bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐D‐BRA‐02: Application of Hypofractionation in the Prostate
Authors: Pollack A
Published: July 2007

Prostate cancer exhibits slow growth with a potential doubling time ranging from weeks to months (median 42 days). From these data emerged a hypothesis that adenocarcinoma of the prostate may behave more like a late reacting tissue. Brenner and colleagues (1) used data from prostate low dose rate permanent seed implants and external beam radiotherapy series and derived an α/β of approximately 1.5. Many other groups have also calculated the α/β ratio to be in the < 3.0 range; yet, hyperfractionation does not seem to compromise outcome after radiotherapy (2). There are many potential pitfalls of these analyses and some investigators have concluded that the α/β for prostate cancer is closer to that for late effects of the surrounding normal tissues (>3).

Understanding the α/β ratio for prostate cancer is key to designing clinical trials that maximize the efficacy of radiotherapy. If the α/β for prostate cancer is lower than the surrounding normal tissues, hypofractionation will afford an advantage in terms of greater sensitivity of prostate cancer to this strategy, as compared to the bladder and rectum. Brenner et al (3) have estimated the α/β for the rectum to be over 5.0. Recently, Fiorino and Valdagni (4) have argued that these estimates may be inaccurate because of variation in, and dependence of toxicity on, the proportion of rectum receiving higher radiation doses.

Clinical results in the PSA/IMRT era using hypofractionation show that this strategy is well tolerated by the surrounding normal tissues, with outcomes consistent with a low α/β. Kupelian et al. (5) have treated a large series of men to 70 Gy at 2.5 Gy per fraction with excellent results. As an offshoot of this strategy, RTOG 04‐15 contrasts this hypofractionation regimen with 73.8 Gy in 1.8 Gy fractions.

The Cleveland Clinic data also prompted us at Fox Chase Cancer Center to devise a randomized hypofractionation trial comparing 76 Gy at 2.0 Gy per fraction to 70.2 Gy at 2.7 Gy/Fx. The latter hypofractionation regimen is equivalent to 84.4 Gy at 2.0 Gy/Fx, assuming an α/β of 1.5. A total of 307 patients were entered from 2002 to 2006. The trial has completed accrual. Acute toxicity in the first 100 men entered shows minor differences between the two treatment groups (6). Analysis of late toxicity during the first year of follow‐up also is revealing little difference. The encouraging results thus far with hypofractionation suggest that more significant hypofractionation (e.g., stereotactic radiotherapy) might be cost‐effective and potentially advantageous.

Objectives

1. To understand the alpha/beta ratio for prostate cancer.

2. To appreciate the efficacy of hypofractionation and resultant toxicity.
MO‐E‐L100J‐01: Enhancement of Signal Performance Through Innovative Pixel Design for Indirect Detection Active Matrix Flat‐Panel Arrays
Authors: Antonuk L , Zhao Q , El‐Mohri Y , Du H , Behravan M , Wang Y , Weisfield R , Yao B , Street R
Published: July 2007

Purpose: Active matrix flat‐panel imager technology is being introduced to an ever‐increasing variety of imaging applications. This has been greatly facilitated by improvements in optical signal collection achieved through innovations in array pixel design. Such improvements are particularly important for applications involving low exposures and high spatial frequencies, where DQE can be strongly attenuated due to relatively high additive electronic noise. In this presentation, recent innovations to pixel design are described and the effect on various signal properties, as determined through measurements and calculations related to novel prototypes, is reported. Method and Materials: Optical and radiation signal measurements were performed on prototype imagers incorporating a series of six increasingly sophisticated array designs, with pixel pitches ranging from 75 to 127 μm. The most recent discrete photodiode array employs aggressive design rules that significantly increase optical fill factor while also incorporating a clamp circuit. Two other array designs incorporate a continuous photodiode structure with the goal of providing an optical fill factor of 100%. Results: The new 127 μm pitch discrete photodiode design achieves a sensitivity consistent with its design goal of an ∼85% optical fill factor while the 75 and 90 μm pitch continuous photodiode designs demonstrate sensitivity corresponding to an ∼95% fill factor. These designs demonstrated no degradation in MTF due to charge sharing and the pixel clamp reduces memory effects at high signal levels. The effects of these enhanced sensitivities on DQE are illustrated and compared to the performance of arrays based on earlier generations of design. Conclusion: Aggressive application of design rules can achieve very high levels of optical fill factor and sensitivity resulting in improvements in DQE. Continuous photodiode designs extend optical fill factors almost to the theoretical limit, even for very small pixels, and are well suited to designs containing more complex pixel circuits.
MO‐E‐L100J‐04: Scatter Rejection and Low‐Contrast Performance of a Slot‐Scan Digital Chest Radiography System with Electronic Aft‐Collimation: A Phantom Study
Authors: Liu X , Shaw C , Lai C , Altunbas M , Chen L , Han T , Wang T
Published: July 2007

Purpose: To investigate scatter rejection and low‐contrast performance of an electronic aft‐collimation based slot‐scan imaging technique for chest imaging. Method and Materials: The slot‐scan imaging technique was implemented with a 1.6 cm wide fan‐beam and a modified flat‐panel (FP) detector for electronic aft‐collimation. During the scan, the leading edge line of the scanning fan‐beam is reset to erase the scatter accumulated while the trailing edge line is read out to acquire the image signals following the fan‐beam exposure. Two images acquired with the same techniques were subtracted from each other for measuring the noise levels. A 2‐mm thick lead plate with a 2‐D array of holes was used to measure the primary signals which were then subtracted from those obtained without the lead plate to determine the scatter components. A 2‐D array of aluminum beads (3mm in diameter) is used as the low‐contrast objects to measure the contrast ratios (CRs) and contrast‐to‐noise ratios (CNRs) for evaluation of the low‐contrast performance in chest images. Results: The slot‐scan imaging method resulted in lower average scatter‐to‐primary ratios (SPRs) and improved CRs, primary signal‐to‐noise ratios (PSNRs) and CNRs than the anti‐scatter grid method. Slot‐scan imaging used in conjunction with grid resulted in further reduction of the SPRs and improvement of CRs. However, in most cases, the PSNRs were degraded and CNRs were at the same level or even degraded. Conclusion: Slot‐scan imaging with electronic aft‐collimation can effectively reject scatter without having to attenuate the primary x‐rays. It resulted in almost doubled CNR improvement as compare to the anti‐scatter grid method. Further improvement by using slot‐scan imaging with an anti‐scatter grid was found to be limited. Conflict of Interest: This work was supported in part by a research grant EB00117 from the NIH‐NIBIB and the research grants CA51248 and CA104759 from the NIH‐NCI.
MO‐E‐L100F‐03: Noninvasive Temperature Imaging Using Diagnostic Pulse‐Echo Ultrasound
Authors: Ebbini E
Published: July 2007

Several ultrasonic parameters are known to have temperature dependence including the speed of sound, attenuation, nonlinearity parameter, etc. Local changes in tissue temperature can be estimated noninvasively using diagnostic pulse‐echo ultrasound. A number of temperature estimation methods have been proposed since the early 1990s with varying levels of success. One method that was investigated by numerous groups is based on minute changes in echo locations due to temperature‐dependent changes in the speed of sound and thermal expansion. Both in vitro and in vivo results have been obtained to demonstrate the feasibility of the method. However, several limitations have been shown to limit the use of this method in practice. In this paper, we describe a true two‐dimensional displacement tracking algorithm with robust temperature estimation from real‐time 2D pulse‐echo ultrasound. The method employs a physics‐based Kalman filter derived from the transient bioheat transfer equation (BHTE). The filter is shown to be effective in rejecting displacement artifacts from tissue motion as well as those resulting from the thermal lens effects.

This lecture will provide a description of the BHTE and the system approach leading to the design of the Kalman filter for tracking the temperature data based on the observed displacements in echo location in the region of interest. The tracking properties of the filter and its ability to reject artifacts from the observed displacements will be illustrated. One‐dimensional and two‐dimensional versions of the filter will be presented and contrasted in terms of their ability to reject displacement artifacts. Comparisons with previously published algorithms will be given using in vivo and in vitro data.

We will also present results on using the Kamlan filter methodology in tracking changes in tissue absorption associated with lesion formation using high intensity focused ultrasound (HIFU). This technique may lead to quantitative parameter imaging for monitoring and control of HIFU treatments under ultrasound image guidance.

The Educational Objectives:

1. Understand the origin of temperature‐dependence of relevant acoustic parameter and their effects on observed pulse‐echo data.

2. Understand the limitations of noninvasive temperature estimation using pulse‐echo data.

3. Understand the connection between the physical model for temperature evolution and robust temperature and parameter tracking in tissue media.
MO‐E‐M100F‐04: Optimizing Low‐Dose Megavoltage Fluoroscopy for 4D Radiotherapy
Authors: Christensen J , Tai A , Chen G , Boettger T , Khamene A , Celi J , Li X
Published: July 2007

Purpose: This study explores the feasibility of using megavoltage fluoroscopy (MVF) for on‐line real‐time verification and guidance for gated/4D treatment delivery. Initial experiences in implementing MVF and methods developed to minimize required dose and optimize the signal‐to‐noise ratio will be presented. Methods and Materials: A Siemens LINAC retrofit with a flat panel imager in the beam direction was used to acquire MVF images with 10242 pixel matrix at 7 frames‐per‐second (fps) using 6 MV photons. Image processing software tools were developed to remove artifacts caused by beam pulsing, dead pixels and stuck bits and to average pixels and video frames. The beam delivery rate was adjusted during MVF acquisition in an attempt to minimize the dose per frame. A phantom designed to test the contrast resolution of kilovoltage fluoroscopy systems was used to assess the MVF image quality at different beam delivery rates. Results: Good quality MVF images with sequences longer than a typical respiratory cycle (5 sec) were obtained with an estimated dose as low as 0.6 cGy. Matching the beam pulse frequency to a multiple of the video frame rate minimized striping artifacts. Image sequences acquired at a frame rate of 3.5 fps and beam delivery rate of 12 MU/min had an SNR of 125; the minimum object resolvable during cine display was 0.063 inch in diameter, and the 0.31 inch diameter object was detectable at 2% contrast. Contrast detectability was improved by averaging video frames, reducing spatial resolution and displaying video in high‐speed cine mode. Conclusions: It is feasible to acquire good quality megavoltage fluoroscopy images using a low dose‐rate treatment beam, indicating that MVF can be used to verify or guide gated/4D treatment delivery in real time (e.g. prior or during treatment delivery). Conflict of Interest: This work was supported in part by Siemens OCS.
MO‐E‐M100F‐05: Fluoroscopic Tracking of Multiple Implanted Fiducial Markers Using Multiple Object Tracking Algorithm
Authors: Tang X , Sharp G , Jiang S
Published: July 2007

Purpose: To develop a multiple fiducial marker tracking system providing precise tumor localization for beam gating and tracking. Method and Materials: We developed a multiple marker tracking system allowing us to track implanted fiducial markers for the treatment of mobile tumors. For each patient, LAT and AP fluoroscopic videos were acquired during the treatment. For each fluoroscopic frame, we first applied a prediction module to predict the marker positions and then a detection module to detect markers in the area around the predicted positions. Then, we applied a multiple object tracking algorithm to identify the true markers among all the detected ones. Breathing pattern information was used to improve the tracking performance. Four criteria were used to identify tracking failures, and when tracking failure happened, the system could immediately inform the user and disable the treatment beam. Results: We compared the performance of the proposed system to a conventional tracking system. To test the robustness of the tracking system, artificial markers were added around the true markers to generate false matches. The conventional system easily misses tracking markers in the presence of artificial markers; furthermore, it cannot detect subsequent tracking failures. Our proposed system could track markers well in the presence of artificial markers, and it could also successfully detect tracking failures. Our proposed system achieved a 0% failure rate almost all the time, and it yielded a low e95 (the maximum marker tracking error at 95% confidence level) — less than 1.5 mm. Conclusion: The proposed marker tracking system can track multiple markers simultaneously without confusion and it is robust enough to continue tracking even when the marker is moving behind bony anatomy. It can also detect tracking failures and inform the user. Conflict of Interest: Research is partially sponsored by an NCI grant (1 R21 CA110177 A 01A1).
MO‐E‐M100F‐06: Intra‐Fraction and Inter‐Fraction Real‐Time Tumor Motion Prediction Using Multiple External Surrogates
Authors: Van Liew S , Mc Avoy T , Dieterich S , D'Souza W
Published: July 2007

Purpose: To determine the feasibility of predicting real‐time tumor positions using multiple external surrogates and Partial‐Least‐Squares (PLS) regression. Methods: Nine patients with lung tumors underwent extracranial stereotactic radiosurgery comprising 3 fractions with the Cyberknife Synchrony™ system. Three LED markers were placed on the patient's abdomen and in close contact with the skin. Synchronous LED marker and tumor marker coordinates were measured periodically using an LED camera and stereoscopic x‐ray images, respectively. PLS performs regression on a small number of latent variables (LVs), which represent the underlying factors responsible for the variation in the output response. They are linear combinations of the original independent variables. The number of LVs in the PLS model was determined by performing a cross‐validation using a training data set and minimizing the error. The LV coefficients were then extracted from the cross‐correlation of input and output variables. Tumor position prediction errors were evaluated for the following scenarios: (1) tumor/external surrogate relationship for a given fraction, (2) predictive model developed in one fraction and applied to other fractions. Prediction errors were compared with standard multiple linear regression (MLR). Results: The mean tumor motion displacement was 7.3 mm for the patient data investigated. The average error for intra‐fraction tumor position prediction based on external markers was 1.47±0.90 mm for PLS and 3.07±1.67 mm for MLR when data from a single fraction was used. When the predictive model from one fraction was applied to the remaining two fractions, the average real‐time inter‐fraction error was 1.48±0.57 mm for PLS and 6.69±3.58 mm for MLR. Conclusion: PLS can predict the tumor position using external surrogates with errors of < 2mm and with superior accuracy compared with MLR. Intra‐ and inter‐fraction prediction errors were statistically similar.
MO‐E‐M100F‐07: Measurement of Delays Between Gating Signals and Beam‐On for Imaging, Static and Dynamic Treatments
Authors: Balter P
Published: July 2007

Purpose: To determine the delays between gating signals and delivery of kV imaging and MV treatment beams for static, enhanced dynamic wedge, and IMRT treatments. Method and Materials: All measurements were taken on a linear accelerator (Trilogy, Varian Medical Systems, Palo Alto, CA), equipped with kV imaging and respiratory gating. A phantom simulating regular motion was used to trigger the gating system. Delivery of both kV imaging and MV treatment beams were monitored using a diode connected to an analog electrometer operating in current mode. The electrometer's voltage output and the gating signal were both monitored by a multichannel oscilloscope. Traces were recorded comparing the diode output to the gate signal. The MV beam was monitored during delivery of static, enhanced dynamic wedge and IMRT fields. For the IMRT field the diode received only scattered radiation resulting in poor signal‐to‐noise but the results were still sufficient for this work. Results: The delay between the gating signal and beam on signal was found to be unmeasurable for the static MV beam, and 30 and 50 msec respectively for the wedged and IMRT beams. The delay for the kV beam was 300 msec. Because tumors can move up to 2 cm in a 5 sec breathing cycle, a 300 msec delay can result in up to a 4 mm position error; however, because gating is generally done at expiration or inspiration where the velocity is at a minimum, the uncertainty should be much lower. Conclusion: There is no appreciable delay between gating signals and MV irradiation. There is a delay between kV imaging and gating signals but the clinical consequences can be minimized by gating where tumor velocity is minimal.
MO‐E‐M100J‐01: Anatomical Imaging
Authors: Mageras G
Published: July 2007

This presentation surveys imaging systems, their limitations and expectations for target and organ‐at‐risk position determination, delineation and respiratory motion estimation. Discussion will focus on systems that are in current clinical use. Imaging techniques at simulation usually attempt to use the same patient breathing conditions as at treatment, among them, breath hold, free breathing, coached breathing, or abdominal compression. CT remains the dominant standard for anatomical imaging of external beam radiotherapy simulation. CT acquisition techniques for motion estimation include breath hold at different inspiration levels, or more recently, respiration‐correlated CT (RCCT), involving retrospective sorting of axial images by means of a respiration signal. A limitation of RCCT is that images at a given position along the patient are confined to a single respiratory cycle, and assumes that the breathing pattern is repeatable, which is known to be violated to some extent depending on the patient. Further, images are acquired over several cycles and resorted into a single one; thus cycle‐to‐cycle changes in breathing pattern lead to artifacts. Coached breathing attempts to achieve more repeatable breathing and has shown varying degrees of improvement in some patients. Breath‐hold CT fidelity is similarly dependent on breath‐hold repeatability. Ideally imaging over several breath cycles is desirable, but imaging dose imposes limitations with RCCT, while patient fatigue limits breath‐hold CT. A possible future direction of development is to complement CT with modalities that can image over several cycles with little or no additional dose. For example, repeat MRI in the sagittal plane provides not only a self‐consistent image in terms of respiratory motion but also an estimate of cycle‐to‐cycle variation in motion extent, which is valuable for evaluating the sensitivity of a treatment plan to such variation.

Education Objectives:

1. Understand the current technological advances in radiotherapy imaging at simulation to provide spatial information and respiratory motion estimation;

2. Understand the limitations, current expectations, and possible further improvements of these imaging systems.
MO‐E‐M100J‐04: Planning Target Volume Determination
Authors: van Herk M , Wolthaus J , Sonke JJ , Remeijer P , Damen E , Lebesque JV
Published: July 2007

Treatment planning should be based on a high fidelity representation of the patient's anatomy, as it will be at time of treatment. The imaging setup (couch, immobilization, alignment) should therefore be representative for the treatment situation. When basing a treatment plan on a single scan (which is current clinical practice), the optimal imaging strategy is therefore to create an anatomical model that is as close as possible to the “average” anatomy. For random organ motion, plan optimization can therefore be achieved by averaging the geometry of multiple scans (i.e., adaptive radiotherapy). For periodic motion it has been proposed to use a scan with the organs as close as possible to their time‐weighted average position — by selecting a single scan out of 4DCT. Using these methods, the systematic errors due to treatment preparation are minimized and the dose distributions will be very close to a full 4D planning (using all scans out of a 4DCT scan). Using image guidance some other error sources can be eliminated. However, even with image guidance there are residual errors: such as uncertainty in GTV and CTV delineation, in image registration, and in setup correction and uncertainty due to intra‐fraction motion. Currently, simple margin recipes are used to estimate the correct CTV‐PTV margin such that the net effect of all these uncertainties does not compromise the goal of the treatment: eradicate the tumor while sparing normal tissues. One should be aware, however, that the most simple margin recipes are based on many assumptions: such as Gaussian distributions, penumbra width in water, systematic error SD > random error SD, and plans with a more or less uniform dose distribution. In case of image guidance for lung tumors all of these assumptions break down, and simple recipes typically will overestimate the required margin. Based on a more detailed analysis, it appears that the margin that can be used for hypofractionated lung radiotherapy can be very small (1 cm or less), even for large respiratory amplitudes (2 cm).

Educational Objectives:

1. Understand the need for a representative planning CT, i.e., minimize systematic errors.

2. Understand the difference between systematic and random errors, and the effect that respiratory motion has on the delivery of radiotherapy.

3. Understand the need for margins, even in case of image‐guided. radiotherapy.

4. Understand the derivation of margins for image‐guided radiotherapy of lung cancer.
MO‐E‐BRB‐02: Incorporating Open Standards Into Online Medical Physics Education
Authors: Antolak J
Published: July 2007

Purpose: Graduate students, residents, and allied health professionals rely on medical physicists to help them learn about medical physics, and online learning is increasingly being used to supplement or replace traditional didactic education. Free and Open Source Software (FOSS) versions of course management and authoring software are available for creating and managing media for online courses. These software packages can be easier to use in the long run because they tend to be more standards compliant, which makes maintenance of the content more manageable. Methods and Materials: FOSS course management software was implemented to supplement a yearly physics course offered to residents. Management of the system was relatively easy, and incorporating materials from a variety of sources was relatively straightforward. Additions and updates are immediately reflected in the online course, and features in the software allow the residents to take an active role in their own education. Results: Initially, the online content mirrored the handout binder given to the new residents, and residents adapted very quickly to using the new system. Residents appreciated the almost immediate feedback provided by computer‐graded quizzes, and the course faculty were able to generate reports showing questions that were either more difficult or not covered very well in the lectures. These reports provided the basis for review sessions that were interspersed with the lectures. In the short term, it placed an increased burden on faculty to move materials online, but modifying them is currently somewhat easier. Conclusion: Learning to use FOSS tools to author and manage course materials is one way to create an enhanced learning environment, benefiting both learners and teachers. As we learn to take advantage of more of the features of the software, the learning environment can be enhanced even further and can be applied to more than just resident education.
MO‐E‐BRB‐04: A Grid for Justifying Clinical Staffing Budgets
Authors: Klein E , Low D
Published: July 2007

Purpose: Justification of clinical physics staffing levels is difficult due to the ever increasing time demands to implement new technologies and by lack of direction as how to equate clinical needs with the staffing levels and competency required. When a physicist negotiates staffing requests to administration, she/he often refers to “blue book” (ACR) staffing suggestions, and resources such as the Abt studies. This approach is often met with questions as to how to fairly derive the time it takes to perform tasks properly, and what level of experience is actually required. The result is often insufficient and/or inexperienced staff handling complex and cumbersome tasks. We undertook development of a staffing justification grid to equate the clinical needs to the quantity and quality of staffing required. Method&Materials: The first step is using the Abt study, customized to the clinical setting, to derive time per task multiplied by the anticipated number of such tasks. Inclusion of vacation, meeting, and developmental time is incorporated along with allocated time for education and administration. This is followed by mapping the tasks to the level of competency/experience needed, for example in an academic setting the faculty appointment levels. Non‐staff personal, such as IMRT QA technicians or clerical staff should also be part of the equation. This grid method not only equates the clinical needs with the quantity of staffing, but also generates the personnel budget, based on the type of staff and personnel required. Results: By using the staffing justification grid, we derived strong documentation to justify a substantial budget increase. Conclusion: Though our grid is for a large academic facility, the methodology can be extended to a non‐academic setting, and to a smaller scale. The grid is easily adaptable when changes to the clinical environment change, such as an increase in IMRT or IGRT applications.
MO‐E‐BRB‐05: Raising the Bar by Going Paperless
Authors: Venkatesan J
Published: July 2007

Purpose: This presentation will explore the strategies employed in transitioning to paperless and film‐less department; the challenges, costs, reimbursement issues and the economic value created. Methods and Materials: Differential state analysis was performed using financial, time‐motion and qualitative metrics to examine and evaluate the effects of establishing a fully electronic EMR paradigm for a major hospital‐based RT department. Several project and change management strategies were employed to gain user and clinician acceptance, and to analyze and modify workflows to adapt to the new electronic paradigm. Evaluation and selection of a robust, adaptable and full‐featured EMR, along with imaging and treatment device interfaces was done using multiple data points and clinical references. Results: Once fully implemented, significant efficiencies and increases in productivity were measurable. Time savings and increased efficiencies in chart related activities that now allowed for distributed and simultaneous data access, and distributed image review were dramatic. Further improvements were seen in scheduling, charge capture and billing related activities. Quality measures due to improved and more comprehensive treatment documentation, along with qualitative measures relating to workplace psychology all showed improvement. Conclusion: Although the challenges may seem daunting from a financial and project management perspective, the measurable benefits of a fully paperless and film‐less department demonstrate a net positive benefit. In addition, pay‐for‐quality initiatives and tightening reimbursement standards will demand a level of data richness that can only be obtained from a suitable and fully utilized EMR.
MO‐E‐AUD‐01: Automated CBCT QA for Image‐Guided Radiation Therapy
Authors: Fox T , Elder E , Schreibmann E
Published: July 2007

Purpose: The use of image‐guided patient positioning requires fast and reliable Quality Assurance (QA) methods to ensure the megavoltage (MV) treatment beam coincides with the integrated kilovoltage (kV) imaging and guidance system. This study describes an automated and comprehensive QA procedure to monitor the coincidence of the mechanical, radiation and imaging isocenters using cone‐beam CT (CBCT) and planar X‐ray imaging. Method and Materials: The On‐Board Imaging (OBI) system consists of a kV x‐ray tube and an amorphous‐silicon flat panel imaging detector which are attached to a medical linear accelerator. A Penta‐Guide phantom (Modus Medical Devices Inc. London, Ontario, Canada) with five internal markers and external markers for isocenter position and field sizes was imaged using the CBCT, kV and MV capabilities. The markers' location and size can be automatically determined using our graphical software system. The accuracy of CBCT imaging is assessed by comparison of the extracted marker positions and sizes against the phantom specifications. The coincidence of the imaging and dosimetric isocenters are tested by a similar analysis of the markers extracted from the kV and MV images. Additional tests are also performed such as isocenter stability with gantry angle, image size, collimator angle and size, and gantry angle. Results: The test was performed on all four IGRT‐enabled machines available in our institution. The coincidence between the mechanical, radiation and imaging isocenter are within 1 mm for all four accelerators. Isocenter stability with gantry angle was also within 1 mm. The acquisition of the images took ∼ 5 min, and the automated software analysis took less than 1 min. Conclusion: Our automated image analysis may be used as a daily QA procedure because it is completely automated and uses a single phantom setup.
MO‐E‐AUD‐03: Study of Total Positioning Accuracy of a Newly Developed Image‐Guided Radiotherapy System
Authors: Kaneko S , Takayama K , Nagano K , Narita Y , Kokubo M , Takahashi K , Mizowaki T , Hiraoka M
Published: July 2007

Purpose: The aim of this study was to evaluate system accuracy of our newly developed image‐guided radiotherapy (IGRT) system. Method and Materials: The system has the following structural characteristics; (1) C‐band compact linear accelerator (LINAC), (2) O‐ring shaped gantry, (3) Gimbals mechanism at X‐ray head, and (4) Imaging subsystem. The whole X‐ray head with the LINAC and a MLC is equipped on gimbals mechanism to correct beam direction to isocenter. The imaging subsystem mounted on the O‐ring gantry consists of two sets of a kV X‐ray tube with an image detector, and can obtain either X‐ray images or cone‐beam CT (CBCT) images. By using Electronic Portal Imaging Device, the IGRT system also provides an automatic daily QA tool for total positioning accuracy, which means beam accuracy towards isocenter combined with image‐guiding accuracy. The daily QA requires only 3 minutes. Firstly in this study, to evaluate the image‐guiding accuracy, a spherical metal ball with a diameter of 10 mm was set at given positions within 20 mm from isocenter. X‐ray images or CBCT images were obtained to measure the ball position, and the difference between true and measured position was calculated. Secondly, Mechanical accuracy of beam direction to isocenter was measured in various gantry angles with CCD camera attached to MLC frame. Finally, the combined accuracy was verified by using the daily QA tool. Results: The difference between true and measured position was 0.34 mm in SD and 0.9 mm at the maximum for X‐ray image, then 0.17mm in SD and 0.4 mm at the maximum for CBCT, respectively. Mechanical beam accuracy was within 0.1mm. The combined accuracy was better than 0.5 mm. Conclusion: The IGRT system has suitable accuracy for image‐guided stereotactic irradiation. Conflict of Interest: Research sponsored by New Energy and Industrial Technology Development Organization, Japan.
MO‐E‐AUD‐05: Validating a Video‐Based 3‐D Surface Imaging System and Testing Its Use to Set‐Up CBCT QA Device
Authors: Yang C , Liu T , Guo F , Purdy J
Published: July 2007

Purpose: To validate resolution of a video‐based 3‐D surface imaging system before its clinical use and to test feasibility of using system in setting‐up a cone beam CT (CBCT) QA device to accelerate the total QA process. Method and Materials: A CBCT QA alignment tool called Ball‐Bearing device (BBD) (Elekta Inc.) is designed to check the coincidence between the MV and kV beams' isocenters. The micro‐stepping meter of the BBD allows precision adjustment to better than 0.01 mm in three directions. A foam phantom was added to the BBD in order to generate a large 3‐D surface image which can be detected by a video‐based 3‐D surface imaging system (AlignRT system, VisionRT Ltd., London UK). The BBD‐phantom has been imaged by the AlignRT system with changes in position (0.0 to 8.0 mm) in all three directions independently. The phantom shifts were determined by AlignRT and compared to the preset ones. After this validation test, AlignRT has been used in the initial set‐up of the CBCT device in replacement of the iterative process required to set the BBD to the MV isocenter. By carefully setting‐up the BBD using the iterative imaging method to place the ball‐bearing to MV beam isocenter, a reference image of BBD‐phantom was taken using AlignRT. Subsequently, AlignRT was used in BBD set‐up; multiple tests have been performed and testing continues. Results: AlignRT can detect 0.1 mm change in both lateral and longitudinal directions, 0.3 mm in vertical direction. AlignRT reduced set‐up time for CBCT QA device by a factor of two compared to traditional iterative method. Conclusions: AlignRT can detect fractional mm shifts in the BBD‐phantom; vertical resolution is not as sensitive as horizontal. AlignRT can be used in setting‐up the CBCT QA device (providing appropriate phantom added) and significantly reduces set‐up time.
MO‐E‐BRA‐02: Principles of Adaptive and Robust Control in Treatment Planning
Authors: Sharpe MB
Published: July 2007

Local control by radiation therapy relates directly to the dose delivered to the diseased tissue, but can be limited by the dose tolerated by adjacent structures. This axiom has guided clinical practice into a number of technological shifts over the past several decades. Intensity‐modulated radiotherapy (IMRT) has emerged as an important means to achieve higher doses and to intensify treatment, while simultaneously decreasing the dose in normal tissues. However, the proximity of critical normal organs to disease and geometric uncertainties arising from organ movement continue to present significant challenges in some anatomical sites.

Advances in image‐guided radiation therapy (IGRT) permit more frequent soft‐tissue imaging in the course of treatment delivery, creating opportunities to enhance the accuracy and precision of treatment. A framework for considering image‐guidance strategies and their implications for treatment planning is required. For example, target localization can improve geometric accuracy in the on‐line setting; i.e., during treatment delivery. An off‐line statistical analysis of a patient's images can also enhance precision by supporting the adaptation of margins. Even a complete re‐optimization of the plan is possible, in response to systematic anatomical changes accumulated with the progression of treatment. Frequent re‐optimization is potentially inefficient and expensive, within the constraints of current technologies, clinical practices, and QA standards. Clearly, there are trade‐offs between the level of effort required to an exploit IGRT for adaptive re‐planning, and the potential benefits of re‐planning. The concept of robust optimization points to the possibility designing treatment plans that are tolerant to uncertainties in treatment delivery. Robust plans may reduce the need for routine re‐planning in response to variations in patient setup, organ movement, or progressive changes leading to organ deformation.

This presentation reviews clinical experience with IGRT, and explores the implications, opportunities and challenges for treatment planning in the era of IGRT. The central principles of using IGRT in IMRT treatment planning with respect to requirements for adaptive re‐planning and the design of robust IMRT treatments.

Educational Objectives:

1. To review illustrate clinical applications of IGRT.

2. To describe how the adoption of IGRT can influence external beam treatment planning.

3. To outline how IGRT information is used for re‐planning of IMRT treatments, and in the design of plans that are tolerant to uncertainties in treatment delivery.
MO‐E‐L100E‐01: Writing and Reviewing Medical Physics Papers
Authors: Hendee W , Karellas A , Rogers D , Slattery P
Published: July 2007

There is an art to writing a scientific paper so that it communicates accurately, succinctly, and comprehensively. Developing this art comes with experience, and sharing that experience with younger physicists is an obligation of senior scientists, especially those with editorial responsibilities for the journal. In this workshop, the preparation of a scientific manuscript will be dissected so participants can appreciate how each part is developed and then assembled into a complete paper. Then the review process for the paper will be discussed, including how to examine a paper and write an insightful and constructive review. Finally, we will consider the challenge of accommodating the concerns and recommendations of a reviewer in preparing a revision of the paper.

A second feature of the workshop will be a discussion of the process of electronic submission of a paper for consideration by Medical Physics. The web‐based PeerX‐Press engine for manuscript submission and management will be examined, with attention to special features such as epaps and line‐referencing. Finally, new features of Medical Physics will be explained, such as Vision 20/20 manuscripts, Physics Letters and the standardized formatting of book reviews.

Education Objectives:

1. Improve the participants' abilities to write a scientific manuscript.

2. Understand the review process for Medical Physics manuscripts and how to participate in and benefit from it.

3. Appreciate the many features of the PeerX‐Press electronic management process for Medical Physics manuscripts.

4. Develop a knowledge of new features of Medical Physics.
TU‐A‐BRB‐01: Imaging for Planning/Verification: In‐Room Imaging
Authors: Brock K
Published: July 2007

Multi‐modality imaging is improving the accuracy and precision in treatment planning by including more information in the initial model of the patient. The goals of imaging for treatment planning are to determine the boundaries and functional information of the tumor and critical normal structures. Quantification of physiological motion has also become increasingly important in highly conformal treatment planning. Obstacles for imaging include improving contrast, limiting artifacts, improving temporal and spatial resolution, and reducing or eliminating the interference of motion.

Combining the soft tissue imaging of MR, functional imaging of MR, CT, PET and SPECT with geometrically robust CT imaging improves the definition of the tumor and critical normal structures. In addition, dynamic information can be accurately quantified and incorporated into the treatment planning process through 4D imaging capabilities in CT and repeat MR imaging. Reducing motion artifacts allows improvement in tumor definition. Methods of reducing the interference of motion on image acquisition include suspending the motion, through voluntary or assisted methods, and reducing the imaging session length, through multi‐slice acquisition and parallel imaging. Optimizing imaging sequences and contrast enhancement and timing improves the ability to define the tumor. The integration of these multi‐modality images into one more complete model of the patient is evolving through the use of automatic registration methods.

The presentation will highlight the benefits of multi‐modality imaging in the treatment planning of tumors in the thorax, abdomen, and pelvis. Image optimization strategies will be discussed for each modality and developments to improve image acquisition and integration into treatment planning will be described.

Educational Objectives:

1. Appreciate the benefits of including multi‐modality imaging in treatment planning.

2. Understand methods to optimize the acquisition of multi‐modality images for accurate treatment planning, including sequences, postprocessing, and timing.

3. Identify technical developments to improve image acquisition and integration into treatment planning.
TU‐A‐BRB‐02: Imaging for Planning/Verification: In‐Room Imaging
Authors: Papanikolaou N
Published: July 2007

It was not too long ago when CT based treatment planning was reserved for the few patients that was critical to have volumetric imaging, and treatment verification was limited to planar films of mediocre quality from a megavoltage imaging source. Today, we use multi‐modality based planning (CT, MRI, PET etc) and we employ sophisticated imaging tools and techniques to verify the correct delivery of the treatment. Such imaging capabilities include electronic portal imaging devices coupled with megavoltage (MV) or kilovoltage (kV) x‐ray sources, MV and kV cone beam CT, ultrasound guidance, optical systems, MV computed tomography, CT on rails and others. The goal of any in‐room imaging device is to verify that the patient setup is accurate and in accordance to the treatment plan. While some modalities allow for pre‐treatment verification, others can also provide on‐treatment verification feedback. The choice of the modality to use depends largely on user preference but also on the investment the clinic is willing to make to purchase the necessary equipment. Nonetheless, image based treatment verification has become a necessary and valuable aspect of our clinical practice and is enabling us to become a lot more aggressive with the planning and delivery of radiation treatments. Image Guided Radiation Therapy (IGRT) is undoubtedly the future of radiation therapy.

In this presentation we will discuss some of the most popular methods of imaging for treatment verification techniques. Clinical examples will also be presented to demonstrate the implementation, use, and clinical experience with these modalities.

Educational Objectives:

1. Review of existing image based treatment verification modalities.

2. Discuss pros and cons of each modality and appropriateness of use.
TU‐SAMS‐L100J‐03: Optimizing CT Image Protocols With Respect To Quality and Radiation Dose
Authors: Cody D , Kofler J
Published: July 2007

CT technology continues to develop at a rapid pace, offering imaging options and features that can dramatically improve image quality. Multichannel systems are now commonplace and the number of channels continues to increase, allowing greater coverage per rotation, shorter scan times, and thinner images. Isotropic volumetric data acquisition permits retrospective reconstructions of many different image thicknesses and reformats can be created through multiple planes. These and many other advances have escalated and expanded the utility of CT imaging as a core diagnostic tool.

However, coupled with the improved CT technology is the increased complexity of operating the scanners and the elevated potential of increasing the radiation dose. CT operators must choose from multiple options, many of which are interdependent, for the control of the multitude of available features. The impact of each of these options on image quality and radiation dose can range from subtle to substantial, and may not necessarily be obvious to the operator.

This lecture will focus on the clinical implications of CT scan parameters and provide guidance on achieving an optimal compromise between image quality and radiation dose when constructing CT scan protocols.

Educational Objectives:

1. Understand the influence of primary CT scan parameters on image quality and radiation dose.

2. Learn how to use imaging task‐specific priorities with consideration for radiation dose when determining scanner settings.
TU‐B‐BRB‐01: Monte Carlo — II: Clinical Impact
Authors: Ma C
Published: July 2007

This presentation is aimed at facilitating participants with the clinical application of Monte Carlo dose calculation algorithms in radiotherapy treatment planning and dosimetry verification. Following a brief introduction to the clinical implementation and commissioning of the Monte Carlo dose calculation software detailed discussions will be given on the actual and potential clinical impact of Monte Carlo dose calculation algorithms on conventional electron beam therapy and advanced mixed beam treatments.

Patient treatment plans generated using conventional dose calculation algorithms and Monte Carlo methods will be compared with the causes of the dose discrepancies discussed. Further discussions will be conducted on the use of Monte Carlo dose calculation as a radiotherapy treatment QA tool to validate individual patient plans and as an investigation tool to improve target dose conformity and normal tissue sparing using novel treatment techniques.

Educational Objectives:

1. To introduce important aspects of clinical implementation and commissioning of Monte Carlo dose calculation algorithms for radiotherapy treatment planning.

2. To describe the role of Monte Carlo dose calculation in electron therapy and advanced mixed beam treatment planning.

3. To describe the applications of Monte Carlo dose calculations in treatment planning and beam delivery QA for advanced radiotherapy treatments.