bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐D‐AUD‐03: Characterization of a 2D Ionization Chamber Array for IMRT QA
Authors: Shtraus N , Curran B , Moran J , Litzenberg D
Published: July 2007

Background and Purpose: Measurement‐based methods of quality assurance (QA) for Intensity Modulated Radiotherapy (IMRT) fields often include individual field verification at a neutral gantry angle using film or other 2D detector in addition to a composite ionization chamber check. Unfortunately, film is time‐consuming to use. Diode systems are currently available but these arrays are limited in size and spacing of the diodes. This work characterizes a new 2D ionization chamber array (MatriXX, Scanditronix‐Wellhofer) that can be used for treatment verification at neutral and planned gantry angles. Material and methods: The 2D array consists of 1020 ion chambers, arranged in a 32×32 cm2 grid. Each chamber is separated by 7.62 mm center to center and has a volume of 0.08 cm3. Properties such as linearity, reproducibility, pressure dependence, homogeneity, and accuracy of the 2D array have been evaluated for 6 and 16MV beams at neutral and planned gantry angles. Results: The 2D array response was found to be linear with dose from 0–800 cGy. The 2D array readings were reproducible to within a SD of ±0.14%. Examination of the array's pressure dependence, homogeneity, sensitivity as a function of ion chamber location, and the interpolated dose showed accuracies of better than 0.3%. Absolute dose measurements were done with the array and a calibrated ion chamber. Agreement was better than 0.6%. TPR measurements were made and found to agree with commissioning data in our planning system (UMplan). Measurements done using a 2 × 2 cm2 field placed randomly around the array show a standard deviation of 0.21%. Delivery of IMRT plans using multiple gantry angles showed excellent agreement with calculated results. Conclusions: The 2D array offers an excellent solution to simplifying QA and saving time, particularly for IMRT pre‐treatment QA. The device can be used for both relative and absolute dose measurements.
WE‐D‐AUD‐07: Temporal, Dosimetric, and Geometric Precision of Gated Step‐And‐Shoot Intensity Modulated Radiation Therapy
Authors: Wiersma RD , Xing L
Published: July 2007

Purpose: Due to the complicated technical nature of gated RT, electronic and mechanical limitations may affect the precision of delivery. The purpose of this study is to investigate the temporal, dosimetric, and geometric accuracies of gated RT. Method and Materials: A Varian Trilogy, equipped with a RPM system, is used to examine the accuracy of both un‐gated and gated deliveries. Data recorded using radiographic films and EPIDs allow extraction of geometric and system response accuracy. The dosimetric precision of each segment making up a step‐and‐shoot IMRT treatment plan is individually recorded and analyzed using ionization chamber methods. Results: The time required from when the target object enters the specified phase to when the radiation beam is actually turned on is approximately ∼ 0.15 s. This time error is systematic and is the same for both normal and SS‐IMRT gated deliveries. Dosimetric data from 50+ repetitions of a fixed segment dose for both un‐gated and gated deliveries are obtained. At higher dose rates, the dosimetric errors are seen to become greater in the gated case. A geometric comparison of the un‐gated to gated RT delivery show clear positional inconsistencies in the thicker outer MLC leafs in the non‐gated case. These leaf positional discrepancies are attributed to motion of the thicker outer leaf pairs while the radiation beam is on. Conclusion: A system response time of ∼150 ms is obtained using a simple moving phantom procedure. Dosimetrically we have found that gating negatively effects dose accuracy by interruption of the “overshoot” effect. This interruption could lead to large dosimetric errors, especially for plans consisting of a large number of small MU segments that are delivered at high dose rates. Geometrically very little error for both un‐gated and gated deliveries are seen, provided that a well‐defined leaf tolerance is used.
WE‐D‐M100J‐08: Cellular Response to Modulated Radiation Fields
Authors: Claridge E , Suchowerska N , Zhang M , Ebert M , McKenzie D , Jackson M
Published: July 2007

Purpose: To investigate cell survival following exposure to spatially modulated beams, as created by intensity modulated radiotherapy (IMRT), using in vitro experiments. Method and Materials: We compared cell survival in modulated fields with cell survival in a uniform control field using malignant melanoma cells (MM576) exposed to a therapeutic megavoltage photon beam. Three different spatial modulations of the field were used: a control “Open” field in which all cells in a flask were uniformly exposed; a “Quarter” field in which 25% of cells at one end of the flask were exposed; and a “Striped” field in which 25% of cells were exposed in three parallel stripes. The cell survival in both the shielded and unshielded regions of the modulated fields, as determined by a clonogenic assay, were compared to the cell survival in the Open field. Results: In the unshielded regions of the irradiated flasks, the cell survival was seen to differ between the three fields for the same delivered dose. For the modulated fields, the regions which received only scattered and leakage dose displayed decreased survival at lower doses, relative to the “Open” field, and increased survival at higher doses. Conclusion: We have found three distinct ways in which the cell survival is influenced by the fate of neighboring cells. The first of these (Type I effect) is the classical Bystander Effect whereby cell survival is reduced when nearby cells receive a high radiation dose but some survive. The Type II effect is an increase in cell survival when nearby cells receive a lethal dose. The Type III effect is an increase in survival for cells receiving a high dose of radiation when nearby cells receive a low dose of radiation. Our observations of the Bystander Effects emphasize the need for improved radiobiological models, which include communicated effects.
WE‐D‐L100E‐01: Cone Beam CT Workshop
Authors: Fahrig R , Siewerdsen J , Jaffray D , Boone J
Published: July 2007

The development of practical large field‐of‐view flat panel x‐ray detectors has lead to an explosion in cone‐beam computed tomography (CT) applications. In this workshop, a number of different clinical applications for cone‐beam CT will be described. Methodologies for addressing issues such as x‐ray scatter, detector lag, and limited field‐of‐view or angular coverage will also be discussed.

C‐arm fluoroscopic systems have been used for image guidance in the operating room for many years. With the advent of flat panel‐based C‐arm systems, the availability of portable, operating room‐based computed tomography systems exists. The three dimensional characteristics of CT will likely improve surgical outcomes involving surgical device implantation. The development of a portable C‐arm‐based CT system, for use in the operating theater as well as in other clinical settings, will be discussed.

Angiographic suites are designed to optimize vascular imaging geometry. Flat panel‐based angiography suites have undergone modifications to allow CT imaging for some specific vascular imaging applications. These systems are also capable of performance in orthopedic applications. The use of such systems in a number of clinical applications will be described, and corrections methods for x‐ray scatter and detector lag will also be presented.

The use of image guidance in radiation therapy applications has skyrocketed, and in many clinical radiation therapy systems, system‐mounted cone‐beam CT systems are available for use for guiding RT delivery. The use of cone‐beam CT for radiation therapy applications will be described, and some of the challenges and limitations of this technology will be discussed.

Overall, a sampling of cone‐beam CT applications will be presented in this workshop. The overall flexibility of cone‐beam CT systems to accommodate the wide range of applications described is a testimony to the long term clinical potential of cone‐beam CT systems. This workshop will also describe some of the compromises and limitations which are required when cone‐beam CT geometry is utilized.
WE‐E‐L100F‐01: After the Discovery: Roentgen's Investigation of “Eine Neue Art Von Strahlen”
Authors: Sprawls P
Published: July 2007

Immediately following Roentgen's discovery of a “Eine neue Art von Strahlen” (new kind of rays), or x‐rays as he later named them, he conducted extensive experiments to determine their properties and possible applications. In this session we follow his thoughts as reported in his three landmark publications and observe many of his experiments through visual recreations of the laboratory activities. We find that he, in investigating this new and different radiation, conceived and used many of the same instruments and techniques used today. Within a few months of intensive research he had discovered, evaluated, and documented essentially every property of x‐radiation.

Educational Objectives:

1. Reflect on Roentgen's thoughts and ideas as he leads across one of the major frontiers in science and medicine.

2. Observe the experiments that demonstrate many characteristics of a new kind of radiation.

3. Appreciate the creative techniques and scientific approach of Roentgen as a model for effective research.
WE‐E‐L100J‐07: Breast CT with Energy Resolved Detection
Authors: Shikhaliev PM
Published: July 2007

Purpose: To evaluate breast CT with energy resolved detection. Methods and Materials: A new breast CT system with energy resolved x‐ray detector and Scanning Multi‐Slit (SMS) data acquisition was evaluated. The SMS CT provides efficient scatter rejection, and uses linear array of photon counting detectors. A breast CT phantom with 14 cm diameter and 50/50 adipose/glandular composition was used. The phantom included carcinoma, adipose, blood, iodine, and CaCO3 as contrast elements. The x‐ray technique was 90 kVp with 660 mR entrance exposure. Photon counting, charge (energy) integrating, and photon energy weighting CT images were generated. The CNR improvement with photon energy weighting was calculated. The CT images with calcium/tissue and iodine/tissue decomposition were generated with dual energy subtraction. The x‐ray spectrum was electronically split into low and high energy parts by photon counting detector to perform dual energy subtraction. Results: CNR of the energy weighting CT images of carcinoma, blood, iodine, and CaCO3 was higher by 19.3%, 19.9%, 29.7% and 40.4%, respectively, as compared to conventional CT. Photon counting dual energy subtraction provided 61% higher CNR as compared to conventional dual kVp dual energy subtraction. CNR of the photon counting dual energy subtracted CT images of CaCO3 was increased by 69% when photon energy weighting was applied to CT projections prior subtraction. CNR improvement of SMS CT due to scatter rejection is 32% as compared to cone beam breast CT. Combination of photon energy weighting with scatter rejecting results in 50%‐85% CNR improvement in SMS CT as compared to conventional CT. Conclusion: Photon counting CT has a potential for improved sensitivity due to higher CNR with scatter rejection, quantum limited detection, and photon energy weighting. It has a potential for improved specificity due to single kVp dual energy subtraction that enables calcium/tissue and iodine/tissue decomposition.
WE‐E‐M100J‐02: Functional Imaging of the Lungs for Treatment Planning
Authors: Guerrero T
Published: July 2007

Delivery of radiotherapy through hypoperfused pulmonary regions for lung cancer treatment has been shown to result in less pulmonary injury in a single prospective trial. This finding suggests a strategy for image‐guided radiotherapy utilizing physiological images in radiotherapy treatment planning for image guidance to avoid the irradiation of highly functional regions and minimize the injury and/or function loss following thoracic radiotherapy. Patients may have inhomogeneous lung function distribution due to tumor invasion of the airway and vascular structures and/or preexisting pulmonary diseases. Imaging studies have found the prevalence of these hypoperfused regions adjacent to the primary tumor from 43 to 74% in non‐small cell lung cancer cases. However, the current thoracic treatment planning practice has been primarily based on using anatomical information from the treatment planning computed tomography (CT). Therefore, the non‐uniform distribution of regional function of normal lung tissue has not been considered in the process of treatment planning. Imaging modalities that have been reported in treatment planning studies to provide image guidance to identify the highly functional regions include single photon emission computed tomography perfusion, hyperpolarized gas magnetic resonance ventilation, and 4D CT derived ventilation imaging. No prospective studies demonstrating improvement in outcome using these modalities for functional image‐guided radiotherapy have yet been reported. Strategies to incorporate functional image guidance include identification of highly functional regions by an expert for avoidance, automated segmentation of pulmonary regions with the highest function for avoidance, and optimization of functional metrics including the dose function histogram.

This lecture will provide an overview of the physiologic origins of the functional imaging methods, post‐acquisition processing, and strategies to integrated functional imaging into thoracic treatment planning.

Educational Objectives:

1. Understand clinical basis for the use of functional imaging for treatment planning.

2. Survey the functional imaging modalities which may be utilized for image‐guidance.

3. Review strategies to integrated functional imaging into thoracic treatment planning.
WE‐E‐M100J‐03: PET‐CT Simulation of Tumors in the Thorax: Pitfalls and Workaround
Authors: Pan T
Published: July 2007

PET/CT simulation of tumors in the thorax suffers from potential misalignment between the CT and the PET images even though the data are acquired in the same imaging session on the PET/CT scanner. The misalignment was caused by the fast acquisition of the CT images in sub‐second temporal resolution and the slow acquisition of the PET data of over several minutes. Current approach of degrading the CT images in spatial resolution does not fix the problem. We will go over the pitfalls resulted from the mismatch of CT and the PET data, and will review a new average CT scan to mitigate this problem, and its potential impact to radiation therapy planning.
WE‐E‐AUD‐01: Artifact Free EBT Film Scanner for Radiotherapy Dosimetry
Authors: Ranade M , DuBose R , Li J , Kozelka J , Simon W , Dempsey J
Published: July 2007

Purpose: To build a high resolution, accurate, 2D optical densitometer that eliminates scanner‐film artifacts commonly observed in radiochromic film dosimetry. Method and Materials: An optical densitometer was built using a stationary light source and detector with a moving film holder attached to a high precision computerized X‐Y stage. The light source was a red LED (633nm), to conform to EBT film absorption peak. Two silicon photo‐detectors were used to measure incident and transmitted light. The LED output was focused to a sub‐millimeter spotsize at the film. Data acquisition was performed with a 16‐bit A/D card in conjunction with commercial software. The densitometer was used with radiographic EDR2 and radiochromic EBT films. Sensiometric curves and three IMRT field scans were acquired with a resolution of 1mm. The results were compared with the MapCHECK diode array measurement under identical geometry. The EBT film was rotated by 90 degrees and rescanned to record orientation effects. Results: A spotsize of 0.8mm was measured at the film using the half razor technique. The EBT film rotated by 90 degrees showed no orientation effect. From the absolute comparison mode of the MapCHECK analysis software, the average passing rates with 3%/3mm criteria were 97.5% for EBT films and 96.6% for EDR2 films. The main difference between EBT and EDR2 measurements were in low dose areas, with EDR2 readings higher. This is most likely due to over response of the radiographic film to scatter radiation. No artifacts were observed in the scanned films. A scan of 15×15cm took 20 minutes to acquire. Conclusion: The LED densitometer provides accurate film dosimetry with 1mm or better resolution. It eliminates the orientation dependence of EBT film dosimetry. The IMRT results compared well with Mapcheck measurements.

This work was supported in part by NCI grant R01‐CA‐100636 and Contract No. HHSN261200522014C.
WE‐E‐AUD‐05: Dosimetric Characteristics of GAFCHROMIC® EBT Film for Therapeutic Electron Beams
Authors: Su F , Shi C , Stathakis S , Esquivel C , Liu Y , Papanikolaou N
Published: July 2007

Purpose: To evaluate the dosimetric characteristics of GAFCHROMIC® EBT film when exposed by high‐energy electron beams. Method and Materials: Studies of the effects of the electron beam treatment parameters on dose calibration curves were performed with GAFCHROMIC® EBT radiochromic films. All films used in this study were from the same batch in order to remove any variability between batches. The films were irradiated in a multilayered 30 × 30 × 25 cm3 solid water phantom with source‐to‐surface (SSD) distance of 100 cm. The effects of electron beam energy, cone size, dose rate, depth, and MU end effect were studied. Results: The dose response curve was found to be independent of the electron energy (−2.2% to 3.6% difference of the averaged scan value). The dose calibration curves of EBT films were independent of MU end effect (from −1.0% to 2.2%) as well as electron beam dose rate (within 1.7%). For the field size dependence due to different electron cones, it is possible to calibrate GAFCHROMIC® EBT films using 10 × 10 cm2, cone size and then evaluate dose distributions resulting from various electron cone sizes. The EBT film did not show any impact of the depth on the dose response curve for electron beams. Conclusions: There was no much influence on dose response curves of GAFCHROMIC® EBT films due to electron beam energy, cone size, dose rate, depth, and MU end effect. The independence of the GAFCHROMIC® EBT on these electron beam dosimetric parameters studied for this kind of newly developed radiochromic film makes it an accurate and versatile dosimetric detector for two‐dimensional dose distribution measurements for therapeutic electron beams.
WE‐E‐AUD‐06: Clinical Prototype of a Plastic Water‐Equivalent Scintillating Fiber Dosimeter Matrix for IMRT QA Applications
Authors: Lacroix F , Archambault L , Gingras L , Beddar S , Beaulieu L
Published: July 2007

Purpose: To develop a clinical prototype of a plastic water‐equivalent scintillating fiber dosimeter array for IMRT beam quality assurance (QA) applications. Method and Materials: A clinical prototype of a scintillating fiber dosimeter array has been developed. The system comprises twenty‐nine (29) 1 mm diameter and 2 mm long (1,6 mm3) scintillating fiber detectors (BCF‐12, Saint‐Gobain, inc.) spaced 1 cm apart encapsulated in a Plastic Water (MedTec inc.) phantom. The detectors are coupled to clear non‐scintillating transport fibers (BCF‐98, Saint‐Gobain, inc.) that collect scintillation photons and transport them to a color charge‐coupled device (CCD) placed on the treatment table outside of the primary beam. A spectral discrimination technique is used to remove the Cerenkov radiation contaminating the scintillation signal. The CCD is encased in a custom designed, Cerrobend shielded aluminum carrying‐case equipped with a custom‐made optical fiber connector enabling reproducible removal and insertion of the fibers. Residual radiative noise on the CCD is removed with a post‐processing algorithm. All dose points are processed simultaneously. Results: Open field crossplane profiles from 4×4 to 20×20 cm2 and a 10×10 cm2 depth‐dose in Plastic Water are compared to ionization chamber (CC13, Wellhofer) measurements in water. The maximum in‐field relative difference across all points and measurements is found to be 0.9% for profiles and 1.6 % for the depth dose. The standard deviation on the scintillation detector response is smaller than 1% in‐field. The optical fiber connector insertion and removal is repeatable to within the measurement resolution (1%). This will allow for “hot swappable” detector modules. Conclusion: The scintillating fiber dosimeter array prototype is found to be accurate, precise and practical. The current system detector capacity exceeds 3500 measurement points per single irradiation. Such array detectors could find application for IMRT QA and general beam dosimetry monitoring measurements.
WE‐E‐BRA‐04: Brachytherapy Source Power Measurements Using a Liquid Helium Active Radiometric Calorimeter
Authors: Holmes S , DeWerd L , Palmer B
Published: July 2007

Purpose: To characterize a liquid helium active radiometric calorimeter for contained power and emitted power measurements. The calorimeter has been used for direct measurement of low dose rate and beta emitting brachytherapy sources. Method and Materials: Measurements were performed by placing a brachytherapy source into a silver absorber whose temperature was actively controlled slightly above that of liquid helium. An electrical substitution method was used; so the difference in power required to maintain a set temperature with and without the source present was attributed to the source itself. Corrections for increased thermal mass of the system during measurement were determined empirically using nonradioactive “dummy” sources, and corrections for escaped energy were calculated using Monte Carlo MCNP5 models. Data were analyzed using a linear least squares approximation of values obtained while the source was in place and after the source was removed. The distance between the fit lines at the time the source was removed was taken as the source power. Individual , , and sources were investigated. Results: Classical variance for preliminary measurements was found to be 60nW. The correction factor for source thermal mass was 0.611μW; and for , , and , respectively, corrections for escaped energy were 1.0000, 1.0045, and 1.0182 for contained power measurements and 1.0081, 1.0101, and 1.0823 for emitted power measurements. Conclusion: Preliminary results reveal improved sensitivity of the instrument over the previous liquid nitrogen version (Rev. Sci. Instrum., 76, 2005). Small thermal drifts during measurement indicate that slight further modifications to the design may be required to anchor the absorbers fully to the actively controlled detector housing. Also, increasing the size and weight of the source insertion cap may also improve measurement repeatability. While preliminary data are promising, further measurements will improve dataset statistics for both radioactive sources and the measured correction factor.
WE‐E‐BRA‐05: Reducing the Frequency of Linac Output Check: A Statistical Model of Linac Output Fluctuation Based On a 3 Year History to Evaluate New Tolerances as a Function of Test Frequency for 12 Linear Accelerators
Authors: Bouchard H , Carrier J
Published: July 2007

Purpose: The study is based on a formalism to model the fluctuation of 12 linac outputs during a 3 year period. From a semi‐empirical statistical model and TG‐40 recommendations, a QA program is built from calculated action levels as a function of test frequency and time‐dependant probability distributions. Method and Materials: The linac output data is analyzed to fit a statistical model taking into account a systematic and a random component in the daily fluctuation. A 3 year history of daily output measurements totalizing 71 independent energies of photons and electrons is used to evaluate the parameters in each model. Action levels are calculated as a function of test frequency from obtained models based on tolerances defined in TG‐40. A confidence level of 95% is used to define the QA program such that machine output is kept within given limits, the latter being obtained by fitting tolerance functions with TG‐40 action levels. Measurement uncertainties are taken into account in the model and Gaussian statistics are used in the formalism. Results: Comparison between models and data history are in agreement with Gaussian statistics. For each linac and energy, tolerance functions are obtained from data history and new action levels are used with reduced test frequency. The tolerance of 2% recommended by TG‐40 for monthly output constancy check is reduced to values ranging from 1.2% to 1.8% for a test frequency of two months. Linac calibration frequency is reassessed to values ranging from 4 to 12 months. Conclusion: While daily check should be kept constant to prevent unpredictable variations, the frequency of output check can be reduced using new action levels based on a program‐defined limit and confidence level. Probability distributions can be used to evaluate linac calibration frequency based on machine stability. The model can be extended to other linac parameters.
TH‐C‐M100E‐01: Numerical Feasibility Study of a Novel Absorbed Dose to Water Calorimeter‐Based Standard for 192Ir HDR Brachytherapy
Authors: Sarfehnia A , Stewart K , Podgorsak E , Seuntjens J
Published: July 2007

Purpose: To study the feasibility of developing a new standard for absorbed dose to water based on water calorimetry for high dose rate iridium‐192 brachytherapy sources. Method and Materials: The heat conduction pattern generated in water by the Nucleotron microSelectron‐HDR brachytherapy source was simulated using Comsol Multiphysics™ software. Source self‐heating due to self‐attenuation of photons was calculated with GEANT4. A smooth, well‐behaved three‐dimensional function was fit to the entire dose distribution data using TableCurve3D™. The heat‐loss correction Kc was calculated as the ratio of the temperature in the calorimeter under ideal conditions to realistic conditions. Results: The feasibility of a water calorimeter based absorbed dose standard is determined by a balance between the requirements to obtain sufficient signal to perform a reproducible measurement, the effects of heat loss on the measured signal, and the positioning uncertainties. Due to self‐absorption, the source equilibrium temperature was found to be above the ambient temperature by a constant amount that depends only on setup conditions and source activity. For the source inside its nylon‐12 catheter inserted into water, the steady state excess temperature per unit source activity was found to be 0.5671 K/Ci. The source temperature reached 96% of its steady state temperature after 60 s. Conduction correction factors Kc were calculated for several exposure times and at various measurement points away from the source inside the calorimeter. A total exposure time between 140 s and 240 s at a distance that receives a minimum of 1 Gy of dose was found to allow reduction of Kc to below 0.1% of unity. Conclusions: Water calorimetry for HDR brachytherapy is feasible and total uncertainties of significantly better than 5% on the dose can be achieved with current water calorimetry techniques and instruments.
TH‐C‐M100E‐02: Optically Stimulated Luminescence of Aluminum Oxide Detectors for Radiation Therapy Quality Assurance
Authors: Danzer J , Dudney C , Seibert R , Robison B , Harris C , Ramsey C
Published: July 2007

Purpose: The purpose of this experiment was to: 1) Determine if a commercially available detector system used for monitoring personnel exposure could be adapted for use as a radiation therapy dosimetry system; and 2) Evaluate the system's performance as an in‐vivo dosimeter and its ability to measure absolute surface dose, isocenter dose, and normal tissues dose in a phantom as part of patient‐specific IMRT quality assurance. Method and Materials: The dosimeters were evaluated for: 1) Signal decay; 2) Field size dependence; 3) Energy dependence; and 4) Angular dependence using the Landauer, InLight MicroStar system. In‐Vivo dosimetry measurements were taken for 22 patients treated on a Varian 21EX. The Landauer system was also tested for its ability to measure absolute dose from helical tomotherapy treatments. Results: The variation between dosimeters was evaluated and found to be ±1.6%. The dosimeters appeared to over‐respond in the first 10 minutes, however, after 10 minutes the chips were within 1 percent of the steady‐state reading. Unlike other detectors, the Al2O3 dosimeters showed no field size, energy, or angular dependence. The agreement between the dosimeters and the calculated doses for the in‐vivo dosimetry patients was 2.2±6.1 cGy or 3.7±2.5%. The dosimeters were also tested for their ability to measure absolute dose inside an IMRT phantom. The agreement between the dosimeters and the calculated doses was 0.1±5.3 cGy or 0.7±6.7%. Conclusion: dosimeters can be a convenient, inexpensive alternative to TLDs, MOSFETS, and Diodes. The agreement between calculated and measured doses for in‐vivo dosimetry and IMRT QA is comparable to TLDs, MOSFETS, and Diodes. The dosimeters can be quickly read and analyzed after 10 minutes (to allow time for signal decay). The dosimeters do not appear to have an energy, field size, or angular dependence. In addition, the detectors can be erased and re‐used.
TH‐C‐M100E‐05: Fabricating a Customized Gating System for Large Bore AcQSim CT Scanner
Authors: Sohn J W , Barritt B , Daher G , Turnbull J P , Park S B , Chankong V , Monroe J I , Klahr P
Published: July 2007

Purpose: A customized gating system was developed for a large bore CT scanner to produce gated images for use with an active breathing control (ABC) system. Operator triggering following a breath hold is replaced by an electronic gating signal from a bellows. A breathing phantom was constructed and imaged to insure accurate gating. Methods and Materials: A bellows strap wraps around the patient to monitor breathing during CT scans. A universal serial port (USB) cable provides power to the bellows sensor via the circuit box. Bellows signals route to the computer from the circuit box via another USB cable. Operators can set a threshold point in the breathing cycle that corresponds to an ABC breath‐hold to trigger the CT scanner. Software generated signals gate the CT through the circuit box. Unique to this system is an option to scan continuously while the patient is holding a breath, in contrast to commercial gated‐CT systems which take one image per breathing cycle. A breathing phantom was created using a computer programmed actuator, step‐motor, and off‐set ball. A sine wave modeled on human breathing was fed to the actuator. The moving range was 2.10 cm anterior‐posterior and 1.05 cm in lateral direction. The diameter and motion period was 6.4 cm and 5.54 sec. Phantom images taken were: stationary non‐gated, moving gated, and three un‐gated while moving. All image sets were analyzed with the Pinnacle planning system. Volumes generated from contours where used as a metric to determine imaging accuracy. Results: Target volumes of stationary and gated imaging were 146.8 and 145.5cm3, respectively (1% agreement). However, the discrepancies between stationary and all three un‐gated scans ranged from 4.84 to 5.45% with significant shape distortion.

Conclusions: We successfully created a custom gating system for a large‐bore CT simulator.
TH‐C‐M100E‐08: Evaluation of Multiple‐Isocenter IMRT Planning Technique for Field Matching with Limited Collimator Field Size
Authors: Fallon K , Xiao Y , Machtay M , Galvin J
Published: July 2007

Purpose: The Elekta Beam Modulator with fully integrated miniMLC has the precision suited for the treatment of smaller tumors. However, the maximum collimator length in the inf/sup direction is 16 cm when most of the head and neck target sizes have a larger dimension. This study used a multi‐isocenter IMRT planning technique with overlapping fields generated using inverse planning. Measurements have been taken to evaluate plans in terms of volume dose and delivery accuracy. The total monitor units for this technique were compared with a standard IMRT plan. Methods and Materials: Ten patients were planned with multiple beam arrangements; eight beam directions for the upper tumor volume without the supraclav and three to four beam arrangements for the lower tumor volume and supraclav. Treatment planning was performed on a CMS/XiO workstation. Treatment fields were delivered on a flat acrylic phantom containing EDR2 film. Isodose distributions were exported from XiO and compared to the measured data using Omni‐Pro software. Results and Conclusions: Multi‐isocenter techniques provide good coverage to the tumor volume while sparing organs at risk. Film distributions show that XiO does not model the effective tongue and groove that is evident in the film measurement. The magnitude of the tongue‐and‐groove dose decrease is on the order of up to 10%. An analysis of the gamma values shows that even with this discrepancy the agreements between plan and measurement were acceptable. The plans are not significantly degraded with small table inaccuracies on the order of 2mm. The total monitor units for multi‐centered plan increased 20% compared to single isocenter delivery.

IMRT planning techniques using two or more isocenters for this collimator show clinically acceptable results when splitting the geometry.
TH‐C‐M100F‐02: Beam of Laser‐Accelerated Protons: Generation and Characterization
Authors: Velchev I , Lin T , Fourkal E , Fan J , Li J , Ma C , Orimo S , Ogura K
Published: July 2007

Purpose: To experimentally demonstrate the generation of proton beams by a novel technique based on the interaction of high‐power laser pulses with thin solid‐state targets. To fully characterize the beam of particles emitted from the laser accelerator and to compare its properties with the theoretically predicted divergence and energy spectrum. Method and Materials: We have built an experimental set‐up for generation of laser‐accelerated protons. The high‐power laser pulses are produced by a chain of lasers and amplifiers and are delivered to the target in a shielded vacuum chamber. The sharply focused laser beam creates light intensity in excess of 1×1018 W/cm2. The cross‐section of the proton beam is directly imaged using a CR39 nuclear track detector situated at a fixed distance behind the target. The energy spectrum on the beam axis was recorded by a proton spectrometer (Thomson parabola) that was assembled and calibrated in our lab. An alternative method for energy evaluation utilizing a set of calibrated mylar range‐filters was used as well. Results: The angular distribution of the proton beam was determined from the CR39 images. Full divergence angle of 40° was measured, confirming the theoretical predictions. Our preliminary measurements were conducted at lower laser power (7 TW). Therefore, the energy spectrum of the proton beam revealed thermal (Maxwellian) distribution with cut‐off energy slightly less than 1 MeV. Conclusion: We demonstrated the acceleration of protons using powerful laser pulses and fully characterized the generated proton beam. Considerable improvements associated with increased laser intensity and novel target design are discussed as well. The experimental results presented here are the first step toward the generation of therapeutic proton beams with controlled characteristics using lasers.
TH‐C‐M100F‐10: Neutron Dose From Thin, Thick Targets and Passive Proton Beam Delivery Systems
Authors: Perez‐Andujar A , DeLuca P , Newhauser W
Published: July 2007

Purpose: Due to possible radiobiological implications that neutrons might have during proton therapy this work focuses on the determination of which components of a proton therapy treatment nozzle contribute the most to neutron production for passive systems. Method and Materials: The LANL Code MCNPX is used to simulate a proton beam interacting with components of a passive treatment nozzle. Several treatment nozzle geometries are simulated. During the first simulations, a 200 MeV proton beam interacts with targets of 10 MeV, 20 MeV thickness and stopping (thick) targets. Several materials were used as targets: lead, aluminum, graphite, water, and polyethylene. The neutron flux was scored in a water phantom 1 m away from the point of maximum neutron production in the target and used to determine the neutron dose asfunction of neutron emission angle. The second set of simulations is for a double scatter passive system. A 200 MeV proton beam interacts with a high‐Z to low‐Z (lead‐lucite) rotational modulation wheel, a low‐Z to high‐Z (lucite‐lead) scatterers and a collimation system. The resultant neutron dose for 100 mm spread‐out Bragg Peak (SOBP) is investigated. Results: The neutron dose was higher for thick targets than for thin targets. This behavior was consistent among all target's materials. The neutron production was forward‐peaked with a maximum at around 15°. For low‐Z and high‐Z materials, there was a large neutron flux contribution for energies below 20 MeV. For thin and thick targets the high‐Z materials produced the greatest amount of neutrons, although the thin targets produced the most energetic ones. Conclusion: We noted that the high‐Z material components are producing the highest amount of neutrons while decreasing the energy of the beam by 10% produces an increment of approximately 30% increase in neutron production.
TH‐D‐L100J‐06: Streaming Architectures for Cone‐Beam CT Image Reconstruction and Deformable Registration
Authors: Singh H , Kandasamy N , Folkert M , Sharp G
Published: July 2007

Purpose: To develop data‐parallel algorithms for tomographic reconstruction and deformable registration within a stream‐processing paradigm, and execute them on cheap stream processors such as graphics processing units (GPUs). Method and Materials: In the computer sciences, the stream‐processing paradigm is emerging as a cost‐effective way of solving large‐scale parallel computing problems. This is due to the recent introduction of high‐performance stream‐processing hardware such as the Cell processor and GPUs—both are commodity stream (or vector) processors, designed specifically to support large‐scale parallel computing on a single chip. This presentation describes how to use the stream‐processing model to significantly accelerate the complex problems of data reconstruction and fusion for radiotherapy. Highly data‐parallel models were developed for: (1) the Feldkamp, Davis, and Kress (FDK) reconstruction algorithm, and (2) Demon's algorithm for optical‐flow based deformable registration. These models were implemented within the Brook programming environment and executed on an nVIDIA 8800 GPU. Results: The performance of GPU‐based implementations of the FDK and Demon's algorithms was analyzed using data obtained from an IGRT testbed of a preserved swine lung. The results indicate a substantial speedup of up to 17 times for FDK, and up to 33 times for Demons, when compared with a 2.4 GHz Intel Duo‐Core processor. In addition, the GPU was found to be capable of high‐quality reconstructions, with differences within a few Hounsfield unit. Conclusions: Results indicate that data‐parallel image‐processing algorithms, when properly designed and executed on a GPU, achieve significant speedup when compared to high‐end desktop CPUs. The acceleration of key data‐processing stages will decrease the time needed to perform image‐guided patient positioning and analysis.
TH‐D‐M100F‐02: The Development of a Realistic Digital PET Lung Phantom for the Evaluation of Tumor Volume Segmentation Techniques
Authors: Aristophanous M , Penney B , La Riviere P , Pelizzari C
Published: July 2007

Purpose: A problem encountered in the development of novel tumor volume segmentation techniques for PET images is the lack of a reliable method for evaluating their performance on clinical scans. We have developed a digital lung phantom to address this problem. Method and Materials: The three main components in the creation of the digital phantom were the voxel‐based Zubal anthropomorphic phantom, the simSET package for PET simulations and the creation of digital lesions. The Zubal phantom was used as input to the simSET software to obtain PET simulated projections and then the separately created digital lesions were fed as input to simSET to obtain lesion projections. Those were added to the Zubal phantom projections, which were then reconstructed to obtain the simulated abnormal PET lung scans. In order to test the accuracy of the digital phantom in representing real situations, the results were compared both qualitatively and quantitatively with real clinical scans. We compared image intensity histograms and statistical measures from regions of interest (ROIs) taken from the lung, the mediastinum and the tumors of both clinical and simulated cases. Results: The visual comparison of the image intensity histograms from different regions showed no significant differences in the appearance of the image intensity distributions. This was confirmed by comparing measurements of fractional standard deviation and skewness from the different regions. Adding more inhomogeneity to the digital lesions resulted in more realistic appearing lesions. Conclusion: Our results suggest that the constructed digital phantom can closely model real clinical scans. The full control over the lesion's size, shape and intensity and the activity in normal anatomy that this digital phantom offers, along with improvements that can come from the addition of motion and more inhomogeneity can make this phantom a powerful tool in the evaluation of PET segmentation methods.
TH‐D‐M100F‐06: Surface Smoothing of a Tubular Structure Using a Non‐Shrinking Algorithm
Authors: Chen Y , Paskalev K , Horwitz E , Price R , Buyyounouski M , Ma C , Pollack A
Published: July 2007

Purpose: The modeling of a 3D structure by interpolating a stack of 2D contours may result in an unrealistic faceted shape, even though each contour is smooth. A difficulty with geometric smoothing is that the surface can shrink after a number of iterations. This work investigates the use of a non‐shrinking smoothing algorithm in structure delineation for radiotherapy treatment planning. Materials and methods: The surface of a tubular structure is parameterized by an interpolating function using original contour data points in cylindrical coordinates. The center of the polar coordinates for each axial contour is placed on a smooth fitting function while the contour is still a single‐valued function. By interpolation the surface is re‐sampled into a set of evenly spaced vertices. In an iterative process each vertex is shifted by an average displacement vector from its neighbor vertices and scaled by a factor. Each step of iteration involves two shifts for every vertex with the scaling factor in opposite signs, in order to avoid shrinkage. The iterative process stops after a desired smoothness is achieved with all average displacement vectors smaller than a specified tolerance. This method is tested on five prostate IMRT cases. The axial contours of smoothed structure are displayed with the original contours for validation by three physicians. Results: The resulting surface appeared smooth in all projections. The physician approved the new contours for all five patients. The volume change for each structure was less than 2%. Treatment planning using smoothed CTVs and PTVs reduced the numbers of MU and MLC segments by 8 – 11%. Conclusions: A technique was developed for smoothing a structure surface constructed using 2D contours. The calculation was fast for 3D contouring. Our planning results suggested that unrealistically irregular target shapes can have adverse effects on dose conformity and delivery efficiency.
TH‐D‐M100F‐08: Development and Evaluation of An Automatic Contour Propagation Method for 4D Radiotherapy
Authors: Lin L , Shi C , Liu Y , Swanson G , Papanikolaou N
Published: July 2007

Purpose: To develop and evaluate automatic contour propagation method for 4D radiotherapy Method and Materials: 4D CT images of one lung cancer patient and dynamic phantom images were acquired and resorted into ten respiratory phases. Demons deformable registration was performed to find the deformation field from the end‐exhale fixed phase to moving phases such as the end‐inhale phase. Regions of interest (ROIs) were contoured in the fixed phase with the Pinnacle3 treatment planning system. The planar parallel contours were reconstructed as the 3D binary mask image data which has zero value outside and non‐zero value inside of the 3D outline of contouring. The 3D contour image data were transformed to another moving phase using the deformation field from the image registration result. On each 2D plane the binary image boundary was found to trace the closed intersection points. To assess the quality of the automatic contour propagation method, the contour for the moving phase was delineated manually. Visual inspection between the contour propagation and manual contour was performed as the qualitative evaluation. Two indices were used as the quantitative examination. One was the match index to indicate how well two contour sets match each other. The other was volume difference evaluation between two contour sets. Results: The demons deformable registration results show good alignment for both the phantom and the patient. The match index between manual and automatic contouring ranged from 0.96 to 0.99 for the dynamic phantom and from 0.95 to 0.99 for the lung patient. The volume differences were between 0.75 and 2.97 percent for the dynamic phantom and between 1.50 and 7.32 percent for the lung patient. Conclusions: The proposed automatic contour propagation method is simple and feasible without surface construction. It is a variable method for defining the ROIs for large amount of 4DCT data sets.
TH‐D‐M100J‐02: Quantitative Interstitial Multispectral Diffuse Optical Tomography of Human Prostate Using a Priori Structure Information
Authors: Zhou X , Zhu T , Finlay J , Li J , Dimofte A , Hahn S
Published: July 2007

Purpose: To develop an interstitial multispectral diffuse optical tomography (iDOT) system to quantify optical properties, drug concentration and tissue oxygenation of prostate before and after photodynamic therapy (PDT). Method and Materials: iDOT system uses continuous‐wave measurements from 12 motorized isotropic detectors inserted in the prostate. Optical properties of prostate were reconstructed using single‐wavelength measurements at 732nm. Six point‐sources were introduced interstitially. Multispectral iDOT acquired the absorption spectra in 650–850nm region emitted from 6 optic fibers connected to a halogen lamp. The multispectral method directly reconstructs tissue chromophore concentrations and Mie scattering factors through incorporation of a priori anatomic information and spectral properties. The accuracy and convergence of the reconstruction algorithms were tested in mathematical phantoms with known geometry and optical property distribution. Clinical iDOT were performed on 12 patients for single‐wavelength optical property measurement and 2 patients for spectral measurements. Results: Phantom study results demonstrated that iDOT can reliably recover the optical properties, chromophore concentrations and scattering factors in clinical‐relevant geometries with fast convergence. In clinical studies, the averaged reconstructed pretreatment μa and μs′ at 730nm varied between .003mm−1 and .162cm−1(mean .03±.02mm−1) and .11 and 4.4mm−1 (mean 1.4±1.1mm−1) among 12 patients. The absorption coefficients for some patients were significantly reduced post‐treatment due to photobleaching of the photosensitizer. For multispectral measurements, the pretreatment total hemoglobin concentration was found between 51μM and 370μM, with oxygen saturation of 67%–90%. There was no significant change post‐treatment. The pretreatment photosensitizer concentration varied from 1.4 to 9.2ng/mg for 2 patients. Up to 66% decrease of photosensitizer concentration was observed in one patient in the post‐treatment measurements. Conclusion: Preliminary clinical results showed significant inter‐ and intra‐prostatic variation in tissue optical properties, oxygenation and photosensitizer concentration, suggesting that parameters other than anatomical information should be considered for PDT treatment planning.