bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐445: Variations of Rectal Dose Estimation Using Rectal Markers in HDR Cervical Brachytherapy
Authors: Wang Z , Jaggernauth W , Malhotra H K , Podgorsak M B
Published: July 2007

Purpose: In the treatment of cervical cancer using high‐dose‐rate (HDR) brachytherapy, high rectal dose often limits the tumorcidal dose. In film based brachytherapy, rectal dose is usually computed using rectal markers. However, positions of these markers can vary relative to the anterior rectal wall. This retrospective study analyzes the potential inaccuracy in rectal dose estimation due to variations of marker placement in a multi‐fractionated HDR treatment regimen. Method and Materials: Five Patients treated with multiple‐fraction tandem and ovoid HDR brachytherapy were selected. By adequate packing the vagina, there was little inter‐fractional variation of the actual rectum position. Therefore, variations of rectal makers were due to their locations relative to the wall. For each patient (with 3–4 fractions), the plan of the first fraction was selected as the reference plan. Simulation films of all the other fractions were matched with the films of the reference plan based on bony anatomies. Rectal dose points specified based upon the rectal markers of all different fractions were then digitized into the reference plan after film matching. Dose prescription and dwell weights in the reference plan were set to be identical to the original treatment plan. The rectal doses within each group of rectal points were then analyzed. Results: Our results have shown that inter‐fractional variations of rectal marker locations to specify the rectal dose are up to 0.5–0.8 cm. The resulting differences in rectal dose values are 42.4%, 23.3%, 25.6%, 6.8% and 50.4% for each patient, respectively. Conclusion: Care should be taken when using rectal markers as reference points for estimating rectal dose in HDR cervical brachytherapy. Positions of the markers inside the rectum relative to the wall can vary and cause underestimation of the dose to the rectum. The true rectal dose should be determined by the most anterior point among all fractions.
SU‐FF‐T‐450: Verification of the Source Tech Medical Model STM1251 I‐125 Air‐Kerma Strength in Japan
Authors: Sumida I , Takahashi Y , Ito A , Nose T , Oguchi M , Yamashita T , Yoshioka Y , Inoue T
Published: July 2007

Purpose: We investigated the difference between measured and manufacturer's stated source strength in a single model STM1251 seeds. Materials and methods: A well‐type ionization chamber with a single seed holder was used to measure source strength of 2412 seeds before implant for 34 patients. The air kerma strength was only used 0.279 U for all cases. The mean source strength used for each patient was compared with the manufacture stated value. The deviation from the measured value was compared with the tolerance level of the recommendation of AAPM TG‐40. Results: Measured source strength was higher than the manufacture stated value with median 1 % (range: −2 to 5 %). Sixteen seeds of all 2412 seeds (0.7 %) were over 5 % different from the manufacture stated value. Standard deviation from the mean value was median 2.2 % (range: 1.1 to 2.5 %) in each patient. Conclusion: A single seed assay was performed for the model STM1251 seed. The manufacture stated strength of the seeds agreed well with the measured value. Our study was helpful as guidance for the permanent prostate implant using the model STM1251 seed.

(Submission Withdrawn).
SU‐FF‐T‐452: Whole Pelvic IMRT Treatment for Post Operative Gynecological Malignancies, Sheba Experience
Authors: Alezra D , Rabin T , Menhel J , Symon Z , Pfeffer R
Published: July 2007

Background and Purpose: To evaluate the use of IMRT treatment for post operative gynecological malignancies for better organ at risk sparing to reduce treatment toxicity that will allow dose escalation. Creating guidelines for that treatment. Recognize treatment limits and problems in ITPS and QA for very large IMRT volumes and fields. Patients and Methods: five patients were selected with endometrial cancer treated postoperatively. Bladder, rectal wall, small and large bowel were delineated as organs at risk. A seven field IMRT plan prescription dose 50.4 Gy and compared with conformal 4 fields plan (DVH). QA performed with film dosimetry and ion chambers. Results: significant improvements were observed for irradiated volume of rectal wall and bladder. With IMRT the average irradiated volume of small and large bowel was reduced dramatically and the impact of IMRT was large for postoperative patients, in one patient treatment volume was very large (24833cc of normal tissue) the ITPS could calculate only if the calculation grid was 10mm spaced, that lead to a disagreement in QA and patient was treated 3D conformal. Conclusions: IMRT significantly reduced the absolute volume of rectal wall, bladder and bowel irradiated at the prescribed dose level in post operative gynecologic patients. Due to large treatment volumes we have to be aware of disagreements between calculations and dosimetry.
SU‐GG‐AUD‐01: Exit Dosimetry Treatment Verification Using Auto‐Associative Kernel Regression
Authors: Seibert R , Ramsey C , Robison B , Outten S , Garvey D , Hines W
Published: July 2007

Purpose: The purpose of this work was to develop a novel technique for automatically evaluating exit dosimetry on tomotherapy systems using auto‐associative modeling that is robust and has the capability to learn complex detector data relationships, even with detector data with a low temporal resolution and beam attenuation from the patient. Method and Materials: Delivery sequences from 3 patients were used in this study. Each delivery sequence was modified by reducing the opening time for random individual MLC leaves by random amounts. The error and error‐free treatments were delivered with different phantoms in the path of the beam. Multiple auto‐associative kernel regression (AAKR) models were developed and tested by the investigators using combinations of the sinogram data sets. AAKR is a non‐parametric model that is used to predict correct values when supplied a group of sensor values that is corrupted. Models were tested using the data containing errors. However, models were never developed with data which had the same object in the path of the beam as the dataset it was testing. This allowed the testing of the model's error detection capabilities in the presence of attenuation. Results: The results show that the model correctly distinguished the MLC positional error from changes in attenuation. The model identified errors in compressed detector data that had been summed over 94 frames. Generally, errors greater than 7 milliseconds were visually discernable. Some smaller errors could be detected, but it depended on the position of the erroneous leaf in the projection and the actual projection shape. Conclusion: The results presented suggest that AAKR modeling could be used to monitor and eventually improve the reliability of radiation delivery. This method has the potential to play a noteworthy role in determining and possibly correcting for the types of machine‐related errors that occur during actual patient treatments.
SU‐GG‐AUD‐02: Dose Convolution Filter: Incorporating Spatial Dose Information Into Tissue Response Modeling
Authors: Huang Y , Joiner M , Liao Y , Burmeister J
Published: July 2007

Purpose: Radiotherapy treatment planning commonly involves analysis of static dose distributions and corresponding Dose Volume Histograms (DVHs). However, such analysis does not account for biological effects of spatial variations in the physical dose distribution. We introduce the Dose Convolution Filter (DCF) model capable of incorporating spatial dose information in plan analysis and optimization, and integrating biological factors such as cell migration and bystander effects into physical dose distributions. The DCF model should allow more accurate prediction of tissue response from complex radiotherapy dose distributions, and can facilitate modeling of the effects of patient motion. Method and Materials: We use a Gaussian convolution filter with standard deviation, σ, determining the degree of dose washout. To test this model, filtered dose distributions are applied to a NTCP model to calculate tissue response. As an illustration, we determine σ from existing rat spinal cord data, and compare model‐predicted NTCP with published data. We also simulate the GRID technique, in which an open field is collimated into many pencil beams. Results: After applying DCF, an NTCP model can predict dependence of tissue response on variations in spatial dose distribution. The model successfully fits the rat spinal cord data with a predicted value of σ=2.6±0.5mm, consistent with 2mm migration distances of remyelinating cells. Moreover, it enables the correct prediction of a high relative seriality for spinal cord. Finally, this model also predicts the sparing of normal tissues by the GRID technique when the size of each pencil beam becomes comparable to σ. Conclusion: The DCF model incorporates spatial dose information and offers an improved way to estimate tissue response from complex radiotherapy dose distributions. It does not alter the prediction of tissue response in large homogenous fields, but successfully predicts increased tissue tolerance in small or highly non‐uniform fields.

Partially supported by Varian Medical Systems.
SU‐GG‐AUD‐04: Localizing Through Optimization of Image Acquisition Rate and Tube Current in X‐Ray Fluoroscopy‐Guided Therapy
Authors: Siddique S , Jaffray D
Published: July 2007

Purpose: Numerous models exist that relate the parameters of an imaging system to the image quality. Unfortunately, very little is known about the relation between the parameters of an imaging modality and the corresponding targeting precision which is of key importance in many image‐guided procedures. The purpose of this study is to explore the relation between imaging parameters and the geometric precision that can be achieved, and to show that such relations can be exploited in a framework in which the geometric objectives of a therapy can be used as feedback to drive the parameters of an imaging system and the associated therapy within constraints. Method and Materials: The task of localizing a sphere that is subject to respiratory motion and imaged under X‐ray fluoroscopy is considered. Two cases are considered: (i)a system that modulates the temporal sampling frequency using feedback of uncertainty while tracking the sphere in order to maintain a specified maximum spatial uncertainty while minimizing exposure, and (ii)a system that modulates the tube current in order to maintain the localization uncertainty within the specified level as the sphere traverses a noise field. The performance of the proposed system is contrasted with a similar system that does not employ feedback of uncertainty. Results: It is observed that a relation exists between the localization uncertainty and the imaging parameters considered, namely, the temporal sampling frequency and the tube current. The use of uncertainty as feedback allows tradeoffs between targeting precision and imaging parameters to be controlled. Conclusion: The proposed framework can: (i)automatically maintain the geometric objectives of the therapy whenever possible and report to the operator when these objectives cannot be achieved, (ii)optimize the system parameters by dynamically assigning them based on feedback of performance, and (iii)reduce the level of human intervention required to carry out the therapy.
MO‐A‐M100J‐01: Performance Evaluation for New‐Technology CT Systems: Dual‐Source CT
Authors: McCollough C
Published: July 2007

Computed tomography technology continues to evolve at a rapid pace. Recent technical innovations include dual‐source CT, 256‐channel CT, and cone‐beam angio CT. In this three‐part presentation, the impact of each of these new technologies on physics performance evaluations will be considered.

In dual‐source CT, two x‐ray tubes and two data acquisition systems are mounted orthogonally on the same rotating gantry. The system can be used to perform traditional CT scanning similar to the 64‐slice system from the same manufacturer; 85 msec temporal resolution imaging; dual source 160 kW imaging; or dual‐energy imaging. The impact of two x‐ray sources and two data acquisition systems on performance testing is relatively straightforward, as the doses from each source are simply additive. However, to assess image quality in a clinically‐relevant manner, a proper understanding of typical scan parameters is essential. Several suggested scan modes for image quality evaluation will be presented.

Educational Objectives:

1. Understand the design of dual‐source CT.

2. Recognize typical dose values from each source and from clinical protocols.

3. Gain familiarity with the image quality associated with typical clinical scan protocols.
MO‐A‐BRB‐01: Review of the AAPM TG‐105
Authors: Chetty IJ , Rogers DWO
Published: July 2007

Despite its proven accuracy and the potential for improved dose distributions to influence treatment outcomes, the long calculation times previously associated with MC simulation rendered this method impractical for routine clinical treatment planning. However, the development of faster codes optimized for radiotherapy calculations and improvements in computer processor technology have substantially reduced calculation times to, in some instances, within minutes on a single processor. Several commercial vendors have released or are currently in the process of releasing MC algorithms for photon and/or electron beam treatment planning. Consequently, the accessibility and use of MC treatment planning algorithms may well become widespread in the radiotherapy community. With MC simulation, dose is computed stochastically using first principles; this method is therefore quite different from conventional dose algorithms. Issues such as statistical uncertainties, the use of variance reduction techniques, the ability to account for geometric details in the accelerator treatment head simulation, and other features, are all unique components of a MC treatment planning algorithm. Successful implementation by the clinical physicist of such a system will require an understanding of the basic principles of MC techniques.

Educational Objectives:

1. To provide an educational review of the physics of the MC including discussion of methods used for coupled photon and electron transport.

2. To review the methods used to improve the simulation efficiency.

3. To briefly review the vendor transport codes currently used for clinical treatment planning.

4. To describe the development of treatment head models for clinical treatment planning.

5. To discuss the factors associated with MC dose calculation within the patient‐specific geometry, such as statistical uncertainties, CT‐to‐material, and reporting of dose‐to‐medium versus dose‐to‐water.

6. To discuss the issues associated with experimental verification of MC algorithms.

7. To briefly review the potential clinical implications of MC calculated dose distributions.

8. To provide example timing comparisons of the major vendor MC codes in the clinical setting.
MO‐B‐BRB‐01: Quality Assurance in Stereotactic Radiosurgery and Fractionated Stereotactic Radiotherapy
Authors: Solberg T , Shepard D
Published: July 2007

Stereotactic radiosurgery involves the high‐dose irradiation of cranial neoplasms delivered in a single fraction. In the 50‐plus years since it was first introduced, stereotactic radiosurgery has become a standard of care in the treatment of brain tumors, vascular malformations, functional disorders, and pain. Modern radiosurgery can be performed non‐invasively and on an outpatient basis while maintaining an extremely high degree of accuracy. Within the past ten years, the field of radiosurgery has seen numerous technological enhancements including: (1) the development of dedicated devices for stereotactic delivery; (2) the use of relocatable frames to facilitate fractionated delivery; (3) the development of “frameless” approaches; and (4) the application to extracranial tumor sites. Each of these developments has been accompanied by its own challenges in assuring targeting and dosimetric accuracy. In this presentation we review the technologies for stereotactic localization and treatment of cranial targets with particular emphasis on the quality assurance aspects associated with establishing and maintaining a clinical radiosurgery program. Specifically, the presentation will:

1. Differentiate the technologies used in the delivery of stereotactic radiosurgery including linac‐based techniques (both conventional and robotic) and the Gamma Knife.

2. Define the treatment planning parameters for linac‐based and Gamma Knife stereotactic radiosurgery.

3. Discuss measures for assuring accuracy in stereotactic localization and dose.

4. delivery for linac‐based and Gamma Knife stereotactic radiosurgery.
MO‐B‐M100F‐01: Proton Therapy
Authors: Smith A , Paganetti H
Published: July 2007

The clinical advantages of proton beams have become widely recognized and there has recently been a significant increase in interest for building additional proton therapy facilities. There are currently over 25 institutions worldwide treating patients with proton beams and over 50,000 patients have been treated. There are at least 25 new facilities in various stages of planning and building. However, the fraction of patients treated with protons each year remains extremely small compared to the total number of cancer patients treated with external beam photons and electrons. The advantage of proton beams lies primarily in their excellent dose localization as compared to that which can be achieved using photon beams. Due to the Bragg peak characteristic in the depth dose of proton beams, the integral dose from proton therapy is significantly less that that for photon treatments. This allows higher doses to be delivered to target volumes, resulting in increased rates of local control, and lower doses delivered to critical normal tissues, resulting in decreased rates of treatment‐related morbidity. There are many challenges associated with increasing the accessibility of proton therapy not the least of which is the very limited number of clinical staff with knowledge of and training in proton therapy. The aim of the present Continuing Education Course is to provide a basic understanding of the rationale for proton therapy, physics of proton beams, technology of proton beam acceleration and transport, delivery of proton treatments, proton treatment planning and clinical results of proton therapy.

Educational Objectives:

Understanding of

1. the physical characteristics of proton beams and interactions in tissues.

2. the beam production and treatment delivery technology for proton beams.

3. the clinical commissioning of proton therapy beams.

4. the basic principles of proton treatment planning.

5. the clinical results for proton therapy.
MO‐C‐AUD‐00 — Introduction: Imaging as a Biomarker for Therapy Response: Challenges, Opportunities and Initiatives
Authors: Martel M
Published: July 2007

Imaging as a biomarker for drug and radiation therapy response is emerging as an important area of research. The NIH has formed a Biomarker Consortium with several agencies of the federal government to leverage NIH and Industry funds to develop standardized methods for biomarkers that includes imaging. (http://www.fnih.org/Biomarkers%20Consortium/Biomarkers_home.shtml). The role of imaging as a biomarker poses unique problems for image data collection and analysis across different imaging platforms, as the latter factors increase the uncertainty of measurement, (NIST workshop agenda and report: http://usms.nist.gov/workshops/bioimaging.htm). The AAPM is well positioned to address standards for quality assurance for all imaging modalities, system performance, and development of clinical decision software tools for measurement of therapy response. For this symposium, speakers will discuss:

The role of imaging as a biomarker,

• Potential funding sources for this work at NIH,

• Leveraging therapy physics experience in the NCI's Radiation Research Program that can be applied to measurement of therapy response,

• How imaging societies can become engaged to address this research area and promote more standardized methods for biomedical imaging.
MO‐C‐AUD‐01: The Emerging Role of Imaging as a Biomarker for Response
Authors: Schwartz L
Published: July 2007

Radiologic images have been used for decades to gauge the effectiveness of various therapeutic interventions. In the areas of oncology, cardiovascular disease, neurology, arthritis and osteoporosis, imaging plays a vital role in decision‐making regarding effectiveness of therapy for an individual patient. Increasingly, imaging also is being utilized during all phases of therapeutic drug development, resulting in speedier drug discovery and, in some instances, ensuring a drug's safety. There has been an “explosion” in use of biomarkers in drug discovery.

Many imaging biomarkers are already commonly used, such as tumor size measured at CT to reflect tumor burden;T2 hyperintensity detected at brain MR imaging to reflect the burden of Multiple Sclerosis; and bone density determined on DEXA studies to assess for osteoporosis. One major benefit of imaging biomarkers is that the findings may be evaluated and quantified for changes over time. Newer imaging biomarkers are also playing a role in drug discovery, such as dynamic contrast‐enhanced MR imaging to assess for vascular flow to tumors; molecular imaging in the functional evaluation of cardiac, neurologic and oncologic processes; and CT in the evaluation of cystic fibrosis. The complexity in imaging biomarkers is increasing not only with the number of available imaging and post‐processing techniques, but perhaps even more importantly, with the number and diversity of relevant therapeutic options. Increasingly, it is becoming clear that a single imaging biomarker alone can be misleading, but is more robust when combined with other imaging or non‐imaging biomarkers.

Educational Objectives:

1. Understand the role of imaging in monitoring response to therapy.

2. Understand the issues and clinical complications of imaging as a biomarker.

Research sponsored by Astrazeneca Corporation.
MO‐C‐AUD‐02: NIH Roadmap, Public‐Private Partnerships and the Biomarker Consortium
Authors: Mittleman B
Published: July 2007

The NIH mission to improve the public health through biomedical research is accomplished by conducting research directly, by funding research through grants and contracts, and increasingly by partnering with any of a wide variety of partners. The synergy possible through the leveraging of NIH resources with the strengths of industry, professional societies, patient advocacy organizations, and academic partners allows work that cannot be done by any of the partners alone to be realized. Moreover, partnership can also facilitate increasing efficiency, economy and speed for translation of discovery to the public. The NIH Roadmap Public‐Private Partnership(PPP) Program is the center of such activities and policies, programs and examples of PPPs will be described, as well as ways that AAPM might take advantage of partnership opportunities.

Educational Objectives:

1. Understand the NIH position on PPPs.

2. Understand PPP Policies and programs.

3. Learn how new PPPs can be initiated.
MO‐D‐L100J‐03: Generating Patient Specific Motion Models Using a Navigator Channel and a Liver Population FEM Motion Model
Authors: Nguyen T‐N , Moseley JL , Dawson LA , Jaffray DA , Brock KK
Published: July 2007

Purpose: To incorporate motion information from 2D images using a navigator technique and finite element modelling (FEM) to generate patient‐specific 3D motion models. Methods and Materials: A liver population motion model was created using a FEM deformable image registration platform, MORFEUS, to simulate liver deformation during a respiratory cycle. Twenty patient's exhale livers were constructed from the population FEM, and then deformed into their inhale livers. Deformation maps were generated and used to check the accuracy of the navigator‐updated patient models. NavigatorView, an in‐house algorithm, places a rectangular navigator channel to define a region of interest on 2D image slices. An operator chosen navigator is placed on the exhale image while another navigator is automatically placed at the corresponding location on the inhale image. Motion was calculated as the shift required to align the intensity profiles within the channels at the superior dome and the inferior tip of the liver on coronal CT slices and simulated radiograph images. The navigator shifts were used in a weighting equation to generate patient‐specific motion models from the population motion model. Results: The average accuracy ± standard deviation of the navigator channel at the superior and inferior edges is 0.12 ± 0.12cm and 0.25 ± 0.25cm respectively. The navigator‐updated patient‐specific models was 100% and 80% successful of the 20 patient cases for the coronal CT and simulated radiograph slices respectively, where a successful case achieved an accuracy error less than the image voxel size (0.25cm). Conclusions: The navigator technique allows for updating patient‐specific 3D motion models from a liver population model using more easily acquired 2D images. This can be a useful tool for image‐guided therapeutics, such as intra‐fraction image guided tracking during radiotherapy, where 2D data may be more rapidly acquired.

Research sponsored by the National Cancer Institute of Canada — Terry Fox Foundation.
MO‐D‐L100J‐04: Non‐Rigid Registration Based Respiratory Motion Models of the Lung Using Two Parameters
Authors: McClelland J , Blackall J , Tarte S , Hughes S , Hawkes D
Published: July 2007

Purpose: Single parameter motion models based on the phase of a respiratory signal can model the motion over an average respiratory cycle. Two parameter models based on amplitude and gradient may also be able to model some of the inter‐cycle variation. We present a method of constructing two parameter motion models and evaluate different functions for the model. Method and Materials: A reference CT volume is non‐rigidly registered to free breathing CT data. A function is then fitted to each of the control point displacements that define the registrations, relating them to the respiratory parameter(s). Three different functions were evaluated on data from an example patient: a 1D cyclic b‐spline function relating the displacements to phase, a 2D linear function, and a 2D 3rd order polynomial function, both relating the displacements to amplitude and gradient. Models built from each of the functions were used to produce transformations at the same parameter values as the registration results. Models were built both leaving out the target registration and including it. Sample points covering the entire region of interest were deformed using the model results and the registration results, and the differences in the displacements of the points were calculated. Results: The mean differences, when using all registrations and when leaving out the target respectively, were 0.53 mm and 0.67 mm for the 1D cyclic b‐spline function, 0.59 mm and 0.71 mm for the 2D linear function, and 0.43 mm and 0.96 mm for the 2D polynomial function. Conclusion: These results suggest that the performance of the 2D linear function is comparable to the 1D b‐spline function. The 2D polynomial function models the data more accurately but would appear to ‘over‐fit’ the data.
MO‐D‐L100F‐01: Progress in In‐Line Phase‐Sensitive X‐Ray Imaging
Authors: Wu X , Liu H
Published: July 2007

Since Roentgen discovered x‐ray and performed the first x‐ray imaging over 100 years ago, x‐ray medical imaging has always been based on the biological tissue's differences in x‐ray attenuation. However, x‐ray‐tissue interaction causes x‐ray phase shifts as well, and the phase‐shift differences between different tissues are about one thousand times larger than their attenuation differences. The phase‐sensitive x‐ray imaging hence allows not only visualizing the tissues with very low attenuation‐contrast, but also quantifying tissue's projected electron densities by means of the phase retrieval.

In this presentation we first introduce the concept of spatial coherence of x‐ray wavefield and elucidate the mechanism of x‐ray phase‐contrast formation. We then review recent progress in the in‐line phase—sensitive x‐ray imaging.

Educational Objective:

1. Elucidate the mechanism of x‐ray phase—contrast formation.

2. Review recent progress in the in‐line phase—sensitive x‐ray imaging.
MO‐D‐L100F‐03: New Developments in Digital Breast Tomosynthesis
Authors: Lo JY , Singh S , Dobbins JT , Samei E
Published: July 2007

Digital tomosynthesis is one of the most exciting recent developments in breast imaging. By modifying existing full field digital mammography systems, one can achieve this type of limited‐angle cone‐beam CT imaging which produces 3D slice images of the breast. Overlapping dense tissue in mammography is one of the most common causes for unnecessary callbacks as well as missed cancers. Since the 3D images remove such overlapping tissue, breast tomosynthesis can improve radiologists' specificity by obviating unnecessary callbacks. It can also improve sensitivity by allowing easier detection and characterization of breast cancers which might otherwise be obscured. Most remarkably, tomosynthesis can achieve all this with a scan that is comparable to the speed, resolution, cost, and dose of conventional mammography. For these reasons, tomosynthesis stands poised as the only imaging technique with the potential to completely replace the current role of mammography as the primary tool in breast cancer screening and diagnosis.

This presentation will cover both the hype and hope surrounding breast tomosynthesis. From a medical physics perspective, the latest results will be reviewed from recent studies to optimize radiographic techniques, acquisition modes, and reconstruction algorithms. In addition, emerging results will be surveyed from advanced applications including display/visualization, computer aided detection, and contrast enhanced tomosynthesis. Finally, the clinical promise and risks of this new technology will be discussed using initial clinical trial results.

This research was supported in part by research grants from Siemens Medical Solutions, US Army Breast Cancer Research Program, and NIH/NCI.

Educational Objectives:

1. Understand the difference between breast tomosynthesis and dedicated breast CT.

2. Appreciate the many medical physics issues involved in the development and optimization of breast tomosynthesis.

3. Understand the clinical promise and concerns of using breast tomosynthesis.
MO‐D‐L100F‐04: Imaging With Distributed Source Arrays
Authors: Pelc N
Published: July 2007

While the vast majority of x‐ray imaging procedures use a single x‐ray source, a growing number require measurement of x‐ray transmission from different locations. These exams are generally performed by moving a single x‐ray source to many positions. Examples include computed tomography (CT) and tomosynthesis. At the same time, several technologies are now becoming more available that enable to construction of source arrays, i.e., a large number of sources that can be turned on in sequence. The purpose of this presentation is to explore the capabilities and benefits of imaging with these source arrays.

In CT, small deflections of the x‐ray focal spot (on the order of a millimeter) have been used to improve data sampling. Multiple sources or much larger deflections (on the order of centimeters) in the axial direction can be quite useful for increasing the thickness of the imaging slab in a single scan while reducing cone beam artifacts. Distributing sources in the circumferential direction can dramatically reduce the mechanical rotation needed to obtain a complete data set and therefore can shorten the scan time. The recently introduced dual source CT system is the most recent incarnation in this direction. The limiting case is CT scanning with no mechanical rotation, as in electron beam CT. An array of sources separated in the circumferential direction can also be used to reduce the size of the detector array. This can lead to a reduction in detected x‐ray scatter and perhaps in the adoption of more advanced detector technologies. It also provides a reasonable method for optimization of the incident intensity distribution, thereby potentially reducing the dose to the patient while also tailoring the distribution of quantum noise across the image.

In tomosynthesis, as in CT, measurements from different directions are used to produce tomographic information, albeit with imperfect spatial separation due to data insufficiency. Nonetheless, tomosynthesis can be powerful in many settings where obtaining complete CT data is difficult, and is gaining popularity. Data acquisition with mechanical motion of a single source is limiting both in the needed imaging time and in the number of projections that can be obtained. A small number of projections makes the blurring function (the “crosstalk” from one location to another from imperfect spatial separation) very discrete and potentially distracting to the viewer. Source arrays can be used to produce tomosynthesis images with very short imaging time and smooth blurring functions, both of which are preferred.

Thus, there are significant benefits from the use of distributed sources. The author anticipates that these source arrays will become more widely adopted.

Research sponsored by GE Healthcare.

Educational Objectives:

1. become familiar with the types of source arrays and their capabilities.

2. understand the benefits of source arrays in computed tomography.

3. understand the benefits of source arrays in tomosynthesis.
MO‐D‐M100F‐03: Latest Clinical Development for GI
Authors: Willett C
Published: July 2007

There has been significant progress in the technical delivery of radiation therapy in GI cancer. These innovations have included the use of intensity modulated radiation therapy, image guidance radiation therapy, and stereotactic radiation therapy. One of the key goals is judicious use of this technology. This lecture will highlight current efforts as well as future avenues of clinical research in the use of sophisticated radiation delivery in the treatment of GI malignancies.
MO‐D‐AUD‐02: Liquid Scintillation‐Based Proton Residual Range Measurement Using a Dynamic Biological Lung Phantom
Authors: Folkert M , Mori S , Chen G
Published: July 2007

Purpose: To test and apply a scintillation‐based method to directly observe proton residual range and range variation in a dynamic biological lung phantom. Method and Materials: The dynamic biological lung phantom using a preserved swine lung has previously been compared to human lung and evaluated as an experimental platform for IGRT studies. Fiducial markers and a 5 cc artificial tumor were placed in the lung, and the phantom was imaged on a GE Lightspeed CT in 4D mode before and after seed and “tumor” implantation. The resulting 10‐phase DICOM datasets were evaluated in terms of anterior‐posterior (AP) water‐equivalent path length (WEL) variation throughout the ventilatory cycle. The preserved swine lung was irradiated in the AP direction with a 170 MeV proton beam through a 1 cm × 10 cm slit aperture. Proton residual range and range variation were directly observed using a custom‐built lucite chamber filled with scintillating fluid, monitored during irradiation by a video camera. Images were then analyzed using ImageJ to determine residual proton range. Results: WEL analysis on the imaged lung suggests a range of lung WEL values between 8 and 25 mm (average ∼16 mm). Peak calculated WEL difference at the tumor margin after implantation during ventilatory motion was approximately 5mm. Irradiation of the phantom demonstrated regional range variation across the lung on the order of 13 mm, with total WEL values equivalent to calculated values. Residual range variation due to ventilatory motion was less significant, at some points on the order of ±2.4 mm. Conclusion: The dynamic biological lung phantom in conjunction with the scintillation chamber has been shown to be a simple, inexpensive, and effective tool for the measurement of proton residual range and significant residual range variation in a complex biological system.
MO‐D‐AUD‐04: A Comparison of Heterogeneity Correction Algorithms Within a Lung PTV
Authors: Alvarez P , Molineu A , Hernandez N , Followill D , Ibbott G
Published: July 2007

Purpose: To compare the measured dose distribution with the planned distribution over a PTV centrally located within the lung when heterogeneity corrections are taken into account. Method and Materials: The Radiological Physics Center's anthropomorphic thorax phantom includes a target (∼ 1 g/cm3) centrally located in the left lung (∼ 0.33 g/cm3). The phantom was sent to 25 institutions, each of which was instructed to design and deliver a stereotactic treatment plan. The plan was intended to deliver 20Gy (homogeneous calculation) to ⩾ 95% of the PTV and limit the lung dose at point 2 cm from the PTV edge to 11.7 Gy. The institutions were asked to recalculate the dose distribution with the heterogeneity correction using the monitor units determined from the homogeneous calculated plan. TLD and radiochromic films were used as dosimeters within the target region. Results: A total of 17 institutions met the phantom irradiation criteria: +/− 5% for DTLD/DInst, and +/−5mm DTA on all sides of the PTV, based on the heterogeneous calculated plan. For these irradiations, the delivered doses over the central 80% of the PTV were compared to the planned doses along 3 orthogonal profiles through the PTV. An average of 85% of the points in the profiles from the cases calculated with the superposition/convolution algorithm were within 5% of the calculation, while only 69% of the points from the plans using pencil beam and Clarkson were within the 5% of the plan. Conclusions: The superposition/convolution heterogeneity correction algorithm showed better agreement with the measured dose distribution across the PTV than the pencil beam and Clarkson algorithms because it more accurately accounted for the lack of lateral scatter.

Work supported by PHS grant CA10953 and CA081647 from the NCI, DHHS.
MO‐D‐M100J‐01: Dose Painting With Intensity Modulated Proton Therapy and Intensity Modulated X‐Ray Therapy: A Comparison
Authors: Flynn R , Barbee D , Bowen S , McCall K , Bentzen S , Mackie T , Jeraj R
Published: July 2007

Purpose: To compare intensity modulated proton therapy (IMPT) versus intensity modulated x‐ray therapy (IMXT) for the delivery of nonuniform dose prescriptions based on hypoxia‐imaging, so‐called dose painting. Materials and Methods: IMXT delivered with helical tomotherapy (HT) was compared to IMPT delivered with spot scanning (SS) and distal gradient tracking (DGT). The novel DGT method places beam spots where dose prescription gradients occur along the pencil beam axis. Fundamental dosimetric properties of each modality were assessed by creating optimized plans for 144 variations of a cylindrical phantom with six boost regions embedded inside a base tumor region. Clinical cases with biologically conformal dose prescriptions based on PET with the ‐ATSM hypoxia imaging radiopharmaceutical were planned. The effects on the nonuniform dose distribution of delivering IMPT on a 180° arc versus equi‐spaced beams spread over 360° were investigated. Results: Phantom studies showed that nonuniform dose plan quality for tomotherapy, SS, and DGT, was similar, but DGT plans were most sensitive to phantom size and boost region proximity. IMPT reduced normal tissue integral dose by a mean factor of around two relative to IMXT. Clinical dose deviations from the prescription were comparable for all modalities, but arc IMPT deliveries markedly reduced normal tissue dose and improved critical structure sparing without compromising the dose distribution in the tumor. Conclusions: In the target volume, IMXT and IMPT deliver comparable nonuniform dose distributions. IMPT offers improved integral normal tissue dose and sparing of critical structures over IMXT, as was the case for uniform dose deliveries. DGT reduces required beam spots by a factor of about three relative to SS. IMPT dose painting will require similar management of intrafractional patient motion as for IMXT, with the additional consideration of proton spot placement uncertainty.

TR Mackie has a conflict of interest due to financial interest in TomoTherapy, Inc.
MO‐D‐M100J‐08: Effect of a Biologically‐Based Prescription Function in IMRT Dose Optimization
Authors: Bowen S , Flynn R , Bentzen S , Jeraj R
Published: July 2007

Purpose: The feasibility of delivering deliberately heterogeneous dose distributions based on biological image data is related to transformations that map the image data to dose prescription values, which is currently unknown. We created optimized dose distributions that were based on four possible image‐to‐dose‐prescription transformations to determine their delivery feasibility. Materials and Methods: Tomotherapy photon dose calculations were performed for a canine with a nasopharyngeal tumor using the Convolution/Superposition algorithm. Linear, square root, quadratic, and Gompertz transformations between the standard uptake values (SUV) from ‐ATSM PET images and the prescriptions were implemented to yield weighted distributions of prescribed dose boosts in regions of expected radio‐resistant hypoxic cells. Maximum dose boosts were constrained to reflect clinically realistic whole tumor doses and constant normal tissue doses. Optimized heterogeneous dose distributions were found by minimizing a voxel‐by‐voxel quadratic objective function in which all tumor voxels were given equal importance weightings. Results: The planned non‐uniform dose distributions founded on hypoxia maps display variability between preservation and resolution of biological heterogeneities. Whereas the linear transform preserved the SUV distribution with similar heterogeneities in the prescription, the square root and quadratic transforms softened or sharpened heterogeneities in respective prescriptions. The square root dose plan matched its prescription well due to shallow dose gradients but failed to resemble the hypoxia map, while the quadratic plan poorly matched its prescription due to steep gradients but resembled the PET scan. The linear planned dose distribution matched both its prescription and the biological image fairly well. Conclusions: Simple transformations investigate the importance of knowing given prescriptions exactly to deliver non‐uniform dose distributions from biological images. Transformations that blur heterogeneities lead to dose distributions that match their prescriptions coupled with loss of conformality to the PET images. Those preserving heterogeneities lead to less well‐matched distributions but do conform to the scans.
MO‐D‐BRA‐01: Hypofractionated RT: Biological Basis and Clinical Application in the Prostate and Lung
Authors: Bentzen SM
Published: July 2007

Hypo‐fractionation, the delivery of radiation therapy with a dose per fraction >2.0 Gy, was introduced in curative radiotherapy in many centers all over the World in the period from WWII to the mid‐1970's, mainly for health economics reasons. Clinical studies published in the late 70's and early 80's showed that these schedules were often associated with excessive late toxicity compared to standard fractionation schedules, and hypo‐fractionation was abandoned in most centers. In hindsight, this negative experience largely resulted from the over‐estimation of tolerance doses in hypo‐fractionated schedules arising from the Ellis NSD formula. Logically, this historical clinical experience does not exclude that hypo‐fractionation can be acceptable or even advantageous under certain defined circumstances.

The current status of the linear‐quadratic bio‐effect model in clinical practice is reviewed. Two clinical settings, where hypo‐fractionation is considered, are presented and discussed: (1) definitive radiotherapy for nonsmall cell lung cancer (NSCLC); (2) definitive radiotherapy for prostate cancer.

For both NSCLC and prostate cancer the current interest in the development and clinical testing of safe hypo‐fractionation regimens springs partly from the improved physical dose distribution achievable with 3D conformal radiotherapy or IMRT. This provides a window of opportunity for escalating dose per fraction. But there is also a biological rationale for hypo‐fractionation in these two tumor types — and a slightly different one in the two cases! For NSCLC there is strong evidence that shortening the overall treatment time creates a favorable efficacy:toxicity ratio with respect to late toxicity: hypo‐fractionation is a convenient way of delivering accelerated radiotherapy. In other words, we are trading in time for dose per fraction. For prostate cancer, there are no good reasons to believe that there is a strong time factor. However, there is increasingly convincing evidence that the α/β ratio for this tumor type is low, perhaps even lower than for the dose‐limiting rectal side‐effects. This alone creates a case for exploring hypo‐fractionation in this disease.

Hypo‐fractionation schedules are being tested in controlled clinical trials in several tumor types at the moment. These schedules should not be introduced in the clinic without appropriate evidence that they are safe and effective. However, based on our improved knowledge of clinical radiobiology, it appears that hypo‐fractionation schedules may yield a beneficial therapeutic ratio and/or a superior cost‐effectiveness in some clinical indications.

Learning objectives:

After this session the participants should be able to:

1. Recognize the limitations of the traditional linear‐quadratic model.

2. Summarize the changes in biological understanding of dose fractionation that have occurred over the last 10–15 years.

3. Explain the rationale behind the current interest in hypo‐fractionation in NSCLC and prostate cancer.
MO‐D‐L100E‐01: Ultrasound QC Workshop
Authors: Larson S , Pfeiffer D
Published: July 2007

Quality control (QC) testing of ultrasound scanners is important to verify the proper and consistent operation of these devices in diagnostic imaging. The increasing popularity of the American College of Radiology's ultrasound accreditation program and the upcoming Task Group 128 report, Development of QC Test Procedures for Endorectal Ultrasound Imaging, emphasize the importance of establishing a strong ultrasound quality assurance (QA) program. The American College of Radiology's ultrasound accreditation program requires a QA program be established for all ultrasound scanners, but the nature of this QA program is left largely to the discretion of the medical physicist or physician in charge. This year's workshop has been streamlined to provide information on and hands‐on experience with the types of tests recommended for a comprehensive ultrasound QA/QC program. Two brief presentations on QC testing of general‐purpose ultrasound and of endorectal ultrasound equipment particularly for prostate brachytherapy will be followed by 90 minutes of hands‐on demonstrations with experienced instructors. Various tools and phantoms for QC testing of ultrasound scanners and transducers will be available for demonstration.

Educational Objectives:

1. To learn the basics of ultrasound QC testing with a goal toward establishing a comprehensive QA program.

2. To gain experience with various test tools for ultrasound QC.