bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐FF‐T‐107: Selective Extended Field IMRT Can Protect Larynx and Adequately Treat the Lower Neck Lymph Nodes in Head and Neck Cancer
Authors: Qi P , Xia P 
Published: April 2010

Objectives: Radiation dose to the larynx has been a major concern in the treatment of head and neck cancer. The use of splitting field (SF) IMRT can improve the dose to the larynx but it may result in inadequate tumor coverage and dosimetric uncertainties at the matchline. In this study, we propose a selective extended field (SEF) method to avoid the use of splitting field while reducing the larynx dose and achieving the adequate tumor coverage. Materials and Methods: Five nasopharyngeal patients with the gross tumor volume extended to the lower neck were treated with extended field (EF)‐IMRT. SEF IMRT plans were created by extending only three anterior and anterior oblique beams to the supraclavicular region while the other fields were restricted to the superior of the vocal cord. For comparison, SF‐IMRT plans were also created and matched with the conventional AP field. All plans were compared based on the tumor volume coverage, mean dose to the larynx while meeting other planning requirement in RTOG protocol of 0225. Results: The average doses to 95% (D95) of the pGTVs and pCTV were 67.10 ± 6.56 Gy, 70.65 ± 1.62 Gy, 72.74 ± 1.76 Gy and 55.21 ± 3.41 Gy, 57.17 ± 1.51 Gy, 59.92 ± 1.01 Gy for SF, SEF, and EF‐IMRT plans, respectively. The tumor dose coverage in SF IMRT plans was the worst among three methods. Accordingly, the average mean doses to the larynx were 29.25 ± 5.61 Gy, 29.41 ± 2.99 Gy, 41.87 ± 10.61 Gy, respectively. The mean dose to the larynx in EF‐IMRT plans were the highest among the three methods. Conclusions: The selective extended field IMRT provides adequate tumor dose coverage and protects the larynx with the similar mean dose as the SF method.Research is supported by Siemens Corporation.
SU‐FF‐T‐127: Perhipheral Dose of Tungsten Powder Compensator (WPC) Based IMRT
Authors: Maurizo A , Jang S , Watchman C , Hamilton R 
Published: April 2010

Purpose: To characterize the peripheral dose (PD) of the newly developed compensator system based on tungsten powder (WPC) and to compare with MLC‐based IMRT. Method and Materials:. WPCs molded with different thicknesses of tungsten powder for comparison with MLC‐based plans were loaded into Elekta‐SLi block‐tray. Absorbed doses along the CAX and 2cm outside the field edge were measured for thickness of 1–7 cm at 1cm‐increments, at depths of dmax, 5cm and 10cm for photon energies of 6 and 15MV. Equivalent‐MLC thicknesses were calculated by constraining the total CAX dose and total MU for each compensator thickness. Absorbed doses along the CAX and 2cm outside the field edge were measured for the MLC‐equivalent thickness using Farmer chamber. In addition, PD for a WPC‐based clinical IMRT plan was compared to the equivalent MLC plan. Results: PD with tungsten thickness of 4cm, normalized to 10Gy along the CAX, was found to increase from 35 to 142cGy with increasing field size(5×5cm2 to 20×20cm2 at dmax) and from 74 to 85cGy with depth(dmax to 10cm with 10×10cm2 field). PD at dmax increased 204% by varying tungsten thickness from 1cm to 7cm. PD increased linearly with field size and was energy‐dependant only for the deeper depths where the PD became greater for 6MV than for 15MV. With increasing depth and decreasing field size, WPC‐based PD values became nearer to those of MLC‐based PD in trend. However, at the smallest field (5×5cm2), WPC showed lower PD than MLC. WPC‐based PD of a clinical plan measured 2cm outside the field edge, were ∼60% higher than that of MLC‐based plan. Conclusion: Mean WPC‐based PD was 60% higher than MLC‐based PD, however it was equivalent to 1.5% of the prescription dose of 2Gy/fraction.Conflict of Interest: Research sponsored by Axellis Ltd.
SU‐FF‐T‐280: Evaluation of the Accuracy, and Energy Dependence of the Nano‐Dot Dosimeters
Authors: Dini S , Jamshidi A , Hussain E , Pottes L , Liu G , Meigooni A 
Published: April 2010

Purpose: Characteristics and clinical application of the diode, TLD, and Nano‐dot have been studied by various investigators. However, there is a limited publication on clinical application of the Nano‐dot detectors (Landauer®)1. Despite the detailed investigations on characteristics of Nano‐dot, such as time, temperature, and depth, there is no data on energy dependence and accuracy of this dosimeter. The goal of this project is to evaluate the accuracy, energy dependence, and also positional dependence of the Nano‐dots in their clinical applications. Material and method: Accuracy and energy dependence of the Nano‐dot response have been investigated using the megavoltage photon and electron beams from Varian Clinac 2100/EX2 Linear Accelerator. The irradiated in tissue equivalent phantom material were read using a MircoStar reader. The responses of the Nano‐dots were converted to absorbed dose by calibrating the reader using a set of calibrated Nano‐dots which were irradiated in the calibration condition for doses ranging from 0.0 to 400 cGy. The measured absorbed doses for other irradiated Nano‐dots were analyzed as a function of beam energy and dose. Results: The results of these investigations show that the response of the Nano‐dots are very reproduceable (<0.2%). However, up to 5% variation among different Nano‐dots exposed to the same dose and the same beam energy has been observed. These dosimeters are less sensitive to higher energy photon beams. Accurate localization of the Nano‐dots on the patient is a significant factor on clinical application of this detector. Conclusion: Nano‐dots must be carefully calibrated for the different beam energy. Therefore, using the same calibration factors on the MicroStar reader, one has to verify that the results to be corrected appropriately, if it is used for other beam energies.1. Paul A. Jursinic, “Characterization of optically stimulated luminescent dosimeters, OSLDs, for clinical dosimetric measurements, Med. Phys. 34 (12) 4594–4604 (2007).
SU‐FF‐T‐291: Verification of In‐Vivo Dosimetry in TomoTherapy Treatments
Authors: Chen Q , Lu W , Schnarr E , Ruchala K , Olivera G 
Published: April 2010

Purpose: The implementation of in‐vivo dosimetry for a TomoTherapy® treatment system is described. The accuracy of the in‐vivo dosimetry is verified with phantom study. The prospect of replacing the film measurement in pretreatment DQA with the in‐vivo dosimetry is studied. Method and Materials: The exit detectors responses for each MLC leaf are measured with a series of solid water stack thicknesses and table heights during a calibration procedure. These measured responses forms a database that is used to reconstruct the incident fluence from the exit detector signal. The database could also be formed by scaling the gold standard database with necessary calibration procedure. The reconstructed incident fluence is then used as input to the dose calculator to get the reconstructed in‐vivo dose. Six different plans (tumor on or off center, under 1.0cm, 2.5cm and 5.0 cm field width respectively) are delivered on a phantom (Tomo® Cheese Phantom). The in‐vivo dose is compared with planned dose and ion‐chamber measurements. DQA plans in patient archives from several clinical sites are retrospectively studied. The in‐vivo dose is compared with the planned dose. Results: The reconstructed incident fluence agreed with the planned fluence within +/− 4%. In‐vivo dose agreed with the planned and ion‐chamber measured dose within +/− 1.5%. The accuracy is well within the normal 3% action level for DQA plan. The in‐vivo dose can be computed within 3 minutes normally in retrospective study mode and it could be computed real‐time during the delivery. Conclusion: TomoTherapy's in‐vivo dosimetry implementation achieves good accuracy. It could be a tool used in a program that performs a filmless DQA that could saves hours of time.Conflict of Interest: Research sponsored by TomoTherapy Inc
SU‐FF‐T‐294: Design and Validation of a Source Deployment Test for An Intra‐Ocular Sr‐90/Y‐90 Brachytherapy Source
Authors: Holmes S , Micka J , DeWerd L 
Published: April 2010

Purpose: To determine whether a well‐type ionization chamber can be used to verify proper source deployment of an approximately 2.5mm long 90Sr/90Y source pellet used to treat wet age‐related macular degeneration; to optimize the measurement geometry; and to verify that the apparatus functions as predicted by the model. Method and Materials: The Monte Carlo code MCNP5 was used to investigate optimal design parameters for a collimating well chamber insert intended to verify whether a 90Sr/90Y brachytherapy source is fully deployed to within 0.25mm of the stainless steel delivery cannula end plug. The source position for measurements was not known a priori with this resolution, so a precise retraction of the source for measured validation of the calculated data was not possible. An alternate method for validation of the MCNP5 model was devised to be substantially similar to the retracted source geometry but to allow corresponding measurements to be made in a well controlled geometry. As part of this investigation, a well chamber transfer standard for reference measurements was established and variations between production models of both straight reference cannulae and treatment cannulae were experimentally determined. Results: The Monte Carlo models indicated that a fully deployed source should generate between 16% and 20% of the open field straight cannula measurement used as a reference value. For the offset source measurements, the measured data concurred with MC values to within 1% (0.1% of the reference signal), thus validating the calculations. Measured variation between reference cannulae was ±0.3% and between clinical cannulae without the collimating insert was ±0.9%. Measurements were reproducible within ±0.2% standard deviation. Conclusion: This work validates the MCNP5 model used to calculate the signal range generated by an acceptably deployed 90Sr/90Y source in the collimating well chamber insert.Conflict of interest: This investigation was funded in part by NeoVista, Inc.
SU‐FF‐T‐306: Optically Stimulated Light Dosimetry: Commissioning of An Optically Stimulated Luminescence (OSL) System for Remote Dosimetry Audits, the Radiological Physics Center Experience
Authors: Aguirre J , Alvarez P , Followill D , Ibbott G , Amador C , Tailor A 
Published: April 2010

For the last 30 years the Radiological Physics Center (RPC) has used TLD dosimetry to conduct remote audits of beam output of photon and electron beams and energy checks for electron beams. Acrylic blocks containing capsules of TLD powder were sent for each beam. Powder was used as a single‐use disposable dosimeter. The RPC has previously described the use of the remote audits to identify units with beam measurements exceeding 5% and 5 mm. The system uncertainty is 1.5% (1 standard deviation) indicating high confidence in the 5% threshold for acceptability.OSL dosimeters have been available since 1992. Several publications have described their use for dose measurements at therapeutic levels. After a promising initial evaluation, the RPC decided to purchase and commission OSL dosimeters and instrumentation with the goal of implementing an OSL‐based system into the remote audit program.As part of the commissioning procedure, the depletion characteristics of OSL dosimeters were studied as they relate to the number of readings, the reader and the changes after annealing. Dark current and standard signal characteristics of the reader were evaluated and compared against factory specifications. The mechanical properties of the reader positioning characteristics were also tested.Because OSL dosimeters have unique sensitivities, response factor was determined and analyzed in terms of its variability with each reader, annealing cycle and cumulative dose. Dose dependence was also tested against annealing and accumulated dose. Energy dependence factors and fading characteristics were determined.A group of dosimeters from a single production was purchased and commissioned for use. Dose response, energy and fading characteristics for the batch were defined together with the design of a reading session and a quality assurance program.This work was supported by PHS CA010953 awarded by NCI, DHHS
SU‐FF‐T‐311: Calibration of Lot 47207‐01I GAFCHROMIC EBT Film Using the Xoft Axxent X‐Ray Source
Authors: Kelley L , Axelrod S , Rusch T 
Published: April 2010

Purpose: To determine the absolute dose delivered for a given exposed optical density of GAFCHROMIC® EBT film over a range of 0.25 to 14 Gy and over a range of distances from 1cm to 4cm in water for a Xoft Axxent® Model S700 X‐ray Source. Method and Materials: GAFCHROMIC film is used for dose delivery validation for the Xoft x‐ray source and associated applicators used to deliver prescription dose distributions. Custom Gammex RMI 457 Solid Water™ film fixtures were designed to locate both a PTW34013 ionization chamber and a film coupon at precise distances from the x‐ray source. The fixtures complete integral rotations around the x‐ray source during exposures to minimize azimuthal effects. Three sets of 12 exposures were performed for the dose range at each distance. Film coupons were scanned with an Epson® Expression® 10000XL scanner and the maximum pixel value was determined for each coupon corresponding to the calibrated ionization chamber measured dose. Results: The measured maximum pixel values for each data set were fit to a 5th order polynomial. Calibration coefficients were determined at different distances from the x‐ray source to investigate spectral differences. All fits were well behaved with residuals within ±4%. Differences between the fitted dose as a function of distance were small, indicating little sensitivity of the film to the range of source spectra. This calibration was applied to Xoft Axxent Vaginal Applicator validation study films, producing good agreement with the isodose contours predicted by BrachyVision™ treatment planning software. Conclusion: A precise calibration of GAFCHROMIC EBT film was performed for the Xoft x‐ray source using a PTW 34013 ionization chamber. It showed no significant difference in the measured optical density for a given measured dose over a distance range of 1cm to 4cm.Conflict of Interest: Research sponsored by Xoft, Inc.
SU‐FF‐T‐382: Ball‐Cube II: A New Film‐Based QA Tool to Characterize Stereotactic Dose Delivery
Authors: Purwar A , Main W , Leonovich A , Sorensen T 
Published: April 2010

Purpose: To evaluate Ball‐cube II (Accuray Incorporated, Sunnyvale, CA), an improved film‐based QA tool for Stereotactic Radiosurgery (SRS). Method and Materials: Ball‐cube II consists of four plastic sections connected together with clips. It accommodates two pieces of radiochromic EBT film (ISP Corporation, Wayne, NJ) in orthogonal planes. The primary advantage of Ball‐cube II over its predecessor “Ball‐cube I” is that it has four 0.1 inch (2.54 mm) film alignment posts, which when used with matching laser cut film lead to a precise and reproducible fit, thus minimizing errors due to film positioning. The alignment posts also have embedded copper markers to allow automatic registration of the film with the RT dose distribution. These markers are sufficiently visible to be located in the CT image, but are small enough to distinguish them from embedded gold fiducials used for patient alignment and tracking. Ball‐cube II has additional improvements, e.g., nylon nuts in the original design were replaced with clips, which enables easier and faster loading of the film and eliminates the possibility of over tightening the screws, which can cause the film to darken. The cube sits in an anthropomorphic head phantom and can be tracked using either the embedded gold fiducials or bony anatomy. The phantom treatment process is performed just as with a patient: CT image acquisition, treatment planning and phantom irradiation. The films are analyzed to compute spatial targeting error. Ball‐cube II and its predecessor were compared by performing 10 spatial targeting tests for each. Results: The mean targeting error is equivalent (0.40 vs. 0.39 mm), but the standard deviation is 46% smaller for Ball‐cube II (0.07 vs. 0.13 mm). Conclusion: The Ball‐cube II design reduces uncertainty in film analysis with precise film positioning and automatic dose‐to‐film registration.Research sponsored by Accuray Incorporated.
SU‐FF‐T‐405: Dose to Water Versus Dose to Medium in Proton Beam Therapy
Authors: Paganetti H 
Published: April 2010

Purpose: Dose in radiation therapy is traditionally reported as dose‐to‐water, Dw. Monte Carlo (MC) dose calculations report dose‐to‐medium, Dm. A methodology is needed to convert Dm into Dw for comparing MC and planning system results. This work addressed the following questions for proton therapy: What formalism allows the conversion from Dm to Dw?1. Can we convert MC calculated Dm into Dw retroactively or do we have to convert during particle tracking?2. What is the difference between Dm and Dw when analyzing patient data in terms of dose distributions, dose volume histograms and absolute doses?3. Is there a difference in the predicted beam range between Dm and Dw?Method: We did develop a formalism to convert Dm into Dw for proton beam dose calculations. Three different methods are introduced, an approximate method based on relative stopping power which allows retroactive conversion, a method considering energy dependent relative stopping powers, and a method incorporating nuclear interaction events as well. A total of 33 patient fields were analyzed. MC calculated dose distributions, dose volume histograms and absolute doses to assess the clinical significance of differences between Dm and Dw were compared. Results: We found that the difference between the three conversion methods was within 1% in most cases when analyzing mean doses to contoured structures. Further, we found that the difference between Dm and Dw can be up to 10% for high CT numbers. The difference is clinically insignificant for soft tissues. For proton beams stopping in bony anatomy, the predicted beam range can differ by 2–3 mm when comparing Dm and Dw. Conclusion: For comparison between MC and analytical dose distributions in proton therapy, a dose conversion is required. However, retroactive conversion seems to be sufficiently accurate in most cases, except for the end of range.
SU‐FF‐T‐410: Simulation of Large X‐Ray Fields Using Independently Measured Source and Geometry Details
Authors: Sawkey D , O'Shea T , Taranenko V , Faddegon B 
Published: April 2010

Purpose: Measure and simulate dose distributions from a 6 and 18 MV x‐ray linac with open jaws, including asymmetry, with independent measurements of the source and geometry details. Materials and Methods: Energy of the incident electron beam was measured by removing the target and flattening filter and measuring the percent‐depth ionization curve of the raw beam. Spot size was measured with an alternating layer spot camera. Treatment head parameters were determined from disassembly of the treatment head, or deduced from the penumbra position. Flattening filter density was determined by weighing it. Distance between target and flattening filter determined from position of the penumbra in the diagonal profiles. Simulations were with EGSnrc. Measurements and simulations were done both with and without the flattening filters. Results: Measured and simulated dose distributions inside the treatment field agreed to 1%/1mm. The exception was the buildup region with no flattening filters, where measurements were greater than simulation by 3–5%, corresponding to a 1 mm shift. This suggests the Roos chamber over‐responded to low energy electrons. Conclusions: Close agreement betweem measurement and simulation was obtained, with simulation parameters determined independently. It was not necessary to remove the flattening filters to obtain the simulation parameters.Support from NIH R01 CA104777‐01A2 and Siemens OCS.
SU‐FF‐T‐427: Monte Carlo Dose Distributions From Photon Beams Obtained with the Bethe‐Heitler and NIST Bremsstrahlung Cross‐Sections
Authors: Fragoso M , Faddegon B , Chetty I 
Published: April 2010

Purpose: Reports on Monte Carlo‐based clinical dose calculations have identified a paucity of information on the influence of cross‐sections on such calculations. A recent investigation on BEAMnrc‐based linac phase space (PHSP) calculations showed systematic differences (up to 3%) between fluence distributions computed using the Bethe‐Heitler (BH) and NIST bremsstrahlung cross‐sections. To understand the impact of these differences, we performed a study involving dose calculations in simulated water and heterogeneous phantoms. Method and Materials: DOSXYZnrc was used to calculate the dose distributions from a 6 MV (Siemens, Primus) photon beam. BEAMnrc was used to generate PHSP files, using the BH and NIST bremsstrahlung cross‐sections, for field sizes ranging from 5×5 to 40×40 cm2. Dose was computed in phantoms composed of water and heterogeneous media, including air, lung, bone and aluminum slabs, following the ICCR benchmark. The voxel dimensions were set to 5×5×2 mm3 (x, y, depth dimensions). Results: MC‐calculated dose distributions using the NIST and BH bremsstrahlung cross‐sections agreed within 2% for all geometric configurations and field sizes considered, including at interfaces in the ICCR benchmark phantom. Larger differences (up to 4%) were noted for the 40×40 cm2 field size, due to statistical fluctuations resulting primarily from the higher latent variance in the PHSP file for this large field size. Conclusions: Despite relatively large, systematic differences observed in the fluence distributions generated with the NIST and BH bremsstrahlung cross‐sections, calculated dose distributions in water and heterogeneous phantoms agreed within 1–2% on average. On the other hand, the insensitivity of dose distributions in phantom illustrates the importance of studying fluence distributions in MC‐based dose calculations, particularly when generating beam models from PHSP. Though we have shown that the differences in the fluence distributions have no impact in dose calculations, further investigation is needed on the cause of this discrepancy.Acknowledgement: NIH‐R01CA106770, NIH‐R01CA104777
SU‐FF‐T‐460: Comparison of Dose Distributions for Proton Machines with In‐Room Energy Degradation with Variable Energy Machines
Authors: Wang S , Gordon J , Langenegger A , Siebers J 
Published: April 2010

Purpose: To compare entrance and out‐of‐target dose values obtainable for single energy proton therapy treatment device with in‐room energy degradation with a device that has variable energy selection. Method and Materials: MCNPX Monte Carlo simulations are utilized to create a hypothetical dual‐scattering proton treatment delivery device in which a 250 MeV proton beam is delivered to the treatment room, independent of the desired treatment depth. Energy degradation is achieved in‐line using a carbon range shifter located 1.2 m upstream of the isocenter location. Calculations of in‐phantom depth‐dose and in‐air lateral and distance scans are performed for numerous range‐shifter and range‐modulator wheel settings to provide sufficient input data for a proton dose calculation algorithm. In‐phantom and patient dose distributions for this device are compared with those for a delivery device capable of variable room entrance energies from 70–210 MeV. Results: For a 6×6×4 cm3 target located at 10 cm and 5 cm depth in a water phantom, entrance doses for a single energy device are 69% and 73.8%, respectively, while the variable energy entrance doses are 61% and 64.4%. For a one‐field head‐and‐neck treatment plan, the single energy out‐of‐target doses are 5.7% higher than the variable energy device. Conclusions: The proton machine with in‐room energy degradation shows higher entrance dose than the machine with continuous entrance energy due to increased energy straggling in the beam. Further investigations are warranted to establish the potential clinical significance of such deviations.Conflict of Interest: This work was funded in part by Varian Medical Systems.