield Units Calibration with Adaptive Compensation of Beam Hardening for a Dose Limited Breast CT System
Authors: Yang K , Kwan A , Burkett G , Boone J
Published: July 2006

Purpose: Hounsfield Units calibration with adaptive compensation of beam hardening for a dose limited breast CT system. Method and Materials: Following a complete cone beam CT scan of the target object (a human breast), geometrical parameters of the object, including the mass center location and maximum radius from the mass center were calculated promptly. These parameters were used to compute X‐ray projection images of a water cylinder based upon photon attenuation in the cylinder and detector response. Projection images of the target object were corrected prior to reconstruction by logarithmic subtraction of the water cylinder projection images. CT images relative to the Hounsfield Units (HU) scale were produced after cone beam reconstruction of the corrected projection images. Custom built water phantoms were tested with various inserts, including polyethylene, polystyrene, PMMA, nylon, polycarbonate and Teflon, with a density range from 0.92g/cm3 to 2.2g/cm3. Results: A wide range of breast diameters (10cm–18cm) and compositions (0%–100% glandular) were evaluated, and reconstructed and scaled HU values demonstrated excellent uniformity, linearity and consistency. Typical HU values were within 5% of theoretical values. The proposed method was applied to clinical breast scans. The “cupping” artifact caused by beam hardening in the original image was corrected as expected. Conclusion: Conventional methods of Hounsfield Units conversion are based on the scan of few fix‐sized water phantoms and lack the flexibility to compensate for the beam hardening from objects with various sizes. The introduced noise from water phantom scans is also not negligible, especially for a dose limited breast CT system with much lower mAs than whole body CT systems. The proposed method can compensate for beam hardening over a wide range of breast diameters and compositions without increasing noise contents in the image.
SU‐FF‐I‐07: Characterization of a Novel Anthropomorphic Plastinated Lung Phantom
Authors: Yoon S , Henry R , Bouley D , Fahrig R
Published: July 2006

Purpose: To quantify the anatomical and imaging characteristics of a novel anthropomorphic lung phantom constructed using plastination. Method and Materials: The pig's thorax was scanned in‐vivo at known partial pressures on a clinical CT (Siemens Sensation 16, 120kVP, 100mAs, recon 0.54×0.54×0.75mm∧3). The lungs were extracted, inflated, and fixed by intra‐tracheal perfusion of 10% formalin while the pulmonary vessels were injected with Silastic E RTV silicone. The specimen was dehydrated (remove and replace tissue fluid with an organic solvent) in cold acetone and the lungs were impregnated with a curable silicone polymer via slow decreasing pressure. Finally, the polymer was polymerized using a curing agent. The plastinated phantom was then scanned (120kVp, 200mAs, 0.43×0.43×0.75mm∧3). Anatomical features, volume measurements, and CT values were compared using in‐vivo and phantom clinical CT reconstructions. Results: The plastinated phantom is stable on the timescale of years and retains major anatomical features of the in‐vivo lung. The phantom airway volume was 66% of the in‐vivo measurement at inspiration but equal to the measurement at expiration. Vessel and lung volume comparisons were complicated by incompletely filled vessels and air pockets inside the phantom; nevertheless, lung volume measurements differed by less than 15%. Mean CT values of the cardiac tissue in the phantom (168 +/− 46) were 132 HU higher than in‐vivo (36 +/− 87). Mean CT values of the pulmonary tissue were nearly equivalent for both datasets, attributed to an 11% decrease in the apparent tissue density due to over‐inflation during plastination. Conclusion: This work shows that the novel plastinated lung phantom retains the anatomical and imaging characteristics of an in‐vivo lung. This accurate and complex lung phantom has many uses including imaging system comparisons, providing a known, stable reproducible complex background for visibility studies and will be used for our own studies in lung tomosynthesis optimization.