bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐FG‐303‐08: PET‐Detectable Bimetallic (Zn@Au) Nanoparticles for Radiotherapy and Molecular Imaging Applications
Authors: Cho J , Wang M , Gonzalez‐Lepera C , Zubarev E , Cho S
Published: June 2015

Purpose:

A technical challenge in clinical translation of GNP‐mediated radiotherapy is lack of in‐vivo imaging tools for monitoring biodistribution of GNPs. While several modalities (x‐ray fluorescence, photoacoustic, etc.) are investigated, we propose a potentially more effective technique based on PET imaging. We developed Zn@Au NPs whose Zn core acts as positron emitters when activated by protons, while the Au shell plays the original role for GNP‐mediated radiosensitization.

Methods:

Spherical Zn NPs (∼7nm diameter) were synthesized and then coated with ∼7nm thick Au layer to make Zn@Au NPs (∼20nm diameter). A water slurry containing 29mg of Zn@Au NPs was deposited (<10µm thickness) on a thin cellulose target and subsequently baked to remove the water. The cellulose matrix was placed in an aluminum target holder and irradiated with 14.5MeV protons from a GE PETtrace cyclotron with 4µA for 5min. After irradiation the cellulose matrix with the NPs was placed in a dose calibrator to assay radioactivity. Gamma spectroscopy using a HPGe detector was conducted on a very small fraction (<1mg) of the irradiated NPs.

Results:

We measured 158µCi of activity 32min after end of bombardment (EOB) using 66Ga setting on the dose calibrator (contribution from the cellulose matrix is negligible) which decreased to 2µCi over a 24hrs period. A gamma spectrum started one hour after EOB on the small fraction and acquired for 700sec showed a strong peak at 511keV (∼40,000 counts) with several other peaks (highest peak <1200 counts) of smaller magnitude.

Conclusion:

Strong 511keV gamma emission from proton‐activated Zn cores can potentially be utilized to image the biodistribution of Zn@Au NPs using a PET scanner. The developed Zn@Au NPs are expected to retain radiosensitizing capability similar to solid GNPs, while observable through PET imaging for human‐sized objects. Moreover, bioconjugated PET‐detectable GNPs would allow a new option to perform molecular imaging.
MO‐FG‐204‐06: A New Algorithm for Gold Nano‐Particle Concentration Identification in Dual Energy CT
Authors: Chen L , Shen C , Ng M , Zeng T , Lou Y , Jia X
Published: June 2015

Purpose:

Gold nano‐particle (GNP) has recently attracted a lot of attentions due to its potential as an imaging contrast agent and radiotherapy sensitiser. Imaging the GNP at its low contraction is a challenging problem. We propose a new algorithm to improve the identification of GNP based on dual energy CT (DECT).

Methods:

We consider three base materials: water, bone, and gold. Determining three density images from two images in DECT is an under‐determined problem. We propose to solve this problem by exploring image domain sparsity via an optimization approach. The objective function contains four terms. A data‐fidelity term ensures the fidelity between the identified material densities and the DECT images, while the other three terms enforces the sparsity in the gradient domain of the three images corresponding to the density of the base materials by using total variation (TV) regularization. A primal‐dual algorithm is applied to solve the proposed optimization problem. We have performed simulation studies to test this model.

Results:

Our digital phantom in the tests contains water, bone regions and gold inserts of different sizes and densities. The gold inserts contain mixed material consisting of water with 1g/cm3 and gold at a certain density. At a low gold density of 0.0008 g/cm3, the insert is hardly visible in DECT images, especially for those with small sizes. Our algorithm is able to decompose the DECT into three density images. Those gold inserts at a low density can be clearly visualized in the density image.

Conclusion:

We have developed a new algorithm to decompose DECT images into three different material density images, in particular, to retrieve density of gold. Numerical studies showed promising results.
MO‐FG‐207‐01: Technological Advances and Challenges: Experience with the First Integrated Whole‐Body PET/MRI
Authors: Laforest R.
Published: June 2015

The use of integrated PET/MRI systems in clinical applications can best benefit from understanding their technological advances and limitations. The currently available clinical PET/MRI systems have their own characteristics. Thorough analyses of existing technical data and evaluation of necessary performance metrics for quality assurances could be conducted to optimize application‐specific PET/MRI protocols. This Symposium will focus on technical advances and limitations of clinical PET/MRI systems, and how this exciting imaging modality can be utilized in applications that can benefit from both PET and MRI.

Learning Objectives:

To understand the technological advances of clinical PET/MRI systems

To correctly identify clinical applications that can benefit from PET/MRI

To understand ongoing work to further improve the current PET/MRI technology

Floris Jansen is a GE Healthcare employee.
MO‐FG‐201‐02: High‐Impact Presentations
Authors: Weiker T.
Published: June 2015

Oral presentations are one of the most important tools to advance education, scientific research, and clinical excellence in medical physics. Medical physicists do not often captivate their audiences like a Steve Jobs keynote or a TED talk, but every physicist can learn to engage their audiences and deliver their message in a memorable way using their own personality and style. This interactive session will teach attendees to discover their own style and voice and to use it to engage and connect with their audiences. Audience reception and response will be reviewed in terms of the speaker's executive presence and content, as well as research on the psychology of audiences and physiology of speakers. Physicists will learn how to organize and mentally prepare themselves as well as their PowerPoint slides.

Learning Objectives:

Develop executive presence: poised under pressure to deliver a message in a relaxed, casual, and credible way

Connect with an audience by creating harmony between the content and the visual and audible elements of a presentation

Confidently deliver engaging presentations in the individual's voice and personality

Heidi Weiker and Tanya Weiker are co‐owners of Spherica LLC.
MO‐FG‐210‐03: Intraoperative Ultrasonography‐Guided Positioning of Plaque Brachytherapy in the Treatment of Choroidal Melanoma
Authors: Lamb J.
Published: June 2015

Ultrasound (US) is one of the most widely used imaging modalities in medical practice. Since US imaging offers real‐time imaging capability, it has becomes an excellent option to provide image guidance for brachytherapy (IGBT). (1) The physics and the fundamental principles of US imaging are presented, and the typical steps required to commission an US system for IGBT is provided for illustration. (2) Application of US for prostate HDR brachytherapy, including partial prostate treatments using MR‐ultrasound co‐registration to enable a focused treatment on the disease within the prostate is also presented. Prostate HDR with US image guidance planning can benefit from real time visualization of the needles, and fusion of the ultrasound images with T2 weighted MR allows the focusing of the treatment to the specific areas of disease within the prostate, so that the entire gland need not be treated. Finally, (3) ultrasound guidance for an eye plaque program is presented. US can be a key component of placement and QA for episcleral plaque brachytherapy for ocular cancer, and the UCLA eye plaque program with US for image guidance is presented to demonstrate the utility of US verification of plaque placement in improving the methods and QA in episcleral plaque brachytherapy.

Learning Objectives:

To understand the physics of an US system and the necessary aspects of commissioning US for image guided brachytherapy (IGBT).

To understand real time planning of prostate HDR using ultrasound, and its application in partial prostate treatments using MR‐ultrasound fusion to focus treatment on disease within the prostate.

To understand the methods and QA in applying US for localizing the target and the implant during a episcleral plaque brachytherapy procedures.
MO‐F‐CAMPUS‐T‐02: An Electronic Whiteboard Platform to Manage Treatment Planning Process
Authors: DiCostanzo D , Thompson S , Woollard J , Gupta N , Ayan A
Published: June 2015

Purpose:

In an effort to improve patient safety and streamline the radiotherapy treatment planning (TP) process, a software based whiteboard had been developed and put in use in our facility

Methods:

The electronic whiteboard developed using SQL database (DB) and PHP/JavaScript based web interface, is published via department intranet and login credentials. The DB stores data for each TP process such as patient information, plan type, simulation/start dates, physician, dosimetrist, QA and the current status in planning process. Users interact with the DB per plan and perform status updates in real time as the planning process progresses. All user interactions with the DB are recorded with timestamps so as to calculate statistical information for TP process management such as contouring times, planning and review times, dosimetry, physics and therapist QA times. External beam and brachytherapy plans are categorized according to complexity (ex: IMRT, 3D, HDR, LDR etc) and treatment types and applicators. Each plan category is assigned specific timelines for each planning process. When a plan approaches or passes the predetermined timeline, users are alerted via color coded graphical cues. When certain process items are not completed in time, pre‐determined actions are triggered such as a delay in treatment start date.

Results:

Our institution has been using the electronic whiteboard for two years. Implementation of pre‐determined actions based on the statistical information collected by the whiteboard improved our TP process. For example, the average time for normal tissue contouring decreased from 0.73±1.37 to 0.24±0.33 days. The average time for target volume contouring decreased from 3.2±2.84 to 2.37±2.54 days. This increase in efficiency allows more time for quality assurance processes, improving patient safety.

Conclusion:

The electronic whiteboard has been an invaluable tool for streamlining our TP processes. It facilitates timely and accurate communication between all parties involved in the TP process increasing patient safety.
MO‐F‐CAMPUS‐T‐01: Radiosurgery of Multiple Brain Metastases with Single‐Isocenter VMAT: Optimizing Treatment Geometry to Reduce Normal Brain Dose
Authors: Wu Q , Snyder K , Liu C , Huang Y , Li H , Chetty I , Wen N
Published: June 2015

Purpose:

To develop an optimization algorithm to reduce normal brain dose by optimizing couch and collimator angles for single isocenter multiple targets treatment of stereotactic radiosurgery.

Methods:

Three metastatic brain lesions were retrospectively planned using single‐isocenter volumetric modulated arc therapy (VMAT). Three matrices were developed to calculate the projection of each lesion on Beam's Eye View (BEV) by the rotating couch, collimator and gantry respectively. The island blocking problem was addressed by computing the total area of open space between any two lesions with shared MLC leaf pairs. The couch and collimator angles resulting in the smallest open areas were the optimized angles for each treatment arc. Two treatment plans with and without couch and collimator angle optimization were developed using the same objective functions and to achieve 99% of each target volume receiving full prescription dose of 18Gy. Plan quality was evaluated by calculating each target's Conformity Index (CI), Gradient Index (GI), and Homogeneity index (HI), and absolute volume of normal brain V8Gy, V10Gy, V12Gy, and V14Gy.

Results:

Using the new couch/collimator optimization strategy, dose to normal brain tissue was reduced substantially. V8, V10, V12, and V14 decreased by 2.3%, 3.6%, 3.5%, and 6%, respectively. There were no significant differences in the conformity index, gradient index, and homogeneity index between two treatment plans with and without the new optimization algorithm.

Conclusion:

We have developed a solution to the island blocking problem in delivering radiation to multiple brain metastases with shared isocenter. Significant reduction in dose to normal brain was achieved by using optimal couch and collimator angles that minimize total area of open space between any of the two lesions with shared MLC leaf pairs. This technique has been integrated into Eclipse treatment system using scripting API.
MO‐F‐CAMPUS‐J‐05: Using 2D Relative Gamma Analysis From EPID Image as a Predictor of Plan Deterioration Due to Anatomical Changes
Authors: Piron O , Varfalvy N , Archambault L
Published: June 2015

Purpose:

One of the side effects of radiotherapy for head and neck (H&N) cancer is the patient's anatomical changes. The changes can strongly affect the planned dose distribution. In this work, our goal is to demonstrate that relative analysis of EPID images is a fast and simple method to detect anatomical changes that can have a strong dosimetric impact on the treatment plan for H&N patients.

Methods:

EPID images were recorded at every beam and all fractions for 50 H&N patients. Of these, five patients that showed important anatomical changes were selected to evaluate dosimetric impacts of these changes and to correlate them with a 2D relative gamma analysis of EPID images. The planning CT and original contours were deformed onto CBCTs (one mid treatment and one at the end of treatment). By using deformable image registration, it was possible to map accurate CT numbers from the planning CT to the anatomy of the day obtained with CBCTs. Clinical treatment plan were then copied on the deformed dataset and dose was re‐computed. In parallel, EPID images were analysed using the gamma index (3%3mm) relative to the first image.

Results:

It was possible to divide patients in two distinct, statistically different (p<0.001) categories using an average gamma index of 0.5 as a threshold. Below this threshold no significant dosimetric degradation of the plan are observed. Above this threshold two types of plan deterioration were seen: (1) target dose increases, but coverage remains adequate while dose to at least one OAR increases beyond tolerances; (2) the OAR doses remain low, but the target dose is reduced and coverage becomes inadequate.

Conclusion:

Relative analysis gamma of EPID images could indeed be a fast and simple method to detect anatomical changes that can potentially deteriorates treatment plan for H&N patients.

This work was supported in part by Varian Medical System
MO‐F‐CAMPUS‐I‐03: CT and MR Characteristics of Some Specialty 3D Printing Filaments
Authors: Lam K
Published: June 2015

Purpose:

To quantify the Hounsfield Unit and demonstrate MR signal of specialty 3D printer filaments that are recently made available to fused deposition modeling (FDM) 3D printers as raw materials to print 3D objects such as phantoms and patient specific boluses or shields.

Methods:

We acquired 2.85mm diameter batches of ColorFabb copperfill metal filament, Soft PLA filaments of different colors (Red, Blue, White, Beige, Black), BendLay filament, Taulman Bridge filament, NinjaFlex water semi‐transparent thermoplastic elastomer filament, Light Cherry Wood LAYWOO‐D3 filament, as well as the more commonly used polylactic acid (PLA) filament and acrylonitrile butadiene styrene (ABS) filament. We also included 2.5mm diameter silicone, polyurethane, neoprene, and nitrile rubber (soft Buna‐N) o‐ring cords for comparison. These filaments were arranged in a 4×4 array in a 5cm × 15cm × 15cm block of UHMW polyethylene. CT scan of 1mm slice thickness was performed with a cranial SRS protocol. MR scan was performed with an ultra‐short echo time point‐wise encoding time reduction with radial acquisition (UTE PETRA) protocol in a water bath. The CT and MR of these different materials were imported into Eclipse. In order to reduce the contribution of partial volume effect, the maximum HU of each material were determined in 4 slices and averaged.

Results:

The copperfill filament HU was saturated at 2975. Soft PLA filaments had HU in the range of 400–500. PLA and NinjaFlex were 100–200 HU. Taulman Bridge filament was about 63 HU. LAYWOO‐ D3, ABS, and BendLay filaments were between −60 to −30 HU. Overall, the HU of these specialty filaments spanned the range from −60 to >3000. The materials were also visible in the UTE MR image.

Conclusion:

The wide range of materials available to FDM 3D printing made possible the fabrication of various objects for medical physics to emulate different tissues.
MO‐F‐CAMPUS‐T‐01: IROC Houston QA Center's Anthropomorphic Proton Phantom Program
Authors: Lujano C , Hernandez N , Keith T , Nguyen T , Taylor P , Molineu A , Followill D
Published: June 2015

Purpose:

To describe the proton phantoms that IROC Houston uses to approve and credential proton institutions to participate in NCI‐sponsored clinical trials.

Methods:

Photon phantoms cannot necessarily be used for proton measurements because protons react differently than photons in some plastics. As such plastics that are tissue equivalent for protons were identified. Another required alteration is to ensure that the film dosimeters are housed in the phantom with no air gap to avoid proton streaming. Proton‐equivalent plastics/materials used include RMI Solid Water, Techron HPV, blue water, RANDO soft tissue material, balsa wood, compressed cork and polyethylene. Institutions wishing to be approved or credentialed request a phantom and are prioritized for delivery. At the institution, the phantom is imaged, a treatment plan is developed, positioned on the treatment couch and the treatment is delivered. The phantom is returned and the measured dose distributions are compared to the institution's electronically submitted treatment plan dosimetry data.

Results:

IROC Houston has developed an extensive proton phantom approval/credentialing program consisting of five different phantoms designs: head, prostate, lung, liver and spine. The phantoms are made with proton equivalent plastics that have HU and relative stopping powers similar (within 5%) of human tissues. They also have imageable targets, avoidance structures, and heterogeneities. TLD and radiochromic film are contained in the target structures. There have been 13 head, 33 prostate, 18 lung, 2 liver and 16 spine irradiations with either passive scatter, or scanned proton beams. The pass rates have been: 100%, 69.7%, 72.2%, 50%, and 81.3%, respectively.

Conclusion:

IROC Houston has responded to the recent surge in proton facilities by developing a family of anthropomorphic phantoms that are able to be used for remote audits of proton beams.

Work supported by PHS grant CA10953 and CA081647
MO‐F‐CAMPUS‐T‐02: Dosimetric Accuracy of the CrystalBallâ„¢: New Reusable Radiochromic Polymer Gel Dosimeter for Patient QA in Proton Therapy
Authors: Avery S , Kraus J , Lin L , Kassaee A , Maryanski M
Published: June 2015

Purpose:

To evaluate the accuracy of monoexponential normalization in a new class of commercial, reusable, human‐soft‐tissue‐equivalent, radiochromic polymer gel dosimeters for patient‐specific QA in proton therapy.

Methods:

Eight formulations of the dosimeter (sealed in glass spheres of 166 mm OD), were exposed to a 150 MeV proton beam (5 cm × 5 cm square field, range 15 cm, modulation10 cm), with max dose ranging from 2.5 Gy to 20 Gy, depending on formulation. Exposed dosimeters were promptly placed in the commercial OCTOPUS™ laser CT scanner which was programmed to scan the central slice every 5 minutes for 20 hours (15 seconds per slice scan). This procedure was repeated several times. Reconstructed data were analyzed using the log‐lin scale to determine the time range over which a monoexponential relaxation model could be applied. Next, a simple test plan was devised and delivered to each dosimeter. The OCTOPUS™ was programmed to rescan the central slice at the end of each volume scan, for signal relaxation reference. Monoexponential normalization was applied to sinograms before FBP reconstruction. Dose calibration was based on a volume‐lookup table built within the central spherical volume of 12 cm diameter. 3D gamma and sigma passing rates were measured at 3%/3mm criteria down to 50% isodose.

Results:

Approximately monoexponential signal relaxation time ranges from 25 minutes to 3.5 hours, depending on formulation, followed by a slower‐relaxation component. Noise in reconstructed OD/cm images is less than 0.5%. Dose calibration accuracy is better than 99%. Measured proton PDDs demonstrate absence of Bragg‐peak quenching. Estimated number of useful cycles is at least 20, with a theoretical limit above 100. 3D gamma and sigma passing rates exceed 95%.

Conclusion:

Monoexponential normalization was found to yield adequate dosimetric accuracy in the new class of commercial radiochromic polymer gel dosimeters for patient QA in proton therapy.
MO‐F‐CAMPUS‐T‐04: Utilization of Optical Dosimeter for Modulated Spot‐Scanning Particle Beam
Authors: Hsi W , Li Y , Huang Z , Sheng Y , Deng Y , Zhao J , Zhao F , Sun L , Moyers M
Published: June 2015

Purpose:

To present the utilization of an optical dosimeter for modulated spot‐scanning carbon‐ion and proton beams during the acceptance test of Siemens IONTRIS system.

Method and Materials:

An optical dosimeter using phosphor scintillation was developed to map and interactively analyze the shapes and sizes of spots over 190 energies for ProTom modulated‐scanning system. The dose response to proton had been characterized with proper pixel calibration at ProTom system. The dose response was further studied at 0.7 cm depths by uniform 8cm in‐diameter fields of 424.89 MeV/u (E290) carbon‐ions and 215.18MeV (E282) protons at IONTRIS system. The virtual source axial distances (vSAD) of carbonions and protons of IONTRIS system was investigated by measuring either variations of spot position or field size at five different locations to Isocenter. By measuring lateral profiles of uniform doses with varied thin‐thicknesses of chest‐board pattern and placing the scintillation plate at near to the distal edge, range variations at different off‐axis‐distances (rOAD) were examined. Relative accuracy and reproducibility of beam range were measured for three beam ranges with a ramping block at front of scintillation plate.

Results:

Similar dose response was observed for high energies of carbon ions and protons. Mean vSAD at X and Y axes were 744.1 cm and 807.4cm with deviation of 7.4cm and 7.7cm, respectively. Variation of rOAD was within 0.35 mm over 10cm for both protons and carbon ions. Accuracy of measuring relative distal range using the ramping block was 0.2mm. Measured range over repeated three times for each range were within 0.25mm at same room, and within 1.0mm between four rooms.

Conclusions:

The optical dosimeter could efficiently measure the virtual source distance. And, to measure small range variation at different off‐axial locations, and for the relative beam range between rooms during acceptance test of a modulated spot‐scanning particle system.
TU‐A‐304‐02: Treatment Simulation, Planning and Delivery for SBRT
Authors: Yang Y.
Published: June 2015

Increased use of SBRT and hypo fractionation in radiation oncology practice has posted a number of challenges to medical physicist, ranging from planning, image‐guided patient setup and on‐treatment monitoring, to quality assurance (QA) and dose delivery. This symposium is designed to provide updated knowledge necessary for the safe and efficient implementation of SBRT in various linac platforms, including the emerging digital linacs equipped with high dose rate FFF beams. Issues related to 4D CT, PET and MRI simulations, 3D/4D CBCT guided patient setup, real‐time image guidance during SBRT dose delivery using gated/un‐gated VMAT or IMRT, and technical advancements in QA of SBRT (in particular, strategies dealing with high dose rate FFF beams) will be addressed. The symposium will help the attendees to gain a comprehensive understanding of the SBRT workflow and facilitate their clinical implementation of the state‐of‐art imaging and planning techniques.

Learning Objectives:

Present background knowledge of SBRT, describe essential requirements for safe implementation of SBRT, and discuss issues specific to SBRT treatment planning and QA.

Update on the use of multi‐dimensional (3D and 4D) and multi‐modality (CT, beam‐level X‐ray imaging, pre‐ and on‐treatment 3D/4D MRI, PET, robotic ultrasound, etc.) for reliable guidance of SBRT.

Provide a comprehensive overview of emerging digital linacs and summarize the key geometric and dosimetric features of the new generation of linacs for substantially improved SBRT.

Discuss treatment planning and quality assurance issues specific to SBRT.

Research grant from Varian Medical Systems
TU‐AB‐BRD‐00: Task Group 100
Authors: Huq M. Saiful
Published: June 2015

Current quality assurance and quality management guidelines provided by various professional organizations are prescriptive in nature, focusing principally on performance characteristics of planning and delivery devices. However, published analyses of events in radiation therapy show that most events are often caused by flaws in clinical processes rather than by device failures. This suggests the need for the development of a quality management program that is based on integrated approaches to process and equipment quality assurance. Industrial engineers have developed various risk assessment tools that are used to identify and eliminate potential failures from a system or a process before a failure impacts a customer. These tools include, but are not limited to, process mapping, failure modes and effects analysis, fault tree analysis. Task Group 100 of the American Association of Physicists in Medicine has developed these tools and used them to formulate an example risk‐based quality management program for intensity‐modulated radiotherapy. This is a prospective risk assessment approach that analyzes potential error pathways inherent in a clinical process and then ranks them according to relative risk, typically before implementation, followed by the design of a new process or modification of the existing process. Appropriate controls are then put in place to ensure that failures are less likely to occur and, if they do, they will more likely be detected before they propagate through the process, compromising treatment outcome and causing harm to the patient. Such a prospective approach forms the basis of the work of Task Group 100 that has recently been approved by the AAPM. This session will be devoted to a discussion of these tools and practical examples of how these tools can be used in a given radiotherapy clinic to develop a risk based quality management program.

Learning Objectives:

Learn how to design a process map for a radiotherapy process

Learn how to perform failure modes and effects analysis analysis for a given process

Learn what fault trees are all about

Learn how to design a quality management program based upon the information obtained from process mapping, failure modes and effects analysis and fault tree analysis.

Dunscombe: Director, TreatSafely, LLC and Center for the Assessment of Radiological Sciences; Consultant to IAEA and Varian

Thomadsen: President, Center for the Assessment of Radiological Sciences

Palta: Vice President of the Center for the Assessment of Radiological Sciences
TU‐CD‐304‐03: Dosimetric Verification and Preliminary Comparison of Dynamic Wave Arc for SBRT Treatments
Authors: Burghelea M , Poels K , Gevaert T , Tournel K , Dhont J , Hung C , Eriksson K , Simon V , De Ridder M , Verellen D
Published: June 2015

Purpose:

To evaluate the potential dosimetric benefits and verify the delivery accuracy of Dynamic Wave Arc, a novel treatment delivery approach for the Vero SBRT system.

Methods:

Dynamic Wave Arc (DWA) combines simultaneous movement of gantry/ring with inverse planning optimization, resulting in an uninterrupted non‐coplanar arc delivery technique. Thirteen SBRT complex cases previously treated with 8–10 conformal static beams (CRT) were evaluated in this study. Eight primary centrally‐located NSCLC (prescription dose 4×12Gy or 8×7.5Gy) and five oligometastatic cases (2×2 lesions, 10×5Gy) were selected. DWA and coplanar VMAT plans, partially with dual arcs, were generated for each patient using identical objective functions for target volumes and OARs on the same TPS (RayStation, RaySearch Laboratories). Dosimetric differences and delivery time among these three planning schemes were evaluated. The DWA delivery accuracy was assessed using the Delta4 diode array phantom (ScandiDos AB). The gamma analysis was performed with the 3%/3mm dose and distance‐to‐agreement criteria.

Results:

The target conformity for CRT, VMAT and DWA were 0.95±0.07, 0.96±0.04 and 0.97±0.04, while the low dose spillage gradient were 5.52±1.36, 5.44±1.11, and 5.09±0.98 respectively. Overall, the bronchus, esophagus and spinal cord maximum doses were similar between VMAT and DWA, but highly reduced compared with CRT. For the lung cases, the mean dose and V20Gy were lower for the arc techniques compares with CRT, while for the liver cases, the mean dose and the V30Gy presented slightly higher values. The average delivery time of VMAT and DWA were 2.46±1.10 min and 4.25±1.67 min, VMAT presenting shorter treatment time in all cases. The DWA dosimetric verification presented an average gamma index passing rate of 95.73±1.54% (range 94.2%–99.8%).

Conclusion:

Our preliminary data indicated that the DWA is deliverable with clinically acceptable accuracy and has the potential to further improve the plan quality.

This collaborative work was supported by the Flemish government through the Hercules foundation and corporate funding from BrainLab AG. The first and the sixth author are financially supported by Brainlab AG. The other authors have no conflict of interest.
TU‐CD‐304‐06: Using FFF Beams Improves Tumor Control in Radiotherapy of Lung Cancers
Authors: Vassiliev O , Wang H
Published: June 2015

Purpose:

Electron disequilibrium at the lung‐tumor interface results in an under‐dosage of tumor regions close to its surface. This under‐dosage is known to be significant and can compromise tumor control. Previous studies have shown that in FFF beams, disequilibrium effects are less pronounced, which is manifested in an increased skin dose. In this study we investigate the improvement in tumor dose coverage that can be achieved with FFF beams. The significance of this improvement is evaluated by comparing tumor control probabilities of FFF beams and conventional flattened beams.

Methods:

The dosimetric coverage was investigated in a virtual phantom representing the chest wall, lung tissue and the tumor. A range of tumor sizes was investigated, and two tumor locations – central and adjacent to the chest wall. Calculations were performed with BEAMnrc Monte Carlo code. Parallel‐opposed and multiple coplanar 6‐MV beams were simulated. The tumor control probabilities were calculated using the logistic model with parameters derived from clinical data for non‐small lung cancer patients.

Results:

FFF beams were not entirely immune to disequilibrium effects. They nevertheless consistently delivered more uniform dose distribution throughout the volume of the tumor, and eliminated up to ∼15% of under‐dosage in the most affected by disequilibrium 1‐mm thick surface region of the tumor. A voxel‐by‐voxel comparison of tumor control probabilities between FFF and conventional flattened beams showed an advantage of FFF beams that, depending on the set up, was from a few to ∼9 percent.

Conclusion:

A modest improvement in tumor control probability on the order of a few percent can be achieved by replacing conventional flattened beams with FFF beams. However, given the large number of lung cancer patients undergoing radiotherapy, these few percent can potentially prevent local tumor recurrence for a significant number of patients.
TU‐CD‐BRB‐01: Normal Lung CT Texture Features Improve Predictive Models for Radiation Pneumonitis
Authors: Krafft S , Briere T , Court L , Martel M
Published: June 2015

Purpose:

Existing normal tissue complication probability (NTCP) models for radiation pneumonitis (RP) traditionally rely on dosimetric and clinical data but are limited in terms of performance and generalizability. Extraction of pre‐treatment image features provides a potential new category of data that can improve NTCP models for RP. We consider quantitative measures of total lung CT intensity and texture in a framework for prediction of RP.

Methods:

Available clinical and dosimetric data was collected for 198 NSCLC patients treated with definitive radiotherapy. Intensity‐ and texture‐based image features were extracted from the T50 phase of the 4D‐CT acquired for treatment planning. A total of 3888 features (15 clinical, 175 dosimetric, and 3698 image features) were gathered and considered candidate predictors for modeling of RP grade≥3. A baseline logistic regression model with mean lung dose (MLD) was first considered. Additionally, a least absolute shrinkage and selection operator (LASSO) logistic regression was applied to the set of clinical and dosimetric features, and subsequently to the full set of clinical, dosimetric, and image features. Model performance was assessed by comparing area under the curve (AUC).

Results:

A simple logistic fit of MLD was an inadequate model of the data (AUC∼0.5). Including clinical and dosimetric parameters within the framework of the LASSO resulted in improved performance (AUC=0.648). Analysis of the full cohort of clinical, dosimetric, and image features provided further and significant improvement in model performance (AUC=0.727).

Conclusions:

To achieve significant gains in predictive modeling of RP, new categories of data should be considered in addition to clinical and dosimetric features. We have successfully incorporated CT image features into a framework for modeling RP and have demonstrated improved predictive performance. Validation and further investigation of CT image features in the context of RP NTCP modeling is warranted.

This work was supported by the Rosalie B. Hite Fellowship in Cancer research awarded to SPK
TU‐CD‐BRB‐09: Prediction of Chemo‐Radiation Outcome for Rectal Cancer Based On Radiomics of Tumor Clinical Characteristics and Multi‐Parametric MRI
Authors: Nie K , Shi L , Hu X , Chen Q , Yue N , Sun X , Niu T
Published: June 2015

Purpose:

To evaluate the tumor clinical characteristics and quantitative multi‐parametric MR imaging features for prediction of response to chemo‐radiation treatment (CRT) in locally advanced rectal cancer (LARC).

Methods:

Forty‐three consecutive patients (59.7±6.9 years, from 09/2013 – 06/2014) receiving neoadjuvant CRT followed by surgery were enrolled. All underwent MRI including anatomical T1/T2, Dynamic Contrast Enhanced (DCE)‐MRI and Diffusion‐Weighted MRI (DWI) prior to the treatment. A total of 151 quantitative features, including morphology/Gray Level Co‐occurrence Matrix (GLCM) texture from T1/T2, enhancement kinetics and the voxelized distribution from DCE‐MRI, apparent diffusion coefficient (ADC) from DWI, along with clinical information (carcinoembryonic antigen CEA level, TNM staging etc.), were extracted for each patient. Response groups were separated based on down‐staging, good response and pathological complete response (pCR) status. Logistic regression analysis (LRA) was used to select the best predictors to classify different groups and the predictive performance were calculated using receiver operating characteristic (ROC) analysis.

Results:

Individual imaging category or clinical charateristics might yield certain level of power in assessing the response. However, the combined model outperformed than any category alone in prediction. With selected features as Volume, GLCM AutoCorrelation (T2), MaxEnhancementProbability (DCE‐MRI), and MeanADC (DWI), the down‐staging prediciton accuracy (area under the ROC curve, AUC) could be 0.95, better than individual tumor metrics with AUC from 0.53–0.85. While for the pCR prediction, the best set included CEA (clinical charateristics), Homogeneity (DCE‐MRI) and MeanADC (DWI) with an AUC of 0.89, more favorable compared to conventional tumor metrics with an AUC ranging from 0.511–0.79.

Conclusion:

Through a systematic analysis of multi‐parametric MR imaging features, we are able to build models with improved predictive value over conventional imaging or clinical metrics. This is encouraging, suggesting the wealth of imaging radiomics should be further explored to help tailor the treatment into the era of personalized medicine.

This work is supported by the National Science Foundation of China (NSFC Grant No. 81201091), National High Technology Research and Development Program of China (863 program, Grant No. 2015AA020917), and Fund Project for Excellent Abroad Scholar Personnel in Science and Technology.
TU‐CD‐BRB‐12: Radiogenomics of MRI‐Guided Prostate Cancer Biopsy Habitats
Authors: Stoyanova R , Tachar M , Erho N , Lynne C , Abraham S , Patel M , Buerki C , Lam L , Jorda M , Kryvenko O , Ishkanian A , Abramowitz M , Davicioni E , Pollack A
Published: June 2015

Purpose:

Diagnostic prostate biopsies are subject to sampling bias. We hypothesize that quantitative imaging with multiparametric (MP)‐MRI can more accurately direct targeted biopsies to index lesions associated with highest risk clinical and genomic features.

Methods:

Regionally distinct prostate habitats were delineated on MP‐MRI (T2‐weighted, perfusion and diffusion imaging). Directed biopsies were performed on 17 habitats from 6 patients using MRI‐ultrasound fusion. Biopsy location was characterized with 52 radiographic features. Transcriptome‐wide analysis of 1.4 million RNA probes was performed on RNA from each habitat. Genomics features with insignificant expression values (<0.25) and interquartile range <0.5 were filtered, leaving total of 212 genes. Correlation between imaging features, genes and a 22 feature genomic classifier (GC), developed as a prognostic assay for metastasis after radical prostatectomy was investigated.

Results:

High quality genomic data was derived from 17 (100%) biopsies. Using the 212 ‘unbiased’ genes, the samples clustered by patient origin in unsupervised analysis. When only prostate cancer related genomic features were used, hierarchical clustering revealed samples clustered by needle‐biopsy Gleason score (GS). Similarly, principal component analysis of the imaging features, found the primary source of variance segregated the samples into high (≥7) and low (6) GS. Pearson's correlation analysis of genes with significant expression showed two main patterns of gene expression clustering prostate peripheral and transitional zone MRI features. Two‐way hierarchical clustering of GC with radiomics features resulted in the expected groupings of high and low expressed genes in this metastasis signature.

Conclusions:

MP‐MRI‐targeted diagnostic biopsies can potentially improve risk stratification by directing pathological and genomic analysis to clinically significant index lesions. As determinant lesions are more reliably identified, targeting with radiotherapy should improve outcome. This is the first demonstration of a link between quantitative imaging features (radiomics) with genomic features in MRI‐directed prostate biopsies.

The research was supported by NIH‐ NCI R01 CA 189295 and R01 CA 189295; E Davicioni is partial owner of GenomeDx Biosciences, Inc. M Takhar, N Erho, L Lam, C Buerki and E Davicioni are current employees at GenomeDx Biosciences, Inc.
TU‐CD‐BRA‐06: 3D Reconstruction From 2D CineMRI Orthogonal Slices: A Feasibility Study
Authors: Paganelli C , Lee D , Kipritidis J , Greer P , Riboldi M , Keall P
Published: June 2015

Purpose:

The ideal image guidance strategy to acquire complete spatio‐temporal information for the patients during therapy. MRI‐Linacs come close to this ideal, but there are spatial and temporal trade‐offs. Several authors have proposed simultaneous orthogonal images as a guidance strategy for MRI‐Linac. In order to estimate the missing 3D information from the 2D orthogonal images we present a feasibility study on the reconstruction of a 3D volume directly from 2D orthogonal CineMRI slices for MRI‐guided treatment.

Methods:

A 4DCT XCAT lung tumor phantom was generated in two respiratory phases (i.e. exhale and inhale) with 3cm diaphragm motion. We simulated the cine acquisition by extracting sagittal and coronal orthogonal slices from the inhale XCAT phantom. Then, we performed DIR between the selected slices at the inhale phase with the corresponding ones at exhale. An interpolation of the derived motion field was performed in the RL, AP and SI directions, thus obtaining a 3D motion field that was used to warp the exhale phase and obtain a 3D estimation of the inhale phase (i.e. estimated_inhale volume). As validation we compared the estimated_inhale volume with the inhale phase (i.e. ground truth). We also applied the method on one CineMRI lung patient image set, where inter‐leaved sagittal/coronal cineMRI images were available.

Results:

The estimated_inhale volume resulted comparable with the ground truth. The distance between landmarks identified in the two respiratory phases was quantified as 24.8±7.2mm for exhale/estimated _inhale, vs.21.9±9.8mm for exhale/inhale. Tumor motion between exhale and estimated_inhale was 28.3mm, consistent with the measured diaphragm motion (i.e. 30mm). The patient results confirmed that the estimated_inhale volume compensated for organ motion (i.e. diaphragm distance between inhale and estimated_inhale was within 4.7±2.4mm).

Conclusion:

The method provided a framework for the volumetric reconstruction from 2D orthogonal slices. The application to a patient case showed the capability to account for organ motion.
TU‐CD‐BRA‐09: Accuracy of Deformable Image Registration in Homogeneous Regions: The Impact of Regularisation
Authors: Larrue A , Cifor A , Gooding M
Published: June 2015

Purpose

Deformable Image Registration (DIR) consists of computing a deformation field to provide an anatomical mapping between the images to be aligned. The deformation field is regularized to prevent over‐fitting, ensure numerical stability, and support the assumption that natural deformations are smooth. The aim of this work is to evaluate the impact of the regularization on the accuracy of the DIR in homogeneous regions where strong image features are not present to guide the mapping.

Methods

The “DIR Validation dataset” (http://www.creatis.insa‐lyon.fr/rio/dir_validation_data) providesbenchmark data for evaluating 3D CT registration algorithms. It consists of six 4DCT lung datasets, with landmarks identified on the end‐exhalation and end‐inhalation phases. Images were registered using image‐based commercial DIR software (Mirada RTx, Mirada Medical, UK). Lungs were segmented and the contours used for structure‐based registration method, thus simulating a fully homogenous region by blinding registration to the underlying image. Target and Surface registration errors (TRE, SRE) were measured at different values of the regularization parameters.

Results

Structure‐based registration showed similar boundary alignment at low regularisation (mean SFE: 0.41 ± 0.07mm) compared to image‐based DIR (0.38±0.17mm), but internal TRE was much worse (5.1±2.1mm cf. 1.4±0.6mm). As regularisation increased internal TRE decreased slightly (minimum 4.2±1.9mm) however this corresponded to an increase in SFE (maximum: 0.9±0.18mm).

Conclusion

While image‐based DIR can align the internal structures in this case, sometimes few internal structures may be visible in clinical practice (e.g. some tumours, liver, brain). The use of structure‐based registration simulated registration within homogenous regions, while allowing comparison with internal TRE. This study demonstrates that while regularization creates a smooth deformation within such regions but it is not necessarily an accurate one, even where the structure boundary is well aligned. Assessment of the deformation grid is helpful for evaluating registrations in such areas.

A. Larrue, A.Cifor, and M.Gooding are employees of Mirada Medical
TU‐CD‐204‐00: CT Scanner Hardware and Image Quality Assessment
Authors: Dong Frank
Published: June 2015

For practicing medical physicists, CT image quality assessment is, in general, limited to the ones required by ACR and based on the axial images, such as CT number uniformity, image noise, contrast‐to‐noise ratio (CNR), and high contrast resolution. However, with more advanced technologies introduced by CT vendors, just assessing these basic image quality metrics may not be enough. Noise power spectrum (NPS), characterizing the signal noise component at each spatial frequency, is a powerful tool to predict the CT performance related to lesion detectability and noise texture. The quality of coronal and sagittal reformatted images is, in a large part, determined by the slice profile. How to accurately assess the slice profile is important for clinical medical physicists but not well recognized.

Automatic tube current modulation (ATCM) has been adopted by major CT manufacturers, to maintain image quality across the scan range. The way how ATMC works varies significantly among vendors. A “standard” method is needed to evaluate the performance of this critical dose‐saving and image quality improvement technique. As dual energy CT becomes more readily available for routine clinical use, the need of image quality assessment metrics unique to the dual energy CT mode is becoming urgent.

The session will facilitate the discussion of NPS and its application in the evaluation of FBP and iterative reconstruction. This session will also present the methods to measure the slice profile and characterize the performance of ATCM. The last part of this session will focus on the physics of CT dual energy mode, as well as unique image quality metrics to evaluate the performance of the dual energy mode.

Learning Objectives:

Be familiar with procedures on how to correctly compute CT noise power spectrum

Understand why basic image quality metrics used for FBP may not be sufficient to characterize the performance of advanced iterative reconstruction

Understand CT slice profile and how to accurately measure it

Be familiar with ATCM from major CT vendors and how to evaluate its performance

Understand different hardware approaches for dual energy CT

Be familiar with image quality metrics relevant to dual energy mode

Schmidt: Employee of Siemens Healthcare

Fan: Employee of GE Healthcare