bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐A‐213CD‐03: Information Source Mapping in Prior‐0Image‐Based Reconstruction
Authors: Stayman J , Prince J , Siewerdsen J
Published: June 2012

Purpose: While reconstruction methods that include prior images can provide spectacular results on highly under sampled and noisy CT data, the reliability of features in volume estimates remains a major question. Specifically, how can one determine whether a specific feature arises from the measurements or the prior image? We present a first step toward answering this question using a novel decomposition of prior‐image‐based reconstructions that traces the contribution of information from each source (i.e., from the current measurement data and from the prior image). Methods: We have developed a novel analytic framework for decomposing prior‐image‐based reconstructions, such as those formed by prior‐image‐ constrained compressive sensing (PICCS) or prior‐image penalized likelihood estimation (PI‐PLE) reconstructions. Two terms arise ‐ one a function of the measurement data and the other a function of the prior image. Each term also represents an image volume that can be used to form an ‘information source map’ (ISM), illustrating the spatially varying contribution of information and the source of specific features in the reconstruction. Results: We apply the analytic decomposition and ISM approach to a simulated lung nodule surveillance scenario where a prior image (without a lung nodule) is incorporated into both PICCS and PI‐PLE reconstructions of sparse tomographic data (in which a lung nodule appears). Information source maps correctly identify the measurement data as the source of the nodule feature and quantify the how various adjustable PICCS and PI‐PLE parameters increase the reliance on the prior image when larger prior‐image parameter strengths are selected.Conclusion: The proposed ISM analysis allows one to visualize the propagation of information from the prior image and the current measurement data into resulting reconstructions. These maps quantify and provide confidence that specific features arise from the current data (and not the prior image), identify regions of change, and guide selection of reconstruction parameters. This work supported in part by NIH grant 2R01‐CA‐112163.
TU‐G‐BRB‐06: Improving the Dose Distribution and Delivery Efficiency in IMRT Inverse Planning by Iteratively Reweighted L1‐Norm
Authors: Kim H , Li R , Xing L
Published: June 2012

Purpose: Compressed sensing with L1‐norm based total‐variation (TV) regularization has been successfully applied in IMRT inverse planning by generating piecewise constant fluence maps. L1‐norm was chosen primarily due to its computational efficiency; for sparse signal recovery, an ideal approach is to use L0‐norm (the number of non‐zero elements) or Lp‐norm (p<:1). It is, however, difficult to implement in practice as it is a non‐convex problem. The goal of this work is to introduce a substitute and yet effective method, which can further reduce the fluence‐map complexity and enhance delivery efficiency in IMRT inverse planning, while not damaging the conformal dose distribution. Methods: We propose to use an algorithm based on iteratively reweighted L1‐norm. The algorithm consists of solving a sequence of weighted L1‐norm minimization problems where the weights used for the next iteration are computed from the value of the current solution. In this work, a TV solver, called TFOCS, was used for each iteration. The proposed algorithm was evaluated on a prostate case for IMRT inverse planning. The treatment plans were evaluated by the conformation number (CN) and the modulation index (MI). Results: The iteratively reweighted L1‐norm outperforms the L1‐norm based TV method for fluence‐map optimization in both conformal dose distribution and delivery efficiency. Significantly, the proposed method by reweighting the TV form enables higher or similar conformal dose distribution with lower field complexity. At 60 segments, the complexity of the fluence‐map (MI) was reduced by 20%, while producing higher CN. This improvement will be more effective as the dose conformity gets stronger. Conclusions: The proposed method with the iteratively reweighted L1‐norm achieves more conformal dose distribution and improves the delivery efficiency by reducing the fluence‐map complexity compared with the conventional TV minimization for IMRT inverse planning.
TU‐G‐BRB‐07: Improve PTV Dose Distribution by Using Spatial Information in IMRT Optimization
Authors: Uribe‐Sanchez A , Zarepisheh M , Jia X , Jiang S
Published: June 2012

Purpose: The spatial distribution of radiation dose within the PTV does have clinical significance. For instance, if hot/cold spots in the PTV cannot be avoided, high doses are preferred to be located in the center, and low doses at the peripheries. However, traditional plan optimization models for IMRT usually treat equally voxels inside the same structure, failing to incorporate those location preferences. We present a re‐optimization model that, while preserving the quality of an initial treatment plan represented by DVH curves, incorporates spatial information for voxels inside the PTV into the optimization to generate a more desirable dose distribution. Methods: Our re‐optimization model incorporates a convex function that penalizes the deviation of the dose received by each voxel from an individual reference value. For PTV, the reference values per voxel match the ideal redistribution of the initial PTV dose, where voxels close to the boundary receive the low doses, while voxels in the center receive the high doses. For OAR, the reference value per voxel corresponds to its dose from the initial plan. In addition to the structure‐based weighting factors in traditional planning approaches, we incorporated individual penalty weights for PTV voxels. Structure‐based factors are calibrated according to the difference from the reference DVH curves, while voxel‐based, according to the difference to reference value. Results: We tested our model in four gynecologic cancer cases. For each case, we compare the resulting dose distribution within the PTV to that from the initial plan. It is observed that without sacrificing the plan quality represented by DVH curves, our re‐optimization model generates more desirable PTV dose distributions. Conclusions: We have presented a re‐optimization model that, by incorporating spatial location information for PTV voxels, yields to more clinically favorable dose distributions with similar DVH curves. This work is supported by Varian Medical Systems through a Master Research Agreement.
TU‐G‐BRB‐09: A Bregman Iteration Method for IMRT Optimization with Dose‐Volume Histogram Constraints
Authors: Jia X , Uribe‐Sanchez A , Jiang S
Published: June 2012

Purpose: Dose‐volume histogram (DVH) is a clinically relevant criterion to evaluate treatment plan quality. It is hence desirable to incorporate the associated DVH constraints in treatment plan optimization. Yet, these constraints usually lead to difficulties due to their non‐convex nature. This project develops an algorithm to solve the intensity modulated radiation therapy (IMRT) optimization problem with DVH constraints considered via a Bregman iteration. Methods: We consider an objective function of a quadratic form with different overdose and underdose penalties, subject to DVH constraints. The constrained optimization problem is converted into a sequence of unconstrained problems via Bregman iteration approach, which are then solved sequentially using gradient‐descent algorithm with inexact line search. The objective functions in those unconstrained optimization problems contains terms that requires the computation of DVH values. In practice, this is achieved by approximating the Heaviside step‐functions in the expression of a DVH curve by a smoothed arctangent function. This approach also allows for the computation of gradient of the objective functions during optimization process. Results: We have tested our algorithm in the context of 7‐field IMRT treatment planning for prostate cancer in 4 patient cases. Clinically relevant DVH constraints are considered for PTV, rectum, and bladder. In all the cases, the algorithm is able to find the solutions that satisfy all the DVH constraints, while as DVH constraints may be violated when the Bregman algorithm is not applied. The local‐minima problem caused by the non‐convex constraints is not observed, which may be ascribed to the good quality of the initial dose distribution obtained after a standard IMRT optimization problem without DVH constraints. Conclusions: We have developed an algorithm to solve the IMRT optimization problem with DVH constraints using Bregman iteration approach. Tests conducted in prostate cancer cases have demonstrated the validity of our algorithm and its effectiveness.
TU‐G‐BRA‐01: 4D Monte Carlo Simulations of Beam and Patient Motion Using EGSnrc/BEAMnrc
Authors: Heath E , Badragan I , Popescu I
Published: June 2012

Purpose: To develop a 4D Monte Carlo method that simulates continuous beam and patient motion using the EGSnrc Monte Carlo code. Methods: The simulation method links the collimator and gantry settings on a particle‐by‐particle basis to the respiratory phase of the patient at which it is delivered. This synchronization was achieved by implementing two novel particle sources into the defDOSXYZnrc Monte Carlo code which calculates dose in a deforming patient geometry. Validation in a virtual lung phantom was performed for static and tracking beam scenarios. Dose delivery of a RapidArc plan on a commercial dynamic thorax phantom was simulated using RPM and linac log files from the plan delivery. The effects of interplay between the beam and phantom motion were quantified by performing simulations with and without motion synchronization. Results: Simulations in the virtual phantom demonstrate recovery of the static dose profile when the MLC sequence tracks the tumor motion. Simulations of the RapidArc plan delivery showed dose variations of up to 9% of the prescribed dose between plans calculated with and without interplay effects. Conclusions: A 4D Monte Carlo method for EGSnrc has been developed which can calculate dose for combined beam and patient motion. Unlike discretized approaches, this method can calculate the dose distribution in a single simulation. Using treatment log files, this tool can reconstruct the dose actually delivered to a patient, accounting for respiratory motion and interplay effects.
TU‐G‐BRA‐02: Development of a 4D‐MRI Technique for MRgRT
Authors: Stanescu T , Tadic T , Moseley D , Jaffray D
Published: June 2012

Purpose: To develop a 4D‐MRI technique tailored for the daily patient setup verification and offline assessment of dynamic delivery for MR‐guided adaptive radiotherapy. Methods: The method consists of a sequential acquisition of 2D‐cine data at neighbouring locations covering a certain volume of interest. Subsequently, 4D data is generated by sorting and binning the images as a function of their organ motion phase (e.g., due to breathing). The phantom and patient data was acquired on a 3T Siemens Verio a 2D‐cine turbo flash with a flip‐back pulse sequence. The image sorting was performed using a sinogram generated by subsequently collapsing each image in the 2D‐cine series into one pixel line along the direction of organ motion and stacking these pixel lines into a 2D image map. The phase 3D volumes were generated by synchronizing the information resolved at each 2D‐cine slice location. The 4D‐MRI technique was used to assess offline the accuracy of VMAT delivery. This was done by reformatting the MR data to generate BEV projections for each VMAT segment (spatial location and timing) and subsequently evaluate the dose accumulation maps in the target and adjacent treated volume. A 4D‐MRI‐based workflow was designed for liver SBRT on a linac‐MR on rails MRgRT platform, which is under development at our institution. Results: The 4D‐MRI technique showed very good performance when benchmarked against 4D‐CT, 4D‐CBCT, and 2D‐cine MR phantom and patient liver data. The technique was used to assess the VMAT delivery for multiple scenarios considering different target treatment margins, including the case of realtime tracking. Conclusions: The proposed 4D‐MRI technique is a feasible approach for the assessment of daily pre‐treatment target location and motion on an MRgRT platform consisting of an MRI scanner (goal: imaging) moving on rails to interact with a linac (goal: deliver treatment) via a robotic patient table.
TU‐G‐BRA‐05: Intra‐Fraction Motion Management for Prostate SBRT: Clinical Experience and Imaging Frequency Analysis
Authors: Agazaryan N , Sharma G , Kupelian P , Steinberg M , King C
Published: June 2012

Purpose: To clinically evaluate the intra‐fraction motion management performance of an IGRT protocol established for hypo‐fractionated SBRT prospective Phase IIa trial for the treatment of localized prostate cancer. Specifically, to analyze patient data to determine the adequacy of imaging frequency. Methods: Novalis Tx equipped with Exactrac was used for stereoscopic imaging and localization based on three implanted fiducial markers. For intra‐fraction motion management, two nearly 360‐degree RapidArcs were split to four half‐arcs. Following initial Exactrac positioning, CBCT is obtained for volumetric evaluation of bladder and rectal filling and position confirmation. The patient is then stereoscopically imaged prior to the delivery of each half‐arc and repositioned when 2 mm tolerance is exceeded. Data from 66 patients with 330 fractions and 2597 image pairs has been analyzed. Results: Following the initial Exactrac and CBCT, mean treatment time from first arc to treatment end was 6.7 mins. ver the course of 66 treatments, patients were repositioned on 257 occasions. On average patients were repositioned 11.9% of the time (SD 10.0%, range 0–40.5%). The mean distance these patients were repositioned was 3.5 mm (SD 1.7 mm, range 2.0–8.5 mm). Of all repositions, 53.5% (SD 29.2%, range 0–100%) occurred before delivery of first arc; in addition, patient repositioning frequency following any half‐arc was 9.1% (SD 9.9%, range 0–45%) over the treatment course. Nine patients did not require repositioning throughout the treatment course while nine patients required repositioning more than 25% of the time. Conclusions: Current imaging protocol for intra‐fraction motion management fits the clinical workflow. Frequency analysis indicates that the intra‐fraction imaging is not excessive. Due to the time spent on performing and analyzing the additional CBCT after initial Exactrac localization, 53.5% of repositions occur preceding first arc. Future analysis will include quantitative dosimetric consequences and tolerances utilized for repositioning patients in this study. Member of Brainlab Academy Speakers Bureau Varian Industry Grant ‐ Rapid Arc: Radisurgical and SBRT Applications, May 2009‐ May 2011
TU‐G‐BRA‐06: Motion Adaptive Rotational Intensity Modulated Radio Therapy (MA‐RIMRT) with Image Guidance
Authors: Paidi A , Neacsu F , Aguilar W , Bose S , Bani‐Hashemi A , Maltz J
Published: June 2012

Purpose: Commercial intensity‐modulated‐arc‐therapy (IMAT) implementations rely on a 100% beam‐on duty‐cycle to achieve high efficiency. With moving targets, real‐time tracking or gating may be applied. Tracking is technically challenging and gating reduces efficiency by lowering the duty‐cycle. By combining burst‐mode rIMRT (in which all dose is administered while the gantry is within a few degrees of a beam optimization point [OP]), with a motion pre‐emption strategy and intrafractional imaging, we demonstrate an efficient implementation of motion‐adaptive rIMRT. Methods: 1. An rIMRT plan is created with 36–72 OPs. A gantry rotating at 6 degrees/s takes 3–6s to reach successive OPs. This co‐incides with the natural breathing period. 2. A Fourier‐descriptor‐based trajectory model is fitted to target features identified in pre‐treatment CBCT projections. The model predicts feature location at any combination of gantry angle and breathing phase. 3. The model sets the gantry speed to place the gantry at the next beam OP just in time as the target arrives at the planned position. In‐line projection images are acquired immediately before and during beam delivery. Treatment ensues only if the target position is correct (verification completes within 50ms, so maximum misdelivery possible at 2000MU/min is within 2MU). In cases of irregular breathing, the system gracefully defaults to gated‐IMRT. Results: For a MA‐rIMRT delivery of 750MU at 2000MU/min, treatment duration increases from 154s (regular rIMRT) to 199s (5s respiration cycle). Conclusions: With predictable patient breathing, MA‐rIMRT delivery times are competitive with conventional IMAT. High treatment accuracy is easily achieved, since there is no tracking lag and since the beam shape is static during delivery. Contemporary linacs rely on non‐realtime communication systems (typically Ethernet) to control time‐critical elements such as the MLC. Since such variable‐delay systems pose formidable problems in terms of predictive control, our approach offers a pragmatic alternative to tracking. Siemens Medical Solutions USA
TU‐G‐BRA‐08: Understanding the Performance of Control Limit‐Based Monitoring of Respiratory Surrogate Tumor Motion Models
Authors: Malinowski K , Diwanji T , McAvoy T , D'Souza W
Published: June 2012

Purpose: To develop an understanding of mechanisms underlying the performance of a control‐limit‐based monitoring technique for detecting errors in respiratory surrogate tumor displacement models. Methods: Five lung cancer patients underwent 13 dynamic magnetic resonance imaging sessions on a 1.5 T scanner using a TrueFISP sequence (200 images, 5 sagittal slices, 8mm slice thickness, interleaved acquisition, TE 1.29 msec, TR 2.57 ms, 60° flip angle, matrix 176×256 matrix, in‐plane spatial resolution 1.6–2.2 mm each direction, 1028 bandwidth). Tumors were localized in the images at 0.4 Hz for 500 sec. Five respiratory surrogates affixed to the abdomen were optically tracked during imaging. Surrogate‐based tumor motion models were created by applying partial‐least‐squares regression to the first 30 sec of data. Hotelling's statistic and the input variable squared‐prediction‐error for each subsequent sample were compared to training data‐based control limits to predict errors >3mm. The experiment was repeated in tumor motion and respiratory surrogate signal simulations that isolated measurement precision, period variations, amplitude variations, end‐exhale variations, tumor drift, and gross patient motion. Sampling rates of 0.1–30 Hz (0.1–0.4 Hz for patient data) were evaluated. Results: For patient data sampled at 0.4 Hz and 0.1 Hz and 95% sensitivity, specificities were 8% and 17%. In comprehensive simulations tuned to 95% sensitivity, specificity increased from 33% at 0.1 Hz to 69% at 30 Hz. With measurement noise or tumor drifts alone, specificities were 99–100% and sensitivities were 0–1%. Gross patient motion was detected with sensitivity of 100% and specificity of 97%. For end‐exhale variations, sensitivity was 97%, and specificity was 57%. Respiratory cycle amplitude and period variations had no effect on monitoring performance. Conclusions: Contributors to control‐limit‐based monitoring performance included sampling rate, end‐exhale variations, measurement noise, and tumor drifts but not patient motion, period variations, or amplitude variations. Simulation results were qualitatively in agreement with patient results. Supported in part by grant CA124766 from the NIH/NCI and the Achievement Rewards for College Scientists scholarship.
TU‐G‐BRA‐09: Utility of 4D‐PET/CT for ITV Definition
Authors: Bergamo A , Sandhu A , Rahn D , Song W
Published: June 2012

Purpose: The potential role of four‐dimensional (4D) positron emission tomography (PET)/computed tomography (CT) in defining the internal target volume (ITV), relative to the standard three‐dimensional (3D) PET/CT, was examined. Methods: Eleven patients with respiratory‐induced tumor motion (8 lung, 2 liver, and 1 pancreas) were imaged using 3D and 4D FDG [18F] Fluorodeoxyglucose PET/CT scans while in the radiation therapy treatment position. Both 3D and 4D PET ITV's were manually contoured by two expert radiation oncologists based on their clinical judgment. Similar window and level values were used for both 3D and 4D PET images to ensure consistency in ITV representation. For 4D PET, five breathing phases were used to contour the ITV that would encompass the full tumor motion. Student t‐test was performed to determine significance in the 3D and 4D volume difference. Results: Analysis of 11 patient tumors was conducted for calculation of 3D and 4D PET average volumes, standard deviation, percent difference, and t‐test significance. 4D PET average volume values were consistently larger than 3D PET average volumes over all eleven patient cases for both radiation oncologists. Results of radiation oncologist #1 revealed: 4DVOL‐AVG = 40.2 +/− 59.8 cc, 3DVOL‐AVG = 32.5 +/− 55.5 cc with %DIFF = 32.4 +/− 30.9% and p < 0.05. Likewise, results of radiation oncologist #2 shows: 4DVOL‐AVG = 48.1 +/− 66.1 cc, 3DVOL‐AVG = 39.9 +/− 60.7 cc with %DIFF = 27.8 +/− 18.7% and p \lt; 0.03. Both t‐test results show statistical significance. Conclusions: The use of 4D PET images may lessen the probability of tumor volume underestimation due to undetected tumor motion when using the 3D PET modality. With 4D PET, a more accurate ITV which includes breathing motion may Result in improved radiation treatment delivery to the full, appropriate tumor volume, thus potentially improving treatment outcomes.
TU‐G‐217BCD‐03: Sensitivity of Peripheral CDTI100 to X‐Ray Tube Starting Angle
Authors: Vanderhoek M , Bakalyar D
Published: June 2012

Purpose: Reproducible measurements of CDTI100 are required for ACR accreditation. On CT scanners without a fixed x‐ray tube starting angle, the variation of peripheral CTDI100 regularly exceeds the ACR variation criteria of 5%. We investigated the sensitivity of CT peripheral exposure to x‐ray tube starting angle. Methods: Axial scans were performed using a Philips Brilliance 6 CT scanner, varying the x‐ray tube starting angle, rotation time, and collimation width. To eliminate table attenuation, exposure was measured in air at isocenter and at 16 cm off‐center using a 10 cm pencil ionization chamber. A video camera was used to determine the initial angular position of the gantry at the start of each x‐ray exposure. Exposure variation was measured using coefficient of variation (CV) and range. Results: At isocenter, variation of exposure was minimal (average CV, 0.1%; average range, 0.4%) demonstrating machine output consistency. At 16 cm, however, the variation of exposure was substantial (average CV, 3%; average range, 11%; maximum range, 17%) due to its dependence upon the x‐ray tube starting angle, which suggests an asymmetry of the radiation output. Peripheral exposure was independent of collimation width but strongly depended upon rotation time, with increased variation for shorter rotation times (exposure ranges of 17%, 9%, 6% for 0.5, 1.0, 1.5 s, respectively). This data suggests that the dose is delivered for approximately 100 ms longer than the time required for a complete rotation. Conclusion: Peripheral CTDI100 can vary considerably (∼20%) when the x‐ray tube starting angle changes. Long rotation times can substantially reduce this variation. In addition, averaging peripheral exposures acquired randomly, or at properly spaced starting angles can further reduce this variation, yielding a reliable average peripheral exposure. Corollary: CT scanners with a fixed x‐ray tube starting angle may yield a reproducible systematic error in peripheral CTDI100.
TU‐G‐217BCD‐08: The Relationship of Image Noise and Organ Dose as a Function of Patient Size for Abdominal CT Exams at 5 Different Dose Levels When Tube Current Modulation Is Used
Authors: Zhang D , Khatonabadi M , Cagnon C , DeMarco J , McNitt‐Gray M
Published: June 2012

Purpose: To investigate the relationship of image noise and organ dose as a function of patient size for abdominal CT exams at a 5 different dose levels when tube current modulation is used. Methods: This IRB approved study selected 20 patients scanned by a Siemens Sensation64 CT scanner with CareDose4D turned on. Images at lower dose levels (20%, 30%, 50%, and 70%) were simulated for each patient. Noise for each image set was obtained by drawing an ROI in a homogeneous region in the liver. Radiation dose to liver was obtained using a previously validated Monte Carlo simulation package. The perimeter of the patient at the liver level was also obtained. Results: Noise and liver dose were plotted as a function of patient size for the 100% dose level image sets. Noise behaves roughly as a linearly function of patient perimeter. This is consistent to the principle of CareDose4D: higher noise is acceptable in larger patients due to the intrinsic better contrast from extra fat tissue. As patient size increase, liver dose also increases in a nearly linear fashion, except for two extra large patients. In addition, noise was plotted as function of liver dose for all the image sets (including all 5 dose levels). For each patient, the noise approximately decreases in an inverse square root relationship as the dose increases, as expected. Larger patients' images have higher noise at the same liver dose. Therefore higher organ dose is required to achieve a similar noise level. Conclusions: This study investigated the relationship between image noise, organ dose and patient size. The results showed that with CareDose4D: (a) both noise and liver dose increases as patient size increases; (b) larger patients require a higher organ dose in order to have a similar noise level as a smaller patient. For Michael McNitt‐Gray: Institutional research agreement, Siemens AG Recipient research support Siemens AG
TU‐G‐217A‐01: Dynamic Contrast Enhanced Magnetic Resonance Imaging (DCE‐MRI) for High‐Resolution Lung Perfusion Evaluation in Pulmonary Neoplasms Prior to Radiotherapy
Authors: Diwanji T , Feigenberg S , D‘Souza W , Mistry N
Published: June 2012

Purpose: To propose using Dynamic Contrast Enhanced‐ MRI (DCE‐MRI) for a high‐resolution, pre‐treatment evaluation of lung perfusion in patients with lung cancer who will receive radiation therapy. The second goal is to benchmark the performance of DCE‐MRI against the gold standard: scintigraphy perfusion‐scan. Methods: DCE‐MRI and scintigraphy V/Q scans were acquired for 4 lung cancer patients prior to radiation therapy. DCE‐MRI relies on a single bolus injection of a paramagnetic contrast agent (Gd‐DTPA) that produces a transient signal enhancement on a T1 sensitive imaging sequence. By mapping the signal changes into contrast agent concentration curves, one can use techniques developed for indicator dilution to calculate perfusion estimates of pulmonary blood flow (PBF), blood volume, and mean transit time. The images were corrected for volumetric changes induced by respiratory motion using a non‐rigid registration technique. 3D masks of the right and left lung fields were manually contoured on the initial MRI volume using MATLAB and applied to the PBF maps. These maps were subsequently collapsed in the A‐P‐ dimension to create coronal 2D projections consistent with the scintigraphy V/Q images. Left and right lung fields were divided into 3 sections of equal height, and signal intensity computation was carried out analogous to the analyses performed on scintigraphy scans. Kendall's tau rank correlation coefficients were used to compare lung perfusion estimated using DCE‐MRI to the perfusion portion of the V/Q studies. Results: The non‐parametric Kendall's tau correlation coefficient ranged between 0.93–0.96 for PBF and scintigraphy perfusion. There is a 2X improvement in spatial resolution when compared to SPECT‐perfusion. Conclusions: There was a strong correlation between the DCE‐MRI and scintigraphy V/Q estimates of perfusion with statistically significant rank correlations. These results indicate that DCE‐MRI is a viable high‐resolution imaging modality for the evaluation of pre‐treatment lung perfusion in patients with lung cancer.
TU‐G‐217A‐04: Assessment of Cerebral Autoregulation by Inducing Acute Hypertension in Rats
Authors: Li G , Shih Y , Garza B De La , Kiel J , Duong T
Published: June 2012

Purpose: We developed a rat model of acute hypertension by occluding the descending aorta and used cerebral blood flow (CBF) MRI to evaluate cerebral autoregulation (CA) under normocapnia and hypercanpia. This method avoids potential pharmaceutical complications and can be repeatedly applied in the scanner. The long term goal is to apply this approach to study CA in rat models of chronic hypertension, stroke and diabetes. Methods: 9 Long‐Evans rats were used for MRI and blood‐gas measurements. They were mechanically ventilated under normocapnia, and then hypercapnia. Blood pressure (BP) was modulated by a balloon catheter placed in the descending aorta near diaphragm. MRI studies were performed on an 11.7 T MRI using continuous arterial spin labeling. Modulation paradigm: OFF‐ ON(1min)‐OFF. The mean CBF and BOLD (extracted from non‐labeled images) signals of the cerebrum was reported. The changes of CBF, BP and BOLD (▵CBF, ▵BP and ▵BOLD) from the baseline to the occlusion period were analyzed. Total 23 trials under normocapnia and 21 trails under hypercapnia were performed. Results: CBF, BOLD, BP, arterial pO2 and pH increased significantly during the occlusion under both hypercapnia and normocapnia. BP elevation was sustainable. After initial instant transient increase, CBF returned toward the baseline at a faster(p=0.047) rate under normocapnia than under hypercapnia(∼3x). Under normocapnia, ACBF was not linearly correlated to ▵BP(p=0.53). The absence of correlation and faster returning rate under normocapnia indicates CA. By contrast, under hypercapnia, ACBF increased linearly with ABP(p=0.002), which indicates autoregulation impairment. %▵CBF vs. %▵BOLD remained linearly correlated under both conditions. Conclusions: We developed a model of acute hypertension in rat for use in the MRI scanner. CBF MRI results indicated that there were apparent CA under normocapnia but was markedly impaired under hypercapnia. This approach sets the stage for study of CA in rat models of chronic hypertension, stroke and diabetes.
TU‐G‐217A‐07: Magnetic Nanoparticle Quantitation: Compensating for Relaxation Effects
Authors: Weaver J , Zhang X , Toraya‐Brown S , Reeves Daniel , Perreard Irina , Fiering S
Published: June 2012

Purpose: Our hypothesis was that the weight of magnetic nanoparticles could be accurately estimated from the magnetic spectroscopy of nanoparticle Brownian motion (MSB) signal. Quantification is critical to bio‐sensing and histology and is becoming more important in medical imagining. A nanoparticle assay is important in histology and bio‐sensing where antibody targeted magnetic nanoparticles are used to mark specific protein expression. Quantitative imaging of magnetic nanoparticles is also important in applications including hyperthermia and nanoparticle drug delivery. Two factors make quantitative estimates very difficult to achieve: relaxation effects that change the signal produced by each nanoparticle and non‐nanoparticle iron that confuses mass spectroscopy measurements. We introduce a method only sensitive to nanoparticle iron that compensates for relaxation effects that achieves quantitative estimates of the number of magnetic nanoparticles in a sample. Methods: Samples with varying quantities of iron oxide nanoparticles (100 nm mean hydrodynamic diameter) and varying quantities of glycerol were prepared. The samples contained from 1.46 mg to 0.05 mg nanoparticles and from 0% to 27% glycerol. MSB signals were recorded for each sample. The relaxation time was calculated using previously reported methods. The MSB signals were then shifted in frequency to compensate for the change in relaxation time. The scaling of the normalized MSB signal that approximates the reference sample is the weight of nanoparticles present in the sample. The apparatus used was built for 1.5 mL liquid samples; a system for smaller samples would be more sensitive. Results: The RMS percentage error in the weight of nanoparticles was 4.9%. The RMS error in the weight of nanoparticles was 0.018 mg iron. Other sources of iron such as blood did not bias the estimates. Conclusions: The method presented makes accurate MSB estimates of the weight of nanoparticles. Acknowledgement: NIH‐NCI 1U54CA151662‐01 NIH‐NCI 1U54CA151662‐01
TU‐G‐217A‐09: Feasibility of Bowel Tracking Using Onboard Cine MRI for Gated Radiotherapy
Authors: Noel C , Olsen J , Green O Pechenaya , Hu Y , Parikh P
Published: June 2012

Purpose: Bowel toxicity can be difficult to manage in the treatment of abdominal cancers. The bowel experiences large motion during treatment, causing it to enter high‐dose regions. Real‐time MR imaging during radiotherapy allows for potential visualization and dosimetric avoidance of the bowel during treatment. To investigate the feasibility of real‐time ‘bowel‐gated’ treatment using onboard MRI, we assessed two bowel‐tracking algorithms on 32 cine imagesets acquired with the ViewRay hybrid MR‐ radiotherapy unit. Methods: The Viewray(TM) System, which is an integrated 0.35T MR‐Co‐60 system that is pending 510k approval, was used to acquire 32 cine image sets in 5 patients under an IRB‐approved trial. Each imageset was acquired in 2D (coronal or sagittal orientation) for an average duration of 0.5‐2.5 minutes at a frame rate of 4 frames/s. The initial position of the bowel was manually contoured on the first image frame. Two algorithms were evaluated in tracking bowel from its initial position throughout its motion for the duration of the cine set ‐ a normalized cross‐ correlation (NCC) algorithm, and a weighted NCC (WNCC) algorithm. To assess the tracking feasibility and accuracy of these two methods, the initial contour was virtually shifted with the tracked motion and displayed on tracked cine images. The agreement between the shifted contour and the border of the bowel was manually inspected and noted for each frame. Results: Both algorithms successfully tracked 31/32 cases in 100% of frames. The WNCC algorithm outperformed the NCC algorithm in speed, with a mean processing speed of .007s versus .013s, respectively, and captured a greater range of motion in all cases. Conclusions: The demonstrated feasibility of bowel tracking on cine MR imagesets indicates its potential successful use in real‐time bowel tracking and gated radiotherapy. While both algorithms performed well, the WNCC algorithm was superior in processing speed and sensitivity to bowel motion.
TU‐G‐218‐01: Lessons Learned from Misadministrations and Accidents in Radiation Therapy Part I: Teletherapy
Authors: Foster R
Published: June 2012

The recent publicity received by the radiation oncology community regarding misadministrations, accidents and overdoses has renewed the medical physicists' focus on safety. However, many other accidents have preceded these. Are these recent incidents similar to older ones and could they have been prevented had the medical physics community applied the lessons learned from previous incidents? Certainly technology is more advanced, but adherence to established doctrines and recommendations from our professional societies could have prevented the majority of these accidents. In this presentation, recent and much older accidents and misadministrations in radiation therapy that have been reported in the media will be presented. These events serve as teaching moments for the clinical physicists and opportunities to assess our own strategies and clinical programs with the goal of providing safe and reliable treatment deliveries. The recommendations and QA that have been established in the literature will be presented in concert with events that have either been near‐misses or grave accidents. This presentation will focus on both conventional linac delivery and the more sophisticated treatments such as SRT and IMRT.

Learning Objectives:

1. To review and understand the causes of various external beam treatment misadministrations and accidents reported in the media.

2. To review and understand corrective and preventative actions that should be in place in order to safely administer external beam RT.

3. To review and understand the recommendation for safety by the ASTRO, ACR, and AAPM and the ABS.

4. To review and understand the ASTRO Six Point Protection Plan.
TU‐G‐218‐02: Enhancing Our Safety Culture by Understanding Recent Mishaps (Part 2): Brachytherapy
Authors: Libby B
Published: June 2012

The AAPM and other associated professional societies and governmental bodies (ACR, ASTRO, ABS, NCRP, IAEA, ICRP, and NRC) are fully committed to providing the highest quality brachytherapy treatments in an effective and safe manner. Although the history of our profession can demonstrate extraordinary effectiveness in our conscientious and comprehensive approach to the radiation treatment of cancer, there have been accidents and misadministrations in brachytherapy, and we must be committed to understanding and learning from the open communication of reported medical events, whether through the media or in reports issued by national and international bodies. In this presentation several medical events in brachytherapy that have occurred and been reported will be presented and coupled with corrective actions that should have been in place. The established literature on safety and quality assurance for brachytherapy is also presented.

Learning Objectives:

1. To review and understand the root causes of brachytherapy medical events that have been reported in the media and to governmental and associated bodies.

2. To review and understand corrective actions that should be in place in order to safely administer brachytherapy treatments.

3. To review and understand the various established recommendations for the safe delivery of brachytherapy from the AAPM and associated bodies in order to foster a culture of safety surrounding brachytherapy treatments.

4. To discuss communication that needs to take place among users, treatment planning system makers, and seed vendors in order to foster the use of identical terminology so that a possible source of treatment error can be eliminated.
WE‐C‐BRCD‐01: Radiation Therapy Safety: Past, Present and Future
Authors: Pawlicki T , Huq M , Mutic S , Low D
Published: June 2012

Attendees are taught an efficient organizational framework for Part II exam preparation that maximizes high‐yield active learning study activities and minimizes low‐yield study activities. This method is then combined with a productive group‐based study technique. The format and scope of the Part II ABR exam in radiotherapy physics is described, and the eligibility requirements are reviewed. High‐yield and low‐yield study activities are defined and examples are discussed in detail. A problem‐based strategy for limiting the scope of study material is described. A method for studying in groups by distributing delegable tasks among multiple group members and ensuring their completion is described.

Learning Objectives

1. Understand the scope of material covered on Part II of the ABR radiotherapy physics exam and which references to study for the exam.

2. Be able to design and execute an efficient study plan that enables an active learning approach.

3. Learn to use group study techniques to enhance efficiency.
WE‐A‐211‐03: IOMP: Guidance on Education and Training Requirements for Medical Physicists
Authors: Lopes M. Carmo
Published: June 2012

Purpose: To present the IOMP recommendations on the roles and responsibilities of medical physicists and the corresponding basic requirements for education and training (E&T). Special focus will be given to the development of E&T efforts in Asian‐Pacific countries and Europe. Methods: In line with its mission, IOMP is publishing new Policy Statements on “Role and Responsibilities of the Medical Physicist” and “Basic Requirements for Education and Training of Medical Physicists”. IOMP is also proposing a new Model Curriculum that is already available on‐line at http://emerald2.eu/mep_11.html. This e‐book includes 39 papers, various e‐Learning and Open source materials, International Education/Training projects and University courses from 27 countries. This first volume is including a strong participation of Asian‐Pacific countries, represented at AFOMP. Also AFOMP developed “Policy Statement No. 3: recommendations for the education and training of medical physicists in AFOMP countries” in 2011. At the European level we must refer the Medical Physics Expert European Project. The main objectives of the European Commission project ‘Guidelines on Medical Physics Expert’ are to provide for improved implementation of the provisions relating to the Medical Physics Expert (MPE) as it was defined in the Council Directive 97/43/EURATOM, known as the Medical Exposures Directive, (MED) and the recently proposed recast Basic Safety Standards (BSS) Directive. This includes harmonization of the mission statement, education and training of the MPE among the Member States of the European Union. Results: In all of these initiatives the expected results point to the identification of gaps in education contents, identification of minimum education and training requirements and definitions of required knowledge, skills and competences in Medical Physics. Conclusions: It is certainly a role of IOMP to contribute to the guidance on the harmonization of the different educational pathways and approaches all over the world.
WE‐A‐BRB‐02: Characterization of a New Cervical Applicator for Use with the Axxent 50kVp EBx Source
Authors: Kelley L , Holt R , Rusch T , Walawalkar A , Lum A
Published: June 2012

Purpose: To characterize the dosimetric properties of a new cervical applicator designed for the Xoft 50 kVp X‐ray Electronic Brachytherapy (eBx) system. Methods: The Axxent Cervical Applicator was developed to treat invasive cancer of the cervix using the existing Xoft Axxent Controller and X‐ray source. This applicator is a Henschke‐type design, consisting of a central tandem with ovoids mounted on the distal end of colpostats on either side. Filtration through the thin‐walled titanium tandems and colpostats allows for improved dose penetration, lowering the surface dose and reducing the dose to non‐target tissues. Dose profiles in a plane parallel to the straight, 15 degree, 30 degree, and 45 degree curved tandems were measured using GAFChromic EBT2 film. The tandem depth dose was calculated and the dose profile was compared to the distribution calculated using Varian BrachyVision treatment planning software. Results: The dose measured within 1.5 mm of the surface of the tandem was 6.4 +/‐ 0.4 times the dose at 2.0 cm for all curvature tandems measured. The maximum dose near the surface was 6.8 times the 2.0 cm dose. The dose rate in water for a nominal strength source at 2.0 cm from the centerline of the tandem was 24 +/‐ 3 Gy/hr. The ovoids produced 35 +/‐ 1 Gy/hr at a distance of 2.0 from the colpostat centerline. Dose profiles agree with expectations to within 10% over the majority of the treatment volume out to 2 cm. Conclusions: The Axxent Cervical Applicator can be used to treat cervical cancer using eBx with the Xoft X‐ray Source. Dose profiles measured for each tandem compare well with the profiles expected from the treatment planning software. Titanium filtering produces improved dose penetration resulting in a lower surface ‐ Point A dose ratio comparable to that of Ir‐192 and Cs‐ 137. Research supported by Xoft ‐ a subsidiary of iCAD
WE‐A‐BRB‐04: Comparison of the Radiation and Thermal Dose Distributions of a Novel Thermo‐Brachytherapy Seed
Authors: Warrell G , Shvydka D , Gautam B , Parsai E
Published: June 2012

Purpose: A novel thermo‐brachytherapy seed implant recently developed by our group combines a radioactive source (I–125) with a ferromagnetic core, capable of producing heat when placed in an alternating magnetic field. The seed is intended for concurrent hyperthermia and brachytherapy treatments for deep‐seated solid tumors. The maximized heat production is achieved when all implants are aligned along the magnetic field direction. For optimal coverage, the planned thermal and radiation dose distributions should be closely matched. As the algorithm used by the commercial treatment planning software is inadequate for accurate calculation of the dose distribution from parallel seeds at short distances, a Monte Carlo (MC) model was developed and utilized for comparison of the radiation and thermal distributions. Methods: A model consisting of an array of seeds separated from each other by 1 cm, oriented parallel to the magnetic field direction, was studied in a cylindrical water phantom. The radiation dose distribution was obtained with the MC code MCNP5. The thermal distribution was modeled for various magnetic field intensities and frequencies, and accounts for heat loss due to blood perfusion using a finite element analysis (FEA) package COMSOL Multiphysics. Results: A radiation dose distribution obtained from the MC calculations accounts for the interseed shielding effect and assumes non‐random (parallel) orientation of the seeds. A comparison between this dose distribution and thermal coverage data calculated by the FEA method shows that they may be made to coincide closely by adjusting the magnetic field intensity and frequency. Conclusions: Maximum heating and optimal thermal coverage are obtained when the thermo‐brachytherapy seeds are orientated in the direction of the magnetic field. For a specific seed placement a thermal distribution similar to the radiation dose distribution can be achieved via seed alignment and adjustments of the frequency and intensity of the applied magnetic field. Nothing to doisclose
WE‐A‐BRB‐06: 3D In‐Patient Dose Reconstruction from the PET‐CT Imaging of Y‐90 Microspheres for Metastatic Cancer to the Liver
Authors: Fourkal E , Veltchev I , Koren S , Lin M , Ma C , Meyer J , Doss M , Yu M
Published: June 2012

Purpose: The development of radioembolization with SIR‐Spheres represents a significant advance in the treatment of patients with metastatic disease to the liver. This technique has evolved to use a formula for dose calculation that relies on body surface area as the main determinant of dose. However, what is prescribed is not dose, but rather activity. It has been traditionally thought that the tracer 90Y is a pure electron emitter. However, the decay of 90Y has also a minor ß+ branch to the first excited state of 90Zr, with 34 ppm branching ratio. While the positron emission is rare, it can be observed in a PET scan. Therefore the main objective of this work is to develop a new method for 3D dose reconstruction based on the PET imaging of a patient injected with SIR‐Spheres. Methods: Using Fluka Monte Carlo code, the voxel dose kernel (VDK) was calculated for 90Y source of size equal to that of the PET scanner voxel size. Subsequently, the convolution of the VDK with measured PET data was performed to recover the absorbed dose. The absolute dose calibration was done by taking the ratio of the measured positron activity to the known activity due to electrons Results: The developed model was used to reconstruct the dose distribution for two patients treated with 90Y microspheres. The 3D dose calculation was subsequently superimposed on the patient's CT information to provide a complete description of the absorbed dose to the liver, tumor and adjacent structures. Conclusions: The proposed method offers significant improvement in characterization of the dose deposited by SIR‐Spheres with the hope that this may help answer some of the clinical questions concerning the influence of the dose distribution on the response rate, progression‐free or overall survival.