bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐97: Application of a Rotatable Isocentric Phantom for Determining Geometric Errors in Gantry Rotation of a Complete LINAC System Including EPID and OBI
Authors: Zuessman N , Chu K , Grant D , Li T , Deady M
Published: July 2006

Purpose: With the onset of on‐board‐imaging (OBI) and 2D‐2D matching programs to determine table shifts in IGRT, QA tests are needed to assess the accuracy of these shifts. Hence, the purpose of this study was to investigate geometric inaccuracies in that could occur within a LINAC with EPID and OBI due to gravity effects when the gantry is rotated. Method and Materials: A rotatable isocentric phantom (Modus Medical Devices) was aligned to the lasers in our CT simulator. CT scans with 1mm slice thicknesses were transferred to the Eclipse TPS. DRR's were generated and exported into our IMPAC R&V system. The phantom was then aligned to the lasers in the Linac room. A Varian iX LINAC with EPID and OBI was used to obtained orthogonal pairs of images with the gantry set to 0°, 90°, 180°, and 270°. For each image the phantom was rotated such that its top surface was parallel to the imaging detector. The Varian 2D‐2D image matching program on the OBI computer was used to determine the geometric inaccuracies. Results: The initial set up of the phantom immediately revealed a misalignment of 2.5mm in the external lasers in the CT simulator. In addition, the CT scanner table sagged as much as 3.9 cm as it entered and passed the bore with an 68kg on the table. Imaging on the Linac with the MV or kV source at 0° (top) showed images that were perfectly aligned. However, when the kV source and detector was used at 270° or 90°, the images were up to 2mm off due to gravity effects. Conclusions: A technique was developed to determine the geometric inaccuracies found in a LINAC with EPID and OBI. Equipment sag showed that table shifts of less than 2mm may not be real or needed.
SU‐FF‐T‐98: Application of DAVID, a Multi‐Wire Ionisation Chamber for in Vivo‐Verification of IMRT and Conformal Dose Distributions
Authors: Poppe B , Beyer D , Rubach A , Harder D , Willborn K
Published: July 2006

Purpose: In this work we present first clinical results obtained with the DAVID chamber. Methods and Material: The DAVID system (PTW Freiburg, Germany) is a flat, translucent multi‐wire ionization chamber for daily in‐vivo verification of IMRT beams. It is placed in the accessory holder of the linear accelerator. Each detection wire of the chamber is positioned exactly in the projection line of two opposing leafs of the MLC. The signal of each detection wire is proportional to the line integral of the ionization density along this wire, therefore it is directly proportional to the opening of the associated leaf pair. The number of measurement channels equals the number of leaf pairs. The sum of all wire signals is a measure of the dose‐area product of the transmitted photon beam and of the total radiant energy administered to the patient. Results: After a successful dosimetric verification of an IMRT plan, the values measured by the DAVID system are stored as reference values. During daily treatment the signals are re‐measured and compared to the reference values. In case of a deviation beyond a threshold a warning occurs. Because the DAVID system operates as an ionization chamber, disadvantages which might be observed in other devices, such as aging, are not to be expected. Furthermore, the influences on the beam characteristics are negligible. Conclusion: Clinical examples demonstrate that the DAVID system is a relevant tool to improve the reliability of IMRT treatments. Conflict of Interest: The DAVID system was developed in cooperation with PTW‐Freiburg, Germany.
SU‐FF‐T‐99: Application of Dose Uncertainty Model for Plan Evaluation
Authors: Jin H , Chung H , Suh T , Palta J , Kim S
Published: July 2006

Purpose: To provide the applications of dose uncertainty model for intensity‐modulated radiation therapy (IMRT) plan evaluation. Method and Materials: The dose uncertainty in radiation therapy is proportional to the product of dose gradient and spatial displacement (space‐oriented uncertainty) and inversely proportional to dose level (non‐space‐oriented uncertainty). Since both dose uncertainties are assumed independent, the total dose uncertainty is their square root of quadratic sum . If the dose distribution consists of multiple fields, the total uncertainty is the square root of quadratic sum of dose uncertainties of all beam segments. To apply the uncertainty model to IMRT plan evaluation, three patients were selected and three different step‐and‐shoot IMRT plans for each patient were made with 95% of planning target volume (PTV) covered by prescribed dose (180 cGy) using Philips Pinnacle3. Three‐dimensional (3‐D) dose uncertainty distributions were calculated with 1% relative dose uncertainty at the prescribed dose level and 1 mm spatial displacement along each Cartesian axis as one standard deviations assuming Gaussian distribution. The uncertainty distributions added to and subtracted from the calculated dose distribution were employed to make isodose lines with 95% confidence interval (1.96σ). The plans with the isodose lines of each patient were compared to choose more preferable plan. In addition, the uncertainty‐volume‐histogram (UVH) was developed as an additional tool for plan evaluation. Results: By observing possible overdose and underdose regions within PTV with 95% confidence level, better plan evaluation was accomplished. Moreover, the plans that might bring less possible damage to organs at risk could be selected by considering both the dose bounds and UVHs of each organ. Conclusion: The 95% isodose bound and UVH are new useful tools for better IMRT plan evaluation. The uncertainty model can bring a new paradigm of plan evaluation by avoiding the choice of a plan of high risk.
SU‐FF‐T‐100: Application of Statistical Process Control to IMRT Quality Assurance
Authors: Fang B , Shoale J , Pawlicki T , Boyer A
Published: July 2006

Purpose: An investigation was undertaken to determine the efficacy of the application of statistical process control (SPC) methods to the quality assurance measurements for individual patients prior to the application of intensity‐modulated radiation therapy (IMRT). Method and Materials: SPC is a quality control methodology developed by industrial engineers. IMRT treatments were delivered using 6MV and 18MV x‐ray beams produced by a medical linear accelerator equipped with a 120‐leaf multi‐leaf collimator. Treatment plans for delivering IMRT were computed for fifteen patients using a commercial treatment planning system. A “phantom plan” was calculated for each patient. To compute the “phantom plan”, the patient's virtual simulation CT data set was replaced by a CT scan of an ellipsoidal water equivalent phantom. The dose distribution was recomputed using the machine parameters that had been computed for the patient. Measurements of dose were made using a calibrated 0.2 cc Farmer‐type ionization chamber in the water equivalent phantom. The dose was delivered using the same computer files that were to be used for treating the patient, and exactly the same medical linear accelerator parameters. The dose measured at points in the phantom was compared with the dose computed at the same points in the “phantom plan”. The dose differences were analyzed using the methods of SPC. For each patient a sample size of 2 was used. SPC Charts were constructed for the remaining ten patient cases employing the control limits derived from the first five cases. Additional studies of the performance of SPC were made using measurements with controlled errors introduced into the treatment delivery. Results: The patient cases remained in statistical process control. Addition measurement demonstrated that the SPC graphs detected intentionally introduced errors. Conclusion: Statistical Process Control is a practical technique for analyzing the patient specific quality assurance data for IMRT.
SU‐FF‐T‐101: Application of the Post‐Processing Dose Tool (PPD) to Dosimetrically Compare Gamma Knife and Hi Art Tomotherapy
Authors: Shi C , Penagaricano J , Yan Y , Papanikolaou N
Published: July 2006

Purpose: To develop a tool that enables us to process the dose matrix generated by the same or different radiation treatment planning system. Method and Materials: A Matlab tool was developed in order to post‐process the dose matrix generated from different treatment planning systems. Currently, the tool can import the dose matrix from Pinnacle3, Tomotherapy, Nomos Corvus and gamma knife planning computers. Tumor contours can also be imported. Using the tool one can calculate region‐of‐interest dose statistics, dose volume histograms (DVH), 2D dose maps, 3D dose maps, effective uniform dose (EUD), biological uniform dose (BUD), and dose profiles. The software tool can produce a comprehensive report that includes all the calculation. The software has been used to facilitate a comparison study between Tomotherapy and Gamma Knife for radiosurgical cases. The conformality index, defined as the ratio of the prescribed dose divided by target volume, was used to evaluate the treatment plans. Maximum dose, minimum dose, means dose, DVH and treatment time were also parameters used in the comparison. Results: Five gamma knife patients have been selected as candidates for the dose comparison between tomotherapy and gamma knife. All five patients had single brain lesions. Results show that tomotherapy can achieve the same DVH with higher dose conformality as compared to GK. However, the treatment volume of the lower dose lines (<10 Gy) is higher than gamma knife. Conclusion: A Matlab tool has been developed for post‐processing dose matrices generated by different treatment planning systems. The tool has been applied on comparison of the radio surgery cases between tomotherapy and gamma knife. The comparison results show that tomotherapy can deliver radio surgical precision and achieve the same results as gamma knife considering conformality index, maximum dose, minimum dose and mean dose in the tumor.
SU‐FF‐T‐104: Arc Sequencing — An Inverse Planning Technique for Intensity Modulated Arc Therapy
Authors: Shepard D , Earl M , Cao D
Published: July 2006

Purpose: Intensity modulated arc therapy (IMAT) is a rotational approach to IMRT in which the leaves of the multileaf collimator move continuously during arced beam delivery. Overlapping arcs are used to deliver optimized intensity patterns from each beam direction. Despite the promising nature of IMAT, its potential has gone largely unrealized due to a lack of robust inverse planning tools. To address this, we have developed an IMAT arc sequencing algorithm that translates optimized intensity maps into deliverable IMAT plans. Material and Methods: The arc‐sequencing algorithm uses simulated annealing to simultaneously optimize the aperture shapes and weights throughout each arc. The sequencer enforces the delivery constraints while minimizing the discrepancies between the optimized and sequenced intensity maps. The performance of the arc sequencer has been tested for ten patient cases. An IMRT plan was developed for each case using the Pinnacle3 treatment planning system, and the arc sequencer translated the optimized plans into deliverable IMAT plans. Results: Ten IMAT patient plans were developed covering the following sites: 3 prostate, 3 brain, 2 head‐and‐neck, 1 lung, and 1 pancreas. Seven coplanar IMAT plans were created using an average of 4.6 arcs and 685 monitor units. Additionally, three noncoplanar plans were created using an average of 16 arcs and 498 monitor units. The results demonstrate that efficient IMAT delivery plans can be developed that combine the dosimetric advantages of arc therapy with the dose painting capabilities of IMRT. Only modest degradation was seen between the pre and post sequenced plans. Plan accuracy was verified using Monte Carlo dose calculations with each arc approximated as static beams separated by two degrees. An average sequencing time of under 25 minutes was observed. Conclusions: An arc‐sequencing algorithm has been developed that can serve as the first robust inverse planning tool for IMAT.
SU‐FF‐T‐107: Assessment of Dental Amalgam Backscatter with a Beacon Transponder Embedded Mouthpiece for Real‐Time Tracking During Head and Neck IMRT
Authors: Ye J , Werner B , Mate T , Zeller T
Published: July 2006

Purpose: A mouthpiece embedded with Beacon® transponders (Calypso Medical) for continuous localization and tracking during IMRT head and neck irradiation was evaluated for backscatter to the oral mucosa. Dental amalgam can generate excessive backscatter dose to the oral mucosa during treatment. Study objectives were to measure backscatter dose from amalgams, transponders and mouthpiece relative to the oral mucosa. Method and Materials: A dental phantom having 16 of 28 teeth containing amalgam, and a prototype acrylic mouthpiece embedded with 3 transponders (1mm depth) were fabricated. To simulate overlying oral mucosa, a 1.5cm bolus was placed over the dental phantom and mouthpiece for baseline measurements. A TN502RD MOSFET dosimeter and TLD chips (3×3×1mm) with a 6 MV photon beam 10×10 cm2 field (Elekta Precise) with and without mouthpiece were used for measurements. Backscatter was measured with and without the mouthpiece at a source‐to‐detector distance of 100 cm in a single field. To assess dosimetric effects of amalgam in the presence of the mouthpiece, a parallel‐opposed field beam setup was used. Results: Standard amalgam causes dose increases of 24–29% at the tissue interface; however, backscatter decreases rapidly to 7–8% at 0.8mm depth. MOSFET and TLD measurements show the mouthpiece reduced backscatter dose by 15% (at 0.4 mm) for single beam and 6–8% for parallel‐opposed beams. The transponders (1.8mm × 8.5mm) in the mouthpiece do not generate measurable additional backscatter. Conclusion: A mouthpiece when used for continuous target localization and tracking, can effectively reduce backscatter dose caused by amalgams, potentially decreasing mucositis. Embedded transponders do not generate measurable backscatter dose. Conflict of Interest: Mate and Zeller have a financial interest in Calyspo Medical.
SU‐FF‐T‐108: Automatic Machine Commissioning for a Helical Tomotherapy Machine
Authors: Olivera G , Cravens B , Cox A , De Souza C , Ruchala K , Lucas D , Chen Q , Lu W , Henderson D
Published: July 2006

Purpose: Develop and validate a new automated procedure to fully commission a helical tomotherapy machine with minimal human intervention and in a very short period of time. Compare the results of a commissioning using data based on water tank measurements and not using water tank measurements. Method and Materials: The process was performed in 5 HiArt helical tomotherapy machines. All of the machines where set to match a gold standard machine base on PDD, field sizes, output and output factors, and leaf characteristics. In a first pass, measurements were performed using water phantom for all of the commissioning measurements. After that, the same machine was verified using a new procedure (twinning) to generate a new gold standard under different measurement conditions. To determine data analogous to PDD an aluminum step wedge was used. The step wedge was mounted on the couch and was automatically moved in and out of the beam (as many times as needed) to determine energy through attenuation measurements. In order to determine the profiles a 2D arm was mounted on the machine to determine profiles in air. Also output and output factors were determined under the same conditions twinning. After that all the machines were detuned from the gold standard and then were set back to the gold standard using the twinning procedure and verified with the water tank. Results and Conclusions: It was possible to match machines to a reference gold standard either using water tank measurements or the twinning process. The later was less error prone and was 7 times faster than using water tank. Also, can be implemented almost without human intervention.
SU‐FF‐T‐109: Automation of Monte Carlo Simulations For A Proton Therapy System
Authors: Zheng Y , Newhauser W , Fontenot J , Koch N
Published: July 2006

Purpose: To develop a code system to automate the processes associated with Monte Carlo simulations of a clinical proton therapy system. Method and Materials: A software system was developed that accepts a clinical prescription (beam range, range modulation, and field size) and generates a complete Monte Carlo simulation input file that includes all major components in the M. D. Anderson passively scattered treatment head plus one of several user‐selectable phantoms. The simulations are automatically submitted to a 130 dual‐CPU cluster. Post processing scripts were also developed to analyze the simulation results and generate required configuration data for the Varian Eclipse treatment planning system. Quality assurance procedures, such as design inspection, unit test, incremental integration test, regression test, and integration test, were performed to ensure the code system produces correct results. The code system was written in mainly C language, with some shell scripts, and it runs on the LINUX operating system. Results: A code system has been developed to automatically generate MCNPX input files, run simulations and perform post‐processing of simulation results for a proton therapy system. The code system has been used to simulate dose profiles and generate required data for commissioning the M. D. Anderson proton therapy system. Over one thousand dose profiles were generated for different beam configurations by the code system in two months. Example beam data will be presented. Conclusion: The automated Monte Carlo code system has proved to be a useful tool for simulations of clinical applications in proton therapy. It allows for rapid modeling of proton therapy systems and the results of this study suggest that data from Monte Carlo simulations will play an increasingly prominent role in proton therapy projects, i.e., pre‐clinical design, commissioning studies and routine clinical tasks.
SU‐FF‐T‐110: Benchmarking MCNP Low‐Energy Bremsstrahlung Modeling for Electronic Brachytherapy Simulations
Authors: Rivard MJ , Axelrod S , Rusch TW
Published: July 2006

Purpose: Electronic brachytherapy (eBx) sources have been used clinically for over a decade; however, dosimetric characterization methods using measurements or calculations are not well‐established. Monte Carlo methods for simulating electron transport, and subsequently photon production, have not been benchmarked to the same degree as for photon‐emitting HDR 192Ir or LDR 125I brachytherapy sources. Materials & Methods: Towards better understanding the capabilities of MCNP5 to simulate radiation transport for the Xoft Axxent eBx source, this study presents a comparison of calculated MCNP5 results obtained using coupled electron:photon transport with measured bremsstrahlung spectra from the literature. Given the electron energy and target material, MCNP5 bremsstrahlung modeling accounts for photon energy, angle, and probability based on the cross‐sections and angular distributions from NIST (Seltzer and Berger, 1985). The Axxent eBx source currently operates at 50 kV with electrons bombarding a ∼ 1 μm thick high/low Z target. Pertinent high/low Z comparisons for thin targets, defined as materials thin enough to produce negligible electron absorption in the target, were available from Motz and Placious (1958) using 50 kV on 5 nm Au and 63 nm Al, from Cosslett and Dyson (1957) using 10 kV on 25 nm Au, and from Doffin and Kuhlenkampff (1957) using 34 kV on 25 nm Al. Results: Comparisons of calculations and experimental data indicate that bremsstrahlung angular peak, relativistically shifted forward, agreed within a few degrees with measurements in the literature. However, the overall simulated distribution exhibited angularly invariant regions in the forward direction, attributed to MCNP low‐energy physics simplifications of the NIST dataset. Given that the brachytherapy target is ∼ 50 times thicker, with resultant smearing of the energy/angular distributions, the practical impact of this effect is under investigation, and complementary EGSnrc simulations are in progress. Conflict of Interest: This research was sponsored in part by Xoft, Inc.
SU‐FF‐T‐116: Calibration of the Perkin Elmer AG9 Flat Panel Portal Imager for Exit Dosimetry
Authors: Chen H , Chen J , Morin O , Descovich M , Aubry J , Aubin M , Pouliot J
Published: July 2006

Purpose: The new and highly sensitive amorphous‐silicon AG9 flat panel portal imager by Perkin Elmer allows imaging with extremely low doses. The purpose of this work is to establish the dosimetric response of the panel. Dosimetric calibration of the detector is also a necessary step for a dose reconstruction program under investigation. Methods and Materials: A convolution model was developed to map the flat panel images to equivalent dose in water at a depth of 1.5cm. The three model parameters are the flat‐panel and water energy‐deposition kernels, the flat‐panel‐to‐water‐dose conversion function, and the pixel sensitivity matrix. They account for differing flat‐panel and water energy responses, field size effects, and the panel's pixel nonuniformity. To determine these parameters, identical setups with the flat panel and with a water phantom were used to carry out numerous measurements. To validate the model, 10cm and 5cm square fields were delivered through 16cm of solid‐water slabs and a cylindrical solid‐water QA phantom. The flat‐panel converted dose profiles were compared with that measured in the Wellhofer water tank. Results: Both the flat‐panel and water kernels decrease sharply with distance. The magnitude of the flat‐panel kernel was greater, possibly due to the additional scatter in the high‐density panel material. The conversion function varies with the off‐axis distance and is nearly linear as the attenuation thickness varies. The sensitivity matrix values were approximately within 1% of unity, demonstrating good pixel uniformity of the panel. Validation tests showed that the model‐extracted dose agrees with measurements to within 1%. Conclusion: A good understanding of the dosimetric response of the AG9 flat panel was achieved. The developed convolution model was shown to be accurate and suitable for generating energy‐fluence maps for 3D dose reconstruction. Conflict of Interest: Research supported by Siemens.
SU‐FF‐T‐117: Can Current Prostate IMRT Be Further Improved with Immersive Virtual Reality Simulation?
Authors: Shang C , Williams T , Beavis A , Ward J , Sims C , Phillips R
Published: July 2006

Purpose: To further optimize beam orientations for axial 7‐field prostate IMRT plans with enhanced geometric volume analysis utilizing an immersive virtual reality simulation, a software which enhances the visualization of simulation using 3D stereo‐scopic data projection. Materials and Method: Eight prostate IMRT cases were selected, in which 7 beams were equi‐spaced in the axial plane, for a supine patient. D95 of PTV was normalized to 45.0Gy, the dose used for the initial treatment course. Beam geometry was then further optimized using an immersive virtual reality simulation tool — RTStar (provided by the U. Hull, UK). Consequently, with the exception of the AP field, all beam projections were rotated more anteriorly. Viewing through the most posterior beams, only 50% of overlap between PTV and the rectum was observed. In addition, two anterior oblique beams were tilted off the axial plane, 20° inferiorly, to clear the bladder. Use of the 3D stereo‐scopic viewing eliminated risk of collision with the patient. Comparable IMRT plans were then calculated with similar modulation intensity level and number of MLC segments. Results: A better dose homogeneity of PTV was indicated by 1.9% reduction in global maximal dose (p<0.01), and 1.3% reduction of dose value in 5% high dose region of PTV (p=0.02). Some rectal dose improvement was suggested with a 2.3% lowered hot spot with 10cc rectum enclosure (p=0.04). The bladder mean dose and the high dose value involving in 30cc bladder were reduced by 12.9% (p<0.01) and 3.9% (p=0.02) respectively. Conclusions: Immersive virtual reality simulation benefited the process in optimizing the beams used in this study. A deliverable, non‐coplanar beam arrangement improved dose homogeneity of PTV, dose sparing to the bladder and reduced high rectal dose in prostate IMRT. Research sponsored by Boca Raton community hospital corporation.
SU‐FF‐T‐120: Characterisation of Dose in SBRT Lung Via Monte Carlo
Authors: Rassiah P , Fuss M , Blough M , Hussey D , Lancaster J , Papanikolaou N , Salter B
Published: July 2006

Purpose: To accurately characterize the doses received by static lung lesions, as well as doses to the critical structures for the serial tomotherapeutic IMRT delivery method used for SBRT in our clinic. Method: 77 SBRT lung patients previously treated with doses calculated using the effective path length/Finite size pencil beam (EPL/ FSPB were retrieved. The critical structures (ipsi‐lateral lung, contra‐lateral lung, major airways, spinal cord and esophagus) were redelineated in order to standardize the contouring. All plans were run with Monte Carlo (MC), EPL/FSPB and No inhomogeneity correction (NI/FSPB). The intensity maps and MUs were the same for all three plans. The minimum, maximum and mean target doses were compared with MC calculation used as the benchmark. The normalized total dose, NTD; minimum, mean and maximum doses for critical structures were also compared. Results: The mean CTV volume of the 90 lesions presented here is 35.6 cm3 (range: 0.3–370.2 cm3). The minimum dose to both CTV and PTV were overestimated by the EPL/FSPB algorithm by an average of 17.3 ± 7.8% and 20.6 ± 10.8% of prescribed dose respectively. The absolute mean deviation in the minimum CTV and PTV doses were 5.7% (0.2–20.1) and 10.6% (0.03–27.3) respectively with NI. The magnitude of deviation depends on target location (embedded dense soft tissue, surrounded by lung and its proximity to a more dense interface) and dimensions. The minimum dose, mean dose and NTD for the lungs were in good agreement with MC. Larger, localized discrepancies exist for maximum dose. Doses to the other critical structures were generally in good agreement with those predicted by MC. Conclusion: MC dose calculation may prove valuable in accurately assessing the delivered dose in SBRT and may, thus, contribute to a more informed decision on the optimal dose and fractionation scheme.
SU‐FF‐T‐123: Characterization of MOSFET Response to the Xoft X‐Ray Brachytherapy Source
Authors: Axelrod S , Rusch T
Published: July 2006

Purpose: To study the response characteristics of MOSFET dosimeters in the energy range of the Xoft Axxent Electronic Brachytherapy system. These devices can be used to measure skin dose in breast HDR treatments. While MOSFETs have flat energy response at energies above 1 MeV, at the lower energies relevant to this device spectral dependence is anticipated. Therefore it is important to characterize the response for the source both bare and filtered by varying amounts of absorber to simulate different source‐to‐skin distances. Method and Materials: The Thomson‐Nielsen MobileMOSFET dosimetry system was characterized with respect to a calibrated air ionization chamber for a Xoft Axxent x‐ray source operating at 50 kVp. A sequence of aluminum absorbers were introduced to study how changes in the spectrum due to filtering affect the cross calibration of the MOSFETs. The Thomson‐Nielsen system supports continuous readout at 10 second intervals while under irradiation, allowing detailed comparison of the time series of dose readings, and an evaluation of the real‐time capabilities of the system. Results: Thomson‐Nielsen MOSFETs had excellent linearity, with deviations throughout irradiation up to 14 Gy on the order of 3% or less. Changes in calibration as a function of absorber thickness were observed, and can be characterized by degree of change per fraction of attenuation. Conclusion: Thomson‐Nielsen MOSFET dosimeters provide skin dose measurement capability with an accuracy on the order of 3%, providing corrections are applied to account for the distance from source to skin. Without these corrections the errors will be as much as 60% compared to an unfiltered source, but in practical use, where significant filtering will always be present, uncorrected errors are likely to be no more than 10%. Conflict of Interest: Xoft Inc. is currently in educational and commercialization discussions with several MOSFET system suppliers.
SU‐FF‐T‐126: Clinical Experience Using Dynalog Files for Verification of IMRT Delivery
Authors: Rice R , Wang J , Marcus L
Published: July 2006

Purpose: Validation of IMRT field delivery and the dynamic leaf movement during treatment is an important part of the IMRT QA procedure. In the past this was done using film during treatment. In this presentation, we summarize our experience using the dynalog files to validate the delivered fluence pattern of individual IMRT fields for each patient. Method and Materials: The DynaLog files were generated during IMRT delivery on Varian Trilogy and 21EX linear accelerators. They represent the actual leaf movement, as MLC leaf positions were recorded, during delivery, every 50 ms. Argus IMRT QA software was used to interrogate the dynalog files after delivery for evaluation. The delivered and planned fluence pattern can be displayed for comparison as well as fluence difference and Gamma function values. Maximum and average fluence difference and Gamma function values can be employed for quantitative analysis, as well as actual versus planned leaf positions and speeds. The pass/fail status of each IMRT field can be set based on pre‐determined parameters. Results: We have employed the Argus IMRT QA software in analyzing the fluence patterns and leaf motions for all IMRT fields used for patient treatment. Several hundred fluence patterns were analyzed on 100 patients treated so far. The average and maximum gamma function value of each field was analyzed to determine appropriate limits for the pass/fail criteria in accordance with our clinical data. Conclusion: Verification of delivered fluence patterns is an important part of the IMRT QA process. It assures the accuracy of IMRT delivery on a daily basis. With the aid of Argus IMRT QA software, validation of all the fields used for IMRT treatment can be performed within minutes for qualitative and quantitative analysis. With the proper choice of limits for test parameters, this approach further ensures the quality of IMRT delivery.
SU‐FF‐T‐128: Clinical Implementation of a New Elekta Dedicated‐Stereotactic Linac Into Radionics Treatment Planning System
Authors: Heydarian M , Esnaashari N , Van Prooijen M , Islam M
Published: July 2006

Introduction: A new Elekta “Synergy S” dedicated stereotactic machine has been commissioned and clinically implemented. This linac has special features, including a kV cone beam CT (CBCT) and a multileaf collimator (MLC) system, termed as “Beam Modulator” (BM), with no back up jaws. Dosimetric parameters of the BM are compared with those of Radionics mini multileaf collimator (MMLC). The two MLC systems have different dosimetric parameters, chiefly due to different shapes, field sizes and isocentric distances. The effects of these differences on tumour dose coverage and sparing organs at risk (OAR) are evaluated. Methods and Materials: The leaf thickness and maximum field size at the isocentre are 4mm and 16×21cm for the BM and 3.75mm and 10×12cm for MMLC. The leaf‐bottom isocentric distances of the two systems are 45.2cm and 33cm, respectively. Radionics treatments planning (XKnife RT3.01) is used for planning comparison. Dose penumbras and percentage depth doses were measured using diode detector and XV2 films for different field sizes. CBCT doses were measured using an ion‐chamber and MOSFET. Two different clinical cases were chosen for the treatment planning comparison. RESULTS: MMLC dose penumbras (80–20%) at dmax for a 9.6×10.4cm field were 5.4mm and 5.6mm for the leaf sides and leaf ends, respectively and 5.8mm and 6.5mm for BM. As a result, Radionics MMLC has the advantage of better sparing of OARs. Also, Radionics MMLC delivered the prescribed doses using fewer segments and less number of monitor units by up to 20%. The CBCT dose to head phantom was in the range of 1.5 to 3.0 cGy per scan. Conclusion: In this work it is shown that the above MLC systems are overall clinically comparable, with Radionics MMLC marginally better sparing normal tissues. The Elekta BM however has the advantage of larger field size and better isocentric clearance.
SU‐FF‐T‐132: Clinical Validation of Solid IMRT with the Pinnacle3 Radiation Treatment Planning System
Authors: Savitskij D , Nelms B , Gluckman G
Published: July 2006

In this work, we investigate a new “Solid IMRT” solution that works with the Pinnacle3 treatment planning system. The .decimal Solid IMRT solution involves exporting the ideal Open Density Matrices (ODM) from the Pinnacle3 treatment planning system, optimizing the transformation of each ODM into an array of solid modulator thicknesses with a special software package, and importing these thicknesses and necessary supporting information to Pinnacle3 for the final dose calculation. In order to validate the process and the accuracy of the IMRT dose delivery, three Solid IMRT plans (a prostate, a head and neck, and a breast) were created in Pinnacle3. The plans had the following number of beams/gantry angles: prostate plan, 5; head & neck plan, 7; and the breast plan, 2. Solid IMRT modulators were designed, built, and verified for individual beams. In order to conduct QA on the fabricated solid modulators, both film and diode array dose measurements were collected. The measured dose distributions were analyzed vs. calculated QA planar doses from the TPS. The process yielded high‐quality dose distributions and excellent agreement between the calculated and measured dose values. This study presents a valuable solution that enables Pinnacle users to upgrade to Solid IMRT delivery. Research sponsored by .decimal, Inc. corporation.
SU‐FF‐T‐135: Commissioning of Multi‐Leaf Collimator for Fast Neutron Therapy
Authors: Yudelev M , Mogili N , Hwang T , Farr J , Maughan R
Published: July 2006

Purpose: To collect and analyze data required for modeling of d(48.5)+Be fast neutron beam and shaped by newly installed multi‐leaf collimator (MLC) replacing previously used multi‐rod collimator (MRC). Method and Materials: The MLC is of semi‐focused design and consists of 60 leaf pairs operated under vision control. The leaf ends are straight, while the sides of the leaves are tapered to match the beam divergence and project 5 mm at isocenter plane. The leaf thickness is 300 mm of steel, and the MLC is the primary beam shaping device. The measurements along the central axis as well as lateral profiles were done in a water phantom. In the build‐up region the central axis depth dose curves were combined with data obtained from the measurements using thin window extrapolation ionization chamber. The output factors were defined at 0.9 cm depth in phantom and in free air by means of small volume Tissue Equivalent (TE) ionization chamber and miniature pin diode. In addition TE/Mg(Ag) paired ionization chambers were used to separate the neutron and gamma components in phantom as well as in free air. Results: No significant variations of the central axis depth doses were observed compared to MRC. Penumbra measured between tapered leaf sides was smaller than penumbra measured between straight leaf ends. The differences were largest at shallow depths and for large field sizes: 7 mm for 25 × 25 cm2 field decreasing to less than1 mm for fields smaller than 15 × 15 cm2. Linear relationship between the actual leaf end position and field size was observed. The gamma component at 0.9 cm depth in phantom increased with the field size from 1.5% to 3% and from 0.4% to 0.74% in air. Conclusion: A set of beam data measured for neutron MLC was used in beam modeling.
SU‐FF‐T‐136: Commissioning of the EYEPLAN V3.01 at LLUMC
Authors: Ly A , Benson B , Moyers M , Amos R
Published: July 2006

Purpose: To update the technology that has been utilized for designing proton dose distributions for the treatment of ocular melanoma at Loma Linda University Medical Center since 1990. Method and Materials: For the past decade the treatment planning system utilized for ocular melanomas at LLUMC has been a Digital VAX 4 workstation. This workstation utilizes software that was developed at MGH specifically for the treatment of ocular melanomas. Although the system has proven useful in the treatment planning process, the technology is antiquated and can be improved by switching to a PC based platform. A new eye treatment planning system has been commissioned and implemented at LLUMC. The new system, EYEPLAN 3.01, is PC based and was developed by CCO, Radiotherapy Quality System in Clatterbridge, England. Following treatment machine data entry into the new treatment planning system, the commissioning process consisted of the following: Confirmation of correct clip entry orientation, proton range and modulation values, lateral margins, and dose volume histograms. Several plans have been duplicated on both the old system and EYEPLAN for comparison. Results: Proximal and distal range comparisons are within 0.2mm. In the patient plan comparisons the same tumor range was generated to within 0.1mm. In addition the isodose distributions showed virtually no visible differences. The aperture cutouts generated by each of the programs were within 0.5mm. Finally, EYEPLAN 3.01 has the capability of including an eyelid in the path of the beam. Conclusions: The state‐of‐the‐art PC based treatment planning system, EYEPLAN, has been successfully commissioned for clinical use at Loma Linda University Medical Center. Comparisons made between the old planning system and EYEPLAN suggest that the design of proton dose distributions remain consistant.
SU‐FF‐T‐143: Comparison of Major Monte Carlo Codes in Physics Modeling and Sampling Efficiency
Authors: Jiang H
Published: July 2006

Purpose: The Monte Carlo method is able to provide the most accurate radiation dose calculations. On the other hand, one issue that needs to be addressed is the reliability of the physics models in the Monte Carlo codes. The purpose of this study is to seek for a much more thorough interpretation of this issue. Methods and Materials: Several general‐purpose Monte Carlo codes have already been widely used in many aspects of medical physics. Four well known Monte Carlo codes (EGSnrc, MCNP, GEANT4, and PENELOPE) are included in this investigation. The source codes are carefully studied, and the sampling techniques for each interaction for photons and electrons are evaluated in terms of accuracy and efficiency. The influence of the differences in physics modeling on radiation dose calculations is also analyzed. Results: All the four Monte Carlo codes present a certain extent of approximations in physics modeling, due to the lack of differential cross sections (with respect to energy and direction) and the consideration of simulation efficiency. The difference in sampled energy and angular distributions can be quite appreciable under some situations, and the difference in sampling efficiency can be significant as well. Conclusions: To faithfully simulate a physical interaction of radiation particles with matter with a Monte Carlo code, the physics processes have to be accurately modeled. However, the reality is that some approximations are inevitable. There are already several investigations on comparisons of the Monte Carlo codes, and both good agreements and discrepancies were reported. Since the previous studies were primarily based on simply applying the codes to some basic situations (such as PDDs and profiles in water), little in‐depth understanding of the causes of the discrepancies was provided. Our investigation provides a source‐code level interpretation of this issue.
SU‐FF‐T‐144: Comparison of MLC and Solid Modulation in Pediatric Patients Receiving IMRT
Authors: Roeske J , Cao J , Aydogan B , Nelms B , Mundt A
Published: July 2006

Purpose: Intensity modulated radiation therapy (IMRT) offers the potential of reducing the volume of normal tissue irradiated, and thus may provide significant benefit in pediatric patients. However, the total number of monitor units (MUs) associated with MLC‐based IMRT (MLC‐IMRT) may be 2–5 times higher than conventional planning, resulting in higher total body doses. Solid modulator‐based IMRT (SM‐IMRT) may provide significantly fewer MUs, and thus lower total body doses. The goal of this study is to compare MLC‐IMRT with SM‐IMRT treatment planning and delivery in the pediatric setting. Methods and Materials: Representative pediatric sites (brain, orbit, neck and abdomen) were used in this analysis. For each case, a 5–9 beam MLC‐IMRT plan was generated with the XiO treatment planning system (CMS Inc., St Louis, MO) using 6 MV photons. Dose volume histograms (DVHs) were calculated and the total number of MUs was recorded. Using the same input parameters, a second plan was then generated for each patient with SM‐IMRT. In both cases, 10 intensity levels were utilized. The total MUs and DVHs for the PTV and surrounding normal tissues were compared for each pair of plans. Results: In general, both the MLC‐IMRT and SM‐IMRT plans were comparable. Only minor differences in the DVHs were noted in the low dose region (20–40% of the prescription dose). However, the total number of MUs was significantly different. The average number of MUs for the MLC‐IMRT plans and the SM‐IMRT plans were 797 and 428, respectively (p=0.05). Measurements of the total body doses in a pediatric phantom will also be presented. Conclusions: SM‐IMRT plans result in significantly fewer MUs compared to MLC‐IMRT plans. Pediatric patients may benefit from the reduced total body doses, and hence reduced risk of secondary malignancies associated with this approach. Disclosure: Supported in part by CMS Inc. and Decimal Inc.
SU‐FF‐T‐146: Comparison of the Gliasite Radiation Therapy System (RTS) with Intensity Modulated Radiation Therapy (IMRT) for Intracranial Tumors
Authors: Mesina C , Wood C , Desobry G , Avery S , Lustig R
Published: July 2006

Purpose: To compare the Gliasite Radiation Therapy System (RTS) to intensity modulated radiation treatment (IMRT) with respect to dose distribution to both the tumor bed and to critical structures. Method and Materials: At our institution, between January 2002 and January 2005, 30 patients were treated with the Gliasite RTS. A group of 20 patients for whom magnetic resonance imaging (MRI) studies were available was selected out of this sample. Patients were originally treated with the Gliasite RTS to a dose of 6000 cGy prescribed to 1 cm beyond the periphery of the balloon catheter and delivered over 6 days. Utilizing MRI studies with the balloon catheter in place, the same patient group was then planned for IMRT, and the dose distributions to the tumor bed and to critical structures were compared. Results: The range of Gliasite RTS balloon catheter sizes was 4–35 cc. The range of source activities was 154.2 – 418.8 mCi. The Gliasite RTS delivered significantly less dose to the 50% volumes of critical structures versus IMRT. IMRT delivered significantly more dose to the clinical target volume (CTV) at the 100% (4936 vs. 4351 cGy, p=0.02), 99% (5725 vs. 5083 cGy, p=0.001), and 95% target volumes (6052 vs. 5723 cGy, p=0.03) versus the Gliasite RTS. There was no significant difference between IMRT and the Gliasite RTS with respect to the dose delivered to the 90% volumes of the CTV. Conclusion: The Gliasite RTS consistently provided more sparing of critical structures compared to IMRT for intracranial tumors. However, IMRT delivered a higher dose to the CTV that more closely approximated the prescribed dose. The choice of treatment modality must be weighed between the desire to protect normal tissue and the need to maximize dose to target volumes.
SU‐FF‐T‐147: Comprehensive Cyberknife QA‐A 2 Year Experience
Authors: Desai P , Parry C , D'Souza M , Medbery C
Published: July 2006

Purpose: The 6MV X‐band robot mounted linac in a CyberKnife(CK) system is more compact and maneuverable than conventional S‐band linacs. Long term mechanical and radiation output stability of this linac is crucial for the sub‐millimeter accuracy needed for stereotactic radiosurgery (SRS). The versatility of the CK allows for both extracranial and intracranial SRS use. The synchrony system tracks patient breathing thereby enabling precise irradiation of moving tumors. We evaluate the mechanical and radiation stability of the CK and the targeting error of synchrony with respect to variations in simulated anterior‐posterior(AP) motion using a ball‐cube phantom inside which gafchromic film is orthogonally positioned. Methods and Materials: CK output is monitored by a vented chamber unlike a sealed chamber used in conventional linacs. A daily calibration factor(CF) is obtained to correct for the changes in temperature, pressure and output. Absolute output, flatness, symmetry penumbra, End‐to‐End and Iso‐post tests are done monthly to verify the accuracy of the dose distribution and alignment of the X‐ray tube and detectors respectively. A 2D motion platform was fabricated to simulate respiration. The amplitude of motion ranged between 1cm and 3cm, a dose of 3000cGy from a 3 path fiducially tracked plan were given to the phantom at the 62% iso‐dose line The films were analyzed using End‐to‐End software and the total targeting error in the AP direction was determined. Results: Over two years of clinical use the linac output variation decreased steadily from 2% to below 1% while flatness, symmetry, and penumbra were well within CK specifications. The averaged CF was 1.011±0.008MU/cGy, the static targeting error was 0.8 ± 0.047mm and the synchrony targeting error was 1.63±0.056mm. Conclusion: We conclude that the CK mechanical system delivers the required targeting accuracy in both synchrony and static treatments, while the radiation instability is less than 2 %.
SU‐FF‐T‐151: Conservation of Integrated Reference Air Kerma
Authors: Song H , Wu Q , Steffey B , Yin F
Published: July 2006

Purpose: To demonstrate the conservation rule of the integrated reference air kerma (IRAK). Method and Materials: For a brachytherapy photon source whose radial dose functions is flat over the clinical distance range, the dose falls off with the inverse square of distance. If we assume further that the photon spectrum does not change with distance in tissue and the kerma in tissue can be substituted for radiation dose, it follows that both the photon particle and energy fluences obey the inverse square law. Under these assumptions, the photon fluence integrated over any arbitrary isodose surface, which is proportional to the integrated reference air kerma (IRAK), is conserved as long as the isodose surface contains all the brachytherapy sources, regardless of the distribution of the activity or equivalently the shape of the isodose surface. Results: One application of this conservation law is that the total dwell time (proportional to IRAK) of a plane implant is proportional to the total area of the prescription dose isodose surface. A quick second check QA program is established based on this relation for our intra‐op HDR using HAM applicator. Another application is to calculate the area of the absolute isodose surface assuming all the distributed activity is placed on one single point. The total area of spherical isodose surface is simply , where r0 is the reference radial distance of 1 cm, Λ the dose rate constant, S the source activity, T the total dwell time, and D prescription dose. This area should equal the isodose surface area for an plan with optimized dose distribution achieved by redistributing the same amount of activity within tissue. Two examples, one HDR planar implant and the other Patterson‐Parker nomogram, are given in the supporting material. Conclusion: The IRAK conservation rule has both theoretical and practical values.