bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐C‐137‐03: Implementing and Evaluating Aperture Morphing for CBCT‐Based Adaptive Planning
Authors: Zhao A , Godley A , Stephans K
Published: July 2013

Purpose: To implement and test a novel application of an online adaptive re‐planning technique, segment aperture morphing (SAM), to kV cone‐beam CT (CBCT). Methods: Five IMRT prostate patients with kV CBCT image guidance were chosen. The patients were re‐planned with Panther planning system (Prowess), 5 mm margin, prescribed PTV D95 of 76 Gy, prostate D100 of 78 Gy. Daily contours were generated on nine CBCTs each using ABAS (Elekta). SAM, as implemented in Panther, then executes to morph apertures based on changes in the beams eye view target shape thereby correcting for both deformation and translation of the target through MLC adjustments. The 45 SAM plans were compared to the current standard of IGRT based shifts. The Panther re‐plan, SAM and shifted plan calculations were done without heterogeneity corrections to avoid uncertainties in CBCT electron density. The DVH parameters used in treatment planning were compared between SAM and shifted. Results: The SAM method provided significantly better target coverage, P<0.0002 for all target DVH parameters. SAM maintained target coverage with average prostate D100 of 78Gy and PTV D95 76Gy, while repositioning left the target under‐dosed at 72Gy. SAM also decreased rectal dose, in particular reducing V60 from 15.4 to 14.0% (P=0.0185). On average bladder dose is lower for repositioning but this at the cost of considerably reduced target coverage, (shifted bladder dose correlates to target dose with an r2∼0.2.) In all but one fraction, the prostate is best covered by SAM. The contour generation takes ∼20‐60 seconds, SAM is instantaneous and the dose calculation ∼20 seconds. Conclusion: Aperture morphing based on target shape change determined by auto‐segmentation consistently and significantly improves target coverage and reduces rectal dose compared to rigid IGRT shifts. It is a viable method for CBCT‐based adaptive planning. A research version of ABAS was provided by Elekta AB, Stockholm, Sweden, and a research version of Panther by Prowess Inc, Concord, CA.
TH‐C‐137‐08: Dosimetric Quality of An Automatic IMRT Planning Method for Head and Neck Cancer Cases
Authors: Yuan L , Pang T , Ge Y , Li T , Yin F , Wu Q Jackie
Published: July 2013

Purpose: To evaluate the dosimetric quality of an automatic IMRT planning method for Head and Neck (HN) cancer cases. Methods: Eighteen HN cancer patients are planned with nine equally spaced IMRT beams. The OAR dose sparing objectives for each plan (primary and boost) are generated automatically by the OAR DVH prediction models based on the patient anatomy. The DVH models are trained by prior IMRT plans. The predicted DVHs are sampled and transformed into a template based dosevolume constraints and optimization priorities which are utilized by the plan optimization algorithm. Only one round of optimization was performed for each case without any human intervention. The dosimetric parameters of the OARs and PTV in the automatically generated plans (auto‐plans) are evaluated against those from the clinical plans by a paired comparison method. Results: The average PTV dose homogeneity (D2%–D99%) in the auto‐plans is 5.5 Gy, which is comparable with that in the clinical plans (5.4 Gy). For the OARs, the means (standard deviation in parenthesis) of the differences of the dosimetric parameters in the auto‐plans compared with the clinical plans are (in Gy): parotids D50%: −2.5 (9.4), oral cavity D50%: −0.9 (3.5), larynx D50%: −1.3 (9.7), pharynx D2%: −0.3 (3.6), spinal cord D2%: − 2.2 (4.0), brainstem D2%: −0.9 (3.9), mandible D2%: −0.4 (1.3). The negative mean values indicate the OARs can be further spared in average. However, the differences of the dosimetric parameters are not statistically significant for all the other OARs except spinal cord (p=0.002), which is due to large spinal cord dose reduction in several auto‐plans even when the spinal cord dose in the corresponding clinical plans have met the physician's dose sparing constraint. Conclusion: The automatic IMRT planning method utilizing the DVH prediction models can generate plans with dosimetric quality comparable to clinical IMRT plans generated by experts. Partly supported by NIH/NCI and a Varian master research grant.
TH‐C‐WAB‐06: Target Volume Delineation Study of Compressed Sensing Cone‐Beam CT for Head‐And‐Neck and Breast Cancer Patients During Radiation Therapy
Authors: Zhang H , Tan W , Sonke J
Published: July 2013

Purpose: Cone‐beam (CB) computed tomography (CT) is widely used for image guided radiotherapy. Compressed sensing (CS) based CBCT reconstruction techniques are investigated to improve CBCT image quality to facilitate adaptive radiotherapy applications. The purpose of this study was to assess the impact of CS image quality improvements on delineation uncertainties of targets and organs‐at‐risk in head‐and‐neck (H&N) and breast cancer patients. Methods: Eight H&N and eight breast patients were selected. Each H&N patient had one planning CT (CTP) and three repeat CTs (CTR), and each beast patient had one CTP and one CTR. The corresponding CBCTs on the same day of CTR were reconstructed by both the conventional filtered back‐projection (CBCTCON) and compressed sensing (CBCTCS) methods. All CTR, CBCTCON, and CBCTCS were rigidly registered to their CTP. Then gross tumor volume (GTV), parotid glands, spinal cord, and sternocleidomastoid muscles were manually delineated for H&N cancer patients, and the breast and tumor bed (TB) for breast cancer patients. The delineated volumes were determined, and the impact of image quality differences were quantitatively assessed by dice similarity coefficient (DSC), and the shortest perpendicular distance (SPD) between contours of two images. The paired T‐test was used for statistical comparison. Results: The average volume ratio of CBCTCS/CBCTCON was 0.96, which indicated delineated volumes of CBCTCS were smaller than CBCTCON. The results of DSC and SPD from H&N and breast patients demonstrated that CBCTCS was closer to CTR than CBCTCON, where CTR was considered as the golden standard and they were statistically significant. In the temporal direction of H&N patient, a trend of decreasing DSC in GTV was found to suggest anatomic changes. Conclusion: This study demonstrated that CS CBCT improves delineation accuracy in H&N and breast cancer patients over conventional reconstruction. The results suggest that CS CBCT has potential for image guided adaptive interventions. This research was sponsored by CTMM, project Breast CARE (grant 03O‐104).
TH‐C‐WAB‐09: Diffusion Weighted MRI of Esophageal Cancer
Authors: van Lier A , Meijer G , Moerland M , Lever F , Reerink O , Vulpen M , Lagendijk J , Lips I , van den Berg C
Published: July 2013

Purpose: To investigate the potential of diffusion weighted MRI for esophageal cancer imaging for treatment volume definition, and to determine the need for geometrical correction of DWI images. Methods: Three patients with esophageal cancer were included in this study. A heavily diffusion weighted free‐breathing DWI scan (b=800 s/mm2) with echo‐planar readout was optimized to reduce the effect of field distortions. Additionally, a B0 map (main magnetic field map), a T2w MRI and a CT were obtained and co‐registered. Two radiation‐oncologists delineated the primary tumour on the T2w image. High contrast between restricted (= tumor) and less restricted diffusion enabled definition of the tumour volume by thresholding. Geometrical inaccuracy of DWI images arises from inhomogeneities in the main magnetic field and the low bandwidth in the phase encoding direction; therefore inaccuracies can retrospectively be corrected using the B0 map. The dice coefficient between the delineated tumor volume and the original or correct DWI‐based tumor volume was determined. Results: In all patients, a region with restricted diffusion was observed in the esophagus. In one of the patients, also restricted diffusion was observed in adjacent (mediastinal) lymph node(s). Geometrical correction of the DWI images increased dice coefficient between the delineated volume and the thresholded volume (before: 0.75, 0.71, 0.74, after: 0.86, 0.79, 0.9,. respectively). Conclusion: DWI of the esophagus shows excellent contrast between healthy and suspicious tissue. This enabled definition of the tumour volume using a threshold. After geometrical correction the tumour volume was in closer agreement with the delineated volume. Geometrical correction may be also useful for direct comparison of (co‐registered) DWI, PET and CT images. In future, accuracy and robustness of geometrical correction will be studied in a larger patient group. Furthermore, the use of DWI for treatment reponse monitoring and detection of metastatic mediastinal lymph nodes will be investigated.
TH‐C‐WAB‐10: Gradient Assisted Non‐Connected Automatic Region (GANAR) Algorithm: Towards Robust PET‐Based Target Definition
Authors: Galavis P , Holden J , Paliwal B , Jeraj R
Published: July 2013

Purpose: To develop and validate a PET‐based segmentation method that is robust under varying acquisition modes and reconstruction parameters. Methods and Materials: Gradient Assisted Non‐connected Automatic Region (GANAR) method generates texture feature images to segment distinct properties of the tumor with an optimized non‐connected region‐growing algorithm (twelve contours are generated). An expectation‐maximization algorithm is used to define the final region of interest. By incorporating texture feature information and parameter optimization, GANAR is less sensitive to acquisition mode and reconstruction parameters. The accuracy of GANAR was assessed using thirteen inhomogeneous and irregular‐shaped lesions from a Monte Carlo phantom simulated PET phantom. The robustness of GANAR was assessed using FDG PET/CT images of twenty patients acquired in 2D and3D modes, and reconstructed with varying parameters. In total, ten reconstructions per patient were used. The Dice and Modified Hausdorff Distance (MHD) metrics were used to quantify accuracy and robustness. GANAR was compared against conventional methods, such as threshold‐based, gradient‐based and region‐growing. Results: Using Dice, GANAR (0.89±0.04) was more accurate than the threshold (0.83±0.07), gradient (0.75±0.07), and region‐growing (0.80±0.08) methods. Likewise, using MHD GANAR (0.2±0.1 cm) was more accurate than the threshold (0.4±0.2 cm), gradient (0.5±0.1 cm), and region‐growing (0.4±0.2 cm) methods. GANAR was also more robust with higher Dice coefficient ranges of [0.85–0.98], than the threshold [0.69–0.93], gradient [0.66–0.98], and region‐growing [0.46–0.91] methods. Similarly, the GANAR's MHD ranges [0.02–0.18]cm was smaller than that of threshold [0.08–0.23]cm, gradient‐based [0.01–0.26]cm and region‐growing [0.13–0.70]cm methods. Conclusion: A new robust segmentation method was developed and validated against simulated PET phantoms and patient FDG PET/CT data. In both accuracy and robustness, the new method outperformed conventional segmentation algorithms.
TH‐C‐141‐03: A Machine Learning Algorithm‐Based Risk Stratification of Prostate Gland Lesions Using Quantitative and Texture Features From Diffusion Weighted MRI
Authors: Tyagi N , Tang X , Yan D , Nandalur K
Published: July 2013

Purpose: To propose a machine learning algorithm‐based risk stratification method of prostate gland lesions using quantitative and texture features derived from diffusion weighted MRI (DW‐MRI). Methods: 43 patients with biopsy‐proven prostate cancer underwent DW‐MRIs of the prostate using an optimized single‐shot echo planar imaging sequence at 3T. Quantitative apparent diffusion coefficient (ADC) maps were generated via a mono‐exponential fit using three b‐values (50, 400 and 800s/mm2). 43 lesions were identified in peripheral zone (pz) and 13 in central gland (cg). Statistical and textural parameters were extracted from these lesions. Patients were grouped into low, intermediate and high risk group based on NCCN risk scoring guideline. 16 quantitative parameters (mean, kurtosis, percentile etc) and 5 texture parameters (energy, entropy, correlation, contrast and homogeneity) were calculated for each patient. Artificial Neural Network (ANN) was applied to classify patients into one of the three risk groups based on their MRI parameters. A sub‐group of patients were used as ANN training samples, and the rest was used as test samples. Classification accuracy, precision, and sensitivity were reported. Results: Both statistical and texture parameters showed strong correlation to Gleason score for only PZ tumors and not CG tumors. Classification sensitivity performed using 5 texture parameters for all tumors, pz tumors and cg tumors was 100%, 98% and 91% respectively. Sensitivity using quantitative parameters only was 97%, 95% and 100%. Finally using all the parameters, sensitivity was 93%, 95% and 81% implying that adding texture information is not very sensitive for cg tumors as compared to pz tumors. The positive predictive value (PPV) was 100% for all the above cases. Conclusion: ANN is a reasonably accurate algorithm with high sensitivity and PPV to classify prostate MRIs into risk groups. Further analysis will be done on the minimum number of training points required for the proposed technique.
TH‐C‐141‐04: Feasibility of MR Relaxometry‐Guided Synthetic CT Image Formation for MRI‐Based Radiation Treatment Planning
Authors: Paulson E
Published: July 2013

Purpose: Recently, several groups have begun investigating methods to generate synthetic CT images from MRI images to facilitate MRI‐based radiation treatment planning. The goal of this work was to determine the feasibility of a novel approach for generating synthetic CT images using MR relaxometry guidance. Methods: MR relaxometry images of the head and pelvis were acquired on three volunteers using a Siemens 3T scanner. Rapid T1 mapping was performed by linear least squares fitting of the Ernst model to multiple flip angle (2, 5, 10, 15 deg) images acquired with a 3D FLASH sequence and corrected for B1+ inhomogeneities using a custom, 3D actual flip angle imaging (AFI) sequence. Rapid T2* mapping was performed by linear least squares fitting of eight echo time (2.9–29.1 ms) images acquired with a 3D FLASH sequence. Vendor‐provided 3D distortion correction was applied to all images to correct for gradient nonlinearity distortions. Tissue classification was performed based on published values of T1 and T2* at 3T. Electron densities (EDs), obtained from ICRU Report 46, were assigned to the segmented structures. Synthetic CT images were generated by combining the segmented ED structures and applying an inverted CT‐ED conversion table from a clinical radiation treatment planning system. Results: Total scan time for the MR relaxometry and AFI images was approximately ten minutes. T1 maps generated with B1+ correction demonstrated high uniformity compared to T1 maps obtained without correction. The combination of T1 and T2* maps was necessary to classify tissues in the head and pelvis regions. Synthetic CT images were successfully generated and transferred onto a radiation treatment planning system. Conclusion: Generation of synthetic CT images for MRI‐based radiation treatment planning using MR relaxometry‐guidance is feasible. Further investigations will compare synthetic CT images generated using the proposed approach to actual CT images in patients.
TH‐C‐141‐09: A Comparison of MRI Distortion Between Scanners and Sequences for Radiotherapy Purposes
Authors: Walker A , Holloway L , Liney G , Metcalfe P
Published: July 2013

Purpose: To quantify the magnitude and distribution of system related geometric distortion present in MR images and determine the clinical radiotherapy sites for which this distortion is likely to have most impact. Methods: A commercially developed phantom conforming to AAPM standards for testing uniformity and linearity was imaged on 4 different MRI scanners. Similar T1 and T2 weighted clinical protocols were assessed. Each sequence and scanner had varying protocol parameters. Additionally, the direct impact of altering the receiver bandwidth (7.69 – 76.8kHz) on distortion and signal to noise was conducted on a standard spin echo sequence. The position of each phantom grid point was determined using in‐house MATLAB code, then compared to the known position as verified by a CT scan of the phantom to obtain the deformation matrix. Positions of anatomical sites (breast, lung, cervix, prostate and H&N) were determined by analysing radiotherapy contoured data for 10 patients per site to establish the range of distortions occurring within these regions. Results: Distortions were observed to range from 0mm – 8.9mm in magnitude. Maximum distortion values measured across one of the similar clinical spin echo sequences tested varied from 2.75mm – 8.94mm. Similarly, comparison of a gradient echo sequence showed maximum distortions varied from 2.56mm – 3.33mm. Increasing the bandwidth reduced the maximum distortion present in the image by 3.49mm, at the cost of SNR. While distortion magnitudes and distributions varied, in most sequences the distortions began exceeding 2mm beyond a radial distance of 100mm from isocentre, where the oral cavity, lungs and breast lie. For regions where the prostate, cervix and brain stem lie, distortions were below 2mm. Conclusion: This work displays the variations in distortions present in MR images for different sequences and scanners. Distortions are of greatest magnitude in areas where the lung and breast would be located for radiotherapy purposes.
TH‐C‐141‐10: Error of Template Matching for Tracking Tumor Motion Is No Larger Than Inter‐Operator Variability
Authors: Shi X , Diwanji T , Mooney K , D' Souza W , Mistry N
Published: July 2013

Purpose: Recently, template matching has been proposed to track tumor motion using cine‐MRI images. However, the technique has been tested primarily on blood vessels in healthy subjects. In this work, we demonstrate the utility of automated template matching in patients with thoracic tumors. We also compare the variability in predicting tumor position using template matching and 3 human operators. Methods: Five patients with non‐small cell lung cancer (NSCLC) were recruited in a prospective study. Cine‐MRI imaging was performed while the patients were instructed to breathe normally. True FISP (fast imaging in steady state) cine‐images were obtained in the sagittal plane. The centroids of the tumors were determined manually by 3 operators and also by the automatic template matching technique. The differences both in the AP and SI directions between the automatic and manual methods and the inter‐operator variability were calculated respectively and compared. Results: For all patients the variability between automatic and human operators in the SI direction was less than the inter‐operator variability. For 4 out of 5 patients the variability between automatic and human operators in the AP direction was less than the inter‐operator variability. However, the variability in 1 patient was higher by 14%. This is attributed to out‐of‐plane motion that currently is not captured using the cine‐MRI imaging. Conclusion: The effectiveness of template matching to estimate tumor position during respiratory motion was tested in patients with lung cancer. Results show that, the difference between the automatic and manual methods was comparable to the inter‐operator variability. Future efforts to integrate on‐board MRI imaging with linear accelerators can benefit from automated tumor tracking with template matching. Furthermore, the technique can also be utilized to replace the laborious manual tracking process necessary to establish the ground‐truth when evaluating external surrogates of tumor motion. NIH/NCICA 122403
TH‐C‐141‐12: Evaluation of Potential Internal Target Volume for Liver Tumor with Consideration of Respiratory Variation Using Cine MRI
Authors: Akino Y , Oh R , Masai N , Shiomi H , Inoue T
Published: July 2013

Purpose: Although four‐dimensional CT (4DCT) is valuable for evaluating the respiratory motion and internal target volume (ITV) for liver stereotactic body radiotherapy (SBRT), 4DCT cannot consider the respiratory variation. Here, we developed a novel technique to evaluate the potential ITV with consideration of respiratory variation using cine‐magnetic resonance imaging (cine‐MRI). Methods: We retrospectively evaluated 6 patients who received liver SBRT in 2012. The planning CT (pCT) was acquired with free breathing, and then 4D‐CT and cine‐MRI images were also acquired with the same set‐up condition. The respiratory signal was derived from the peak of the diaphragm on cine‐MRI frames. The motion vectors of 500 feature points in consecutive two frames were calculated using pyramidal implementation of the Lucas‐Kanade optical flow algorithm. The contour of tumor, blood vessel near tumor, or liver was delineated on one frame and the corner points of the contour were shifted onto the other frames using the motion vectors and then the tumor trajectory was calculated. On pCT images, gross tumor volumes delineated on the inspiration and expiration phases of 4D‐CT were three‐dimensionally translated using the tumor trajectory calculated with sagittal and coronal cine‐MRI. The distribution of the existence probability of the tumor was evaluated. Results: The concordance between ITV determined with 4D‐CT and potential ITV were evaluated with Dice similarity coefficient (DSC). When the voxels with the existence probability higher than cut‐off values were considered as potential ITV, the maximum DSC for each patient was 0.88 (range 0.84% to 0.93) and the cut‐off for maximum DSC was 24.5% (range 17% to 32%). Conclusion: We developed a novel technique to evaluate the potential ITV of liver tumor with consideration of the respiratory variation. Potential ITV may be approximately 20% larger than ITV determined with 4DCT. The volume will be larger for patients with large variation in respiration.
TH‐C‐103‐03: Iterative CT Reconstruction Via Minimizing Adaptively Reweighted Total Variation
Authors: Zhu L , Niu T
Published: July 2013

Purpose: Iterative reconstruction via total variation (TV) minimization has demonstrated great successes in accurate CT imaging from under‐sampled projections. When projections are further reduced, over‐smoothing artifacts appear in the current reconstruction especially around the structure boundaries. We propose a practical algorithm to improve TV‐minimization based CT reconstruction on very few projection data. Methods: The L‐0 norm approach is more desirable from the perfective of further reducing the projection views. To overcome the computational difficulty of the non‐convex optimization of the L‐0 norm, we implement an adaptive weighting scheme to approximate the solution via a series of TV minimizations for practical use in CT reconstruction. The weight on TV is initialized as uniform ones, and is adaptively changed based on the gradient of the reconstructed image from the previous iteration. The iteration stops when a small difference between the weighted TV values is observed on two consecutive reconstructed images. Results: On the digital Shepp‐Logan phantom, the proposed method reduces reconstruction errors in the conventional TV minimization from 7.3% to 1.4% with 20 projections, and from 25% to 6.5% with 15 projections. With 20 projections on the Catphan600 phantom, our method reduces contrast errors in the ROIs from 45 HU to 6 HU. The rise width at the object edges in the image is also reduced by 40%, showing a substantial image resolution improvement. Conclusion: By adaptively reweighting TV in iterative CT reconstruction, we successfully further reduce the projection number for the same or better image quality. The technique is attractive in the applications of CT reconstruction on a small size of projection data.
TH‐C‐103‐08: BEST IN PHYSICS (IMAGING) — A Hybrid 4D Cone Beam CT Reconstruction Algorithm for Highly Under‐Sampled Projections From the 1‐Minute Cone Beam Scan
Authors: Yan H , zhen x , Folkerts M , Pan T , Cervino L , Jiang S , Jia X
Published: July 2013

Purpose: To facilitate fast and accurate 4D image guidance for lung and upper abdomen radiotherapy, we propose a novel 4D cone beam CT (4D‐CBCT) reconstruction algorithm that offers high‐quality images from highly under‐sampled projections under the conventional 1‐min CBCT scan. Methods: As opposed to conventional reconstruction approaches via image intensity domain, our method integrates patient‐specific CT information and reconstructs 4D‐CBCT image via motion vector domain. It solves an optimization problem, where a deformation vector field is determined, such that, when being used to deform the patient prior CT image, the projections match the measurements. We develop a forward‐backward splitting (FBS) method to solve this problem. Specifically, an intermediate variable is introduced to split the original problem into two iteratively preformed sub‐problems, i.e., reconstruction of the intermediate variable based on projections and the currently reconstructed 4DCBCT image, and deformable registration between the prior image and the intermediate variable. This hybrid algorithm achieves a solution with both right geometrical information defined by measured CBCT projections and correct intensity values from the prior CT, yielding high quality 4D‐CBCT images. Both experiments on a moving ball phantom and patient studies have been performed to validate the proposed method. Results: Even with very limited number of projections from a 1‐min CBCT scan, artifacts‐free 4D‐CBCT images with correct HU values can be obtained by the proposed algorithm in both phantom and patient studies. To validate the anatomical geometry accuracy, the ground‐truth ball center location along the superior‐inferior direction is compared to that measured in the reconstructed 4D‐CBCT. Satisfactory agreements (0.364mm average and 0.504mm maximum error) are observed. Conclusion: A hybrid 4D‐CBCT reconstruction algorithm is developed for highly under‐sampled projections from the conventional 1‐min CBCT scan. It is capable of reconstructing high‐quality images free of under‐sampled streaking with accurate HU values. This work is supported in part by NIH (1R01CA154747‐01), Varian Medical Systems through a Master Research Agreement, the Early Career Award from Thrasher Research Fund, and the University of California Lab Fees Research Program.
TH‐C‐103‐09: Potential Gains of Incorporating Iterative Reconstruction Into 4DCT
Authors: Glide‐Hurst C , Price R , Adams J , Chetty I
Published: July 2013

Purpose: IGART requires high quality, volumetric imaging for routine feedback and cumulative dose analysis. We propose to incorporate iterative reconstruction (IR) into 4DCT to reduce imaging dose while maintaining image quality, to facilitate routine 4DCT for IGART. Methods: Static thorax phantom CTs (100–500 mAs) and 4DCTs (200–800 mAs) of an in‐house deformable lung phantom undergoing respiration were acquired. IR was applied to phantom data at Levels 1–6 (L1–L6), corresponding to noise reduction factors of 0.89−0.55, with respect to filtered backprojection (FBP). Mean and standard deviation (μ and σ (image noise), respectively) were calculated via region of interest (ROI) analysis. Contours were assessed via Dice Similarity Coefficients (DSCs). Profile analysis evaluated boundary preservation between IR levels. Contrast to noise ratio (CNR) and dose savings were quantified. Raw 4DCT projections for 10 patient datasets (5 lung, 5 liver, 120–140 kVp, ∼800 mAs) were retrospectively reconstructed with FBP and IR levels L1–L6. ROI analyses (tumor and nearby lung/liver) were conducted. Results: For the thorax phantom, comparable noise was obtained between L6 IR at 100 mAs and FBP at 600 mAs at 6‐fold dose savings. In the deformable phantom, maximum CT number discrepancy occurred between FBP and L6 (4 HU, 300 mAs). Profile analysis revealed negligible boundary differences between FBP and IR. CNR increased with increased IR level across mAs settings (0.7–2.2% for L3 and 1.4–3.5% for L6 with respect to FBP). Near perfect DSC was calculated at all IR levels. Substantial noise reduction was observed for all liver cases (L3 and L6 reduced ∼24 ± 2.8% and 45.2 ± 2.9%, respectively), although not for lung (∼2–4%). Conclusion: IR reduced noise while improving CNR and preserving boundary information. ∼6‐fold dose reduction was possible while maintaining similar noise characteristics. A prospective trial is warranted to optimize mAs and IR, and further integrate IR‐4DCT into IGART. The submitting institution holds research agreement with Philips Healthcare.
TH‐C‐103‐11: Accelerated Barrier Optimization Compressed Sensing (ABOCS) for CT Reconstruction with Improved Convergence
Authors: Niu T , Zhu L
Published: July 2013

Purpose: Recently, we proposed an algorithm of accelerated barrier optimization compressed sensing (ABOCS) for iterative CT reconstruction. The previous implementation of ABOCS uses gradient projection (GP) with a Barzilai‐Borwein (BB) step‐size selection (GP‐BB) to search for the optimal solution. Despite the high computational efficiency of each iteration, the algorithm does not converge stably due to its non‐monotonic behavior. We further improve the convergence of ABOCS using a modified Nesterov method and investigate the ABOCS performance on patient data. Methods: To implement the Nesterov method for ABOCS, we first modify the objective function to make it continuous and differentiable. The traditional Nesterov algorithm requires Lipschitz and strong convex constants of the objective as inputs. These two parameters, however, are difficult to calculate in the ABOCS optimization framework, especially due to the large‐size and ill‐posed system matrix in the CT reconstruction as well as the singularities in the total‐variation term. We therefore apply the unknown‐parameter Nesterov (UPN) approach to adaptively estimate the parameters during the optimization. Results: Comparison studies are carried out on studies of computer simulation, physical phantom and head‐and‐neck patient. In all of these studies, the ABOCS results using UPN show more stable and faster convergence than those of the GPBB implementation. As shown in the simulation study, UPN achieves the same image quality as that of GPBB, but reduces the iteration numbers by 50%. In the Catphan600 phantom study, a high‐quality image with relative reconstruction error (RRE) less than 3% compared to the full‐view Result is obtained using UPN with 17% projections (60 views). Using 25% projections (91 views), the proposed method reduces the RRE from 21% as in the FBP results to 7.3% on the head‐and‐neck patient. Conclusion: As compared to GPBB, our new method significantly improves the convergence with higher stability and less iterations.
TH‐C‐144‐02: Experimental Study of Discrete Prompt Gamma Lines for In‐Vivo Proton Range Verification
Authors: Verburg J , Riley K , Seco J
Published: July 2013

Purpose: A novel method for in vivo proton beam range verification is presented, using energy‐resolvable proton‐induced prompt gamma lines. Methods: Prompt gamma‐rays emitted near the end‐of‐range of a clinical proton beam originate from transitions between the lower states of excited nuclear reaction products. We developed a prompt gamma‐ray detection system with the aim of resolving the resulting discrete gamma lines. The ability to quantify the strength of these lines can provide valuable information for in vivo range verification: known cross sections may be used as prior knowledge, and uncertainties resulting from differences in tissue composition could be reduced. A LaBr3:Ce scintillation detector was used, which provides high energy resolution. The pulses from the photomultiplier tube were acquired with analog‐to‐digital converters at high sampling rates, synchronized to the cyclotron radiofrequency to separate the quasi‐continuous neutron‐induced background from the prompt gamma signals of interest. Results: Preliminary measurements were performed with a 150 MeV proton pencil‐beam targeted on the center of a water phantom with a 15 cm diameter. A 1 cm lead slit collimator was used perpendicular to the beam direction, centered at the end‐of‐range. The acquired gamma spectra show the 6.13 MeV gamma line from oxygen‐16, and its escape peak, can be clearly resolved with an energy resolution of ∼1% FWHM. Conclusion: Our results show the feasibility of measuring discrete prompt gamma lines using a practical detection system. These gamma lines can be attributed to specific nuclear reactions with established properties, potentially enabling accurate proton range verification using a small number of measurement points. Experiments with different collimators and proton energies are currently being performed to determine an optimal configuration for range verification.
TH‐C‐144‐11: Radiological Physics Center (RPC) Approval of Proton Centers for NCI‐Sponsored Clinical Trials
Authors: Summers P , Ibbott G , Moyers M , Grant R , Followill D
Published: July 2013

Purpose: To describe the approval process for enrolling patients on NCI‐funded cooperative group clinical trials with proton therapy and the impact of data obtained from the process. Methods: Institutions interested in participating in clinical trials with proton therapy must first complete five RPC‐coordinated approval steps for each proton delivery Method: a) completion of the proton facility questionnaire; b) annual monitoring of beam output; c) electronic transfer of treatment plans; d) successful completion of baseline anthropomorphic proton phantoms; and e) successful completion of a dosimetry review visit and corresponding site visit report. The RPC implemented a new fee structure for proton therapy site visits on 1/1/2013, establishing a cost‐share between the NCI/MGH Federal Share Funds and the institutions visited. These visits consist of QA review as well as dosimetric measurements with an ion chamber, 2D ion chamber array, and multi‐layer ion chamber to evaluate treatment delivery. Once an institution is approved for clinical trials with protons, there may be additional credentialing for specific trials, such as irradiations of the RPC's protocol‐specific anthropomorphic proton phantoms. Results: To date, the RPC has approved eight proton centers for use of proton therapy in clinical trials. These approvals cover scattered, uniform scanning, and spot scanning proton therapy delivery techniques. The RPC has performed 12 proton therapy site visits and has consensus data to establish acceptance criteria for site visit measurements that will ensure clinical trial consistency. With some institutions going through the approval process for a second or third delivery modality, the RPC anticipates eight proton centers will have 12 new beam delivery systems approved for use of proton therapy in clinical trials by the end of 2013. Conclusion: The RPC's proton therapy approval process and credentialing requirements help ensure consistency across clinical trial participants. Work supported by grants CA10953, CA059267, and CA81647 (NCI, DHHS).
TH‐C‐144‐12: On the Modelling of Facility‐Specific PET Imaging for Proton Treatment Verification: Experimental Validation and Inter‐Facility Comparison
Authors: Bauer J , Hildebrandt M , Unholtz D , Kurz C , Parodi K
Published: July 2013

Purpose: We report on an experiment‐driven approach to validate the Monte‐Carlo (MC) modelling for Positron‐Emission‐Tomography (PET)‐based post‐therapeutic proton treatment verification. The presented strategy was pursued to overcome (1) uncertainties in the available nuclear cross‐section data and (2) facility‐specific uncertainties due to the irradiation technique and due to the imaging characteristics of the installed PET device. Furthermore, we show a comparison of production rates of the most relevant PET radionuclides, estimated from measurements at two treatment facilities using different PET‐imaging and data processing concepts. Methods: At our hospital‐based facility, several homogeneous phantoms were irradiated with mono‐energetic proton beams. The induced PET signal was detected with a full‐ring PET/CT‐scanner shortly after beam delivery. Separation of different radionuclide contributions to the measured signal was achieved by analysing the activity decay in dynamically reconstructed time‐resolved PET images. The resulting spatially resolved activity maps were used to tune the modelling of the most relevant radionuclide production processes. These measurements were compared to data acquired at another facility with a proto‐type dual head PET camera, employing a different data processing concept. Results: The MC modelling was adjusted to accurately reproduce the measurements at our facility. The activity signal level could be predicted within a few percent and we found a range agreement of better than 0.6 mm, which constitutes a crucial property for the clinical purpose of beam range verification. The inter‐facility comparison of production rates estimated from independent PET measurements show a reasonable overall agreement. However systematic discrepancies are observed, which suggest an impact of the different imaging and data processing concepts. Conclusion: The results of the inter‐facility comparison confirm the importance of a facility‐specific experimental validation of the MC modelling. The presented experimental strategy can also be applied at other facilities to minimize uncertainties in the activity prediction for PET‐based proton treatment verification. The presented work was funded by the German Federal Ministry for Research and Education (BMBF) under the grant agreement number 01IB08002F.
TH‐E‐137‐01: Status of ART in the Clinic
Authors: Li X , Mayr N , Yan D , Jaffray D
Published: July 2013

Adaptive Radiation Therapy (ART) is state of the art radiotherapy approach which delivers individualized treatment based on treatment feedback via integrating most likely imaging and planning in the treatment delivery process. There are two major aspects: (1) adaptive treatment planning (i.e., design of the optimal plan adaptive to the best available morphological and biological changes during the treatment, and (2) robust and accurate delivery of the optimized plan to the patient. Strategies for ART include on‐line and off‐line approaches. Accumulated clinical data have demonstrated the need for ART in clinical settings, assisted by the wide application of IMRT and IGRT. The technology for ART has advanced significantly in the last few years and is moving into the clinic rapidly, and has drawn greater attention in the radiation oncology community. The purpose of this session is to review and update clinical physicists and dosimetrists on this exciting and rapidly developing area.

Learning Objectives:

1. Understanding rationale, indications and promise of ART

2. Review of imaging, planning, and delivery technologies for ART

3. Recent technology developments

4. Clinical implementation, workflow, QA, cautions and initial clinical experience for using ART at several tumor sites.
TH‐F‐105‐01: BEST IN PHYSICS (THERAPY) — The Emergence of Non‐Uniform Spatio‐Temporal Fractionation Schemes Within the Standard BED Model
Authors: Unkelbach J , Zeng C , Engelsman M
Published: July 2013

Purpose: We consider the fractionation problem in intensity‐modulated proton therapy (IMPT). It is known that a low α/β ratio in the normal tissue favors a hyperfractionated regimen. In contrast, a low α/β ratio in the tumor gives rise to hypofractionation. However, in current clinical practice, the patient is treated with the same dose distribution in each fraction. We demonstrate that the standard biologically equivalent dose (BED) model gives rise to non‐uniform fractionation schemes, i.e. for an intermediate range of α/β ratios, it can be optimal to deliver distinct dose distributions in different fractions. Methods: We consider the simultaneous optimization of IMPT dose distributions and the fractionation scheme. This is achieved by simultaneously optimizing multiple (possibly distinct) IMPT plans for different fractions. To that end, we consider an objective function based on the cumulative BED distribution delivered over all fractions. Results: It is shown that the optimal treatment regimen may consist of distinct IMPT plans. For proton therapy this has an intuitive explanation: The dose in the entrance region of the proton beam is mostly independent of the range. Thus, an incident proton beam can primarily irradiate the distal part of the tumor in one fraction, and the proximal part in the subsequent fraction ‐ without significantly changing the dose in the normal tissue. This can be interpreted as the possibility of hypofractionating subregions of the tumor while continuing to hyperfractionate in the normal tissue. Conclusion: To date, the determination of the fractionation scheme and the optimization of the spatial dose distribution in IMRT and IMPT are considered independently. Here, we demonstrate that both problems are interdependent. In particular, the therapeutic ratio can potentially be improved by delivering distinct dose distributions in different fractions.
TH‐F‐105‐03: Experimental Design and Preliminary Results for High‐Resolution and High‐Throughput In‐Vitro Measurements of Proton RBE
Authors: Guan F , Mohan R , Dinh J , Kerr M , Perles L , Mirkovic D , Titt U , Zhu X , Gillin M , Meyn R , Lin S , Grosshans D
Published: July 2013

Purpose: To design, develop and test a novel system for rapidly acquiring large amounts of in‐vitro RBE data for protons as a function of LET, dose per fraction, dose rate, end point, and oxygenation for a wide range of cell lines. Methods: Using the Geant4 Monte Carlo toolkit, we designed a specialized range compensator to simultaneously expose cells plated in 96 wells (12 columns by 8 rows) to different doses and variable LETs from selected portions of pristine proton beams from the entrance to points just beyond the Bragg peak. The use of 96‐well plates can facilitate future high‐throughput and high‐resolution measurements. To minimize the spread of LET, we utilized monoenergetic uniformly scanned proton beams. Using a sequence of entrance doses and variable LETs, an RBE matrix related to different pairs of doses and LETs can be acquired in a relatively small number of exposures. In this study, we utilized the standard clonogenic assay for lung‐cancer cell lines grown in 96‐well plates. The compensator is mounted in the scanning beam snout with the beam directed toward the ceiling. In each exposure, one 96‐well plate was positioned downstream for irradiation. Results: Experimental data for lung cancer cells exposed to 79.7 MeV protons showed a significant increase in cell kill as a function of LET at locations close to the distal edge of the Bragg peak. For LET values of 8.34, 11.6, 13.5 and 14.6 keV/μm, the surviving fractions were found to be 0.24, 0.18, 0.088 and 0.031 at 4 Gy and 0.11, 0.074, 0.024 and 0.0035 at 6 Gy. Conclusion: The experimental design developed is a viable approach to rapidly acquire large amounts of accurate in‐vitro RBE data. We plan to further improve the design to achieve higher accuracy and throughput, thereby facilitating the irradiation of multiple cell types. NCI grant P01CA021239
Merging physical parameters and laboratory subjective ratings for the soundscape assessment of urban squares
Authors: Brambilla Giovanni , Maffei Luigi , Di Gabriele Maria , Gallo Veronica
Published: July 2013

An experimental study was carried out in 20 squares in the center of Rome, covering a wide range of different uses, sonic environments, geometry, and architectural styles. Soundwalks along the perimeter of each square were performed during daylight and weekdays taking binaural and video recordings, as well as spot measurements of illuminance. The cluster analysis performed on the physical parameters, not only acoustic, provided two clusters that are in satisfactory agreement with the “a priori” classification. Applying the principal component analysis (PCA) to five physical parameters, two main components were obtained which might be associated to two environmental features, namely, “chaotic/calm” and “open/enclosed.” On the basis of these two features, six squares were selected for the laboratory audio-video tests where 32 subjects took part filling in a questionnaire. The PCA performed on the subjective ratings on the sonic environment showed two main components which might be associated to two emotional meanings, namely, “calmness” and “vibrancy.” The linear regression modeling between five objective parameters and the mean value of subjective ratings on chaotic/calm and enclosed/open attributes showed a good correlation. Notwithstanding these interesting results being limited to the specific data set, it is worth pointing out that the complexity of the soundscape quality assessment can be more comprehensively examined merging the field measurements of physical parameters with the subjective ratings provided by field and/or laboratory tests.
Evaluation of moving-coil loudspeaker and passive radiator parameters using normal-incidence sound transmission measurements: Theoretical developments
Authors: Leishman Timothy W. , Anderson Brian E.
Published: July 2013

The parameters of moving-coil loudspeaker drivers are typically determined using direct electrical excitation and measurement. However, as electro-mechano-acoustical devices, their parameters should also follow from suitable mechanical or acoustical evaluations. This paper presents the theory of an acoustical method of excitation and measurement using normal-incidence sound transmission through a baffled driver as a plane-wave tube partition. Analogous circuits enable key parameters to be extracted from measurement results in terms of open and closed-circuit driver conditions. Associated tools are presented that facilitate adjacent field decompositions and derivations of sound transmission coefficients (in terms of driver parameters) directly from the circuits. The paper also clarifies the impact of nonanechoic receiving tube terminations and the specific benefits of downstream field decompositions.
Inversion for a moving spherical target's positional, structural, and speed parameters
Authors: Fawcett John A. , Dosso Stan E.
Published: July 2013

The broadband scattering characteristics of a target may be used to distinguish its echoes from those of clutter. In a shallow water situation, the echo from the target will consist of a sequence of pulses corresponding to the various coherent combinations of incident and backscattered multipath arrivals. Thus, the interference effects of the waveguide propagation can have a significant effect upon the received echo and thus also affect the classification of the target from the echo. In addition, the target may be moving, in which case the received echo is also Doppler-shifted. The purpose of this paper is to investigate the simultaneous determination of a spherical target's position (range and depth) within a waveguide, its radial speed, its radius, its shell thickness, and the elastic parameters of the shell. It will be shown that many of these parameters can be accurately estimated from a single wideband echo, even in the presence of significant noise. The marginal probability distributions of the parameter values will also be investigated. It will be seen that the positional and speed parameters of the sphere can be determined to high precision. The other parameters are determined with varying degrees of precision.
REVIEWS OF ACOUSTICAL PATENTS
Authors: Fulop Sean A. , Rice Lloyd
Published: July 2013

The purpose of these acoustical patent reviews is to provide enough information for a Journal reader to decide whether to seek more information from the patent itself. Any opinions expressed here are those of the reviewers as individuals and are not legal opinions. Printed copies of United States Patents may be ordered at $3.00 each from the Commissioner of Patents and Trademarks, Washington, DC 20231. Patents are available via the Internet at http://www.uspto.gov.