bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐C‐M100F‐02: Simultaneous Irradiation of Prone Breast and Regional Lymph Nodes Using Helical Tomotherapy
Authors: Kainz K , White J , Herman J , England M , Li X
Published: July 2007

Purpose: We investigate the capability of helical tomotherapy to simultaneously irradiate the involved breast and regional lymph‐node groups for breast‐cancer patients simulated in prone position. Method and Materials: We generated helical tomotherapy treatment plans for ten patients (five left breast, five right), each simulated with the involved breast suspended downward. Our target structures were the ipsilateral breast and the supraclavicular, axillary, and internal mammary chain nodes. Each target was to receive 45 Gy ± 5%. The region‐at‐risk (RAR) structures considered were the ipsilateral and contralateral lungs, contralateral breast, heart, spinal cord, esophagus, and thyroid. Results: The requirement for V45 ⩾ 95% was met for all target structures. The minimum point dose objective of 42.8 Gy was achieved for all lymph‐node structures, but for the ipsilateral breast the minimum dose on average was slightly less. The maximum point dose objective of 47.3 Gy was not achieved for any target structure; on average, it was 49.5 Gy. Among the RAR structures, contralateral breast V5 was kept below 2%. For left‐breast patients, the DVH goals for the heart were met; however, for right‐breast patients, although the aim was for the heart to receive zero dose, V10 was typically 0.4%. The other RAR DVH objectives that were not met were those for the ipsilateral lung V5 (the goal was 60% or less; 67% was achieved on average) and the esophagus V5 (the goal was 30% or less; the average was 41%). Conclusions: Helical tomotherapy can simultaneously cover the breast and regional lymph nodes with uniformity comparable to that achieved conventionally. The high ipsilateral‐lung V5 may be the primary limitation for clinical application, since there are reports that respiratory complications may correlate with the volume of lung irradiated to relatively low doses. All other RAR doses can be kept to clinically acceptable levels.
WE‐C‐M100F‐03: Underestimation Of Low‐Dose Radiation in Conventional Treatment Planning of Intensity‐Modulated Radiation Therapy
Authors: Jang S , Liu H , Mohan R
Published: July 2007

Purpose: In radiation therapy of thoracic cancers (e.g. lung cancers), a high volume of low‐dose radiation may lead to severe and fatal pulmonary complications. The purpose of this work is to investigate dosimetric accuracy in low‐dose regions from commercial treatment planning systems (TPS) and consequent clinical implications for using IMRT in treating lung and thoracic cancers. Methods and Materials: We retrospectively reviewed thoracic‐cancer patients treated with IMRT at our institution and for whom high‐grade lung complications occurred. These IMRT plans were evaluated and were recomputed using a Monte‐Carlo‐based (MC) treatment planning system (TPS) that explicitly accounts for modeling of the machine head and MLCs. Dose calculations from 2 commercial TPSs (Pinnacle and Corvus systems) were compared with those obtained from the MC system and measurements. Various factors that could contribute to the difference in IMRT dose calculations were analyzed, including tissue heterogeneity effect, MLC modeling, and beam modeling. Results: Significant dosimetric errors (∼25%) were found in the low‐dose regions below 5 Gy in the commercial TPSs. Accuracy of dose calculations in the high‐dose tumor regions was acceptable (< 5%). In regions < 5 Gy of IMRT plans, MLC transmission, leakage, and scattering were found to be important contributors to the dose. These factors were also spatially variant and field‐size dependent. Without explicit modeling of the MLCs, severe underestimation of the low‐dose volume could occur in commercial TPS. The degree of low‐dose error was particularly greater in IMRT plans with larger target volumes and higher degrees of beam modulation. Conclusions: Treatment planners should be aware of potentially significant underestimation of low doses in IMRT treatment plans for thoracic and other cancer sites. More accurate modeling of MLCs and low‐dose calculation may be achieved by using a Monte‐Carlo‐based planning system.
WE‐C‐M100F‐07: The Treatment of Bilateral Orbital Lymphoma with Solid Modulator IMRT
Authors: Wichman B , Radice V , Cashon K , Hoskins B , Kiefer E
Published: July 2007

Purpose: To determine the feasibility of solid modulator IMRT (SM‐IMRT) for a patient with bilateral orbital lymphoma and to compare this technique with historically used methods. Method and Materials: After immobilization and CT simulation, a CTV was contoured consisting of the entire orbital volume minus the globes. A 3 mm margin was added to generate a PTV. A dose of 34 Gy in 2 Gy fractions was prescribed to the PTV. Dose constraints were placed on the lacrimal glands, lenses, optic chiasm, and pituitary. Treatment plans were constructed for SM‐IMRT, wedged pair fields, and en face photon fields. Due to acute symptoms, treatment commenced with en face photons while planning continued. A fourth plan consisting of mixed SM‐IMRT/en face photons was constructed. Results: Acceptable target coverage was obtained with all four plans. The SM‐IMRT plan offered significant sparing to the lenses, optic chiasm, and pituitary. The mixed SM‐IMRT/en face photon plan (13 of 17 fractions IMRT) also offered significant sparing, though not at the level of the pure SM‐IMRT plan. The maximum dose objective of 30 Gy for the lacrimal glands was almost met with the SM‐IMRT plan (10% over 30 Gy). The wedged pair plan produced the most homogeneous target dose, though only because there was no attempt to sculpt dose to avoid critical structures as with SM‐IMRT. SM‐IMRT was chosen for further patient treatment. Quality assurance tests on the modulators showed excellent agreement between planning system calculations and measured dose, validating the data transfer and modulator milling process. Conclusion: SM‐IMRT is a feasible treatment modality for bilateral orbital lymphoma. The technique offers the ability to spare critical structures that is impossible with traditional techniques. Dose can be modeled accurately for the solid modulators. A drawback of this or any IMRT technique is the longer treatment plan preparation time.
WE‐C‐M100F‐08: Use of Adaptive Filtering and Relative Intensity Limits in Deliverable IMRT Optimization to Improve Delivery Efficiency
Authors: Dogan N , Wu Y
Published: July 2007

Purpose: To investigate the effect of adaptive filtering, relative intensity limits, and fluence matrix resolution in deliverable IMRT optimization on MU efficiency and plan quality for dynamic MLC delivery. Method and Materials: An adaptive filtering method that filters the optimized intensities as needed in combination with different relative intensity limits were used to reduce MUs needed to deliver the beams. The adaptive filtering parameters were adjusted so that it achieved the optimal results. A deliverable‐based optimization that incorporates beam‐delivery constraints directly into the IMRT optimization process was used. H&N and prostate cases were used to evaluate the quality and complexity of each plan. Each case was optimized with and without adaptive filtering and in combination with a series of relative intensity limits for fluence matrix resolution of 1.5 mm to 6 mm. The IMRT plans were evaluated in terms of dose‐volume statistics, MUs, and the complexity of fluence matrix resolution. Results: Up to 47.5% reductions in MUs were achieved using adaptive filtering in combination with relative intensity limits. When the adaptive filtering is on, the use of a relative intensity limit of 1.5 further reduced the total MUs by 6.3% and 15.9% for a fluence matrix resolution of 3‐ and 6mm respectively. Adaptive filtering in combination with relative intensity limits was able to reduce the total MUs without significantly changing the prostate and nodal PTV coverages. The changes in critical structure doses were negligible. The similar results have been obtained for the H&N case included in the study. Conclusion: The adaptive filtering was able to significantly reduce total MUs without compromising the plan quality for deliverable IMRT optimization process. The use of relative intensity limits in combination with adaptive filtering did not have a significant effect on MU efficiency as compared to the use of adaptive filtering alone.
WE‐C‐BRA‐01: Introduction
Authors: Nahum A
Published: July 2007

Advances in technology and in computing have given us computer‐controlled linear accelerators equipped with multileaf collimators and wonderful 3D graphics workstations to perform treatment planning; additionally we have conceptual advances such as stereotaxy (cranial and extra‐cranial) intensity modulation (IMRT), helical tomotherapy and protons. But the bottom line in radiotherapy is radiobiology, radiobiology, radiobiology. If we don't know how to convert ‘physics’, i.e. dose distributions, into estimates of clinical outcome then these wonderful technological advances will remain ‘toys’ for physicists to play with.

Radiobiology has traditionally concerned itself with determining surviving fraction vs. (uniform) dose curves for human tumour cell lines. However, in the 3D era we need models which connect dose distributions (and fractionation regimens) in tumours and normal tissues (generally in the form of dose‐volume histograms) with the probabilities of tumour (local) control — TCP — and of complications — NTCP. Such models now exist and their active use in treatment planning ushers in the era of Conformal Radiobiology.

Educational Objectives:

1. Appreciate the limitations of technology‐driven dose‐based radiotherapy.

2. Appreciate the limitations of ‘classical’ radiobiology in the conformal era.

3. Understand what is meant by ‘Conformal Radiobiology’.
WE‐C‐BRA‐02: Parameters for and Use of NTCP Models in the Clinic
Authors: Yorke E
Published: July 2007

Delivery of adequate tumor dose without causing excessive normal tissue complications is the driving principle of modern radiation therapy. Resulting dose distributions in normal tissues are very different from the “partial organ irradiation” distributions that characterize the simple beam arrangements of earlier days. Further, the growing popularity of hypofractionation drastically widens the range of biological effective doses within organs at risk (OAR). The clinical physicist is faced with uncertainty as to what aspects of an OAR dose distribution require special consideration in treatment plan design and evaluation.

Normal tissue complication probability (NTCP) models are one way to account for the full dose distribution. For most serious toxicities, statistical models from various outcomes analyses help direct the planner toward dose‐volume limits. There are also several semi‐mechanistic models, each with a set of parameters that must be adjusted to describe existing data. But for conditions that differ greatly from those under which they were ‘commissioned’, two models for the same endpoint and starting from the same input dose distribution do not necessarily predict the same NTCP. A working group, with joint participation from AAPM, ASTRO and RTOG, is being established to, among other things, reconcile model differences and provide clinical guidelines in the near future.

In this presentation, common NTCP models for several major dose‐limiting toxicities will be described, including parameters sets gleaned from literature review. Problems and pitfalls of integrating and interpreting diverse studies and applying them to an individual clinic's practice will be discussed and real‐world examples of application to clinical decisions will be presented.

Educational Objectives:

1. Understand the important features of the most widely‐used NTCP models.

2. Understand how the model parameters affect predictions of normal tissue dose‐volume responses.

3. Understand some of the complexities of implementing these models into routine clinical practice.
WE‐D‐L100J‐02: Effect of Matrix Size On SNR and Contrast Ratio On Super‐Resolution Processing of PET Images
Authors: Chang G , Pan T , Qiao F , Clark J , Mawlawi O
Published: July 2007

Objectives: Super resolution (SR) techniques reconstruct a high resolution image from a series of low resolution images taken from different points of view of the same object. The aim of this abstract is to investigate how CR and SNR vary with SR processing of images initially reconstructed using different matrix sizes. Methods: A Jaszczak phantom with a hot spot insert was scanned on a DISCOVERY STE PET/CT scanner. The phantom was filled with 0.34uCi/cc and scanned for 15 minutes in 2D. A NEMA IEC phantom containing six spheres was also scanned for 3 minutes in 2D using a sphere‐to‐background ratio of 5.34:1. SR images of 512*512 were then generated for all acquired data using 3 different matrix sizes and image combinations: A) 64 images of 64*64, B) 16 128*128, and C) 4 256*256. In each case, the pixel grid was offset by 1 mm along the X and Y axes. All reconstructions were done using OSEM with a FOV of 51.2 cm. In addition, each original low resolution image was up‐sampled to a 512*512 image. Resolution and contrast ratio were assessed by plotting line profiles across cylinders of different sizes in the Jaszczak phantom of each high resolution image (SR and up‐sampled) while SNR was determined by drawing ROIs on all spheres and background in the IEC phantom. In addition, 5 lung nodule patient studies were processed using these 6 methods and assessed visually. Results: Line profiles showed that the contrast ratio constantly increased from A to C by 180%, while the SNRs decreased by 56%. SR images always produced higher CR (143–214%) and lower SNR (65–78%) compared to their up‐sampled counterparts. Comparison of patient studies showed that method B had the best overall image quality. Conclusion: SR processing using 16 128*128 images results in the optimum clinical image quality.
WE‐D‐L100J‐03: Model Based Respiratory Motion Compensation Using Static PET Acquisition
Authors: Qiao F , Pan T , Clark J , Mawlawi O
Published: July 2007

Purpose: Model based respiratory motion compensation in PET imaging usually assumes PET data to be acquired in gated mode and then models motion during the image reconstruction process (gated‐MC). In this abstract we introduce and evaluate a new approach whereby motion compensation is performed on static PET data while an overall motion is incorporated into the system model (static‐MC). Method and Materials: A phantom consisting of two hot spheres placed in a warm background was scanned using the GE DST PET/CT scanner. One sphere was stationary while the other moved sinusoidally (2cm excursion, 5sec period) in the axial direction during the scan. A 4D‐CT was then performed followed by a list‐mode PET scan of 3 minutes, with gating signals injected into the list‐data stream. The PET data were then unlisted into a single static as well as 10 gated sinograms. Motion was either estimated by registering the 4D‐CT image sequence (RM) or derived from the true sinusoidal motion (TM). Images were reconstructed using OSEM and the following combinations of motion and acquisition schemes were compared: 1) TM+gated; 2) RM+gated; 3) TM+static; 4) RM+static. Evaluation was done by visual inspection and line profiles. In addition, a plot of contrast recovery rate (CRR) versus noise was generated by changing the number of reconstruction iterations. Results: Both static‐MC and gated‐MC approaches showed similar CRR at the same noise level. Visual inspection and line profiles showed that when using TM, the Gated‐MC and Static‐MC had similar image qualities; however with RM, the Gated‐MC performed better. Furthermore, the change in CRR when using RM versus TM was larger for the static‐MC when compared to the gated‐MC approach (3.1% static‐MC compared to 0.2% gated‐MC). Conclusion: Motion compensation without gating PET acquisition is feasible. However, the static‐MC approach is more sensitive to inaccuracies in motion estimation.
WE‐D‐L100J‐07: High‐Resolution Digital Ultrasonic Thermometers
Authors: Malyarenko E , Heyman J , Chen‐Mayer H , Tosh R
Published: July 2007

Purpose: To develop and test 1) fully digital μK‐resolution ultrasonic thermometer for non‐invasive measurements of absorbed radiation dose in water; 2) rapid ultrasonic 2D temperature mapping system for precise characterization of radiation beam intensity profiles. Method and Materials: Monitoring tiny phase shifts of ultrasonic signals in water heated by ionizing radiation allows assessing water temperature changes at the μK level. Instead of the analog frequency‐driven Pulsed Phase‐Locked Loop (PPLL) used in the earlier work to track signal phase, the current system relies on fast digital phase algorithms that extract signal delay with resolution of 100ppb and better. Another ultrasonic system was built to produce 2D temperature maps in water. This system contains a 128‐element, 14″‐diameter circular transducer array operating in a tomographic fan‐beam data acquisition mode. The system acquires temperature maps in seconds and allows monitoring evolution of thermal processes in time. Results: The single‐channel digital ultrasonic thermometer demonstrated resolution equivalent or better than analog PPLL‐based prototype at overall lower noise level. The 2D temperature mapping system was constructed and went though a preliminary testing round. It monitored evolution of temperature profile in the cylindrical tank every 3–4 seconds acquiring each time a 64‐projection data set with 45 rays per projection. After extracting phase information from the acoustic waveforms the system reconstructed a sequence of phase shift images and converted them to temperature maps using newly developed calibration procedure. The maps were combined into movies to watch temperature evolution dynamics. Conclusion: The digital high‐resolution ultrasonic thermometer demonstrated performance improvement and will replace its analog predecessor in the radiation‐testing lab. The 2D ultrasonic temperature mapping system was successfully tested with a light radiation heating source. We plan to continue characterizing its spatial and temperature resolution and incorporate all findings into a next‐generation prototype for ionizing radiation testing.

Research sponsored by NIST.
WE‐D‐L100F‐01: Highly Accelerated MRI Using Undersampled Acquisition and HYPR Processing
Authors: Mistretta C , Wieben O , Velikina J , Wu Y , Johnson K , Korosec F , Fain S , Block W , Wu Y , Perry J , Keith L , Kecskemeti S , Khansa I , Wang K , Grist T , Reeder S , Lum D , Turk A , Aagard‐Kienitz B , Turski P
Published: July 2007

During the past several years there has been a growing body of research developments that might be considered the beginning of a “Post Nyquist Era” in medical imaging. Investigators at Stanford and Cal Tech have shown that the iterative non‐Fourier reconstruction “Compressed Sensing” method can be used to reconstruct single images with far less than the required number of Nyquist samples [1,2] for image data sets that satisfy certain sparsity requirements. The recent developments in parallel imaging also permit the reconstruction of relatively artifact free images by synthesizing missing k‐space information using sensitivity profiles from multiple coils[3,4]. Our group has been investigating the use of VIPR, a vastly undersampled radial imaging technique [5,6] that almost immediately provides full spatial resolution after a small number of excitations at the expense of streak artifacts. In 3D these artifacts are quite incoherent and provide little degradation of image quality. Data undersampling factors of several hundred relative to the Nyquist criterion have been achieved. Recently VIPR has been combined with a new reconstruction method called HYPR (HighlY constrained PRojection reconstruction) [7] that exploits the spatio‐‘temporal’ redundancy in medical image sequences involving any serial change in an imaging variable such as time, echo time, diffusion tensor encoding direction, etc. Using HYPR in combination with VIPR, angular undersampling factors on the order of 1000 in phase contrast angiography have been achieved with good image quality. A fundamental characteristic of HYPR is its ability to provide higher SNR than competing acceleration technique. The HYPR technique has been applied to X‐ray CT angiography where clinically acceptable time‐resolved angiographic image series have been reconstructed using 1/46th of the conventional x‐ray dose.

Educational Objectives

1. To understand the advantages of 3D radial undersampling for increasing spatial and temporal resolution.

2. To understand how HYPR provides further acceleration with substantial preservation of SNR.

3. To understand how HYPR may be applied in a wide variety of medical imaging applications.
WE‐D‐L100F‐02: Parallel Magnetic Resonance Imaging (or, Scanners, Cell Phones, and the Surprising Guises of Modern Tomography)
Authors: Sodickson D
Published: July 2007

Today, parallel data acquisition approaches are used widely in MRI, both for clinical diagnostic imaging and for research applications. Whereas in a traditional sequential MRI scan, data are collected one point and one line at a time in the presence of varying magnetic field gradients, parallel MRI uses spatial information from arrays of radiofrequency detector coils to acquire multiple data points simultaneously, thereby circumventing basic limits on imaging speed and efficiency associated with traditional sequential approaches. The use of RF coil information in combination with the traditional Fourier information available from field gradients increases the complexity of image reconstruction. In fact, parallel MR image reconstruction may be represented as a generalized linear inverse problem. This formulation highlights connections with other modalities as well as shedding light on both the potential and the limitations of parallel imaging. In this talk, the fundamentals of parallel MR image acquisition and reconstruction will be reviewed. Analogies with X‐ray computed tomography, MIMO wireless communication, and magnetoencephalography will be explored, and some future directions in parallel MR reconstruction algorithms, hardware design, and clinical applications will be surveyed.

Educational Objectives:

1. Understand the basic physical principles of parallel MR data acquisition and the basic mathematical principles of parallel MR image reconstruction.

2. Recognize analogies with other imaging modalities and communication technologies.

3. Identify fundamental physical (electrodynamic) limits of performance of parallel MRI systems.

4. Appreciate some of the most common current and the most promising future clinical applications of parallel MRI.
WE‐D‐L100F‐03: Direct and Indirect Magnetic Resonance Visualization of Tissue Architecture and Function: From Micro to Nanostructure
Authors: Wehrli F W
Published: July 2007

“Form follows function” is one of the most fundamental principles underlying evolution of all organisms. Thus the desire to visualize tissue architecture has been a key driver behind all forms of microscopy starting with the magnifying lens, and leading to optical and, eventually, electron microscopy. During the past two decades methods have emerged that allow nondestructive imaging of the internal 3D structure of tissues by micro magnetic resonance (μ‐MRI) and computed tomography (μ‐CT) at resolutions of 5–50μm. MRI's unique sensitivity to biologic processes such as the interaction of water with biomolecules makes it particularly attractive as an investigational tool in biomedicine. However, the practically achievable resolution is determined by signal‐to‐noise and ultimately, diffusion, and in vivo by our ability to correct for physiologic motion. Though below the resolution limit of k‐space μ‐MRI, indirect detection techniques such as q‐space imaging, which exploit restricted diffusion, can be shown to provide quantitative information at sub‐μm resolution in some instances. This lecture intends to provide an overview of the methodology and to discuss various applications ranging from quantifying the architectural and mechanical changes of trabecular bone architecture in response to intervention in humans, to measurement of axon diameters in the mouse spinal cord by q‐space MRI using 50T/m home‐built gradients.
WE‐D‐M100J‐04: Prediction of Lung Radiation‐Induced Pneumonitis Using the Support Vector Machine Algorithm
Authors: Chen S , Zhou S , Zhang J , Marks L , Das S
Published: July 2007

Purpose: To build and test a Support Vector Machine (SVM) model to predict the occurrence of lung radiation‐induced Grade 2+ pneumonitis. SVM is a sophisticated statistical technique that is capable of using complex hypersurfaces to separate the cases with and without pneumonitis. Method and Materials: Two SVM models were built using data from 235 patients with lung cancer treated using radiotherapy (34 diagnosed with pneumonitis). One model (SVMall) selected input features from all dose‐volume and non‐dose factors. For comparison, the other model (SVMdose) selected input features only from lung dose‐volume factors. The models were built with in‐house developed software that employed a unique strategy to sequentially add/remove/substitute features. The SVM models were tested using ten‐fold cross‐validation, wherein 1/10th of the data were tested, in turn, using the model built with the remaining 9/10th of the data. Results: The input features selected to build SVMall were the lung generalized equivalent uniform dose (EUD) with exponents a=1.2, 1.3, 1.4, chemotherapy prior to radiotherapy (yes/no), tumor location (central/peripheral), gender, and histology (adenocarcinoma/other; small cell/other). The input features for SVMdose were EUD a = 1.1, 1.3, 1.4, lung volume receiving > 48 Gy (V48), and V50. Both models selected EUD a ≈ 1 (EUD a=1 is the mean lung dose, which frequently appears as a strong predictor of radiation pneumonitis in literature). The area under the cross‐validated SVMall Receiver Operating Characteristics curve was 0.76 (sensitivity/specificity = 74%/75%), compared to the corresponding SVMdose area of 0.71 (sensitivity/specificity = 68%/68%). SVMall was statistically superior (p=0.01), indicating that non‐dose features significantly contribute to separating patients with and without pneumonitis. Conclusions: The SVM model constructed from dose and non‐dose input factors is a valuable prospective tool for predicting the occurrence of radiation‐induced lung pneumonitis.
WE‐D‐BRA‐01: MLC Based Delivery and Serial Tomotherapy Experience
Authors: Salter B
Published: July 2007

IMRT, by virtue of the increased degrees of delivery freedom available, requires the utilization of advanced optimization approaches (so‐called inverse planning techniques). While such inverse planning optimization approaches make possible the solution of these otherwise intractably large problems, they impose unique challenges with regard to the treatment of multiple targets with different desired total delivered dose levels. In this session we will discuss and characterize these challenges and discuss various “workarounds” to these problems, along with their potential implications and ramifications.
WE‐D‐BRA‐02: Helical Tomotherapy Experience
Authors: Ramsey C
Published: July 2007

Helical tomotherapy is a rotational radiation therapy delivery technique that combines pre‐treatment CT‐based image‐guidance and Intensity‐Modulated Radiation Therapy (IMRT) using a fan‐beam delivery. Helical tomotherapy treatments are delivered by a continually rotating gantry mounted on a slip ring system, which permits power and communications to be passed from the rotating to stationary sub‐systems. Treatments are delivered with both the gantry and the couch in continuous simultaneous motion. Thus, helical tomotherapy can continuously deliver intensity‐modulated radiation from 360° in a transverse plane about the patient.

In addition to its ability to deliver IMRT, helical tomotherapy systems also have the ability to obtain Megavoltage CT (MVCT) images of the patient in the treatment position prior to each treatment fraction. Daily positional uncertainties and anatomical changes (such as weight loss, tumor response, etc…) can be minimized by utilizing CT‐based pre‐treatment imaging. As such, the position of the tumor relative to the treatment beam can be corrected prior to treatment by moving the patient with appropriate superior‐inferior, anterior‐posterior, lateral, pitch, roll, and/or yaw offsets.

The combination of precise positioning of the target volume and the rotational nature of the delivery make helical tomotherapy well suited for simultaneously delivering differential doses to multiple targets. Treatment sites that are large in the superior‐inferior direction are easily treated with helical tomotherapy. Multiple target volumes up to meter in length can be treated in a single helical tomotherapy delivery sequence. This can be useful for treating multiple metastases throughout the body while avoiding nearby critical structures. Head and Neck patients can be treated with integrated boosts with minimal dose spillover, dumping, hot spots, or critical structure problems. Shrinking lung tumors can be treated with a simultaneous integrated volume‐adapted boost (SIVAB) that allows dose escalation to the residual tumor mass without compromising normal tissue tolerance and dose to areas at risk for microscopic tumor spread. For prostate patients that are at risk for nodal involvement, the regional lymph nodes, the seminal vesicles, and the prostate can be simultaneously targeted and treated to different doses.

This lecture will provide an overview of clinical scenarios utilizing differential dose delivery with helical tomotherapy. The advantages and disadvantages of helical tomotherapy will be discussed for each clinical example.

Educational Objectives:

1. Provide a brief overview of the helical tomotherapy system's imaging and treatment capabilities.

2. Present clinical scenarios for utilizing differential dose delivery with helical tomotherapy.

3. Discuss potential applications of adaptive differential dose delivery.
WE‐E‐L100J‐01: Simulation of Tomosynthesis Mammograms with Cone Beam CT Images of Mastectomy Breast Specimens
Authors: Shaw C , Han T , Chen L , Altunbas M , Lai C , Liu X , Wang T , Yang W , Whitman G
Published: July 2007

Purpose: To describe and discuss about a technique to simulate digital mammograms and tomosynthesis images with cone beam CT images of mastectomy breast specimens. Method and Materials: To allow x‐ray images to be simulated, cone beam breast CT images of a mastectomy breast specimen were acquired at 80 kVp and used to generate a 3‐D map of linear attenuation coefficients for mammographic x‐rays. The map was then deformed to generate a new map for a compressed breast. A software re‐projector was developed and used to compute projection images for a stationary detector and a linearly shifted x‐ray source. A special re‐projector was developed to preserve the contrast of microcalcifications (MCs). The resulting images were then used to reconstruct tomosynthesis mammograms using various reconstruction algorithms. Results: We have successively used cone beam CT images of mastectomy breast specimens to generate 3‐D maps of attenuation coefficients to model compressed breasts and to use them to simulate digital mammograms and tomosynthesis images. It was found that MCs clearly visible in cone beam CT images were not visible in regular mammograms but faintly visible in tomosynthesis images. The MCs were clearly visible in both MC enhanced mammograms and the tomosynthesis images reconstructed from them. Conclusions: Cone beam CT images may be used to model a compressed breast for simulating mammograms and tomosynthesis images. Cone beam CT images are superior to regular or tomosynthesis mammograms in depicting MCs within their resolution limit. MC enhanced re‐projection, however, could be useful in displaying the cone beam CT images with the more conventional appearances of regular and tomosynthesis mammograms while maintaining the contrast and visibility of MCs in the CT images.

This work was supported in part by a research grant EB00117 from the NIH‐NIBIB and a research grant CA104759 from the NIH‐NCI.
WE‐E‐L100J‐02: A Phantom Study of Contrast‐Enhanced Dual Energy Mammography (CEDEM)
Authors: Huang S , Zheng D , Boone J , Yang K , Packard N
Published: July 2007

Purpose: To optimize and study the effectiveness of CEDEM using simple breast‐equivalent phantoms in the experimental setting. Method and Materials: The experimental evaluation of CEDEM was performed using a dedicated cone‐bream breast CT scanner in our laboratory, with the system operating in stationary imaging mode. A series of physical phantoms approximating the anatomical complexity of the breast were fabricated. Polyethylene and water were used for the adipose and glandular aspects of the breast phantom, respectively, due to their similar x‐ray attenuation characteristics. Holes of various sizes were randomly drilled on the polyethylene slabs to create an “anatomical” noise pattern. Rectangular cells (cuvettes) filled with various iodine concentrations were placed in a polyethylene slab to maintain a homogeneous projected iodine thickness (mg/cm2). When imaged experimentally, the polyethylene slab with five cuvettes of various iodine concentrations was overlaid with a number of the slabs with pseudo‐anatomical noise distributions while immersed in a plastic container filled with water. Data were acquired at 55 kVp and 100 kVp (suggested by computer optimization) with additional elemental filters (0.1 – 0.3 mm copper filtration), and dual‐energy subtracted images were produced. Results: Preliminary results were acquired at 55 kVp and 100 kVp (0.3 mm additional copper filtration). The sensitivity to iodine contrast agent in the dual‐energy subtracted image (signal‐difference‐to‐noise ratio (SDNR) per mg/cm2) was evaluated and found to be linear with concentration. The influence of the breast phantom thickness, composition, and dose on contrast enhancement at different kVp combinations will be presented. Conclusion: The effectiveness of CEDEM with an anatomical‐complex phantom was evaluated. The results indicate that the dual‐energy subtracted image can enhance the iodine contrast agent with background anatomical structures. This approach may be useful for the evaluation of the kinetic curve in contrast enhanced breast imaging procedures.
WE‐E‐L100J‐05: Radiation Dose to Tissues From Mammography
Authors: Sechopoulos I , Suryanarayanan S , Vedantham S , D'Orsi CJ , Karellas A
Published: July 2007

Purpose: To compute the radiation dose to different tissues of the body from a standard mammogram. Method and Materials: Using the Geant4 Monte Carlo toolkit, a simulation was developed in which the human body was represented using a mathematical anthropomorphic phantom. A total of 66 different organs and tissues were simulated, including the uterus, which was used to compute the dose to the fetus during early‐stage pregnancy. The imaged breast was represented as compressed, and in both the cranio‐caudal and the medio‐lateral oblique views. At each energy level, the simulation emitted 60 million monochromatic x‐rays and recorded the location of each interaction and the amount of energy deposited. The dose to the red bone marrow and to the bone surfaces of each bone was estimated separately. The monochromatic data was used to compute the resulting dose for different typical polyenergetic mammographic spectra, and the values were normalized to the resulting glandular dose to the breast, resulting in the dose ratio. The effectiveness of using a lead shield between the patient and the x‐ray field was also investigated. Results: Only 16 organs and skeletal tissues received a dose higher than 0.10% of the glandular dose to the breast. Of the organs, the contralateral breast received the highest dose ratio with 0.62%. Of the skeletal tissues, the sternum received the highest dose, with a dose ratio of 2.36% to the bone surface and 0.56% to the bone marrow. The dose to the uterus and fetus received a maximum dose ratio of <10−5. The lead shield did not lower the dose values substantially. Conclusion: The radiation dose to all tissues outside the x‐ray field, including the fetus, during standard mammography is extremely low.
WE‐E‐M100F‐06: Latency Measurements and Demonstration of a 4D Electromagnetic Localization System for LINAC Beam Gating
Authors: Shepard DM , Housley DJ , Afghan MKN , Sargent B , Peterson J , Newell J
Published: July 2007

Purpose: The Calypso® 4D Localization System uses electromagnetic fields to localize and track Beacon® transponder implants. In this study, we used the Calypso® System to perform real‐time beam gating based on transponders mounted to a dynamic phantom. The system's latency was studied in conjunction with a Varian linac to determine feasibility of enabling gated radiation therapy delivery for respiratory applications. Method and Materials: An acrylic transponder holder with three embedded Beacon® transponders was placed 6 cm from the center of a rotating disk on a dynamic phantom. Film measurements were made with a 2 cm by 2 cm field delivered in a static, dynamic‐gated, and dynamic‐non‐gated fashion. A linear gating window with a 2 mm width was used for the film demonstration. Latency measurements compared an in‐volume / out‐of‐volume signal obtained directly from the dynamic phantom to the target‐current signal from the linac. The target signal represents the measured current in the MV electron beam, and is directly correlated to the presence (or absence) of the treatment beam. The investigational prototype gating system does not used predictive modeling; the linac beam is enabled when the transponder is within the gating window based solely on the last position estimate of the transponder. Results: Film measurements demonstrated that signals from a prototype electromagnetic gating system can be used to effectively trigger the beam on/off state of a linac. The combined, motion‐triggered latency of the localization system and linac was 65 msec to disable the beam and 75 msec to enable the beam. Conclusion: Use of wireless electromagnetic implanted transponders has the potential to enable real‐time linac beam gating with the latency and update rates required for respiratory applications without the use of predictive algorithms.
WE‐E‐M100F‐07: Prostate Intrafraction Motion Measurement Using KV Fluoroscopy During Treatment Delivery
Authors: Adamson J , Wu Q
Published: July 2007

Purpose: Margin reduction for prostate radiotherapy is limited by uncertainty in prostate localization during treatment. We investigate the feasibility and accuracy of measuring prostate intrafraction motion using kV fluoroscopy performed simultaneously with radiotherapy. Method and Materials: Three gold coils used for target localization are implanted into the patient's prostate gland before undergoing a hypofractionated online image‐guided step‐and‐shoot IMRT on an Elekta Synergy. At each fraction the patient is aligned using a CBCT, treatment delivery and fluoroscopy are performed simultaneously, and a post‐treatment CBCT is acquired with the patient still on the table. To measure the intrafraction motion we developed an algorithm to register the fluoroscopy images to the projection images of the post‐treatment CBCT, and we combined information from fluoroscopy images at different gantry angles to obtain the motion of the coils in 3D. The accuracy and robustness of this technique were evaluated by comparing measured results with those from an independent clinical 3D CBCT registration. Results: The coils can be detected and successfully registered using fluoroscopy images for all gantry angles, and at some angles they can be tracked with frequency > 1 Hz. Fluoroscopy images containing MV scatter can be detected and if necessary removed to improve image quality. The mean of the difference between our intrafraction measurement technique and the independent 3D CBCT registration for 40 measurements was 0.04 ± 0.47 mm, −0.07 ± 0.76 mm, and −0.21 ± 0.80 mm in the RL, AP, and SI axes respectively. Conclusion: These results show that measuring prostate intrafraction motion using kV fluoroscopy is feasible and can be performed with sub‐millimeter accuracy and adequate temporal resolution. Future work includes improving 2D registration to account for prostate rotation and deformation, and reporting clinical results. Conflict of Interest: Partially supported by NIH Grant CA118037.
WE‐E‐AUD‐02: Dose Rate Measurements of An Electronic Brachytherapy Source Using Thermoluminescent Dosimeters in Water
Authors: Pike T , Davis S , Palmer B , DeWerd L
Published: July 2007

Purpose: To measure the dose rate of an electronic brachytherapy source using thermoluminescent dosimeters (TLDs) in water. Method and Materials: Dose rates from several Xoft Axxent™ electronic brachytherapy sources were measured using TLD microcubes (1 mm × 1 mm × 1 mm). The sources were operated at 50 kV and at a beam current of 100 μA. Measurements were done in liquid water to avoid the large conversion from water mimicking plastics to liquid water at low energies. A Virtual Water™ apparatus was designed to position the TLD microcubes in water specifically so that no Virtual Water™ was between the sources and microcubes during irradiation. The design allowed for the placement of 12 TLDs in 30° increments around the source on the transverse axis. A positioning disk was designed to accurately position the center of the TLDs at 3 cm from the center of the source and to position the center of the sources at the same height as the center of the TLDs. Air kerma rate measurements were done with a well‐type ionization chamber fitted with a custom‐built aluminum source holder. The measured air kerma rates were used to calculate the desired irradiation time to deliver an estimated 70 and 130 cGy dose to water at 3 cm from the sources. Results: The dose rates measured with the TLD microcubes were lower than the Monte Carlo predicted values. Air kerma rates measured were also determined to be lower than the Monte Carlo predicted values, but the measured ratio of dose rate to air kerma rate agreed with the Monte Carlo predicted values. Conclusion: TLDs can be used in water to determine dose rates of electronic brachytherapy sources, but further work is necessary to confirm measured values. Conflict of Interest: Funding for this research was provided by Xoft, Inc.
WE‐E‐BRA‐03: Modelling Ionisation Chamber Response to Non‐Standard Beam Configurations
Authors: Tantot L , Bouchard H , Seuntjens J
Published: July 2007

Purpose: To present a framework for the calculation of ionisation chamber response to arbitrary modulated fields as a convolution of responses to narrow fields and to test this approach for realistic chamber geometries in open fields. Materials and Methods: Using the EGSnrc/C++ Monte Carlo (MC) class library system, the response of a detailed model of the Exradin #a12 chamber was calculated for and 6 MV pencil beams sweeping over a flat phantom. A pencil beam response kernel was collected for an irregularly spaced array of pencil positions. A procedure was developed to reconstitute chamber response in modulated fields by convolution of pencil beam response over the modulated field fluence. We tested the accuracy of this approach by comparing in open fields the relative calibration coefficients obtained for realistic chamber geometries reconstituted from pencil beam kernels with calibration coefficients obtained directly. Results: MC kQ values within 0.1% and 0.4% of TG‐51 for 6 MV and 18 MV photon beams, respectively. Pencil beam kernels showed that the response of the chamber is strongly dependent on the geometrical details of the chamber for pencil beam positions hitting areas such as chamber tip, tip of the electrode, etc. Open field reconstituted chamber response was in agreement with direct calculations of the open field response to within 0.3% for and 6 MV photon beams. Conclusions: Ionisation chamber response in modulated fields is strongly dependent on the details of the delivery. However, we can accurately account for it with our method, in which chamber response in arbitrarily modulated radiation beams can be calculated by convolving pre‐calculated response kernels over the actual fluence profile used in the delivery of modulated radiotherapy. These techniques will allow guidance of chamber‐based IMRT QA procedures by correcting chamber readings during deliveries that potentially provoke electronic disequilibrium.
TH‐C‐AUD‐08: Comparison of Tomotherapy Dose Distributions for 6MV X‐Rays and Different Cobalt‐60 Source Designs Using Monte Carlo Methods
Authors: Joshi Chandra P , Darko Johnson , Dhanesar Sandeep K , Vidyasagar P B , Schreiner L John
Published: July 2007

Purpose: To investigate intensity modulated dose distributions for Co‐60 based tomotherapy with cylindrical and rectangular shaped source geometries for a typical head and neck case using Monte Carlo (MC) methods. Method and Materials: EGSnrc/BEAMnrc MC code has been used to model three Co‐60 tomotherapy units and a 6 MV (Varian 2100EX) unit. Two of the Co‐60 units, consisting of modified collimator systems with customized binary multi‐leaf collimator (BMLC) were modeled for 3 and 5 cm long rectangular sources and SADs of 70 and 80 cm, respectively. The other units were a conventional Co‐60 unit (T780c) with 2 cm diameter cylindrical source (MDS Nordion, Canada) and a 6 MV Linac with an addon MIMiC BMLC (NOMOS, USA). All the Co‐60 sources had identical active volumes.

EGSnrc/DOSXYZnrc MC code was used to calculate the intensity modulated beamlets and fan beam dose profiles in a water phantom. The intensity modulated energy fluence profiles from a 6 MV Linac and two Co‐60 units using the same beam segments will be compared. Tomotherapy treatment plans for a typical H&N case were calculated. All plans were optimized for PTV, two neck nodes and the spinal cord using the same optimization parameters. The treatment planning was provided by an in‐house inverse planning system based on a multi‐objective gradient‐search approach using MC calculated dose data. Results: Comparisons of optimized dose distributions, dose difference maps and dose area histogram will be presented. Despite significant differences in fluence profiles for Co‐60 and 6 MV beams, optimized dose distribution for all plans met the dose‐volume and tolerance criteria. However, the integral doses are potentially higher for Co‐60 plans particularly with longer source size and shorter SAD. Conclusions: Co‐60 based tomotherapy with appropriate source and BMLC design is dosimetrically viable.

Research supported (in‐kind) by MDS Nordion, Canada.