bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐F‐CAMPUS‐J‐04: Setup Uncertainties in the Mediastinum Area for IMRT Treatment of Lymphoma Patients
Authors: Aristophanous M , Court L
Published: June 2015

Purpose:

Despite daily image guidance setup uncertainties can be high when treating large areas of the body. The aim of this study was to measure local uncertainties inside the PTV for patients receiving IMRT to the mediastinum region.

Methods:

Eleven lymphoma patients that received radiotherapy (breath‐hold) to the mediastinum were included in this study. The treated region could range all the way from the neck to the diaphragm. Each patient had a CT scan with a CT‐on‐rails system prior to every treatment. The entire PTV region was matched to the planning CT using automatic rigid registration. The PTV was then split into 5 regions: neck, supraclavicular, superior mediastinum, upper heart, lower heart. Additional auto‐registrations for each of the 5 local PTV regions were performed. The residual local setup errors were calculated as the difference between the final global PTV position and the individual final local PTV positions for the AP, SI and RL directions. For each patient 4 CT scans were analyzed (1 per week of treatment).

Results:

The residual mean group error (M) and standard deviation of the inter‐patient (or systematic) error (Σ) were lowest in the RL direction of the superior mediastinum (0.0mm and 0.5mm) and highest in the RL direction of the lower heart (3.5mm and 2.9mm). The standard deviation of the inter‐fraction (or random) error (σ) was lowest in the RL direction of the superior mediastinum (0.5mm) and highest in the SI direction of the lower heart (3.9mm) The directionality of local uncertainties is important; a superior residual error in the lower heart for example keeps it in the global PTV.

Conclusion:

There is a complex relationship between breath‐holding and positioning uncertainties that needs further investigation. Residual setup uncertainties can be significant even under daily CT image guidance when treating large regions of the body.
TU‐F‐CAMPUS‐J‐05: Fast Volumetric MRI On An MRI‐Linac Enables On‐Line QA On Dose Deposition in the Patient
Authors: Crijns S , Glitzner M , de Senneville B Denis , Kontaxis C , Maenhout M , Bol G , Lagendijk J , Raaymakers B
Published: June 2015

Purpose:

The introduction of the MRI‐linac in radiotherapy brings MRI‐guided treatment with daily plan adaptions within reach. This paradigm demands on‐line QA. With its ability to perform continuous volumetric imaging in an outstanding soft‐tissue contrast, the MRI‐ linac promises to elucidate the dose deposition process during a treatment session. Here we study for a prostate case how dynamic MRI combined with linac machine parameters and a fast dose‐engine can be used for on‐line dose accumulation.

Methods:

Prostate imaging was performed in healthy volunteer on a 1.5T MR‐scanner (Philips, Best, NL) according to a clinical MR‐sim protocol, followed by 10min of dynamic imaging (FLASH, 4s/volume, FOV 40×40×12cm3, voxels 3×3×3mm3, TR/TE/α=3.5ms/1.7ms/5°). An experienced radiation oncologist made delineations, considering the prostate CTV. Planning was performed on a two‐compartment pseudoCT (air/water density) according to clinical constraints (77Gy in PTV) using a Monte‐Carlo (MC) based TPS that accounts for magnetic fields. Delivery of one fraction (2.2Gy) was simulated on an emulator for the Axesse linac (Elekta, Stockholm, SE). Machine parameters (MLC settings, gantry angle, dose rate, etc.) were recorded at 25Hz. These were re‐grouped per dynamic volume and fed into the MC‐engine to calculate a dose delivered for each of the dynamics. Deformations derived from non‐rigid registration of each dynamic against the first allowed dose accumulation on a common reference grid.

Results:

The DVH parameters on the PTV compared to the optimized plan showed little changes. Local deformations however resulted in local deviations, primarily around the air/rectum interface. This clearly indicates the potential of intra‐fraction adaptations based on the accumulated dose. Application in each fraction helps to track the influence of plan adaptations to the eventual dose distribution. Calculation times were about twice the delivery time.

Conclusion:

The current Result paves the way to perform on‐line treatment delivery QA on the MRI‐linac in the near future.
WE‐E‐304‐01: SBRT Credentialing: Understanding the Process From Inquiry to Approval
Authors: Followill D.
Published: June 2015

SBRT is having a dramatic impact on radiation therapy of early‐stage, locally advanced cancers. A number of national protocols have been and are being developed to assess the clinical efficacy of SBRT for various anatomical sites, such as lung and spine. Physics credentialing for participating and implementation of trial protocols involve a broad spectrum of requirements from image guidance, motion management, to planning technology and dosimetric constrains. For radiation facilities that do not have extensive experiences in SBRT treatment and protocol credentialing, these complex processes of credentialing and implementation could be very challenging and, sometimes, may lead to ineffective even unsuccessful execution of these processes. In this proposal, we will provide comprehensive review of some current SBRT protocols, explain the requirements and their underline rationales, illustrate representative failed and successful experiences, related to SBRT credentialing, and discuss strategies for effective SBRT credentialing and implementation.

Learning Objectives:

Understand requirements and challenges of SBRT credentailing and implentation

Discuss processes and strategies of effective SBRT credentailing

Discuss practical considerations, potential pitfalls and solutions of SBRT implentation
WE‐E‐BRB‐01: Clinical Usage of Knowledge Based Treatment Planning
Authors: Zhang X.
Published: June 2015

The knowledge‐based treatment planning automation has evolved from academic research from the clinical application with the involvement of the major industry TPS vendors. Previous work proved the concept that IMRT or VMAT plans can be designed without or with minimal human intervention. Recently, the major industry vendors start releasing the automatic planning product such as Philips automatic treatment planning, Varian's Rapidplan, and RaySearch's autoplan. Many centers start to evaluate and use the automatic planning products from TPS vendors. It is more and more becoming evident that automatic planning will be routinely used in the clinic.

The first presentation will focus on the knowledge modeling for clinical treatment planning. The presenter will introduce the algorithm and theory for developing the dose volume histogram (DVH) model, summarize the results on the validation of the DVH model, and discuss the application of DVH for the automatic treatment planning. The second presenter will focus on the clinical use of the automatic treatment planning. The presenter will give an overview of the several automatic treatment planning tools including the tools developed commercially and in‐house, present the early experience of using those tools, and discuss the application of the tools in the routine clinical use and in the quality control of the treatment planning.

Learning Objectives:

Describe the algorithm and theory behind the knowledge based treatment planning automation.

Clinical experience of using automatic planning in clinical trial and patient treatment

Early clinical experience of using commercial automatic planning approach

The application of automatic planning approach to perform quality assurance of treatment plan.

XD obtain the research funding from Varian Medical System, Philips Medical System and Funding support form Sister Institution Network Fund of MD Anderson, XD is also a founder of Global Oncology One
WE‐EF‐BRA‐08: Cell Survival in Modulated Radiation Fields and Altered DNA‐Repair at Field Edges
Authors: Bartzsch S , Eismann S , Oelfke U
Published: June 2015

Purpose:

Tissue damage prognoses in radiotherapy are based on clonogenic assays that provide dose dependent cell survival rates. However, recent work has shown that apart from dose, systemic reactions and cell‐cell communication crucially influence the radiation response. These effects are probably a key in understanding treatment approaches such as microbeam radiation therapy (MRT). In this study we tried to quantify the effects on a cellular level in spatially modulated radiation fields.

Methods:

Pancreas carcinoma cells were cultured, plated and irradiated by spatially modulated radiation fields with an X‐ray tube and at a synchrotron. During and after treatment cells were able to communicate via the intercellular medium. Afterwards we stained for DNA and DNA damage and imaged with a fluorescence microscope.

Results:

Intriguingly we found that DNA damage does not strictly increase with dose. Two cell entities appear that have either a high or a low amount of DNA lesions, indicating that DNA damage is also a cell stress reaction. Close to radiation boundaries damage‐levels became alike; they were higher than expected at low and lower than expected at high doses. Neighbouring cells reacted similarly. 6 hours after exposure around 40% of the cells resembled in their reactions neighbouring cells more than randomly chosen cells that received the same dose. We also observed that close to radiation boundaries the radiation induced cell‐cycle arrest disappeared and the size of DNA repair‐centres increased.

Conclusion:

Cell communication plays an important role in the radiation response of tissues and may be both, protective and destructive. These effects may not only have the potential to affect conventional radiotherapy but may also be exploited to spare organs at risk by intelligently designing irradiation geometries. To that end intensive work is required to shed light on the still obscure processes in cell‐signalling and radiation biology.
WE‐EF‐BRA‐10: Prophylactic Cranial Irradiation Reduces the Incidence of Brain Metastasis in a Mouse Model of Metastatic Breast Cancerr
Authors: Smith D , Debeb B , Larson R , Diagaradjane P , Woodward W
Published: June 2015

Purpose:

Prophylactic cranial irradiation (PCI) is a clinical technique used to reduce the incidence of brain metastasis and improve overall survival in select patients with acute lymphoblastic leukemia and small‐cell lung cancer. We examined whether PCI could benefit breast cancer patients at high risk of developing brain metastases.

Methods:

We utilized our mouse model in which 500k green fluorescent protein (GFP)‐labeled breast cancer cells injected into the tail vein of SCID/Beige mice resulted in brain metastases in approximately two‐thirds of untreated mice. To test the efficacy of PCI, one set of mice was irradiated five days after cell injection with a single fraction of 4‐Gy (two 2‐Gy opposing fields) whole‐brain irradiation on the XRAD 225Cx small‐animal irradiator. Four controls were included: a non‐irradiated group, a group irradiated two days prior to cell injection, and two groups irradiated 3 or 6 weeks after cell injection. Mice were sacrificed four and eight weeks post‐injection and were evaluated for the presence of brain metastases on a fluorescent stereomicroscope.

Results:

The incidence of brain metastasis in the non‐irradiated group was 77% and 90% at four and eight weeks, respectively. The PCI group had a significantly lower incidence, 20% and 30%, whereas the other three control groups had incidence rates similar to the non‐treated control (70% to 100%). Further, the number of metastases and the metastatic burden were also significantly lower in the PCI group compared to all other groups.

Conclusion:

The timing of irradiation to treat subclinical disease is critical, as a small dose of whole‐brain irradiation given five days after cell injection abrogated tumor burden by greater than 90%, but had no effect when administered twenty‐one days after cell injection. PCI is likely to benefit breast cancer patients at high risk of developing brain metastases and should be strongly considered in the clinic.
WE‐EF‐BRA‐11: Precision Partial‐Tumor Irradiation of Dorsal Rodent Mammary Tumors
Authors: Malcolm J , Boss K , Dewhirst M , Oldham M
Published: June 2015

Purpose:

To introduce a pre‐clinical treatment technique on a micro‐irradiator to treat specific volumes of dorsal mammary tumors in BALB/c mice while sparing lungs and spine. This technique facilitates pre‐clinical investigation of tumor response to sub‐optimal radiation treatments in which a portion of the tumor is unirradiated, known as a “marginal miss”. In‐vitro data suggests that partial tumor radiations trigger a more aggressive phenotype in non‐irradiated, regional tumor cells via bystander effects. As the lung tissue is spared, the impact of marginal miss on the development of pulmonary metastasis may be assessed.

Methods:

End to end test was performed on three BALB/c mice as proof of concept for larger studies. 1Gy was delivered on the micro‐irradiator employing previously unexplored lateral parallel‐opposed diamond and/or triangle‐shaped beams. The margins of the treatment beam were defined using a combination of tumor palpation, barium fiducial markers, and real‐time fluoroscopic images. The dose distribution was independently verified with kilovoltage beam Monte Carlo dose calculations with 7% statistical uncertainty and double exposure images. As a final step, the technique was used in a larger pre‐clinical study (15Gy, 36 BALB/c mice) and lung metastasis in response to tumor irradiation of 100%, 50% and 0% was quantified.

Results:

For the Monte‐Carlo dose calculations, the dose volume histograms established a maximum dose within the un‐irradiated and radiated portions of the mammary tumor of 0.3Gy and 1.5Gy respectively, with a sharp gradient at the boundary. 100% of the lung volume received less than 0.5Gy. This technique proved suitable for a pre‐clinical marginal miss study with 50% more lung metastases in partially‐radiated mouse models compared to completely.

Conclusion:

We have developed a novel treatment technique for partial or full irradiation of dorsal mammary tumors incorporating lung sparing.The technique will be useful for exploring the phenomena of aggressive tumor phenotype that may arise from miss‐irradiation.
WE‐EF‐303‐01: FEATURED PRESENTATION: Hydrogel Fiducial Markers for In‐Vivo Proton Therapy and Range Verifications Using PET
Authors: Cho J , Campbell P , Wang M , Alqathami M , Mawlawi O , Li H , Sahoo N , Kerr M , Zubarev E , Cho S
Published: June 2015

Purpose:

Currently there are no clinically used techniques for in‐vivo proton treatment/range verification. Our aim was to develop patient implantable markers that can be visualized in CT/x‐ray for treatment‐planning/beam‐positioning, and also in PET for proton treatment/range verification.

Methods:

Biocompatible/biodegradable hydrogel polymers were immersed in O18‐enriched water and O16 water, respectively to create O18‐water hydrogels (0.5 cm3) and O16‐water hydrogels (1 cm3) (both >99% water and <1% polymer). Also, 5–8 µm Zn powder was suspended in O16 water and O18‐enriched water and cross‐linked with hydrogel polymers to create Zn/16O‐water hydrogels (30%/70% mass ratio, <1% polymer) and Zn/18O‐water hydrogels (10%/90%). A block of extra‐firm “wet” tofu (12.3×8.8×4.9 cm, ρ⁼1) immersed in water was injected with Zn/O16‐water hydrogels (0.9 cm3 each) at four different depths using an 18 gauge needle. Similarly, Zn/18O‐water hydrogels (0.9 cm3) were injected in a different tofu phantom. As a reference, both 16O‐water and O18‐water hydrogels in petri‐dishes were irradiated in a “dry” environment. The hydrogels in the “wet” tofu phantoms and “dry” petri‐dishes were CT‐scanned and treatment‐planned. Then, they were positioned at the proton distal dose fall‐off region and irradiated (2 Gy) followed by PET/CT imaging.

Results:

Significantly high PET signals were observed only at O18‐water hydrogels in the “dry” environment. Zn/O16‐water hydrogels injected in the tofu phantom showed outstanding CT visibility but provided no noticeable PET signals. Zn/O18‐water hydrogels in the “wet” tofu showed excellent CT visibility and moderate PET visibility, however, weaker PET signals than the “dry” environment possibly due to O18‐water leaching out.

Conclusion:

The developed hydrogel markers can be used as universal fiducial markers due to their CT/PET/MRI/US visibility. Their PET visibility (possibly contributed more by activated O18‐water than Zn) after proton irradiation can be utilized for proton therapy/range verification. More investigation is needed to slow down the leaching of O18‐water.
WE‐EF‐303‐02: BEST IN PHYSICS (JOINT IMAGING‐ THERAPY): A Comprehensive Simulation of Image Guided Beam Gating for Liver Tumor Treatments Using Scanned Proton Therapy
Authors: Zhang Y , Knopf A , Weber D , Lomax A
Published: June 2015

Purpose:

To evaluate the effectiveness of image guided beam gating for PBS liver treatments under realistic breathing conditions.

Methods:

We have previously proposed a Beams’ Eye View (BEV) X‐ray image system as an online motion monitoring device for deriving a gating signal for PBS proton therapy. Using dedicated 4D dose calculations (4DDC), in this work we have simulated gated liver treatments using three amplitude‐based gating windows (10/5/3mm) based on motion extracted from BEV imaging of fiducial markers or the diaphragm. In order to improve motion mitigation, BEV guided gating has also been combined with either volumetric (VS) or layered (LS) rescanning. Nine 4DCT(MRI) liver data‐sets have been used for the investigation, which not only consider realistic patient geometries but also motion variations between different breathing cycles. All 4D plans have been quantified in terms of plan homogeneity in the PTV (D5‐D95), the total estimated treatment time and the beam‐on duty cycle.

Results:

Neither gating nor rescanning can fully retrieve a comparable plan homogeneity to the static case, and considerable reductions of the duty cycle (<10%) were observed as a Result motion variations when small gating windows are used. However, once combined with rescanning, dose homogeneity within 1% of the static plan could be achieved with reasonable prolongation of the treatment time for all 9 subjects. No differences were observed between the efficacy of layered or volumetric re‐scanning, or of gating signals extracted from fiducial or diaphragm motions. However, layered rescanning may be preferred over volumetric rescanning when performed in combination with gating as it is generally more time‐efficient and dosimetrically robust to patient and motion variations

Conclusion

Combining BEV beam gating with rescanning is an efficient and effective approach to treating mobile liver tumours, and is equally effective if either the diaphragm or fiducial markers are used as motion surrogates.
WE‐EF‐303‐06: Feasibility of PET Image‐Based On‐Line Proton Beam‐Range Verification with Simulated Uniform Phantom and Human Brain Studies
Authors: Lou K , Sun X , Zhu X , Grosshans D , Clark J , Shao Y
Published: June 2015

Purpose:

To study the feasibility of clinical on‐line proton beam range verification with PET imaging

Methods:

We simulated a 179.2‐MeV proton beam with 5‐mm diameter irradiating a PMMA phantom of human brain size, which was then imaged by a brain PET with 300*300*100‐mm^3 FOV and different system sensitivities and spatial resolutions. We calculated the mean and standard deviation of positron activity range (AR) from reconstructed PET images, with respect to different data acquisition times (from 5 sec to 300 sec with 5‐sec step). We also developed a technique, “Smoothed Maximum Value (SMV)”, to improve AR measurement under a given dose. Furthermore, we simulated a human brain irradiated by a 110‐MeV proton beam of 50‐mm diameter with 0.3‐Gy dose at Bragg peak and imaged by the above PET system with 40% system sensitivity at the center of FOV and 1.7‐mm spatial resolution.

Results:

MC Simulations on the PMMA phantom showed that, regardless of PET system sensitivities and spatial resolutions, the accuracy and precision of AR were proportional to the reciprocal of the square root of image count if image smoothing was not applied. With image smoothing or SMV method, the accuracy and precision could be substantially improved. For a cylindrical PMMA phantom (200 mm diameter and 290 mm long), the accuracy and precision of AR measurement could reach 1.0 and 1.7 mm, with 100‐sec data acquired by the brain PET. The study with a human brain showed it was feasible to achieve sub‐millimeter accuracy and precision of AR measurement with acquisition time within 60 sec.

Conclusion:

This study established the relationship between count statistics and the accuracy and precision of activity‐range verification. It showed the feasibility of clinical on‐line BR verification with high‐performance PET systems and improved AR measurement techniques.

Cancer Prevention and Research Institute of Texas grant RP120326, NIH grant R21CA187717, The Cancer Center Support (Core) Grant CA016672 to MD Anderson Cancer Center
WE‐EF‐303‐08: Proton Radiography Using Pencil Beam Scanning and Novel Micromegas Detectors
Authors: Dolney D , Mayers G , Newcomer M , Bollinger D , Desai N , Lustig R , Teo B , Maughan R , Solberg T , Hollebeek R
Published: June 2015

Purpose:

While the energy of therapeutic proton beams can be adjusted to penetrate to any given depth in water, range uncertainties arise in patients due in part to imprecise knowledge of the stopping power of protons in human tissues. Proton radiography is one approach to reduce the beam range uncertainty, thereby allowing for a reduction in treatment margins and dose escalation.

Methods:

The authors have adapted a novel detector technology based on Micromesh Gaseous Structure (“Micromegas”) for proton therapy beams and have demonstrated fine spatial and time resolution of magnetically scanned proton pencil beams, as well as wide dynamic range for dosimetry. In this work, proton radiographs were obtained using Micromegas 2D planes positioned downstream of solid water assemblies. The position‐sensitive monitor chambers in the IBA proton delivery nozzle provide the beam entrance position.

Results:

Radiography with Micromegas detectors and actively scanned beams provide spatial resolution of up to 300 µm and water‐equivalent thickness (WET) resolution as good as 0.02% (60 µm out of 31 cm total thickness), with the dose delivered to the patient kept below 2 cGy. The spatial resolution as a function of sample rate and number of delivered protons is found to be near the theoretical Cramer‐Rao lower bound. Using the CR bound, we argue that the imaging dose could be further lowered to 1 mGy, while still achieving sub‐mm spatial resolution, by relatively simple instrumentation upgrades and beam delivery modifications.

Conclusion:

For proton radiography, high spatial and WET resolution can be achieved, with minimal additional dose to patient, by using magnetically scanned proton pencil beams and Micromegas detectors.
WE‐EF‐303‐09: Proton‐Acoustic Range Verification in Proton Therapy
Authors: Ahmad M , Xiang L , Xing L
Published: June 2015

Purpose:

We investigated proton‐acoustic signals detection for range verification with current ultrasound instruments in typical clinical scenarios. Using simulations that included a realistic noise model, we determined the theoretical minimum dose required to generate detectable proton‐acoustic signals.

Methods:

An analytical model was used to calculate the dose distributions and local pressure rise (per proton) for beams of different energy (100 and 160 MeV) and spot widths (1, 5, and 10 mm) in a water phantom. The acoustic waves propagating from the Bragg peak were modeled by the general 3D pressure wave equation and convolved with Gaussian kernels to simulate various proton pulse widths (0.1 – 10 ms). A realistic PZT ultrasound transducer (5 cm diameter) was simulated with a Butterworth band‐pass filter, and ii) randomly generated noise based on a model of thermal noise in the transducer. The signal‐to‐noise ratio was calculated, determining the minimum number of protons and dose required per pulse. The maximum spatial resolution was also estimated from the signal spectrum.

Results:

The calculated noise in the transducer was 12–28 mPa, depending on the transducer center frequency (70–380 kHz). The minimum number of protons were on the order of 0.6–6 million per pulse, leading to 3–110 mGy dose per pulse at the Bragg peak, depending on the spot size. The acoustic signal consisted of lower frequencies for wider pulses, leading to lower noise levels, but also worse spatial resolution. The resolution was 1‐mm for a 0.1‐µs pulse width, but increased to 5‐mm for a 10‐µs pulse width.

Conclusion:

We have established minimum dose detection limits for proton‐acoustic range validation. These limits correspond to a best case scenario with a large detector with no losses and only detector thermal noise. Feasible proton‐acoustic range detection will require at least 10⁷ protons per pulse and pulse widths ≤ 1‐µs.
WE‐EF‐204‐00: The Joint AAPM‐WMIS Symposium: Linking Pre‐Clinical and Clinical Trials: Co‐Clinical Trials
Authors: Cao Yue
Published: June 2015

As molecular biology breakthroughs in understanding cancers and other diseases, hundreds of new drugs wait testing. In the last decade, mouse models have been evolved to better mimic human diseases genetically and biologically. These reliable mouse models allow us to determine which genetic elements, pathways and mutations impact on therapy. The co‐clinical trial strategy is to conduct a human clinical trial for a therapeutic drug and test it in mouse models at the same time. This strategy has the potential to accelerate the drug testing process and identify the patient population that will respond to the drug. Imaging plays an important role in co‐clinical trials. In this symposium, four speakers will discuss advancements and issues in pre‐clinical imaging, murine models, imaging hardware and software, and funding opportunities in co‐clinical trials.

Learning Objectives:

Multi‐modality pre‐clinical imaging hardware and software, and new technologies (e.g., hyperpolarized MRI)

Selection of animal models from physiological and genetic perspectives with examples in colon, pancreatic and lung cancers

NCI funding opportunities
WE‐EF‐207‐04: An Inter‐Projection Sensor Fusion (IPSF) Approach to Estimate Missing Projection Signal in Synchronized Moving Grid (SMOG) System
Authors: Zhang H , Ren L , Kong V , Zhang Y , Giles W , Jin J
Published: June 2015

Purpose:

A synchronized moving grid (SMOG) has been proposed to reduce scatter and lag artifacts in cone beam computed tomography (CBCT). However, information is missing in each projection because certain areas are blocked by the grid. A previous solution to this issue is acquiring 2 complimentary projections at each position, which increases scanning time. This study reports our first Result using an inter‐projection sensor fusion (IPSF) method to estimate missing projection in our prototype SMOG‐based CBCT system.

Methods:

An in‐house SMOG assembling with a 1:1 grid of 3 mm gap has been installed in a CBCT benchtop. The grid moves back and forth in a 3‐mm amplitude and up‐to 20‐Hz frequency. A control program in LabView synchronizes the grid motion with the platform rotation and x‐ray firing so that the grid patterns for any two neighboring projections are complimentary. A Catphan was scanned with 360 projections. After scatter correction, the IPSF algorithm was applied to estimate missing signal for each projection using the information from the 2 neighboring projections. Feldkamp‐Davis‐Kress (FDK) algorithm was applied to reconstruct CBCT images. The CBCTs were compared to those reconstructed using normal projections without applying the SMOG system.

Results:

The SMOG‐IPSF method may reduce image dose by half due to the blocked radiation by the grid. The method almost completely removed scatter related artifacts, such as the cupping artifacts. The evaluation of line pair patterns in the CatPhan suggested that the spatial resolution degradation was minimal.

Conclusion:

The SMOG‐IPSF is promising in reducing scatter artifacts and improving image quality while reducing radiation dose.
WE‐EF‐207‐06: Dedicated Cone‐Beam Breast CT with Laterally‐Shifted Detector: Monte Carlo Evaluation of X‐Ray Scatter Distribution and Scatter‐To‐Primary Ratio
Authors: Shi L , Vedantham S , Karellas A
Published: June 2015

Purpose:

To determine the spatial distribution of x‐ray scatter and scatter‐to‐primary ratio (SPR) in projections during cone‐beam breast CT (CBBCT) with laterally‐shifted detector that results in coronal (fan‐angle) truncation.

Methods:

We hypothesized that CBBCT with coronal truncation would lower SPR due to reduction in irradiated breast volume, and that the location of maximum x‐ray scatter fluence (scatter‐peak) in the detector plane can be determined from the ratio of irradiated‐to‐total breast volume, breast dimensions and system geometry. Monte Carlo simulations (GEANT4) reflecting a prototype CBBCT system were used to record the position‐dependent primary and scatter x‐ray photon fluence incident on the detector without coronal truncation (full fan‐angle, 2f=24‐degrees) and with coronal truncation (fan‐angle, f+ f=12+2.7‐degrees). Semi‐ellipsoidal breasts (10/14/18‐cm diameter, chest‐wall to nipple length: 0.75xdiameter, 2%/14%/100% fibroglandular content) aligned with the axis‐of‐rotation (AOR) were modeled. Mono‐energy photons were simulated and weighted for 2 spectra (49kVp, 1.4‐mm Al HVL; 60kVp, 3.76‐mm Al HVL). In addition to SPR, the scatter maps were analyzed to identify the location of the scatter‐peak.

Results:

For CBBCT without fan‐angle truncation, the scatter‐peaks were aligned with the projection of the AOR onto the detector for all breasts. With truncated fan‐beam, the scatter‐peaks were laterally‐shifted from the projection of the AOR along the fan‐angle direction by 14/38/70‐pixels for 10/14/18‐cm diameter breasts. The corresponding theoretical shifts were 14.8/39.7/68‐pixels (p=0.47, 2‐tailed paired‐ratio t‐test). Along the cone‐angle, the shift in scatter‐peaks between truncated and full‐fan angle CBBCT were 2/2/4 ‐pixels for 10/14/18‐cm diameter breasts. CBBCT with fan‐angle truncation reduced SPR by 14/22/28% for 10/14/18‐cm diameter breasts. 60kVp reduced SPR by 21–25% compared to 49kVp. Peak SPR for CBBCT with fan‐angle truncation (60kVp) were 0.09/0.25/0.73 for 10/14/18‐cm diameter breasts.

Conclusion:

CBBCT with laterally‐shifted detector geometry and with appropriate kVp/beam quality reduces SPR. If residual scatter needs correction, the location corresponding to scatter‐peak can be analytically computed.

This work was supported in part by NIH R01 CA128906. The contents are solely the responsibility of the authors and do not reflect the official views of the NIH or NCI.
WE‐EF‐207‐07: Dual Energy CT with One Full Scan and a Second Sparse‐View Scan Using Structure Preserving Iterative Reconstruction (SPIR)
Authors: Wang T , Zhu L
Published: June 2015

Purpose:

Conventional dual energy CT (DECT) reconstructs CT and basis material images from two full‐size projection datasets with different energy spectra. To relax the data requirement, we propose an iterative DECT reconstruction algorithm using one full scan and a second sparse‐view scan by utilizing redundant structural information of the same object acquired at two different energies.

Methods:

We first reconstruct a full‐scan CT image using filtered‐backprojection (FBP) algorithm. The material similarities of each pixel with other pixels are calculated by an exponential function about pixel value differences. We assume that the material similarities of pixels remains in the second CT scan, although pixel values may vary. An iterative method is designed to reconstruct the second CT image from reduced projections. Under the data fidelity constraint, the algorithm minimizes the L2 norm of the difference between pixel value and its estimation, which is the average of other pixel values weighted by their similarities. The proposed algorithm, referred to as structure preserving iterative reconstruction (SPIR), is evaluated on physical phantoms.

Results:

On the Catphan600 phantom, SPIR‐based DECT method with a second 10‐view scan reduces the noise standard deviation of a full‐scan FBP CT reconstruction by a factor of 4 with well‐maintained spatial resolution, while iterative reconstruction using total‐variation regularization (TVR) degrades the spatial resolution at the same noise level. The proposed method achieves less than 1% measurement difference on electron density map compared with the conventional two‐full‐scan DECT. On an anthropomorphic pediatric phantom, our method successfully reconstructs the complicated vertebra structures and decomposes bone and soft tissue.

Conclusion:

We develop an effective method to reduce the number of views and therefore data acquisition in DECT. We show that SPIR‐based DECT using one full scan and a second 10‐view scan can provide high‐quality DECT images and accurate electron density maps as conventional two‐full‐scan DECT.
WE‐EF‐207‐08: Improve Cone Beam CT Using a Synchronized Moving Grid, An Inter‐Projection Sensor Fusion and a Probability Total Variation Reconstruction
Authors: Zhang H , Ren L , Kong V , Zhang Y , Giles W , Jin J
Published: June 2015

Purpose:

To present a cone beam computed tomography (CBCT) system, which uses a synchronized moving grid (SMOG) to reduce and correct scatter, an inter‐projection sensor fusion (IPSF) algorithm to estimate the missing information blocked by the grid, and a probability total variation (pTV) algorithm to reconstruct the CBCT image.

Methods:

A prototype SMOG‐equipped CBCT system was developed, and was used to acquire gridded projections with complimentary grid patterns in two neighboring projections. Scatter was reduced by the grid, and the remaining scatter was corrected by measuring it under the grid. An IPSF algorithm was used to estimate the missing information in a projection from data in its 2 neighboring projections. Feldkamp‐Davis‐Kress (FDK) algorithm was used to reconstruct the initial CBCT image using projections after IPSF processing for pTV. A probability map was generated depending on the confidence of estimation in IPSF for the regions of missing data and penumbra. pTV was finally used to reconstruct the CBCT image for a Catphan, and was compared to conventional CBCT image without using SMOG, images without using IPSF (SMOG + FDK and SMOG + mask‐TV), and image without using pTV (SMOG + IPSF + FDK).

Results:

The conventional CBCT without using SMOG shows apparent scatter‐induced cup artifacts. The approaches with SMOG but without IPSF show severe (SMOG + FDK) or additional (SMOG + TV) artifacts, possibly due to using projections of missing data. The 2 approaches with SMOG + IPSF removes the cup artifacts, and the pTV approach is superior than the FDK by substantially reducing the noise. Using the SMOG also reduces half of the imaging dose.

Conclusion:

The proposed technique is promising in improving CBCT image quality while reducing imaging dose.
WE‐EF‐207‐09: Single‐Scan Dual‐Energy CT Using Primary Modulation
Authors: Petrongolo M , Zhu L
Published: June 2015

Purpose:

Compared with conventional CT, dual energy CT (DECT) provides better material differentiation but requires projection data with two different effective x‐ray spectra. Current DECT scanners use either a two‐scan setting or costly imaging components, which are not feasible or available on open‐gantry cone‐beam CT systems. We propose a hardware‐based method which utilizes primary modulation to enable single‐scan DECT on a conventional CT scanner. The CT imaging geometry of primary modulation is identical to that used in our previous method for scatter removal, making it possible for future combination with effective scatter correction on the same CT scanner.

Methods:

We insert an attenuation sheet with a spatially‐varying pattern ‐ primary modulator‐between the x‐ray source and the imaged object. During the CT scan, the modulator selectively hardens the x‐ray beam at specific detector locations. Thus, the proposed method simultaneously acquires high and low energy data. High and low energy CT images are then reconstructed from projections with missing data via an iterative CT reconstruction algorithm with gradient weighting. Proof‐of‐concept studies are performed using a copper modulator on a cone‐beam CT system.

Results:

Our preliminary results on the Catphan(c) 600 phantom indicate that the proposed method for single‐scan DECT is able to successfully generate high‐quality high and low energy CT images and distinguish different materials through basis material decomposition. By applying correction algorithms and using all of the acquired projection data, we can reconstruct a single CT image of comparable image quality to conventional CT images, i.e., without primary modulation.

Conclusion:

This work shows great promise in using a primary modulator to perform high‐quality single‐scan DECT imaging. Future studies will test method performance on anthropomorphic phantoms and perform quantitative analyses on image qualities and DECT decomposition accuracy. We will use simulations to optimize the modulator material and geometry parameters.
WE‐EF‐207‐11: Energy and Depth Response of Thermoluminescent Dosimeters and Ionization Chambers in Water for Kilovoltage X‐Ray Beams
Authors: Lawless M , Palmer B , DeWerd L
Published: June 2015

Purpose:

To assess the effects of changes in beam quality on detector response in the kilovoltage energy range by modulating the x‐ray tube voltage and the measurement depth in water.

Methods:

Measurements were performed with TLD‐100 and TLD‐100H thermoluminescent dosimeters and an A12 farmer‐type ionization chamber. To assess the energy response of the detectors, irradiations were performed at a depth of 3 cm in a custom‐built thin‐window water phantom using the moderately filtered x‐ray beams at the UWADCL (20 kVp‐250 kVp) and a Co‐60 beam.The x‐ray beams and detectors were modeled using the EGSnrc Monte Carlo code. The model was validated by simulating dose to the collecting volume of an A12 farmer chamber and comparing it with measured A12 signal as a function of depth. Dose was tallied to each detector and to water for comparison with measurements. Simulations were used to calculate the predicted energy response, which was compared to the measured response of each detector. Dose to each detector and dose to water as a function of depth were also simulated.

Results:

Detector output per dose to water was found to deviate by up to 15%, 20% and 30% as a function of energy relative to Co‐60 for the A12, TLD‐100H and TLD‐100, respectively. The EGSnrc simulations produced results similar to the measurements for ionization chambers, but discrepancies of up to 30% were observed for TLD‐100H. Simulated detector response as a function of depth was found to vary by up to 3%.

Conclusion:

These results suggest that changes in beam quality in kilovoltage x‐ray beams can have a significant impact on detector response. In‐water detector response was found to differ from the previously investigated in‐air response. Deviations in detector response as a function of depth were less significant, but could potentially cause dosimetric errors if ignored.
WE‐E‐201‐02: Phases, Levels, Controls, and All That: An Informal Session On Clinical Trials
Authors: Hipp E.
Published: June 2015

Physicists are often expected to have a solid grounding in experimental design and statistical analysis, sometimes filling in when biostatisticians or other experts are not available for consultation. Unfortunately, graduate education on these topics is seldom emphasized and few opportunities for continuing education exist. Clinical physicists incorporate new technology and methods into their practice based on published literature. A poor understanding of experimental design and analysis could Result in inappropriate use of new techniques. Clinical physicists also improve current practice through quality initiatives that require sound experimental design and analysis. Academic physicists with a poor understanding of design and analysis may produce ambiguous (or misleading) results. This can Result in unnecessary rewrites, publication rejection, and experimental redesign (wasting time, money, and effort).

This symposium will provide a practical review of error and uncertainty, common study designs, and statistical tests. Instruction will primarily focus on practical implementation through examples and answer questions such as: where would you typically apply the test/design and where is the test/design typically misapplied (i.e., common pitfalls)? An analysis of error and uncertainty will also be explored using biological studies and associated modeling as a specific use case.

Learning Objectives:

Understand common experimental testing and clinical trial designs, what questions they can answer, and how to interpret the results

Determine where specific statistical tests are appropriate and identify common pitfalls

Understand the how uncertainty and error are addressed in biological testing and associated biological modeling.
WE‐EF‐210‐01: Advances in Coherent Image Formation and Volume Imaging in Ultrasound
Authors: Rao B.
Published: June 2015

Recent advances in ultrasound‐related technologies have had a significant impact on enhancing image quality as well as offering new approaches for quantitative ultrasonic imaging and therapeutic applications. The presentations associated with this session will provide an overview of advances in ultrasound image formation, the development of using nanoparticles for therapeutic ultrasound applications, as well as approaches for assessing the intrinsic viscoelastic properties of tissue and methods for monitoring tissue response to therapy.

Learning Objectives:

Develop a general understanding of new technologies associated with enhanced ultrasound image formation and volume imaging.

Develop an understanding of new ultrasound‐based technologies for quantitative assessment of intrinsic tissue properties.

Develop an understanding of novel approaches for ultrasound‐mediated non‐invasive therapeutic applications.

Dr. Rao is an employee of Siemens Ultrasound
WE‐EF‐210‐05: Diagnosis and Quantification of Liver Steatosis with Quantitative Ultrasound Backscatter Technique
Authors: Andre M , Heba E , Han A , Lin S , Wolfson T , Ang B , Gamst A , Erdman J , O'Brien W , Sirlin C , Loomba R
Published: June 2015

Purpose:

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in the United States, affects 30% of adult Americans and may progress to more serious diseases. Liver biopsy is the standard method for diagnosing NAFLD. MRI can accurately diagnose and quantify hepatic steatosis but is expensive. Sonography with qualitative interpretation by radiologists is lower cost, more accessible but less sensitive for detection. The objective of this study, using MRI proton density fat fraction (PDFF) as reference, is to assess the accuracy for diagnosing and quantifying steatosis with two quantitative US parameters‐‐ backscatter coefficient (BSC) and attenuation coefficient (AC)‐‐derived from RF signals using the calibration phantom technique.

Methods:

We performed a prospective, cross‐sectional analysis of a cohort of adults (n=204) with NAFLD (MRI‐PDFF≥5%) and without NAFLD (controls). Subjects underwent MRI‐PDFF and BSC and AC US analyses of the liver on the same day. Patients were randomly assigned to training (n=102, mean age 51±17 years, mean body mass index 31±7 kg/m2) and validation (n=102, mean age 49±17 years, body mass index 30±6 kg/m2) groups; 69% of patients in each group had NAFLD.

Results:

BSC provided AUC 0.98 (95% CI 0.95–1.00, p<0.0001) for diagnosis of NAFLD; the optimal BSC cut‐off provided sensitivity, specificity, positive and negative predictive values (PPV, NPV) of 87%, 91%, 95%, and 76%, respectively. AC provided AUC 0.89 (95% CI 0.81–0.96, p<0.0001) for diagnosis of steatosis; the optimal AC cut‐off provided sensitivity, specificity, PPV, NPV of 80%, 84%, 92%, and 66%, respectively. BSC and AC both correlated significantly with MRI‐PDFF (P<0.0001).

Conclusion:

QUS BSC and AC can accurately diagnose and quantify hepatic steatosis, using MRI‐PDFF as reference. With further validation, QUS may emerge as an inexpensive, widely available tool for NAFLD assessment.

General support: NIH R01 CA111289, K23 ‐DK090303, AmerGastroAssoc Found, TF Williams Scholarship, S3000 scanner loaned by Siemens, Sucampo, JA Hartford Found, Atlantic Philanthropies Amer Gastroenterological Assoc. Agencies had no role in design/conduct of study, collection, management, analysis or interpretation of the data; preparation, review, or approval of the manuscript.
WE‐EF‐210‐06: Ultrasound 2D Strain Measurement of Radiation‐Induced Toxicity: Phantom and Ex Vivo Experiments
Authors: Liu T , Torres M , Rossi P , Jani A , Curran W , Yang X
Published: June 2015

Purpose:

Radiation‐induced fibrosis is a common long‐term complication affecting many patients following cancer radiotherapy. Standard clinical assessment of subcutaneous fibrosis is subjective and often limited to visual inspection and palpation. Ultrasound strain imaging describes the compressibility (elasticity) of biological tissues. This study's purpose is to develop a quantitative ultrasound strain imaging that can consistently and accurately characterize radiation‐induce fibrosis.

Methods:

In this study, we propose a 2D strain imaging method based on deformable image registration. A combined affine and B‐spline transformation model is used to calculate the displacement of tissue between pre‐stress and post‐stress B‐mode image sequences. The 2D displacement is estimated through a hybrid image similarity measure metric, which is a combination of the normalized mutual information (NMI) and normalized sum‐of‐squared‐differences (NSSD). And 2D strain is obtained from the gradient of the local displacement. We conducted phantom experiments under various compressions and compared the performance of our proposed method with the standard cross‐correlation (CC)‐ based method using the signal‐to‐noise (SNR) and contrast‐to‐noise (CNS) ratios. In addition, we conducted ex‐vivo beef muscle experiment to further validate the proposed method.

Results:

For phantom study, the SNR and CNS values of the proposed method were significantly higher than those calculated from the CC‐based method under different strains. The SNR and CNR increased by a factor of 1.9 and 2.7 comparing to the CC‐based method. For the ex‐vivo experiment, the CC‐based method failed to work due to large deformation (6.7%), while our proposed method could accurately detect the stiffness change.

Conclusion:

We have developed a 2D strain imaging technique based on the deformable image registration, validated its accuracy and feasibility with phantom and ex‐vivo data. This 2D ultrasound strain imaging technology may be valuable as physicians try to eliminate radiation‐induce fibrosis and improve the therapeutic ratio of cancer radiotherapy.

This research is supported in part by DOD PCRP Award W81XWH‐13‐1‐0269, and National Cancer Institute (NCI) Grant CA114313.