bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐76: Analysis of a Novel Method of IMRT QA Using EPID‐Acquired QA Planes
Authors: Rasmussen K , Nelms B , Tome W
Published: July 2007

Purpose: To assess the efficacy and quantify the accuracy of a novel method for IMRT QA in which the measured dose plane is derived from an EPID image. Method and Materials: aSi EPID data was acquired and converted using a novel method based on a machine‐specific beam model to estimate QA dose planes from mega voltage (MV) EPID images. Dose planes were calculated in a homogeneous, water‐equivalent QA phantom using the model and an acquired MV EPID image with no additional buildup required on the EPID.

Specific parameters, such as field size output dependency, dose redistribution kernel, potential off‐axis corrections and absolute dose calibration, were measured to create the model that is based on the raw EPID files.

QA dose planes were compared to ion chamber measurements, MapCHECK® measurements, and planar fluences generated by ADAC Pinnacle3® TPS. MapCHECK® and ion chamber (IC) measurements were taken at multiple depths at a source to detector distance (SDD) of 100cm. Dose planes in homogenous media were estimated using EPID images acquired at a distance of 140cm SDD. Data was collected for both 6 MV and 10 MV energies to determine the accuracy of the model for these two energies. Results: Preliminary sample analysis demonstrates that the dose planes estimated by the model using EPID images of complex IMRT fields result in >98% pass rate of all point measurements from MapCHECK®, employing a 3% dose or a 2mm distance to agreement criterion. Agreement between MapCHECK® and IC measurements were within 1%. Conclusion: This novel method shows promise as a tool for IMRT QA with reasonable accuracy. Setup, acquisition and analysis can be performed in a more time efficient manner than is possible with current methods of IMRT QA. Conflict of Interest: This work was partially funded by Sun‐Nuclear Co.® and Canis Lupus LLC.
SU‐FF‐T‐78: Analysis of Setup Accuracy for Invasive Frame‐Based Stereotatic Radiosurgery (SRS) Patients Using Cone Beam Computed Tomography (CBCT)
Authors: Chang J , O'Meara W , Yamada Y , Amols H
Published: July 2007

Purpose: To evaluate the setup accuracy of invasive frame‐based stereotactic radiosurgery (SRS) patients using cone‐beam computed tomography (CBCT). Method and Materials: Each patient participating in this institutional‐approved prospective protocol was immobilized with a Brown‐Roberts‐Wells (BRW) frame and scanned on a CT simulator for treatment planning (2mm slice thickness). The patient was transferred to the treatment room and setup to the BRW coordinates of the planning isocenter. Before treatment was delivered, the patient was CBCT scanned with the CT localizer attached to the BRW frame. A CBCT scan of a BB at the treatment isocenter was also acquired to evaluate the apparatus accuracy of the BRW frame system. Systematic shifts between CBCT and treatment isocenters were measured independently from an orthogonal pair of projection images of a BB at the treatment isocenter, and were used to identify the treatment isocenter in the patient CBCT scan. BRW coordinates of the treatment isocenter of the patient scan were compared with the planning BRW coordinates to evaluate the localization accuracy. The patient CBCT scan was then co‐registered with simulation CT to determine the setup accuracy. Results: Three patients were successfully recruited to date. The average apparatus accuracy (Euclidean distance between the BRW coordinates of the planning isocenter and the BB) was 0.46±0.39 mm (mean ± one standard deviation). The average localization accuracy was 0.88±0.18 mm. The total setup accuracy of the invasive SRS frame was 1.63±1.39 mm with major sources of error in the superior‐inferior (0.43±2.18 mm) and anterior‐posterior (0.33±0.79 mm) directions. Conclusion: The apparatus error generated by the BRW frame system was comparable to earlier reports. Although the localization accuracy for patient treatment was slightly worse, significant setup errors were observed due to patient sag. Volumetric CBCT scan was therefore recommended even for invasive frame‐based SRS to correct this problem.
SU‐FF‐T‐79: Analysis of the Virtual Wedge Implementation by the AAA Algorithm in the Varian Eclipse TPS
Authors: Both S , Bieda M , Dimofte A , Zhu T
Published: July 2007

Purpose: To evaluate accuracy of VW implementation by the Varian Eclipse AAA Calculation Algorithm Material and Methods: A 6MV Siemens Oncor Linac beam was used to deliver symmetric and asymmetric VW (15, 30, 45, 60) profiles for a range of field sizes (5×5cm2 to 15×15cm2). All measurements were performed in absolute dose mode using a 2D diode array (Mapcheck, SunNuclear FL), at 100cm SAD and depth of 5cm under water equivalent conditions.

The Varian Eclipse TPS software v.8, AAA calculation algorithm was used to determine the VW fluence maps in a water equivalent phantom. All measured and calculated Linac central axis values were analyzed. A relative and absolute comparison was conducted for all calculated and measured fluence maps using the Mapcheck Software v.3.01.08.00. Theoretical calculations of the VW factors were performed and compared with the ones calculated based one measured data. The measured output factors were compared with the calculated ones using our PennMU software and the Eclipse TPS AAA calculation algorithm. Results and discussions: All measured and theoretical symmetric VW wedge factors and output factors were in agreement. Differences up to 82% were found for asymmetric VW output comparison between the Eclipse AAA algorithm calculated output factors and the measured ones. The differences increase with the degree of asymmetry of the field and the VW angle. The data analysis suggest that the Eclipse AAA TPS defines the wedge factor to the central axis of the beam rather then to the central of the machine (VW factor definition). The relative fluence map analysis showed that over 95% of the VW measured profile are within 3%/3mm (%Diff/DTA). Conclusion: We found that the VW clinical implementation for the Eclipse TPS AAA algorithm, v.8, is valid for symmetric fields only and large errors can result for asymmetrical fields.
SU‐FF‐T‐80: Analytical and Monte‐Carlo (GEANT4) Calculations of Collimator Scatter of Proton Beams
Authors: Ulmer W , Schaffner B
Published: July 2007

Purpose: Collimator scatter of proton beams is being implemented in the proton dose model in ECLIPSE (Varian). Due to the energy loss and angular scatter distributions at the collimator walls (brass) the spectrum of scatter protons is rather intricate. This contribution is significant for the ‘horns’ of transverse profiles verified in the initial plateau of Bragg curves. Using an analytical integration procedure of Bethe‐Bloch equation and its application to the Molière multiple scatter model the calculated contributions are compared with measured data and Monte‐Carlo calculations (GEANT4). The production of secondary protons and radiation effects is determined by an integration of the inelastic cross‐section of the corresponding wall material over the energy. Method and Materials: Monte‐Carlo calculations have been carried out with GEANT4. Measurement data of transverse profiles and Bragg curves have been made available by the Harvard cyclotron and the proton center of MD Anderson (Houston). Results: Material properties and collimator length have an influence to the beam‐line (energy spectrum, fluence, angular distribution). Since the collimator edge act as further proton source, the distance to the water tank significantly affects the Bragg curves of small field sizes (from 0.5 × 0.5 cm2 to 2 × 2 cm2). For larger field sizes the collimator scatter leads to ‘horns’ in the transverse profiles and to a buildup effect in the initial plateau of Bragg curves. Conclusion: Monte‐Carlo and analytical calculations are in good agreement with measurement data. A practical impact is also application of proton beams to the stereotactic radiotherapy. Conflict of Interest: Varian Medical Systems.
SU‐FF‐T‐82: Angular Distribution of Photon Energy Spectra Emitted by Low‐Energy Interstitial Brachytherapy Sources
Authors: Chen Z , Khan S , Nath R
Published: July 2007

Purpose: The cylindrical geometry associated with the current low‐energy interstitial brachytherapy sources is known to produce lesser dose near the ends of each source that are 1) highly dependent on source construction and 2) potentially harmful to a successful brachytherapy treatment. The aim of this work was to establish an experimental technique for quantitative determination of the angular variation of photon energy spectra emitted by the low‐energy sources. Method and Materials: A high‐purity Germanium detector designed for low‐energy photon spectrometry was used to measure the energy spectra emitted by brachytherapy sources. A remote‐controlled source holder was constructed to hold the source at a desired source‐to‐detector distance with minimum disturbance to the emitted photons and to precisely rotate the source around a radial axis in the source's bisector. Two source models, one constructed with traditional titanium encapsulation and the other with a novel polymer encapsulation were used to test the experimental setup and to study the dependence of angular spectra distribution on source construction. Results: Larger than 40% reduction in photon fluence was observed near the ends of both source models relative to the fluence emitted along the radial direction in their bisectors. The use of polymer encapsulation resulted in minimal encapsulation‐induced spectral hardening to the photons emitted by bare . It also resulted in improved spatial isotropy of the emitted photon fluence as compared to the titanium encapsulation. Additional variations in angular fluence distribution that were linked to specific source construction features were also observed. Conclusions: The angular distribution of photon energy spectra emitted by low‐energy brachytherapy sources can be measured with high accuracy (better than 4%) using a high‐resolution photon spectrometer. This complete spectral information is needed for accurate determination of dose distribution around each source and for optimizing the source design to reduce fluence anisotropy.
SU‐FF‐T‐83: Application of a New Taxonomy for Radiotherapy Error Reporting and Results of a Five‐Year Review
Authors: Bissonnette J‐P , Medlam G
Published: July 2007

Purpose: We present a framework to accrue and analyze and report on radiation therapy errors and near‐miss events, from decision to treat to final treatment. A systematic and quantitative analysis of this data has provided insights for the identification of program areas requiring attention and for the allocation of limited resources for quality assurance and error elimination initiatives in a large clinic. Method and Materials: All reported radiation therapy incidents and near‐miss events from 2001 to 2006 were analyzed, under a research ethics board approval. Each report was staged according to the type (prescription or geometry), cause (location, documentation, non‐compliance, laterality, prescribed change, human error, planning/dosimetry, software/hardware malfunction, accessory), and clinical impact (none, minor, moderate, severe). Furthermore, each report identified what stage of a generalized radiation therapy process (booking, scanning, planning, review, and treatment) the incident or near‐miss event occurred. Results: 863 incident and near‐miss reports were analyzed. The average error rate over five years was stable at 1.8±0.4%, with a majority of errors related to prescription issues. An average of 0.66 severe error per year was observed. Over the course of five years and several technological changes, the occurrence of events due to accessories (wedges, immobilization), prescribed changes to treatment parameters, non‐compliance to treatment protocols, and location have decreased, while documentation events have risen. The proportion of incidents is highest at the planning and treatment stages, with these with highest impact occurring at the latter stage. Conclusion: The incident rate at our clinic has remained low and stable at our clinic over several technological and process changes. The framework has allowed the assessment of trends in radiation therapy treatment incidents in a clinic that has undergone significant changes in technology and processes, including image‐guidance and IMRT, over the course of five years and has identified new risk factors.
SU‐FF‐T‐84: Application of GAFCHROMIC® EBT Film for in Vivo Dosimetry with Total Body Irradiation (TBI) Radiotherapy
Authors: Su F , Shi C , Stathakis S , Papanikolaou N
Published: July 2007

Purpose: To demonstrate the viability of GAFCHROMIC® EBT film as an in vivo, dosimeter for total body irradiation (TBI) procedures. Method and Materials: Dosimetry results are reported for six anatomical regions (i.e. head, shoulder, chest, umbilicus, hip and thigh) on an anthropomorphic phantom irradiated using a standard procedure of lateral TBI technique in our facility. The films and thermoluminescence dosimeters (TLD) were taped to the phantom with adequate bolus to ensure that the dosimeters were at a depth of electronic equilibrium. To establish the film calibration curve, film samples (2.5 × 1.5 cm2 in size) were placed at the isocenter of the accelerator (SAD=100 cm) at depth of 10cm in a water equivalent solid phantom. The GAFCHROMIC® EBT films were exposed to doses from 0 to 400 cGy (with 50 cGy increment) using a 20 × 20 cm2 field size. The films were scanned with the Vidar VXR‐16 scanner and analyzed with Image J software. Results: The results indicated that the measured doses at all points as obtained by the GAFCHROMIC® EBT films are in good agreement with the prescribed doses, varying from −3.15% to 1.46%. The comparison of the GAFCHROMIC® EBT dosimetry against the TLD analysis showed a similar agreement (variance from −4.08% to 0.55%). Conclusions: GAFCHROMIC® EBT film is a viable dosimetry tool providing comparable results as those obtained using TLDs. The elimination of the film processor that usually introduces uncertainties, the almost water equivalent density, the water resistance, and insensitivity to room light are some of the advantages of the EBT films, which make the films easier to handle and a good candidate for in vivo dosimetry in TBI and possibly other radiotherapy applications.
SU‐FF‐T‐85: Assessing the Reliability of Film and Semiconductor Detector in Measurement of Central Axis Depth Dose of Electron Beams
Authors: Piriyasang D
Published: July 2007

Purpose: To investigate the possibility of using the Kodak X‐Omat V film for the central axis depth‐dose measurements of electron beams.

Method and materials: The X‐Omat V films were exposed in a MED‐TEC film phantom cassette with parallel orientation to produce central axis depth dose curves. These film data were compared with the measured percentage depth dose curves by using a Scanditronix scanning water phantom with both RK ion chamber and electron diode. Measurements were made at a source to surface distance (SSD) of 100 cm for the electron energies between 6 and 20 MeV on a Varian Clinac 2100C linear accelerator for field sizes of 6 × 6 cm2 to 20 × 20 cm2. Results: The comparison of the central axis depth dose parameters, R100, R90, R50, and RP measured by the film and diode with respect to the IC's values showed that the difference did not indicate the dependence either on the energy or cone size. In the buildup region, the film presented higher percent depth dose values for most energies and cone sizes but beyond the depth of maximum dose (R100), the results were opposite. The difference of every parameter for both film and diode was within the acceptable value of ±2 mm. Conclusions: The ionization chamber and diode measurements appear to be more reliable than the film measurements, but film is particularly useful for new electron cutout data where access to accelerator beam time is limited.
SU‐FF‐T‐87: Attenuation Due to Bronchial Stents in 192Ir HDR Brachytherapy
Authors: Mota H , Austerlitz C , Gay H , Allison R , Bonnerup C , Downie G , Sibata C
Published: July 2007

Purpose: Evaluate the radiation attenuation from bronchial stents during endobronchial HDR brachytherapy. Materials and Methods: The radiation attenuation of several commercially available bronchial stents was analyzed with an ionization chamber. The stents were divided into three groups: Nitinol mesh (0.5 mm thickness), polyester mesh with silicone coating (1.0 mm thickness); and solid silicone (1.5 mm thickness). A solid cerrobend cube with 9 cm sides was molded into an irradiation cell to produce a collimated beam. The cube had a 4 mm diameter hollow cylindrical shaft in its center for inserting the HDR catheter. A pyramidal shaped opening perpendicular to the axis of the cylindrical shaft served as primary collimator with 1.5 × 1.5 cm aperture. A secondary collimator with 3 × 3 cm aperture was positioned 12 cm from the source. The distance from the source to the center of the ionization chamber was 20 cm. The field size at the chamber position was 5 × 5 cm. The stents were cut longitudinally so that each could be mounted flat on the secondary collimator. The field size at the SDD was verified with Gafchromic film. The attenuation of the radiation beam was evaluated by taking the ratio between the air kerma rate at the SDD with and without the stent. Results: The Nitinol stent attenuated the beam by 0.8%, the polyester/silicone by 2.8%, and the silicone 3.3%. Conclusions: The attenuation due to bronchial stents has been measured and can be accounted for since it can be as high as 3.3%. Whether this correction is clinically relevant should be evaluated. Moreover the stent thickness can serves as spacer to help reduce the dose on the bronchial surface for as much as 20%, as determined by Monte Carlo calculation in previous publication.
SU‐FF‐T‐89: Automated “prostate‐Only” Registration of CT/MR Images for Post‐Implant Dosimetric Assessment of Permanent Seed Brachytherapy
Authors: Sloboda R
Published: July 2007

Purpose: To determine the ability of a normalized mutual information (NMI) algorithm to perform automated “prostate only” rigid‐body registration of CT/MR prostate images for I‐125 seed post‐implant dosimetric assessment. Method and Materials: CT/MR image volumes for three patients were obtained approximately 4 weeks post‐implant. CT data were acquired using a non‐helical scan with 3.0 mm slice thickness and ∼0.3 mm pixel pitch. MR data at 1.5T were obtained using two pulse sequences: T2‐weighted with TE/TR=91/4748 ms, and balanced fast‐field echo (B‐FFE) with TE/TR=9.6/4.8 ms. A surface coil (Sense Cardiac) was used to acquire axial slices 3 mm thick with no gap having a pixel pitch of ∼0.3 mm. NMI‐based registration was performed using the MatchLab module in the Analyze 7.0 software package, which affords control of an extensive range of registration parameters. These parameters were varied systematically to determine their influence on registration accuracy. Results: Automated “prostate only” registration of T2‐weighted MR images with CT was unsuccessful. For B‐FFE‐weighted MR, registration to sub‐millimeter accuracy transaxially and millimeter accuracy in the scan direction was achieved for all three patients using a common set of registration parameters. These parameters served to define a box‐shaped registration volume containing mostly prostate, eliminate CT intensities below −100HU, sample 6400 points per image slice, create 8‐level individual and joint entropy histograms, and specify a transformation search strategy. Analysis of additional clinical data is ongoing. Conclusion: Automated “prostate only” registration of CT/MR images of the implanted prostate to sub‐millimeter accuracy transaxially and millimeter accuracy in the scan direction is feasible. Achieving this level of accuracy requires appropriate and sufficient information content in the MR images (which a B‐FFE sequence can provide), pre‐selection of imaging data containing the most relevant information, and specification of appropriate NMI algorithm search parameters.
SU‐FF‐T‐90: Automated Computer Optimization for 3D Treatment Planning of Breast Irradiation
Authors: Chen G , Ahunbay E , Li X
Published: July 2007

Purpose: The conventional manual trial and error method (MTEM)for generating 3DCRT dosimetry plans for breast irradiation is time consuming and labor intensive, and does not always lead to an optimal plan. The purpose of this work is to develop an automated optimization tool to eliminate MTEM. Method and Materials: A software package with GUI was developed with Matlab to interface with a commercial planning system (XiO, CMS). The package is capable of (1) accepting inputs of structure contours, prescription, 3D dose maps for each of 16 possible beams (two beam angles, two beam energies, open and 60 degree wedge with anterior, superior and inferior wedge orientations) from XiO, (2) optimizing beam weights to achieve uniform target dose and dose‐volume constraints for critical structures, and (3) outputting optimized beam weights into XiO for final dose calculation. The dose distributions and dose volume histograms generated with the package for five representative whole‐breast irradiation cases are compared with those generated from MTEM by experienced dosimetrists. Results: All plans generated by the automated optimization package are equal to or better than those generated by MTEM in terms of their target dose uniformity and normal tissue sparing. Ratio of the uniformity index for the optimization plan and that for the manual plan ranged from 1.0 to 1.04. The average time for the optimization is approximately 15 minutes on a Pentium‐4 3 GHz CPU. The entire process for generating a plan with the automated optimization is about four times faster than MTEM with an experienced dosimetrist. Conclusion: A computer automated package that is capable of generating optimized 3DCRT dosimetry plan for breast irradiation is developed. It can generate plans equal to or better than those generated with MTEM but with significantly reduced time and effort. The optimization package is being implemented in the clinic.
SU‐FF‐T‐92: Automating Treatment Planning System QA
Authors: Kirk M , Gong X , Chu J
Published: July 2007

Purpose: To develop software which both increases the comprehensiveness of the AAPM recommended treatment planning system (TPS) quality assurance and decreases the time required to complete it. Method: The AAPM Task Group Report ♯40 recommends a monthly check of the “checksum” or a constancy check of monitor unit (MU) calculations for a subset of all possible beam configurations. An in‐house, Interactive Data Language (IDL) based software program was developed to perform the TPS QA. The program was designed to interface with the Pinnacle TPS to automate these tests. First, a Pinnacle script was developed to calculate a comprehensive set of beams configurations belonging to commissioned machines. After computation the 2×2×2 mm grid for each beam is automatically exported and saved. Second, the IDL software imports this dose grid and compares it on a voxel‐by‐voxel basis to the dose grid created after commissioning. Any nonzero deviation would direct the physicist to the specific beam parameters to check. Results: For each energy of each machine, the program exports a list of baseline, calculated and their percent difference for various field size and beam modifier combinations. The program is quite sensitive to beam data modification. A slight modification such as 1% change in MU or a 1mm shift in isocenter from their baseline configuration produced an identifiable change in the sum of the dose grid. Conclusions: Our in‐house software successfully automates the TPS QA process. It maximizes the benefit‐vs‐cost ratio by providing a highly sensitive constancy check of the TPS beam data while minimizing physicist involvement.
SU‐FF‐T‐93: Beam Characterization of the Equinox Cobalt‐60 Treatment Unit
Authors: Angers C , Cygler J
Published: July 2007

Purpose: Beam penumbra, symmetry, flatness and surface dose have been measured for the Equinox cobalt‐60 external beam therapy system using both source to surface distance (SSD) and source to axes distance (SAD) setups. Method and Materials: All data were measured using a 100 cm Equinox teletherapy unit manufactured by MDS Nordion. This newly designed unit features asymmetric jaw capability and has a source to diaphragm distance of 50 cm. The unit was installed with a 2.0 cm diameter C‐146 source. Beam data were measured using a Scanidtronix / Wellhofer Blue Phantom water tank equipped with a p‐type Silicon detector (PFD3G) or a CC13 ion chamber. OmniPro Accept software, version 6.2, was used to manipulate the data and to calculate penumbra, flatness and symmetry according to IEC 976 definitions. Surface dose measurements were independently confirmed with GafChromic film and MOSFETs. Results: Percent depth dose measurements were compared to BJR Supplement 25 data with good agreement for field sizes up to 12×12 cm and reasonable agreement for larger field sizes and depths. Relative surface dose measurements indicated that the IEC 60601‐2‐11 criteria of 90% for the maximum field size may be exceeded when an 80 cm SSD setup is used. Beam flatness, symmetry and penumbra parameters have changed little from previously manufactured units and are reported for square field sizes ranging from 1 cm to 40 cm. Conclusion: This investigation demonstrates that the beam characteristics of the Equinox unit do not differ significantly from previous units. In order to reduce surface dose to IEC stated levels; it is recommended that an electron filter be utilized on the 80 cm machine for field sizes exceeding 900 square cm. Conflict of Interest: MDS Nordion provided financial support for this project.
SU‐FF‐T‐94: Benchmark Measurements in Heterogeneous Phantoms Under Conditions of Electronic Disequilibrium
Authors: Pillai S , Solberg TD , Medin PM , Chetty IJ
Published: July 2007

Purpose: To perform systematic measurements of photon beam characteristics under conditions of electronic disequilibrium for the purpose of benchmarking dose algorithms. Method and Materials: Slab phantoms consisted of styrofoam (ρ=0.03g/cm3), lung‐equivalent (ρ=0.21g/cm3), and bone‐equivalent (ρ=1.7g/cm3) materials, embedded within solid water. Ion chambers with active volumes of 0.125cm3 and 0.015cm3 and EDR2 film were used to measure depth dose and off‐axis photon beam characteristics within several phantom geometries. Experiments were conducted for field sizes from 2×2 to 25×25cm, for 6 and 23MV photon beams produced from a Siemens accelerator. Results: In the styrofoam phantom, the average agreement between the two ion chambers was within 2% for both energies with maximum differences of 9% observed in the sharp dose falloff region for small field sizes due to chamber volume effects. The 0.125cm3 chamber over‐estimated dose in the sharp falloff regions within the low density heterogeneities at the smallest field sizes, due to increased volume averaging. Relative dose film measurements demonstrated sharper penumbral gradients than ion chambers. Dose reduction in the lower density phantoms was enhanced with reduced material density and field size, and increased beam energy. Depth dose calculations differed by up to 20% and 10% versus measurements in the lung phantom for the 6 and 23MV beams, respectively. These discrepancies were partly attributed to a poorer fitting beam model for 23MV photons. Calculations were on average within 4% of measurements in the bone phantom for the 6MV beam, but larger differences (∼ 12%) were found for 23MV photons, likely due to increased pair production at this energy. Point dose calculations differed from measurements in a lung/tumor phantom by 6% for 3×3cm, 6MV photons. Conclusion: Measurements under conditions of electronic disequilibrium are confounded by many factors and must be performed with utmost care for algorithmic verification at the ±2% level.

Acknowledgement: NIH/NCI‐R01CA106770.
SU‐FF‐T‐97: Characterization of Amorphous Silicon Flat Panel Imager for Dose Measurements
Authors: Szabo J , Khan R , Ostapiak O
Published: July 2007

Purpose: The major objective of the work was to categorize the dosimetric response of a Varian aS500 type Electronic Portal Imaging Device (EPID) for dose measurements. Method and Materials: For a 6MV beam from a Varian 21EX linear accelerator, reproducibility of EPID pixel response, dose rate effect, and cumulative dose linearity were studied. In addition, scatter characteristics and depth doses were also determined using the EPID. A Capintec ion chamber in a polystyrene miniphantom and a Wellhöfer water phantom were used for comparative measurements. Results: The EPID response was found to be independent of dose rates from 100 MU/min to 600 MU/min at larger source to detector distances. However, pixel saturation was observed for dose rates beyond 300 MU/min with the EPID placed at the isocentre. Raw pixel response was reproducible to within 2 % when measured over a period of 6 weeks. Changes in scatter conditions with field size were also measured for the EPID. The EPID scatter was found to be in between 5 to 10 cm of a full water phantom. The gray scale response is linear with the dose to the portal imager. The validity of inverse square relationship was also tested to be within 0.5%, for the EPID at various distances from the source. Conclusions: The depth dose data measured with EPID showed good correspondence with that measured with a thimble type ionization chamber in a water phantom. Compared to ionization chamber data, open beam profiles measured with EPID show flat response in high dose region, rapid fall‐off in high dose gradients (> 30%/cm), and higher penumbra tail. The agreement with the ion chamber measurements could be improved if the flood field correction is performed to restore off‐axis variation of beam profile. In general the EPID qualifies as a useful tool for planar dose measurements.
SU‐FF‐T‐100: Characterization of the Elekta Stereotactic Body Frame (SBF) for Use in SBRT Planning
Authors: Becker S , Jozsef G , De Wyngaert J
Published: July 2007

Purpose: To measure the attenuation of the Elekta Stereotactic Body Frame (SBF) for use in stereotactic body radiotherapy (SBRT) and compare the values to those predicted by the Eclipse treatment planning system (TPS). Depending on the angles of delivery, treatment beams transverse varying thicknesses and densities of the frame. This leads to differential attenuation depending on beam angles. Method and Materials: The frame was first tested by measuring attenuation of a 6MV beam delivered over various gantry angles. An ion chamber was positioned in the center of the frame at isocenter. The dose was measured for various gantry angles, which were compared to the anterior beam (gantry 0°). In order to test the ability of Eclipse TPS to properly account for the frame, a solid homogeneous phantom was placed in the frame and then imaged with a CT scanner. Two plans were generated; one with the frame included in the external “Body” contour and one without. The plans were adjusted to deliver the same MUs. The phantom was then treated and the dose was measured at the isocenter. The measured doses were then compared to the two calculated plans. Results: The attenuation of the frame was found to be a function of the beam entry point and ranged from 4 to 9%. When the frame and phantom were contoured in Eclipse, the calculated MUs for each field agreed to within 2% of the measured dose. Conclusion: The Elekta SBF attenuates the radiation beam and must be accounted for in planning. This can be accomplished in the Eclipse TPS by including the frame in the “Body” contouring. If the frame is not taken into account, it will result in an underdose of approximately 5% for each lateral and posterior field, ranging from 4 to 9%.
SU‐FF‐T‐101: Characterizing Output for a Static TomoTherapy Field
Authors: Gibbons J , Smith K , Hesston R
Published: July 2007

Purpose: To determine in‐air and in‐phantom output factors for a static TomoTherapy beam. Method and Materials: Measurements and computer simulations of in‐air output ratios (Sc) and in‐phantom output factors (Scp) have been made for a static TomoTherapy beam. In‐air measurements were made at a depth of 10 cm in a commercial mini‐phantom for field widths ranging from 1.8 cm to 40 cm, for 2.5‐cm and 5.0‐cm jaw selections. Measurements were made at source‐chamber distances (SCDs) of 85 cm and 105 cm. In‐phantom measurements were made at a depth of 10 cm in a full size virtual water phantom for the same field sizes and at an SCD of 85 cm. Data were normalized to the values for the largest available field size (40 × 5 cm2). Both in‐air and in‐phantom measurements were compared with simulations made on the TomoTherapy planning system using simulated CT datasets of the full size and mini‐phantoms. Results: In general, measured and simulated data agreed within 2% for the output factors determined in this work. Measured and simulated Scps varied steeply (∼ 15%) for the field sizes investigated. In contrast, Scs showed little changes with field size or SCD, although the measured data demonstrated a slightly greater variation with field size than the simulated results. Results were consistent between data taken for different jaw selections, with the best agreement observed for the determined phantom scatter factors, Sp. Conclusion: The lack of a flattening filter in the TomoTherapy beam explains the small variation of Sc with field size and SCD. Thus, Scp is due primarily to phantom scatter, which should not vary greatly between TomoTherapy machines. The determination of output factors may be used in the verification of treatment planning doses, both for helical and static deliveries.

Supported in part by a research agreement with TomoTherapy, Inc.
SU‐FF‐T‐102: Clinical Beam Tuning of Low‐Energy Electron Beams: Matching Varian and Siemens Linear Accelerators
Authors: O'Daniel J , Kudchadker R , Zullo J , Gillin M
Published: July 2007

Purpose: Tuning nominal energies on linear accelerators is useful for matching machines of different vendors and for altering energies to match clinical needs. In this study we investigated matching a Varian 2100EX 4MeV electron beam to a Siemens Primus 5MeV electron beam. Method and Materials: The 4MeV beam of a Varian 2100EX linear accelerator was tuned via a significant shunt‐voltage adjustment to match the 5MeV beam of a Siemens Primus linear accelerator. The percent depth‐depth dose (PDD) curves and off‐axis profiles for multiple field sizes were compared to validate the beam matching. Data was collected with a CC04 cylindrical chamber in water and with a parallel‐plate ion chamber in plastic water® (Computer Imaging Reference Systems, Inc., Norfolk, VA). Results: The PDD from the parallel‐plate and cylindrical ion chambers agreed within 1.1% and 2.5% for the 3×3cm2 and 10×10cm2 fields respectively. There was also good agreement in the PDD of the tuned 4MeV (referred to as 4MeV* post‐tuning) and 5MeV beams. The depth of Dmax was identical. Differences in the practical range were only 1mm. The PDD had the best agreement for the 3×3cm2 field (⩽1.5% to depth of D90), followed by the 10×10cm2 field (⩽2.0% to depth of D90) and the 25×25cm2 field (⩽2.5% to depth of D90). Larger disagreements occurred in the dose falloff region beyond D90, typically 2–7%. The off‐axis profiles for the 4MeV* and 5MeV beams showed good agreement for the 10×10cm2 field (⩽2%). However, there was a substantial loss in flatness for the 25×25cm2 field (5.5% for 4MeV*, 2.4% for 5MeV). We believe these differences are caused by the original 4MeV Varian scattering foil, which was not changed to reflect the greater energy of the 4MeV* beam. Conclusion: The Varian 4MeV and Siemens 5MeV beams were successfully matched, allowing oncologists to utilize these machines interchangeably.
SU‐FF‐T‐104: Clinical Field Matching Using Intraoperative 90‐Y Brachytherapy Plaques
Authors: Folkert M , Mauceri T , Hollows M , Chen G
Published: July 2007

Purpose: A foil in a semi‐cylindrical polycarbonate plaque has been developed and used to intraoperatively irradiate the dura for sarcomas of the spine in 16 patients. As smaller plaques are easier to place in restricted surgical fields, an investigation of field matching requirements was undertaken to evaluate the possibility of multiple site irradiations using small plaques. Method and Materials: Using a brachytherapy treatment plaque and a cylindrical dosimetry phantom with the same radius, irradiations were performed using radiochromic film (GafChromic HS). 2 Gy was delivered, and the plaque was then moved to a position that would abut (0 mm) or overlap (1.5 mm, 3.0 mm, 4.5 mm, or 6.0 mm) with the previous plaque placement and an additional 2 Gy was delivered. Simulated field matching irradiations based on the plaque dose profile were also generated for 0 to 5 mm overlaps in 1 mm increments. Results: Measured peak % prescribed dose (%PD) and gap width below the 90% prescribed dose level (G90%) were determined to be −87% and 11.6 mm when abutting; −60% and 6.2 mm with 1.5 mm overlap; and −47% and 5.0 mm with 3.0 mm overlap. The dose profile was effectively flat with 4.5mm overlap and a peak overdosage of +34% was observed with 6.0 mm overlap. The simulated %PD and G90% were determined to be −84% and 9.5 mm when abutting; −77% and 8.2 mm with 1.0 mm overlap; −65% and 7.0 mm with 2.0 mm overlap; −45% and 5.0 mm with 3.0 mm overlap; and −17% and 2.5 mm with 4.0 mm overlap. A peak overdosage of +18% was observed with 5.0 mm overlap. Conclusion: A 5 mm plaque placement overlap provides for adequate field matching with the plaque, improving its clinical utility and allowing for greater flexibility in the surgical environment.
SU‐FF‐T‐105: Clinical Implementation of a Sector‐Integration Method for Calculating Electron Output Factors
Authors: Vossler M , Helmuth K
Published: July 2007

Purpose: To develop a spreadsheet that enables a physicist or dosimetrist to quickly determine electron‐beam cutout factors for irregularly‐shaped apertures. Method and Materials: Cutouts with circular apertures from 10cm to 1cm diameter were fabricated to fit inside a 10×10cm electron applicator. The cutout factor for each was measured for five electron energies at two depths (dmax and R90). A polynomial fit to the data yielded the cutout factor as a function of aperture radius for each energy‐depth combination. A spreadsheet was written that estimates the cutout factor for an irregularly‐shaped cutout by dividing the cutout into sectors, calculating the cutout factor for each sector, and taking the average. Results: The spreadsheet was tested using 10 electron cutouts from actual patient treatments. For each cutout, the cutout factor was measured for all five energies at both depths. The spreadsheet was used to estimate the cutout factor for each cutout at each energy and depth. We determined that 16 sectors were sufficient for a quality result. Except for cases where the cutout was especially narrow and concave, the spreadsheet estimated the cutout factor to within 1% of the measured value. Conclusion: The spreadsheet correctly estimated the cutout factor for most clinical situations, and took only a few minutes to use. Using this spreadsheet reduces the need for the physicist to measure the cutout factor directly, which can be a considerable time savings. It also removes any need to use less‐accurate approximations.
SU‐FF‐T‐170: Dosimetric Characterization of a 2D Diode Array Detector in Passive Scattering Proton Beams
Authors: Liengsawangwong P , Ding X , Arjomandy B , Lii M , Sahoo N , Amos R , Gillin M , Zhu X
Published: July 2007

Purpose: To evaluate the dosimetric properties of a two‐dimensional (2D) diode array detector in passive‐scattered proton beams (PSPBs). Materials and Methods: The diode array detector, MapCHECK™, was characterized for PSPBs. The relative sensitivity of diodes and absolute dose calibration were determined using a 250 MeV beam. The measured pristine Bragg curves (PBCs) by MapCHECK™ were compared with the results of an ion chamber (IC) using a range shift method. The water‐equivalent thickness (WET) of MapCHECK™ buildup was also determined. The inverse square dependence, linearity, and other proton dosimetric quantities measured by MapCHECK™ were also compared with IC. The change of absolute dose response of MapCHECK™ as a function of accumulated dose was used as an indicator of radiation damage. 2D dose distribution with and without compensator were measured and compared with treatment planning system (TPS) results. To facilitate the comparison, in‐house software called MU Scaler, was developed. Results: The measured PBCs by MapCHECK™ are virtually identical to those measured by IC for 160, 180, and 250 MeV proton beams. The WET of MapCHECK™ buildup is determined to be 1.7 cm. The inverse square result of MapCHECK™ is the same as the IC results, within ±0.4%. The linearity of MapCHECK™ is within 1% compared to IC data for MUs larger than 10. All other dosimetric quantities are within 1.3% of IC results. The absolute dose response of MapCHECK™ has been changed by 7.4% after accumulating total dose of 170 Gy. Good results are observed for 2D dose distribution for patient treatment fields with and without compensator when compared with TPS results. Conclusions: MapCHECK™ is a convenient and useful tool for 2D dose distribution measurements of PSPBs. Variation of dose response of MapCHECK™ with total accumulated dose should be carefully monitored.
SU‐FF‐T‐171: Dosimetric Comparison of Cesium‐131 and Palladium‐103 for Permanent Prostate Brachytherapy
Authors: Musmacher J , Byrnes R , Satchwill K , Rumpf L
Published: July 2007

Purpose: To evaluate the dosimetric differences in treatment planning between Cesium‐131 and Palladium‐103 in prostate brachytherapy. Introduction: Due to the short half‐life of Cesium‐131 and the energy emitted, when compared to Palladium‐103, planning guidelines must be established. This study focuses on seed count, dose to critical structures and homogenous dose distribution. Materials and Methods: Thirty patients were planned using Varian's Variseed 7.1, both with Palladium‐103 and Cesium‐131 for monotherapy, to a prescribed dose of 125Gy and 115 Gy respectively. The average gland size was 28.48 cc. All volumes were contoured and sources were placed using Palladium‐103 at an activity of 2.0u. Another treatment plan was developed using Cesium‐131 at an activity of 2.0u. All prostatic contours were identical between the two treatment plans for each patient. The following quantities were derived from each plan: total seed count, total needle count, D90, V150, V100, V90, V80, R100, and U10. Results: In the series, there was a decrease of 17.46% planned seeds (70 vs. 59) and 6% planned needles (18 vs. 17) when planning for Cesium‐131 as compared to Palladium‐103. There was a decrease in the V150 of 35.53% (39.31% for Cs131 vs. 60.97% for Pd103), while maintaining an average D90 of 115.46% for Cs131 and 115.29% for Pd103. There was a decrease in the R100 of 44.23% (0.15cc for Cs131 vs. 0.28cc for Pd103). A small decrease in U10 of 1.98% was also noted. Conclusion: Cesium‐131 as an alternative to Palladium‐103 for prostate brachytherapy is favorable in this study as it reduces the overall seeds and needles needed for implants while offering an improved homogeneous dose distribution; reducing the overall dose to the rectum and prostatic urethra. Further studies on these patients are in progress to assess the actual post‐implant dosimetry and morbidity associated with Cesium‐131.
SU‐FF‐T‐172: Dosimetric Comparison of MapCheck with Monte Carlo Simulations
Authors: Luo W , Yin F , Ma C , Fan J , Song H
Published: July 2007

Purpose: This study is to verify IMRT QA MapCheck measurement using Monte Carlo simulations. Method and Materials: MapCheck (Sun Nuclear) contains 445 silicon diode detectors arranged in a 22×22‐cm2 area, of which 221 are located in the 10×10 cm2 center. The diode spacing is 7.07 mm in the central portion and 14.14 outside of this area. The 2‐cm water equivalent build‐up is inherent in the device and additional 3‐cm build‐up is used for IMRT QA plan delivery at an SAD of 100 cm. The EGS4/MCSIM Monte Carlo package was used in this study. The MLC leaf sequence files for the IMRT plans were used for the Monte Carlo simulation. Results: Ten prostate and head‐and‐neck IMRT QA plans were generated on the Eclipse treatment planning system and delivered on Varian machines. The average field size for the prostate plans was 9×6 cm2, and 14.5×16.7 cm2 for the head‐and‐neck cases. For the prostate plans, the average dose at the reference point was 94.3 cGy by Mapcheck and 92.9 cGy by Monte Carlo. The difference was 1.5 %. For the head‐and‐neck plans, MapCheck measured 70.0 cGy while Monte Carlo predicted 69.5 cGy (a 0.7 % difference). The dose errors given by MapCheck and Monte Carlo were also compared. In the case of the prostate IMRT, MapCheck gave a dose error of 1.0 %, while Monte Carlo showed 0.5 %. In the case of head‐and‐neck, the 0.5 % of dose error by MapCheck was close to that (0.8 %) by Monte Carlo. Conclusions: MapCheck can perform accurate dose measurement for IMRT QA. Considering the limitations of the detectors and design such as low spatial resolution, however, the Monte Carlo simulation can be used to verify MapCheck systematically and help improve its functions in future design.
SU‐FF‐T‐177: Dosimetric Evaluation of a Monte Carlo IMRT Treatment Planning System with the MIMiC
Authors: Rassiah‐Szegedi P , Fuss M , Sheikh‐Bagheri D , Szegedi M , Papanikolaou N , Stathakis S , Salter B
Published: July 2007

Purpose: To evaluate a pre‐release version of a Monte Carlo planning system (PEREGRINE 1.6b, NOMOS, PA), which incorporates the modeling of serial tomotherapy IMRT treatments with the binary Multileaf Intensity Modulating Collimator (MIMiC). The intent of validation was to investigate the accuracy of doses calculated by a conventional finite size pencil beam / Effective path length (FSPB/EPL) algorithm for lung lesions treated on the stereotactic body radiation therapy dose regime via serial tomotherapy. Method and Materials: PEREGRINE, developed by Lawrence Livermore National Laboratory and licensed to NOMOS Corporation for distribution uses the BEAMnrc MC code. Doses calculated by PEREGRINE were compared against measurements in homogenous and inhomogenenous materials carried out on a Varian 600C with a 6 MV beam. Phantom studies (CIRS lung phantom) simulating various sized unit density lesions located centrally in the lung were also carried out to explain some of the large dose discrepancies seen in the dose calculations with small lesions. Results: PEREGRINE calculations agreed to within 2% in water and up to 3% for measurements in inhomogeneous phantom containing lung, bone and unit density tissue. Inhomogeneous phantom studies revealed that dosimetric error seen in the lesion with the FSPB/EPL increased as the lesion size decreased, up to 13.5 % in the center of a 1 cm lesion compared to a less than 1% prediction by PEREGRINE. Conclusion: PEREGRINE 1.6b (MC) provides an accurate method of calculating dose to lung lesions. The dose differences observed between MC and FSPB/EPL is significant and should be considered when reporting and prescribing dose to lung lesions.