bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐308: Mobius FX Evaluation and Comparison Against a Commercial 4D Detector Array for VMAT Plan QA
Authors: Vazquez Quino L , Huerta Hernandez C , Morrow A , Massingill B , Rangaraj D 
Published: July 2016

Purpose:To evaluate the use of MobiusFX as a pre‐treatment verification IMRT QA tool and compare it with a commercial 4D detector array for VMAT plan QA.Methods:15 VMAT plan QA of different treatment sites were delivered and measured by traditional means with the 4D detector array ArcCheck (Sun Nuclear corporation) and at the same time measurement in linac treatment logs (Varian Dynalogs files) were analyzed from the same delivery with MobiusFX software (Mobius Medical Systems). VMAT plan QAs created in Eclipse treatment planning system (Varian) in a TrueBeam linac machine (Varian) were delivered and analyzed with the gamma analysis routine from SNPA software (Sun Nuclear corporation).Results:Comparable results in terms of the gamma analysis with 99.06% average gamma passing with 3%,3mm passing rate is observed in the comparison among MobiusFX, ArcCheck measurements, and the Treatment Planning System dose calculated. When going to a stricter criterion (1%,1mm) larger discrepancies are observed in different regions of the measurements with an average gamma of 66.24% between MobiusFX and ArcCheck.Conclusion:This work indicates the potential for using MobiusFX as a routine pre‐treatment patient specific IMRT method for quality assurance purposes and its advantages as a phantom‐less method which reduce the time for IMRT QA measurement. MobiusFX is capable of produce similar results of those by traditional methods used for patient specific pre‐treatment verification VMAT QA. Even the gamma results comparing to the TPS are similar the analysis of both methods show that the errors being identified by each method are found in different regions. Traditional methods like ArcCheck are sensitive to setup errors and dose difference errors coming from the linac output. On the other hand linac log files analysis record different errors in the VMAT QA associated with the MLCs and gantry motion that by traditional methods cannot be detected.
SU‐F‐T‐313: Clinical Results of a New Customer Acceptance Test for Elekta VMAT
Authors: Rusk B , Fontenot J 
Published: July 2016

Purpose:To report the results of a customer acceptance test (CAT) for VMAT treatments for two matched Elekta linear accelerators.Methods:The CAT tests were performed on two clinically matched Elekta linear accelerators equipped with a 160‐leaf MLC. Functional tests included performance checks of the control system during dynamic movements of the diaphragms, MLC, and gantry. Dosimetric tests included MLC picket fence tests at static and variable dose rates and a diaphragm alignment test, all performed using the on‐board EPID. Additionally, beam symmetry during arc delivery was measured at the four cardinal angles for high and low dose rate modes using a 2D detector array. Results of the dosimetric tests were analyzed using the VMAT CAT analysis tool.Results:Linear accelerator 1 (LN1) met all stated CAT tolerances. Linear accelerator 2 (LN2) passed the geometric, beam symmetry, and MLC position error tests but failed the relative dose average test for the diaphragm abutment and all three picket fence fields. Though peak doses in the abutment regions were consistent, the average dose was below the stated tolerance corresponding to a leaf junction that was too narrow. Despite this, no significant differences in patient specific VMAT quality assurance measured were observed between the accelerators and both passed monthly MLC quality assurance performed with the Hancock test.Conclusion:Results from the CAT showed LN2 with relative dose averages in the abutment regions of the diaphragm and MLC tests outside the tolerances resulting from differences in leaf gap distances. Tolerances of the dose average tests from the CAT may be small enough to detect MLC errors which do not significantly affect patient QA or the routine MLC tests.
SU‐F‐T‐315: Comparative Studies of Planar Dose with Different Spatial Resolution for Head and Neck IMRT QA
Authors: Hwang T , Koo T 
Published: July 2016

Purpose:To quantitatively investigate the planar dose difference and the γ value between the reference fluence map with the 1 mm detector‐to‐detector distance and the other fluence maps with less spatial resolution for head and neck intensity modulated radiation (IMRT) therapy.Methods:For ten head and neck cancer patients, the IMRT quality assurance (QA) beams were generated using by the commercial radiation treatment planning system, Pinnacle3 (ver. 8.0.d Philips Medical System, Madison, WI). For each beam, ten fluence maps (detector‐to‐detector distance: 1 mm to 10 mm by 1 mm) were generated. The fluence maps with larger than 1 mm detector‐todetector distance were interpolated using MATLAB (R2014a, the Math Works,Natick, MA) by four different interpolationMethods:for the bilinear, the cubic spline, the bicubic, and the nearest neighbor interpolation, respectively. These interpolated fluence maps were compared with the reference one using the γ value (criteria: 3%, 3 mm) and the relative dose difference.Results:As the detector‐to‐detector distance increases, the dose difference between the two maps increases. For the fluence map with the same resolution, the cubic spline interpolation and the bicubic interpolation are almost equally best interpolation methods while the nearest neighbor interpolation is the worst.For example, for 5 mm distance fluence maps, γ≤1 are 98.12±2.28%, 99.48±0.66%, 99.45±0.65% and 82.23±0.48% for the bilinear, the cubic spline, the bicubic, and the nearest neighbor interpolation, respectively. For 7 mm distance fluence maps, γ≤1 are 90.87±5.91%, 90.22±6.95%, 91.79±5.97% and 71.93±4.92 for the bilinear, the cubic spline, the bicubic, and the nearest neighbor interpolation, respectively.Conclusion:We recommend that the 2‐dimensional detector array with high spatial resolution should be used as an IMRT QA tool and that the measured fluence maps should be interpolated using by the cubic spline interpolation or the bicubic interpolation for head and neck IMRT delivery.This work was supported by Radiation Technology R&D program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning (No. 2013M2A2A7038291)
SU‐F‐T‐322: A Comparison of Two Si Detectors for in Vivo Dosimetry
Authors: Talarico O , Krylova T , Lebedenko I 
Published: July 2016

Purpose:To compare two types of semiconductor detectors for in vivo dosimetry by their dependence from various parameters in different conditions.Methods:QED yellow (Sun Nuclear) and EDP (Scanditronix) Si detectors were radiated by a Varian Clinac 2300 ix with 6 and 18 MV energies. 10 cm thickness water equivalent phantom consisted of 30×30 cm2 squared plates was used for experiments. Dose dependencies for different beam angles (0 – 180°), field size (3–40 cm), dose (50 – 300 MU), and dose rates (50 – 300 MU/min) were obtained and calibrated with Standard Farmer chamber (PTW).Results:Reproducibility, linearity, dose rate, angular dependence, and field size dependence were obtained for QED and EDP. They show no dose‐rate dependence in available clinical dose rate range (100–600 MU/min). Both diodes have linear dependence with increasing the dose. Therefore even in case of high radiation therapy (including total body irradiation) it is not necessary to apply an additional correction during in vivo dosimetry. The diodes have different behavior for angular and field size dependencies. QED diode showed that dose value is stable for beam angles from 0 to 60°, for 60–180° correction factor has to be applied for each beam angle during in vivo measurements. For EDP diode dose value is sensitive to beam angle in whole range of angles.Conclusion:The study shows that QED diode is more suitable for in vivo dosimetry due to dose value independence from incident beam angle in the range 0–60°. There is no need in correction factors for increasing of dose and dose rate for both diodes. The next step will be to carry out measurements in non‐standard conditions of total body irradiation. After this modeling of these experiments with Monte Carlo simulation for comparison calculated and obtained data is planned.
SU‐F‐T‐326: Diode Array Transmission Detector Systems Evaluation
Authors: Hoffman D , Dyer B , Kumaran Nair C , Katuri Y , Rong Y , Benedict S 
Published: July 2016

Purpose:A new transmission detector, Delta4 Discover, developed by Scandidos (Uppsala, Sweden) was evaluated for external photon beam verification and quality assurance. The device is an array of 4040 diodes designed to be mounted on the linac accessory tray to measure photon field shape, position and fluence during patient treatment. Interfractional measurements are compared to a baseline measurement made during delivery quality assurance. The aim of this work is to evaluate the stability of the device and its effect on the shape and magnitude of the treatment beam.Methods:Beam profiles, percent depth dose, and beam attenuation was measured for 6, 10, and 15 MV photon beams with and without the device in place for 1×1 and 30×30 cm2 fields. Changes in profile and percent depth dose was quantified to evaluate the need to recommission the treatment beam, or account for the device with a tray factor. The stability of the radiation measurements was evaluated by measuring the deviation of each diode measurement during repeated prostate VMAT treatment delivery.Results:Photon beam profiles changed by < 1.25% in the nonpenumbra regions of the 30×30 cm2 beam. Percent depth dose curves show a 5–7% increased dose at depths < 2.5cm, but agreed within 1% at depths > 2.5cm. This indicates increased skin dose, similar to the use of a physical beam wedge. The device attenuated 6, 10, and 15 MV photon beams by 1.71±0.02%, 1.36±0.03%, and 1.17±0.03%, respectively. The diode array reproduced dosimetric measurements within 0.5% standard deviation for repeated prostate VMAT measurement.Conclusion:The device demonstrated stabile radiation measurements, while not changing the treatment beam shape in a clinically significantly manner. Use of this device can be accounted for with a tray factor, as opposed to recommissioning the treatment beam.
SU‐F‐T‐396: Impact of Shoulder Deformation for Head and Neck VMAT
Authors: Uchida Y , Tachibana H 
Published: July 2016

Purpose:For head and neck VMAT (HN‐VMAT), variations of position and deformation of patient's shoulders is a concern to affect inaccuracy of dose distribution. It has been reported that the setup error of the shoulders was variable from 5 mm – 1 cm. The beams of the HN‐VMAT pass through the shoulders. We assessed the impact of shoulder deformation to dose distribution for HN‐VMAT.Methods:One HN‐VMAT plan was generated using a patient's CT. The patient's CT was deformed using ImSimQA (Oncology Systems Limited, Shrewsbury, Shropshire, UK) to generate several patterns of the shoulders’ deformations when the right and left humeral heads were shifted with 3, 6, and 15 mm in the superior and inferior directions (SI), 3, 5, and 15 mm in the anterior and posterior directions (AP), and 5 and 15 mm in the right or left direction (LR). DVH comparison was performed in the different deformation patterns. The dosimetric parameters of D95% for CTV70Gy, CTV60Gy and CTV54Gy and dmax for Spinal cord were also measured. Gamma index evaluation (Criteria: 3%/2mm) was performed to exhibit clinically tolerable area in the comparison.Results:DVH comparison shows similar for all structures. As the comparison for the dosimetric parameters, the variations of D95% in the LR and AP were within 1%. There were larger variations in the SI than those in the other directions, however were within 1.5%. In gamma index evaluation, the small spots with higher gamma index values were appeared when the shift was 6 mm, however the pass ratio was 99.13%.Conclusion:HN‐VMAT should be robust for shoulder deformation and geometric accuracy within 6 mm from patient's setup and image‐guided radiotherapy may be clinically acceptable for target dose coverage or normal tissue dose sparing.
SU‐F‐T‐399: Migration of Treatment Planning Systems Without Beam Data Measurement
Authors: Tolakanahalli R , Tewatia D 
Published: July 2016

Purpose:Data acquisition for commissioning is steered by Treatment Planning System (TPS) requirements which can be cumbersome and time consuming involving significant clinic downtime. The purpose of this abstract is to answer if we could circumvent this by extracting data from existing TPS and speed up the process.Methods:Commissioning beam data was obtained from a clinically commissioned TPS (Pinnacle™) using Matlab™ generated Pinnacle™ executable scripts to commission a secondary 3D dose verification TPS (Eclipse™). Profiles and output factors for commissioning as required by Eclipse™ were computed on a 50 cm3 water phantom at a dose grid resolution of 2mm3. Verification doses were computed and compared to clinical TPS dose profiles as per TG‐106 guidelines. Standard patient plans from Pinnacle™ including IMRT and VMAT plans were re‐computed keeping the same monitor units (in order to perform true comparison) using Eclipse™. Computed dose was exported back to Pinnacle for comparison to original plans. This methodology enables us to alleviate all ambiguities that arise in such studies.Results:Profile analysis using in‐house software for 6x, showed that for all field sizes including small MLC generated fields, 100% of infield and penumbra data points of Eclipse™ match Pinnacle™ generated and measured profiles with 2%/2 mm gamma criteria. Excellent agreement was observed in the penumbra regions, with all data points passing DTA criteria for complex C‐shaped and S‐shaped profiles. Patient plan dose volume histograms (DVHs) and isodose lines agreed well to within a 1.5% for target coverage.Conclusion:Secondary 3D dose checking is of utmost importance with advanced techniques such as IMRT and VMAT. Migration of TPS is possible without compromising accuracy or enduring the cumbersome measurement of commissioning data. Economizing time for commissioning such a verification system or for migration of TPS can add great QA value and minimize downtime
SU‐F‐T‐402: The Effect of Extremely Narrow MLC Leaf Width On the Plan Quality of VMAT for Prostate Cancer
Authors: Kim J , Park S , Kim J , Choi C , Park J 
Published: July 2016

Purpose:To investigate the effect of multi‐leaf collimators (MLCs) with leaf width of 1.25 mm on the plan quality of volumetric modulated arc therapy (VMAT) for prostate cancer.Methods:A total of 20 patients with prostate cancer were retrospectively selected. Using a high definition MLC (HD MLC), primary and boost VMAT plans with two full arcs were generated for each patient (original plan). After that, by shifting patient CT images by 1.25 mm in the cranio‐caudal direction between the 1st and the 2nd arc, we simulated fluences made with MLCs with leaf width of 1.25 mm. After shifting, primary and boost plans were generated for each patient (shifted plan). A sum plan was generated by summation of the primary and boost plan for each patient. Dose‐volumetric parameters were calculated and compared.Results:Both homogeneity index (HI) and conformity index (CI) of the shifted plans were better than those of the original plans in primary plans (HI = 0.044 vs. 0.040 with p < 0.001 and CI = 1.056 vs. 1.044 with p = 0.006). Similarly, the shifted plans for boost target volume showed better homogeneity and conformity than did the original plans (HI = 0.042 vs. 0.037 with p = 0.006 and CI = 1.015 vs. 1.009 with p < 0.001). The total body volumes of the original plans irradiated by the prescription dose were larger than those of the shifted plans in sum plans (60.9 cc vs. 49.0 cc with p = 0.007).Conclusion:Use of extremely narrow MLCs could increase dose homogeneity and conformity of the target volume for prostate VMAT.This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2015R1C1A1A02036331).
SU‐F‐T‐408: On the Determination of Equivalent Squares for Rectangular Small MV Photon Fields
Authors: Sauer OA , Wegener S , Exner F 
Published: July 2016

Purpose:It is common practice to tabulate dosimetric data like output factors, scatter factors and detector signal correction factors for a set of square fields. In order to get the data for an arbitrary field, it is mapped to an equivalent square, having the same scatter as the field of interest. For rectangular fields both, tabulated data and empiric formula exist. We tested the applicability of such rules for very small fields.Methods:Using the Monte‐Carlo method (EGSnrc‐doseRZ), the dose to a point in 10cm depth in water was calculated for cylindrical impinging fluence distributions. Radii were from 0.5mm to 11.5mm with 1mm thickness of the rings. Different photon energies were investigated. With these data a matrix was constructed assigning the amount of dose to the field center to each matrix element. By summing up the elements belonging to a certain field, the dose for an arbitrary point in 10cm depth could be determined. This was done for rectangles up to 21mm side length. Comparing the dose to square field results, equivalent squares could be assigned. The results were compared to using the geometrical mean and the 4Xperimeter/area rule.Results:For side length differences less than 2mm, the difference between all methods was in general less than 0.2mm. For more elongated fields, relevant differences of more than 1mm and up to 3mm for the fields investigated occurred. The mean square side length calculated from both empiric formulas fitted much better, deviating hardly more than 1mm and for the very elongated fields only.Conclusion:For small rectangular photon fields, deviating only moderately from square both investigated empiric methods are sufficiently accurate. As the deviations often differ regarding their sign, using the mean improves the accuracy and the useable elongation range. For ratios larger than 2, Monte‐Carlo generated data are recommended.SW is funded by Deutsche Forschungsgemeinschaft (SA481/10‐1)
SU‐F‐T‐409: Modelling of the Magnetic Port in Temporary Breast Tissue Expanders for a Treatment Planning System
Authors: Yoon J , Heins D , Zhang R 
Published: July 2016

Purpose:To model the magnetic port in the temporary breast tissue expanders and to improve accuracy of dose calculation in Pinnacle, a commercial treatment planning system (TPS).Methods:A magnetic port in the tissue expander was modeled with a radiological measurement‐basis; we have determined the dimension and the density of the model by film images and ion chamber measurement under the magnetic port, respectively. The model was then evaluated for various field sizes and photon energies by comparing depth dose values calculated by TPS (using our new model) and ion chamber measurement in a water tank. Also, the model was further evaluated by using a simplified anthropomorphic phantom with realistic geometry by placing thermoluminescent dosimeters (TLD)s around the magnetic port. Dose perturbations in a real patient's treatment plan from the new model and a current clinical model, which is based on the subjective contouring created by the dosimetrist, were also compared.Results:Dose calculations based on our model showed less than 1% difference from ion chamber measurements for various field sizes and energies under the magnetic port when the magnetic port was placed parallel to the phantom surface. When it was placed perpendicular to the phantom surface, the maximum difference was 3.5%, while average differences were less than 3.1% for all cases. For the simplified anthropomorphic phantom, the calculated point doses agreed with TLD measurements within 5.2%. By comparing with the current model which is being used in clinic by TPS, it was found that current clinical model overestimates the effect from the magnetic port.Conclusion:Our new model showed good agreement with measurement for all cases. It could potentially improve the accuracy of dose delivery to the breast cancer patients.
SU‐F‐T‐413: Calculation Accuracy of AAA and Acuros Using Cerrobend Blocks for TBI at 400cm
Authors: Lamichhane N , Studenski M 
Published: July 2016

Purpose:It is essential to assess the lung dose during TBI to reduce toxicity. Here we characterize the accuracy of the AAA and Acuros algorithms when using cerrobend lung shielding blocks at an extended distance for TBI.Methods:We positioned a 30×30×30 cm3 solid water slab phantom at 400 cm SSD and measured PDDs (Exradin A12 and PTW parallel plate ion chambers). A 2 cm thick, 10×10 cm2 cerrobend block was hung 2 cm in front of the phantom. This geometry was reproduced in the planning system for both AAA and Acuros. In AAA, the mass density of the cerrobend block was forced to 9.38 g/cm3 and in Acuros it was forced to 8.0 g/cm3 (limited to selecting stainless steel). Three different relative electron densities (RED) were tested for each algorithm; 4.97, 6.97, and 8.97.Results:PDDs from both Acuros and AAA underestimated the delivered dose. AAA calculated that depth dose was higher for RED of 4.97 as compared to 6.97 and 8.97 but still lower than measured. There was no change in the percent depth dose with changing relative electron densities for Acuros.Conclusion:Care should be taken before using AAA or Acuros with cerrobend blocks as the planning system underestimates dose. Acuros limits the ability to modify RED when compared to AAA.
SU‐F‐T‐417: Dosimetric Evaluation of Dose‐To‐Medium Vs. Dose‐To‐Water Using Acuros XB for Lung, Spine and Head‐And‐Neck Plans
Authors: Yu S , Rosenzweig D , Pacella M 
Published: July 2016

Purpose:This study evaluates the dosimetric differences between dose‐to‐medium (Dm) and conventional dose‐to‐water (Dw) reporting using Varian's Acuros XB (AXB) dose calculation algorithm with actual patient treatment plans.Methods:Twelve patients were selected: four head‐and‐neck (HN) (2 Gy × 33–35 fractions), four lung SBRT (10–12 Gy × 5 fractions) and four spine SBRT (6–8 Gy × 5 fractions) cases. All treatment plans were optimized using the Varian Eclipse Progressive Resolution Optimizer (version 13.6) to meet objectives of institutional guidelines. After the optimization process, each plan was calculated using both Dw and Dm options within AXB. The calculated treatment plans were normalized such that the prescribed dose covered at least 95% of the PTV. The dose‐volume histograms were evaluated for various dosimetric parameters. The percent difference between the two options is calculated as (AXB_Dw − AXB_Dm)/AXB_Dm *100.Results:The largest difference between AXB_Dw and AXB_Dm was seen in the mandible structure for HN cases, where AXB_Dw was up to 10% higher than AXB_Dm results (5.3%–10.2%). AXB_Dw was also higher for PTV maximum dose in these cases, ranging from 2.5%–5.7%. Among all other dosimetric parameters in HN, Spine and lung SBRT plans; the differences between AXB_Dw and AXB_Dm were within 5%. We also noted that AXB_Dw was consistently higher (1.8–3.8%) for cord in lung SBRT, and was consistently lower for esophagus/bowel in spine SBRT (−5% − −2.9%).Conclusion:The preliminary dosimetric results from our clinical study show that the selection of either Dm or Dw in AXB is not likely to produce significant dosimetric differences in most clinical cases. However, Dw can be different by up to 10% in bony anatomy compared to Dm. Therefore, Dm is the preferred option to achieve the greatest accuracy in both target and critical structure, providing a smooth transition from conventional to state‐of‐the‐art treatment planning.