bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐460: Comparative in Vitro Study of Cell Survival Following IMRT and Acute Dose Delivery
Authors: Moiseenko V , Duzenli C , Durand R
Published: July 2006

Purpose: To investigate cell kill from IMRT fields compared to acute dose delivery. Method and Materials: Survival was assayed in vitro for three cell lines: Chinese hamster V79 fibroblasts, human cervical carcinoma SiHa and colon adenocarcinoma WiDr. An actual head and neck seven field dynamic IMRT plan produced for Varian iX, 120 Millennium MLC linear accelerator was used. The calculated IMRT dose (Cadplan, Palo Alto) to the point of irradiation in the acrylic phantom was 2.1Gy. This was verified by measurements with an IC10 ionization chamber. Two IMRT dose delivery scenarios were explored: 1. normal delivery, irradiation time of 5min 10s, and 2. IMRT delivery with a 5min break for MLC re‐initialization after three fields were delivered, irradiation time of 10min. For comparison the same dose of 2.1Gy was delivered by parallel‐opposed pair (POP) in 75s, 20s beam‐on time per beam. Survival data were obtained in the dose range up to 10.5Gy to establish the linear‐quadratic survival curves. Results: An increased cell survival following irradiation with IMRT fields was observed for all cell lines. V79 cells showed the smallest increase: 0.833±0.018 (95% confidence limits) from POP compared to 0.860±0.040 for IMRT with MLC re‐initialization. This increase was very pronounced for the radiosensitive SiHa cell line: 0.390±0.046 for POP irradiation compared to 0.591±0.080 from IMRT requiring MLC re‐initialization. Although variable between cell lines, projections made for a 30 fraction treatment showed substantial reduction in cell kill. Conclusions: We observed an increase in cell survival from IMRT fields compared to acutely delivered dose. This increase was persistent, but not always statistically significant. Projections for a fractionated treatment showed that consequences of this increased cell survival are substantial with a very large variation between cell lines. This projection, however, does not account for features present in vivo, for example reoxygenation and reassortment.
SU‐FF‐T‐466: A Single Dose Calibration Method for IMRT QA Film Dosimetry Using Gafchromic® EBT Film
Authors: Baker J , Telivala T , Reinstein L
Published: July 2006

Purpose: In order to decrease the workload for IMRT QA film dosimetry we propose a simple method for Gafchromic® EBT film calibration using a pre‐measured batch calibration curve (BCC) which is mathematically scaled with a single dose exposure (SDE) for each subsequent IMRT QA session. We evaluate how the SDE method corrects for post exposure density growth and temperature dependence in addition to inter film response homogeneity. Method and Materials:

Each of five EBT films, from a single production lot, were exposed to doses of 22.5, 43.1, 84.4, 147.4, 209.1, and 291.2 cGy. Measurement of the resulting response curves were performed at times ranging from 0.7 to 52 hours post exposure on a Macbeth TD932 point densitometer customized with a 636nm band pass filter and 16 bit digitizer for increased sensitivity, yielding 35 curves in all. The BCC was generated from a film measured at 0.7 hours and fit to the equation . To test the method, net optical density (NOD) data for the remaining 34 curves was scaled to fit the BCC using 209.1 cGy as the SDE. The scaling factor is the ratio of the actual measured NOD of the SDE, and the NOD predicted by the BCC for this dose. The new scaled calibration is used to predict all 204 test doses, which were then compared to the actual delivered doses. Results: Using the single uncorrected BCC resulted in an average error for the 204 dose points of 11.9 cGy. However, scaling according the method described reduced the average measured dose error to 1.1 cGy. Conclusion: The single dose exposure method described here is an accurate and time efficient calibration procedure for IMRT QA film dosimetry. Conflict of Interest: Partially supported by International Specialty Products.
SU‐FF‐P‐05: Medical Physics Situation in Colombia
Authors: Machado N , Plazas M
Published: July 2006

Purpose: To describe the current situation of the Medical Physics field in Colombia concerning to human resources, physics infrastructure (radiation oncology centers, radiation machines, treatment planning systems, dosimetry systems, nuclear medicine and diagnostic facilities, imaging devices and radiation protection systems), academic programs, medical physics societies and regulatory institutions. Method and Materials: For this presentation we have taken as reference some studies carried out in Colombia during the last few years as follows:

• Evaluation of radiation oncology facilities in Colombia, an audit study conducted to evaluate the radiotherapy centers and the quality of assistance for cancer patients.

Comparison among Medical Physics academic programs offered in the world, specially those carried out in the Latino‐American region. Results: Up to the date the mentioned study was conducted, there was 46 radiation therapy centers in Colombia and only 14 had medical physicists.

The number of nuclear medicine centers existing in Colombia was approximately 47, mainly concentrated in Bogotá, where 22 of them are located. Currently the number of medical physicists working in the nuclear medicine facilities in Colombia is really scarce.

Worldwide it can be seen that North America is the region with the greatest number of universities offering Medical Physics Master programs. In the Latin American context, Mexico had the greatest number.

The statistical distribution of diagnostic x ray machines was about 53000 in Latin‐American countries and the number of medical physicist working to these centers is very low. There is human resources shortage, especially for Medical Physicists in the radiation oncology, nuclear medicine and diagnostic facilities. There are some academic programs in Medical Physics. Currently there is a increasing interest from universities in Colombia to create medical physics under and postgraduate programs.
MO‐A‐330A‐01: Recent Advances in Digital Mammography
Authors: Yaffe M
Published: July 2006

Digital mammography was developed to address several technical limitations of screen film mammography with the goal of improving the accuracy of detecting breast cancer. The recent publication of the results of the ACRIN DMIST study has demonstrated such an improvement in a subset of women, notably, younger women and those with dense breasts. Nevertheless, the study also indicated that a significant fraction of cancers were not detected by either film or digital mammography. This is likely due to a number of reasons including the biology of the cancers, inadequate conspicuity of the lesions and variability of the skills of the radiologists. While it probably is not possible to detect all these cancers with mammography there are promising new techniques that can be developed on the platform of digital mammography to improve detection. One of these is computer‐aided detection, the use of computer artificial intelligence algorithms to identify patterns in the digital images that are suspicious for the presence of cancer. These provide some of the advantages of double reading of the mammograms (interpretation by two different radiologists), a process known to improve the sensitivity of cancer detection. Another new technique is contrast‐enhanced digital mammography (CEDM), which images leakage of an iodine contrast agent from microscopic vessels formed in the vicinity of a growing tumour. By imaging this tumour angiogenesis, cancers that are invisible on mammography might be seen. In addition, better information about the extent of the disease will be helpful in planning therapy. In mammography all of the anatomy in the 3‐dimensional breast is superimposed in two dimensions to form the image. Tomosynthesis and breast CT provide three‐dimensional images to separate the structures within the breast, possibly allowing tumors to be seen more easily and eliminating the overlap of structures from different parts of the breast that can falsely resemble a cancer. Telemammography can help improve the accessibility of high quality mammography in sparsely‐populated communities. In this presentation, the current status and the potential of these exciting new techniques will be considered.

Disclosure:

Martin Yaffe's laboratory carries out research on topics related to digital mammography in collaboration with GE Healthcare. Martin Yaffe is a member of the Scientific Advisory Board of XCounter.

Educational Objectives:

1. Become familiar with current challenges in breast cancer imaging.

2. Learn about new techniques that are available or under development to address these challenges.
MO‐A‐330D‐01: Advances in PET Technology ‐ New Crystals and Detector Designs
Authors: Fahey F
Published: July 2006

Over the past ten years, the use of clinical PET, particularly in the field of oncology, has increased dramatically. More recently, the introduction of hybrid PET/CT scanners has led to an enhanced ability to provide anatomical correlation to the functional findings on the PET scan. And lastly, the growing field of molecular imaging has led to the development of a variety of dedicated PET systems for small animal imaging. In the clinical arena, the goal is to develop scanners with higher sensitivity and count rate capability to be able to acquire whole body scans more efficiently. Efficiency is essential with respect to small animal imaging as well, but it must be accomplished with very high spatial resolution. This presentation will review the basics of PET imaging with a look towards the advances being made to address the needs of these two very different imaging tasks. The use of 2D versus 3D will be discussed as well as the effect using different crystal materials. Other advances being actively pursued such as the use of time‐of‐flight PET will also be discussed.

Educational Objectives:

After attending this presentation, the attendee will be able to list 2 advantages and 2 disadvantages of 3D PET compared to 2D PET for clinical, whole body imaging, name 3 different materials used in state‐of‐the‐art PET scanners and list 2 advantages of each, and discuss two potential advantages for time‐of‐flight PET.
MO‐A‐ValB‐01: Tradeoffs in Image Quality and Radiation Dose for CT
Authors: McNitt‐Gray M
Published: July 2006

In CT scanning, image quality has many components and is influenced by many technical parameters. While image quality has always been a concern for the physics community, clinically acceptable image quality has become even more of an issue as strategies to reduce radiation dose — to all patients, but especially to pediatric patients— has become a focus in many radiology practices.

The purpose of this presentation will be to first describe several of the components of CT image quality — noise, slice thickness (Z‐axis resolution), low contrast resolution and high contrast resolution— as well as radiation dose and to describe how each of these may be affected by technical parameter selection. This presentation will pay particular attention to the tradeoffs that exist between different aspects of image quality, especially when the reduction of radiation dose is one of the objectives.

The presentation will then explore several mechanisms that can be used to reduce radiation dose in CT exams and the implications for the diagnostic image quality of the exam. Specifically, the implications of varying the tube current*time product (mAs), pitch or tablespeed (or for axial imaging, the table increment), slice thickness, beam energy (kVp), patient (or phantom) size and dose reduction options (such as tube current modulation) will be described for both radiation dose and diagnostic image quality. Finally, this presentation will emphasize that the tradeoffs between radiation dose and image quality are clinical‐task dependent; that is, the goals of the clinically indicated exam dictate what aspect of image quality may be emphasized for that exam (low contrast resolution or high contrast spatial resolution, etc.) and this will have implications for the amount of radiation dose reduction that is acceptable. This will be illustrated with examples from selected diagnostic imaging exams.

Educational Objectives:

1. Understand key components of image quality in CT scanning as well as reinforce CT radiation dose concepts.

2. Understand the impact that technical parameter selection has on the various aspects of image quality and radiation dose.

3. Examine the tradeoffs between various aspects of image quality and radiation dose.

4. Examine the impact of these tradeoffs on a few clinical imaging protocols and illustrate the task‐dependence of image quality requirements.
MO‐A‐224A‐01: Treatment Planning Optimization Parameters ‐ MD
Authors: Marks L
Published: July 2006

Three‐dimensional radiation therapy (RT) planning tools provide detailed information regarding the degree of radiation exposure to different volumes of organs. Presently, we have incomplete knowledge regarding the tolerance doses for different normal tissue organs. The classic “Emami paper” (IJROBP 1991) provided broad dose/volume guidelines for 3D RT planning, based on somewhat limited clinical data. More recently, there has been dramatic increase in the number and quality of clinical studies that attempt to relate dose/volume parameters to normal tissue risks. Presently, dosimetric parameters predictive for injury are available for several organs (e.g. the lung, heart, esophagus, parotid, and brain), and additional/better data is rapidly accumulating. However, for most organs, the presently‐available predictive models are suboptimal. The continued challenges include: non‐uniform definitions of toxicity (e.g. radiologic vs. analytic vs. symptomatic), clinical comorbidities that make the diagnosis of RT‐induced toxicity uncertain, the confounding effects of concurrent chemotherapy (that is being used with increasing frequency), and multiorgan nature of some clinical endpoints. Further, it is not clear if the dose/volume guidelines developed in the “3D era” are applicable in the hypofractionated/radiosurgery/IMRT era. Extreme caution is warranted to the extrapolation of dose/volume guidelines beyond the scope within which they were defined. For example, the variable fraction size delivered to the surrounding normal tissues with IMRT/radiosurgery is fundamentally different than the relatively‐uniform fraction sizes received by the normal tissues in the 3D era. Since most normal tissue effects are very sensitive to fraction size, this variable needs to be considered. IMRT actually makes the decision‐making process more complex for the physician, as we now have greater flexibility regarding where to deposit the “extraneous/incidental” RT dose. Thus, the need for better dose/volume guidelines, that include consideration of fraction size, has increased with IMRT. When normal tissue dose/volume data becomes more robust, we will be better able to exploit the full potential of 3D/IMRT to minimize radiation‐induced normal tissue injury.
MO‐A‐224C‐01: Daily Localization I: KV/CBCT
Authors: Yin F , Yoo S , Wang Z , Godfrey D , Wu Q
Published: July 2006

Daily target localization is a critical step to secure accurate delivery for 3‐D conformal radiation therapy and intensity‐modulated radiation therapy. One emerging technology using in‐room kilovoltage (kV) imaging has shown to be very promising for targeting treatment volumes. The major advantages of using kV imaging are 1) its comparable contrast between soft tissue and bone structure to that in simulation images, 2) real‐time high resolution fluoroscopic imaging, 3) lower radiation dose to patient compared to conventional MV imaging, and 4) availability of reconstructing tomographic images (for example, cone‐beam CT) using 2‐ D kV projection images. At present, different types of in‐room kV imaging systems are being developed for different applications such as in‐room CT on rail, ceiling‐mounted dual‐source/detector configuration, and gantrymounted single source/detector system. In terms of clinical applications, some generate 2‐D radiographic images for target verification based on bony marks or implanted surrogator while others generate 3‐D tomographic images for target verification based on both soft tissues and bony structures. Some could be used for viewing organ motion to verify applied margin while others could be used for monitoring target motion to verify dynamic delivering or gated treatment. Issues related to the risk and benefit between imaging information and radiation dose using 2‐D or 3‐D imaging, the geometric accuracy of imaging systems, trade‐off between treatment accuracy vs. time required to carry on imaging and manipulation process, early image‐guided protocols for basic clinical applications, etc. will be discussed. Some new developments related to effective and efficient use of in‐room kV and MV imaging, tomographic image reconstruction using limited number and angle projections have shown very promising for future clinical applications.

This lecture will describe the commercially avaialbe kV imaging systems, as we as their applicable clinical protocols, acceptance testing and commissioning processes, basic QA requirements, system limitations, and potential future developments.

Educational Objectives:

1. Understand the latest commercial available technologies for in‐room kV and CBCT systems.

2. Understand the basic functionalities of in‐room kV imaging system.

3. Understand the basic imaging applications.

4. Understand the basic system limitations and QA.
MO‐B‐330D‐01: Design and Performance Characteristics of Computed Radiographic Acquisition Technologies
Authors: Schaetzing R
Published: July 2006

Digital Radiography (DR) using Storage Phosphors, also known as Computed Radiography (or CR), has been commercially available for a quarter of a century. Each new generation of scanners and screens has brought improvements in image quality, throughput, physical size and cost. With these improvements has come a high level of clinical acceptance, with a corresponding displacement of screen/film systems as the standard for projection radiography acquisition.

Scanner improvements include better, more reliable light sources, more efficient light collection systems, higher quality photodetectors, and better electronics. The latest CR scanner advances have done away with traditional flying‐spot (point‐at‐a‐time) scanning in favor of line‐at‐a‐time scanning, bringing significant throughput, image quality, and size advantages. At the same time, advances in the design and manufacture of powder‐based, particle‐in‐a‐binder CR screens, or image plates, have enabled improved inherent signal and noise properties (x‐ray absorption, Modulation Transfer Function, Noise Power Spectra, Detective Quantum Efficiency, etc.), and a better matching of screen absorption and emission spectra to the scanner characteristics. Screens with transparent substrates have produced improved image quality due to the ability to extract latent image signal from both sides of the screen. The latest storage‐phosphor screen materials can be grown in needle form, similar to the scintillators used in indirect flat‐panel detectors, resulting in dramatically improved image sharpness and higher x‐ray absorption due to the absence of binding material.

This presentation will review the form, function and performance of CR systems, with an eye towards more recent developments. The current state of the art in CR will be placed into the larger context of newer DR acquisition systems (e.g., active‐matrix flat panels), looking at the advantages and disadvantages of each. Advances made in CR technologies in recent years portend continued expansion of CR‐based medical imaging.

Educational Objectives:

1. Describe the form and function of today's computed radiography (CR) systems.

2. Identify the main factors that influence the image quality of CR systems.

3. Compare modern CR systems to other acquisition technologies.

4. Describe the latest and future developments in CR.

Conflict of Interest Statement

The author is employed by Agfa Corporation.
MO‐D‐330A‐01: Retrospective Sorting of 4D CT Into Breathing Phases Based On Imaging Analysis of a Fixed‐Geometry Fiducial
Authors: Hoisak J , Kaus M , Purdie T , Jaffray D
Published: July 2006

Purpose: To evaluate a novel fiducial method for retrospective sorting of four‐dimensional computed tomography (4D‐CT). Breathing‐induced motion and deformation of internal anatomy confounds planning and delivery of radiotherapy. Patient‐specific assessment of respiratory motion using 4D‐CT is becoming more clinically accepted as it depicts discrete sampling of the internal anatomy throughout the respiratory cycle. Various strategies for sorting the images exist. External strategies rely on integration of a motion sensor with the CT device but may lack robustness with respect to sensor location. Internal strategies based on image analysis alone may not be robust enough. This work proposes a hybrid retrospective sorting method based on an easily positioned fiducial device that does not require additional hardware and is usable with any multi‐slice or helical CT scanner. An image‐processing algorithm automatically extracts the breathing phase of each slice by fiducial position and sorts images into phases accordingly. Method and Materials: A 50 cm rod‐like device covering the entire field‐of‐view is placed along the patient, providing a well distinguishable fiducial position in each CT slice without impacting image quality. Image analysis determines the fiducial centroid position in each slice with sub‐mm accuracy, allowing phase‐based binning of the image slices according to breathing phase. To validate the method, a motion phantom with the rod affixed was subject to a cine 8‐slice CT scan with 2.5 mm slice thickness. Images were sorted with the fiducial method and compared with images sorted by a commercial 4D‐CT system. Results: Phase‐sorted images of the phantom were reconstructed using the fiducial method. Image quality was comparable to those reconstructed by the commercial 4D‐CT system. Conclusions: Image analysis of a rod fiducial allows retrospective sorting of 4D CT according to breathing phase. This method does not require additional hardware, interfacing with the CT scanner, or manual interaction with the images.
MO‐D‐330A‐02: Motion Artifact Correction Using a Novel Data Consistency Condition
Authors: leng S , Nett B , Chen G
Published: July 2006

Purpose: During diagnostic x‐ray CT imaging procedures or image guided radiotherapy, image quality will be degraded if target organs move during the data acquisition. This can be caused by patients' occasional motion or by intrinsic motion like cardiac and respiratory motion. The inconsistency in the projection data is the major reason for the image quality degradation. We present and validate a method to improve the consistency of the projections using a novel Fan‐beam Data Consistency Condition (FDCC) such that the image quality can be improved. Method and Materials: Computer‐simulated dynamic phantoms are generated and projection data are acquired from these dynamic phantoms. Using the FDCC, individual projection data from one view of fan‐beam projections can be estimated from filtering all the other projection data acquired from different view angles. Then those projections contaminated by motion are re‐estimated using the FDCC, resulting in a corrected sinogram. A standard Fan‐beam Filtered Back Projection (FBP) reconstruction algorithm is then used to reconstruct images from the corrected sinograms. Motion artifacts can be alleviated using this procedure. Results: Images are reconstructed from both the original sinogram where projections are contaminated by motion and the corrected sinogram after applying the FDCC. Strong motion artifacts are observed in the images reconstructed from the contaminated sinogram while improvement can be found in the reconstructed images using the corrected sinogram. Conclusions: A novel method using the new FDCC is proposed to combat the motion artifacts due to the temporal inconsistency in the projection data. Numerical simulations were conducted to demonstrate the potential of this correction scheme to mitigate motion artifacts. Thus, the preliminary numerical results indicate that the FDCC has potential use in combating both cardiac and respiratory motion in CT imaging.
MO‐D‐330A‐03: Correction of Streaking Artifacts in CT Images and Its Influence On Monte Carlo Dose Calculations
Authors: Bazalova M , Palefsky S , Beaulieu L , Verhaegen F
Published: July 2006

Purpose: To quantify the impact of streaking artifacts in CT images due to metal implants in patients on Monte Carlo dose calculation and to determine the impact of their correction. Method and Materials: For CT artifact correction a method of interpolation of missing data in sinograms was developed. Three contrast phantoms were constructed containing two steel cylinders that produced streaking artifacts. CT scans of the phantoms were obtained and the images were corrected for the artifacts. Three sets of Monte Carlo dose calculations (MCDC) using EGSnrc/DOSXYZnrc code were performed. Dose was calculated on: (1) the original CT image, (2) the CT artifact corrected image, and (3), the exact phantom geometry. The dose distributions of the original CT images and the CT artifact corrected images were then compared to the dose calculated on the exact geometry. Results: A calibration point for metal had to be added to the default EGSnrc CT calibration curve to improve dose calculation results. Additional improvement in dose calculation results and in image quality was noted after the artifact correction was done. MCDC without adding the extra calibration point and without correction for streaking artifacts was found to lead to large dose errors. The error in dose calculations performed with the default calibration was found to be 25% in the original CT images. The error improved greatly when the CT images were corrected for artifacts and when the extended calibration was used; the error decreased then to less than 2 %. Conclusion: This work proves that the correction of streaking artifacts is important for MCDC; it significantly decreases dose calculation error and it improves image quality. The work also suggests that for MCTP an additional calibration point for a metallic material should be added to the default CT calibration curve.
MO‐D‐330A‐07: A Stationary Scanning X‐Ay Imaging System Based On Carbon Nanotube Field Emitters
Authors: Zhang J , Yang G , Rajaram R , Quan E , Lee Y , Lalush D , Lu J , Chang S , Zhou O
Published: July 2006

Purpose: Most tomographic imaging systems available today use a single x‐ray source and multiple projection images are obtained by rotating the x‐ray source around the object. Therefore the data acquisition rate is limited by the gantry rotation speed, which is approaching the physical limit. We proposed to develop a novel stationary scanning x‐ray imaging system based on carbon nanotube field emission x‐ray (FEX) technology. Instead of a single x‐ray source the proposed system is based on a multi‐pixel FEX source. The new scanner promises a dramatically faster data acquisition rate by reducing or totally eliminating the mechanical motion. Method and Materials: We have constructed a prototype stationary scanning x‐ray imaging system with an array of 9 individually addressable x‐ray source pixels, each of which can produce a different projection image of the object. The core of this novel x‐ray imaging technology is a gated carbon nanotube field emission cathode array. By programming the gate voltage of the cathode array, the multi‐pixel x‐ray source can generate an electronically triggered scanning x‐ray beam and produce multiple projection images from different viewing angles without mechanical motion. A Hamamatsu C7921 flat panel x‐ray sensor was used to collect all 9 projection images. Results: Tomosynthesis images of a mouse and a standard breast‐imaging phantom (Stereotactic Needle‐biopsy Tissue Equivalent Phantom, Nuclear Associates, NY) using the prototype stationary scanning x‐ray imaging system are acquired. Tomosynthesis reconstructions were applied to the breast phantom. The slice images reconstructed using an iterative reconstruction algorithm clearly show the internal structures of the breast‐imaging phantom at different depths. Conclusion: We have developed a stationary scanning x‐ray imaging system using a carbon nanotube based multi‐pixel FEX source. The mechanical motion free approach can lead to a faster and simplified tomographic imaging system.

Conflict of Interest: Research partially supported by Xintek Inc.
MO‐D‐ValB‐07: Comparison of Inline and Orthogonal Imaging and Treatment Beam Geometries for Monitoring the Motion of Implanted Markers
Authors: Suh Y , Dieterich S , Keall P
Published: July 2006

Purpose: The purpose of this study is to investigate the accuracy of different 2D methods monitoring implanted markers, compared to 3D method for real‐time tumor tracking radiotherapy. The different imaging‐treatment beam geometries were the imaging beam parallel to treatment beam (inline) and orthogonal to treatment beam.

Method and Materials: The 3D motion datasets of ten patients from Cyberknife treatments were used. For given beam angles, the positions of implanted markers were calculated and its geometric uncertainty was quantified for two 2D monitoring methods. Since neither can monitor the motion of markers in the imaging beam axis, the geometric errors were determined in that direction with respect to the treatment beam. Assuming that 3D pre‐treatment online positioning was performed and thus errors are predominantly random, treatment margins due to the limitations of 2D methods were quantified. For the orthogonal monitoring, margin, M=1.65σ, was used with the assumption of zero systematic errors; while for the inline, the required margin can be calculated by integrating the probability density function of the geometric uncertainty with the dose falloff along the beam direction. Results: In terms of couch motion, the positioning uncertainty is lowest for coplanar treatments, consistent with predominantly superior‐inferior motion. Regarding gantry angles, it is lowest for lateral beams, consistent with the smallest left‐right motion. The average positioning uncertainty along the imaging beam axis is 0.05–0.16cm (1 SD) with maximum values for individual patients ranging 0.09–0.33cm, which result in 0.08–0.26cm margins for orthogonal monitoring.Conclusion: The impact of the geometric relationship between the imaging and treatment beam has been studied by quantifying the error from out of plane motion for inline and orthogonal imaging‐treatment geometries. The errors for inline geometry result in negligible additional margin required. In the absence of other errors, the orthogonal monitoring contributes up to 0.26cm to the total margin.
MO‐D‐ValB‐08: Fluoroscopic Tracking of Lung Tumor Mass Without Implanted Fiducial Markers
Authors: Cui Y , Dy J , Sharp G , Alexander B , Jiang S
Published: July 2006

Purpose: To develop techniques for direct lung tumor tracking in fluoroscopic images without implanted markers. Method and Materials: During the patient setup session, a pair of 15 second orthogonal fluoroscopic images are taken and processed off‐line to generate reference templates. Each breathing cycle is divided into 12 phase bins. Setup image frames falling in a specific bin are motion‐enhanced and averaged, and an ROI that contains the tumor is selected to be the reference template for that phase bin. Each reference template corresponds to a tumor position in the image. During the treatment, as soon as a fluoroscopic image is acquired, the cross‐correlation score between each reference template and this image is maximized by allowing small shifts of the template in both X and Y directions. Then the tumor position is derived by averaging the tumor centroid coordinates in those templates of high scores (above 85% of the maximum score). For comparison, tumor position in each image frame was also marked by a clinician. Results: We tested our algorithm on six sequences of fluoroscopic images from six lung cancer patients. The automatically detected tumor centroid coordinates agree well with the manually marked results, with an average error of 1 mm. Conclusion: This study demonstrates the feasibility of tracking lung tumor mass in fluoroscopic images without implanted fiducial markers. Future research will concentrate on further improvement of the accuracy and robustness, and reducing the computational cost.

The project is partially supported by NCI grant (1 R21 CA110177 A 01A1) and NSF Grant No. IIS‐0347532.
MO‐D‐ValA‐03: Inverse Planning Optimization with Organ Motion Probability
Authors: Bortfeld T , Trofimov A , Chan T , Martin B , Paganetti H , Jiang S
Published: July 2006

Organ motion blurs dose distributions. The blurring can be described in a statistical way by use of a motion probability (density) function (PDF). The motion‐blurred dose distribution is obtained by a convolution of the “sharp” (static case) dose distribution with the motion PDF. This holds true for both inter‐ and intra‐fraction motions. In the case of intra‐fraction motions an “interplay” effect is superimposed on top of the blurring effect. It has been shown that the interplay effect averages out during the course of a fractionated treatment, and that it is usually negligible after a typical number of fractions. The convolution model relies on the linear superimposition principle, which holds true for dose values but not for the biological effect. This issue has recently been addressed and will be discussed.

Several investigations have now looked at the feasibility of un‐doing the motion blur through the use if intensity‐modulation. In principle it should indeed be possible to de‐convolve the motion PDF from the intensity maps, in order to compensate motion effects. This approach has been called 4D optimization or 4D inverse planning. Motion de‐convolution cannot, however, compensate motion effects exactly and it cannot be applied in a naïve straight‐forward way, because that would lead to undeliverable intensity maps with sharp spikes and negative values. The method of choice is rather to include the motion PDF in the IMRT optimization process. It has been shown that this can indeed yield a surprisingly high degree of motion compensation and it can even compete with other motion compensation methods such as gated delivery. However, this is only true if the motion characteristics (the PDF) are known with great precision. If the actually realized motion PDF deviates substantially from the planned PDF, the method becomes less useful and can, in principle, make things worse. More recently, uncertainties in the knowledge of the motion characteristics have been taken into account by use of robust optimization techniques. With these one can now compensate for motion effects in an approximate way for a large class of motion characteristics. In terms of the sparing of normal structures, the results are in between the use of conventional margins and the idealistic case of perfect motion compensation. The resulting intensity maps exhibit “horns”, which can shave off a few mm from the margins.

Educational Objectives:

1. Understand the concepts of motion blur and PDF.

2. Understand the idea of de‐blurring a dose distribution through “4D” motion optimization.

3. Be able to discuss the relative potential and limitations of 4D motion optimization in comparison with margins and gating.
MO‐D‐230A‐01: A Nontraditional Method of Providing Radiation Protection Instruction at a Large Health Science Center
Authors: Brinkley B , Thompson M , Bolus N , Dowd S
Published: July 2006

Purpose: To test the hypothesis that the combined online/lecture format was as effective as the lecture‐only format for students who took the University of Alabama at Birmingham (UAB) radiation safety course. Method and Materials: In the 4th quarter of 2001 the University of Alabama at Birmingham (UAB) converted its traditional classroom radiation safety course, taught exclusively in a classroom setting four times each year, to a combined online‐classroom format in which the majority of the course is taught online. This change was instituted in an effort to minimize the time spent in the classroom for UAB research personnel. This format should provide the additional benefit of self‐paced instruction for course participants. A statistical analysis was performed on the average first‐attempt test scores of the tests (number of tests=334) taken during a two‐year period before the online transition (average score=75.5), and the average first‐attempt test scores of the tests (number of tests=359) taken during a two‐year period after the online transition (average score=74.1.) Results: A two‐tailed Student's t‐test was performed on the data. The t‐value was 1.73, and P(T<=t) was 0.083. At α=0.05, the null hypothesis that the two averages are equal cannot be rejected. Conclusion: The online course format appears to be as effective a method of radiation safety instruction as the more traditional, exclusively‐classroom method of instruction. This presentation also reviews steps under consideration to improve the current online course to make it a more effective tool in radiation safety instruction.
MO‐D‐230A‐03: Patient Planning Management System
Authors: Kirk M , Chu J C H
Published: July 2006

Purpose: The goal is to develop a dynamic automated patient management program. This software will be able to track the status of the patient's treatment plan and remind the responsible parties of intermediate deadlines. Alerts are sent each morning to the radiation oncologist, residents, dosimetrists, and physicists about the current stage of the treatment planning. Method: The patient planning management software was written in Visual Basic 7.0 and incorporates Microsoft Excel's spreadsheet. The programs display is viewable over anywhere in the department. The program shows each patient's data in a separate row and color coded according each radiation oncologist. The patient's CT and start date are entered for each patient. The deadlines included are that for the approval of the PTV and normal tissue, plan approval, and completion. The program will change the color of the patient's data from yellow (warning) and red (alarm) based upon approaching deadlines. Results: This planning software continuously updates patient information. This program eliminates the time consuming process of paging, emailing, and tracking down responsible parties to communicate completion of various tasks. Since the inception of this software the mean time interval to complete a plan has decreased by 30%. The mean time required to get target volumes approved has dropped 25%. One significant benefit is the 50% increase in time between the completion date and start date. Without an increase the overall planning time, this has allowed more time for physics checks, quality assurance, and therapist review. Conclusions: In the face of increasing patient numbers the dynamic automated patient management software has enabled our department to complete our patient's plans in a more efficient manner. This increased efficiency allows all responsible staff adequate time to complete their responsibilities for each patient.
MO‐D‐230A‐04: Dedicated PET‐CT and MR‐Simulators in a State‐Of‐The‐Art Radiation Treatment Facility
Authors: Bourland J , Flowers K , Huey K , Shaw E
Published: July 2006

Purpose: To provide dedicated, integrated PET‐CT and MR simulation and imaging devices in the radiation treatment clinic for purposes of advanced oncologic imaging. Method and Materials: A planning team was established for design of radiation oncology facilities as part of a new comprehensive cancer center. Physicist input included emphasis on combined biological‐anatomical (termed “bioanatomic”™) imaging for a research program in Bioanatomic Imaging and Treatment (BAIT), provision of state‐of‐the‐art treatment devices for IMRT, radiosurgery, and HDR, and analyses of digital medical informatics. PET‐CT and MR simulator specifications were delineated at a time of rapid technology development for both modalities, and included capabilities for gated PETCT acquisition and high‐resolution MR spectroscopy. Results: Facility design includes dedicated rooms for Conventional, PET‐CT, and MR simulation. BAIT simulator devices selected are 8‐slice PET‐CT and 3.0T MR, each with “marking” lasers and virtual simulation tools. PET‐CT s“imulation includes respiratory gating. 3.0T MR simulation includes spectroscopic, diffusion, and perfusion imaging. Radiation safety aspects include shielding for ionizing radiation (PET‐CT) and radiofrequency and magnetic fields (3.0T MR). PET‐CT and MR simulators are centrally located to facilitate patient flow and physician access. PET‐CT and MR simulations are being performed under the auspices of multidisciplinary clinical and research oversight committees. Operators are paired as one imaging technologist (PET‐CT or MR) and one radiation therapist per simulator. Conclusion: Vision for the Bioanatomic Imaging and Treatment Program has been coupled with the opportunity for a new comprehensive cancer center facility to provide multi‐slice PET‐CT and 3.0T MR simulation in the radiation treatment clinic. Using a collaborative multidisciplinary approach, image‐based research protocols have been developed for specific disease sites, and experience is being gained with use of dedicated, integrated PET‐CT and MR simulation. Conflict of Interest: BAIT Program research partners include Varian Medical Systems and GE Healthcare.
MO‐D‐230A‐07: Analysis of Couch Sag and Couch Deflection in Several EXACT Couches
Authors: Movahed A , Sen A , Podgorsak M , Paliwal B
Published: July 2006

Purpose: To measure couch sag and couch deflection in several EXACT Couches. Method and Materials: Couch sag was evaluated for EXACT Couches at three positions: tip, center and base with the couch fully extended in treatment position. In each case, measurements were made with no weight and with 84, 142, and 319 lbs uniformly distributed over the couch surface. Couch deflection was evaluated with SSD readings to the couch surface using the mechanical backpointer at isocenter and digital read out. Measurement were repeated with the couch at nominal SSDs of 100 cm, 110 cm and 120 cm and with rails closed together in the middle. Same measurements were performed with Picker CT couch for comparison. Results: We found 9 mm deflection from the tip to the base of couch (fully extended) with no weight on the surface. According to Varian service personnel, design of EXACT Couches follows IEC specification and Exact Couch manufacturers provided a +5mm deflection to counter weight the patient's weight. Our couch was shimmed and brought the sag down to +5mm. EXACT Couch deflection with no weight on surface varied between 5ndash;9mm at five different centers. Sag was same at nominal SSDs. Up to 7mm sag variation was noticed depending upon the weight.

With rails closed together in the middle, about 1mm decrease was noted for the above values. Upto 4mm sag was noticed in CT couch. Unlike Exact couch, CT couch sag decreased at the base. Conclusions: Study demonstrated that the +5mm deflection does not completely counter weight the patient's weight for having leveled surface at the isocenter.

2–5mm sag at tip and up to −7mm at base relative to the amount of weight on couch was noticed. In time +5mm‐shimmed deflection was deteriorated to +7mm. Same results were obtained when couch was loaded.
MO‐D‐224A‐01: Packet‐Level Quality Assurance of MLC Informatics
Authors: Kim D YJ
Published: July 2006

Purpose: To develop a system for real‐time auditing and archiving of MLC treatment data, both static and IMRT, through the passive detection and reconstruction of packet‐level network traffic between the linac control computers and the central database server. Method and Materials: The three computers under observation are the control computers for a Varian 21EX (120‐leaf dynamic MLC) and a Varian 2100‐2 (52‐leaf static MLC) and the central database server running Varis 7 clinical informatics software. The observing system consists of a Linux‐based PC connected via Ethernet to modified network segments of the two linac control computers, running the Ethereal and Snort open‐source network analysis tools in addition to database and web services. After detailed observation of the computers' data transfer protocols and MLC data formats, the system was configured to passively monitor Ethernet traffic during clinical operations and selectively record only those packets containing specific treatment session, field, and MLC details to a database. Finally, a custom PHP‐MySQL script was written to reassemble, convert, and present this binary data in human‐readable, web‐accessible format. Results: The system successfully reconstructs and stores the network‐detected MLC configurations for all fields in a treatment fraction, seconds after the patient file is opened at either treatment computer. Its application to IMRT QA is both real‐time MLC auditing (e.g. verify that the MLC data received by the server matches that of the previous fraction, 10–15 minutes before treatment delivery) and as an off‐line archive of transmitted MLC configuration data. Conclusion: This system demonstrates that the examination of network traffic can provide a useful and innovative tool for radiotherapy QA. Its informatics‐centered approach to IMRT QA contrasts with and complements the numerous delivery‐centered techniques, which focus on dosimetric verification of MLC sequences that are known to have been transmitted to the linac computer without error.
MO‐D‐224A‐02: Clinical Experience in Using EPID for Quantitative Verification of IMRT Dose Distributions
Authors: Wang JZ , Rice R , Marcus L
Published: July 2006

Purpose: The purpose of this work is to investigate the advantages of using an electronic portal imaging device (EPID) as part of our clinical IMRT QA procedure. We present our experience with the quantitative verification of the planar dose distribution for patient‐specific IMRT treatment plans. Method and Materials: Our treatment machines which are used for IMRT delivery are equipped with amorphous silicon EPIDs. The planning system used for routine IMRT treatment planning calculates planar dose at a predefined source to plane distance (SPD) as part of the EPID‐based QA process. For quantitative analysis, dosimetric calibration of the EPID was required, in addition to the standard imager calibrations of the PortalVision imaging device. Basic dosimetric characteristics of the system were initially evaluated using fields with known dosimetry. Absolute dose calibration produces results comparable to ion chamber measurements. The patient IMRT QA fields were delivered prior to treatment and recorded. We have selected 100 cases from our routine IMRT case load for analysis using this procedure. Results: The verification of dose distributions was performed using portal dosimetry in Vision, after beam delivery. The overlay of the acquired and the calculated planar doses as isodose lines provided a useful qualitative evaluation. For further quantitative analysis, the gamma relative evaluation (GRE) was used on each field for every patient. The GRE scores were normally greater than 0.99 for prostate patients and greater than 0.98 for Head and Neck cases or large pelvic fields. Conclusion: Planar dose verification is an important part of the IMRT QA procedure. With the aid of portal dosimetry using EPID, the QA of an IMRT plan can be performed in 30 minutes, saving considerable time compared to film dosimetry. With proper dosimetric calibration, quantitative analysis further ensures excellent quality assurance of IMRT planning and delivery.