bluuebunny/crossref_metadata_2025_split huggingface dataset:
TH‐D‐224C‐06: An Optimal MLC Quality Assurance Procedure Using EPID
Authors: Mamalui‐Hunter M , Li H , Low D 
Published: July 2006

Purpose: IMRT QA is extremely time consuming and labor intensive, while IMRT delivery is complex. The purpose of this work is to develop an automated and quantitative IMRT QA process utilizing an EPID. One of the aspects of this is testing of MLC leaf position accuracy. The Memorial‐Sloan‐Kettering strip test was modified to provide an automated EPID‐based process.Method and Materials: To provide a baseline fluence map, Kodak XV film was irradiated to obtain an open field 2D beam profile, which was fitted with a Gaussian and used in the image correction routine. We used a strip test consisting of seven adjacent segments with an intentional gap of nominally 0.5 mm. The gap was intentionally varied for the positions located at regularly placed hexagonal regions in order to create a set of calibration curves. A fitting technique using a Lorentzian type function was developed to determine the dose‐peak‐height, dose‐peak‐position and FWHM. Results: The standard deviation of dose‐peak‐height at each abutment for traditional Memorial‐Sloan‐Kettering pattern was of the same order of magnitude as that of the average over the entire image. In contrast, in our pattern a difference of an order of magnitude was observed, which indicated the reducing of cross‐talk effect from adjacent leaves. The leaf positioning error can be identified by using standard calibration curves of dose‐peak‐height vs. gap. The coordinate of dose‐peak‐position is found to be an extremely sensitive indicator of leaf error with sub‐pixel standard deviation. Conclusions: This procedure is able to identify MLC positional errors less than 0.5 mm by using a fitting technique and by reducing the cross‐talk effect. Conflict of Interest: Research sponsored by Varian Corporation.
TH‐D‐ValA‐06: A Novel, Heterogeneity Inclusive, Pencil‐Beam Based Algorithm to Improve Lung IMRT Using the Corvus Planning System
Authors: Romesberg M , Pino R , Rubin R , Denisi J , Nizin P 
Published: July 2006

Purpose: We investigate a new finite‐size pencil‐beam algorithm for calculating absorbed photon dose in heterogeneous media of arbitrarily varying density for inverse planning in CORVUS treatment planning system and evaluate its performance modeling heterogeneous systems and in optimization of an IMRT lung plan. Method and Materials: A new FSPB is developed by extending a phenomenological model (Med. Phys 26:1893–1990, 1999) for the central‐axis absorbed dose in therapeutic photon beams for heterogeneous media. The model's parameters are rescaled based on the density of the medium. A differential equation is introduced to model the interface build‐up processes of CAX primary and scatter dose. Primary dose profiles are calculated using density‐dependent kernel integration, interpolated in the FSPB axis direction and evaluated depending on the density at the point of interest. Scatter dose profiles are computed using scatter integration and evaluated locally. Results: The new heterogeneity inclusive FSPB was implemented in a development version of CORVUS. Original and new FSPB dose calculations were compared with Monte Carlo calculations performed using PEREGRINE. For a heterogeneous semi‐slab phantom and for an IMRT lung plan, the dose distribution generated by the new FSPB agrees well with MC results, while the original one shows substantial discrepancies. IMRT plan optimizations were carried out using both original and new FSPB, and then a final dose calculation was performed using PEREGRINE. The plan calculated using the new FSPB shows better target conformality than the one computed using the original FSPB. Conclusion: The new FSPB possesses greatly improved accuracy as demonstrated in a variety of phantom and patient cases, both for dose calculation and IMRT optimization. FSPB best features were preserved with little extra computational overhead promising accurate and fast inverse planning and real‐time dose sculpting and dose volume histogram manipulation.Research sponsored by North American Scientific, NOMOS Radiation Oncology Division.
TH‐D‐ValA‐07: Clinical Use of Monte Carlo in Proton Therapy: Pencil‐Beam Algorithm Vs Monte Carlo for Proton Therapy of Skull‐Base and Para‐Spinal Tumors
Authors: Paganetti H , Parodi K , Adams J , Kooy H 
Published: July 2006

Introduction: Pencil beam algorithms rely on kernels to model proton range in density‐scaled water equivalent material. Monte Carlo dose calculation methods are more accurate by design. This study addresses the issue of clinical significance of differences between a commercial pencil‐beam algorithm and Monte Carlo dose calculation.Skull‐base or para‐spinal tumors are challenging for dose calculations due to interfaces between high and low density areas in the irradiated volumes. In addition, for para‐spinal cases, there are often metallic implants that not only distort the CT image but also affect the accuracy of dose calculations. Methods: Proton treatment planning is done at our institution by using FOCUS/XiO (CMS Inc.). To do full Monte Carlo based dose calculation the treatment head was modeled including a simulation of the modulator wheel rotation as well as aperture and compensator. The patient CT data information was converted into materials with explicit element composition and density. All secondary particles were tracked.Treatment plans designed with the treatment planning program were recalculated with the Monte Carlo code and compared by analyzing dose distributions and dose volume histograms. Results: In general, we found good agreement. Small differences are in part due to the difference between dose to medium and dose to water. Significant differences were found in and near air cavities as well as in areas affected by high density implants. Conclusion: For some tumors in the head and neck region and near the spine, Monte Carlo based dose calculation shows significant differences compared to pencil‐beam algorithms. Consequently, at our institution, a sub‐set of the patient population receives Monte Carlo dose calculation to assist in treatment planning.
TH‐E‐330A‐07: Evaluation of Scatter Mitigation Strategies for X‐Ray Cone‐Beam CT
Authors: Lasio G , Williamson J 
Published: July 2006

Purpose: Linac‐mounted cone‐beam CT (CBCT) imaging is a promising approach for improving the soft‐tissue targeting accuracy of external‐beam radiotherapy. However, the large proportion of signal due to scattered radiation results in large cupping artifacts and reduced contrast‐to‐noise ratio (CNR), hampering delineation of soft‐tissue structures. The goal of this investigation is evaluate the impact of three scatter mitigation strategies: scatter removal (SR), subtractive scatter corrections (SSC), and anti‐scatter grids (ASG) on CBCT image CNR.Method and Materials: A one‐dimensional model was developed that to predict image noise, intensity, and contrast from the photon flux incident upon the flat‐panel detector. Using previously published scatter‐to‐primary ratio (SPR) data, the impact of Poisson signal statistics, Gaussian readout noise, reconstruction filter, and total air‐kerma on image uniformity, contrast, and CNR was evaluated. Using previously measured CBCT scatter and primary grid transmission; the impact of ASGs, SSR, and SR (e.g., via bowtie filters) was evaluated. In addition, synthetic polyenergetic CBCT projections of cylindrical low‐contrast threshold phantoms, including compound Poisson process noise, were used to evaluate the impact of scatter mitigation on filtered backprojection (FBP) images. Results: Relative to complete SR, typical CBCT scatter reduces CNR by 30%–70% depending on patient diameter. Both 1D analysis and simulated images demonstrate that SSC effectively reduces cupping artifacts but does not improve CNR. ASGs with high scatter selectivity (>5) or large primary transmission (>0.7) modestly increase (20–30%) CNR for thick subjects. However, ASGs diminish CNR for smaller body sections or for exposure levels where additive noise dominates sinogram signal statistics. Conclusion: Correcting CBCT sinograms for scatter radiation is effective in reducing structural image artifacts but does not improve CNR. Antiscatter grids effectively suppress scatter artifacts but improve CNR only in selected clinical settings. This project was supported in part by a grant from Varian Medical Systems.
TH‐E‐224A‐01: Planning and Delivery of Dynamically Modulated Electron Radiotherapy
Authors: Klein E , Vicic M , Ma C , Low D , Li J 
Published: July 2006

Purpose: Evaluate capabilities of modulating electrons using the installed multileaf collimators, computing modulated electron dose distributions using Monte Carlo (MC) and optimizing the dose distributions. Materials and Methods: The modulated electron radiotherapy (MERT) evaluation was conducted with a Varian 120leaf MLC for 6–20 MeV. To provide a sharper penumbra, measurements were conducted with short SSDs (70–85cm). Aperture sizes (AS) ranging from 7–100mm (surface) were configured for measurements and modeling, using BEAMnrc MC code with 109 particles incident on the exit window and DOSXYZnrc for phantom dose calculations. Parameter included: Voxel size 0.2×0.2×0.1cm3, photon and electron transport energy cutoffs 0.01MeV and 0.521MeV, respectively. Verification measurements were performed with film and micro‐ion‐chambers. Calculated and measured data were analyzed in MatLab. Once validation of static fields was successfully completed, modulated portals (segmented and dynamic) were configured for treatment and composed for calculation using DOSXYZ. Results: Beam penumbra sharpness degraded with: decreasing energy and AS; and increasing SSD. PDD decreased significantly with AS. Nearly identical profiles when fluences were delivered by segmental and dynamic MLC sequences. The exception was in the peripheral and bremmstrahlung dose, which was higher in the segmented and dynamic deliveries, respectively. Calculations agreed with measurement within a distance‐to‐agreement of <3mm. With segmented delivery, we found it necessary to introduce small (∼1.5mm) gaps between segments to retain ranges desired in the particular segment's path. The treatment time to deliver 5 segments of 3 energies, was ∼90s, including console reprogramming. Conclusions: This study shows that MERT is feasible and provides conformal electron‐beam dose distributions.Acknowledgement: The primary author thanks Varian for technical support.
TH‐E‐224A‐04: IMRT Film QA in a Heterogeneous Anthropomorphic Phantom
Authors: Ranade M , Lynch B , Li J , Dempsey J 
Published: July 2006

Purpose: To study the agreement of heterogeneous IMRT treatment planning dose calculations with radiochromic film (RCF) and radiographic film (RGF) measured in anthropomorphic heterogeneous phantoms. We intend to use heterogeneous‐phantom film dosimetry to improve IMRT quality assurance (QA). Method and Materials: A commercial heterogeneous anthropomorphic head‐and‐neck phantom, with equivalent tissue bone, soft tissue and air regions was employed for dosimetry verification (CIRS, inc.). High sensitivity EBT radiochromic film (ISP, Inc.) and EDR2 radiographic film (Kodak) were employed simultaneously for film dosimetry. The phantom had 12 axial sections, each 25mm thick, with alignment pins and a compression plate. We selected a plane containing bone, soft tissue and an air gap for IMRT verification. The RCF and RGF were cut to match the selected plane, inserted between the sections and light sealed. A 6MV IMRT head & neck treatment plan with 7 beams was delivered using a commercial linac (Varian Clinac 2100/CD). The RCF was scanned avoiding artifact described in a companion work using a CCD film scanner (Epson 1680 scanner). The dose distributions were compared with the treatment plan. Results: Both RCF and RGF disagree with the treatment plan dose near the air cavities by 15%. Away the air cavities 5% agreement was obtained with RCF. Pronounced artifacts were observed in the RGF that were not observed in the RCF. Conclusion: IMRT dosimetry and quality assurance can be improved by using anthropomorphic phantoms that incorporate realistic heterogeneities such as bone, soft tissue and air gaps, and corrections to dose calculations can be applied. We hypothesize that RGF suffers from Cerenkov in air cavities and in less opaque phantom materials, and this will be investigated in further studies.This work was supported in part by NCI grants R01‐CA‐100636 and N43‐CM‐52214.
TH‐E‐224C‐02: Performance Assessment of a Deterministic Method Incorporating Coupled Photon‐Electron Transport for Photon Beam Dose Calculations On Acquired CT Data
Authors: Wareing T , Failla G , Vassiliev O , Barnett A , McGhee J , Titt U , Horton J , Mourtada F 
Published: July 2006

Purpose: To evaluate the performance of a neutral and charged particle deterministic solution method for external photon beam dose calculations using acquired CT data. Methods and Materials: The Attila® radiation transport code, which solves the differential form of the linear Boltzmann transport equation for neutral particles and the Boltzmann‐Fokker‐Planck transport equation for charged particles, has been adapted for calculating dose distributions from acquired CT images. Comparisons were made with the Monte Carlo code EGSnrc (DOSXYZnrc) for a sample prostate treatment consisting of 8 10×10 cm2 open beams with a realistic 6 MV photon spectrum. The Attila computational mesh consisted of 125,000 arbitrary tetrahedral elements, of approximately uniform size, which encompassed an imaged torso region. CT numbers were mapped to the Attila tetrahedral elements using one of four materials: air, tissue, adipose tissue, and bone, each having four discrete densities. Attila dose was determined at the image resolution by extracting the energy dependent particle flux at each 1×1×2.5 mm3 pixel from Attila's calculated linear discontinuous finite element spatial representation, and multiplying by the energy dependent dose deposition response for that pixel material and density.The DOSXYZnrc calculation used 2.5×2.5×2.5 mm3 voxels, and was run until an average statistical uncertainty of 0.4% was achieved for voxels in the target region. Results: Computational times Attila and DOSXYZnrc were 36 CPU minutes (2.4 GHz Opteron processor) and approximately 8,500 CPU minutes, respectively. Employing a deterministic electron cut‐off below 300 keV reduced the Attila computational time to 22 CPU minutes. Agreement between both codes was excellent in both high and low dose regions, with differences less than 2%/2mm for greater than 95% of points on a 2‐D plane through the entire torso. Conclusions: A general purpose deterministic solver was successfully applied for dose calculations using CT image data.Research funded by NIH grant 1R43 CA105806‐01A1.
TH‐E‐230A‐05: Development of An Integrated Software Platform for Treatment Documentation and Outcome Analysis for IGRT
Authors: Chen G , Schultz C , Li X 
Published: July 2006

Purpose: Information generated in IGRT is tremendous. The long‐term goal of this work is to develop a software package (named RAPID, Research Analysis Platform and IGRT Databases) that is capable of storing patient diagnostic, treatment and follow‐up data for IGRT, which documents treatment outcome, and allows dose‐response analysis based on biophysical models. Presented here are several key components of this development. Method and Materials: The RAPID consists of a database, software tools and auxiliary applications. The database, developed using FileMaker software, includes modules for storing demographics, diagnosis, treatment, and follow up data. Diagnostic and planning images of different modalities (e.g., CT, PET, MR, US) and treatment verification images (e.g., CT, US, radiography) can be stored in DICOM format. Using an integrated auxiliary application these images can be brought into the desktop. The database is integrated with another software package, CERR, developed at Washington University, allowing display of contours and dose distributions on planning images. Various software tools are developed to perform dose response analysis that is linked to documented treatment outcome. For example, treatment related toxicity definitions for a given anatomic site were incorporated into the database, allowing standardized documentation of toxicity which, in turn, facilitates dose‐response analysis. Calculations of EUD, TCP and NTCP are enabled based on 3D dose distributions. Results: The newly developed RAPID is found to be useful. Patient data collected in our clinic for two anatomic sites have been entered into the system. Analysis of treatment and follow‐up toxicity was effectively carried out using the RAPID. With a FileMaker server installed to host the database, users can access password‐protected information remotely.Conclusion: We have developed a software platform, RAPID, to facilitate storage and analysis of IGRT clinical outcome data.
TH‐E‐ValA‐04: IMRT Delivery to a Moving Target by Dynamic MLC Tracking: Delivery for Targets Moving in Two Dimensions in the Beam's‐Eye View
Authors: McQuaid D , Webb S 
Published: July 2006

Purpose: To outline a new modification of the dMLC delivery technique enabling the tracking of a target moving through rigid‐body translations in a 2D loop in the beam's eye view and the accuracy of the delivery versus that of deliveries with no tracking and of 1D tracking techniques with patient intensity‐modulated beams (IMB) is quantified.Method and Materials: Leaf trajectories calculated in the target reference frame were iteratively synchronized assuming regular target motion. This allowed the leaves defined in the lab reference frame to simultaneously follow the target motion and to deliver the required IMB without violation of the leaf maximum‐velocity constraint. The leaves are synchronized until the gradient of the leaf position at every instant is less than a calculated maximum. The delivered fluence in the target reference frame was calculated with a simple primary‐fluence model. The new 2D tracking technique was compared with the delivered fluence produced by no‐tracking deliveries and by 1D tracking deliveries for 33 clinical IMBs. Results: The RMS difference between the desired and the delivered IMB was 15.4±3.3 MU for the case of a no‐tracking delivery; 10.9±2.3 MU for the case where one component of motion was corrected and 6.8±1.6 MU for the 2D tracking delivery. The residual error is due to interpolation and sampling effects. The 2D tracking delivery technique requires an increase in the delivery time evaluated as between 0 and 50% of the unsynchronized delivery time for each beam with a mean increase of 13% for the IMBs tested. Conclusion: The 2D tracking dMLC delivery technique allows optimized IMBs to be delivered to moving targets with increased accuracy and with acceptable increases in delivery time. When combined with realtime knowledge of the target motion at delivery time this technique facilitates improved target conformity relative to no‐tracking deliveries and allows margin reduction.
Sci‐Thur PM Therapy‐02: Accounting for the off‐axis detector response for improved a‐Si EPID dosimetry
Authors: McCurdy BMC , Rickey DW , Malkoske KE 
Published: July 2006

In portal imaging applications using an a‐Si electronic portal imaging device (EPID), a calibration procedure must be performed before clinical images may be acquired. This calibration procedure incorporates a dark‐field image acquisition and a flood‐field image acquisition. Every clinical image is corrected by subtraction of the dark field image and then division by the flood‐field image. The flood‐field image exhibits two main features, the pixel‐to‐pixel sensitivity (present due to inherent limitations in the manufacturing process), and the beam profile shape as measured by the detector (a function of off‐axis distance, ie. energy spectra and incident fluence). While it is necessary to correct for the pixel‐to‐pixel sensitivity, the beam profile shape as measured by the detector is also removed by this process, which is undesirable for dosimetric applications. This work develops an approach which allows for the pixel‐to‐pixel sensitivity correction to be made, while still preserving the inherent response of the detector to the incident beam.The approach consists of directly measuring the beam profile shape independently from the pixel‐to‐pixel sensitivity. This profile information may then be reintroduced into the clinical image. The beam profile measurement is achieved by building a small “point” detector using materials that are analogous to the clinical EPID. The point detector is scanned in two dimensions across the open radiation flood‐field at the same source‐to‐detector distance used for clinical flood‐field acquisition. Clinical images are then multiplied by this acquired 2D profile (normalized to central axis) to reintroduce the beam profile shape.
Sci‐Thur PM Therapy‐05: Evaluation of male pelvic phantom for megavoltage cone‐beam computed tomography
Authors: Schaly B , Varchena V , Au P , Pang G 
Published: July 2006

Computed tomography (CT)‐based image guidance has the feature of including the tumour as well as normal tissue in the image localization process during radiation treatment. We propose to use a new anthropomorphic male pelvic phantom (CIRS Inc.) to test the feasibility of using a linear‐accelerator‐based megavoltage (MV) cone‐beam CT system for imaging the prostate. The objective of this work is to verify the tissue‐equivalency of the phantom to determine whether it is representative of prostate cancer patients. We evaluated the phantom in two ways. (1) The linear attenuation coefficient was determined by measuring the photon transmission through uniform samples of the phantom materials (e.g., prostate, muscle, bladder, etc.) using (2) The phantom material CT numbers (kVCT) were compared to CT number data acquired from randomly selected planning CT scans of prostate cancer patients at our institution. The measured linear attenuation coefficients agreed to ∼ 1% of the manufacturer's specifications, while the reproducibility of the measurement was ∼ 1%. The kVCT numbers in the phantom were also in good agreement with the manufacturer's specifications and the patient data. However, the bony structures are comprised of solid average bone equivalent material (cortical and trabecular bone), which caused artifacts within some regions of the kVCT images. However, MVCT imaging is expected to suppress these artifacts. These findings indicate that the phantom is representative of prostate cancer patients and will be a valuable tool in investigating the feasibility of MV cone‐beam CT.This work was partially supported by Siemens Medical Solution USA, Inc.