bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐H‐BRA‐02: The Physics of Magnetic Field Isolation in a Novel Compact Linear Accelerator Based MRI‐Guided Radiation Therapy System
Authors: Low D , Mutic S , Shvartsman S , Chmielewski T , Fought G , Sharma A , Dempsey J
Published: July 2016

Purpose:

To develop a method for isolating the MRI magnetic field from field‐sensitive linear accelerator components at distances close to isocenter.

Methods:

A MRI‐guided radiation therapy system has been designed that integrates a linear accelerator with simultaneous MR imaging. In order to accomplish this, the magnetron, port circulator, radiofrequency waveguide, gun driver, and linear accelerator needed to be placed in locations with low magnetic fields. The system was also required to be compact, so moving these components far from the main magnetic field and isocenter was not an option. The magnetic field sensitive components (exclusive of the waveguide) were placed in coaxial steel sleeves that were electrically and mechanically isolated and whose thickness and placement were optimized using E&M modeling software. Six sets of sleeves were placed 60° apart, 85 cm from isocenter. The Faraday effect occurs when the direction of propagation is parallel to the magnetic RF field component, rotating the RF polarization, subsequently diminishing RF power. The Faraday effect was avoided by orienting the waveguides such that the magnetic field RF component was parallel to the magnetic field.

Results:

The magnetic field within the shields was measured to be less than 40 Gauss, significantly below the amount needed for the magnetron and port circulator. Additional mu‐metal was employed to reduce the magnetic field at the linear accelerator to less than 1 Gauss. The orientation of the RF waveguides allowed the RT transport with minimal loss and reflection.

Conclusion:

One of the major challenges in designing a compact linear accelerator based MRI‐guided radiation therapy system, that of creating low magnetic field environments for the magnetic‐field sensitive components, has been solved. The measured magnetic fields are sufficiently small to enable system integration.

This work supported by ViewRay, Inc.
TU‐H‐BRA‐08: The Design and Characteristics of a Novel Compact Linac‐Based MRI Guided Radiation Therapy (MR‐IGRT) System
Authors: Mutic S , Low D , Chmielewski T , Fought G , Hernandez M , Kawrakow I , Sharma A , Shvartsman S , Dempsey J
Published: July 2016

Purpose:

To describe the design and characteristics of a novel linac‐based MRI guided radiation therapy system that addresses RF and magnetic field interference and that can be housed in conventional radiotherapy vaults.

Methods:

The MR‐IGRT system will provide simultaneous MR imaging combined with both simple (3D) and complex (IMRT, SBRT, SRS) techniques. The system is a combination of a) double‐donut split solenoidal superconducting 0.345T MRI; and b) a 90 cm isocenter ring‐gantry mounted 6MV, flattening filter‐free linac coupled with a stacked doubly‐focused multileaf collimator with 4 mm resolution. A novel RF shielding and absorption technology was developed to isolate the beam generating RF emissions from the MR, while a novel magnetic shielding sleeve system was developed to place the magnetic field‐sensitive components in low‐magnetic field regions. The system design produces high spatial resolution radiation beams with state‐of‐the art radiation dose characteristics and simultaneous MR imaging.

Results:

Prototype testing with a spectrum analyzer has demonstrated complete elimination of linac RF inside the treatment room. The magnetic field inside of the magnetic shielding was well below the specification, allowing the linear accelerator to operate normally. A novel on‐gantry shimming system maintained < 25 ppm magnetic field homogeneity over a 45 cm spherical field of view for all gantry angles.

Conclusion:

The system design demonstrates the feasibility coupling a state‐of‐the art linac system with a 0.345T MRI, enabling highly conformal radiation therapy with simultaneous MR image guidance.

S. Mutic's employer (Washington University) has grant with ViewRay; D. Low is former ViewRay scientific advisory board member (ended October 2015); T. Chmielewski, G. Fought, M. Hernandez, I. Kawrakow, A. Sharma, S. Shvartsman, J. Dempsey are employees of ViewRay with stock options (Dempsey has leadership role and Dempsey/Kawrakow have stock).
TU‐H‐BRA‐09: Relationship Between B0 and the Contrast‐To‐Noise Ratio (CNR) of Tumour to Background for MRI/Radiotherapy Hybrids
Authors: Wachowicz K , DeZanche N , Yip E , Volotovskyy V , Fallone B
Published: July 2016

Purpose:

To investigate the relationship in MRI between B0 and the contrast‐to‐noise ratio (CNR) of various tumour/normal tissue pairs. This study is motivated by the current interest in MRI/radiotherapy hybrids, for which multiple magnetic field strengths have been proposed. CNR is the single most important parameter governing the ability of a system to identify a tumour in real time for treatment guidance. The MRI community has long since recognized that the SNR of a well‐designed MR system is roughly proportional to B0, the polarizing magnetic field. However, the CNR between two tissues is much more complicated ‐ dependent not only on this signal behavior, but also on the different relaxation properties of the tissues.

Methods:

Experimentally‐based models of B0‐dependant relaxation for various tumour and normal tissues from the literature were used in conjunction with signal equations for MR sequences suitable for rapid realtime imaging to develop field‐dependent predictions for CNR. These CNR models were developed for liver, lung, breast, glioma, and kidney tumours for spoiled‐gradient echo (SGE) and balanced steady‐state free precession (bSSFP) sequences.

Results:

In all cases there was an improved CNR at lower fields compared to linear dependency. Further, in some tumour sites, the CNR at lower fields was found to be comparable to, or sometimes higher than those at higher fields (i.e. bSSFP CNR for glioma, kidney and liver tumours).

Conclusion:

Due to the variation of tissue relaxation parameters with field, lower B0 fields have been shown to perform as well or better (in terms of CNR) than higher fields for some tumour sites. In other sites this effect was less pronounced. It is the complex relationship between CNR and B0 that leads to greater CNR at 0.5 T for certain tumour types studied here for fast imaging.

B. Gino Fallone is a co‐founder and CEO of MagnetTx Oncology Solutions (under discussions to license Alberta bi‐planar linac MR for commercialization)
TU‐H‐202‐01: Introduction to CT Ventilation Imaging: Principles, Validation and Clinical Translation
Authors: Yamamoto T.
Published: July 2016

CT ventilation imaging is an exciting functional imaging modality that combines four‐dimensional computed tomography (4DCT) and deformable image registration (DIR) to provide exquisite ventilation maps of the lung. CT ventilation imaging can be used for:

Functional avoidance in thoracic radiation therapy,

Imaging longitudinal changes in regional lung function for treatment assessment and adaptation,

Image‐assisted diagnosis of non‐oncologic respiratory diseases.

CT ventilation imaging uses CT, a predominantly anatomic imaging modality, and through imaging processing creates functional images. CT ventilation imaging provides functional images that are higher resolution, faster and cheaper to perform than the clinical standard, SPECT. Indeed the number of CT ventilation abstracts presented at the AAPM meeting has been doubling every two years. With the world's‐first clinical trial of CT ventilation functional image‐guided radiation therapy now underway, the first dedicated scientific symposium will educate and stimulate AAPM members from both radiology and radiation oncology.

This symposium will compare the foundations of CT ventilation imaging with competing MRI, PET and SPECT ventilation imaging methods, and details the first clinical trial of CT ventilation imaging for functional avoidance in lung cancer radiation therapy. The spatial‐temporal nature of pulmonary ventilation, response maps to radiation and the design of predictive models will be presented. Validation efforts and challenges will also be discussed, from clinical outcome correlations in single time point and longitudinal studies, to cross‐modality image comparisons in the first multi‐institutional CT ventilation imaging challenge.

The panel will discuss the future role of CT ventilation imaging, and what level of physiologic validation is needed for applications in radiation oncology and beyond.

Learning Objectives:

Learn the principles of CT ventilation imaging and how ventilation images are acquired with MRI, PET and SPECT

Understand the methods used to benchmark CT ventilation and the correlations between CT ventilation imaging and clinical outcomes

Recognize the clinical applications of CT ventilation imaging in radiation oncology and beyond

Australian NHMRC Fellowship. Australian NSW Cancer Institute Fellowship.; Y. Vinogradskiy, The authors acknowledge NIH R01CA200817 grant and Stat of Colorado grant.; T. Yamamoto, This study was supported in part by the American Cancer Society and the Dean of the University of California Davis School of Medicine (ACS IRG‐95‐125‐13). Philips Radiation Oncology Systems loaned us a research version of the Pinnacle3 treatment planning system.; J. Bayouth, Funding support from NCI

R01 CA166703; J. Kipritidis, This work has been supported by a Cancer Institute NSW Early Career Fellowship and an NHMRC Australia Fellowship.

No commercial funding was received for this work.
TU‐H‐207A‐08: Estimating Radiation Dose From Low‐Dose Lung Cancer Screening CT Exams Using Tube Current Modulation
Authors: Hardy A , Bostani M , McMillan K , Zankl M , Cagnon C , McNitt‐Gray M
Published: July 2016

Purpose:

The purpose of this work is to estimate effective and lung doses from a low‐dose lung cancer screening CT protocol using Tube Current Modulation (TCM) across patient models of different sizes.

Methods:

Monte Carlo simulation methods were used to estimate effective and lung doses from a low‐dose lung cancer screening protocol for a 64‐slice CT (Sensation 64, Siemens Healthcare) that used TCM. Scanning parameters were from the AAPM protocols. Ten GSF voxelized patient models were used and had all radiosensitive organs identified to facilitate estimating both organ and effective doses. Predicted TCM schemes for each patient model were generated using a validated method wherein tissue attenuation characteristics and scanner limitations were used to determine the TCM output as a function of table position and source angle. The water equivalent diameter (WED) was determined by estimating the attenuation at the center of the scan volume for each patient model. Monte Carlo simulations were performed using the unique TCM scheme for each patient model. Lung doses were tallied and effective doses were estimated using ICRP 103 tissue weighting factors. Effective and lung dose values were normalized by scanspecific 32 cm CTDIvol values based upon the average tube current across the entire simulated scan. Absolute and normalized doses were reported as a function of WED for each patient.

Results:

For all ten patients modeled, the effective dose using TCM protocols was below 1.5 mSv. Smaller sized patient models experienced lower absolute doses compared to larger sized patients. Normalized effective and lung doses showed some dependence on patient size (R2 = 0.77 and 0.78, respectively).

Conclusion:

Effective doses for a low‐dose lung screening protocol using TCM were below 1.5 mSv for all patient models used in this study.

Institutional research agreement, Siemens Healthcare; Past recipient, research grant support, Siemens Healthcare; Consultant, Toshiba America Medical Systems; Consultant, Samsung Electronics
TU‐H‐206‐02: Novel Linearly‐Filled Derenzo PET Phantom Design
Authors: Graves S , Cox B , Farhoud M , Valdovinos H , Jeffery J , Eliceiri K , Barnhart T , Nickles R
Published: July 2016

Purpose:

To design a linearly‐filled Derenzo positron emission tomography (PET) phantom, eliminating the extraneous radioisotope volumes in a conventional reservoir‐type design. This activity reduction combined with the elimination of bubbles in smaller phantom channels would significantly reduce personnel dose, radioisotope cost, and would improve image quality by reducing out‐of‐slice activity scatter.

Methods:

A computer‐aided design (CAD) was created of a modular Derenzo phantom consisting of three phantom layers with gaskets between the layers. The central piece contains the active pattern volume and channels connecting adjacent rods in a serpentine pattern. The two end‐pieces contained an inlet and an outlet for filling purposes. Phantom prototypes were 3D printed on a Viper Si2 stereolithography machine. The two gaskets were fabricated from silicon sheets using a PLS 6.75 laser cutter. Phantoms were held together by pass‐through glass‐filled nylon bolts and nuts. Phantoms were filled with 52Mn, 64Cu, 74Br, and 124I for testing, and were imaged on a Siemens Inveon MicroPET scanner.

Results:

Four phantom prototypes were constructed using male Leur Lock fittings for inlet/outlet ports. 3D printed layers were sanded to ensure proper coupling to the silicon gaskets. The filling volume for each prototype was approximately 2.4 mL. The filling process was found to be rapid, leak‐tight, and with minimal back‐pressure. PET images were reconstructed by OSEM3D, and axial slices along the phantom pattern length were averaged to provide final images. Image distortion was isotope dependent with 52Mn and 64Cu having the least distortion and 124I having the most distortion.

Conclusion:

These results indicate that the linearlyfilled Derenzo design improves on conventional reservoir‐type designs by eliminating potential bubbles in small channels and by reducing activity level, radioisotope volume, radioisotope cost, personnel dose, filling time, and out‐of‐slice activity scatter

The method described in this abstract has been filed as a patent application to the US Patent and Trade Office by the Wisconsin Alumni Research Foundation (WARF).
TU‐H‐206‐05: Investigating the Resistance of GS‐BSSFP to Motion Artifacts
Authors: Hoff M , Andre J , Xiang Q
Published: July 2016

Purpose:

In addition to correcting magnetic field inhomogeneity‐induced banding artifacts in balanced steady state free precession (bSSFP) MRI, preliminary in vivo studies indicate that the geometric solution (GS) also mitigates motion artifacts. The purpose here is to investigate the source of motion artifact correction through simulations, to further ascertain GS‐bSSFP's clinical potential.

Methods:

Four bSSFP MR images with Δθ = 0°, 90°, 180°, and 270° respective phase cycling and TE/TR = 4.2/2.1ms were 1) acquired in vivo with a 3D axially‐oriented sequence on a Philips Ingenia 3T MRI scanner using a flip angle α = 30°, and 180/180/120 matrix size and 1.0/1.0/1.0mm voxel size along frequency/phase/slice directions, and 2) simulated using α = 80°, parameters varied across the field‐of‐view (T1 relaxation = 200–>3000ms, T2 relaxation = 40‐>3000ms, and field inhomogeneity θ = −π−>+π), and added zero‐mean Gaussian noise. The GS (the cross‐point of lines/spokes connecting alternating phase cycles in the complex plane) and complex sum (CS) were computed pixel‐by‐pixel. Simulated data noise was reoriented in each associated spoke's frame of reference in order to derive the noise radiality. Plots were then generated of GS and CS error and deviation as a function of the noise radiality in the original data.

Results:

In vivo data indicates that the GS mitigates motion artifacts relative to the CS in the foramen magnum region. Simulated data indicates that the GS has less error in size and deviation than the CS, and this discrepancy grows as noise radiality increases.

Conclusion:

The GS shows more accuracy than the CS in all tests executed, especially as phasecycled image noise radiality increases. This implies that noise‐like image artifacts such as those caused by motion and flow are suppressed by the GS, inspiring clinical applications of GS‐bSSFP given its additional elimination of banding artifacts.
TU‐H‐206‐09: Acceptance Testing of Ultrasound Systems for Shear Wave Elastography Measurements
Authors: Long Z , Tradup D , Song P , Stekel S , Chen S , Hangiandreou N
Published: July 2016

Purpose:

Acceptance testing of shear wave elastography on ten ultrasound systems is reported. Furthermore, variations in testing procedures related to coupling medium, number of operators, and phantom homogeneity were investigated.

Methods:

Shear wave speed measurements were made on ten systems (GE LOGIQ E9 XDclear 2.0 ultrasound scanner with C1‐6 and 9L transducers). Measurements were acquired using the CIRS Model 039 shear wave liver fibrosis phantoms (“soft” and “hard” phantoms, with stiffness of ∼3.5 and 45 kPa, respectively) at two depths (3 and 7 cm for C1‐6; 1 and 4 cm for 9L), by two operators. Each measurement was repeated for five times without specifying the transducer location on the phantom. 45 ppm salt water (as recommended by QIBA) was used for coupling. Furthermore, phantom homogeneity was investigated by comparing C1‐6 measurements made at five positions marked on each phantom. Three operators acquired C1‐6 measurements on one scanner, and one repeated the measurements after a week. US gel was compared with salt water as a coupling medium.

Results:

Averaged shear wave speed using the ten C1‐6 and 9L transducers are summarized in Table 1. The greatest maximum deviation of an individual measurement from the group mean (Table 2) was 5.4% of the mean and 2.3 times the standard deviation among all groups. Salt water and US coupling gel showed no significant difference. Velocities from the five measurement locations had a maximum deviation of 5.9% or less. The maximum inhomogeneity averaged over the two phantoms and all measurement locations was 2.6%. Inter‐ and intra‐operator coefficients of variation were all ≤ 2.2%.

Conclusion:

The measurement variations were considered to be reasonable, and all equipment was accepted. The use of salt water versus gel for acoustic coupling, single versus multiple phantom measurement locations, or single versus multiple operators would not cause significant differences in acceptance test results.

Pengfei Song and Shigao Chen receive royalties from GE Medical Systems for the shear wave elastography technology.
TU‐H‐CAMPUS‐JeP1‐01: Characterization of a Parameterized Image Similarity Cost Function for Automated Patient and Site Specific DIR Accuracy Optimizations
Authors: Neylon J , Min Y , Hasse K , Low D , Santhanam A
Published: July 2016

Purpose:

Clinical deformable image registration (DIR) accuracy is difficult to quantify, making validation and verification manual and time consuming. It has also been seen that DIR accuracy can be improved by patient and site specific optimization. We previously investigated a cost function to parameterize image similarity metrics (ISMs) and provide a quantifiable comparison of DIR performance. In this abstract, we characterize and optimize the cost function response (CFR) and correlation to target registration error (TRE) in a dense registration parameter space.

Methods:

A validated head‐and‐neck biomechanical model was used to induce clinical deformations in patient kVCT data (source), outputting known ground truth deformation vector fields (DVFs) and simulated CTs of deformed anatomy (target). The source and target were registered repeatedly using an in‐house optical flow DIR, systematically sampling the registration parameter space, and producing TREs and data volumes deformed according to the DIR DVF (warp). Normalized mutual information (NMI) was chosen as the test ISM. The cost function variables (CFV) were also systematically sampled to characterize their effect on the CFR. Sub‐volume analysis was performed on the data, defined by structures of interest in the head‐and‐neck region.

Results:

Strong inverse correlation was observed between the TRE and CFR when the data was subdivided around specific structures like the PTV, parotids, and mandible, reaching values of −0.95. The CFR slope changed by an order of magnitude by manipulating the CFV. Response and correlation were improved by adjusting on a structure specific basis. The CFR achieved a predominantly convex response, which should facilitate its use as an energy term in an optimization scheme.

Conclusions:

Replacing the time consuming, manually placed landmark assessment methodology is necessary for patient and site specific registration optimization to be clinically feasible. The proposed cost function is a promising alternative for fast, fully automated DIR performance quantification.
TU‐H‐CAMPUS‐IeP2‐02: Four‐Dimensional Coronary Artery Visualization Based On Image Propagation
Authors: Liu B , Liang B , Xu X , Guo B , Wei R , Xu S , Zhou F , Wu Q
Published: July 2016

Purpose:

4D visualization of coronary artery using X‐ray angiograms rotationally acquired on C‐arm has many valuable applications, like dynamic roadmapping. In this work we propose and validate a method to visualize 4D artery based on 3D coronary image propagation.

Methods:

After sorting the angiograms into different cardiac phases using nearest‐neighbor ECG gating, a high quality 3D coronary image was reconstructed at one phase using a motion‐compensated iterative reconstruction method. Then the reconstructed image was propagated to other cardiac phases by registering it to the angiograms of each phase (stage I registration). A third‐order B‐spline was used to model the vessel motion and the parameters were solved by maximizing the normalized correlation (NC) between the projections of the 3D image and the angiograms under the constraints of motion smoothness and volume preserving. Because the angiograms corresponding to one phase contain residual vessel motion and the registration method could only match the mean vessel morphology, morphological mismatch still existed between the propagated image and each angiogram. To obtain accurate vessel morphology according to each angiogram, we further registered the propagated image to each angiogram using the aforementioned registration method (stage II registration).

Results:

The proposed method was evaluated on angiograms simulated using 4D XCAT phantom. The reconstructed image at end‐diastolic phase (phase 0%) was consecutively propagated to end‐systolic phase (phase 40%) every 5%. After stage I registration, the mean distance between the propagated and ground truth vessel centerlines was decreased from 2.2±1.2 to 0.6±0.2 mm. The mean centerline distance was further decreased to 0.5±0.2 mm after the stage II registration.

Conclusion:

A 4D coronary artery visualization method based on image propagation was proposed. The experimental results show that accurate 4D morphology of coronary artery could be obtained using this method.

This work was supported by the National Natural Science Foundation of China (61171005).
TU‐H‐CAMPUS‐IeP2‐05: Breast and Soft Tissue‐Equivalent 3D Printed Phantoms for Imaging and Dosimetry
Authors: Hintenlang D , Terracino B
Published: July 2016

Purpose:

The study has the goal to demonstrate that breast and soft tissue‐equivalent phantoms for dosimetry applications in the diagnostic energy range can be fabricated using common 3D printing methods.

Methods:

3D printing provides the opportunity to rapidly prototype uniquely designed objects from a variety of materials. Common 3D printers are usually limited to printing objects based on thermoplastic materials such as PLA, or ABS. The most commonly available plastic is PLA, which has a density significantly greater than soft tissue. We utilized a popular 3D printer to demonstrate that tissue specific phantom materials can be generated through the careful selection of 3D printing parameters. A series of stepwedges were designed and printed using a Makerbot Replicator2 3D printing system. The print file provides custom adjustment of the infill density, orientation and position of the object on the printer stage, selection of infill patterns, and other control parameters. The x‐ray attenuation and uniformity of fabricated phantoms were evaluated and compared to common tissue‐equivalent phantom materials, acrylic and BR12. X‐ray exposure measurements were made using narrow beam geometry on a clinical mammography unit at 28 kVp on the series of phantoms. The 3D printed phantoms were imaged at 28 kVp to visualize the internal structure and uniformity in different planes of the phantoms.

Results:

By utilizing specific in‐fill density and patterns we are able to produce a phantom closely matching the attenuation characteristics of BR12 at 28 kVp. The in‐fill patterns used are heterogeneous, so a judicious selection of fill pattern and the orientation of the fill pattern must be made in order to obtain homogenous attenuation along the intended direction of beam propagation.

Conclusions:

By careful manipulation of the printing parameters, breast and soft tissue‐equivalent phantoms appropriate for use at imaging energies can be fabricated using 3D printing techniques.
TU‐H‐CAMPUS‐JeP2‐03: Machine‐Learning‐Based Delineation Framework of GTV Regions of Solid and Ground Glass Opacity Lung Tumors at Datasets of Planning CT and PET/CT Images
Authors: Ikushima K , Arimura H , Jin Z , Yabuuchi H , Kuwazuru J , Shioyama Y , Sasaki T , Honda H , Sasaki M
Published: July 2016

Purpose:

In radiation treatment planning, delineation of gross tumor volume (GTV) is very important, because the GTVs affect the accuracies of radiation therapy procedure. To assist radiation oncologists in the delineation of GTV regions while treatment planning for lung cancer, we have proposed a machine‐learning‐based delineation framework of GTV regions of solid and ground glass opacity (GGO) lung tumors following by optimum contour selection (OCS) method.

Methods:

Our basic idea was to feed voxel‐based image features around GTV contours determined by radiation oncologists into a machine learning classifier in the training step, after which the classifier produced the degree of GTV for each voxel in the testing step. Ten data sets of planning CT and PET/CT images were selected for this study. The support vector machine (SVM), which learned voxel‐based features which include voxel value and magnitudes of image gradient vector that obtained from each voxel in the planning CT and PET/CT images, extracted initial GTV regions. The final GTV regions were determined using the OCS method that was able to select a global optimum object contour based on multiple active delineations with a level set method around the GTV. To evaluate the results of proposed framework for ten cases (solid:6, GGO:4), we used the three‐dimensional Dice similarity coefficient (DSC), which denoted the degree of region similarity between the GTVs delineated by radiation oncologists and the proposed framework.

Results:

The proposed method achieved an average three‐dimensional DSC of 0.81 for ten lung cancer patients, while a standardized uptake value‐based method segmented GTV regions with the DSC of 0.43. The average DSCs for solid and GGO were 0.84 and 0.76, respectively, obtained by the proposed framework.

Conclusion:

The proposed framework with the support vector machine may be useful for assisting radiation oncologists in delineating solid and GGO lung tumors.
TU‐H‐CAMPUS‐JeP2‐04: Deriving Delivered Doses to Assess the Viability of 2.5 Mm Margins in Head and Neck SBRT
Authors: Lin S , Shang Q , Pirozzi S , Godley A
Published: July 2016

Purpose:

To calculate the delivered dose for head and neck SBRT patients using pre‐treatment images. This delivered dose was then used to determine the viability of 2.5 mm margins.

Methods:

Daily cone beam CTs (CBCTs) were collected for 20 patients along with a planning CT, planned dose, and planning structures. The day 1 CBCT was aligned to the planning CT using the treatment shifts (six degrees of freedom) and then the dose and contours were transferred to the CBCT. The day 1 CBCT becomes the reference image for days 2–5. The day 2–5 CBCTs were also aligned to the planning CT using the treatment shifts given and the dose transferred. The day 2–5 CBCTs were then deformably registered to the day 1 CBCT. The doses delivered on days 2–5 were then deformed to the day 1 CBCT where they could be accumulated. This was achieved with MIM 6.5.1 (MIM Software, Cleveland OH). The accumulated doses for the 20 patients were evaluated against the planned doses using the initial planning criteria as points of comparison.

Results:

The delivered CTV dose conformed to the planned 98.6% coverage, with an average decrease of 2.6% between planned and delivered coverage. This implies the 2.5 mm margin was sufficient. Larger CTVs correlated to smaller differences between planned and delivered coverage. Delivered dose to critical structures including the spinal cord, mandible, brain, brainstem, and larynx was acceptable, with differences between planned and delivered max dose <5% on average. Similarly for the parotid glands, globes, cochlear, optic nerve, lens, and submandibular glands, differences between planned and delivered doses were generally <5%.

Conclusion:

The 2.5 mm margin provided acceptable CTV coverage, adequately accounting for setup errors. Organ at risk sparing was also satisfactory. Small tumor volumes (<20 cc) may require a larger margin to treat effectively.
TU‐H‐CAMPUS‐JeP2‐05: Can Automatic Delineation of Cardiac Substructures On Noncontrast CT Be Used for Cardiac Toxicity Analysis?
Authors: Luo Y , Liao Z , Jiang W , Gomez D , Williamson R , Court L , Yang J
Published: July 2016

Purpose:

To evaluate the feasibility of using an automatic segmentation tool to delineate cardiac substructures from computed tomography (CT) images for cardiac toxicity analysis for non‐small cell lung cancer (NSCLC) patients after radiotherapy.

Methods:

A multi‐atlas segmentation tool developed in‐house was used to delineate eleven cardiac substructures including the whole heart, four heart chambers, and six greater vessels automatically from the averaged 4DCT planning images for 49 NSCLC patients. The automatic segmented contours were edited appropriately by two experienced radiation oncologists. The modified contours were compared with the auto‐segmented contours using Dice similarity coefficient (DSC) and mean surface distance (MSD) to evaluate how much modification was needed. In addition, the dose volume histogram (DVH) of the modified contours were compared with that of the auto‐segmented contours to evaluate the dosimetric difference between modified and auto‐segmented contours.

Results:

Of the eleven structures, the averaged DSC values ranged from 0.73 ± 0.08 to 0.95 ± 0.04 and the averaged MSD values ranged from 1.3 ± 0.6 mm to 2.9 ± 5.1mm for the 49 patients. Overall, the modification is small. The pulmonary vein (PV) and the inferior vena cava required the most modifications. The V30 (volume receiving 30 Gy or above) for the whole heart and the mean dose to the whole heart and four heart chambers did not show statistically significant difference between modified and auto‐segmented contours. The maximum dose to the greater vessels did not show statistically significant difference except for the PV.

Conclusion:

The automatic segmentation of the cardiac substructures did not require substantial modification. The dosimetric evaluation showed no statistically significant difference between auto‐segmented and modified contours except for the PV, which suggests that auto‐segmented contours for the cardiac dose response study are feasible in the clinical practice with a minor modification to the PV vessel.
TU‐H‐CAMPUS‐TeP2‐02: FLASH Irradiation Improves the Therapeutic Index Following GI Tract Irradiation
Authors: Schueler E , Trovati S , King G , Lartey F , Rafat M , Loo B , Maxim P
Published: July 2016

Purpose:

To investigate and characterize the radiobiological effectiveness of very high dose rate radiotherapy (FLASH) compared to conventional irradiation in an in vivo model.

Methods:

The gastrointestinal (GI) tract of C57BL/6 mice were irradiated with doses ranging between 10 and 18 Gy using a custom stereotactic jig. A Varian Clinac 21EX was modified to allow dose rates ranging from 0.05 to 240 Gy/s at the position of the mirror. With the gantry at 180 degrees, the jig holding the individual animals was placed above the mirror to take advantage of the reduced source to target distance. Mice were irradiated with 20MeV electrons. Following irradiation, the mice were monitored twice daily for morbidity and daily for weight changes.

Results:

Mice irradiated with FLASH irradiation had lower weight loss compared to the mice receiving conventional irradiation. Following FLASH irradiation, a maximum weight loss of ∼20% was observed at day 6 with subsequent recovery, while following conventional irradiation, higher weight losses was observed with fewer instances of recovery. Concerning survival, all mice in the conventionally irradiated groups had a 100% mortality in the range of 15.5–18 Gy, while the mice irradiated with FLASH irradiation had a 100% survival in the same range.

Conclusion:

These results have demonstrated proof of principle that FLASH irradiations have a dramatic impact on the overall survival of mice following GI tract irradiations. If the increase in the therapeutic window can be validated and understood, this would revolutionize the field of radiation oncology and lead to increased cure rates with reduced side effects following treatment, resulting in increased quality of life for cancer survivors.

Funding: DoD, Award#:W81XWH‐14‐1‐0014, Weston Havens Foundation, Bio‐X (Stanford University), the Office of the Dean of the Medical School, the Office of the Provost (Stanford University), and the Swedish Childhood Cancer Foundation; BL and PM are founders of TibaRay,Inc.; BL and PM have received research grants from Varian and RaySearch Laboratory.
TU‐H‐CAMPUS‐IeP3‐02: Neurovascular 4D Parametric Imaging Using Co‐Registration of Biplane DSA Sequences with 3D Vascular Geometry Obtained From Cone Beam CT
Authors: Balasubramoniam A , Bednarek D , Rudin S , Ionita C
Published: July 2016

Purpose:

To create 4D parametric images using biplane Digital Subtraction Angiography (DSA) sequences co‐registered with the 3D vascular geometry obtained from Cone Beam‐CT (CBCT).

Methods:

We investigated a method to derive multiple 4D Parametric Imaging (PI) maps using only one CBCT acquisition. During this procedure a 3D‐DSA geometry is stored and used subsequently for all 4D images. Each time a biplane DSA is acquired, we calculate 2D parametric maps of Bolus Arrival Time (BAT), Mean Transit Time (MTT) and Time to Peak (TTP). Arterial segments which are nearly parallel with one of the biplane imaging planes in the 2D parametric maps are co‐registered with the 3D geometry. The values in the remaining vascular network are found using spline interpolation since the points chosen for co‐registration on the vasculature are discrete and remaining regions need to be interpolated. To evaluate the method we used a patient CT volume data set for 3D printing a neurovascular phantom containing a complete Circle of Willis. We connected the phantom to a flow loop with a peristaltic pump, simulating physiological flow conditions. Contrast media was injected with an automatic injector at 10 ml/sec. Images were acquired with a Toshiba Infinix C‐arm and 4D parametric image maps of the vasculature were calculated.

Results:

4D BAT, MTT, and TTP parametric image maps of the Circle of Willis were derived. We generated color‐coded 3D geometries which avoided artifacts due to vessel overlap or foreshortening in the projection direction.

Conclusion:

The software was tested successfully and multiple 4D parametric images were obtained from biplane DSA sequences without the need to acquire additional 3D‐DSA runs. This can benefit the patient by reducing the contrast media and the radiation dose normally associated with these procedures.

Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.
TU‐H‐CAMPUS‐IeP3‐04: Evaluation of Changes in Quantitative Ultrasound Parameters During Prostate Radiotherapy
Authors: Najafi M , El Kaffas A , Han B , Cooper D , Hancock S , Hristov D
Published: July 2016

Purpose:

Clarity Autoscan ultrasound monitoring system allows acquisition of raw radiofrequency (RF) ultrasound data prior and during radiotherapy. This enables the computation of 3D Quantitative Ultrasound (QUS) tissue parametric maps from. We aim to evaluate whether QUS parameters undergo changes with radiotherapy and thus potentially be used as early predictors and/or markers of treatment response in prostate cancer patients.

Methods:

In‐vivo evaluation was performed under IRB protocol to allow data collection in prostate patients treated with VMAT whereby prostate was imaged through the acoustic window of the perineum. QUS spectroscopy analysis was carried out by computing a tissue power spectrum normalized to the power spectrum obtained from a quartz to remove system transfer function effects. A ROI was selected within the 3D image volume of the prostate. Because longitudinal registration was optimal, the same features could be used to select ROIs at roughly the same location in images acquired on different days. Parametric maps were generated within the rectangular ROIs with window sizes that were approximately 8 times the wavelength of the ultrasound. The mid‐band fit (MBF), spectral slope (SS) and spectral intercept (SI) QUS parameters were computed for each window within the ROI and displayed as parametric maps. Quantitative parameters were obtained by averaging each of the spectral parameters over the whole ROI.

Results:

Data was acquired for over 21 treatment fractions. Preliminary results show changes in the parametric maps. MBF values decreased from −33.9 dB to −38.7 dB from pre‐treatment to the last day of treatment. The spectral slope increased from −1.1 a.u. to −0.5 a.u., and spectral intercept decreased from −28.2 dB to −36.3 dB over the 21 treatment regimen.

Conclusion:

QUS parametric maps change over the course of treatment which warrants further investigation in their potential use for treatment planning and predicting treatment outcomes.

Research was supported by Elekta.
TU‐H‐CAMPUS‐IeP3‐05: Computer Aided Diagnosis Employing Automatically Segmented Color‐Specific Regions in Ultrasound Shear Wave Elastography for the Assessment of Chronic Liver Disease
Authors: Gatos I. , Tsantis S. , Kagadis G.C.
Published: July 2016

Purpose:

To assess the role of an automated Computer Aided Diagnosis (CAD) system in differentiation of Healthy Subjects to Chronic Liver Disease (CLD) Patients in terms of liver fibrosis (F0‐F4), using Ultrasound Shear Wave Elastography (SWE).

Methods:

Clinical Dataset consisted of 125 subjects, 55 Healthy (F0) whom condition was validated with Normal Biochemical Markers and clear Clinical History, and 70 with CLD (F1‐F4) whom condition was validated with Liver Biopsy. For each subject an SWE examination on their liver right lobe was performed using Supersonic Imagine's Aixplorer ultrasound system, and an SC6‐1 transducer. The examination was performed using preset default settings for Abdomen/Liver, and according to literature's suggested guidelines. An SWE image was then acquired, and a separation of the colored areas from the grayscale ones was performed. An RGB‐to‐Stiffness algorithm was consequently applied on the resulting image (Stiffness Box), using the nbuilt‐in colormap, to replace RGB values to Stiffness values. A segmentation procedure was employed using thresholds that segment the image to 5 stiffness range clusters (0–6, 6–12, 12–18, 18–24, and 24–30 kPa), and extract 7 features from each cluster (Mean, Median, Standard Deviation, Sample Kurtosis, 10th Percentile, 90th Percentile, and Cluster's Pixel Percentage on the Stiffness Box) deriving 35 features for each SWE image. The computed feature set was then fed to a designed SVM classifier. SVM‐model evaluation was performed by means of exhaustive search, and leave‐one‐out methods.

Results:

Maximum classification accuracy (85.6%) in distinguishing Healthy from chronic liver disease patients was obtained employing three features (Blue mean and Cyan median values, and Red maximum pixel number) with sensitivity and specificity values of 91.9% and 79.3% respectively.

Conclusion:

The proposed CAD system accurately differentiates Healthy to CLD patients assisting in evaluating important factors for performing SWE examination, enriching its guidelines, and aiding clinicians in a more accurate diagnosis.
TU‐H‐CAMPUS‐JeP3‐04: Factors Predicting a Need for Treatment Replanning with Proton Radiotherapy for Lung Cancer
Authors: Teng C , Janssens G , Ainsley C , Teo B , Valdes G , Burgdorf B , Berman A , Levin W , Xiao Y , Lin L , Gabriel P , Simone C , Solberg T
Published: July 2016

Purpose:

Proton dose distribution is sensitive to tumor regression and tissue and normal anatomy changes. Replanning is sometimes necessary during treatment to ensure continue tumor coverage or avoid overtreatment of organs at risk (OARs). We investigated action thresholds for replanning and identified both dosimetric and non‐dosimetric metrics that would predict a need for replan.

Methods:

All consecutive lung cancer patients (n = 188) who received definitive proton radiotherapy and had more than two evaluation CT scans at the Roberts Proton Therapy Center (Philadelphia, USA) from 2011 to 2015 were included in this study. The cohort included a variety of tumor sizes, locations, histology, beam angles, as well as radiation‐induced tumor and lung change. Dosimetric changes during therapy were characterized by changes in the dose volume distribution of PTV, ITV, and OARs (heart, cord, esophagus, brachial plexus and lungs). Tumor and lung change were characterized by changes in sizes, and in the distribution of Hounsfield numbers and water equivalent thickness (WET) along the beam path. We applied machine learning tools to identify both dosimetric and non‐dosimetric metrics that predicted a replan.

Results:

Preliminary data showed that clinical indicators (n = 54) were highly correlated; thus, a simple indicator may be derived to guide the action threshold for replanning. Additionally, tumor regression alone could not predict dosimetric changes in OARs; it required further information about beam angles and tumor locations.

Conclusion:

Both dosimetric and non‐dosimetric factors are predictive of the need for replanning during proton treatment.
TU‐H‐CAMPUS‐TeP3‐05: Evaluation of the Microscopic Dose Enhancement in the Nanoparticle‐Enhanced Auger Therapy
Authors: Sung W , Jung S , Ye S
Published: July 2016

Purpose:

The aim of this study is to apply Monte Carlo simulations to investigate the nanoparticle dose enhancement for Auger therapy.

Methods:

Two nanoparticle fabrications were considered: nanoshell and nanosphere. In the first step, a single nanoparticle was irradiated with Auger emitters. The electrons were scored in a phase space at the outer surface of the nanoparticle with Geant4‐Penelope. In the second step, the previously recorded phase space was used as a source and placed at the center of a cell‐size water phantom. The nanoscale dose was evaluated in water around the nanoparticle with Geant4‐DNA. The dose enhancement factor (DEF) is defined as the ratio of doses with and without nanoparticles. The nanoparticles were replaced by corresponding water nanoparticle with the same size and volume source which represents typical situation of Auger emitters without nanoparticle. Various sizes/materials of nanoparticles and isotopes were considered.

Results:

Nanoshell ‐ Microscopic dose was increased up to 130% at 20 – 100 nm distances from the surface of Au‐125I nanoshell. However, dose at less than 20 nm distance was reduced due to absorbed low energy electrons in gold nanoshell. The amounts and regions of the dose enhancement were dependent on nanoshell size, materials, and isotopes. Nanosphere ‐ The increased amounts of electrons up to 300% and reduced average energy with nanosphere were observed compared with water nanoparticle. We observed localized dose enhancement (up to a factor 3.6) in the immediate vicinity (< 50 nm) of Au‐125 I nanosphere. The dose enhancement patterns vary according to nanosphere sizes and isotopes.

Conclusion:

We conclude that Auger therapy with nanoparticles can lead to change of electron energy spectrum and dose enhancements at certain range. The dose enhancement patterns vary according to nanoparticle sizes, materials, and isotopes.

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP: Ministry of Science, ICT and Future Planning) (No. NRF‐2013M2B2B1075776)
WE‐AB‐204‐01: Welcome
Authors: Curran B.
Published: July 2016

Many efforts have been made to increase diversity in the science workforce. In order for us to be competitive in innovation and ingenuity we need to reach out to any source of intellectual talent. Having greater diversity can only increase the creativity in medical physics. In order for students to succeed academically they need role models and mentors with whom they can identify. Literature has shown that racial and ethnic diversity has both direct and indirect positive effects on the educational outcomes, career advancement and motivation of students. Diversity not only focuses on race, ethnicity and gender, but it can also include socioeconomic status, sexual orientation and more. Underrepresented populations have had low numbers over the years not only in medical physics but also in the sciences in general. With the rapidly changing face of our country we need to address how we attract and train the next generation of scientists to stay competitive. It is necessary to examine the role that diversity and inclusion play in the long term goals of institutions, workplaces and classrooms. To increase innovation we must engage people from all walks of life with different perspectives and life experiences to solve the problems that we will face. Diversity should be viewed as a strategy to achieve our goals instead of acts of good citizenship. Many of today's businesses and corporations have discovered that embracing diversity prepares future leaders in today's global market.

This lecture will provide insight to how differences within our society can drive innovation. We will provide an overview of the role diversity and inclusion plays in the clinic, education and research to develop the future workforce in medical physics.

Learning Objectives:

Understanding the role diversity and inclusion plays in medical physics.

The importance of developing education and research strategies for a global workforce.

How to develop a roadmap to diversity excellence within AAPM.