bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐C‐BRC‐03: AAPM Initiatives in Quantitative Imaging
Authors: Boone JM
Published: April 2010

The Science Council (SC) of the AAPM has initiated the Quantitative Imaging (QI) Initiative, which is an effort focused on moving the field of diagnostic imaging towards a more quantitative footing. While much of the quantitative content of the radiologist report will be generated by the radiologist with perhaps the help of user‐friendly and robust software capable of generating quantitative metrics off of a patient's images, there is an important role for physicists to play in assuring the quantitative integrity of the image data. The QI Initiative currently has three task groups, on PET/CT, on dynamic contrast enhanced MRI, and on CT. The methods and activity of these groups towards achieving their objectives will be discussed. The activity of these three groups has overlap with similar efforts of other societies such as the SNM, ISMRM, and the RSNA, and the interconnections will also be described. The parallel, integrated efforts towards creating a more quantitative future for medical imaging assessment is being driven by the needs of clinical research trials, as well as other payer initiatives such as pay for performance. Long term, the QI Initiative will include a comprehensive array of procedures to reduce variance in the imaging process, by standardization of the acquisition protocols, calibration of the spatial and gray scale output of scanners, incorporation of structured reporting tools to improve accuracy and format consistency, and the development of scientific software capable of extracting accurate QI data from image data.
TU‐C‐303A‐01: Evaluating the Accuracy of Four‐Dimensional Photon Dose Calculations with Phantom Measurements
Authors: Vinogradskiy Y , Balter P , Followill D , Alvarez P , White A , Starkschall G
Published: April 2010

Purpose: Respiratory motion can cause deviations between the intended and delivered dose distributions. Recent work has focused on developing four‐dimensional (4D) dose calculation algorithms, which explicitly account for respiration in the dose calculation process. Before these dose calculations methods can be used clinically, it is necessary to verify their accuracy. The purpose of this study was to evaluate the accuracy of 4D dose calculations with phantom measurements. Methods: Measurements were made using two anthropomorphic phantoms: a rigid moving phantom and a deformable phantom. Two motion patterns were designed to drive both phantoms: a sinusoidal motion pattern and an irregular motion pattern that was extracted from a patient breathing profile. Three plans were generated on each phantom: a single‐beam, a multiple‐beam, and an IMRT plan. Doses were calculated using the 4D dose calculation capabilities of a commercial radiation treatment planning system. Each plan was used to irradiate the phantoms, and doses were measured using TLD and radiochromic film. The measured doses were compared to the 4D‐calculated doses using a measured‐to‐calculated TLD ratio and a gamma analysis. For the TLD and film, relevant passing criteria (5% for TLD and 5%/3mm for gamma) were applied to determine if the 4D dose calculations were accurate to within clinically acceptable standards. Results: All of the TLD measurements met the passing criteria. 42 out of the 48 evaluated films passed the gamma criteria. The films that did not pass the gamma criteria were from the irregular moving rigid phantom. Conclusions: In controlled conditions, 4D dose calculations are accurate to within clinically acceptable standards. In clinical terms, this means that if patient breathing is reproducible, 4D dose calculations will produce accurate dose distributions. Conversely, irregular breathing can produce inaccurately calculated 4D dose distributions. Conflict of Interest: This work is partially supported through an SRA with Philips Healthcare.
TU‐C‐303A‐02: Intrafraction Prostate Motion Monitoring with Cine‐MV and Minimal As‐Needed Onboard KV Imaging
Authors: Liu W , Xie Y , Luxton G , Wiersma R , Xing L
Published: April 2010

Purpose: To examine the feasibility and performance of using treatment MV beam imaging with prior knowledge to estimate 3D prostate intrafraction motion and to instantaneously reposition based on information from minimal usage of on‐board kV imaging during IMRT. Methods and Materials: In contrast with current motion monitoring techniques which seek to accurately and continuously localize a moving target, we attempted for the first step only to detect potential motion beyond a pre‐defined threshold using MV images and in the second step through combined MV‐kV imaging (by turning on the kV imager) to confirm the over‐threshold event as well as obtaining accurate position information which could be used for instantaneously repositioning. EPID images were used to measure 2D prostate displacement in the imaging plane. By taking into account the strong correlation between prostate SI and AP motion, small displacement in the LR direction, and data from a previous IMRT session (different gantry angle), we estimated in‐line prostate motion as well which in turn allowed us to detect potential 3D over‐threshold motion. To minimize the influence from training data, no statistical motion probability distribution information was used. Simulation has been done using 536 patient‐measured trajectories from 17 patients. Experiments were performed on a Varian Trilogy linac using a motion phantom programmed for selected typical trajectories, and the results were compared with simulations. Results: Prostate displacement beyond a set threshold (3mm) was detected for over 99% of the time at the cost of negligible kV dose (< 3 images/fraction on average). The position information required for repositioning was found to have sub‐millimeter accuracy using combined MV‐kV data. Conclusion: Significant reduction of adverse effects of intrafraction prostate motion is achievable. The technique can be readily implemented in clinics and incurs minimal imaging dose to the patient as compared with other stereoscopic imaging techniques.
TU‐C‐303A‐05: On the Need for Multiple External Markers to Predict Tumor Displacement Due to Respiration
Authors: George R , Malinowski K , Dieterich S , D'Souza W
Published: April 2010

Purpose: To study the correlation between external markers and tumor displacement, investigate the need for multiple markers to independently predict tumor displacement and perform a stratified analysis by disease site and tumor location. Methods: Data was acquired from 91 patients undergoing stereotactic body radiation therapy using the Cyberknife Synchrony™ system. The data consisted of three dimensions corresponding to each of three external markers and the tumor. Univariate analysis was performed to determine the correlation between the displacement of individual external markers and the tumor. Multivariate analysis was performed to determine which external marker dimensions (and the number) independently predicted tumor displacement. A stratified univariate and multivariate analysis based on tumor site and location was also performed. Results: Univariate analysis showed that more than one external marker and more than one external marker dimension had a correlation coefficient > 0.5 with the tumor position. Multivariate analysis showed that 2.6 external markers and 4.7 external marker dimensions were needed to independently predict tumor displacement. Each external marker dimension was independently predictive of tumor displacement in an equal number of cases. Conclusions: Univariate shows that more than one external marker and more than one external marker dimension had a strong correlation with the tumor position. Multivariate analysis showed that 2–3 external markers and 4–5 external marker dimensions were independently predictive of tumor displacement. The resulting RMS error between the predicted and actual tumor displacement from the multivariate regression model was approximately 1 mm.
TU‐C‐303A‐10: Site‐Specific Volumetric Analysis of Lung Tumor Motion
Authors: Pepin E , Wu H , Sandison G , Langer M , Shirato H
Published: April 2010

Purpose: To develop a Hidden Markov Model (HMM) of tumor motion behavior for use in adaptive image‐guided radiation therapy (IGRT) to overcome the beam delivery system's inherent mechanical and imaging‐rate latency. As input to the HMM we investigated clinically defined parameters and tumor motion characteristics. Method and Materials: Motion data from 43 lung tumors were collected by tracking an implanted fiducial using a fluoroscopic real‐time tracking system. Data on a total of 1297 radiotherapy fractions were collected and for 637 fractions a convex hull was created over the data points for three consecutive breathing cycles. Statistical analysis led to the removal of outlier points, then the volumes of the hulls were calculated and their shapes visually examined. Tumor location in the lung as defined by bronchial segments was related to the volume and shape of the tumor movement envelope. Results: Outlier points were removed based on data density and tumor velocity limits. It was found that tumors located in the upper apex had smaller volume of movement envelope (<50 mm≈3), whereas tumors located near the chest wall or diaphragm were larger (>70 mm≈3). Tumors attached to fixed anatomical structures had a small volume of movement envelope (<30 mm≈3). Three general shapes described the tumor motion envelopes. Envelope volume and shape was inter‐fractionally consistent. Fifty percent of tumors exhibited largely 1D oscillation; Thirty‐eight percent of tumors had motion enclosed by an ellipsoid envelop with few data points in the center region, six percent of tumors moved in an arc‐like defining a concave shaped movement envelope, and six percent defined a movement envelope that was of hybrid shape. Conclusions: The location‐space correlation and the inter‐fractional consistency of the movement envelope shapes will, in part, inform the development of a HMM to predict lung tumor motion for real‐time beam adjustments in IGRT.
TU‐C‐304A‐01: The Need and Feasibility of a Modern Software for Reporting Patient Doses From CT Scans
Authors: Ding A , Gu J , Liu H , Caracappa P , Xu X
Published: April 2010

Purpose: To demonstrate the need and feasibility to develop a modern software tool for reporting the organ dose and effective dose for patients undergoing CT examinations. Method and Materials: Existing CT dose reporting software do not meet the need because of the simplified anatomical phantoms, updated ICRP data and scanner information. A new software is designed with original dose data derived from Monte Carlo simulations involving CT scanner models from various companies and anatomically realistic phantoms. X‐ray sources and protocols are modeled. The Pregnant Women, Adult Male and Adult Female phantoms are utilized. Organ doses and effective doses are computed using both the ICRP‐60 and the latest ICRP‐103 recommendations. The software is developed using the Visual C♯.NET with a modern graphical user interface (GUI) design to allow a user to specify the patient type, body scan region, and scanner operating parameters. Object‐oriented programming technology allows the phantoms to be displayed in 3D interactively. Results: Compared to values reported by the existing software, the organ dose estimates can be different by a ratio as 0.77 to 1.24 for the organ or tissue covered in the scan range, and 0.13 for the organs out of the scan region between calculations using the anatomically realistic phantoms. In addition to the improved dose accuracy, the new program offers a number pf modern GUI features through which 3D phantoms are vividly inspected for organs that receive a high doses. Based on the user‐specified scanning parameters, organ and effective doses are rapidly reported. Conclusion: Preliminary results have demonstrated the aim of the new software design in addressing the needs for new CT scanners, ICRP recommendations and anatomically realistic phantoms. When fully developed, this new tool is expected to improve both the accuracy and usability in reporting CT doses in the future.
TU‐C‐304A‐03: Stylized MIRD Phantoms Should Be Replaced by Anatomically Realistic Phantoms: Discrepancies In Red Bone Marrow Doses From CT Scans
Authors: Liu H , Zhang J , Caracappa PF , Xu X
Published: April 2010

Purpose: To test the hypothesis that the stylized MIRD phantoms would cause significant error in the estimated red bone marrow (RBM) dose from CT scans in comparison with anatomically realistic phantoms. Method and Materials: The MC model of the CT scanner include the source geometry, movement, source energy spectrum, bow‐tie filter, as well and the beam shape. MCNPX 2.5.0 was used to simulate the RBM dose from various CT scanning procedures. To calculate the absorbed dose to the RBM as a function of photon fluence in the spongiosa and the photon energy, an F4 tally together with a set of DE/DF cards in MCNPX were used to score the photon fluence in MCNPX. The stylized MIRD phantom and the anatomically realistic RPI Adult Male and Adult Female phantoms were implemented in the MCNPX to determine organ doses using the same dose algorithm. Results: For all the cases studied, the RBM doses calculated using RPI adult phantoms were gearter than those obtained from MIRD‐ORNL phantoms. For the chest CT scan, the RBM dose ratio (RPI‐AM to MIRD‐ORNL) is about 1.50 (1.48–1.51), and RBM dose ratio of female phantoms is about 1.28 (1.24–1.32). For the abdominal‐pelvis CT scan, the RBM dose ratios are 1.30 (1.28–1.31) and 1.32 (1.28–1.38) for male and female phantom, respectively. These differences are mainly from the anatomical differences in the phantoms. Conclusion: As the RBM is not uniformly distributed in the human body, the homogeneous bone mixtures definition by MIRD phantoms underestimated the dose by as much as 50% in certain cases. This test concludes that the simplified MIRD phantoms used in existing CT dose software should and can be replaced by realistic phantoms. This is an opportunity to improve the anatomical realism and therefore the associated dose and risk assessments for patients who undergo CT examinations.
TU‐C‐304A‐05: Dose Reductions of Bismuth Shields in Diagnostic Radiology: Measurements and Monte Carlo Simulations
Authors: Kim S , Yoshizumi T , Frush D , Anderson‐Evans C , Toncheva G
Published: April 2010

Purpose: To assess the dosimetric characteristics of bismuth breast shields for a CT beam with ion chamber measurements and Monte Carlo simulations. Method and Materials: Primary attenuation and backscatter effects of both adult and pediatric bismuth superficial organ (e.g. breast) shields were measured with a 0.18‐cc ion chamber and a rectangular slab phantom made of a tissue equivalent material. Simulated CT beams (120 kVp with 100∼400 mAs) were used to irradiate the ion chamber with and without bismuth shields. Both 2‐ply (pediatric) and 4‐ply (adult) bismuth shields (F&L Medical Products, Vandergrift, PA) were placed at the front of the chamber for primary attenuation measurements and at the back of the chamber to measure backscatter radiation. Radiation doses were measured free‐in‐air and in the tissue‐equivalent slabs. Monte Carlo simulations for the same measurement settings were performed by using EGSnrc/BEAMnrc code. Results: Mean radiation dose reduction from primary attenuation was about 23% (2‐ply) and 40% (4‐ply) for the free‐in‐air and tissue slab measurements. The radiation dose increase from backscatter was around 2% for both the 2‐ply and 4‐ply shields. The Monte Carlo simulations produced the dose reduction from primary attenuation was about 20% (2‐ply) and 38% (4‐ply), and the dose increase from backscatter was around 6% for both shields.

Conclusion: Primary attenuation is the dominant factor that induces radiation dose changes in bismuth shields in CT examinations. The dose contribution from backscattered radiation in bismuth shields is very small.
TU‐C‐304A‐07: X‐Ray Tube Current Modulation and Effective Dose Per Unit Dose‐Length Product Conversion Factors in CT Dosimetry
Authors: Tavrides E , He W , Huda W , Yao H
Published: April 2010

Purpose: To quantify how axial and longitudinal x‐ray tube current modulation influence effective dose per unit dose‐length product (E/DLP) conversion factors in chest CT. Method: We simulated a chest CT examination using a 4 cm beam width with projections obtained at every 15° x‐ray tube position at a constant tube output (120 kV). A radiographic patient dosimetry software package (PCXMC) was used to quantify relative patient effective dose as a function of the angular position and longitudinal location (z) of the x‐ray tube. Typical angular and longitudinal mA modulation schemes were obtained from the scientific literature. E/DLP conversion factors were generated for: (a) no mA modulation; (b) angular modulation alone; and (c) longitudinal modulation alone. Results: As the x‐ray tube rotates around the patient, the highest effective dose was at 285° (AP projection) and the lowest effective dose was at 195° (lateral projection), with the maximum to minimum ratio of 2.2. An angular mA modulation scheme with an AP/PA tube current one third of the lateral tube current reduces the E/DLP conversion factor in chest CT by 4.2%. For x‐ray tube movement along the z‐axis, the maximum to minimum ratio of patient effective dose was 3.3. In chest CT imaging, the longitudinal mA modulation changes the tube current approximately seven fold between the central lung area and the upper thorax region above the patient's lungs. Application of this longitudinal mA modulation scheme reduces the E/DLP conversion factor in chest CT by 9.2%. Conclusions: Use of longitudinal and angular mA modulation schemes in chest CT examinations could reduce E/DLP conversion factors by ∼13%.
TU‐E‐303A‐01: Contrasted‐Enhanced Breast Tomosynthesis
Authors: Maidment ADA
Published: April 2010

Digital breast tomosynthesis (DBT) is on the verge of routine clinical use in the United States; every major mammography manufacturer has a prototype under development, numerous clinical trials are in progress and one manufacturer is selling systems in Europe. DBT has been shown to have clear value in increasing the conspicuity of lesions by removing overlaying structures present in mammograms.

Regardless of the advances, DBT is currently limited to the depiction of tumor morphology. We have recently installed a Hologic Dimensions DBT prototype that has been modified to allow contrast‐enhanced (CE) imaging. Both dual‐energy and temporal CE‐DBT are under investigation. In previous work, we have shown that CE‐DBT can provide results concordant with dynamic contrast‐enhanced MR in a group of 17 women with known or suspected breast cancer. Our work continues with technique optimization, reconstruction algorithm development, motion correction, and scatter and other signal dependent corrections. With appropriate corrections, CE‐DBT can accurate quantify contrast agent uptake.

CE‐DBT has potential benefit in a number of roles, as illustrated by breast MR. These roles include screening high‐risk populations, staging cancer patients through identification of multifocal, multicentric and contralateral cancer, and assessment of tumor response to neoadjuvant chemotherapy. Research is also ongoing in the field of targeted radiographic imaging agents for breast cancer.

Learning Objectives:

1. Review the state‐of‐the‐art in DBT system design

2. Describe adaptations necessary to perform quantitative CE‐DBT

3. Exemplify the clinical applications of CE‐DBT

Research support for this project has been provide in part by XCounter AB, General Electric Health Care, and Hologic Corp, in addition to the Komen for the Cure Foundation, the Department of Defense and the Radiological Society of North America.
TU‐E‐303A‐03: Breast CT as a Platform for Image Guided Therapies of Breast Cancer
Authors: Boone JM , Prionas N , Burkett G , Packard N , Yang K
Published: April 2010

Dedicated breast computed tomography (CT) systems were designed and fabricated in our laboratory using off‐the‐shelf components (x‐ray system, detector, and bearing) integrated into a custom designed system. For imaging, a 360 degree acquisition using cone beam geometry is used to acquire 500 projection images which are reconstructed to produce a high resolution ∼512 × 512 × 512 CT volume data set. In addition to the diagnostic imaging capabilities of the bCT scanner, the system appears to be an excellent platform for image guidance of interventional procedures such as robotic biopsy, radiofrequency ablation, and cryoablation. In addition to percutaneous procedures, the bCT system may also be an excellent platform for rotational beam radiation therapy. Computer simulations and physical phantom‐based experiments were used to define the dose distributions possible using the bCT system for radiation therapy. A number of beam energies from 120 kVp to 480 kVp were simulated. Initial results suggest that in addition to homogeneous dose distributions for treating the whole breast, that focused therapeutic approaches using collimators may be possible. The pendent position of the breast with the women prone is also thought to be a more reproducible approach to fractionated radiotherapy of the breast.

Educational goals are to inform the attendee of the possible benefits of breast cancer therapies delivered from a breast CT platform

Research support for this project has been provide in part by Varian Medical Systems, Fuji Medical Systems, and Hologic Corporation, in addition to the NIH
TU‐E‐304A‐05: Internal Dosimetry Calculation to Red Marrow From 131I‐MIBG Treatment in Neuroendocrine Tumor Patients
Authors: Changmuang W , Tuntawiroon M , Chotipanich C
Published: April 2010

Purpose: The aim of this study was to calculate absorbed dose to red marrow using patient‐specific parameters in 14 patients with neuroendocrine tumor after administration of diagnostic dose (37 MBq) of ‐MIBG. Methods and Materials: Whole body and blood clearance of ‐MIBG in each patient were measured with a gamma probe and gamma counting systems, respectively. The effective half‐life, and residence time were derived from whole body retention and blood activity concentration curves. Dose to the red marrow was calculated by using the standard Medical Internal Radiation Dose (MIRD) schema. Results: The mean effective half‐life (23.5 h) determined from whole body measurements was higher than those derived from blood activity concentration (16.6 h). The whole body residence time was 33.9±7.5 hours and the mean absorbed dose to red marrow was 0.25±0.19 mGy/MBq. The calculated mean ± SD of ‐MIBG treatment dose was 13.19±9.18 GBq (n=14). After treatment, thrombocytopenia grade 1 occurred in 4 patients (29%) with a mean time to nadir of 22 days. Leukopenia grade 1 found in 2 patients (14%), grade 2 in 1 patient (7%), grade 3 in 1 patient (7%) and grade 4 in 1 patient (7%) with a mean time to nadir of 48 days. Conclusions: The red marrow dosimetry estimated from patient specific data with a diagnostic dose of ‐MIBG was a good predictor for potential marrow toxicity. The use of this standardized calculation methodology should ultimately improve the planning for ‐MIBG treatment in neuroendocrine tumor patients.
TU‐E‐210A‐01: Dual‐Energy CT with Fast‐KVp Switch
Authors: Hsieh J
Published: April 2010

Purpose: Dual‐energy (DE) CT has received much attention in recent years. There are various approaches to the data acquisition, differing in terms of the simultaneity, geometric alignment, data collection efficiency and completeness, and flexibility. We present a fast‐kVp switching (FKS) method in combination with advanced image generation process, and demonstrate the efficacy of our approach with phantom and clinical results. Methods and Materials: In FKS, the input to the x‐ray tube is rapidly changed between two kVp‐settings in adjacent views. To ensure the signal fidelity, x‐ray generator was redesigned to minimize its input impedance, new scintillating material was developed to reduce the primary speed to a small fraction of a millisecond, and the data acquisition system was designed to sample up to 7Hz frequency. To take full advantage of the co‐registered dual‐energy projections, advanced algorithms were developed to enable projection‐space pre‐processing, calibration, reconstruction, and spectral image displays. These techniques allow the production of mono‐energetic CT images, as well as different material decomposed images. Results: Phantom experiments and computer simulations show that because of the near simultaneous data acquisition in terms of timing and orientation, mis‐registration due to patient motion is kept to a minimized. FKS also allows the projection‐space processing of the dual‐energy signals and results in a significant improvement in terms of beam‐hardening artifacts. Advanced algorithms allow superb noise suppression in the mono‐energetic images as well as material‐decomposed images. Clinical studies demonstrate the importance of beam‐hardening reduction, metal artifact reduction, and the accuracy of material decomposition. Conclusion: We present a fast‐kVp switching approach to the dual‐energy data acquisition and advanced algorithms to the dual‐energy reconstruction. Phantom and clinical experiments have demonstrated that such approach provides superior image quality and clinical utility.
TU‐E‐213A‐01: Quality Assurance for the Leksell Gamma Knife Perfexion™
Authors: Petti P
Published: April 2010

The Leksell Gamma Knife_ Perfexion_ is the latest gamma stereotactic radiosurgery (GSR) unit manufactured by Elekta (Elekta Instrument, AB, Sweden). Introduced in 2006, it is substantially different in design and operation from previous Gamma Knife (GK) models. The major differences are in the collimation system, the configuration of the radioactive 60Co sources, and in the patient positioning system. The Perfexion_ has one fixed tungsten collimator containing 576 different collimating channels, whereas older GK models have one primary collimator, located inside the unit, and 4 interchangeable secondary collimators that are mounted manually. In the Perfexion_, 192 60Co sources are situated on 8 moveable sectors (24 sources per sector), that slide over the collimator placing the sources over the planned collimating channels to deliver the desired radiation shot size. In older GK models, by contrast, 201 60Co sources are fixed in space and arranged in a pseudo‐hemispherical configuration. Finally, for the Perfexion™ the treatment table, which moves with sub‐millimeter accuracy in three orthogonal directions, is the patient positioning system. For older model GK units, patient positioning is accomplished by attaching the Leksell stereotactic frame to the secondary collimator via specialized hardware called trunnions or via the automatic‐patient‐positioner (APS).

The specific goals of quality assurance (QA) for gamma stereotactic radiosurgery include determining the dose rate for the largest available collimator, measuring the relative output factors and beam profiles for each collimator size and comparing the results to those used in or calculated by the treatment‐planning program, and verifying that the radiation focal point coincides with the center of the patient positioning system. Although these QA tasks for GSR units have remained essentially unchanged over the years, new tools and protocols designed for linear accelerator QA have become available that can be applied to QA for GSR devices. With this in mind, a new AAPM Task Group (TG‐178) has recently been formed and charged with updating QA procedures for older GSR devices that have static sources, creating new QA protocols for GSR devices that are characterized by moving sources, and suggesting a protocol for ionization chamber calibration specific to GSR devices.

This lecture will describe the operation of the Leksell Gamma Knife_ Perfexion_ and the unique features of QA for GSR units, with emphasis on the Perfexion_. Some of the questions faced by TG‐178 will be discussed, old QA procedures will be reviewed and possible new QA tests will be suggested.

Learning Objectives:

1. Review QA requirements for GSR units

2. Understand the design differences between older GK models and the Perfexion_ and the implications of these differences on routine QA

3. Become familiar with tools provided by the manufacturer to facilitate GK QA

4. Understand the difficulties associated with dosimetric calibration of GSR units

5. Review the use of radiochromic film for GK QA
TU‐E‐213A‐03: Everything You Need to Know About the Cyberknife, But Were Afraid to Ask
Authors: Masterson‐McGary M
Published: April 2010

The CyberKnife (Accuray, Inc. Sunnyvale, CA) is a stereotactic radiotherapy unit, designed to treat both intracranial and extracranial targets with sub‐millimeter spatial accuracy. An industrial robot has a compact 6 MV x‐band linac as its payload. The robot is able to orient the linac with six degrees of freedom, and to aim its x‐ray beam at the target volume in a non‐isocentric and non‐coplanar fashion. Typically, hundreds of beams (selected from thousands of possible beam angles) are delivered during each treatment fraction. A bi‐plane digital radiography system determines and feeds‐back target position coordinates to the robot throughout treatment, allowing the robot to continuously correct its aim to account for intra‐fraction patient and target movement. The CyberKnife uses several different tracking methodologies depending upon the type of target being treated. Both rigid body and deformable body geometries are employed. Special correlative tracking techniques have been developed to track targets that move with respiration. With nearly real‐time correction for target motion and highly precise dose delivery, the CyberKnife allows the practitioner to employ tighter margins and to deliver high doses per fraction accurately.

This talk is intended to review the unique features of the CyberKnife system, and to discuss how those features require special considerations in site planning, acceptance testing, commissioning, quality assurance, treatment planning, and clinical implementation. Examples of common clinical applications and dose regimens will also be presented.

Learning Objectives:

1. Understand the fundamental design and functionality of the CyberKnife system.

2. Understand the impact of machine design on site planning, acceptance testing, commissioning, treatment planning, as well as system and sub‐system quality assurance.

3. Understand the different clinical considerations associated with robotic SRS and SBRT.

4. Enable the attendee to introduce a CyberKnife system into his/her clinical practice efficiently, effectively, and safely.
WE‐A‐BRD‐03: Gated Radiotherapy for Lung Cancer
Authors: Jiang S
Published: April 2010

Respiratory gated radiotherapy holds promise to reduce the incidence and severity of normal tissue complications and to increase local control through dose escalation for lung cancer patients. In this lecture, we discuss the current status, existing problems, and potential solutions for applying gating techniques to lung cancer treatment. First, the motion artifacts in CT simulation are discussed and the 4D CT scan technique is recommended for treatment simulation of lung cancer patients under gated radiotherapy. Second, we discuss two currently available forms of gated radiotherapy: internal (fluoroscopic) gating and external (optical) gating. Internal gating utilizes internal tumor motion surrogates such as implanted fiducial markers while external gating uses external respiratory surrogates such as markers placed on the surface of the patient's abdomen. The major strengths of external gating are that it is non‐invasive, is relatively easy and does not require any radiation dose for imaging. However, the relationship between the tumor motion and the surrogate signal may change over time, inter‐ and intra‐fractionally. The major strength of the internal gating systems is the precise and real‐time localization of the tumor position during the treatment. The two major weaknesses of internal gating are the risk of pneumothorax for implantation of markers in lung and the high imaging dose required for fluoroscopic tracking. Third, we discuss the potential solutions and future development of gated radiotherapy for lung treatment. We propose the combination of external and internal surrogates (hybrid gating) to solve the imaging dos problem and the direct fluoroscopic tracking of lung mass to avoid seed implantation. Other related issues are also discussed.
WE‐A‐BRC‐02: IMRT for Prostate Cancer
Authors: Price R
Published: April 2010

The prostate is a mobile structure compared to the surrounding bony anatomy. Daily setup, immobilization and localization uncertainties can be addressed by increasing the PTV but may result in additional dose to surrounding normal structures. At FCCC we attempt to reduce the uncertainty by employing daily localization using ultrasound, implanted fiducials or through target tracking using implanted Calypso beacons. We currently use an 8mm growth in all directions except posteriorly where 5mm is typical. Patients with fiducials and those being irradiated in the post‐prostatectomy setting undergo localization via an in‐room CT scanner or CBCT. We have recently begun target tracking on post‐prostatectomy patients as well. All patients are simulated and treated supine without a thermoplastic immobilizer to minimize respiratory related prostatic motion. Patients undergo MR and CT simulations with the rectum empty. These data are fused for target and normal structure delineation for use in treatment planning. Emphasis on soft tissue structures is important to avoid potential systematic localization errors due to the time difference between scans for patients with implanted fiducials or beacons. Dose limiting structures primarily include the rectum, bladder, and femoral heads, but may also include bowel and erectile tissues. We have developed “plan acceptance criteria” based on published data with respect to rectal complications. DVH analysis is used to ensure that the rectal volumes receiving 65Gy and 40Gy are less than 17% and 35%, respectively. Additionally, the bladder volumes receiving 65Gy and 40Gy are less than 25% and 50%, respectively. The volume of either femoral head receiving 50Gy should be less than 10%. PTV coverage should result in at least 95% of the volume receiving the prescription dose. It should be noted that the 3D dose distribution itself plays an important role in IMRT delivery and DVH analysis alone may not be sufficient. The isodose distribution should be such that the 90% and 50% lines do not traverse the half or full width of the rectum on any CT slice, respectively. Dose escalation and hypofractionation regimes continue to be of interest in the treatment of this disease site. However, most delivery techniques require PTV reductions to avoid increased normal tissue toxicity. A quantitative analysis of uncertainties contributing to PTV margins is addressed. Additionally, treatment methods that may not require margin consideration, are discussed. These include fiducial tracking using the Cyberknife and the use of high intensity focused ultrasound (HiFU) ablation.

Learning Objectives:

1. To understand the practical steps associated with IMRT of the prostate

2. To understand the numerical values presented for plan acceptance

3. To be aware of MR‐CT fusion issues for patients with implanted fiducials or beacons

4. To be aware of issues related to PTV reduction
WE‐A‐303A‐01: DCE MRI for Quantitative Assessment of Therapy Response
Authors: Cao Y
Published: April 2010

Dynamic contrast enhanced (DCE) MR imaging is emerging as a promising biomarker for therapy assessment. While initial results from research groups are promising, a significant gap exists between preliminary research studies and practical utilization. In addition to variations in data acquired from different image acquisition techniques, a large variety of pharmacokinetic models have been explored from which to derive quantitative metrics. Examples of such models include those from Patlack, Toft, and Elizabeth, with a number of others in use in various research groups. These models have various levels of complexity, which in general is inversely related to the robustness with which the models perform on imaging data. Furthermore, the selection of an optimal pharmacokinetic model may be highly dependent on the tissue or organ being investigated. Currently, a national effort is underway to help standardize the extraction of physiological parameters from DCE‐MRI and related pharmacokinetic models. This talk explores these issues, comparing various models and their performance, and provides an overview of the areas that need consideration prior to widespread adoption of DCE‐MRI derived model parameters as assessment tools.

Learning Objectives:

1. Understand the strengths and weaknesses of commonly used pharmacokinetic models

2. Understand the influence of image acquisition parameters and image quality on derived quantitative metrics

3. Provide examples of clinical applications
WE‐B‐303A‐01: Stereotactic Breast Biopsy: An Update for Physicists
Authors: Pfeiffer D
Published: April 2010

Stereotactic Breast Biopsy (SBB) often seems to be the poor stepchild of the breast health family. This is exemplified by the fact that the number of units in the voluntary American College of Radiology SBB Accreditation Program measures in the hundreds, compared to over 13,000 units in the Mammography Accreditation Program. However, SBB holds its place as a vital player in the diagnosis of breast cancer. As such, the image quality and performance demands of SBB systems are great. Any object of interest seen on a mammogram must be visible in the SBB image, or the biopsy cannot take place. The purpose of this presentation is to provide an update on Stereotactic Breast Biopsy systems and the clinical demands placed on them. Techniques for testing these systems will be presented. Features of various systems will be discussed. Information regarding the ACR SBBAP will also be presented. Education objectives: 1) To become familiar with the approaches to Stereotactic Breast Biopsy. 2) To gain an understanding of the clinical requirements for these systems. 3) To review quality control requirements and methods for clinical SBB systems.
WE‐C‐BRB‐03: A Medium‐Dependent Correction‐Based Algorithm for Calculating Imaging Dose Resulting From KV X‐Rays
Authors: Pawlowski JM , Coffey CW , Ding GX
Published: April 2010

Purpose: Kilovoltage (kV) x‐rays are increasingly used in image‐guided radiation therapy. Repeated imaging procedures add additional dose to patients. It has been shown that the dose to bone is 3–4 times higher than dose to soft tissue for kV x‐rays. Currently there is no model‐based dose calculation algorithm that can accurately calculate the dose from kV x‐rays. In order to account for the image‐guidance dose to patients in treatment planning it is necessary to develop an accurate algorithm for dose calculations that can be implemented in a commercial treatment planning system for patient dose calculations in the diagnostic energy range. Method and Materials: The new algorithm, referred to as the Medium‐Dependent Correction (MDC), takes into account both the medium physical densities and medium atomic numbers of the absorbing media. The MDC algorithm employs an empirically parameterized correction method which is applicable for arbitrary phantom geometry. The empirical parameters are optimized for a specific kV beam. The dose calculation accuracy of the MDC algorithm was benchmarked against that of Monte Carlo calculations for dose distributions resulting from head and neck and pelvic kV‐CBCT. Results: The dose distributions resulting from calculation using the MDC algorithm were compared to density‐corrected calculations using the Monte Carlo results as the gold standard. Density‐corrected calculations were shown to underestimate the dose to bone by 100–300% and overestimate the dose to soft‐tissue by 10–30%. The MDC algorithm calculated the dose to bone to within 10–30% and soft tissue to within 5–20%. Conclusion: The MDC calculation algorithm overcomes the shortcomings of existing model‐based density correction methods used in kV x‐rays. The algorithm offers similar accuracy to the Monte Carlo method with a fraction of the calculation time and could be implemented in a commercial treatment planning system to include imaging dose in patient treatment planning.
WE‐C‐BRB‐06: Antiproton Radiotherapy: Development of Physically and Biologically Optimized Monte Carlo Treatment Planning Systems for Intensity and Energy Modulated Delivery
Authors: Fahimian B , DeMarco J , Keyes R , Luan S , Zankl M , Holzscheiter M
Published: April 2010

Purpose: Antiprotons have become of interest in radiotherapy due to their higher peak to plateau dose ratio relative to protons and carbon ions, and a beneficial increase in RBE towards the Bragg peak as recently verified by experimental investigations of the AD‐4 collaboration at CERN. An obstacle limiting further research is the lack of a treatment planning system capable of concurrently optimizing the necessary modulation of intensity and energy, while accounting for the variation in biological effectiveness. Here we develop a Monte Carlo based treatment planning system for this purpose and subsequently quantify its performance. Materials and Methods: Dose kernels corresponding to different energy and source configurations were calculated using MCNPX in phantom and voxelized patient CT scans, and then converted to biological equivalent dose using depth dependent RBE weighting factors derived from theory and experiment. Linear equations were formulated for each pixel representing superposition of different kernels weighted by unknown intensities. Algorithms using constrained least square and gradient descent optimization were developed to minimize objective functions measuring the geometric correlation of the planning target volume (PTV) with the calculated distribution, yielding an optimized intensity for beams as function of energy and direction. Results: Biologically optimized treatment plans implemented on a voxelized 38 year old human were in good agreement with the input PTVs, reproducing the PTVs with a mean error of less than 2.24%. Proof of principle demonstrations were successful in producing complicated structures, such resemblance of Einstein, in water phantom with a correlation greater than 93%. Conclusions: We have developed a Monte Carlo treatment planning system for energy and intensity modulated antiproton therapy capable of incorporating depth‐dependency of the RBE, and reproducing complicated PTVs with high accuracy. The work can be readily extended to incorporate more sophisticated objective functions such as NTCP and TCP functionals.
WE‐C‐BRB‐08: Sensitivity of Dosimetric Margin Distribution and Coverage Estimates to Sampling Parameters
Authors: Xu H , Gordon J , Siebers J
Published: April 2010

Purpose: The dosimetric margin distribution (DMD) is a planning tool for evaluating target and normal tissue dose coverage probabilities in the presence of geometric uncertainties. This work evaluates sensitivity of coverage estimates derived from the DMD to the angular increment w at which the DMD is sampled, and the distance search increment d. Method and Materials: The study utilized three plans for localized prostate cancer, with prescribed dose of 79.2Gy and 1cm clinical target volume to planning target volume (CTV‐to‐PTV) margins, planned according to the high dose arm of RTOG0126. Dose was first recalculated with beam fluences convolved with a normal probability density function to simulate the effect of random uncertainties. Dosimetric margins were then calculated between the CTV and the 79.2Gy isodose surface at elevations f from −90° to +90°, and azimuthal angles q from −180° to +180°. In each direction (f,q) the CTV was moved relative to the dose distribution in steps of d until its minimum dose fell below 79.2Gy. Estimated coverage Qest was calculated from the DMD assuming systematic uncertainties (rigid body translations) were normally distributed with standard deviation S along each axis. Minimum and maximum deviations DQest were obtained over a range of S values for w = 5°, 10°, 20° relative to w = 2°, and for d = 0.2, 0.5, 1mm relative to d = 0.1mm. Results: Coverage uncertainty due to finite angular sampling interval w is approximately 0.5% at w = 10° and 1.5% at w = 20°. Uncertainty due to finite step size d is negligible for d £ 0.2 mm, and is approximately 0.6% for d = 1mm. Conclusion: Coverage estimates accurate to ±0.5% will be obtained if the DMD is sampled with w = 10° and d = 0.2 mm. Coverage estimates accurate to this level are desirable for target and normal tissue coverage evaluation in current treatment plans, and to support future treatment planning based on probabilistic coverage criteria.

(Supported by NIH P01CA116602).
WE‐C‐BRB‐10: Acceleration of Protons by High‐Contrast Ultra‐Intense Laser Pulses
Authors: Veltchev I , Tafo A Guemnie , Lin T , Fourkal E , Li J , Fan J , Ma C
Published: April 2010

Purpose: To increase the proton energy generated in a laser‐plasma accelerator by pulse contrast improvement and minimization of phase distortions. Method and Materials: In a redesigned experiment the laser chain has been upgraded to a 150TWlevel and the pulse contrast has been improved by the implementation of double chirped pulse amplification (DCPA) and a cross‐polarized wave (XPW) modulation technique. This novel method of prepulse reduction has been shown to generate contrast levels of the order of 10−10‐10−11. In our new laser system stable XPWis achieved in two‐pass geometry on a single BBO crystal, making the setup compact and versatile. The laser pulse is subsequently stretched and amplified in an additional 4‐pass amplifier. High‐dynamic range third‐harmonic autocorrelator is used for pulse contrast evaluation. The wavefront distortions in the laser pulse are monitored by a 2D micro‐lens array detector. The accelerated protons are registered on a CR‐39 nuclear track detector behind a range filter (for energy measurement). Results: The implementation of the XPWtechnique led to an improvement of the prepulse contrast from 2×10−5 to 5×10−9. The “cleaner” laser pulse allowed us to use thinner targets (<10 ⌈m) and observe more energetic protons (>3.5 MeV). The wavefront distortions due to thermal effects in the amplifier crystals and astigmatism in our imaging systems are monitored and minimized (phase distortion <λ/3) in order to achieve optimum conditions for tight focusing. Conclusion: Proton acceleration in excess of 3.5 MeV has been experimentally demonstrated using a more powerful laser source with better control over the laser pulse parameters. Further experiments to optimize target parameters for higher proton energies are underway using our 150TW laser as a proof that upward scaling of the laser power in a controlled fashion can bring us into the range of therapeutically useful protons.