bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐FF‐J‐28: A Software Tool for On‐Line Real‐Time Verification of Gated Delivery Using Megavoltage Fluoroscopy
Authors: Tai A , Christensen J , Khamene A , Bayouth J , Boettger T , Celi J , Li X 
Published: July 2007

Purpose: To test and to explore the application of a software tool developed for on‐line real‐time treatment verification for 4D/gated radiation delivery using megavoltage fluoroscopy (MVF) acquired with treatment beams. Method and Materials: MVF images were acquired with a flat panel detector installed on a Siemens Linac using 6MV photon beams for phantoms with moving structures and for thoracic cancer patients. A previously developed software, RTReg4D, was used to register acquired MVF with digitally reconstructed radiographs (DRRs) from 4DCT. The MVF frame grabber can be synchronized with the gating signal from Anzai gating device to capture target motion in selected gating window. The isocenter and target contours were transferred from a planning system into RTReg4D and were overlaid on the MVF images, verifying whether the target with residual motion is adequately covered during the gated delivery. Appropriate actions can be initiated should the verification fail. Results: The software tool can effectively and accurately register MVF images with DRRs. The MVF images acquired with a dose as low as 1 cGy were adequate for the registration. In addition, the registration can be performed between the averaged MVF frame of all frames acquired within gating window and the corresponding DRR, further reducing dose required. The accuracy of registration can be better than 3 mm. The entire process is fast. Conclusion: MVF achieves adequate image quality at a low dose. It is practically feasible to use the software tool with MVF for real‐time (prior or during) treatment verification of 4D/gated radiation delivery.Conflict of Interest: This work is sponsored in part by Siemens OCS.
SU‐FF‐J‐67: Tomotherapy MVXCT Numbers Versus RLSP for Various Ions and Materials
Authors: Moyers M , Sun S , Sardesai M , Rightnar S , Sharma A , Rusek A , Sivertz M 
Published: July 2007

Purpose: Optimization of ion radiotherapy and spacecraft shielding is critically dependent upon the relative linear stopping power (RLSP) of each material through which an ion would pass. In radiotherapy, RLSPs for patient tissues are usually obtained by converting kilovoltage x ray computed tomography (KVXCT) numbers; however, some registration and immobilization devices, implant materials, and dosimetry phantoms do not lie on the standard KVXCT number to RLSP conversion curve. KVXCT imaging is also prone to artifacts created by high atomic number and density materials. Ion computed tomography (ICT) could reduce these problems but these systems currently exist only in the research stage and, for abdominal scanning, would require energies and field sizes greater than available with current therapy accelerators and beam delivery systems. Megavoltage x ray computed tomography (MVXCT) may offer an alternative imaging scheme. Methods and Materials: The RLSPs for twenty‐two materials were measured using a parallel plate ionization chamber and scanning water phantom in proton, carbon ion, and iron ion beams. These same materials were scanned using both KVXCT and MVXCT. Results and Discussion: The MVXCT versus RLSP functions for the three ions were almost identical. The functions were approximately bi‐linear but the change in slope was smaller than for the KVXCT curves and deviations between measured and fit data were smaller. Conclusions: An MVXCT number to ion RLSP conversion function has been generated for use in treatment planning. Although the function does not account for the effect of ion nuclear interactions, MVXCT numbers can be used to predict the range of ions and may serve as an intermediate step until ICT is developed. Experiments may now be performed to compare KVXCT and MVXCT based treatment planning in the presence of artifacts and non‐tissue like materials.This work was partially supported by NASA grant NAG‐1943 and NMTB grant DAMD17‐97‐2‐7016.
SU‐FF‐J‐68: Dosimetric Comparison of Patient‐Specific Margins Vs. Uniform Margins for Prostate IMRT Treatments
Authors: Yoo S , Das S , Kim S , Koontz B , Lee W , Light K , Yin F 
Published: July 2007

Purpose: To evaluate the dosimetric improvement of IMRT treatment plans generated with patient‐specific margins compared to uniform margins for prostate cancer patients. Methods and Materials: For 13 prostate cancer patients who underwent IMRT treatment, daily cone‐beam computed tomography (CBCT) scans were acquired during the first week, followed by weekly scans (total of 85 scans) for the remainder of the treatment. Both prostate and seminal vesicles were retrospectively segmented on all CBCTs. The patient‐specific planning target volume (PTVPS) was defined based on a composite volume of both prostate and seminal vesicles from the first four daily CBCTs and the planning CT. A 3‐mm margin was added around the composite volume to obtain PTVPS. As a comparison, we also generated a PTV in the planning CT with a uniform margin (PTVUni) of 10‐mm in all directions, except 5‐mm posteriorly, around the prostate and seminal vesicles. An IMRT plan for each PTV was generated for each patient. Evaluation plans based on each of weekly CBCT were generated to gauge the DVHs resulting from these IMRT plans to the patient volumes segmented on weekly CBCTs. Results: Evaluation plans generated with PTVPS in place of PTVUni resulted in average improvements of 1.4% and 2.8% for V95 of prostate and seminal vesicles, respectively, and average reduction of 7.0% and 4.7% for V50 of bladder and rectum, respectively. Out of 85 weekly CBCT evaluation plans for each PTV, 7.1% of cases showed improvement for V95 of prostate with PTVUni, 40.0% for V95 of seminal vesicles, 28.2% for V50 of bladder and 29.4% for V50 of rectum. Conclusions: Patient‐specific margins, designed using multiple scans, appear to provide little dosimetric benefit with respect to target coverage over a standard uniform margin formulation; sparing critical structures is improved to a greater degree.“Partially supported by Varian Medical Systems”.
SU‐FF‐T‐14: A High MU Efficiency Dynamic MLC Leaf Sequencing Algorithm
Authors: Thongphiew D , Wu Q , Chankong V , Song H , Yin F 
Published: July 2007

Purpose: MU efficiency is a major figure of merit for dMLC leaf sequencing. However, leaf sequencing is often generated with focus on other constraints and the MU efficiency is taken as a byproduct. This work is to develop a new dMLC leaf sequencing algorithm (MinMU) that explicitly minimize the total MU. Method & Materials: At a constant dose rate, the maximum MU efficiency is achieved by minimizing, through optimization, an objective function which is essentially the total beam on time. The constraints considered are: maximum leaf speed, maximum separation between leaves and under dosing caused by tongue‐and‐groove effect. These mixed integer constraints are converted to linear ones by enumerating and eliminating redundant scenarios, for a given intensity map. These steps also help eliminating the infeasible solutions. The optimization was implemented for the Varian Millenium 120‐leaf MLC and was solved with the CPLEX software. Its performance was tested against published algorithms using phantom and real patient treatment fluence maps. Results: The fluence maps in the phantom study were generated with various grid sizes. The MU increases at a much slower rate for the MinMU algorithm than for the published algorithms with finer grid size. The MU efficiency advantage of the MinMU is more pronounced for more complex and larger fluences.Among the 18 fluence maps that were taken from two real head‐and‐neck cancer treatment plans, the MinMU algoithm uses more MU for 2 fluence maps, same MU for 2, and less MU for the rest 14 fluence maps than the commercial treatment planning software. Overall, the MinMU used 10% and 7% less MU for the two plans, respectively. Also, the MinMU reproduced the original optimal fluence with minimal difference. Conclusion: A new dMLC leaf sequencing algorithm is developed. Its high MU efficiency potential is demonstrated.
SU‐FF‐T‐60: Accuracy of Varian Eclipse Dynamic Conformal Arc Dose Calculation
Authors: Duggan D , Ding G , Coffey C , English M , Clark L 
Published: July 2007

Purpose: Dynamic conformal arc (DCA) treatments, in which the aperture is continuously modified to conform to the beams‐eye‐view of the target as the gantry rotates, are potentially the fastest and most efficient method of delivering a conformal treatment, while still achieving results comparable to IMRT. DCA could make stereotactic body radiation therapy (SBRT) more practical and cost‐effective. The purpose of this study is to demonstrate the accuracy of the DCA algorithm of the Varian Eclipse radiation treatment planning system (RTPS). Method and Materials: DCA plans were made for patients who had already received SBRT for Stage I NSCLC or IMRT for prostate cancer. The accuracy of the dose calculation was tested by two methods: The plan was mapped onto a cylindrical plastic phantom, the dose distribution in the phantom was calculated using the same monitor units. Then an ionization chamber was placed in the center of the phantom, the phantom was set up with the chamber at isocenter and the treatment was performed. In the second method, a DCA plan was mapped to a two‐dimensional (2D) ionization chamber array, with the plane of the array at isocenter. The dose distribution was calculated in the plane of the array. This phantom was also set up with the isocenter in the center of the chamber array and the treatment was performed. Results: The point doses measured with an ionization chamber in a cylindrical phantom agreed within ±2% with those predicted by the Eclipse RTPS. The gamma factor for the comparison between the measured and calculated doses in the plane of the 2D chamber array was less than 1 for 95% of the pixels. Conclusion: Our results indicate that the Eclipse DCA can accurately predict dose distributions.Research sponsored by Varian Medical Systems.
SU‐FF‐T‐96: Characteristics of Narrow Field Photon Beam Measurements for a Micro‐MLC Based Radiosurgery System
Authors: Yenice K , Wu T , Tu H , Reft C 
Published: July 2007

Purpose: To determine the response of various detectors in the commissioning of narrow field megavoltage photon beams for a micro‐MLC based radiosurgery system. Method and Materials: We commissioned both a standard and a high dose rate 6 MV photon beams from a Trilogy unit (Varian Medical systems, Palo Alto CA) for the pencil beam algorithm using a micro‐MLC based Radiosurgery system (BrainLAB AG Germany).The loss of lateral equilibrium, high dose gradients, and spectral changes within high energy narrow photon beams imposes restrictions on detector composition and size used for relative measurements. We investigated the response of two p‐type Si‐diodes (Scanditronix photon and stereotactic diodes), a diamond (PTW) detector, a cylindrical (Scanditronix RK chamber) and a micro‐ion‐chamber (Exradin #a16) for depth dose and relative output measurements. Results: Percent depth dose measurement with photon diode (guarded) yielded consistently higher measurements by 1–2% compared to ionization chamber results for larger depths with increasing field sizes. Stereotactic diode measurements of depth doses for field sizes ⩾18×18 mm2 yielded 1–2% lower values compared to ionization chamber results. For field sizes ⩽12×12mm2 photon diode depth dose measurements were higher by 1–5% at depths > 5cm compared to those measured by stereotactic diode. The relative output factors measured by photon diode, diamond detector and both ion chambers were within 1% agreement with each other for all field sizes ⩾ 30×30mm2. The stereotactic diode measurements were lower by ∼2.5% for all but the smallest field size of 6×6 mm2 compared to other detectors. Relative output factors for the high dose rate beam were higher by 2–4% for fields < 18×18mm2 compared to the standard 6 MV photon beam. Conclusion: Measurement of relative output factors and depth doses for megavoltage narrow photon fields require multiple detectors to correctly estimate the true response over the range of measurements.
SU‐FF‐T‐183: Dosimetric Verification of a Commercial Research Irradiator
Authors: Wiesmeyer M , Schaefer M , Hile M , Stojadinovic S , Williamson J 
Published: July 2007

Purpose: To present a collection of simple tests that can be used to verify the dosimetric characteristics of the MDS Nordion Gammacell 40 Extractor Low Dose‐Rate Research Irradiator. Method and Materials: The manufacturer specifies that the irradiator is provided with two 61.1 TBq Cesium 137 sources that together produce a central dose rate of 1.10 Gy/minute ± 15% in its sample tray. In the central 260 mm diameter by 100 mm height region, the specified dose uniformity is ± 7%.Custom measurement jigs were made to fit inside the irradiator's sample trays and assemblies. Ionization chamber readings were made to determine exposure rate constancy and timer errors. Radiochromic film was used to measure dose and dose rate constancy, the attenuation of manufacturer‐provided attenuators, depth dose characteristics in Solid Water™, and uniformity of dose across the sample tray. Thermoluminescent devices (TLD's) were assessed as an alternate means of measuring dose and dose rate constancy. Results: The exposure rate was constant down to two seconds and timer error was about 1.4 seconds. Film measurements showed that dose reduction for the attenuation filters (33%, 60%, 80%) is within 3% of specifications. Film measurements in a central 10×10 cm area showed dose uniformity within about 2%. Depth doses in Solid Water™ showed a variation of about 10%. Film and TLD's yielded similarly accurate dose measurements and constancy estimates. Conclusion: Our facility's irradiator operates within the manufacturer's specifications except for dose variance with depth which may be somewhat greater than 7%. Although the manufacturer provides basic dosimetric information about each irradiator, it is advantageous to verify and expand this information. As with linacs, irradiators must certainly differ from machine to machine and change over time. It is prudent when doing research using these devices to validate their performance under their conditions of usage.
SU‐FF‐T‐195: Effect of Respiratory Gating On the Dose Distributions of Dynamic Wedge and IMRT Treatment Fields
Authors: Lindsay P , Briere T , Balter P , Sadagopan R , Starkschall G , Zhu X , Beddar S 
Published: July 2007

Purpose: To determine the magnitude of error introduced into treatment delivery due to timing effects between respiratory‐gated delivery and dynamic beam delivery (enhanced dynamic wedge (EDW) and step‐and‐shoot intensity modulated radiation therapy (IMRT)). Method and Materials: EDW and IMRT fields were delivered on a linear accelerator (Trilogy, Varian Medical Systems). Gating of the beam was achieved using a commercial respiratory monitoring system (RPM, Varian Medical Systems), and respiratory motion was simulated using a commercial respiratory motion phantom (RPM phantom, Varian Medical Systems). All fields were delivered with no gating, a 1‐mm gating window, and a 2‐mm gating window.Film and ion chamber measurements were made for both EDW and IMRT fields in a water‐equivalent IMRT QA phantom, which was stationary during all measurements. Film measurements used EDR‐2 film, while ion chamber measurements were made with a 0.04 cc volume pin‐point chamber. Leakage current was subtracted from the ion chamber readings.Wedged fields of 15 and 60 degrees were delivered at a dose rate of 600 MU/min. Results were evaluated for the full IMRT plan and for one of the individual beams, at dose rates of 400 and 600 MU/min. Results: All ion chamber measurements were analyzed as percent difference between the gated (1‐mm or 2‐mm gating window) and non‐gated delivery. All differences were less than 1%. There were no significant differences between 1‐mm and 2‐mm gated delivery. Film results, as analyzed from isodose curves and the gamma metric, showed no substantial differences between gated and non‐gated beam delivery. Conclusion: The use of gated treatment delivery of EDW and step‐and‐shoot IMRT fields does not introduce clinically significant differences into the resulting dose distributions, as quantified by film and ion chamber measurements.
SU‐FF‐T‐218: Evaluation of the Exradin #a19 Ion Chamber for Reference Dosimetry in Megavoltage Photon Beams
Authors: McEwen M 
Published: July 2007

Purpose: The Exradin #a19 is a new design of reference‐class 0.6cc ion chamber that externally resembles the NE2571 Farmer chamber but internally is very similar to the well‐known Exradin #a12. This project involved the characterization of a single version of this chamber in high energy x‐rays. Method and Materials: The Exradin #a19 was compared against primary and reference standard ion chamber chambers at the National Research Council of Canada in a range of megavoltage photon beams (6–25 MV). Investigations looked at chamber settling, ion recombination and polarity, and determination of experimental kQ factors. Results: Chamber settling — the chamber response stabilizes very quickly (within 5 minutes), even after a large change in the polarizing voltage.i) The polarity correction was measured for 6 MV and 25 MV beams and found to be small (within 0.15% of unity).ii) The recombination correction showed a linear variation with the dose‐per‐pulse. The correction was similar to that of other Farmer‐type chambers.iii) Beam quality conversion factors were found to be closer to that of the NE2571 than the #a12, which is not consistent with the guidance given in TG‐51. However, with only a single chamber under investigation one cannot draw any definitive conclusions.Conclusion: An initial investigation of the Exradin #a19 Farmer‐type ion chamber suggests that it is fit for purpose for the calibration of megavoltage photon beams. Further work is in progress to evaluate this chamber in kilovoltage x‐ray and high‐energy electron beams.
SU‐FF‐T‐260: In‐Vivo Dosimetry Verification of a 3D Treatment Plan Prescription Dose at a Depth Beyond Dmax Using Diodes
Authors: Roa D , Song H , Ahmad M , He Q , Al‐Ghazi M 
Published: July 2007

Purpose: To provide an in‐vivo verification using diode detectors of a patient prescription dose calculated by a three‐dimensional treatment planning algorithm. Method and Materials: Three models of diodes specially designed for high‐energy photon beams (6‐MV Isorad and QED, and the 20‐MV QED diode detectors manufactured by Sun Nuclear Corporation, Melbourne, Florida) were used to measure the percent depth dose (PDD) of a 6‐MV and 20‐MV photon beams produced by a Varian 2300 C/D Linac. These diodes were not water proof and the measurements were performed at multiple depths in a solid‐water phantom. Results: The measured PDD curves agree within 2% with clinical PDD curves scanned in a water tank to depths up to 25 cm. This allows scaling of the diode dose reading measured at the patient skin to a depth inside the patient which is usually the prescription point or the isocenter for a multiple beam SAD treatment as defined in a 3D treatment plan.In‐vivo measurements were performed on real patients. The doses scaled to the measurement depth were summed for all beams and compared with the calculated value from the treatment planning system (TPS). The treatment sites and agreement are listed below.‐ 10 head and neck cases thus far, 0.4%–6.7% difference between calculated and measured doses,‐ 8 pelvis cases thus far, 1.9%–6.5% difference between calculated and measured doses,‐ 6 breast cases thus far, 2.3%–5.4% difference between calculated and measured doses,4 chest cases thus far, 1.3%–6.7% difference between calculated and measured doses. Conclusion: An in‐vivo dosimetric method has been developed to measure delivered dose to the prescription point at a depth within the patient. Overall agreement between the measured and TPS‐calculated dose to the prescription point falls within ± 7% as recommended by the TG‐62 protocol.
SU‐FF‐T‐403: The Dose‐Volume Differences by Set‐Up Error for Prostate
Authors: Lo C , Huang D , Hong J 
Published: July 2007

Purpose: To simulate the dose‐volume changes by set‐up errors for prostate. Method and Materials: Patient set‐up errors consist of two parts, one for the systematic error, and one for random error. A prostate patient was treated with IMRT has 7.0mm margin in posterior and 9.0mm margin in others. To simplify analysis, the first numerical simulation was no random error present. The systematic errors had a shift of 1.0mm, 2.0mm, and 3.0mm along each axis. Next, the simulation had 1.0mm, 2.0mm, and 3.0mm standard deviation in random error only. We compared the receiving dose of the 95% volume of prostate (D95%), the volume of receiving dose more than 90% and 70% of the prescribed dose (V90% and V70%) for rectum and bladder in each numerical simulation cases. Results: In our simulation cases, the receiving dose of prostate (D95%) is more than 99.95% prescribed dose. A systematic error within 3.0mm in Rt‐Lt direction, the percent volume change of bladder and rectum (V90% and V70%) are less than 2.5%. In the Sup‐Inf direction, no large percent volume change of rectum was found. There are more than 3% volume changes for bladder in the 3.0mm shift of Sup‐Inf direction. The worse results are the percent volume change of rectum in the Ant‐Post. More than 6% volume changes for rectum in 1.0mm shift to anterior.No more than 2.5% volume changes for bladder and rectum within 3.0mm standard deviation (SD) in Rt‐Lt and Sup‐Inf direction. Up to 3.0mm SD in Ant‐Post, rectum volume (V90%) had 5.6% changes apparently. Otherwise, random error has less volume changes than systematic error in our data. Conclusions: The rectum volume change is sensitive to systematic error in Ant‐Post direction. Set‐up should be accuracy in Ant‐Post direction than others. Also, accuracy is more important than precision.
SU‐FF‐T‐429: Treatment Planning Modeling and Dose Delivery Advantages of Standard Linac Without Flattening Filter
Authors: Bayouth J , Shukla H , Pavord D , Nixon E , Siochi R 
Published: July 2007

Purpose: The objective of this study is to determine the accuracy with which treatment planning systems can model dose distributions generated by conventional linear accelerators without the flattening filter, and the potential benefits. Method and Materials: Data was collected on a Siemens Oncor linear accelerator, where the flattening filter has been removed and energy tuned to match a standard 6 MV x‐ray beam but with dose rates of 1000 MU/min. Data was acquired to model and commission four treatment planning systems (Philips Pinnacle, CMS Xio, Nomos Corvus, and Siemens Konrad). Comparisons included: TPS model parameters w/ and w/o flattening filter, measured and computed %dd and profiles, conventional and IMRT dose distributions both via planning and delivery measurements in phantom. Results: Beam energy spectrum characteristics show only a modest softening in the beam since beam tuning matched the filtered 6 MV. Differences are seen in the off‐axis fluence and off‐axis energy softening: the fluence is reduced linearly away from the central axis and the energy spectrum is only slightly reduced by comparison. Dose profiles and %dd were accurately modeled to within 2% and 2mm for all field sizes 2–40 cm. When applied to IMRT treatment plans, the model produced equivalent dose distributions for head‐and‐neck, CNS, and prostate plans; the number of monitor units was slightly increased (∼15%) but the number of segments was identical. Delivery times at 1000 MU/min were shorter (20% reduction), and the IMRT plans delivered had a 30–50% reduction in the number of pixels showing dose‐differences beyond 5%. Conclusion: Treatment planning systems are not only capable of modeling the dose distributions produced without flattening filters, they perform superior than with the filter present, and can reduce common dosimetric errors observed in IMRT phantom studies.Research sponsored by Siemens Medical Solutions corporation.