bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐489: Simulating the Effects of Anti‐Angiogenic Therapy Using Voxel‐Based Biological Parameters Derived From Functional Imaging
Authors: Titz B , Adhikarla V , Kozak K , Jeraj R
Published: April 2010

Purpose: Although anti‐angiogenic agents are being used in combination with standard radiotherapy or radiochemotherapy, the biological response mechanisms are currently not well understood. This study investigates therapeutic response to bevacizumab, a monoclonal antibody to VEGF‐A, using a functional imaging‐based tumor simulation model. Method and Materials: A multiscale tumor growth and radiation therapy response model based upon patient‐specific parameters was extended by implementing response mechanisms to bevacizumab. PET/CT images of cellular proliferation ([]FLT) and hypoxia ([]Cu‐ATSM) in human HNSCC tumors served as simulation input. Treatment with bevacizumab according to a clinical treatment regimen was simulated as an example of anti‐angiogenic therapy. Heterogeneous drug delivery within the tumors was simulated using a four‐compartment pharmacokinetic model coupled with perfusion parameters assessed by DCE‐CT. Within each voxel, response was modeled based on changes in VEGF‐A levels, simulated changes in microvessel density (MVD), and resulting changes in oxygenation levels. Results were compared to follow‐up PET/CT scans of hypoxia and proliferation. Results: Simulating response to a single bevacizumab dose of 10 mg/kg yielded decreased []FLT uptake values as observed in all follow‐up scans. The mean correlation coefficient between simulated and follow‐up []FLT scans was 0.79. However, trends in []Cu‐ATSM uptake values could not be reproduced in all simulation cases, indicating that response time, as well as quantitative changes in hypoxia might depend on additional patient‐specific biological parameters. Simulated MVDs were found to be highly time‐dependent. Conclusion: The implemented model successfully reproduced trends in proliferative response following bevacizumab monotherapy and can be readily integrated into a previously developed radiation response model. Results also suggest that MVD should be used carefully when characterizing treatment response to anti‐angiogenic therapy due to a strong time‐dependence. Upon successful validation, the implemented model could serve as a prospective tool to help identify personalized dosing and sequencing of combination therapies.
SU‐FF‐T‐493: Can An Addition of a Simple Constant to Linear Quadratic Formula Improve Cell Survival Curve Fits for Some Cell Lines?
Authors: McKenna F , Ahmad S
Published: April 2010

Purpose: To investigate the effect of an unrecognized hyper radio‐sensitivity on radiobiological parameters α and β of the linear quadratic odel. Methods and Materials: A Chinese hamster cell line designated “choaa8” and a lung cancer cell line designated “ncih226” were fitted to the inear quadratic (LQ) model (lnS = −αD −βD2) and to a simple constant plus linear quadratic (CLQ) model (lnS = −c −αD −βD2). The χ2/df of each fit was compared to determine which model gives the best fit to the cell survival curve. Results: The linear quadratic χ2/df for the “choaa8” and the “ncih226” are 1.55 and .095 respectively. The simple constant plus linear quadratic χ2/df for the “choaa8” and the “ncih226” are 1.18 and .075 respectively. So the addition of a simple constant to the linear quadratic formula provides greater than 20% improvement to the survival curve fits. The α/β _ratio for the LQ “choaa8” is 11.0, whereas the α/β _ratio for the CLQ “choaa8” is 5.4. The α/β _ratio for the LQ “ncih226” is 5.1, whereas the α/β _ratio for the CLQ “ncih226” is 0 indicating α = 0. So the addition of a simple constant in the linear quadraticformula can have a dramatic effect on the α/β _ratio._ Conclusion: CLQ provided superior fits compared to the LQ for the two data sets mentioned above. The value of the α/β _ratio was heavily dependent on whether or not an addition of a simple constant to linear quadratic formula was used. Further work is required to determine if the improved fit is due to actual physical phenomena such as hyper radio‐sensitivity or an alternative explanation like experimental error or noise in the data.
SU‐FF‐T‐494: Effects of Ionizing Radiation Exposure On Arabidopsis Thaliana
Authors: Kurimoto T , Constable J , Huda A
Published: April 2010

Purpose: The effects of ionizing radiation on plants were examined in order to investigate the possibility of utilizing plants as a biodosimeter. Different radiation doses, ages of radiation exposure, and treatment methods were considered for the analysis of the complex and dynamic mechanisms of ionizing radiation effects. Method and Materials: The investigation was performed by irradiating Arabidopsis thaliana with 6MV x‐ray produced by a linear accelerator. Photosynthesis and respiration rates, chlorophyll fluorescence fv/fm ratio and yield, plant height, total leaf area, stem mass, leaf mass, and above‐ground biomass were measured in order to evaluate both physiological and physical impacts of ionizing radiation. The statistical analysis of the radiation effects with respect to four different total doses (0.5Gy, 5Gy, 50Gy, and 150Gy), two different treatment types (single and fractionated), and three different life stages at irradiation (15‐day, 20‐day, and 25‐day old) revealed the details of dynamic responses of Arabidopsis thaliana to radiation exposure. Results: The age at the time of irradiation is a key to determine the overall effects of radiation exposure, and the irradiated Arabidopsis indicated much greater contrast in physical growth compared to physiological responses immediately after the irradiation. Radiation hormesis was not observed among the irradiated Arabidopsis older than 15‐days. In order to discern such phenomenon in Arabidopsis, perhaps, ionizing radiation needs to be delivered at earlier than 30% of its entire life cycle with the total dose lower than 0.5Gy. Conclusion: The results suggest plants like Arabidopsis are capable of being utilized as a biodosimeter, and further studies can be performed on specific areas (e.g. less than 0.5Gy of very low dose radiation exposure, microscopic analysis of plant cells, etc.) in order to assess the effects of ionizing radiation for a practical application.
SU‐FF‐T‐495: Risk Estimation of Radiation Induced Second Cancers in Prostate Cancer Patient Treated by Intensity Modulated Radiotherapy (IMRT) and Three Dimensional Conformal Radiotherapy (3D‐CRT)
Authors: Sakulsingharoj S , Boonkitticharoen V , Tannanonta C , Kakanaporn C , Iampongpaiboon P
Published: April 2010

Purpose: The main purpose of this study was to determine the organ equivalent dose (OED) from primary beam and scatter components reflecting the second cancer risk in prostate cancer patients treated with 10 MV photon by the intensity modulated radiotherapy (IMRT) compared to the three dimensional conformal radiotherapy (3D‐CRT). Method and materials: Both IMRT and 3D‐CRT plans were optimized for each of the 10 patients using Eclipse Radiation Therapy Planning System (RTPS), from which the differential dose volume histograms (dDVHs) for organs of interest were extracted. The three‐dimensional dose distribution data were used for calculation of the primary beam OED. The scatter dose was measured by thermoluminescence dosimeters 700 (TLD‐700 rods) using an Alderson Rando phantom to simulate the treatment condition according to IMRT and 3D‐CRT plans. Results: IMRT plan induced a significant 2‐fold increase in scatter component of OED compared with 3D‐CRT (p = 0.0092) and a 1.13 fold reduction in primary beam component (p = 0.0001). When the primary and scatter components were combined, the total OEDs for IMRT and 3D‐CRT were 0.41 and 0.43 Gy, respectively. No significant difference could be observed (p = 0.1845). On average, risk of the second cancer from IMRT and 3D‐CRT plans was 12.47 risks/10,000 patients/year. Conclusions: IMRT plan does not induce greater second cancer risk than 3D‐CRT. The average OED for both techniques was 0.42 Gy.
SU‐FF‐T‐497: When Tumor Repopulation Starts? An Outcome Analysis of Radiotherpay for Cervical Cancer
Authors: Wang J , Huang Z , Gao M , Lo S , Yuh W , Mayr N
Published: April 2010

Purpose: The onset time of tumor repopulation remains an unsolved issue for cervical cancer, although 3∼4 weeks have been assumed. The purpose of this study is to determine the onset time (Tk) of cervical cancer based on an outcome analysis. Method and Materials: A total of 80 patients with cervical cancer (stages IB2‐IVA) were included in this study. Four sequential magnetic resonance imaging (MRI) scans were performed before, during and after radiation therapy (RT). The median follow‐up time was 5.5 years (range 0.2–9.4 years). A kinetic model incorporating effects of radiation cell killing, dead‐cell resolving, and tumor repopulation, was introduced to analyze tumor regression data measured by the MRI scans. A series of the onset time (Tk) has been tested for outcome prediction. The derived radiobiological parameters, including cell surviving fraction of 2 Gy (S2) and dead‐cell resolving half‐time (T1/2), were correlated with clinical outcome using the Mann‐Whitney rank‐sum test. Results: Both the model parameters, S2 and T1/2, derived from regression data, correlated significantly with clinical outcome (p<0.0001). The corresponding p‐values for outcome prediction were obtained as a function of the onset time. The optimal value of the onset time for best outcome prediction was Tk=19 days, with an uncertainty range of (14, 35) days. The outcome prediction power of T1/2 was superior to that of S2, and more sensitive to the onset time of tumor repopulation. Conclusion: The onset time of accelerated repopulation of cervical cancer was directly derived from the clinical data using a kinetic model. Our study showed that accelerated repopulation does exist in RT for cervical cancer and has a relatively short onset time. Therefore dose escalation is necessary to compensate the effects of RT protraction.
SU‐FF‐T‐498: Improving Normal Tissue Complication Probability Fits Using Non‐Binary Outcomes
Authors: Das S , Chen S , Yin F , Marks L
Published: April 2010

Purpose: Binary outcomes (toxicity=1, no‐toxicity=0) are frequently used as inputs to fit parametric models. However, in reality, outcomes span the range in‐between these extremes; binary values are used for lack of more precise quantification. We propose a method to estimate non‐binary outcomes, which can then be used to more accurately fit conventional parametric models (e.g., Lyman‐probit, relative‐seriality). Methods and Materials: The non‐binary outcomes were estimated using 4 machine learning algorithms. The algorithms used variables selected from the available data to best‐fit binary outcomes. Based on the fitting, each algorithm outputted binary estimates of whether or not the patient suffered toxicity. By fitting each algorithm to randomly selected subsets of the patient data, multiple binary toxicity estimates were generated for each patient. Averaging these estimates for each algorithm produced a non‐binary estimate. Furthermore, averaging these non‐binary estimates over all algorithms reduced prediction bias. This final algorithm‐averaged non‐binary patient estimate was then used as input to conventional parametric algorithms. This method is demonstrated in the context of radiotherapy‐induced pneumonitis. Results: One‐hundred estimates from each algorithm × 4 algorithms were averaged to produce a non‐binary toxicity estimate for each patient. Both the original binary toxicity outcome and the non‐binary estimate were fitted to the parametric Lyman‐probit and relative‐seriality models. Both parametric models had large confidence interval limits when fitted to the original binary outcomes. The fits improved when using the non‐binary estimates. The improvement was substantially better for the Lyman‐probit model, but only marginally so for the relative‐seriality model. Thus, the Lyman‐probit model is better suited to modeling radiation‐induced pneumonitis, a conclusion that would not have been possible from the original binary outcomes. Conclusions: Non‐binary estimates from machine learning algorithms can be used to not only generate better fits to conventional parametric models, but also to deduce which model is methodologically better suited.
SU‐GG‐BRC‐07: 4DCT‐Based Measurement of Radiation Induced Changes in Pulmonary Function
Authors: Ding K , Reinhardt J , Bayouth J , Buatti J
Published: April 2010

Purpose The present treatment‐planning dosimetry constraints for the lung are based on studies that assume lung tissue is homogeneous in its response to toxicity, irrespective of tissue location or underlying function. No human studies have investigated the relationships between local lung function, spatial radiation dose distribution, and radiation induced lung function changes. We are able to observe radiation‐induced changes in lung tissue function using 4DCT and image registration. Method and Materials Two 4DCT data sets before and after RT from one patient are used in this study. Nonlinear, 3D image registration was applied to register the maximum exhalation image to the maximum inhalation image for the calculation of local lung expansion as a measurement of regional pulmonary function. We compared the changes of pulmonary function before and after RT with planned radiation dose at different locations of the lung. Results The registration accuracy analysis indicated our registration error is on the order of 1 mm. The pulmonary function change in left lung where the tumor is located is larger than it is in right lung (maximum Jacobian change is respectively 0.23 and 0.15). The highest correlation of the pulmonary function change to the delivered radiation dose is in regions which are at the distance of 20 to 25 mm to the tumor region (linear regression, r = −0.73). Further plots between the radiation dose and the pulmonary function change suggest the lung tissue function change is not sole based on radiation dose. Conclusion We described a technique that uses 4DCT, image registration and biomechanical analysis to measure regional lung function. We compared the regional lung function before and after RT to the planned radiation dose distribution and examined the differences at the treatment location and in non‐treatment regions.

Conflict of Interest VIDA Diagnostics, Inc (shareholder).
SU‐GG‐BRC‐08: Improving Buildup Region Measurement Accuracy Using a Surface Location Method
Authors: Ververs J , McEwen M , Siebers J
Published: April 2010

Purpose: To determine the depth of the inflection point in the buildup region of photon beam depth‐ionization curves for 11 cylindrical ionization chambers of differing designs and investigate dependencies of the inflection point on beam energy, electron contamination, and chamber design. Method and Materials: Each ionization chamber is carefully aligned to the water surface using a precision alignment telescope with a custom, high‐precision beam scanning system. Following alignment, depth‐ionization curves are obtained including scanning the chamber beyond the air‐water interface for 6, 10, and 25 MV photon beams. Measurements are made with and without a 1 mm lead foil in the beam for a 10×10 cm2 field. The inflection point in the measured depth‐ionization data is determined by finding the maximum in its second derivative. Results: The location of each chamber‐specific inflection point is invariant to changes in beam energy, electron contamination, and chamber orientation within the 0.5 mm measurement resolution. Eight chambers, whose outer diameters are within 0.7 mm of each other, exhibit inflection points that are within 0.5 mm of one another. The location of each chamber's inflection point is most strongly impacted by its outer radius and corresponds with the shallowest depth at which the chamber is fully submersed in the water, within 0.5 mm. Conclusion: The buildup region inflection point for a given cylindrical chamber is invariant to the beam variations studied and occurs at a depth equal to the chamber outer radius, within measurement resolution, for the 11 ionization chambers studied. Using this dependence, the inflection point can be used as a robust offline check to identify the water surface location and to identify inter‐setup/inter‐user setup variations. Higher quality surface localization can ease beam modeling and improve the quality of treatment planning data.
SU‐GG‐BRC‐10: Shape Matters: Utilization of a Conformal Voxel Technique to Acquire Robust in Vivo Prostate MRSI at Short Echo Times
Authors: Venugopal N , McCurdy B , Drachenberg Darrel , Al Mehairi Salem , Alamri Aziz , Sandhu GS , Sivalingam Sri , Ryner Lawrence
Published: April 2010

Purpose: We seek to improve the quality of in vivo prostate MRSI data acquisition by utilizing an optimized conformal voxel technique coupled with a spatial‐spectral excitation PRESS pulse sequence for short echo time acquisitions. Method and Materials: All subjects were scanned on a GE 1.5T Signa MR scanner equipped with Echospeed gradients. A standard endorectal coil in combination with a torso phased‐array coil was used. The PRESS pulse sequence was modified to include the optimized conformal voxel MR spectroscopic imaging technique (CV‐MRS). This method uses up to twenty Very Selective Saturation (VSS) pulses, automatically positioned in three dimensions, to “conform” the excitation volume to the shape of the prostate, effectively nulling signal from periprostatic lipids. Subjects were scanned using both the standard PRESS and the optimized CV‐MRS techniques at long and short echo times (TE). In vivo prostate spectra were collected and processed using a modified version of LCModel. Results: We observed an average lipid reduction of 60±18% for 17 subjects over the entire prostate when using the optimized CV‐MRS technique as compared to standard MRSI techniques. In specific regions along the peripheral zone, we observed lipid reduction greater than 95%. The effect of reducing the lipid contamination has resulted in a ∼70% improvement in peak identification of key prostate metabolites, based on goodness‐of‐fit parameters. Furthermore, short TE acquisitions have resulted in a substantial increase in the citrate signal, full visualization of the citrate multiplet and other metabolites not seen at long echo times. Conclusion: In vivo implementation of this optimized MRSI technique has confirmed the reduction in peripheral lipid contamination, and improved the quality of spectra throughout the prostate. Furthermore, this is the first demonstration of short TE in vivo prostate MRSI acquisitions, which provides significant signal increase and reveal short TE metabolites to potentially improve prostate cancer detection.
MO‐SAM‐BRB‐02: Proton Physics and Technology
Authors: Smith A
Published: April 2010

The dose localization advantages of proton beams derive primarily from the Bragg peak in the proton stopping distribution. Therefore, the potential clinical gains expected form proton beams are based on physical, rather than biological, considerations. The rationale for proton therapy is based on the hypothesis that the superior dose distributions of proton beams will lead to increased local control; increased disease‐free survival; decreased treatment‐related morbidity; and improved quality of life. The degree to which each of these end‐points can be changed by proton therapy will depend upon the particular disease site, patient population, and other factors. In the last few years there has been a significant increase in interest in proton therapy and as a consequence, many new facilities are being planned and built. There are currently over 25 institutions worldwide treating patients with proton beams and over 55,000 patients have been treated. There are at least 25 new facilities in various stages of planning and building. We will discuss the rationale for proton therapy, the current status of proton therapy, proton physics and dosimetry, and technology for the acceleration and delivery of proton beams. We will also discuss new developments in proton therapy accelerators and treatment delivery systems. Technologies for carbon ion therapy will also be discussed. We will address issues related to the cost of proton treatments relative to the cost of photon treatments and discuss various ways in which the cost of proton therapy can be decreased.

Learning Objectives:

Understand

1. rationale for proton therapy;

2. current status of proton therapy;

3. physical characteristics of proton beams;

4. beam production and treatment delivery technology for proton beams;

5. acceptance testing and clinical commissioning of proton therapy beams; and

6. QA for proton treatments
MO‐A‐210A‐01: Update On Fluoroscopy Physics
Authors: Balter S
Published: April 2010

Radiation usage during fluoroscopically guided interventions can be high enough to warrant careful dosimetry and patient management. Basic compliance with the usual set of local regulatory requirements is sufficient for patient safety in the interventional environments. For example, modern systems meeting all current regulatory dose restrictions are capable of delivering table‐top air kerma rates exceeding 200 mGy/min for normal mode fluoroscopy and 1,500 mGy/min for cinefluorography.

Clinical dosimetry during each complex intervention is facilitated by dosimetric instrumentation built into the fluoroscopic system. The Society of Interventional Radiology has published a standard of practice recommending dosimetry for all interventional procedures. In 2008, the ACR published a technical standard for the use of radiation in fluoroscopic procedures. A DICOM Structured Report for detailed reporting of radiation usage in interventional fluoroscopy has been defined, tested and is currently being deployed in clinical systems. The Joint Commission has included fluoroscopic procedures with skin doses exceeding 15 Gy in its list of sentinel events; with the implicit challenge to facilities that they can prove the absence of such occurrences.

This course reviews technical elements for a program of patient fluoroscopic radiation safety. ICRU diagnostic dosimetric quantities and their fluoroscopic extensions. Construction, dosimetric features, and performance characteristics of modern fluoroscopes. Extended QA protocols for compliance measurements, system characterization and clinical dosimetry. Dose recording and reporting, including DICOM‐DOSE. The Joint Commission fluoroscopy sentinel event.

Learning Objectives

1. Understand dosimetric concepts relating to interventional fluoroscopy

2. Characterize the dosimetric features and performance of a modern fluoroscope

3. Be able to set up a clinical dose recording and reporting policy that will meet clinical and JC requirements.
MO‐B‐BRD‐01: Quality Assurance in Stereotactic Radiosurgery and Fractionated Stereotactic Radiotherapy
Authors: Shepard D , Solberg T
Published: April 2010

In the 50‐plus years since it was first introduced, stereotactic radiosurgery, high‐dose irradiation of cranial neoplasms delivered in a single fraction, has become a standard of care in the treatment brain tumors, vascular malformations, functional disorders, and pain. Modern radiosurgery can be performed non‐invasively and on an outpatient basis, yet with an extremely high degree of accuracy. Within the past ten years, the field of radiosurgery has seen numerous technological enhancements, including: the development of dedicated devices for stereotactic delivery, the use of relocatable frames to facilitate fractionated delivery, the development of image guided and “frameless” approaches, and the application to extracranial tumor sites. Each of these developments is 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.

Learning Objectives:

1. Differentiate how radiation is delivered for Gamma Knife and Linac‐based (conventional and robotic) stereotactic radiosurgery.

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

3. Discuss measures for assuring accuracy in stereotactic localization and dose delivery for Gamma Knife and Linac‐based stereotactic radiosurgery.
MO‐B‐303A‐01: Digital Mammography Update: Design and Characteristics of Current Systems
Authors: Kanal K
Published: April 2010

Full Field Digital Mammography (FFDM) systems are fast becoming popular and replacing conventional film‐screen mammography systems. FFDM systems use a digital detector instead of screen‐film to capture the image of the breast. Several FFDM systems based on different digital detector design and materials are currently available. Some systems are characterized as direct conversion detectors and some are based on indirect conversion process. The digital detectors can be characterized by image quality metrics such as detector quantum efficiency (DQE) and modulation transfer function (MTF).

In this lecture, the physics and technology of the digital detectors used in FFDM will be discussed as well as the advantages and applications arising due to the availability of these systems will be presented. The most recent commercially available systems will also be discussed.

Learning Objectives:

1. Understand the physics of digital detector technology

2. Understand the image quality metrics such as DQE and MTF

3. Recognize that vendors use varying detector technology in FFDM systems

4. Appreciate the advantages and disadvantages of digital mammography systems
MO‐D‐211A‐01: Professional Development for Women in the AAPM
Authors: Garman K , Travis E
Published: April 2010

This session focuses on professional development skills for women. The first speaker, Dr. Karen Garman, is President and Senior Learning Consultant for Healthcare Education, Leadership and Performance, Inc. or HELP Inc. Dr. Garman has over 25 years of experience as an expert in professional development. Dr. Garman will present on time management skills and on dealing with conflict in the workplace. The second speaker is Dr. Elizabeth Travis. Dr. Travis is a Professor in the Department of Experimental Radiation Oncology at MD Anderson Cancer Center and Associate Vice President for Women Faculty Programs. Dr. Travis is also the editor of a book on mentoring “Legends and Legacies: Personal journeys of women physicians and scientists at MD Anderson Cancer Center.” Dr. Travis will discuss the role of mentors as women build their careers.
MO‐D‐BRD‐05: The Proton Beam Therapy Facility at PSI
Authors: Garvey T
Published: April 2010

The centre for proton therapy at the Paul Scherrer Institute was expanded recently following the commissioning of a new superconducting‐magnet cyclotron (COMET) dedicated to patient treatment. The accelerator was built by ACCEL Instruments GmbH (Varian), based on a design from the National Superconducting Cyclotron Laboratory (Michigan State University). The cyclotron is specified to provide a 500 nano‐Ampere beam of protons at a fixed energy of 250 MeV. The large magnetic field (∼ 3T) required at extraction is provided by the superconducting coils. A high power radio‐frequency system, operating at 72.8 MHz (second harmonic of the cyclotron frequency) provides the required acceleration of protons following their emission from a cold‐cathode ion source. The facility has also been up‐graded with the addition of new gantry (Gantry‐2) for patient treatment and a new beam line dedicated to eye treatments (OPTIS2). A novel feature of COMET is the high beam extraction efficiency (> 80%). This limits component irradiation and facilitates the regular maintenance periods which are an important consideration for any patient treatment center where high reliability and availability are required. We will describe the modes of operation of PROSCAN and, in particular, the spot‐scanning technique used to irradiate tumours. Magnetic elements permit rapid transverse deflection of a pencil beam for two dimensional scanning. An energy “degrader” allows rapid scanning in energy over the range of 70 – 238 MeV. This results in a variable depth of penetration of the beam, thus permitting a complete three dimensional scan. The beamlines which transport protons from COMET towards the two patient gantries and to OPTIS2 will also be discussed. They require sophisticated diagnostics for safe and reliable use of the facility. The various diagnostics include ionization chambers, secondary emission monitors and multi‐leaf Faraday cups. They are used to measure beam current, profile, position, halo and loss. The role of the diagnostics as interlocks for safe operation of the beamlines will also be described.

Learning Objectives:

1. Understanding the principle of the spot scanning technique.

2. Understanding the issues concerning diagnostics for safe beam‐line operation.
MO‐D‐BRB‐01: Study of Systemic and Random Errors On VMAT and IMRT Plan Quality and Deliver Accuracy
Authors: Chen F , Rao M , Ye J , Luan S , Shepard D , Cao D
Published: April 2010

Purpose: During the delivery of volumetric modulated arc therapy (VMAT), random errors exist in both the MLC leaf positions and the gantry angle. In this work, we investigated the impact of such random errors on VMAT plan quality and delivery accuracy. The impact of system calibration errors was also examined. For comparison purposes, we performed a similar study on step‐and‐shoot IMRT plans. Material and Method: VMAT plans for three treatment sites (prostate, pancreas and head‐&‐neck) were created using a home‐grown arc sequencer. Next, random and systematic leaf position errors were introduced into these plans with the random errors sampled from Gaussian distributions of varying widths ranging from 1 to 3mm. Two types of systematic errors, including MLC bank shifts in the same direction (Type I: leaf gap unchanged) and MLC bank shifts in opposite directions (Type II: leaf gap increase/decrease). The plan quality variations were compared in the Pinnacle3 planning system. Plans with systematic errors were verified using the MatriXX ion chamber array with gamma evaluation criteria of 3%/3mm. Results: The plan degradation observed for VMAT plans was slightly less as compared to that for fixed‐field IMRT plans when random errors up to 3mm to the leaf positions were introduced. With type I systematic errors of 3mm on leaf positions, the average standard deviation of PTV dose increased by 10.2%. This value increased to 18.4% for the corresponding fixed‐field IMRT plans. A larger impact on the IMRT plans was also observed when type II systematic errors were introduced. The above results were confirmed by plan verification measurements with higher gamma passing rates for VMAT plans when systematic errors were applied. Conclusion: The VMAT delivery technique has better tolerance to random and systematic errors in gantry angle and MLC leaf position errors as compared with step‐and‐shoot IMRT.

Research supported by Elekta.
MO‐D‐BRB‐03: Using a Database of Patient Geometric and Dosimetric Information for Quantitative IMRT Plan Quality Control
Authors: Wu B , Kazhdan M , Ricchetti F , Simari P , Jacques R , Sanguineti G , Chuang M , Taylor R , McNutt T
Published: April 2010

Purpose: To empower IMRT treatment planners with the ability to judge new plans against the performance of similar past plans. Method and Materials: This is accomplished by searching a database of treated patients using the geometric relationships between targets and organs at risk (OARs). We introduce the concept of a shape relationship descriptor to quantify this intuitively important relationship. The overlap volume histogram (OVH) simplifies the complex 3D relationship between a target and an OAR. The OVH is the normalized 1D histogram of the OAR volume within a distance of the target. The OVH descriptor was used to search a patient database, providing a patient specific set of dose volume histograms (DVHs). These DVHs were then presented to the planner to aid their decisions. Results: The method was applied to both parotids of 32 treated head‐and‐neck patients. The 17 parotids that promised the greatest reduction in D50 were selected for re‐planning. These 17 parotids came from 13 patients. Our method indicated that the doses of the other nine parotids of the 13 patients could not be reduced, so they were included in the re‐planning process as controls. Re‐planning with an effort to reduce D50 was conducted on the 26 parotids of these 13 patients. Average reductions of D50 were 6.6Gy for the 17 improvement candidates and 1.9Gy for the controls. Originally, several parotids violated the RTOG planning goal of V(30Gy)⩽50%. Eleven of these were improvement candidates, and re‐planning reduced this number to three. Re‐planning had no impact on the five control parotids that were violating the RTOG planning goal. According to the physician reviews, re‐planning did not degrade target coverage or OAR sparing. Conclusions: Our method offers a patient specific DVH evaluation for OARs, providing an effective mechanism of quantitative IMRT plan quality control.
MO‐D‐BRB‐04: Mixed Integer Models for Elucidating the Tradeoff Between Treatment Time and Plan Quality in VMAT Delivery
Authors: Craft D , Bortfeld T
Published: April 2010

Purpose: Rotational IMRT delivery techniques, such as volumetric modulated arc therapy (VMAT), are alternatives to standard IMRT delivery, claiming faster delivery and equally good dose distributions. In reality there is a cost to faster delivery times. The purpose of this investigation is to understand the tradeoff between plan quality and treatment time in rotational delivery by use of optimization models. Method and Materials: We study a simplified VMAT model for a 2D phantom and construct an exact mixed integer optimization model for it. The model includes treatment time as a constraint, and otherwise does not specify how the delivery is to be done, allowing for either VMAT or IMRT solutions. The model is too large to solve, but we trap the optimal solution between tight upper and lower bounds with additional models. The lower bound solutions are used to warm start the upper bound solutions. We construct Pareto surfaces for the joint tradeoffs of treatment time, tumor maximum dose, and organ at risk mean dose. Results: Upper bounds are within 10% of lower bound solutions. This allows us to conclusively demonstrate that 1) the treatment time constraint becomes more important when high intensity modulation is required to achieve optimal dose distributions, and 2) finding a good feasible VMAT plan is benefitted (by ∼5% in objective value) by warmstarting using the fluence modulation required at each angular location. Conclusion: For problems where the optimal dose distribution has non‐convex iso‐dose lines (to avoid nearby critical structures), the high modulation necessary to achieve such plans translates into longer treatment times. In these cases, when allowed treatment time is small, the optimal solutions show fluence being delivered at every angle — VMAT. If treatment time is allowed to be larger, IMRT plans are found to be optimal.
MO‐D‐BRB‐05: A Novel Dynamic MLC Leaf Sequencing Algorithm for 4D Treatment with Deformable Target Motion Correction
Authors: Xu J , Shi C , Papanikolaou N
Published: April 2010

Purpose: To investigate a dynamic MLC (DMLC) leaf sequencing method for the 4D IMRT delivery. Materials and methods: A 4D CT was obtained and 10 phase CT data sets were created retrospectively. Individual IMRT plan was generated for each phase on Pinnacle treatment planning station, and a 4D plan was created using a deformable image registration technique. Based on the DMLC leaf sequences generated from the plan of each phase, the non‐rigid motion corrected 4D leaf sequence was created by matching the time indexes of the leaf sequences and the breathing cycles of each phase. The 4D leaf sequence was iteratively adjusted for the maximum leaf speed to avoid any beam hold‐offs. At the same time, a rigid motion corrected 4D leaf sequence was calculated by adjusting the leaf center corresponding to the center of mass position of the target in each phase. The opening density map (ODM) of the 4D plan was used to create a traditional no‐motion corrected leaf sequence. All three leaf sequences were delivered by Varian 2100 C/D with Millennium 120 leaf DMLC. The MatriXX (IBA Dosimetry) was used to measure the delivered fluence map every 40 ms. The delivered fluence maps were registered back to the patient's coordinate system. Results: Using the 4D plan ODM as reference, the fluence map from the non‐rigid motion corrected 4D leaf sequence showed a maximum dosimetric difference of 3%. However, the fluence maps from the rigid motion corrected 4D leaf sequence and the no‐motion corrected leaf sequence showed maximum dosimetric differences of 30%. Conclusion: For 4D plan DMLC delivery, the non‐rigid motion corrected leaf sequencing, the rigid motion corrected 4D leaf sequencing and the no‐motion corrected leaf sequencing were investigated. Results showed that the non‐rigid motion corrected leaf sequencing is the one that closest deliverers the 4D plan.
MO‐D‐BRB‐06: Comparison of Dosimetric Inaccuracies Introduced by Intra‐Fraction Respiratory Motion in IMRT and VMAT
Authors: Atkinson P , Glide‐Hurst C , Matuszak M , Yan D
Published: April 2010

Purpose: To compare the dosimetric inaccuracies introduced by intra‐fraction respiratory motion in equivalent IMRT and VMAT plans. Method and Materials: First, a commercial respiratory motion platform was adapted to support the 3D dosimetric phantom. A slit‐field IMRT and equivalent VMAT plan were delivered to the phantom with one‐dimensional (S‐I direction) respiratory motion (cos4 pattern, peak‐to‐peak amplitude = 1.5cm, 15 BPM). A clinical patient IMRT plan and equivalent VMAT plan were also delivered to the moving phantom. The plans were delivered to the phantom with the motion platform both static and dynamic with a range of different starting phases in the respiratory cycle. Measurements were compared using the percent differences (PD) of the dynamic measurements relative to the static measurements. Results: The mean dynamic versus static target PD for non‐clinical IMRT and VMAT fractions were −6.4 ±11.9% and −4.2 ±6.7%, respectively. The mean dynamic versus static target PD for clinical lung IMRT and VMAT fractions were ‐1.1 ..4.2% and ‐0.9 ..3.3%, respectively. The PD of the clinical IMRT plan showed sensitivity toward the relative starting phase of the target, while the clinical VMAT plan did not. This suggested that the IMRT plan experienced a greater degree of the MLC interplay effect than the VMAT plan. After several fractions, IMRT and VMAT dosimetric inaccuracies due to respiratory motion became less distinguished, most notably for the IMRT plan. Conclusion: In the context of stereotactic radiosurgery, in which fewer fractions are delivered, VMAT may be particularly advantageous to reduce discrepancies introduced by intra‐fraction motion.
MO‐D‐BRB‐08: A Hybrid Strategy of Offline Adaptive Planning and Online Image Guidance for Prostate Cancer Radiotherapy
Authors: Lei Y , Wu Q
Published: April 2010

Purpose: In online image‐guided radiotherapy of prostate cancer, the setup error and inter‐fractional motion is eliminated through pre‐treatment imaging and couch correction at each fraction. However, the rotation and deformation is not corrected and only accounted for in planning margin. In this study, we propose a hybrid of online and offline adaptive image‐guidance strategy for both low risk patients (LRP, CTV=prostate) and intermediate risk patients (IRP, CTV=prostate+seminal vesicles). The benefit of margin reduction is evaluated geometrically. Method and Materials: Planning and treatment helical CT images from 25 patients over 412 fractions were used. Online image‐guidance was simulated by matching the center of mass of CTV in treatment CT to planning CT. Offline replanning was performed by constructing the internal target volume (ITV) from the union of position‐corrected CTVs from the first 5 treatment CTs. The volume overlap index (OI) of ITV and CTVs of the remaining fractions were compared with the OIs between PTV from planning CT and the treatment CTVs. Margins from 0 to 10 mm were investigated. Results: The mean ITV volumes are 62.5 and 90.1 cm3 for LRP and IRP, respectively, equivalent to 0.8 and 1.0 mm uniform margin to CTV0 (mean volumes of 55.7 and 78.0 cm3). The margins needed for 99% OI for ITV (V99% = 67.9 and 105.5 cm3) are 1.7 mm and 2.6 mm less than those for the planning CTV (V99% = 84.5 and 144.7 cm3) for LRP and IRP, respectively. Conclusion: The hybrid of online and offline adaptive radiotherapy protocol can effectively account for the patient‐specific interfraction organ motion and setup errors for prostate cancer patients. The planning margin can be reduced further using the hybrid strategy compared with online image guidance alone. Reduced irradiated volume will also lead to decreased toxicity in critical organs.
MO‐D‐BRB‐09: IMRT Ad‐Hoc Adaption ‐ Initial Results for Prostate: A Retrospective Planning Study
Authors: Gainey M , Bratengeier K , Polat B , Meyer J , Flentje M
Published: April 2010

Purpose: A planning study was performed to investigate the geometry‐based adaption of a step and shoot IMRT‐plan. Method and Materials: Six cases with large rectum and prostate deformations were selected. A 9 field IMRT‐plan (A) was planned on a first CT(CT1). The plan fulfilled all requirements for prostate IMRT in our clinic and its quality was comparable to a conventional high‐quality step and shoot IMRT plan. For a second CT(CT2), three plans were considered: the original plan with optimized isocentre position (B), a newly optimised plan (C) and the original plan, adapted using optimization rules (D), based on a geometry‐based concept called “2‐Step IMRT”. Several DVH‐parameters were utilized for quantification of plan quality: CTV D99, central PTV D95, V95 for an outer PTV, V80 and V50 for rectum and bladder. Results: Unlike B, D achieved almost the same target coverage as plan C. For the OARs, the rectum V80 was slightly increased for the original plan. The volume with more than 95% of the target dose was 1.5 ± 1.5 cm3 for C, compared to 2.2 ± 1.3 cm3 for A in CT1 and 7.2 ± 4.8 cm3 in CT2. D resulted in 4.3 ± 2.1 cm3, an intermediate dose load to the rectum. All other parameters were comparable for C and D in contrast to the results from B. Conclusion: The first results for adaptation using the 2‐Step IMRT algorithm are encouraging. The plans were superior to plans with optimised isocentre position B and only marginally worse than a newly optimized plan C. Computerisation is needed to accelerate the procedure, which is currently performed manually. Checks have to be developed to allow an ad‐hoc application of the adapted plan.
MO‐D‐303A‐02: KTool: A Web‐Based Educational Application for Exploration of K‐Space Properties
Authors: Yanasak N , Allison J
Published: April 2010

Purpose: The goal of this project was to develop a web‐based tool (named “KTool”) for visual demonstration of how changes in k‐space data are manifest in changes of MR image appearance. The tool should be usable on a variety of computer platforms for wide‐ranging access by Radiology residency programs. The purpose of this endeavor is to help cultivate an intuitive understanding of what k‐space is, to improve understanding of the relationship between raw data and images produced during the MRI image formation process. Method and Materials: KTool was programmed as an Applet using Java on a Dell Precision workstation with a Linux‐platform, and deployed on the Medical College of Georgia Department of Radiology web‐server. The applet was embedded in a webpage for viewing, and was successfully accessed using computers with three different platforms/environments (Windows XP, Mac OS X, and Redhat Linux). Results: KTool allows the user to examine three different broad concepts of k‐space via different tabbed view panels. First, the user can manipulate k‐space directly via zero‐filling, to demonstrate how image appearance depends on k‐space. Second, the user can visualize—more intuitively and less mathematically—how properties of images and k‐space are reciprocal, related through the symmetry of the forward and inverse Fourier transform. Third, the user can add image artifacts to an image and visualize their appearance in k‐space, to associate malfunctions in MRI equipment during image formation to corruptions in k‐space and to image artifacts. Conclusion: We have introduced a new tool for a more intuitive understanding of k‐space, relying on visualization and intuition instead of mathematics. This tool may be useful for Radiology residency education (e.g., we use it at our institution), or for serving as a reference to the Medical community at large.
MO‐D‐304A‐02: Accurate Noise Modeling of Cone‐Beam CT Projection Data
Authors: Wang J , Xing L
Published: April 2010

Purpose: To study noise properties of low‐dose cone‐beam CT (CBCT) projection data and to improve the performance of statistics‐based image processing algorithms for dose reduction in CBCT with a more accurate projection data noise model. Method and Materials: We first performed repeated scan on an anthropomorphic chest phantom using an Acuity simulator (Varian Medical Systems, Palo Alto, CA). The data acquisition protocols included a tube voltage of 125 kVp, tube current 10 mA and duration of tube pulse 10 ms. At a fixed gantry angle, 500 repeated projections were acquired. From the repeated measurements, we first calculate the mean and variance of each detector pixel and then calculated the correlation coefficients of noise among detector pixels. The knowledge of the noise properties of CBCT projection was incorporated into a statistical image process algorithm based on the penalized weighted least‐squares (PWLS) criterion. The PWLS criterion with the improved noise model was then used to suppress noise in low‐dose CBCT projections. Results: Our analyses on repeated measurements show that the noise correlation coefficients are non‐zero between nearest neighboring pixels of CBCT projection data. An experimental phantom study shows that the PWLS with improved noise model can suppress the noise in low‐dose CBCT effectively without noticeable loss of resolution. Conclusion: Noise is correlated among nearest neighbors of CBCT projection data. An accurate noise model of CBCT projection data is established for statistics‐based image processing algorithm. CBCT dose can be significantly reduced through using the PWLS‐based projection smoothing algorithm that incorporates the projection noise correlation.