bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐E‐224A‐04: Determination of Total Scatter Factors for Stereotactic Radiation Fields by Optimized Fitting of Readings From a Small Ion Chamber and a Mini‐Diode
Authors: Du W , Lerma F , Sakthi N , George R , Schaefer M , Bartee C , Benedict S
Published: July 2006

Purpose: To determine the total scatter factors (TSF) for small radiation fields on the BrainLab micro‐MLC (M3) and cones by fitting the readings from two detectors: a small ion chamber and a mini‐diode. Method and Materials: Outputs were measured for 6MV beams using a small ion chamber (Wellhofer IC3, active volume 28mm3) and a stereotactic diode (Scanditronix DEB050, active volume 0.017mm3). It has been reported that ion chambers (IC) underestimate output for small fields (<20 mm) and diodes overestimate output for large fields (>50mm). Herein outputs at intermediate field sizes (20–50 mm) were used to combine data from the two detectors. The output from IC was normalized to a reference 10×10cm field; the output from diode was scaled to match the output from IC at intermediate field sizes. The scaling was determined with modified least square optimization. The final TSF was composed of scaled diode output for small fields, IC output for large fields, and their averages for intermediate fields. Results: For square fields formed by M3 and secondary jaws, the scaled TSF from diode matched the TSF from IC to within ±0.6% for field sizes 24–60 mm. The diode overestimated TSF of the reference field by 3.2% at depth of 5cm. The IC underestimated TSF by 23%, 5%, 1.4% for 6, 12, 18 mm fields, respectively. Similar results were found for the cones. TSF from diode was 0.702 for the 5mm cone, an improvement of 29% from IC measurement. Conclusion: We have demonstrated that neither IC or diode alone provides accurate TSF for stereotactic fields of all sizes. The diode is more accurate than IC for fields <20 mm, however, we show that the diode should be cross‐compared with an IC using radiation fields of intermediate sizes. A modified least square optimization method is presented for this purpose.
TU‐E‐224A‐05: Intermediate Energy X‐Ray Photons (0.2 – 1.0 MeV) for Radiosurgery: Producing a Beam and Measurement of Radiological Penumbra
Authors: Keller B , O'Malley L , Beachey D , Presutti J , Pignol JP
Published: July 2006

Purpose: The main advantage of stereotactic radiosurgery is the steep dose gradient associated with the intracranial dose distribution. We are examining the effects of x‐ray energy on penumbra and dose gradient. Specifically, we are exploring the reduction in radiological penumbra for intermediate energy x‐ray photons (0.2–1.0 MeV) or so called IEP's. The purpose of this work is two‐fold: 1.) to produce an IEP beam using a medical linear accelerator and 2.) to examine the radiological penumbra associated with this beam. Method and Materials: A Siemens medical linear accelerator was adapted to produce IEP's. PDD measurements versus depth (SSD=100cm,FS=2×2cm2) were done in solid water using a Markus parallel plate ionization chamber (PTW Freiburg). These were compared with Monte Carlo computer simulations (MCNP‐4C). Monte Carlo involved generating x‐ray spectra that impinged upon a SW phantom. A penumbra measurement device (consisting of a half‐beam block) was constructed to examine radiation beam edge profiles using film (Gafchromic EBT) at SSD=100cm,FS=1.1cm2 and depth=2cm. In a separate experiment, film irradiations were done collimating a 3×3mm2 beam using a 10cm thick brass block flush with the SW surface. In all cases, the geometric penumbra (due to the finite source size) was made negligible by having the collimation very close to the phantom. A high‐resolution digital microscope (Axiomat) was used to acquire film profiles. Results: Measured PDD values were 55.4%(surface), 62.6%(5cm), and 34.7%(10cm). Monte Carlo PDD's compared with measurement suggest a nominal 800kV x‐ray beam. For the half‐beam block, the 80%–20% film edge profiles were 0.345mm (IEP) and 2.10mm (6MV). For the 3×3mm2 field, there was a 5‐fold reduction in radiological penumbra (IEP vs. 6MV). Conclusions: A novel intermediate energy photon beam (of nominal energy 800kV) has been produced using a conventional linear accelerator. There is a substantial reduction in radiological penumbra when using IEP's with small fields.
TU‐E‐ValB‐03: Simultaneous Integrated Boost Utilizing IMRT for the Treatment of Breast Cancer
Authors: Kirk M , Dickler A , Chu J , Chen S , Seif N , Mehta P , Griem K
Published: July 2006

Introduction: We compare the dosimetric characteristics of simultaneous integrated boost (SIB) technique utilizing IMRT vs. conventional treatment consisting of medial and lateral tangents followed by an electron boost. Materials and Methods: To date, 5 women at our institution have been enrolled and treated using IMRT with SIB. Patients were treated using 25 fractions of 1.8 Gy to the whole breast (45Gy) while concurrently receiving 25 fractions of 2.4 Gy to tumor bed (60Gy). Conventional treatments were planned using the standard fractionation of 1.8 Gy × 25 fractions to the whole breast followed by 2 Gy × 8 fractions to the tumor bed.

The patient data was used to compile population dose volume histograms (pDVH), based on the mean values and include error bars which represent the 1σ uncertainty of the mean. Results: The mean percent of the BoostPTV volume receiving 60Gy, was slightly higher for the conventional technique compared to SIB (Conventional = 98±1.4%, SIB=95.0±1.0%). The mean volume of the treated breast outside the BoostPTV, PTV45‐Boost, that received greater than 120% of the prescribed dose was more in the Conventional technique then SIB (Conventional=15.9±3.4%, SIB=6.1±1.6%). The mean volume of lung receiving 20Gy was equivalent in both techniques (Conventional=19.8±5.8%, SIB=17.1±5.2%). The mean ipsilateral lung dose was equivalent between techniques (Conventional=10.7±2.2 Gy, SIB=11.9±4.2 Gy). The mean dose to contralateral breast was systematically higher in SIB technique compared to the conventional technique (Conventional=69±39 Gy, SIB=191±126 Gy). The mean volume of the heart that received greater then 30Gy was small for both plans (Conventional=2.8% and SIB=0.4%). Conclusion: IMRT with SIB is feasible and allows patients to complete EBRT in about 20% less time than the standard treatment course. It offers improved dose homogeneity to treated breast, comparable normal tissue sparing, and excellent short term cosmesis.
TU‐E‐ValB‐04: Impact On Nodal Dose Distribution From Daily Fiducial Tracking for IMRT Prostate and Pelvic Node Treatments
Authors: Hsu A , Pawlicki T , King C , Hancock S , Luxton G
Published: July 2006

Purpose: In prostate only treatments, fiducial seeds can be implanted in the prostate and used for accurate daily targeting of the prostate. For high‐risk disease, the regional nodes are simultaneously treated with the prostate using intensity‐modulated radiotherapy thereby sparing the rectum, bladder, bowel, and femoral heads. However, the implanted fiducials do not indicate the position of the nodes as the nodes are anchored to the patient's bony anatomy. Method and Materials: We measured the displacement of the fiducials with respect to the bony anatomy for each treatment fraction as a surrogate for the displacement of the nodes with respect to the prostate from their original planning position. The displacements, taken from the clinical cases were measured to the nearest 0.01 cm, in LR, AP, and SI directions and were used to perform a forward calculation of the IMRT plan that the patient received during treatment. The dose coverage to the nodes, femoral heads and bowel were evaluated using isodose curves and dose volume histograms. Results: Our results indicate for an average patient, the maximum shifts of the seeds with respect to the original DRR position was 0.78 cm inferior, 0.28 cm left, and 0.46 cm posterior. A weighted average of the same directions would be: 0.46 cm, 0.05 cm and 0.13 cm. Forward planning using the weighted average shifts, shows changes in the nodal maximum dose of −0.6% and mean dose −0.2%. The maximum bowel dose changed by −0.5% and the mean dose by −1%. The dose to the left and right femoral heads increased by +2% and +1.2%, respectively. Conclusion: The results indicate that for an average patient the difference in the dose planned to the nodal targets and the organs‐at‐risk are not clinically significant to those received during treatment using fiducial tracking of the prostate.
TU‐E‐ValB‐05: Two Isocenter IMRT with Controlled Junction Dose for Long Volume Sarcomas
Authors: Zeng G G , Heaton R N , Catton C N , Chung P W , Jaffray D A
Published: July 2006

Purpose: Long volume sarcomas are usually treated with a two‐isocenter technique. Due to the sharp dose gradients at the field edges, 3 mm setup uncertainties can cause up to 30% dose variations in the overlap region, potentially increasing dose to the bone and risking subsequent fracture. This dose variation is conventionally reduced by using junction shifts. We have developed a two‐isocenter IMRT technique to spare bone and simultaneously control the junction dose. The technique uses extended dose gradients throughout a junction region to improve the tolerance to setup uncertainties and inverse planning to develop complimentary dose gradients. Methods: An initial dose gradient across a 4–6 cm junction region is induced either with segmented inferior parallel‐opposed beams or using variable dose target junction volumes. Superior IMRT fields, which overlap the junction region, are put and optimize doses superiorly and establish a complementary dose gradient to the initial gradient. Then, segments beams are removed and replaced by inferior isocenter fields to complete dose coverage in the junction region and inferior target. Results: Four lower extremity sarcoma cases have been planned with this technique in Pinnacle 7.6c, demonstrating the following advantages over the conventional technique: Improvement in junction dose uniformity: ±5% target dose heterogeneity for the segments‐induced method and ±3% for the variable‐dose‐volumes method vs. 7% for the conventional moving junction techniques; Improvement in potential error control: for 3 mm setup uncertainties, a): ±5% junction target dose shifts vs. up to ±10% hot or cold spots in the conventional treatment; b): Maintained bone sparing dose in junction vs. risk of increased bone dose. Conclusion: A technique has been developed to permit the application of IMRT to long limb sarcomas with both critical structure sparing and stable junctioning. This technique has applications to other sites where abutting fields offer treatment or efficiency advantages.
TU‐E‐ValB‐06: Direct Aperture Optimization Based Step‐And‐Shoot IMRT with Respiratory Gating
Authors: Ahunbay E , Jursinic P , Li X A
Published: July 2006

Purpose: Validation of respiration gated IMRT on Siemens linear accelerator has not been reported. This work investigates the reliability, accuracy and efficiency of the delivery of respiratory gated IMRT on a Siemens accelerator. Method and Materials: A Siemens Primus accelerator was interfaced with a pressure sensor belt (Anzai Gating system) to deliver step‐and‐shoot IMRT. A series of IMRT fields, including actual patient, as well as custom segmented fields including the “Picket Fence” were delivered with and without gating (interruption) using a variety of different gating parameters (e.g., duty cycle). Radiographic films and 2D diode array (MapCheck, Sun Nuclear) were used to measure dose distributions. The dose distributions measured with and without gating were compared to identify any delivery error from gating. IMRT with multiple beam angles was also delivered, with and without gating, on a cubic motion phantom. Special measurements were made to individually evaluate dark current, small MU non‐linearity and flatness degradation and their cumulative effects on multiple times interrupted fields. Delivery times for MLC and compensator IMRT plans with various segmentations for sample lung and breast cases were compared. Results: Beam characteristics for the Siemens accelerator was not altered by gating and gated IMRT with Siemens/Anzai systems was found to be accurate and reliable. Measured dose distributions agreed with the calculated results and/or with those delivered without gating. Picket fence results with and without beam gating indicated same MLC positioning accuracy during the gating. The delivery times for the DAO‐based IMRT plans that had small numbers of segments were shorter than those for any other types of IMRT plans including compensators and were comparable with those for 3DCRT. Conclusion: The delivery of gated‐IMRT with Siemens/Anzai systems is reliable and accurate. The DAO‐based IMRT is preferred for gated delivery in terms of treatment times.
TU‐E‐230C‐01: Digital Radiography QC Workshop I and II
Authors: Goldman L
Published: July 2006

Computed radiography and digital radiography systems now comprise a large segment of radiography work. It is important that appropriate performance testing and quality control (QC) tools and procedures be made available for these systems. The vendors and/or manufacturers of digital imaging systems may provide‐or make available‐test tools, software and procedures for performance evaluation and routine quality control testing of their digital systems. Currently, such tools and programs vary significantly from manufacturer to manufacturer.

This two‐part workshop will include both formal presentations and hands‐on demonstrations. During the first half of the workshop, each participating vendor or manufacturer will present a brief (12–15 minute) overview of tools and procedures for performance testing and QC of their systems. The second half of the workshop is dedicated to hands‐on demonstrations at table‐top exhibits hosted by each participating vendor. Exhibits will include test tools, workstations and samples of performance testing and QC test procedures.

Companies participating in this workshop will include Agfa, Fuji, General Electric, Kodak, Konica, IDC, LoDox, Philips and potentially others.

Educational Objectives:

1. To understand performance test procedures used by various DR/CR systems.

2. To see types QC test tools and procedures made available with DR/CR systems.

3. To obtain hands‐on demonstration of DR/CR ttesting and QC procedures.
TU‐FF‐A2‐02: Extended Range CT‐Value Analysis in Megavoltage CT Imaging and Therapy
Authors: Ozer M , Hui S , Gerbi B , Higgins P , Alaei Parham , Dusenbery K
Published: July 2006

Purpose: To investigate uses of megavoltage CT (MVCT) scans for high‐Z materials, such as prosthetics, and Fletcher‐Suit applicators. The image quality of kilovoltage CT (kVCT) scans is not clinically useful due to substantial artifacts. We investigated the relationship between MVCT derived “Hounsfield” units (HU) and electron density. Knowing this, we used MVCT scans to the treatment planning process. Then we evaluated the expected dose represented on the plan to actual measured dose taking MVCT derived inhomogeneities into account. Method and Materials: A Siemens 120 kVp CT scanner and 3.5 MeV Tomotherapy unit were used to scan a “Cheese” phantom containing 16 plugs whose relative electron density varied from 0.292 to 8.086. The 3—4 mm slice thickness images were transferred to Eclipse planning station to obtain mean HU. Tomotherapy treatment plans with field width of 2.5 cm, pitch 0.25, and modulation factor 2.5, were completed utilizing extended range HU‐density tables and designed to deliver 2 Gy per fraction to a planning target volume (PTV). An A1SL ion chamber was used for absolute dose measurement, while EDR2 film for evaluation of dose profiles. Results: High‐energy MVCT images compared to the kVCT showed much‐reduced artifact. For unit density and low‐Z materials (tissue equivalent), delivered dose was within 1% of kVCT‐image based plans and within 1.6% of MVCT based plans. kVCT images could not be used for extracting HU in high‐Z material due to saturation in CT numbers. For high‐Z materials, HU were extracted from the MVCT image set. MVCT‐based plans were within 0.6%–5.3% of the target dose depending on the high‐Z material orientation and location compared to the PTV. Conclusion: We show that MVCTbased treatment plans containing high‐Z material can be done accurately. We are exploring clinical applications of this study for patients with prostheses, and intracavitary radiotherapy.
TU‐FF‐A2‐03: Construction and Dosimetry of a Prototype Automated Few‐Leaf Electron Collimator (FLEC) for Delivery of Energy‐Intensity Modulated Electron Therapy
Authors: Al‐Yahya K , Devic S , Verhaegen F , Seuntjens J
Published: July 2006

Purpose: To design and implement an automated “few leaf electron collimator” (FLEC) used for energy modulated electron therapy (EMET) using Monte Carlo‐based treatment planning. This study investigates the optimization of the physical design of the FLEC and provides preliminary validation results of comparison between Monte Carlo calculations and film measurements for complex intensity/energy modulated electron fields using a manual replica of the FLEC. Methods and Materials: The FLEC design was guided by Monte Carlo studies to optimize the physical configuration of the collimator leaves within the linear accelerator. To validate our Monte Carlo‐based treatment planning system, we used a manual FLEC to acquire output of jaws collimated fields using ionization chamber and compared them with Monte Carlo calculation. Calculated two dimensional dose distributions were compared to film measurements obtained using energy‐independent GafChromic® HS films. A gamma‐index analysis quantifying the difference between calculation and measurements is discussed. Results: A prototype of the automated FLEC was constructed with 1.1 cm thick and 3 cm width copper leafs of. The field collimated by the FLEC is backed up by jaw openings following the FLEC projection that provides an optimum field quality. The compact design of the FLEC, including motors, encoders, switches, and necessary wiring, is suitable to be attached to a clinical electron applicator. Software was developed to facilitate remote control of the FLEC system. A comparison between Monte Carlo calculation and film measurements of complex intensity maps shows agreement within tolerated accuracy measures (3% for 3 mm) based on gamma index analysis. Conclusions: The results of this work confirm most of our design objectives and support the potential of using the prototype FLEC for modulated electron therapy delivery. QA procedures for the EMET treatment delivery using the FLEC integrated with the linear accelerator are being investigated.
TU‐FF‐A2‐04: Preliminary Radiological Characterization of An Active Proton Beam Spreading System for Therapeutic Use
Authors: Farr J , Mascia A , Nichiporov D , Hsi W , Allgower C , Schreuder A , Thornton A
Published: July 2006

Purpose: At most proton therapy centers, a clinically useable radiation field is delivered by means of a passive beam spreading system. However, at this proton therapy facility, an active proton beam spreading system has been installed in an isocentric gantry treatment room. Because there exists no standard acceptance test guidelines for an active proton beam delivery system, this presentation serves to report methods and preliminary results from the acceptance testing and early commissioning phase. Method and Materials: Though passive spreading is the most common method of beam formation, the use of metal scatterers reduces the maximum beam range and results in a higher integral dose from concomitant scattered radiation. The active proton beam delivery methods, such as uniform scanning, have the potential of increased range and lower integral dose in comparison to passive spreading. Ionization chamber scans in a step‐by‐step mode in a scanning water phantom were used to acquire the bulk of the data. Results: In the transverse plane perpendicular to the beam axis, the active beam delivery system is capable of delivering a field to within the clinical specification of +/− 2.5%. In addition, the penumbra from the beam delivery system at 5 and 25 cm depth increase from 1.6mm to 10.0mm along the pristine Bragg peak. Along the longitudinal axis, the radiation field meets the range requirement. The SOBP causes a range deficit with the pristine peak of 0.25mm measured from 80–20% dose levels. Also, the SOBP extent flatness exceeds the clinical specification of +/− 2.5% and adjustable with a skewness parameter on the fly. Conclusion: The active beam delivery system at this proton therapy facility is capable of delivering a therapeutically acceptable radiation beam. Furthermore, the active system represents a significant step enroute to the goal of intensity modulated proton therapy.
TU‐FF‐A2‐06: Dynamic IMRT Treatments of Sinus Region Tumors: Comparison of Monte Carlo Calculations with Treatment Planning System Calculations and Ion Chamber Measurements
Authors: Chin D , Jahnke L , Cormack R , Tishler R , Court L
Published: July 2006

Purpose: To compare Monte Carlo (MC) calculations for dynamic IMRT treatments of tumors in the sinus region with Eclipse treatment planning system dose calculations (pencil beam, modified Batho correction), and ion chamber measurements. Methods: The EGS4nrc MC code, BEAMnrc, was commissioned to simulate a Varian 21Ex Linac. The accuracy of the simulation for IMRT plans was evaluated using the RPC head phantom by comparing MC, Eclipse, RPC's TLD results, and ion chamber in solid water phantom measurements. The MC code was then used to simulate dose distributions for 5 patients who were treated using dynamic IMRT for tumors in the sinus region. The results were compared with absolute and relative dose distributions calculated using Eclipse (modified‐Batho inhomogeneity correction). Absolute dose differences were also compared ion chamber results. Results: Comparison of the doses calculated on the RPC phantom using MC, compared with Eclipse, ion chamber, and TLD measurements showed differences of −3.9%, −1.4%, and −2.0%, respectively (MC is colder). Relative dose distributions for the patient plans calculated using MC agreed well with those calculated using Eclipse with respect to targets and critical organs, indicating the modified‐Batho correction is adequate. Average agreement for mean absolute target doses between MC and Eclipse was −2.9±2.2%. Agreement between ion chamber and Eclipse for these patients was −2.2±1.9%, compared with 0.2±2.0% for all head and neck IMRT patients. When Eclipse doses were corrected based on ion chamber results, agreement between MC and Eclipse improved to ‐ 0.7±2.0%. Conclusions: (1) The effect of inhomogeneities in the sinus region is adequately accounted for by the modified‐Batho correction in Eclipse. (2) Both MC and ion chamber results indicate a small systematic uncertainty in the doses calculated using the treatment planning system for this subset of patients.
TU‐FF‐A3‐01: X‐Ray and Optical Monte Carlo Study of Thick, Segmented Scintillators for MV Imaging
Authors: monajemi T , Fallone B , Rathee S
Published: July 2006

Purpose: To study the imaging characteristics of thick, segmented, 2‐D CdWO4 crystal‐photodiode detectors as a function of crystal height, septa material and optical reflectivity, x‐ray beam spectrum and beam divergence using a two‐step Monte Carlo approach involving both x‐ray photon transport at megavoltage (MV) energies and the optical photon transport in scintillator and photodiodes. Method and Materials: We have studied the spatial frequency dependent detective quantum efficiency (DQE) of thick, segmented, 2‐D CdWO4 crystals in contact with silicon photodiode arrays. The energy deposited into the 3‐D voxels (1 × 1 × 1 mm3, septa thickness = 0.15 mm, fill factor = 72%) of the detector for each of the 6 and 3.5 MV x‐ray photons in a normally incident pencil beam was calculated using the DOSXYZnrc user code of the EGSnrc Monte Carol system. The isotropically emitted optical photons in each voxel were calculated using the average CdWO4 optical yield and transported to the photodiode array using DETECT2000 optical Monte Carlo code. A 10° beam divergence angle was also simulated. The detector DQE was calculated using the spatial distribution of optical photons. Results: The DQE increases with the crystal height only if the reflectivity of the septa material is high (0.975). For poor reflectivity (0.65 and 0.8), the increase in the DQE of the taller crystals to MV photons is seriously offset (from 42% to less than 20% for 3 cm tall crystals) by the decreased probability of detecting optical photons. Similarly, the increase in DQE due to the lower energy photons is obtained if the high reflectivity of septa material is maintained for the detector. Beam divergence in thick crystals also reduces the DQE. Conclusion: High reflectivity of the septa in thick, segmented scintillation detectors is very important to achieve high DQE.
TU‐FF‐A3‐03: Investigation of Dose Reduction Strategies for Image Guidance with KV‐CBCT in Radiation Therapy
Authors: Ravindran P , Islam M , Jaffray D
Published: July 2006

Purpose: To explore methods of minimizing the dose to eye (lens) and contra‐lateral breast during image guidance with kilo voltage cone beam CT (kVCBCT) in radiotherapy. Method and Materials: A set of high sensitivity MOSFET, with high bias, was utilized for dose measurements. The MOSFET calibration factors, in terms of cGy/mV, were determined by measuring the response at a depth of 2.0 cm in water against ion chamber. Dose to eye was measured using a head phantom for 360‐degree full rotation, 270‐degree and 195‐degree scans (half rotation plus fan angle). The eye dose was also measured for 195‐degree scan simulating x‐ray tube rotation anterior as well as posterior to the head. Dose to contra‐lateral breast was also evaluated with a Rando phantom. The dose measurements were performed for 120kV beams with mAs values of 0.5, 1, 2 and 3.2 per projection. The images obtained during these measurements were analyzed for image quality. Results: The dose measured on the surface of the eye was less by 50% for 270‐degree scan and by 75% for 195‐degree posterior scan compared to 360‐degree scan. The dose to contra‐lateral breast was less by 30% and 40% for 270 and 195‐degree scans. Excellent image quality was obtained with 0.5 mAs/ projection and 320 projections over a complete rotation scan, however, acceptable image quality also resulted with 195‐degree scan with 75% reduction in eye dose. Reducing the number of projections, over a given arc angle decreased the dose to critical organ, but resulted in artifacts. Conclusion: Reducing the scanning arc resulted in significant reduction in dose without much loss of image quality. A posterior scan reduced the dose to eye considerably without any significant change in the image quality. This work demonstrates that there are opportunities to minimize dose to critical organs without compromising the quality.
TU‐FF‐A3‐04: An In Vivo Comparative Study of the MV and KV Cone Beam Computed Tomography Image Quality of a Lung Patient
Authors: Lim S , Chang J , Yorke E , Mageras G , Lovelock D , Rosenzweig K , Seppi E , Amols H
Published: July 2006

Purpose: To compare image quality, reconstruction artifacts and tumor visibility for kV and MV cone‐beam computed tomography (CBCT) scans reconstructed with the same algorithm. Method and Materials: A protocol lung‐cancer patient was set up in the identical treatment position for kV and MVCBCT using a Varian On‐Board Imager CBCT and an inhouse MVCBCT imaging system. For both scans the gantry made a 1‐minute, 360° continuous rotation. For the MVCBCT, ∼460 projection images were acquired at 6MV for ∼13 MU; for kVCBCT ∼600 projections were acquired using 125 kVp, 80 mA and 25‐ms exposure time per projection, resulting in ∼2cGy at isocenter. Reconstruction was performed using the Feldkamp back projection algorithm. Both scans were registered to the treatment plan CT. The visibility of three selected regions (bronchus, vertebrae, heart) is compared using the corresponding signal‐to‐noise ratio (SNR). The contrast ratio (CR) and contrast‐to‐noise ratio (CNR) at the tumor are also compared for ease of tumor identification. Results: The SNR of bronchus, vertebrae and heart are 25, 34 and 33 respectively for MVCBCT while the corresponding values in kV scan are 17, 33 and 42. For tumor identifiability, CNR and CR are 11 and 2 respectively for MV scan, and 10 and 2 for kV scan. The CNR of the vertebrae in MV and kV cases are 2 and 6. Time to register the kV image is approximately 50% less than MV image. Similar breathing artifacts are present in both scans. Conclusions: Both kV and MV scans deliver usable images. The tumor can be discriminated from the lung background. Higher bone contrast in kV scan helps to reduce time required to register the scan with the planning CT. Conflict of Interest: Research sponsored by NCI Grant P01‐CA59017 and Varian Medical Systems; Research agreement with Varian Medical Systems.
TU‐FF‐A3‐06: Dose Calculation in Presence of a Metallic Object Using Megavoltage Cone‐Beam CT
Authors: Aubin M , Morin O , Aubry J , Chen J , Descovich M , Pouliot J
Published: July 2006

Purpose: CT image artefacts caused by the presence of metallic objects hinder organ delineation and preclude precise dose calculation. In contrast, the presence of high atomic number material has relatively little impact on the image quality of Megavoltage Cone‐beam CT (MVCBCT). The objective of this work was to determine if MVCBCT could be used for accurate dose calculation in the presence of metallic objects.

Material: Experiments were performed with a 16cm diameter cylindrical water‐equivalent phantom. MVCBCT and kVCT images of the phantom were acquired with and without a 1.5 cm diameter steel rod (3 mm wall thickness) sitting on the phantom. Using a treatment planning system, dose distributions were calculated for a 6 MV 10 cm square field AP beam for these configurations. Dose measurements were performed using an ion chamber placed at isocenter and mosfet detectors placed at 35 locations in the phantom. Measured and calculated dose values were compared. Results: Without metal, dose calculated in the phantom using either the kVCT or the MVCBCT image corrected for cupping artefact were all within 2% of each other and of the measured values, showing the ability to use the MVCBCT for dose calculation. In the presence of the metallic object, erroneous density values, around the rod, made dose calculation on the kVCT unreliable. MVCBCT provided correct density values (within 5%) and differences between measured and calculated dose values were on average 3.2% (SD 3.4%). The two largest differences (10.6% and 8.9%) were found in a high dose gradient region below the rod. Conclusion: MVCBCT can be used in a treatment planning system for dose calculation in the presence of metallic objects. Results for non‐cylindrical geometries will also be presented.

This research is supported by Siemens.
TU‐FF‐A4‐02: Diagnostic Medical Physics Performance Evaluation of a Portable Digital Flat Detector System
Authors: Hussain I
Published: July 2006

Purpose: To outline a set of tests to evaluate clinical flat detector performance in terms of image quality, artifact evaluation, detector radiation exposure response and system refresh rate/throughput. Method and Materials: The tests were performed on a Canon CXDI‐50G detector associated with Siemens Axiom Sireskop SD Radiography/Fluoroscopy (R/F) system. For most tests, all image processing filters were turned off and look up table was selected to get unprocessed image data. Detector Dark noise, uniformity and distortion measurements were performed. Relationship between detector exposure, pixel value and detector exposure index was established using three different exposure levels (0.15, 1.13 & 5.7 mR) and R2 calculated. Spatial resolution was determined in four quadrants of the detector. Percent contrast was obtained at three exposure levels with 1 mm Copper filtration. The detector was evaluated for possible ghosting related artifacts between exposures. Detector exposure index (EXI) reproducibility was tested. Refresh rate was measured for the flat detector while used in table top, table bucky and wall bucky mode using all clinical organ program settings. Results: Dark noise EXI was 0 with a pixel value of 0.5. Maximum non uniformity relative to global average was 4.4%. Relationship between detectors exposure, pixel value and exposure index was linear with R2 of 0.9999 and 1 respectively. Spatial resolution was approximately 3.1 lp/mm. Percent contrast was obtained to be 1.22 corresponding to detector exposures of 0.15 mR and 1.13 mR and 0.61 for detector exposure corresponding to 5.7 mR. No ghosting was observed. EXI reproducibility was found to be within 2% of average. No artifacts or distortions were observed. Maximum time to refresh was 20 seconds for Table Top and 19 seconds for Table and Wall Bucky respectively. Conclusion: Detailed performance evaluation of digital flat detectors is an important part of a comprehensive quality assurance program.
TU‐FF‐A4‐03: Post‐Processing Dead Pixel Evaluation for Digital Detectors
Authors: Rutel IB , Yester M , Barnes G
Published: July 2006

Purpose: To investigate and determine a viable method for determining the absolute number of dead pixels from a diagnostic x‐ray digital acquisition output. Method and Materials: In a digital receptor, dead pixels are averaged over surrounding pixels to present an image without artifacts. The absolute number of dead pixels is in general not provided by the manufacturer, but a relative number of pixels from the last check may be reported. Due to the relative difficulty of gaining access to the raw image values, we focus on the least processed images obtainable from a given unit and employ post‐processing techniques to evaluate the pixel information. We use statistical and autocorrelation algorithms to evaluate the likelihood that a given pixel point or line of pixels is aberrant from the expected random noise resulting from several uniform exposures from a digital acquisition detector. Results: We are able to determine that both algorithms provide indications for the line and individual (or grouped) point pixel modifications which are not consistent with random noise. The statistical method (employing both a local and global statistical analysis of noise variations) shows both geometries (point and line defects) but requires statistical averaging over several images to provide relevant point geometry data (we use a minimum of three images to average). The autocorrelation method provides results without the need for averaging. However, by employing the criteria that each of the three images must meet the same correlation requirements, we increase the confidence of the final evaluation results through redundancy. Conclusion: We have developed two independent methods for determining the overall dead pixel information from a digital acquisition detector given three uniform 2223 2006 AAPM Meeting Program 2223 Medical Physics, Vol. 33, No. 6, June 2006 exposures. Both methods provide data for point and line geometries and can be used to provide initial and time logged progression of absolute pixel drop out with time.
TU‐FF‐A4‐04: Intensity Modulation Patterns for Regional Exposure Control with Multiple Angle Slot Scan Imaging: Simulated Annealing Optimization Technique Approach
Authors: Tu S , Shaw C , Liu X , Altunbas M , Lai C , Wang T
Published: July 2006

Purpose: To study the feasibility of using simulated annealing algorithm to determine the intensity modulation patterns for regional exposure control with multiple angle slot scan imaging. Method and Materials: We acquired a digital image from the chest radiography and then processed with a 2‐D Gaussian filter as an exposure equalization mask. Slot scanning exposures at evenly spaced angle between 0 and 180 degrees were used to achieve the ideal exposure distribution. An optimization technique, simulated annealing, was used to search the best intensity modulation patterns. This method is based on the theory of statistical physics and uses Boltzmann probability distribution to locate the minimum energy state. An objective function was mathematically constructed and Metropolis scheme was incorporated into the numerical computation. Various tuning parameters such as the control temperature setting for the annealing schedule were explored and the best combination was empirically chosen. We also calculated the percent root mean square error to quantify the results. Results: A wide range of scanning angles was tested in the study. For 8 projection angles, it took 10 minutes to complete the intensity modulation patterns search in a single processor computer and the percent root mean square error was 12.0%. The percent root mean square error can be further reduced by adding the number of scanning angles. Conclusion: Our study indicated that simulated annealing technique has the potential to determine the optimized intensity modulation patterns. Current work is focused on the reduction of both the computing time and percent root mean square error. Other optimization techniques such as the conjugate gradient method and the applications of parallel computing methods to accelerate the search algorithms are to be investigated.

Supported in part by a research grant EB00117 by the National Institute of Biomedical Imaging and Bioengineering.
WE‐A‐224C‐1: Daily Localization III: Tomotherapy
Authors: Meeks S
Published: July 2006

Helical tomotherapy using the Hi‐ART II is analogous to helical CT imaging where the gantry and the couch are in simultaneous motion. Hence, beam delivery is continuous over all 360 in transverse planes about the patient. Temporal beam modulation is achieved by using a binary multi‐leaf collimator. In addition to its ability to deliver IMRT, the Hi‐ART II has the ability to obtain helical megavoltage CT (MVCT) images. These MVCT images have adequate spatial and contrast resolution for image guidance, and also for identification of many soft‐tissue structures. The incorporation of daily three dimensional soft‐tissue imaging into the radiotherapy process also enables dose recalculation and periodic evaluation of the treatment delivery during a course of radiotherapy. Hence, the subsequent treatment delivery can be modified using a systematic feedback of the geometric and dosimetric information in the previous fractions. This requires many components as feedback, including CT guidance to achieve soft tissue localization, dose recalculation, dose accumulation, treatment evaluation, re‐contouring, and re‐optimization.

This lecture will provide an overview of the physical characteristics of the Hi‐ART II, acceptance testing and commissioning, image quality tests, image registration, basic quality assurance, and an overview of clinical applications. Finally, system limitations and future developments will be addressed.

Educational Objectives

1. Understand the basics concepts of helical tomotherapy.

2. Understand the basic QA requirements and system limitations association with helical tomotherapy.

3. Understand the workflow and issues related to clinical applications of helical tomotherapy, including acquisition, reconstruction, registration and patient alignment.

4. Understand the possibilities of daily soft‐tissue imaging for patient alignment and evaluation of treatment accuracy.
WE‐A‐230A‐01: NCI Talk On Funding
Authors: Deye J
Published: July 2006

The National Institutes of Health is composed of 27 Institutes and Centers, with the National Cancer Institute (NCI) being the oldest and the National Institute of Biomedical Imaging and Bioengineering (NIBIB) the youngest. Medical physicists have a major stake in the pursuits of these institutes since they have a large influence on everything from the research that is funded to the clinical protocols and methods that are employed in both therapy and diagnosis.

Yet these institutes are themselves experiencing very significant extrinsic and intrinsic factors that affect the ways that they interact with the medical community. A partial list would include: the NIH budget in the post‐doubling period; the creation of NIH‐wide Roadmap Initiatives and NCI‐wide Enterprise Initiatives; the adaptation of the NIBIB to the other Institutes; budget set‐asides for the war on terrorism; the dawning of translational research methods; the blurring of boundaries between disciplines; and an increasing role for industry, to name a few.

The ramifications of these changes will be explored with regard to the institute budgets, priorities and relationships; and the presentation will outline some of the current research agendas and the mechanisms which are used to implement them.

Educational Objectives:

1. Understand the structure and processes involved in NIH funded research.

2. Understand the issues surrounding the NIH budget.

3. Understand how to develop a research proposal.
WE‐B‐330D‐01: Digital Image Processing in Radiography
Authors: Flynn M
Published: July 2006

In digital radiography, the transmitted x‐ray beam recorded by a detector is first recorded as raw data related to the energy deposited in the sensitive region of each pixel. Raw data is then transformed to a ‘For Processing’ image by correcting for gain non‐uniformity and bad pixels. Finally, the ‘For Processing’ image is transformed to a ‘For Presentation’ image that is intended for viewing.

The processes used in the presentation transformation have become an ssential element of image quality. These processes include exposure recognition, grayscale rendition, edge restoration, noise reduction, and broad area equalization. The numeric methods used to implement these processes will be reviewed and related to current commercial image processing solutions.

Educational Objectives:

1. Understand how image processing is integrated. into a sequence of steps used in generating a radiograph.

2. Conceptually understand the component processing steps and their effect on image quality.

3. Learn how certain commercial systems implement processing.

4. Understand how processing can be adjusted by a medical physicist to achieve consistent presentation characteristics.
WE‐B‐224A‐01: Shielding III: Practical Examples, Including IMRT, TBI, SRS
Authors: Rodgers J
Published: July 2006

The recently published NCRP Report No. 151, “Structural Shielding Design and Evaluation for Megavoltage X‐ and Gamma‐Ray Radiotherapy Facilities”, presents updated methods and data for radiation therapy room shielding design. These calculational methods are applied in examples representing the more common shielding design situations. A radiation therapy vault with a maze barrier and intended for use with IMRT and TBI procedures is the principal example. Detailed calculations of the barriers and door shielding structures are presented. Procedures for evaluating compliance with the NRC licensing constraint on dose equivalent in‐anyone‐hour are presented. An example of a high‐energy room where photoneutron production is of concern is presented with focus on assessing the dose equivalent at the entrance and the maze door design.
WE‐C‐330A‐01: Robust Tracking of Interventional Tools Under X‐Ray Fluoroscopy Using Particle Filters
Authors: Siddique S , Hatzinakos D , Jaffray D
Published: July 2006

Purpose: Motion estimation is an important problem. In diagnostic and therapeutic interventions, intraoperative motion estimation is needed to guide interventional tools with high precision. In radiation therapy, intrafraction motion estimation is essential to improve the precision with which therapeutic radiation is delivered. The purpose of this study is to estimate the pose (location and orientation) of interventional tools such as needles in an X‐ray fluoroscopic sequence using a particle filter. Method and Materials: Tracking Algorithm: The tools were tracked using a particle filter. Two models are of concern in such an implementation — (i) the observation model was defined on the output of an edge detector by taking transverse and longitudinal samples of the tool, and (ii) the dynamic model was assumed to be given by Brownian motion.

Experimental Setup: The accuracy of the tracking algorithm was validated on an X‐ray fluoroscopy test bench. A modified anthropomorphic Rando™ phantom was placed in the field‐of‐view in order to emulate the background presented by a patient. Two sites on this phantom were used — the pelvis and the thorax. The pelvis presents a case of low signal while the thorax presents a cluttered background. The tool to be tracked was attached to a linear actuator and moved in known increments while capturing fluoroscopic images. The acquired image sequence was then sampled to generate new image sequences for testing the tracking algorithm. Results: The algorithm was robustly able to track the tool under a low signal in the abdomen, and under dense clutter presented by the ribs in the thorax. The rms error in each case was found to be as little as 0.7mm and 0.12mm, respectively. Conclusion: This study demonstrates the robustness of estimation under noise and clutter that can be achieved when tracking tools in a fluoroscopic sequence using a particle filtering approach.
WE‐C‐330A‐03: Seed Segmentation in C‐Arm Fluoroscopy for Brachytherapy Implant Reconstruction
Authors: Vikal S , Jain A , Deguet A , Song D , Fichtinger G
Published: July 2006

Purpose: Intra‐operative dosimetry in prostate brachytherapy critically depends on discerning the 3‐D locations of implanted seeds. The accuracy of 3‐D seed reconstruction step is, in turn, limited by the accuracy with which the position and orientation of individual implanted seed in the fluoroscopic images can be found. A method for robustly segmenting the seeds in fluoroscopic images is proposed here. Methods and Materials: The process of determining the locations and orientations of implanted seeds is sub‐divided into three main steps. In the first step, the image is segmented by shape‐size based morphological approach to eliminate background noise and do away with non‐uniform brightness of the image, to get seed‐like regions. These regions are either single seeds or overlapping multiple seed clusters. In the second step, the regions are analyzed and classified definitively, in a two‐phase statistical process coupled with information extraction from original intensity image, into two classes: single seed and overlapping multiple seed cluster. In the third step, the region belonging to overlapping multiple seed cluster is resolved into its constituent individual seeds through a simple and novel technique. Results: The proposed algorithm was tested on a set of ten clinical fluoroscopic images. The algorithm correctly determines the seeds with overall average of 99.57%. The clusters are not correctly resolved only in two images (2 clusters each, 1.7% and 1.6% of total seeds in respective implants). One false positive (noise labeled as seed) each is reported in two images, both the cases being where the tip of catheter appears to be of the size and shape of seed. Conclusions: The algorithm builds on an existing framework of morphological processing and provides further improvements in classification and cluster resolution. The algorithm appears to be robust and accurate despite the poor resolution of clinical images.