bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐95: Analytical Neutron Shielding Calculations
Authors: Avery S , Maughan R , McDonough J , Goulart D
Published: July 2006

Purpose: The primary purpose of this study is to estimate wall thicknesses that will limit instantaneous dose equivalent rates outside the shielding walls to less than 0.02 mSv hr‐1 in areas that may be occupied by non‐designated workers. The other primary design considerations are the integrated annual dose equivalent and the integrated shift dose equivalent. These integrated dose equivalents have been calculated based on a maximum workload. The design aim has been to achieve levels that are in compliance with the University of Pennsylvania's ALARA commitment and NCRP standards. Material and Methods: In proton therapy, energies at and below 250 MeV produce neutrons when the proton beam is stopped in matter. Hence, the problem of proton shielding is a neutron shielding problem. Experimental data of various cross‐sections for neutron production by energetic protons across the proton energy range of interest (∼10–250 MeV) is not widely available. In order to predict the neutron spectra produced by a 250 MeV proton we used the Monte Carlo code GEANT4 v6.2 to simulate the protons passing through various targets (water, iron, carbon and tungsten) and recording the number of neutrons captured in one steradian. Results: The output of the shielding calculation gives (1) the instantaneous dose equivalent rate, (2) integrated weekly dose equivalent and (3) integrated annual dose equivalent at various points of interest for a defined shielding thickness. These points are sources of maximum dose rates around and inside the vault. Conclusion: We have used analytical techniques and Monte Carlo simulations to investigate neutron shielding considerations for a proposed proton therapy facility that will be situated on the University of Pennsylvania campus. These preliminary results give a good indication of what dose is expected at selected points inside and outside the treatment rooms and around the accelerator vault.
SU‐FF‐T‐102: Application of the Quality Index Methodology for Dosimetric Verification of Build‐Up Effect Beyond Air‐Tissue Interface in Treatment Planning System Algorithms
Authors: Caneva S , Tsiakalos M , Stathakis S , Zefkili S , Mazal A , Rosenwald J
Published: July 2006

Purpose: We have developed and applied a methodology based on quality index (QI) to assess the accuracy of calculations performed on a number of commercial treatment planning systems (TPS) for the case of build‐up effect beyond air‐tissue interfaces. This methodology requires the preliminary constitution of a “reference data set”, obtained experimentally, where correction factors (CF) were calculated as the ratios of the ionization at a depth d beyond the air‐tissue interface to the ionization at the same geometrical point for the reference configuration and for the same number of monitor units. Material and Methods: CFs were obtained from measurements in a phantom that consisted of polystyrene slabs with a 10 cm air‐gap between them. Measurements were performed with a plane parallel ionization chamber at different depths beyond the distal air‐polystyrene interface. They have been repeated with and without the air‐gap at constant source‐detector distance, for a 5×5 cm2 field and for photon energies ranging from 4MV to 23MV and the respective Monte Carlo calculations have been performed the same phantom set‐up. Results: A number of commercial TPS algorithms were tested: users computed CF using basic beam data from their accelerators and these were compared to reference CF for the corresponding QI. Considering that the error in the determination of CF for all beam energies tested should not exceed 6%, at the tested depths only one algorithm calculated CF within this error. The rest of the algorithms overestimated or underestimated CF in the build‐up region. At depth where electronic equilibrium is achieved, results were acceptable for all algorithms. Conclusions: A test that can be easily performed has been designed to validate the calculation algorithm of a TPS for the build‐up effect, using the QI of the incident beam.
SU‐FF‐T‐111: Bladder Dose Distribution in Cylindrical Brachytherapy Treatment
Authors: Xiong L , Viswanathan A , Stewart A , Cormack R
Published: July 2006

Objective: This work compares the characteristics of dose volume histogram (DVH) and dose surface area histogram (DSH) analysis of contoured bladder volumes in HDR vaginal cylinder brachytherapy. Method and Materials: CT scans were obtained on 20 patients with gynecological cancer who received in total 74 fractions of high dose rate brachytherapy treatment to the vaginal cuff, with the vaginal cylinder in situ. As part of an IRB approved study, the patients' bladder filling status was intentionally different for each fraction. The bladder was manually contoured for each treatment fraction including any fluid filling the bladder. The 3D bladder structure was reconstructed and its surface was extracted and represented with a triangular mesh. The dwell locations of the HDR source were identified for each fraction. Dose to each point on bladder was calculated according to the treatment plans. Results: The mean and standard deviation of volume (154.4 ±153.9 in cc) and the surface area (184.4 ± 91.8 in cm2) of the bladder varied with filling status. The bladder filling has caused more variation in DSH than in DVH in the high dose region. The average dose for the most irradiated volume D2cc was 70%±18% of the prescribed dose. The average surface area receiving D2cc was 11.6 ± 2.0 in cm2, or 7.5 ±3.1% of the total surface area compared to 2.4±1.8 % of the bladder volume. DSH is a smooth function with larger variation than DVH for doses over 70% of prescription. Conclusion: The nature of the bladder suggests that the surface area is a more realistic way of describing bladder. While both DVH and DSH may quantify the high dose region, surface area is more sensitive. As such DSH may offer a better correlation to clinical outcome.
SU‐FF‐T‐112: Boost Within a Boost in Permanent Seed Implants: Dosimetric and Clinical Impact
Authors: Beaulieu L , Aubin S , Varfalvy N , Lessard E , Pouliot J , Vigneault E , Martin AG
Published: July 2006

Purpose: Study the dosimetric and clinical impact on the target volume, boost volume (BV) and urethra of performing boosts in seed implants. Method and Materials: 35 localized prostate cancer patients with detailed biopsy results were treated with permanent seed implants Personalized plans in which BV corresponding to regions of positive biopsy were generated intra‐operatively based on a simulated annealing inverse planning algorithm. A second plan was generated for each patient without the BV. The dose objectives are 144 Gy to the prostate with a 3–4 mm margin, 2/3 (1/3) of the prostate covered by 150% (200%) of the prescription dose (PD), urethra V150 less than 10% and D5 should below 220 Gy. Finally, 100% of BV should receive 150% PD (or 216 Gy). Results: Comparing plans without and with BV show no significant change in the number of seeds, needles, prostate V100 and V200 (p>0.37). Prostate V150 and D90 show significant differences increasing from 65% to 70% and from 187 Gy to 191 Gy. By forcing the coverage of the BV, the 150% isodose lines (which extend outside the prostate) shift inside of the prostate. This small increase in prostate V150 leads to significant increases of the BV V150 from 79% (lowest 42%) to 94% (lowest 86%). BV do not translate to higher urethra doses (V150 and D5). BV are relatively small compared to the prostate V150 volumes (average ratio of 18%). Thus multiple seed reconfigurations inside the prostate are achievable to cover BV. Conclusion: Specific areas within the prostate can be boost to receive 150% of the PD with no impact on the urethra. Large volumes of these dose levels are inherent to the procedure. The plans lead essentially to a rearrangement of the seed positions. Potential radiobiological advantages could be obtained at no cost (procedure or time).
SU‐FF‐T‐113: BrachyDose: A New Fast Monte Carlo Code for Brachytherapy Calculations
Authors: Yegin G , Taylor R , Rogers D
Published: July 2006

Purpose: To develop a fast Monte Carlo code based on EGSnrc for accurate dose calculation around brachytherapy sources. Method and Materials: Sources and phantom geometries are modeled by using the Multi‐geometry technique which allows various predefined geometry elements (eg, sources, applicators, catheters) a phantom geometry. Sources such as an HDR Ir‐192 source and LDR I‐125 or Pd‐103 seed sources were modeled. One or more sources from a database can be duplicated many times and placed in arbitrary locations. Besides the above sources, BrachyDose can calculate dose around a miniature x‐ray‐tube source since it is based on EGSnrc. It also can use CT data in the phantom geometry. Variance reduction techniques are applied to speed up computation time. Dose is calculated by scoring the collision kerma using a tracklength estimator. There is an option to reuse every photon which escapes from a seed as if it came from every seed in the implant with same direction relative to the seed itself. Results: The speed of the BrachyDose calculation is specified by the time required to attain an average of 2\% statistics in the central region of an implant of 125 seeds spaced at 5 mm separation in a 1000 cm∧3 cubic phantom. The time required scales roughly as the inverse of the volume of the voxels. On an 2.4 MHz CPU, the computation time is 510 s for 1 mm voxels. The DVHs for 1 mm voxels are significantly different from those in 2 mm voxels. Changing phantom material from water to prostate tissue causes the dose to vary by +/−5% vs dose to water, depending on distance from the seeds. Conclusions: The Monte Carlo code developed is fast enough for routine clinical applications. Calculated dose values include inter‐seed effects and other effects from tissue inhomogeneities.
SU‐FF‐T‐114: Breath Coaching with Visual Feedback for End‐Expiratory Gated Radiotherapy
Authors: Briere T , Jhaveri P , Krishnan S , Crane C , Balter P , Gillin M , Mohan R , Beddar A
Published: July 2006

Purpose: To determine if breath coaching to maintain a consistent breathing amplitude at expiration is feasible in a clinical setting. Method and Materials: This technique consists of two phases of observation and active breathing to restrict the end‐expiratory phase so as to never exceed the lower limit of the gate. The first phase consists of 2 minutes of observation followed by 3 minutes of active breathing using visual feedback, while the second phase consists of 2 minutes of observation followed by 8 minutes of active breathing again using visual feedback. The purpose of the 2‐minute observation periods is to set the end‐expiratory gate at a comfortable level for the patient. Following the first phase the patient assesses whether the lower limit of the gate is appropriate and if it can be maintained in a reproducible manner for an extended period without exhaling below the gate. We have studied ten healthy volunteers of varying ages. The RPM system (Varian) was used to monitor the respiratory cycles of the volunteers. The volunteers self‐monitored their respiration via goggles that were turned on following each 2‐minute observation period. Results: The visual feedback was the key factor to reproducibly maintain the end‐expiratory gate. We were able to determine that all subjects were successful in sustaining their breathing pattern such that they did not exceed the lower limit of the gate and they were all able to do so comfortably. Only one volunteer would have needed to have the gate shifted upwards for actual treatment delivery. Only one volunteer would have needed to have the gate shifted upwards for actual treatment delivery. Conclusion: Breath coaching to maintain a consistent expiratory amplitude is feasible. It should not place a heavy burden on the patient during respiratory‐gated radiotherapy.
SU‐FF‐T‐115: Breathing Phase Information Extraction Method From Non‐Gated CT
Authors: Nurushev T , Smith R
Published: July 2006

Purpose: To evaluate feasibility and clinical usefulness of a new breathing phase extraction method from regular non‐gated CT scans in order to minimize the uncertainty of the dose calculations due to the external and internal motion artifact, also known as breathing “ripple” effect. Method and Materials: Non‐gated CT is acquired as usual for 3‐D patient geometry reconstruction in 3‐D conformal and IMRT treatment planning. A sub‐set of CT slices is then selected based on the timing correlation of the visible “ripple” effect and a new 3D image is made with interpolation. The image extracted with the new method is similar to the images acquired with 4‐D CT. At least two breathing phases can be reliably reconstructed: inhale and exhale. Gated 4‐D CT is also acquired at the same time at four gated phases. Comparison is then made for center of mass coordinates, tumor volume and displacement between extracted and acquired breathing phased images. Results: CT scans from 7 radiosurgery lung and kidney patients were used in this study. The average differences for location and displacement did not exceed 2 mm in Left to Right and Anterior to Posterior directions. Superior‐Inferior difference was up to 4 mm. Volume difference larger for the small tumors and went down when the tumor volume increased. Average volume difference was 9% with standard deviation of 14% for lung tumors with volume less than 10 cubic centimeters, and less than 8% and standard deviation of 6% for larger tumors. Conclusion: The breathing phase extraction method produced results comparable to the gated CT acquisition. While it may not be precise enough for the radiosurgery treatments, it is a good tool for planning fractionated treatments aiding in tumor delineation, defining PTV and assessing dose corrections due to tumor motion. Conflict of Interest:
SU‐FF‐T‐122: Characterization and Use of EBT Radiochromic Film for IMRT Dose Verification
Authors: Zeidan O , Stephenson S , Meeks S , Willoughby T , Wagner T , Kupelian P , Langen K
Published: July 2006

Purpose: To quantify and evaluate the use of the new EBT GafChromic film for its implementation in routine IMRT QA. Method and Materials: The new film was examined using a characterized flat‐bed scanner for several properties including polarization effects with scan angle and delivered dose, dose sensitivity, dose uniformity, OD time evolution post exposure, and dose response in comparison to water. The film high elasticity and relative insensitivity to water immersion allowed for its non conventional use in verifying dose distributions on curved surfaces. The film was wrapped into a cylindrical geometry inside an in‐house built cylindrical phantom and then immersed in water. Calculated dose distributions from the TomoTherapy treatment planning system (TPS) were then compared to the film's measured IMRT deliveries for 10 IMRT cases (5 Head and Neck, 5 prostate). Results: The film's intrinsic polarization was shown to be a function of delivered dose and could significantly affect the scanner's OD output readout. Film uniformity was shown to improve with delivered dose from ±5% for 50 cGy to nearly ±1.5% at 200 cGy. In addition, the film's OD was shown to saturate within 2 hours post exposure to a 2Gy dose, making it the fastest and least noisy RCF film so far. An excellent agreement was found between scanned water and film PDDs indicating the EBT energy response with depth is similar to water. Excellent agreement between predicted and measured isodose distributions and dose profiles were seen using the EBT film based on 10 IMRT deliveries. Conclusions: This work indicates that this new RCF film possesses unique and improved characteristics which allows for its use in routine patient‐specific IMRT QA. These encouraging results have motivated us to design an in‐house cylindrical phantom to verify dose beyond 2D planar surfaces and in water phantoms.
SU‐FF‐T‐124: Clinical Evaluation of the Performance of a Fuzzy Logic Guided Parameter Optimization for Inverse Treatment Planning
Authors: Petersheim M , Yan H , Wenz F , Yin F
Published: July 2006

Purpose: To evaluate the effectiveness of a Fuzzy Logic guided parameter optimization method for inverse treatment planning, in comparison with the results achieved by routine trial‐and‐error method. Method and Materials: The optimization algorithm was developed and integrated into a commercial planning system (Varian Eclipse). 10 prostate IMRT cases previously planned and approved by experienced planners were re‐optimized using this automated method with the same beam geometry. The original dose‐volume histogram (DVH) constraints were used as the initial parameter setup of the automated method. For each organ, the output dose was evaluated based on the percentage of dose received by a specific percentage of volume. The average dose difference between the automated and manual plans was calculated over a set of specified percentage volumes (99%, 80%, 60%, 40%, 20%, 10%, 5%, 1%). In addition, an experienced clinical physicist evaluated the acceptability of the plans generated by the automated method in terms of isodose distributions and DVHs. Results: Adoption of the automated method achieved both a comparable coverage of the planning target volume (PTV) and a substantial dose sparing of organs at risk (OARs). The mean dose was reduced by 30% for bladder, and 25% for rectum. There were few hot spots observed on OARs due to the overemphasis of PTV dose coverage. Conclusion: Preliminary results show that the automated parameter optimization method results in a significant dose reduction of OARs while maintaining a comparable PTV dose coverage. The automated method is able to relieve the burden of routine trial‐and‐error procedures done by planners, and has the potential to improve the resulting plan. However, minor manual intervention is still necessary to incorporate certain case‐specific information, which is beyond the capability of the automated method. This study is partially supported by a research grant from Varian Medical Systems.
SU‐FF‐T‐127: Clinical Feasibility of Jaw‐Only IMRT Plan for Prostate Cancer
Authors: Kim Y , Xia P
Published: July 2006

Purpose: To investigate the feasibility of inverse IMRT plans generated with jaw only, compared to IMRT plans with multi‐leaf collimator (MLC) for patients with the prostate cancer. Method and Materials: For five patients, two different planning techniques were used to generate inverse IMRT plans. One was the aperture‐based IMRT planning using MLC (MLC plans) and the other used jaw only (JO plans), available in a commercial planning system. The conventional 7 beams were employed. The planning goal was to deliver 72 Gy to > 95% of the PTV while keeping 10% of the rectum and 15% of the bladder receiving < 60 Gy and mean dose of the bulb < 30 Gy. For the JO plans, four different numbers of apertures/beam (3, 4, 5, and 6) were tested, compared to the MLC plans set to 3 apertures/beam. All plans (one MLC and four JO plans) for each patient were analyzed using conformal index (COIN), defined endpoint doses to the sensitive structures, total number of segments, and total delivered monitor unit. For each patient, planning dose constraints were kept the same for MLC and JO plans. Results: The COIN values for JO plans were generally increased as the number of apertures/beam increased, up to the same value as the MLC plans. The number of total segments for the JO plans was gradually increased (21, 27, 34, 40) as the number of apertures/beam increased (3, 4, 5, 6), compared to 21 segments for the MLC plans. However, the delivered MU values and doses to sensitive structures were patient‐specific and independent of the number of apertures/beam in JO plans. Conclusion: For centers without MLC collimator, it is possible to deliver inverse planned IMRT plans using jaws only for patients with prostate cancer. Conflict of Interest: Research sponsored by Prowess Inc.
SU‐FF‐T‐129: Clinical Implications of .decimal Solid IMRT with Pinnacle Treatment Planning System
Authors: Gluckman GR , Bell C , Cao Y , Rush S , Farber L , Warner C , Savitskij DV
Published: July 2006

Purpose: Recently, the .decimal Solid IMRT solution has become available to Pinnacle users. We explored the implications of this solution and the appropriateness of its use in the clinic. Method and Materials: Using a Varian 2300EX with 120‐leaf MLC, two Siemens Machines with and without 80‐leaf MLCs, a variety of sites were explored and optimized plans determined for conventional MLC delivery and compared to the .decimal Solid IMRT solution where the ideal Open Density Matrices (ODM) from Pinnacle3 is converted into an array of solid modulator thicknesses using the .decimal p.d software and re‐importing them back into Pinnacle3 for final dose calculation. We investigated the following key practical considerations: (1) What treatment machines would most benefit? (2) How does it impact the overall quality and efficiency in planning? (3) What are the cost benefits or revenue implications? (4) What safety precautions are necessary, i.e. with regard to R&V, Film or Ion Chamber QA? (5) How do treatment times and number of MUs compare to MLC based treatments? (6) How long does it take to implement the solution? (7) What treatment sites most benefit? Results: For the Siemens machines, we found reduction in the planning time, better quality plan and more efficient delivery, with less MUs, faster delivery times and improved agreement in film QA and IC measurements. For the Varian 2300EX with 120‐leaf MLC, the need for solid IMRT was not significant but can prove useful when treating large sites, negating the need for splitting the fields. Conclusion: We the found that solid IMRT solution to be valuable asset to our clinic, allowing our clinic to increase the number of IMRT treatments and treatment sites, extend the life and usefulness of older non‐MLC linear accelerators, provide better quality plans and reduced planning time.
SU‐FF‐T‐130: Clinical Significance Based IMRT QA Approach
Authors: Lian J , Cullip T , Deschesne K , Chang S
Published: July 2006

Purpose: Patient‐specific IMRT treatment quality assurance procedure often consists of the measurement of 2‐dimensional intensity map and absolute dose. The data is compared with the computed results from TPS using a standard pass‐or‐fail criterion. However, the same dose discrepancy may not have the same clinical significance depending on its location. For instance, the consequence of a hot‐spot in PTV is different than in spinal cord. In this project, we intend to develop a method that considers the locations of the dose discrepancy into the IMRT QA pass‐or‐fail decision‐making. Method and Materials: Compensator‐based IMRT treatments and PLUNC were used in this study. The 2‐dimensional dose distribution was acquired with the EDR2 film and Mapcheck. The measured point dose was back‐projected to compute the derived intensity map of the IMRT field. Using the measurement‐derived maps the patient dose is recomputed on the planning CT image. The dose discrepancy points between the original and measured plan were visualized by subtracting two dose grids. The QA test was performed in the 3‐dimentional space with the exclusion of 5% hot‐spots in PTV and cold‐spots in the critical structure. Results: The method was applied on two simulated clinical cases:(1) a 5‐field H&N IMRT with one defective compensator;(2) a 5‐field prostate IMRT plan with intentionally modified QA maps of three fields. In each case, the dose discrepancy points were computed and displayed in the patient CT. The QA passing rate is computed using both conventional 2D and revised 3D method. Conclusions: We reconstruct the 3D dose distribution in patient planning CT from the intensity maps obtained from the 2D IMRT QA measurement. A QA statistics method is proposed to include the location of dose discrepancy points. This approach promises a new IMRT QA pass‐or‐fail standard that considers the clinical significance of dose discrepancy measured in IMRT QA.
SU‐FF‐T‐131: Clinical Use of Linear Array MOSFET for Urethral Dose Verification in Prostate High Dose Rate Brachytherapy
Authors: Sadeghi A , Prestidge B , Lee J , Jurkovic I , Bice W
Published: July 2006

Purpose: To investigate the use of linear array MOSFET as in vivo dosimetry detector to determine the urethral dose for a single and multiple fraction during the prostate HDR treatment. Method and Materials: Commercially available Linear Array MOSFETs with 5 individual MOSFET was inserted into the 18 gage Foley catheter right after the HDR prostate implant. Measurements were performed in 25 patients receiving total of 2400cGy HDR boost in 4 fractions with 600cGy per fraction. The urethra dose was measured right after first fraction for all the patients and also subsequent fraction in 5 patients in terms of reproducibility of urethra dose. The exact location of the MOSFET was determined using radio‐opaque marker and the point dose for each MOSFET was determined using CT‐base treatment planning. Results: A Linear Array MOSFETs was placed in such a way that the first MOSFET being slightly above the bladder neck with the average reading of 75%±18% of the prescribed dose since it is beyond the base of the prostate. The dose was increased to maximum of 128% of the total dose within the prostate gland and decreased to 40% or less of the total dose beyond the apex of the gland. There was an excellent correlation of 2.8% between the MOSFET reading and treatment planning dose calculations. The MOSFET reading comparison between first and second fraction also correlated within 2.3%. Conclusion: MOSFETs are suitable for in vivo dosimetry during prostate high dose rate brachyhterpy not only to verify the dose across the urethra but also to verify that the needles are maintained in its exact same position as the first fraction. Any unexpected variation in urethra dose compared to initial treatment plan can be corrected in the subsequent fraction as a result of this dose verification procedure.
SU‐FF‐T‐133: Commissioning Electron Beams with Monte Carlo Simulation Based On Large Field Measurements
Authors: Faddegon B , Lehmann J , Chen J , Schreiber E
Published: July 2006

Purpose: To commission electron beams using measurements made with the jaws wide open (with no applicator) along with state‐of‐the‐art Monte Carlo simulation. Method and Materials: Central axis depth dose curves and dose profiles of 6–21 MeV Primus electron beams were measured for the 40×40 cm field and a comprehensive set of field sizes for all square applicators. Monte Carlo treatment head and water phantom simulations were done with the EGSnrc system using the BEAM and MCRTP user codes, respectively. The measured data for the 40×40 cm field was used to estimate the source and geometry parameters used in the smaller‐field simulations. Calculated output and dose distributions were compared to measurement. Results: Dose distributions calculated with this large‐field commissioning approach generally compared to 2%/2 mm or better with diode measurement. Relative output factors compared to 2% for the largest field available for each applicator. Output with cut‐outs, relative to the field with no cutout, also agreed within 2%. Conclusion: EGSnrc is sufficiently accurate for commissioning electron beams, given a good match to a few carefully done measurements for the 40×40 cm field with no applicator. This demonstrates the use of Monte Carlo simulation to commission electron beams, with only a few measurements. Measurements needed include the 40×40 cm central axis depth dose curve and cross‐plane and in‐plane profiles at dmax, and the ROF for the largest field of each applicator for all beam energies. Output and dose distributions for small and large fields for each applicator should be measured to verify the accuracy of the simulation.
SU‐FF‐T‐134: Commissioning Enhanced Dynamic Wedges Utilizing Mapcheck Device and Comparing with Film and Ion Chamber Dosimetry
Authors: Badkul R , Myers C
Published: July 2006

Varian Enhanced Dynamic Wedge (EDW) is a wedge technique where no physical modifier is used to create a wedge dose profile. The wedge dose profile is created by sweeping one of the Y jaw from open to closed position while other Y jaw and the X jaws stand still throughout the treatment. Because of the collimator motion, different parts of the field are exposed to the primary beam for different lengths of time. The motion of the jaw is controlled by a computer and the dose vs. collimator relationship to be followed in treatment mode is contained in a dose vs. jaw position table called Segmented Treatment Table (STT). The EDW provides wedge angles of 10°, 15°, 20°, 25°, 30°, 45° and 60° for both symmetric and asymmetric field sizes. EDW does not cause beam hardening and extra scatter to patients as compared to physical wedges. We measured the Wedge profiles using mapcheck device which contains 445 diodes in 2D array at various depths such as Dmax, 5cm, 10cm and 20cm. Dose profiles were also measured using EDR2 film and RIT software and 0.125cc ionization chamber. Profiles were compared with TPS generated profiles. We found that profiles measured with Mapcheck device agrees well within 1–4% with film & ionchamber measurements and TPS calculations. Mapcheck device is a very useful and time saving tool for commissioning and QA of EDW wedges.
SU‐FF‐T‐138: Comparison of Change in Optical Density Between Three Radiochromic Films Due to 100 CGy Dose‐To‐Water Delivered by X‐Rays in the 75 KVp to 18 MV Range
Authors: Rink A , Vitkin A , Jaffray D
Published: July 2006

Purpose: Over the last few decades, optical fiber‐based dosimeters for in vivo measurements have been investigated. One of the attractive features of optical dosimetry is the potential for improved water‐equivalency, compared to methods that use electrical signals. The materials considered thus far have been scintillating and optically stimulated luminescent sensors, doped and scintillating optical fibers, and radiochromic films. Several of the radiochromic films, including GafChromic MD‐55 and HS, have shown a lower response for a given dose when low‐energy (orthovoltage) x‐ray beams were used, compared to a Co‐60 source. This study continues the investigation of suitability of another radiochromic film, GafChromic EBT, for real‐time in vivo point‐based dosimetry by considering its response to a given dose delivered by beams varying in nominal energy. Method and Materials: 1 cm × 1cm pieces of MD‐55, HS and EBT film were irradiated within a 30 cm × 30 cm × 10 cm Solid Water phantom fitted with optical fibers for real‐time measurements. Each exposure delivered a dose of 100 cGy, using x‐ray beams ranging in energy from 75 kVp to 18 MV. Changes in optical density (ΔOD) were compared for the three types of film across all beam energies used. Results: Both MD‐55 and HS films showed a decrease of approximately 35% in ΔOD for a 75 kVp beam compared to a Co‐60 beam. Decrease in response for 225 kVp beam was less pronounced (approximately 15%). Both HS and MD‐55 exhibited this trend, confirming previous reports and validating our technique. The EBT film showed no decrease in response through the orthovoltage range. Conclusion: Due to a near‐constant response of EBT film for a given dose delivered using 75 kVp to 18 MV x‐ray beams, EBT medium is more suitable for in vivo measurements than MD‐55 and HS films.
SU‐FF‐T‐140: Comparison of Dose Prescription Using Single Versus Multiple Reference Points for MammoSite RTS Treatment Planning
Authors: Havnen A , King J , Mirzaei M
Published: July 2006

Purpose: To retrospectively compare dose prescription for MammoSite RTS using single versus multiple reference points through DVH evaluation. Method and Materials: CT images of four women treated with MammoSite RTS were selected for a retrospective study of dose prescription. The balloon was identified and contoured on the CT images using Plato BPS. A PTV was created by volumetrically expanding the balloon volume by 1cm. The final volume, PTV_EVAL consisted of the PTV minus the balloon volume. Six reference points were added along the outside edge of PTV_EVAL. Four points were added at locations lateral to the axis of the catheter, and two points were added along the axis of the catheter. Dose was prescribed to the six points individually, and DVHs of PTV_EVAL were calculated. Then dose was prescribed to 4, 5, and 6 reference points simultaneously, and a new DVH was created for each of those three cases. Results: For each prescription, the V150, V100, V90 and D95 from the DVH for PTV_EVAL were recorded and averaged across the four patients. When dose was prescribed individually to the two points along the catheter axis, the tissue volume receiving excess dose was unacceptable. When dose was prescribed individually to the 4 points lateral to the catheter axis, the coverage became inadequate. Plans in which dose was prescribed to multiple points simultaneously displayed sufficient coverage with lower volumes receiving excess dose. Conclusion: Due to the anisotropy of the source, prescriptions to individual points resulted in unacceptable coverage of the target volume or excess dose to tissue, while prescribing to multiple points simultaneously resulted in both more acceptable coverage and lower volumes of tissue receiving excess dose. Using four lateral points and one axial point resulted in the most target coverage while still limiting excess dose to tissue.
SU‐FF‐T‐141: Comparison Of Inverse Planning Simulated Annealing And Graphical Optimization For Prostate High Dose‐Rate Brachytherapy
Authors: Sankreacha R , Halina P , Morton G
Published: July 2006

Purpose: HDR dose optimization may be performed using a combination of Geometric Optimization (GO) and manual adjustment e.g. Graphical Optimization (GrO), but is time‐consuming. Optimization using anatomy based inverse planning e.g. Inverse Planning with Simulated Annealing (IPSA) can generate a solution in minutes. This study compares optimization using IPSA and GrO for treatment of prostate cancer. Materials and Methods: A retrospective comparison was performed of 63 consecutive patient plans generated and treated using GrO then re‐planned using IPSA. The clinical target volume and critical organs were contoured using PLATO v14.2.6 (Nucletron). A dose of 10Gy per insertion was prescribed to the 100% isodose. Dose optimization was performed using a combination of GO and GrO. For GrO, the isodose was dragged to the desired position, and the system automatically recalculated the appropriate dwell times. For each plan, the following dosimetric comparisons were made between that generated by IPSA and that generated and treated using GrO: prostate V100, V150, V200, urethra V120, Rectal V80, bladder V80, Homogeneity Index (HI) and Conformity Index (COIN). Results: The V100 was slightly lower with IPSA (GrO=97.5%, IPSA=96.7% p=0.001) but with a greater reduction in V150 (GrO=35.6%, IPSA=30.2% p=0.000) and V200 (GrO=12.7%, IPSA=10.7% p=0.000). Similarly, V120 for urethra (GrO=16.1%, IPSA=6.7% p=0.000), V80 for rectum (GrO=2.1%, IPSA=1.3% p=0.000) and V80 for bladder (GrO=2.3%, IPSA=1.3% p=0.000) were significantly lower with IPSA. HI increased (GrO=0.63, IPSA=0.69 p=0.000) while COIN was lower (GrO=0.71, IPSA=0.68 p=0.000). Conclusions: IPSA enables the rapid generation of dose‐optimized plans. The resultant plans provide comparable target coverage but with greater dose homogeneity, a lower high dose volume and lower dose to critical organs. Planning time was reduced using IPSA. This is a significant advantage over other methods of dose optimization in a clinical environment.
SU‐FF‐T‐142: Comparison of Ion Chamber and EPID Portal Dosimetry for Dynamic IMRT QA
Authors: Beltran C , Herman M , Kruse J
Published: July 2006

Purpose: The feasibility of replacing film and ion chamber measurements for dynamic IMRT QA with EPID is investigated. Analytical corrections are explored to account for energy variation and beam hardening not accounted for in the EPID dosimetry software. Method & Materials: The IMRT QA process involves a qualitative check of the fluences with film and a quantitative check of the full plan with an ion chamber (a PTV and OAR point are checked). The difference must be below 5% to pass QA. The predicted and acquired dose fluences to the EPID were qualitatively compared to the predicted and acquired film fluence. Quantitative comparison of the EPID point dose to the ion chamber point dose was done by finding the percent difference between the acquired and predicted EPID point dose, and comparing it to the percent difference of the acquired and predicted ion chamber point dose at the same 3D point. Based on the difference between the predicted and acquired fluence of a test field, an analytical 2D energy response matrix was created to account for the radial energy variation of the beam. A correction based on open and closed fields that accounts for beam hardening due to leaf transmission was developed. Fourteen points were analyzed. Results: EPID and film measurements were equivalent. The ion chamber measurements have a 1‐sigma uncertainty of 2.0%. Point dose comparisons with the standard EPID calibration gives an average difference from the ion chamber measurement of −6.09% with a standard deviation of (stdev) 3.15%. 2D energy correction gives −5.26%, stdev 3.18%. Beam hardening correction gives −1.67%, stdev 3.15%. Both corrections together give −1.46% with 2.78% stdev. Conclusions: The EPID system can replace film; ion chamber replacement is promising but more failure points must be tested. Conflict of Interest: Partial funding provided by Varian Medical Systems.
SU‐FF‐T‐145: Comparison of the Epson Expression 1680 Flatbed and the Vidar VXR‐16 Dosimetry PRO™ Film Scanners for Use in IMRT Dosimetry Using Gafchromic and Radiographic Film
Authors: Wilcox E , Daskalov G , Nedialkova L
Published: July 2006

Purpose: We have investigated the consistency of the newly available self‐developing Gafchromic® EBT film relative to EDR2 for IMRT dosimetry QA when using flatbed scanner as opposing to the well established Vidar VXR‐16. Method and Materials: IMRT plans consisting of seven to nine 6 MV beams were calculated using Pinnacle treatment planning system. The patient specific dose distributions were delivered to the phantom containing either EDR2 or EBT film. The films were scanned with both the Vidar and Epson scanners and analyzed using FilmQA™ (3cognition LLC) software. Comparisons between measured and calculated dose distributions are reported as dose difference (DD) (pixels within ±5%), distance‐to‐agreement (DTA) (3 mm), as well as gamma values (dose difference = ±3%, distance=2 mm). Results: Our preliminary analysis of 9 IMRT cases showed that: (i) Vidar and Epson EBT scans differ on average by 7.2% for DD, 6.3% for gamma, and 8.6% for DTA; (ii) same comparison using EDR2 gives 2.2% for DD, 3.1% for gamma, and 2.2% for DTA; (iii) the Epson EBT and EDR2 scans differ on average by 3.4% for DD, 5.0% for gamma, and 2.9% for DTA; (iv) the same comparison between EBT and EDR2 films using Vidar gives 10.3% for DD, 6.8% for gamma, and 5.1% for DTA. Conclusions: Tissue equivalence, high spatial resolution, energy independence, and self developing properties make the choice of EBT film for IMRT QA more desirable and cost effective than silver based radiographic film. Much better agreement with calculations can be obtained using EBT with a flatbed scanner. While both scanners give equivalent results with EDR2 films, a flatbed scanner in transmission mode is recommended to achieve optimal results with the EBT films.
SU‐FF‐T‐148: Cone‐Beam Reconstruction (CBR) Using a X‐Ray Simulator in Intracavitary Brachytherapy
Authors: Chang J , Suh T , Ji Y
Published: July 2006

Purpose: There are few limitations in conventional CT for localizing the dummy sources due to the slice image which has a certain distance between images. The use of the cone‐beam CT in brachytherapy also has limitations because of the economical efficiency in brachytherapy fields. To overcome former problems, we performed the CBR using x‐ray simulator. Method: The home‐made anthropomorphic pelvic phantom with the localizer and the HDR applicator set was simulated on the digital x‐ray simulator. The images were obtained with 10 degree intervals, and the CBR performed in the limited projections (36, 18, 12, 9 projection). The coronal planes (anterior‐posterior views) of CBR were mainly used for evaluating a CBR results. Results: We could obtain the CBR images with dummy source and artificial anatomic structure in the phantom. The peak pixel intensity and size differences of the dummy sources, which were important factor to distinguish the dummy sources from the backgrounds in coronal planes, were compared with each CBR results of the limited projections. Conclusions: We present the method for accurate source localization in a substitution for cone‐beam CT. This CBR approach provides the exact position of the sources and the delineation of approximate organ structure in brachytherapy planning, thus it could be a useful and economical technique for improving the planning results.
SU‐FF‐T‐149: Conformal Vs. IMRT Concomitant Boosts for IMRT Based Head and Neck Treatment
Authors: Wolfsberger L , Allen A , Tishler R , Court L
Published: July 2006

Purpose: To evaluate conformal 3D‐CRT and IMRT techniques for the boost portion of a concomitant boost treatment schedule for IMRT based head and neck radiation. Method and Materials: Nine‐field IMRT plans were generated using Eclipse for 4 stage IV oropharynx patients, treating all target volumes initially to 57Gy. Two alternative plans were then generated to deliver a 15Gy boost to gross disease: a 3D conformal plan, using 3–4 fields, and 5‐field IMRT plan. Boost volumes ranged from 25–60cc. The IMRT and 3D‐CRT boost plans were evaluated as individual graphic plans and as a cumulative with the first course treatment for a total dose of 72Gy (IMRT/IMRT and IMRT/3D‐CRT combinations). The comparison assessed target coverage, dose to critical structures (parotids, cord and oral cavity), hot spots and number of monitor units (MU). Results: Evaluated as a cumulative plan the IMRT/IMRT technique met all the constraints for critical structures (mean dose to parotid 26Gy, cord max 46Gy) and the hot spots were between 104–106%. The IMRT/3D conformal technique also met the constraints for the critical structures with hot spots between 103–105%. Both cumulative plans achieved 98.6–100% coverage of boost volumes. Evaluated as individual plans both the IMRT and 3D conformal boost plans achieved the desired coverage while keeping the dose to critical structures at a minimum; hot spots were located within the confines of the boost volume. The number of MU's ranged from 250–296 for the 3D‐CRT plan in comparison to 360–562 for the IMRT. Average planning time was 1.0 and 2.5 hours for the IMRT and 3D‐CRT boost, respectively. Conclusion: Both boost techniques are dosimetrically equivalent. Treatment technique can therefore be chosen based on the available clinical recourses.
SU‐FF‐T‐150: Consequence of CT Couch Sag in Radiation Therapy
Authors: Gutiérrez A , Boswell S , Mackie T
Published: July 2006

Purpose: To characterize couch sag on a CT scanner and determine the impact on patient treatments. A CT couch sags as it enters the gantry, and the amount depends on couch design, material, patient weight and distribution. Method and Materials: Four individuals were placed on a CT scanner couch (GE Discovery Lightspeed). A dial indicator was fixed to the bore of the CT scanner to measure couch deflection at the scanning plane when the couch was extended to various lengths. A second experiment was performed to measure sag at various positions for a fixed couch extension. A steel I‐beam with the dial indicator mounted on a rail was placed underneath the CT and tomotherapy couches. Two uniform loads were placed on the couch for three couch extensions and measurements were recorded at discrete locations. Results: Two forms of couch sag relevant to radiotherapy were observed: absolute and intra‐target sag. Absolute sag was shown to be 8.0±0.5 mm. Intra‐target sag depended on the S‐I length of the target and could be 2.3±0.5 mm. Both CT and tomotherapy couches displayed similar sag patterns. Differences in sag between the couches were more pronounced at short cantilevered distances with a maximum difference of 1 mm. Conclusion: A significant amount of sag occurs at the scanning plane resulting in a shearing of the images used for treatment planning. Absolute sag may be corrected by a couch height adjustment but intra‐target sag is a concern for elongated targets. The impact of sag on tomotherapy treatments is minimal since the relative difference in sag patterns between CT and tomotherapy couches is small. However, differences between CT and tomotherapy couch sag have become a concern for facilities treating total marrow irradiation (TMI) fields with tomotherapy. Conflict of Interest: Mackie has a financial interest in TomoTherapyInc.
SU‐FF‐T‐158: Determination of the Energy Spectrum of Bremsstrahlung of Linear Accelerations by Monte‐Carlo Calculations and An Analysis of Depth Dose Curves
Authors: Ulmer W
Published: July 2006

Purpose: The knowledge of the bremsstrahlung spectrum of a linear accelerator (6 MV up to 18 MV) represents the physical base of therapy planning systems. It is obtained by Monte‐Carlo calculations by taking account of the complete beam‐line (geometry/materials). It is also obtained by an analysis of depth dose curves of small fields via Laplace transform, if the electron energy Eel is known (upper limit of photon energy). Method and Materials: Monte‐Carlo calculations with EGSnrc with respect to the beam‐line of 6/18 MV (Varian 2300 C/D) and 6 MV (Varian 600C) have been performed for the AAA algorithm (Eclipse). The analysis of absorption depth dose curves in water (3×3 cm2 / 4×4 cm2 fields) of the mentioned machines has been performed for the central ray and tilted rays with the Laplace transform of a power sequence of Poisson distributions, which provide the reproducing kernel and the energy spectrum. The scatter profiles have been removed by a deconvolution. Results: Monte‐Carlo calculations and the Laplace transform method are in good agreement (standard deviation: ca. 1%) in the above cases. The formal integration of the reproducing kernel provides an analytical spectral distribution function
urn:x-wiley:0094-2405:media:mp1082:mp1082-math-0001 The parameter α and q depend on the radial distance of tilted rays from the central ray at surface. It is also used to fit fluctuations of Monte‐Carlo calculations. Conclusion: The Laplace transform method even works, if only Eel, the measured depth dose curves and profiles of small field sizes are known. A comparison of 6 MV (2300 C/D) with 6 MV (600C) shows that the spectral distribution of the latter case rather corresponds to the 10 MV mode of a 2300 C/D machine. This results from the Pb‐alloy of the flattening filter, whereas the 6/10 MV modes of the 2300 C/D use a Cu‐filter.