bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐E‐330D‐04: Estimation of Cardiologists Radiation Doses Received During Interventional Examinations
Authors: Bor D , Onal E , Olgar T , Caglan A , Toklu T
Published: July 2006

Purpose: The aim of this work is to suggest a simple method for the estimation of cardiologist extremity doses. Method and Materials: The extremity and effective doses of nine cardiologists working at five different angiographic units were measured for 157 interventional examinations. Simultaneous measurement of patient doses were also carried out using a DAP meter separately for each projection. Fluoroscopy time (Tfl), number of radiographic frames (Nrf) were recorded on‐line during these measurements. A Rando phantom was exposed at similar projections with patient studies and one minute of fluoroscopic exposure (DFLx,n) and one frame of radiographic exposure (DRNx,n) were determined for each projection. Scatter radiations from these exposures were also measured at 50, 100 and 150 cm above the floor level at the cardiologist positions for the estimation of legs, wrists and thyroid (or eye) doses. Weighting of projections were determined for the patient group of each cardiologist using the recorded values of Tfl and Nrf Extremity doses, Dx were calculated from the following formula:
urn:x-wiley:0094-2405:media:mp1615:mp1615-math-0001 n gives the projection number and x is the distance from the floor level. Results: Measured and calculated extremity doses for each cardiologist were in good agreement (R= 0.75 for thyroid). The calculated doses for 50cm and 100cm were found within the measured values of left and right legs and wrists. The use of dominant projection data alone still provided comparable results. Conclusion: If there is a lock of personal dosimetry for cardiologists, it could be possible to make an estimation of extremity doses from the of total fluoroscopy time and frame numbers used in the examinations together with the knowledge of scatter radiations at cardiologist positions.
TU‐E‐224A‐03: Image and Dosimetric Verification of Positioning Accuracy for Helical Tomotherapy Intensity Modulated Stereotactic Radiosurgery
Authors: Liu A , Han C , Staud C , Sun S , Schultheiss T , Wong J
Published: July 2006

Purpose: To investigate the accuracy of Helical Tomotherapy for intracranial radiosurgery using Mega‐voltage CT (MVCT) image fusion. Method and Materials: Tomotherapy generates a set of MVCT images which are fused to the treatment planning KVCT to facilitate the patient setup. For intracranial lesions, mutual information matching program using bony anatomy automatically generates the lateral, longitudinal, vertical, pitch, roll and yaw adjustments that are necessary to align the MVCT to KVCT images. In our study, a pReference head phantom immobilized by Nomos Talon system was used to verify the positioning accuracy of MVCT fusion. Three gold‐filled titanium markers inside the head phantom and the localization tip in the Talon system were used as the independent imaging makers to verify the MVCT positioning accuracy. In addition, dosimetric analysis was performed with a 0.015cc pinpoint ion chamber placed inside the phantom during KVCT simulation. A tomotherapy SRS plan with ion chamber sensitive volume as the target was generated and delivered. After MVCT to KVCT auto registration, dosimetric profiles in three directions were measured by stepping the couch away from the registered position. If the registration was perfect, the dose profile peak position should correspond to the registered position. The distance from the maximum dose to the registered location provides the ultimate accuracy of the system, including MVCT imaging accuracy and radiation dose delivery accuracy. Results: The average localization differences between the MVCT and KVCT were 0.92mm in lateral, 0.82mm in longitudinal and 0.60mm in vertical directions. Dosimetric measurements showed 1.3mm offset laterally and 0mm offset in the other two directions. The relative large setup error in the lateral direction is partially due to the manual couch adjustment with mechanical scale in that direction. Conclusions: The MVCT image fusion can be used to setup SRS patients within accuracy comparable to the current SRS standard.
TU‐E‐224A‐06: Frameless Radiosurgery Using Stereoscopic X‐Ray Guidance: System Characteristics and 2 Year Clinical Experience
Authors: MULLINS J , Li S , Pillai S , Medin P , Solberg T
Published: July 2006

Purpose: To evaluate targeting capabilities of a system for image guided “frameless” stereotactic irradiation. Method and Materials: System accuracy was investigated using an anthropomorphic head phantom into which a “hidden target” (radio‐opaque sphere) was inserted. The target was identified on planning CT images and the phantom was fixed to the treatment couch. To align the target to isocenter, stereoscopic kV x‐rays were fused to planning DRRs. AP and lateral verification films were exposed using a 10 mm circular collimator, and the offset of the sphere within the radiation field was recorded. The entire process was repeated 50 times in order to achieve an accurate assessment of positioning capabilities. Retrospective data was evaluated from patients having undergone nearly 600 x‐ray guided single and multi‐fraction stereotactic irradiation procedures. From this data the following were investigated: the nature and magnitude of systematic and random positioning errors present in conventional procedures, confidence limits on the reproducibility of the mask immobilization device used for multi‐fraction treatments, and the potential for replacing rigid head fixation with image guided positioning. Results: In phantom studies, a vector displacement of σ = 0.39 mm relative to the “perfect” isocenter was observed. Based on a sample population of 50, this provides assurance of accuracy at the 95% confidence level.

Improvement in positioning accuracy was observed in multi‐fraction procedures; analysis of 565 fractions showed a mean vector deviation σ = 2.65 mm relative to traditional methods. The largest component of this discrepancy was in the superior/inferior direction. In comparison, a mean vector deviation σ = 1.62 mm was observed in patients for whom rigid fixation was used. Conclusions: Stereoscopic x‐ray imaging is an accurate positioning method for cranial stereotactic irradiation. The system is as accurate as rigid frame‐based methods and can improve the reproducibility of fractionated delivery.
TU‐E‐224A‐07: Evaluation of Dose Calculation of SRT/IMRT for Small Lung Lesions Using Monte Carlo Simulations
Authors: Jin L , Ma C , Li J , Wang L
Published: July 2006

Purpose: To assess the heterogeneity effect on stereotactic radiotherapy (SRT) of small lung lesions using Monte Carlo (MC) simulations and to evaluate the accuracy of dose calculation in a commercial treatment planning system (TPS) (Radionics, XKnifeRT) for SRT planning. Method and Materials: Five patients were randomly selected for this study. For these patients, the sizes of the planning treatment volume (PTV) ranged from 4.2 and 36 cc, and the average densities of the GTV and the ipsilateral lung ranged from 0.659 to 0.93 g/cm3 and from 0.244 to 0.358 g/cm3, respectively. The SRT treatment plans (9 photon beams) for these patients were first generated by the TPS and then recalculated by a MC dose calculation system with the same beam configuration and beam weights as in the TPS. Comparisons between the MC and the TPS calculations were made to assess the differences in isodose distributions, median dose (D50), maximum dose (defined as D1) and minimum dose (defined as D99). Results: Dose indices of D1, D50 and D99 calculated by the TPS for all patients are found to be significantly larger than those of the MC calculations for the PTV. The degree of dose overestimation by the TPS increases with decreasing target volume and target and ipsilateral lung densities. Specifically, for PTV volume sizes from 36 to 4.2 cc, the dose calculated from the TPS in D1, D50, and D99 are overestimated by up to 24.7 %, 32.3%, and 38.9% respectively. Conclusions: Although the TPS can produce accurate (3%/3mm) treatment plans for homogeneous geometry and for large target volumes in the lung, for small lung lesions the dose calculated by the TPS can be significantly overestimated due to inaccurate heterogeneity corrections.
TU‐E‐ValB‐01: Helical Tomotherapy Targeting Total Bone Marrow ‐ Initial Clinical Experience at the University of Minnesota
Authors: Hui S , Verneris M , Higgins P , Gerbi B , Weigel B , Baker S , Fraser C , Tomblyn M , Petryk A , DeFor T , Dusenbery K
Published: July 2006

Purpose: We report here the successful use of Tomotherapy at delivering intensity modulated radiotherapy to the bone and bone marrow spaces along the entire axis of a patient and describe a dosimetric analysis of the total marrow irradiation (TMI) treatment. This is part of a dose escalation trial to determine the maximum tolerated dose (MTD) of TMI when given prior to an alkylator‐intensive conditioning regimen for the treatment of high risk or relapsed solid tumors. Method and Materials: A patient enrolled in a dose escalation study trial received 600 cGy in 3 fractions. Two independent CT image sets (upper and lower part of the body) were obtained. A helical tomotherapy treatment plan was created from this CT image sets. The quality assurance was evaluated with the use of (a) ion chamber and (b) extended dose range film. The isorad‐p cylindrical diodes were used for in‐vivo dosimetry. Results: The patient showed neutrophil engraftment on day 11 and platelet engraftment by day 58. He is currently well at 120 days post transplant with no evidence of disease. The patient developed nausea and vomiting after the first fraction of Tomotherapy TMI. Other than above there were no adverse effects of TMI. The planned radiation conformed to all bone marrow sites. Average doses to lungs, kidneys, heart, and eyes were 50–70% of the prescribed dose for TMI treatments. The dose delivery verifications (pretreatment and in vivo dose measurement) were within ±3–5% of the expected dose calculated from the treatment planning station. Conclusions: We show that helical tomotherapy targeting the bone marrow of the whole body is clinically feasible. The clinical implementation of intensity modulated radiation to conform the radiation dose to all active bone marrow of the whole body opened up the possibility of a dose escalation study for high risk patients.
TU‐E‐ValB‐02: Using Magnetically Collimated Electrons and Narrow Intensity Modulated Tangential Photons for Accelerated Partial Breast Irradiation
Authors: MA L , Chuang C , Xia P , Petti P , Verhey L
Published: July 2006

Purpose: Previous studies have shown that enface magnetic collimation lowers entrance dose and reduces lateral scattering for electron beams. However, dose uniformity is limited at depth for single beam delivery. This study investigates whether adding narrow intensity modulated tangential photon beams would solve the problem and create a new technique for accelerated partial breast irradiation. Method and Materials: Magnetically collimated electron beams were measured and modeled empirically for treatment planning and combined with photon beams on a commercial treatment planning system (Pinnacle 7.6, Philips Medical System). Treatment plans were generated for conformal irradiation of the partial breast using a pair of intensity modulated tangential photon beams plus enface magnetically collimated electron beams. The photon beams were planned via inverse planning with the beam weights of the electron beam adjusted simultaneously. The first MLC segment of the photon beams was fixed to cover the entire planning target volume in the beam's eye view to minimize the effect of target motion. Final treatment plans were analyzed for dose uniformity, for the conformity of the target volume and also for the dose to normal tissues including the skin. Results: The combined beam approach significantly improved dose conformity, e.g., narrower separation between peripheral isodose lines, as compared with using either electron beams or a pair of tangential fields alone. The use of enface electron beams significantly improved the target dose uniformity to better than 10%. Due to magnetic collimation, the skin dose was on average lowered by 18% over the use of conventional electron beam for the technique. Conclusion: Intensity modulated tangential photon beams combined with magnetically collimated electron beams offers a new technique for accelerated partial breast irradiation.
TU‐E‐ValB‐07: A Segmentation and Leaf Sequencing Algorithm for IMAT
Authors: Gladwish A , Chen J , Oliver M , Craig J , Wong E
Published: July 2006

Purpose: To develop an intensity segmentation and leaf sequencing algorithm specifically for intensity‐modulated arc therapy (IMAT), which can be applied to optimized intensity patterns derived from existing commercial IMRT inverse planning software. Methods and Materials: Three phantom cases, as well as a clinical case were planned using a Hi‐Art II (Tomotherapy Inc, WI.) planning station. The end of planning sinograms were then extracted and inputted into our IMAT conversion algorithm. The number of required arcs, deliverable MLC segments for each arc and the relative intensity weighting of each arc were outputted. The number of arcs (modulation) could be controlled by a user parameter, α. The resulting MLC segments were then fed into a fast monte‐carlo dose calculation algorithm, NXEGS (NumeriX, LLC) to obtain 3D dose distributions. Dose statistics (max, min, mean) and dose volume histograms of relevant structures were calculated and compared against the results generated by the Hi‐Art II system. Results: Each plan was converted in under three minutes on a typical desktop PC, with the arc numbers varying between 4 and 15 360° arcs. Qualitatively, the dose distributions obtained from the IMAT plans were similar to the tomotherapy results, as well as planned doses. Quantitatively, the IMAT plans were slightly degraded, with the average dose to normal structures being 7.5% higher for IMAT vs. tomotherapy. However, the IMAT plans generally met planned values, being 9.1% below for maximum doses to normal structures. The number of arcs and therefore the resulting dose distribution could be varied according to α. Conclusions: IMAT segmentation and leaf sequencing produced deliverable IMAT MLC segments and relative arc weights directly from Hi‐Art II optimized plans. The algorithm was computationally efficient, and produced similar dose distributions. Additional optimization could improve resulting dose distributions further. IMAT back‐up for tomotherapy is another potential application.
TU‐FF‐A1‐01: Characterization of EBT Versus MD55 Gafchromic® Films for Relative Dosimetry Measurements
Authors: Alvarez P , Hernandez N , Followill D , Tailor R , Ibbott G
Published: July 2006

Purpose: To evaluate the EBT® radio‐chromic film for relative dosimetry in comparison to MD55®. Method and Materials: For dose‐response study, EBT and MD55 films were irradiated to dose ranges 0–15 and 0–40 Gy respectively. Photon beam energies of 6 and 18 MV were used to study energy dependence. Films were scanned using a scanner from Micro‐densitometer Photoelectron Corporation. The scanner uses a CCD camera. The two diffused‐light beds using light‐emitting diodes, operating at 636 and 665 nm, were used for EBT and MD55 films respectively. For flatfield subtraction at start of a scanning session, in case of EBT, an unirradiated film was scanned employing a black mask covering the light box's area outside the film. In case of MD55, un‐masked light box without a film was scanned for the flat field subtraction. For fading study, films were read over a period 2–20 days after irradiation. For light sensitivity, un‐irradiated films were exposed to florescent light to 6 hour maximum. Results: Unlike MD55, light sensitivity of EBT is found to decrease with pre‐irradiation level. With 2Gy pre‐irradiation, it is comparable to MD55. Fading of EBT is comparable to MD55. The small energy dependence observed beyond 8Gy for EBT is considered negligible. Percent uncertainty in relative‐dose determination from two OD values is obviously expected to increase with separation between the OD values, and to be higher at lower OD levels. It is comparable for both films, and is typically estimated to be 0.8% for determination of 50% of 2Gy. Conclusions: Dosimetry characteristics of EBT are comparable to MD55. Its higher sensitivity to radiation and availability in larger size makes it preferable as a relative dosimeter for RPC use.

Work supported by PHS grant CA10953 and CA81647 awarded by NCI.
TU‐FF‐A1‐03: Comparison of Surface Dose Resulting From SMLC and Compensator‐Based IMRT for Breast Radiotherapy
Authors: Nalichowski A , McDermott P , Burmeister J
Published: July 2006

Purpose: To compare the surface dose to the ipsilateral breast between compensator and MLC‐based IMRT for breast radiotherapy both with and without simulated respiratory motion. Methods & Materials: An anthropomorphic polystyrene breast phantom mounted on a moving platform was used to simulate the human breast and its respiration‐induced motion during radiotherapy. MOSFET dosimeters were placed on the surface of the phantom at 5 approximately uniformly spaced positions in the central axial plane. Two common IMRT treatment techniques were then used to deliver a uniform dose of 1.8 Gy to the simulated breast both with and without simulated respiratory motion with 1 cm amplitude and a period of 4 seconds. Both techniques used the same parallel‐opposed half‐beam‐blocked tangential beams, but one used bismuth polyethylene compensators to create the modulation while the other used the segmental MLC (SMLC) delivery technique to create the modulation. The segment shapes and weights for the SMLC delivery were created from the fringe lines of the compensator maps so that the plans delivered essentially identical dose distributions to the phantom beyond the build‐up region. Results: Respiratory motion did not significantly alter the surface dose for either technique. All five dosimeters measured lower surface doses from the SMLC plans in comparison to the compensator plans. The average surface dose for SMLC delivery of 127 cGy was 6% lower than the average dose of 135 cGy measured for compensator delivery. Conclusion: The secondary and scattered radiation produced in the compensator increases surface dose. The use of SMLC IMRT results in lower dose to the skin than that from compensator‐based IMRT and this fact should be considered when planning breast IMRT cases.
TU‐FF‐A1‐04: Illustrating Manufacturing Variability in Prostate Brachytherapy Seeds Through X‐Ray Spectrometry and Radiochromic Film Measurements
Authors: Mitch M , Mitchell M , Seltzer S
Published: July 2006

Purpose: To illustrate the effects of manufacturing variability on ionization chamber measurements of a batch of “identical” prostate brachytherapy seeds in terms of emergent spectrum, in‐air anisotropy, and internal distribution of radioactive material. Method and Materials: A batch of six “identical” prostate brachytherapy seeds were calibrated in terms of air‐kerma strength using the Wide‐Angle Free‐Air Chamber (WAFAC) at the National Institute of Standards and Technology (NIST). The seeds were subsequently characterized using a variety of experimental techniques including well‐ionization chamber response, x‐ray spectrometry, and radiochromic‐film contact‐exposure measurements. In‐air anisotropy was quantified by the air‐anisotropy ratio, αs, calculated from x‐ray spectrometry measurements performed with the seed rotated at 90‐degree intervals about an axis perpendicular to the mid‐point of the long axis of the seed. Results: Variations in the internal distribution of radioactivity among the six seeds were observed in optical density profiles through the long axes of the seeds, as measured by radiochromic film. X‐ray emergent spectra showed differences in the admixture of silver fluorescence x‐rays between seeds, which modified the average energy of the spectra and thus the relative response of the well chamber and the WAFAC. Variations in αs affected relative ionization chamber response due to the difference in measurement geometry solid angle between the WAFAC (cone of 8 degree half‐angle) and the well chamber (approximately 4π). Conclusions: The effects of variations in emergent spectra and anisotropy were small enough such that the well‐chamber‐to‐WAFAC response ratio for all but one of the seeds was within the 1.00 % tolerance criterion as recommended by the Calibration Laboratory Accreditation Subcommittee of the AAPM. The “out‐of‐tolerance” seed was shown to have an admixture of silver fluorescence x‐rays in the emergent spectrum significantly different than that of previously calibrated seeds of the same design.
TU‐FF‐A1‐05: A Motion Phantom Study On Helical Tomotherapy: The Dosimetric Impacts of Delivery Technique and Motion
Authors: Kanagaki B , Read P , Larner J , Molloy J , Sheng K
Published: July 2006

Purpose: To determine the optimal delivery technique for treating moving targets with Helical Tomotherapy (HT) we measured the dosimetric effects of various motion and Tomotherapy plan parameters using a lung motion phantom. Method and Materials: A motion phantom system was constructed using a programmable motor driving a moving platform. Tomotherapy plans were delivered to a phantom which mimicked lung heterogeneity by using wood inserts with the density of lung tissue and a 3.3cm spherical tissue density material as tumor. A cylindrical planning target volume (PTV) was used with a length and diameter of 3.3cm including the sphere. Treatment plans were created using jaw sizes of 1.04 and 2.47cm with incremental gantry rotation times ranging from (10s) to (60s). Treatments based on these plans were delivered to the phantom with motion periods of 3 and 5 seconds, and amplitudes of +/−6 and 10mm. All plans were normalized to 2.0 Gy fractional doses to 95% of the PTV and Kodak EDR‐2 film was used for 2‐D dose measurements. Axial dose profiles and cumulative dose volume histograms (DVH) of plans for moving and static phantom conditions were compared. Results: Target edge under‐dosing is less with a jaw size of 2.47cm than 1.04cm in this experimental system. Shorter motion periods (3s) and greater gantry rotation (>5 times motion period) resulted in better PTV coverage referenced to static phantoms. Greater than 90% of the PTV received the prescription dose even when the phantom moves +/−10mm. When the gantry rotation time to motion period ratio approached 3 PTV coverage was compromised. Conclusions: PTV expansions smaller than motion excursion may be possible for lung tumor treatment by HT. Larger jaw width provides better target coverage because of the wider inferior/superior penumbra. Increasing the ratio of the gantry rotation time to the motion period improves target edge coverage.
TU‐FF‐A1‐06: A Robust Scalable Parallel Processing System for Radiation Therapy
Authors: Morrill S , Parker B , Brack C
Published: July 2006

Purpose: To develop a robust Linux—based cluster for the parallel computation of problems of interest in a radiation therapy environment. This system should be robust, scalable and easy to manage. It should be constructed from commercially available low cost hardware and use only open source software tools to manage the system. Method and Materials: This cluster was constructed using a distributed memory model with the Message Passing Interface (MPI) protocol. The use of distributed memory requires a fast backbone to efficiently distribute programs and data to the various cluster nodes. This rapid data transfer was accomplished using a Gigabit Ethernet switch which allows a peak transfer rate of 100 Mbytes/sec. The cluster currently consists of 76 CPU's each with a minimum of 512 Mbytes of RAM. The individual nodes run an open source version (Centos 4.0) of the Redhat Enterprise 4.0 Linux operating system. The MPI protocol is implemented using the open source implementation, MPICH. Cluster node management is accomplished using the ROCKS 4.0 shareware toolset. The compilers and debuggers (C++ and FORTRAN for Linux) are Intel 9.0. Finally, the Integrated Development Environment (IDE) is the Eclipse open‐source project v3.0.1 with PHOTRAN extensions. Results: This cluster has recently been commissioned and several benchmark tests have been completed. Factors of 15X – 60X improvement in speed for parallelizable sections of various codes have been demonstrated. Conclusions: This system is robust enough to solve complex problems which were intractable with our previous computational tools. The demonstrated speed improvements will allow for the implementation of codes for problems such as: real‐time dose calculation, fast IMRT optimization, and the convolution of correlated CT datasets to account for patient motion.
TU‐FF‐A2‐01: Feasibility of Cone‐Beam CT Based Treatment Planning
Authors: Yoo S , Yin F
Published: July 2006

Purpose: To investigate the feasibility of cone‐beam computed tomography (CBCT)‐based treatment planning. Methods: HU of material disks in Catphan, HU profiles for homogeneous and inhomogeneous phantoms, and HU values in different tissue areas of brain, thorax and prostate patients were compared in CBCT and CT images. Plans with one beam based on CBCT and CT of phantoms and patients were compared using MU/cGy values and isodose distributions. For patient cases, 3D plans and IMRT plans based on CT images were generated, and then verification plans based on CBCT were generated. The isodose distributions and dose values at the isocenter were compared between two plans. Results: HU values of CBCT are very close to those of CT in Catphan. However, HU profiles of homogeneous and inhomogeneous phantoms in CBCT show inhomogeneous distribution compared to those in CT with large scatter. Large scatter contribution becomes greater in patient cases. The lung or fatty tissue appears with even lower HU values in CBCT than in CT. Resulting MU/cGy differences are generally within 2%, but a beam passing through a significant amount of the lung or bone shows 2 – 3% of MU/cGy difference. The isodose distributions of CBCT‐based verification plans and CT‐based plans for brain and prostate patients are very similar with the dose values less than 2% different. The dose value is about 4% higher in CBCT‐based verification plan than in CT‐based plan for the thorax patient and the isodose distributions in the high dose area inside of the lung shows disagreement between the two plans. Conclusion: This study validates CBCT‐based treatment planning by comparing with the gold standard CT‐based treatment planning. CBCT‐based plans could be used for most cases. However, beams should be selected with a consideration to avoid a large part of lung.

Research partially sponsored by Varian Medical System.
TU‐FF‐A2‐05: A Laser System and Target Design for Proton Acceleration
Authors: Veltchev I , Fourkal E , Lin T , Ma C
Published: July 2006

Purpose: The interaction of powerful laser pulses with solid‐state targets has recently been demonstrated to produce beams of energetic protons. The generation and characterization of laser accelerated protons is nowadays one of the most rapidly developing fields in accelerator physics. On the application side, the development of a cost‐effective and energy efficient way of producing proton beams represents a major breakthrough in hadron therapy. In this work we present a detailed study of the requirements imposed on the laser system in order to achieve extremely high peak intensities, necessary for proton acceleration. Different target designs are experimentally investigated. Method and Materials: The laser system consists of a chain of commercial lasers and amplifiers, based on Titanium doped sapphire crystal as active medium, followed by a custom‐design power amplifier. The technique of chirped‐pulse amplification is employed as the most efficient amplification scheme for ultra‐short laser pulses developed to date. Sharp focusing is achieved by an off‐axis parabolic mirror designed for low losses and minimal aberrations. Frequency resolved optical gating measurements provide the complete laser pulse characterization. Results: After pulse compression in vacuum we achieved 40 fs pulse duration with 1.1 J in each pulse at 10 Hz repetition rate. Focused beam spot size of 8 μm has been accurately measured. We demonstrate capability of obtaining pulses with characteristics suitable for proton acceleration. All stages of the pulse generation, amplification, compression, and conditioning are discussed in detail in this study. Different regimes of acceleration are discussed along with experimental evidence for their realization. Conclusion: We present a detailed characterization of the current state of our laser system and a novel target chamber design. The implications for proton acceleration along with optimization strategies for enhanced proton yield and collimation are discussed as well.
TU‐FF‐A3‐02: Preliminary Investigations Into Combined CT/SPECT Imaging Onboard Therapy Machines
Authors: Bowsher J , Yin F , Greer K , Jaszczak R , Samei E , Willett C
Published: July 2006

Purpose: Functional and molecular (F&M) imaging onboard radiation therapy machines would allow for targeting of functional tumor volume, and avoiding of healthy tissue, by guiding and modifying radiation beams, in the treatment room, based on real‐time F&M information. This capability might be particularly critical when tumor is located within deformable internal organs. When deformable structures do not present adequate contrast in the CT image, precise localization of tumor and healthy‐tissue can be difficult using onboard CT alone. Also, since some F&M properties can change on the time scale of an hour, onboard F&M imaging may be important for its temporal proximity to therapy. Given the benefits of onboard F&M imaging and the essentiality of onboard CT, the purpose of this study is to investigate the feasibility of using flat‐panel detectors (FPDs) to accomplish both CT and SPECT onboard therapy machines. Method and Materials: A 10 mCi point source of Tc99m was placed 100 cm from a bar phantom, with a FPD immediately behind the phantom. Data were acquired for 10 seconds. A signal‐to‐noise ratio (SNR) was computed with signal given by difference in mean activities in the exposed and bar‐covered regions and noise given by standard deviation of amplitudes in the 0.776‐mm‐wide exposed‐region pixels. Results: The bar phantom was clearly visualized. The measured SNR was 4. Conclusion: Additional experiments will be required to evaluate FPD SPECT when radiotracer is distributed over an extended source and a collimator is employed. Since FPDs have not been designed for SPECT, only limited SPECT performance can be expected. However, these initial characterizations of FPD SPECT may support FPD design modifications, such as thicker scintillators, that enable combined SPECT/CT imaging using FPDs mounted onto therapy machines.
TU‐FF‐A3‐05: Dosimetric Effect of Cupping Artefact in MVCBCT Images of the Head and Neck Region
Authors: Aubry J , Morin O , Maltz J , Chen H , Descovich M , Aubin M , Beaulieu L , Pouliot J
Published: July 2006

Purpose: To quantify the dose calculation accuracy achievable with 3D anatomical images obtained by Megavoltage Cone‐Beam Computed Tomography (MVCBCT) for the head and neck region (H&N). Method and Materials: MVCBCT images of inserts of different density immersed in water were obtained. This allowed the tuning of the parameters used for the image reconstruction. A MVCBCT number versus material density curve was also extracted for dose calculation purposes. MVCBCT images of a Rando phantom head were then acquired on a linac treatment couch with two different gain image calibrations and in two different positions relative to the room isocenter. Voxel‐based and band‐pass filter cupping artifact reduction methods were applied on all MVCBCT images. Images of the same phantom were also obtained with a kVCT. All images were transferred to a treatment planning system and dose calculations performed with various beam configurations. The dose differences obtained with the kVCT images and the MVCBCT images were analyzed using a gamma index function. Results: At best, 96.1% and 98.8% of the dose points calculated with the MVCBCT images were within the dose calculated with the kVCT image by [2%, 2 mm] and [3%, 3 mm], respectively. The worst cases observed had fractions of 87.7% and 96.3% of the dose points that agreed within [2%, 2 mm] and [3%, 3 mm], respectively. The cupping artifact reduction methods tested did not significantly improve the dose calculation for most cases. Conclusion: With proper calibration, dose calculations with MVCBCT images in the H&N region are feasible with an accuracy of [3 %, 3 mm] or less. The cupping artifact for H&N imaging does not lead to important dose calculation errors. Dose calculation with patient MVCBCTs and treatment plans are ongoing. Conflict of Interest: Research sponsored by Siemens OCS.
TU‐FF‐A4‐01: Instrumentation Noise Equivalent Exposure (INEE) Representation for High Sensitivity X‐Ray Imaging Detectors
Authors: Yadava G , Rudin S , Kuhls A , Patel V , Bednarek D , Hoffmann K
Published: July 2006

Purpose: For modern high‐sensitivity digital imaging detectors operating at fluoroscopic exposure rates, the additive instrumentation readout noise may prevent desirable optimal quantum‐limited performance. A formalism and experimental validation of the representation of instrumentation noise in terms of the equivalent x‐ray entrance exposure to the detector is presented as a more practical noise measure than the equipment‐invasive measurement of electrons per pixel. Method and Materials: The instrumentation noise in terms of exposure equivalent is added in quadrature to the quantum noise to give the total measurable noise. Experimental validation was done using two different CCD‐based detectors: a high‐sensitivity microangiographic fluoroscope (MAF) and a less sensitive microangiographic detector (MA). Both detectors have a CsI(Tl) phosphor coupled to a fiber‐optic taper followed by a CCD camera (the MAF additionally has a variable‐gain light amplifier between the taper and the CCD). To determine the INEE for both detectors, a least‐squares regression technique was used to fit the measured data to the theoretical equation relating the signal‐to‐noise ratio squared SNR2 to the detector entrance exposure. Results: The SNR2 versus exposure plot deviates from linear behavior at lower exposures as expected, and closely follows the modeled equation used to derive the INEE. The measured INEE for the high‐sensitivity MAF was 0.034 μR and that for the MA was 10.8 μR. Conclusion: A formal treatment of the instrumentation noise in terms of the detector entrance exposure was developed and validated by using two different CCD based systems of different sensitivity. This study demonstrates that the INEE is a practical way to gauge the range of quantum‐limited performance for clinical x‐ray imaging detectors, with the implication that detector performance at exposures below the INEE will be instrumentation‐noise limited rather than quantum‐noise limited.

(Partial support from NIH Grants R01EB002873, R01NS43924, and Toshiba Medical Systems Corporation).
TU‐FF‐A4‐05: Temporal Subtraction of Lateral Chest Radiographs
Authors: Engelmann R , Armato S , Doshi D , Sensakovic W , Starkey A , MacMahon H
Published: July 2006

Purpose: Radiologists routinely compare multiple radiographs of the same patient to identify interval change in anatomy and pathology. The temporal subtraction images that facilitate this comparison have been limited to posteroanterior radiographs. Since the lateral view provides diagnostically important information, the purpose of this study was to develop an automated method for the subtraction of temporally sequential lateral chest radiographs and to evaluate the quality of the resulting images. Method and Materials: An automated method was developed to digitally subtract pairs of lateral chest radiographs. First, multiple rotated versions of the “previous” lateral radiograph were generated. For each of the rotated previous images, the apex of the lungs was identified through gray‐level profile analysis. A 251 × 215 mm subimage was then extracted near the apex and used as a template for cross‐correlation with the “current” radiograph. The translation and rotation parameters that yielded the highest correlation were used to rigidly transform the “previous” radiograph, which was then subtracted from the current radiograph to yield the temporal subtraction image. 30 pairs of lateral chest radiographs were subtracted. An observer rated the quality of each temporal subtraction image using a 1 (“very poor”) to 5 (“excellent”) scale. Results: The average registration accuracy rating was 4.0. 83% (25/30) of the subtraction images were rated as “acceptable” or better (3.0 or higher). Conclusion: Our technique for the automated subtraction of temporally sequential lateral chest radiographs generates a high percentage of subtraction images with acceptable registration accuracy. Such a method is expected to provide a valuable supplement to the conventional posteroanterior temporal subtraction images that have proven beneficial in the diagnostic evaluation of interval change in chest radiography.

S.A. and H.M. hold warrants to shares in R2 Technology, Inc.; H.M. consultant for Riverain Medical and Median Technologies.
TU‐FF‐A4‐06: Variation in Dual‐Energy Chest Radiography Among Systems Using Identical Digital Flat Panel Detectors
Authors: Devaraju V , Willis C
Published: July 2006

Purpose: To study the variation of dual‐energy chest radiography systems by measuring Spectral Quality Factor (SQF) and subtracted‐image Noise Quality Factor (NQF) defined by Alvarez, Seibert, and Thompson (2004)1. SQF depends on the x‐ray energy spectrum and detector DQE. NQF is a measure of noise in the subtracted image, which depends on SQF and detected signal levels. Method and Materials: Stepwedges of aluminum and polycarbonate duplicating the original work and a 4.8 mm thick acrylic slab were radiographed in dual energy chest mode at 120 and 60 kVp using 15 systems (XQ/i, XR/d, and XR/dII; GE Medical Systems; Milwaukee, WI). Exposure levels of approximately 16, 24, 47, and 57 mR were measured free‐in‐air, corrected to the surface of the acrylic slab. SQF was calculated from effective linear attenuation coefficients, slopes of logarithm of pixel values behind each step relative to an uncovered area versus step thickness from raw images of each stepwedge at low and high energy. NQF was the slope of SNR2 in the soft‐tissue image of the smallest step of the polycarbonate stepwedge versus entrance exposure. Results: Alvarez, et al. compared three dual‐energy detector technologies, reporting results in relative terms, including variation of ±5% in SQF for an individual unit like ours. Our SQF was approximately 1.2×10−8 mm−2 ±14%. They reported NQF of 0.18 mR−1 estimated from Fig.10 using images subtracted by their own algorithm. Our NQF was approximately 0.16 mR−1 ±9% using images subtracted by the clinical system. Conclusions: SQF and NQF are useful indicators of dual energy system performance that can be determined in a practical setting with clinical systems. Values for our flat panel systems are in general agreement with previous reports.
WE‐A‐330A‐01: Breast CAD in the Digital Era
Authors: Giger M
Published: July 2006

Use of output from a computerized analysis of a breast image by radiologists may help them in the tasks of detection or diagnostic, and potentially improve the overall interpretation of breast images and the subsequent patient care. Many factors motivate the attempts to aid or automate radiological diagnosis. Inadequacies in interpretation performance may be due to the presence of image noise or normal anatomical structure as well as to known limitations in the human search and perception process. Developments in breast CAD have led to clinically‐used detection systems in screening mammography and preclinical classification systems for diagnostic breast imaging. Diagnostic breast CAD systems provide output for the characterization of lesions on special‐view mammography, breast sonography, and breast MRI in order to aid in patient management decisions, such as biopsy decisions. As imaging continues to expand in the digital era, computer‐aided diagnosis (CAD) may become an integrated tool in the online diagnostic workup of suspect breast lesions using multi‐modality images and advanced PACS. This presentation reviews research in computerized analysis of mammographic, sonographic, and magnetic resonance breast images for detection and diagnosis. It will include the characterization of lesions and the estimation of the probability of malignancy for use in the diagnostic workup of suspect lesions. CAD systems in diagnostic workup usually involve having the computer extract the margin of the lesion from the surrounding parenchyma, extract characteristics (features) of the lesions, merge these computer‐extracted features into an estimate of the probability of malignancy, and as an option, retrieve automatically similar lesions from an online reference library. The aim of CAD in diagnostic workup is to increase classification sensitivity and specificity as well as to reduce intra‐and inter‐observer variability. While the breadth and depth of CAD is increasing, continued and expanded efforts are needed for collecting and confirming databases, establishing methods for evaluation, integrating effectively and efficiently with PACS and RIS systems, and providing means for clinical evaluation.

Learning objectives:

1. To appreciate the development of CAD in multi‐modality imaging for detection and diagnosis of breast cancer.

2. To understand the benefits and challenges as CAD moves into the digital era and is integrated with PACS and HIS.

3. To recognize the necessary steps for advancing and integrating CAD clinically.

COI: Maryellen Giger is a shareholder and consultant, and receives research funding from R2 Technology, Inc.
WE‐A‐330D‐01: PET Scanner Quality Assurance
Authors: Kemp B
Published: July 2006

Quality assurance of PET scanners must be performed on a regular basis to maintain and confirm proper scanner performance. These procedures should track system stability and be sensitive to changes in scanner operation. The quality control and calibration of a PET scanner includes detector and electronic characterizations such as adjustment of PMT gain, definition of crystal and energy maps and coincidence timing calibration. These characterizations are applied to the PET data during acquisition. A PET quality control regimen includes system corrections such as normalization, calibration and, in the case of non‐PET/CT systems, blank scans. The calibration correction is used to convert the reconstructed image pixel values into activity concentration and it may be used to compensate for the axial sensitivity variation of the scanner. These characterizations are applied to the PET data after acquisition.

The NEMA PET NU2‐2001 standard should be followed for acceptance testing. This standard uses a polyethylene phantom of 700mm axial length with a line source to measure scatter fraction, count losses and randoms. The measurement of sensitivity is conducted with a line source surrounded by known absorbers, and the sensitivity with no absorbers can be found by extrapolation. The intent of the image quality measurement is to mimic a whole body scan using a torso phantom containing hot and cold spheres of various diameters (representing lesions) in a warm background.

This presentation will focus on the calibrations and corrections required to maintain proper system performance. The presentation will also describe the rationale and methodology of the NEMA NU2‐2001 performance standards.

Educational Objectives:

1. Describe the calibrations required to properly detect the location of a coincident event.

2. Describe the post acquisition corrections required to minimize image artifacts.

3. Describe NEMA NU2‐2001 PET performance standards.
WE‐A‐ValB‐01: Multi‐Slice CT Image Reconstruction
Authors: Hsieh J
Published: July 2006

Over the past decade, x‐ray computed tomography has experienced tremendously technological advancements: the introduction of helical/spiral and multi‐slice/volumetric acquisition. These advancements not only allow improved image quality and enable new clinical applications, but also significantly increase the technical challenges associated with image reconstruction.

The first part of this lecture will cover the fundamentals of image reconstruction. For the ease of understanding, we start with an explanation of the central slice theorem (Fourier slice theorem). Both theoretical and intuitive approaches are used to illustrate the concept. The reconstruction algorithm is then extended to fan beam geometry by mathematical derivation and graphic description.

Using the central slice theorem as the foundation, reconstruction algorithms for helical acquisition are discussed in the second part of the lecture. We analyze, for single slice, the major difference between helical and step‐andshoot acquisitions. Implications of different reconstruction approaches on image quality and computational complexity are also discussed.

Cone beam reconstruction discussion will start with one of the most popular algorithms: FDK algorithm. The derivation of the algorithm from the fan‐beam case is first described and its extension to helical/spiral acquisition is then presented. The lecture ends with a discussion on some of the most recent advances in cone beam reconstruction, including both approximate and exact methods.

Jiang Hsieh is an employee of GE Healthcare Technologies.

Educational Objectives:

1. Learn the fundamentals of x‐ray CT reconstruction.

2. Understand recent advancements in reconstruction algorithms.
WE‐A‐224A‐01: IMRT Modeling Influence On Planning
Authors: Dempsey J
Published: July 2006

The quality of an intensity modulated radiation therapy (IMRT) treatment plan can be strongly influenced by the physical and mathematical models underlying a clinical planning system. This lecture provides an overview of the models that are commonly employed for purposes of treatment planning for megavoltage (MV) photon‐beam IMRT achieved through multi‐leaf collimator (MLC) delivery. IMRT treatment planning models will be examined which include models of: ionizing‐radiation dose computation; fluence‐map optimization; MLC delivery sequence optimization; dosimetric plan evaluation; and “biologic” plan evaluation. Models will be studied with focus on the assumptions, merits, and limitations involved with different models. The differences between reality and the models will be explored. Emphasis will be placed on plan characteristics that exist in reality but are not reflected in the model of the IMRT delivery. The influence of the algorithms employed to implement the models will also be discussed including methods that involve discretization, rounding, and limited numerical precision. Practical examples that demonstrate the influence of modeling differences on IMRT plan quality will be presented.

Educational Objectives:

1. Understand the influence of the choice of physical models employed in clinical IMRT.

2. Understand the assumptions, merits, and limitations involved with different IMRT planning models.

3. Review the conditions where IMRT modeling is suspect and requires careful scrutiny in clinical implementation.