bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐A‐BRF‐10: Quantification of Subject‐Specific Susceptibility‐Related Geometric Distortion in Clinical Liver MRI for Radiation Therapy
Authors: Zhu T , Matakos A , Feng M , Lawrence T , Cao Y
Published: July 2014

Purpose:

Subject‐specific susceptibility‐induced B0 inhomogeneity affects the geometric accuracy of MRI images, with potential impact on the accuracy of treatment planning and image guidance. This study quantifies individual distortions for patients with intrahepatic tumors.

Methods:

Liver MRI scans of 13 patients who were enrolled in an IRB approved study were acquired on a 3T scanner (Skyra, Siemens). Clinical contrast‐enhanced images were acquired by a 3D Volume Interpolated Breath‐Hold Examination (VIBE) sequence with TE/TR =1.65/4.3ms, voxel size = 2.5×2.5×3mm (axial sets) or 3.5×3.5×5mm (coronal sets), and frequency‐encoding (FE) bandwidth of 440Hz/pixel. B0 inhomogeneity was evaluated by acquisition of dual gradient echoes (GRE) with TE1/TE2/TR =4.92/7.38/106ms, a voxel size of 3.5×3.5×3.75mm, a FE bandwidth of 290Hz/pixel and breath‐hold. The phase difference maps from the two echoes were unwrapped using a quantitative MRI analysis software package (FSL, FMRIB, Oxford, UK). The resulting calculated B0 inhomogeneity maps (ΔB0 in Hz) were converted to voxel distortion maps in the FE direction (ΔX in mm) corresponding to the VIBE images.

Results:

Maximum susceptibility‐induced distortions were observed in the liver dome near the diaphragm. Using results from coronal VIBE images in this study as examples, we observed clusters of voxels displaced close to or greater than ΔX=3.5mm (440 Hz in ΔB0) in the VIBE images of the liver in 3 patients, and greater than 2 mm but less than 3.5 mm in 12 patients. On average, approximately 14% of imaged liver voxels had distortions ΔX>±1mm (ΔB0>±125Hz) and 1% of the voxels had ΔX>±2mm (ΔB0>±250Hz).

Conclusion:

Although advanced MRI techniques, like VIBE, permit faster acquisitions allowing for breath‐held examinations with limited motion‐induced artifacts, this study suggests that localized distortions due to subject‐specific susceptibility variations can occur and require additional advanced corrections based on measuring patient‐specific B0 inhomogeneity maps.

The authors would like to acknowledge funding support from NIH R01EB016079 and NIH/NCI RO1 CA132834.
TH‐A‐18C‐07: Noise Suppression in Material Decomposition for Dual‐Energy CT
Authors: Dong X , Petrongolo M , Wang T , Zhu L
Published: July 2014

Purpose:

A general problem of dual‐energy CT (DECT) is that the decomposition is sensitive to noise in the two sets of dual‐energy projection data, resulting in severely degraded qualities of decomposed images. We have previously proposed an iterative denoising method for DECT. Using a linear decomposition function, the method does not gain the full benefits of DECT on beam‐hardening correction. In this work, we expand the framework of our iterative method to include non‐linear decomposition models for noise suppression in DECT.

Methods:

We first obtain decomposed projections, which are free of beam‐hardening artifacts, using a lookup table pre‐measured on a calibration phantom. First‐pass material images with high noise are reconstructed from the decomposed projections using standard filter‐backprojection reconstruction. Noise on the decomposed images is then suppressed by an iterative method, which is formulated in the form of least‐square estimation with smoothness regularization. Based on the design principles of a best linear unbiased estimator, we include the inverse of the estimated variance‐covariance matrix of the decomposed images as the penalty weight in the least‐square term. Analytical formulae are derived to compute the variance‐covariance matrix from the measured decomposition lookup table.

Results:

We have evaluated the proposed method via phantom studies. Using non‐linear decomposition, our method effectively suppresses the streaking artifacts of beam‐hardening and obtains more uniform images than our previous approach based on a linear model. The proposed method reduces the average noise standard deviation of two basis materials by one order of magnitude without sacrificing the spatial resolution.

Conclusion:

We propose a general framework of iterative denoising for material decomposition of DECT. Preliminary phantom studies have shown the proposed method improves the image uniformity and reduces noise level without resolution loss. In the future, we will perform more phantom studies to further validate the performance of the purposed method.

This work is supported by a Varian MRA grant.
TH‐A‐18C‐11: An Investigation of KV CBCT Image Quality and Dose Reduction for Volume‐Of‐Interest Imaging Using Dynamic Collimation
Authors: Parsons D , Robar J
Published: July 2014

Purpose:

The focus of this work was to investigate the improvements in image quality and dose reduction for volume‐of‐interest (VOI) kV‐CBCT using dynamic collimation.

Methods:

A prototype iris aperture was used to track a VOI during a CBCT acquisition. The current aperture design is capable of one‐dimensional translation as a function of gantry angle and dynamic adjustment of the iris radius. The aperture occupies the location of the bow‐tie filter on a Varian OBI system. CBCT and planar image quality was investigated as a function of aperture radius, while maintaining the same dose to the VOI, for a 20 cm diameter cylindrical water phantom with a 9 mm diameter bone insert centered on isocenter. Corresponding scatter‐to‐primary ratios (SPR) were determined at the detector plane with Monte Carlo simulation using EGSnrc. Dose distributions for various anatomical sites were modeled using a dynamic BEAMnrc library and DOSXYZnrc. The resulting VOI dose distributions were compared to full‐field distributions.

Results:

SPR was reduced by a factor of 8.4 when decreasing iris diameter from 21.2 cm to 2.4 cm (at isocenter). Similarly, this change in iris diameter corresponds to a factor increase of approximately 1.4 and 1.5 in image contrast for CBCT and planar images, respectively, and similarly a factor decrease in image noise of approximately 1.7 and 1.5. This results in a measured gain in contrast‐to‐noise ratio of a factor of approximately 2.3 for both CBCT and planar images. Depending upon the anatomical site, dose was reduced to 10%–70% of the full field value along the central axis plane and down to 2% along the axial planes, while maintaining the same dose to the VOI compared to full‐field techniques.

Conclusion:

The presented VOI technique offers improved image quality for image‐guided radiotherapy while sparing the surrounding volume of unnecessary dose compared to full‐field techniques.
TH‐A‐9A‐04: Incorporating Liver Functionality in Radiation Therapy Treatment Planning
Authors: Wu V , Epelman M , Feng M , Cao Y , Wang H , Romeijn E , Matuszak M
Published: July 2014

Purpose:

Liver SBRT patients have both variable pretreatment liver function (e.g., due to degree of cirrhosis and/or prior treatments) and sensitivity to radiation, leading to high variability in potential liver toxicity with similar doses. This work aims to explicitly incorporate liver perfusion into treatment planning to redistribute dose to preserve well‐functioning areas without compromising target coverage.

Methods:

Voxel‐based liver perfusion, a measure of functionality, was computed from dynamic contrast‐enhanced MRI. Two optimization models with different cost functions subject to the same dose constraints (e.g., minimum target EUD and maximum critical structure EUDs) were compared. The cost functions minimized were EUD (standard model) and functionality‐weighted EUD (functional model) to the liver. The resulting treatment plans delivering the same target EUD were compared with respect to their DVHs, their dose wash difference, the average dose delivered to voxels of a particular perfusion level, and change in number of high‐/low‐functioning voxels receiving a particular dose. Two‐dimensional synthetic and three‐dimensional clinical examples were studied.

Results:

The DVHs of all structures of plans from each model were comparable. In contrast, in plans obtained with the functional model, the average dose delivered to high‐/low‐functioning voxels was lower/higher than in plans obtained with its standard counterpart. The number of high‐/low‐functioning voxels receiving high/low dose was lower in the plans that considered perfusion in the cost function than in the plans that did not. Redistribution of dose can be observed in the dose wash differences.

Conclusion:

Liver perfusion can be used during treatment planning potentially to minimize the risk of toxicity during liver SBRT, resulting in better global liver function. The functional model redistributes dose in the standard model from higher to lower functioning voxels, while achieving the same target EUD and satisfying dose limits to critical structures.

This project is funded by MCubed and grant R01‐CA132834.
TH‐C‐18A‐12: Evaluation of the Impact of Body Size and Tube Output Limits in the Optimization of Fast Scanning with High‐Pitch Dual Source CT
Authors: Ramirez Giraldo J , Mileto A. , Hurwitz L. , Marin D.
Published: July 2014

Purpose:

To evaluate the impact of body size and tube power limits in the optimization of fast scanning with high‐pitch dual source CT (DSCT).

Methods:

A previously validated MERCURY phantom, made of polyethylene, with circular cross‐section of diameters 16, 23, 30 and 37cm, and connected through tapered sections, was scanned using a second generation DSCT system. The DSCT operates with two independently controlled x‐ray tube generators offering up to 200 kW power reserve (100 kW per tube). The entire lenght of the phantom (42cm) was scanned with two protocols using: A)Standard single‐source CT (SSCT) protocol with pitch of 0.8, and B) DSCT protocol with high‐pitch values ranging from 1.6 to 3.2 (0.2 steps). All scans used 120 kVp with 150 quality reference mAs using automatic exposure control. Scanner radiation output (CTDIvol) and effective mAs values were extracted retrospectively from DICOM files for each slice. Image noise was recorded. All variables were assessed relative to phantom diameter.

Results:

With standard‐pitch SSCT, the scanner radiation output (and tube‐current) were progressively adapted with increasing size, from 6 mGy (120 mAs) up to 15 mGy (270 mAs) from the thinnest (16cm) to the thickest diameter (37 cm), respectively. By comparison, using high‐pitch (3.2), the scanner output was bounded at about 8 mGy (140 mAs), independent of phantom diameter. Although relative to standard‐pitch, the high‐pitch led to lower radiation output for the same scan, the image noise was higher, particularly for larger diameters. To match the radiation output adaptation of standard‐pitch, a high‐pitch mode of 1.6 was needed, with the advantage of scanning twice as fast.

Conclusion:

To maximize the benefits of fast scanning with high‐pitch DSCT, the body size and tube power limits of the system need to be considered such that a good balance between speed of acquisition and image quality are warranted.

JCRG is an employee of Siemens Medical Solutions USA Inc.
TH‐C‐12A‐03: Development of Expanded Field Irradiation Technique with Gimbaled X‐Ray Head
Authors: Ono T , Miyabe Y , Yamada M , Sawada A , Kaneko S , Monzen H , Mizowaki T , Kokubo M , Hiraoka M
Published: July 2014

Purpose:

The Vero4DRT has a maximum field size of 150×150 mm2. The purposes of this study were to develop an expanded field irradiation technique using a unique gimbaled x‐ray head of Vero4DRT and to evaluate its dosimetric characteristic.

Methods:

The expanded field irradiation consisted of four separate fields with 2.39 degree gimbal rotation around orthogonal two axes. The central beam axis for each field shifted 40 mm from the isocenter for longitudinal and lateral directions, and thus, the field size was expanded up to 230×230 mm2. Adjacent region were created at the isocenter (center‐adjacent expanded‐field) and 20 mm from isocenter (offadjacent expanded‐field). To create flat dose distribution in the combined piecewise‐fields, the overlapping and gaps regions on the isocenter plane were adjusted with the gimbal rotating and the MLC. To evaluate dosimetric characteristic of the expanded‐field, films inserted in water‐equivalent phantoms at 50, 100 and 150 mm depth were irradiated and the field size, penumbra, flatness and symmetry were analyzed.In addition, the expandedfield irradiation technique was applied to IMRT. A head and neck IMRT field, which was planned for the conventional linac (Varian Clinac iX), was reproduced with the expanded‐field of the Vero4DRT. The simulated dose distribution for the expanded IMRT field was compared to the measured dose distribution.

Results:

The field size, penumbra, flatness and symmetry of center‐ and off‐ adjacent expanded‐fields were 230.2–232.1 mm, 7.8–10.7 mm, 2.3–6.5% and –0.5–0.4% at 100 mm depth. The 82.1% area of the expanded IMRT dose distribution was within 5% difference between measurement and simulation, which was analyzed upper 50% dose area, and the 3%/3 mm gamma pass rate was 98.4%.

Conclusions:

The expandedfield technique was developed using the gimbaled x‐ray head. To extend applied targets, such as whole breast irradiations or head and neck IMRT, the expanded‐field technique would be effective.
TH‐C‐12A‐08: New Compact 10 MV S‐Band Linear Accelerator: 3D Finite‐Element Design and Monte Carlo Dose Simulations
Authors: Baillie D , St. Aubin J , Fallone B , Steciw S
Published: July 2014

Purpose:

To design a new compact S‐band linac waveguide capable of producing a 10 MV x‐ray beam, while maintaining the length (27.5 cm) of current 6 MV waveguides. This will allow higher x‐ray energies to be used in our linac‐MRI systems with the same footprint.

Methods:

Finite element software COMSOL Multiphysics was used to design an accelerator cavity matching one published in an experiment breakdown study, to ensure that our modeled cavities do not exceed the threshold electric fields published. This cavity was used as the basis for designing an accelerator waveguide, where each cavity of the full waveguide was tuned to resonate at 2.997 GHz by adjusting the cavity diameter. The RF field solution within the waveguide was calculated, and together with an electron‐gun phase space generated using Opera3D/SCALA, were input into electron tracking software PARMELA to compute the electron phase space striking the x‐ray target. This target phase space was then used in BEAM Monte Carlo simulations to generate percent depth doses curves for this new linac, which were then used to re‐optimize the waveguide geometry.

Results:

The shunt impedance, Q‐factor, and peak‐to‐mean electric field ratio were matched to those published for the breakdown study to within 0.1% error. After tuning the full waveguide, the peak surface fields are calculated to be 207 MV/m, 13% below the breakdown threshold, and a d‐max depth of 2.42 cm, a D10/20 value of 1.59, compared to 2.45 cm and 1.59, respectively, for the simulated Varian 10 MV linac and brehmsstrahlung production efficiency 20% lower than a simulated Varian 10 MV linac.

Conclusion:

This work demonstrates the design of a functional 27.5 cm waveguide producing 10 MV photons with characteristics similar to a Varian 10 MV linac.
TH‐C‐12A‐12: Veritas: An Open Source Tool to Facilitate User Interaction with TrueBeam Developer Mode
Authors: Mishra P , Lewis J , Etmektzoglou T , Svatos M
Published: July 2014

Purpose:

To address the challenges of creating delivery trajectories and imaging sequences with TrueBeam Developer Mode, a new open‐source graphical XML builder, Veritas, has been developed, tested and made freely available. Veritas eliminates most of the need to understand the underlying schema and write XML scripts, by providing a graphical menu for each control point specifying the state of 30 mechanical/dose axes. All capabilities of Developer Mode are accessible in Veritas.

Methods:

Veritas was designed using QT Designer, a ‘what‐you‐is‐what‐you‐get’ (WYSIWIG) tool for building graphical user interfaces (GUI). Different components of the GUI are integrated using QT's signals and slots mechanism. Functionalities are added using PySide, an open source, cross platform Python binding for the QT framework. The XML code generated is immediately visible, making it an interactive learning tool. A user starts from an anonymized DICOM file or XML example and introduces delivery modifications, or begins their experiment from scratch, then uses the GUI to modify control points as desired. The software automatically generates XML plans following the appropriate schema.

Results:

Veritas was tested by generating and delivering two XML plans at Brigham and Women's Hospital. The first example was created to irradiate the letter ‘B’ with a narrow MV beam using dynamic couch movements. The second was created to acquire 4D CBCT projections for four minutes. The delivery of the letter ‘B’ was observed using a 2D array of ionization chambers. Both deliveries were generated quickly in Veritas by non‐expert Developer Mode users.

Conclusion:

We introduced a new open source tool Veritas for generating XML plans (delivery trajectories and imaging sequences). Veritas makes Developer Mode more accessible by reducing the learning curve for quick translation of research ideas into XML plans. Veritas is an open source initiative, creating the possibility for future developments and collaboration with other researchers.

I am an employee of Varian Medical Systems.
TH‐E‐BRE‐10: Independent Verification of Monitor Units for Volumetric Modulated Arc Therapy (VMAT)
Authors: Chen X , Bush K , Ding A , Xing L
Published: July 2014

Purpose:

A challenging problem in VMAT is how to independently validate the monitor units (MUs) of the treatment plan for a patient generated by the treatment planning system (TPS). In this work we establish a novel framework for independent MU verification of VMAT.

Methods:

The proposed MU verification technique is based on the relationship between the absorbed dose and the weighed sequence of station points. In VMAT, the dose at a point can be expressed as a sum of contributions from all the station points (or control points). To proceed, we first obtain the matrix elements which characterize the dosimetric contribution of the involved station points by computing the doses at a series of voxels, typically on the prescription surface of the VMAT treatment plan, with unit MU setting for all the station points. This dose matrix is calculated using an in‐house Monte Carlo (MC) software. The MUs of the station points are then derived by minimizing the least‐squares difference between doses computed by the TPS and that of the MC for the selected set of voxels. The technique is applied to sixteen clinical cases with a variety of energies, disease sites and TPS dose calculation algorithms.

Results:

For cases without tissue density inhomogeneity, the independently computed MUs agree with that of TPS to within 2.7% for all the station points. For lung cases, the MC‐calculated MUs differ significantly from that of the treatment plan computed using AAA. However, the discrepancies are reduced to within 3% when the TPS dose calculation algorithm is switched to a transport equation‐based technique (AcurosTM).

Conclusion:

An independent MU calculation method is developed, for the first time, for patient specific VMAT treatment plan QA.
TH‐E‐BRF‐01: Exploiting Tumor Shrinkage in Split‐Course Radiotherapy
Authors: Unkelbach J , Craft D , Hong T , Papp D , Ramakrishnan J , Salari E , Wolfgang J , Bortfeld T
Published: July 2014

Purpose:

In split‐course radiotherapy, a patient is treated in several stages separated by weeks or months. This regimen has been motivated by radiobiological considerations. However, using modern image‐guidance, it also provides an approach to reduce normal tissue dose by exploiting tumor shrinkage. In this work, we consider the optimal design of split‐course treatments, motivated by the clinical management of large liver tumors for which normal liver dose constraints prohibit the administration of an ablative radiation dose in a single treatment.

Methods:

We introduce a dynamic tumor model that incorporates three factors: radiation induced cell kill, tumor shrinkage, and tumor cell repopulation. The design of splitcourse radiotherapy is formulated as a mathematical optimization problem in which the total dose to the liver is minimized, subject to delivering the prescribed dose to the tumor. Based on the model, we gain insight into the optimal administration of radiation over time, i.e. the optimal treatment gaps and dose levels.

Results:

We analyze treatments consisting of two stages in detail. The analysis confirms the intuition that the second stage should be delivered just before the tumor size reaches a minimum and repopulation overcompensates shrinking. Furthermore, it was found that, for a large range of model parameters, approximately one third of the dose should be delivered in the first stage. The projected benefit of split‐course treatments in terms of liver sparing depends on model assumptions. However, the model predicts large liver dose reductions by more than a factor of two for plausible model parameters.

Conclusion:

The analysis of the tumor model suggests that substantial reduction in normal tissue dose can be achieved by exploiting tumor shrinkage via an optimal design of multi‐stage treatments. This suggests taking a fresh look at split‐course radiotherapy for selected disease sites where substantial tumor regression translates into reduced target volumes.
TH‐E‐BRF‐09: Gaussian Mixture Model Analysis of Radiation‐Induced Parotid‐Gland Injury: An Ultrasound Study of Acute and Late Xerostomia in Head‐And‐Neck Radiotherapy
Authors: Liu T , Yu D , Beitler J , Tridandapani S , Bruner D , Curran W , Yang X
Published: July 2014

Purpose:

Xerostomia (dry mouth), secondary to parotid‐gland injury, is a distressing side‐effect in head‐and‐neck radiotherapy (RT). This study's purpose is to develop a novel ultrasound technique to quantitatively evaluate post‐RT parotid‐gland injury.

Methods:

Recent ultrasound studies have shown that healthy parotid glands exhibit homogeneous echotexture, whereas post‐RT parotid glands are often heterogeneous, with multiple hypoechoic (inflammation) or hyperechoic (fibrosis) regions. We propose to use a Gaussian mixture model to analyze the ultrasonic echo‐histogram of the parotid glands. An IRB‐approved clinical study was conducted: (1) control‐group: 13 healthy‐volunteers, served as the control; (2) acutetoxicity group − 20 patients (mean age: 62.5 ± 8.9 years, follow‐up: 2.0±0.8 months); and (3) late‐toxicity group − 18 patients (mean age: 60.7 ± 7.3 years, follow‐up: 20.1±10.4 months). All patients experienced RTOG grade 1 or 2 salivary‐gland toxicity. Each participant underwent an ultrasound scan (10 MHz) of the bilateral parotid glands. An echo‐intensity histogram was derived for each parotid and a Gaussian mixture model was used to fit the histogram using expectation maximization (EM) algorithm. The quality of the fitting was evaluated with the R‐squared value.

Results:

(1) Controlgroup: all parotid glands fitted well with one Gaussian component, with a mean intensity of 79.8±4.9 (R‐squared>0.96). (2) Acute‐toxicity group: 37 of the 40 post‐RT parotid glands fitted well with two Gaussian components, with a mean intensity of 42.9±7.4, 73.3±12.2 (R‐squared>0.95). (3) Latetoxicity group: 32 of the 36 post‐RT parotid fitted well with 3 Gaussian components, with mean intensities of 49.7±7.6, 77.2±8.7, and 118.6±11.8 (R‐squared>0.98).

Conclusion:

RT‐associated parotid‐gland injury is common in head‐and‐neck RT, but challenging to assess. This work has demonstrated that the Gaussian mixture model of the echo‐histogram could quantify acute and late toxicity of the parotid glands. This study provides meaningful preliminary data from future observational and interventional clinical research.
TH‐E‐17A‐02: High‐Pitch and Sparse‐View Helical 4D CT Via Iterative Image Reconstruction Method Based On Tensor Framelet
Authors: Guo M , Nam H , Li R , Xing L , Gao H
Published: July 2014

Purpose:

4D CT is routinely performed during radiation therapy treatment planning of thoracic and abdominal cancers. Compared with the cine mode, the helical mode is advantageous in temporal resolution. However, a low pitch (∼0.1) for 4D CT imaging is often required instead of the standard pitch (∼1) for static imaging, since standard image reconstruction based on analytic method requires the low‐pitch scanning in order to satisfy the data sufficient condition when reconstructing each temporal frame individually. In comparison, the flexible iterative method enables the reconstruction of all temporal frames simultaneously, so that the image similarity among frames can be utilized to possibly perform high‐pitch and sparse‐view helical 4D CT imaging. The purpose of this work is to investigate such an exciting possibility for faster imaging with lower dose.

Methods:

A key for highpitch and sparse‐view helical 4D CT imaging is the simultaneous reconstruction of all temporal frames using the prior that temporal frames are continuous along the temporal direction. In this work, such a prior is regularized through the sparsity transform based on spatiotemporal tensor framelet (TF) as a multilevel and high‐order extension of total variation transform. Moreover, GPU‐based fast parallel computing of X‐ray transform and its adjoint together with split Bregman method is utilized for solving the 4D image reconstruction problem efficiently and accurately.

Results:

The simulation studies based on 4D NCAT phantoms were performed with various pitches (i.e., 0.1, 0.2, 0.5, and 1) and sparse views (i.e., 400 views per rotation instead of standard >2000 views per rotation), using 3D iterative individual reconstruction method based on 3D TF and 4D iterative simultaneous reconstruction method based on 4D TF respectively.

Conclusion:

The proposed TF‐based simultaneous 4D image reconstruction method enables high‐pitch and sparse‐view helical 4D CT with lower dose and faster speed.
TH‐E‐17A‐03: Development and Evaluation of a 4D‐CBCT Scheme Based On Simultaneous Motion Estimation and Image Reconstruction
Authors: Dang J , Gu X , Ouyang L , Pan T , Wang J
Published: July 2014

Purpose:

To develop and evaluate the performance of a novel 4D‐CBCT reconstruction scheme based on simultaneous motion estimation and image reconstruction (SMEIR) through patient studies.

Methods:

The SMEIR algorithm consists of two alternating steps: 1) motion‐compensated CBCT reconstruction; and 2) motion model estimation from the projections directly. In step 1, projections from all phases are used to reconstruct a reference phase 4D‐CBCT by explicitly considering the motion models between different phases. In step 2, updated inverse consistent motion models are obtained directly from projections by matching the measured projections to the forward projection of the deformed reference phase 4D‐CBCT. Motion model estimation was implemented on GPU to increase the computation efficiency. Two lung cancer patients were scanned for 4.5 and 5.7 minutes. Totally 1679 and 1982 projections were acquired and grouped into 10 phases. To evaluate SMEIR algorithm performance on conventional 1‐minute CBCT scan, projections at each phase were down‐sampled by factors ranging from 2 to 10. 4D‐CBCT were reconstructed from down‐sampled projections using FDK, total variation minimization (TV) and SMEIR. Using 4D‐CBCT reconstructed from fully sampled projections as a reference, relative errors of image and tumor motion trajectory were analyzed to quantify performances of different reconstruction algorithms.

Results:

SMEIR algorithm outperforms FDK and TV in both reconstruction accuracy and tumor tracking accuracy. When averaged projection number per phase decreases to 18 in two patients, relative reconstruction errors for FDK, TV and SMEIR are 38.00%, 11.72% and 9.59%, respectively. The maximum tumor tracking errors are 2.53 mm, 2.05 mm, and 0.68 mm for FDK, TV and SMEIR, respectively.

Conclusion:

Patient studies show that the SMEIR algorithm achieves 1‐mm tumor tracking accuracy when the average projection number per phase reduces to 18. SMEIR algorithm enables the use of conventional 1‐minute CBCT for accurate motion modeling and 4D‐CBCT reconstruction.
TH‐E‐17A‐08: Estimation of Image Quality of 4‐Dimensional Computed Tomography (4DCT) Via Fourier Analysis of Corresponding 1D Breathing Surrogate
Authors: Caraveo M , Wei J , McNamara J , Rimner A , Yorke E , Li G
Published: July 2014

Purpose:

Motion artifacts are common in patient 4DCT, leading to an illdefined tumor volume with variation up to 110% or setting up a poor foundation with low imaging fidelity for tumor motion study. We developed a method to estimate 4DCT image quality by establishing a correlation between the severity of motion artifacts in 4DCT images and the periodicity of corresponding 1D respiratory wave‐function (1DRW) surrogate used for 4DCT reconstruction.

Methods:

Fast Fourier Transformation (FFT) was applied to analyze 1DRW periodicity, defined as the sum of the 5 largest Fourier coefficients, ranging in 0–1. Distortional motion artifacts of cine‐scan 4DCT at the junctions of adjacent couchposition scans around the diaphragm were identified in 3 categories: incomplete, overlapping and duplicate. To quantify these artifacts, the discontinuity of the diaphragm at the junctions was measured in distance and averaged along 6 directions in 3 orthogonal views. Mean and sum artifacts per junction (APJ) across the entire diaphragm were calculated in each breathing phase. To make the APJ inter‐patient comparable, patientspecific motion was removed from APJ by dividing patient‐specific diaphragmatic velocity (displacement divided by the mean period, from FFT analysis of the 1DRW) and the normalized APJ was defined as motion artifact severity (MAS). Twenty‐five patients with free‐breathing 10‐phase 4DCT and corresponding 1DRW surrogate datasets were studied.

Results:

A mild correlation of 0.56 was found between 1DRW periodicity and 4DCT artifact severity. Higher MAS tends to appear around mid inhalation and mid exhalation and the lowest MAS tends to be around full exhalation. The breathing periodicity of >0.8 possesses minimal motion artifacts.

Conclusion:

The 1D‐4D correlation provides a fast means to estimate 4DCT image quality. Using 1DRW signal, we can retrospectively screen out high‐quality 4DCT images for clinical research (periodicity>0.8) and prospectively identify poor breathers as candidates of breath coaching prior to 4DCT scan.

This research is in part supported by NIH (U54CA137788/132378). MC would like to thank MSKCC summer medical student research program supported by National Cancer Institute and hosted by Department of Medical Physics at MSKCC.
TH‐E‐17A‐10: Markerless Lung Tumor Tracking Based On Beams Eye View EPID Images
Authors: Chiu T , Rozario T , Bereg S , Klash S , Kearney V , Liu H , Jiang L , Foster R , Mao W
Published: July 2014

Purpose:

Dynamic tumor tracking or motion compensation techniques have proposed to modify beam delivery following lung tumor motion on the flight. Conventional treatment plan QA could be performed in advance since every delivery may be different. Markerless lung tumor tracking using beams eye view EPID images provides a best treatment evaluation mechanism. The purpose of this study is to improve the accuracy of the online markerless lung tumor motion tracking method.

Methods:

The lung tumor could be located on every frame of MV images during radiation therapy treatment by comparing with corresponding digitally reconstructed radiograph (DRR). A kV‐MV CT corresponding curve is applied on planning kV CT to generate MV CT images for patients in order to enhance the similarity between DRRs and MV treatment images. This kV‐MV CT corresponding curve was obtained by scanning a same CT electron density phantom by a kV CT scanner and MV scanner (Tomotherapy) or MV CBCT. Two sets of MV DRRs were then generated for tumor and anatomy without tumor as the references to tracking the tumor on beams eye view EPID images.

Results:

Phantom studies were performed on a Varian TrueBeam linac. MV treatment images were acquired continuously during each treatment beam delivery at 12 gantry angles by iTools. Markerless tumor tracking was applied with DRRs generated from simulated MVCT. Tumors were tracked on every frame of images and compared with expected positions based on programed phantom motion. It was found that the average tracking error were 2.3 mm.

Conclusion:

This algorithm is capable of detecting lung tumors at complicated environment without implanting markers. It should be noted that the CT data has a slice thickness of 3 mm. This shows the statistical accuracy is better than the spatial accuracy.

This project has been supported by a Varian Research Grant.
TH‐E‐17A‐11: Tracking Tumor’s Boundary in MV Image Sequences for Image‐Guided Radiation Therapy
Authors: Zhang X , Homma N , Narita Y , Takai Y , Ichiji K , Abe M , Sugita N , Yoshizawa M
Published: July 2014

Purpose:

To develop a level set method (LSM)‐based algorithm to track the tumor’s boundary in MV image sequences for image‐guided radiation therapy (IGRT).

Method:

Four MV image sequences, each of which consists of 100 frames at frame rate of 7.5 Hz, are acquired by using the electronic portal imaging device (EPID) (Varian Medical Systems, Pal Alto, USA) during the treatment of lung cancer. In the first frame of each sequence, we roughly delineate an initial contour of the target tumor by hand. Using a LSM‐based algorithm, the initial contour can automatically shape itself to fit the tumor, and eventually detect the tumor’s boundary. We then employ the tumor’s boundary obtained from the previous frame as the initial contour in the subsequent frame, so that the LSM‐based method can drive this initial contour to the tumor’s boundary quickly and fulfill a tracking task.

Results:

The proposed method has been evaluated on four MV image sequences. The mean tracking errors were 0.23, 0.29, 0.37, and 1.18 mm, and their corresponding standard deviations were 0.97, 0.75, 1.2 and 1.48 mm, respectively.

Conclusion:

Compared with conventional tumor tracking techniques, the proposed system is capable not only of tracking the tumor’s position, but also of detecting the tumor’s boundary varying with the respiration during the treatment. Considering current radiation therapy technique, for example, dynamical multi‐leaf collimator (DMLC) has been widely applied in clinical treatment, this study indicates the potential for significant accuracy improvement in radiation therapy.

This work was partially supported by a research grant from Varian Medical Systems (Palo Alto, California).
SU‐A‐BRF‐01: Education Council Symposium: Online Education in Medical Physics
Authors: Dobbins J , Prisciandaro J , Bloch C , Gingold E , Starkschall G , Oldham M , Sprawls P , Xiao Y
Published: July 2014

Online education is rapidly becoming an important means of communicating content in educational activities across a broad spectrum of fields, including medical physics. We are currently at a point of broad change in educational strategies and methodologies, and the use of online content is likely to play an increasingly important role in medical physics education going forward. This symposium, sponsored by the AAPM Education Council, will consider the current state of online educational opportunities in medical physics as well as what options may become available in the near future.

Specific topics to be covered include an overview of the scope and opportunity of online education in medical physics; current resources including available online content, the AAPM Virtual Library and Online Learning Center, AAPM/RSNA online educational modules, and software tools for creating online content; and considerations of future uses of massively‐open online courses in medical physics education. Finally, a collaborative model of medical physics education using online resources will be described.

Learning Objectives:

Understand the range of opportunities available for online education in medical physics

Learn of existing resources available for medical physics education

Understand how to use software tools to create online educational content

Understand a collaborative model of medical physics education using online resources
SU‐C‐16A‐03: Direction Modulated Brachytherapy for HDR Treatment of Cervical Cancer
Authors: Han D , Webster M , Scanderbeg D , Yashar C , Choi D , Song B , Devic S , Ravi A , Song W
Published: July 2014

Purpose:

To investigate a new Directional Modulated Brachytherapy (DMBT) intra‐uterine tandem using various 192‐Ir after‐loaders.

Methods:

Dose distributions from the 192‐Ir sources were modulated using a 6.3mm diameter tungsten shield (18.0g/cm3). The source moved along 6 longitudinal grooves, each 1.3mm in diameter, evenly spaced along periphery of the shield, The tungsten rod was enclosqed by 0.5mm thick Delrin (1.41g/cc). Monte Carlo N particle (MCNPX) was used to calculate dose distributions. 51million particles were calculated on 504 cores of a supercomputer. Fifteen different patients originally treated with a traditional tandem‐and‐ovoid applicator, with 5 fractions each, (15 patients X 5 fxs = 75 plans) were re‐planned with the DMBT applicator combined with traditional ovoids, on an in‐house developed HDR brachytherapy planning platform, which used intensity modulated planning capabilities using a constrained gradient optimization algorithm. For all plans the prescription dose was 6 Gy and they were normalized to match the clinical treated V100.

Results:

Generally, the DMBT plan quality was a remarkable improvement from conventional T&O plans because of the anisotropic dose distribution of DMBT. The largest difference was to the bladder which had a 0.59±0.87 Gy (8.5±28.7%) reduction in dose. This was because of the the horseshoe shape (U‐shape) of the bladder. The dose reduction to rectum and sigmoid were 0.48±0.55 Gy (21.1±27.2%) and 0.10±0.38 Gy (40.6±214.9%), respectively. The D90 to the HRCTV was 6.55±0.96 Gy (conventional T&O) and 6.59±1.06 Gy (DMBT).

Conclusion:

For image guided adaptive brachytherapy, greater flexibility of radiation intensity is essential and DMBT can be the solution.
SU‐C‐19A‐01: A Simple Deep Inspiration Breath Hold System
Authors: Rasmussen B , Duelge J , Baldwin B , Valenti M , Hunsader A , Kaznowski L , Blackburn J , Chu K
Published: July 2014

Purpose:

Deep Inspiration Breath Hold (DIBH) Radiation therapy for left sided breast can reduce dose to the lungs and heart. The purpose of this work is to illustrate how to implement a simple method of DIBH for simulation and treatment using equipment readily available in most radiation oncology clinics.

Methods:

For simulation and treatment, a foam block is placed on the patient's abdomen or chest and a horizontal laser mounted on a movable slide is aimed at the center of the foam block. After a coaching session the block is marked at the average free breathing position and average DIBH position. The position of block relative to laser can be seen by the patient via prism glasses as well as the radiation therapists via a video camera system. Simulation CT scans and treatment delivery are performed under DIBH conditions. Imaging and treatment are performed by manually turning the beam on once the patient has achieved DIBH after being given verbal instructions.

Results:

Manually triggered imaging was used daily to verify DIBH reproducibility for all patients treated using this system. Sets of before and during port images were used to ensure patient position was appropriate for treatment. Results of the laser on block method were compared to a sister facility using surface mapping techniques for DIBH and the two methods were found to have clinically equivalent reproducibility.

Conclusion:

The laser and block system was found to be simple to implement and robust during patient treatment. This system can be created from readily available materials at low cost and provides adequate feedback to patient and therapists. During treatment images document the reproducibility of setup and give confidence to clinicians that this method is reproducible from day to day.
SU‐C‐19A‐07: Influence of Immobilization On Plan Robustness in the Treatment of Head and Neck Cancer with IMPT
Authors: Bues M , Anand A , Morse B , Kruse J , Liu W , Shen J , Keole S , Patel S
Published: July 2014

Purpose:

We evaluated the effect of interposing immobilization devices into the beam's path on the robustness of a head and neck plan.

Methods:

An anthropomorphic head phantom was placed into a preliminary prototype of a specialized head and neck immobilization device for proton beam therapy. The device consists of a hard low density shell, a custom mold insert, and thermoplastic mask to immobilize the patient's head in the shell. This device was provided by CIVCO Medical Solutions for the purpose of evaluation of suitability for proton beam therapy. See Figure 1. Two pairs of treatment plans were generated. The first plan in each pair was a reference plan including only the anthropomorphic phantom, and the second plan in each pair included the immobilization device. In all other respects the plans within the pair were identical.

Results:

In the case of the simple plan the degradation of plan robustness was found to be clinically insignificant. In this case, target coverage in the worst case scenario was reduced from 95% of the target volume receiving 96.5% of prescription dose to 95% of the target volume receiving 96.3% of prescription dose by introducing the immobilization device. In the case of the complex plan, target coverage of the boost volume in the worst case scenario was reduced from 95% of the boost target volume receiving 97% of prescription dose to 95% of the boost target volume receiving 83% of prescription dose by introducing the immobilization device. See Figure 2.

Conclusion:

Immobilization devices may have a deleterious effect on plan robustness. Evaluation of the preliminary prototype revealed a variable impact on the plan robustness depending of the complexity of the case.

Brian Morse is an employee of CIVCO Medical Solutions.
SU‐C‐BRE‐04: Microbeam‐Radiation‐Therapy (MRT): Characterizing a Novel MRT Device Using High Resolution 3D Dosimetry
Authors: Li Q , Juang T , Bache S , Chang S , Oldham M
Published: July 2014

Purpose:

The feasibility of MRT has recently been demonstrated utilizing a new technology of Carbon‐Nano‐Tube(CNT) field emission x‐ray sources. This approach can deliver very high dose(10's of Gy) in narrow stripes(sub‐mm) of radiation which enables the study of novel radiation treatment approaches. Here we investigate the application of highresolution (50um isotropic) PRESAGE/Optical‐CT 3D dosimetry techniques to characterize the radiation delivered in this extremely dosimetrically challenging scenario.

Methods:

The CNT field emission x‐ray source irradiator comprises of a linear cathode array and a novel collimator alignment system. This allows a precise delivery of high‐energy small beams up to 160 kVp. A cylindrical dosimeter (∼2.2cm in height ∼2.5cm in diameter) was irradiated by CNT MRT delivering 3 strips of radiation with a nominal entrance dose of 32 Gy.A second dosimeter was irradiated with similar entrance dose, with a regular x‐ray irradiator collimated to microscopical strip‐beams. 50um (isotropic) 3D dosimetry was performed using an in‐house optical‐CT system designed and optimized for high resolution imaging (including a stray light deconvolution correction). The percentage depth dose (PDD), peak‐to‐valley ratio (PVR) and beam width (FWHM) data were obtained and analyzed in both cases.

Results:

High resolution 3D images were successfully achieved with the prototype system, enabling extraction of PDD and dose profiles. The PDDs for the CNT irradiation showed pronounced attenuation, but less build‐up effect than that from the multibeam irradiation. The beam spacing between the three strips has an average value of 0.9mm while that for the 13 strips is 1.5 mm at a depth of 16.5 mm. The stray light corrected image shows line profiles with reduced noise and consistent PVR values.

Conclusion:

MRT dosimetry is extremely challenging due to the ultra small fields involved. This preliminary application of a novel, ultra‐high resolution, optical‐CT 3D dosimetry system shows promise, but further work is required to validate and investigate accuracy and artifacts.

This work was supported by NIH R01CA100835
SU‐C‐BRE‐06: Radiobiological Advantage of Very Rapid Irradiation
Authors: Rafat M , Bazalova M , Palma B , Kozak M , Jiang D , Dunning M , McCormick D , Nelson J , Hemsing E , Lartey F , Graves E , Koong A , Maxim P , Loo B
Published: July 2014

Purpose:

To characterize the effect of very rapid dose delivery as compared to conventional therapeutic irradiation times on clonogenic cell survival.

Methods:

We used a Varian Trilogy linear accelerator to deliver doses up to 10 Gy using a 6 MV SRS photon beam. We irradiated four cancer cell lines in times ranging from 30 sec to 30 min. We also used a Varian TrueBeam linear accelerator to deliver 9 MeV electrons at 10 Gy in 10 s to 30 min to determine the effect of irradiation time on cell survival. We then evaluated the effect of using 60 and 120 MeV electrons on cell survival using the Next Linear Collider Test Accelerator (NLCTA) beam line at the SLAC National Accelerator Laboratory. During irradiation, adherent cells were maintained at 37oC with 20%O2/5%CO2. Clonogenic assays were completed following irradiation to determine changes in cell survival due to dose delivery time and beam quality, and the survival data were fitted with the linear‐quadratic model.

Results:

Cell lines varied in radiosensitivity, ranging from two to four logs of cell kill at 10 Gy for both conventional and very rapid irradiation. Delivering radiation in shorter times decreased survival in all cell lines. Log differences in cell kill ranged from 0.2 to 0.7 at 10 Gy for the short compared to the long irradiation time. Cell kill differences between short and long irradiations were more pronounced as doses increased for all cell lines.

Conclusion:

Our findings suggest that shortening delivery of therapeutic radiation doses to less than 1 minute may improve tumor cell kill. This study demonstrates the potential advantage of technologies under development to deliver stereotactic ablative radiation doses very rapidly.

Bill Loo and Peter Maxim have received Honoraria from Varian and Research Support from Varian and RaySearch.