bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐683: Robustness Analysis of Multiple Filed Optimized IMPT Plans for Head & Neck Patients Treated at MD Anderson Cancer Center
Authors: Li Y , Li H , Jingqian W , Zhu X , Li Y , Frank S , Zhang X 
Published: June 2015

Purpose:Our center's clinical outcome data so far indicated that excellent local control for the head and neck patients treated using multiple field optimized (MFO) IMPT technique have been achieved. The purpose is to determine the robustness of those IMPT plans and provide the clinician the knowledge of the degree of the robustness which will not compromise the local control and is safe for the normal tissue.Methods:A fast and approximate dose calculation method is developed to calculate the dose for the IMPT plan under different setup and range uncertainties. The dosimetric index evaluated using this method are compared with those calculated using the dose calculation model in TPS. A worst case scenario robustness analysis method is implemented using the fast dose calculation method. 100 head neck plans treated using MFO IMPT were retrospectively analyzed using implemented robustness analysis method. The lowest dose received by 95% target (D95) and the highest dose received by 5% target (D5) of GTV, CTV1, CTV2, CTV3, mean dose of parotid glands, cochlea and brain and the minimum dose in the most radiated 1 cm3 volume (D1cc) of spinal cord and brain stem were compared between nominal plans and plans in the worst case scenario.Results:For GTV, CTV1 CTV2 and CTV3, D95 in worst scenario are lower by 2.08, 4.59, 5.25 and 5.46 Gy than nominal plan, while D5 are higher by 1.14, 0.98, 0.85 and 1.21 Gy. D1cc of brain stem and spinal in worst scenario are higher by 3.37 and 1.95 Gy than nominal plan. The mean dose of parotid glands, cochlea and brain are higher by 3.52, 3.69 and 0.64 Gy respectively.Conclusion:The robustness analysis data from the clinically treated patients enables the clinician to gauge the degree of robustness in their clinical practice when adopting MFO IMPT technique for patient treatment.
SU‐E‐T‐687: Scatter Factors Comparison of 6MV FFF and Energy Matched 6MV EqFFF
Authors: Sigamani Ashokkumar , Nambiraj Arunai , Sinha S N , Yadav Girigesh , Rajesh T , Raman Kothanda , Kaviarasu K , Narayanan S , Meerza Kazem 
Published: June 2015

Purpose:To compare the Collimator scatter factor (Sc), Phantom scatter factor (Sp) and Total scatter factors (Sc,p) of 6MV FFF and energy matched 6MV FFF (6MV eqFFF)Methods:The flattening filter and primary collimator are the major sources of producing the scattered radiation. In this study, the field sizes from 5 × 5 cm2 to 40 × 40 cm2 compared for 6MV FFF and 6MV eqFFF. We measured Sc,p with CC 13 chamber at the depth of 10 g/cm2 using IBA blue water phantom and Sc measured with CC 13 chamber at the depth of 10 g /cm2 using columnar phantom (TG 74) for 6MV FFF and 6MV eqFFF x‐ray beams from a Siemens — ARTISTE(6MV eqFFF ) and Varian True beam (6MV FFF) linear accelerator. The Sp values derived from the Sc,p and Sc Values.Results:All the values of Sc,p, Sc and Sp are normalized to 10 × 10 cm2 field size. The measured values of Sc,p for 6MV FFF and 6MV eqFFF varies from 0.9404 to 1.0760 and 0.9690 to 1.0283 respectively. The Sc values for 6MV FFF and 6MV eqFFF varies from 0.9880 to 1.133 and 0.9882 to 1.0075 respectively. The Sp values for 6MV FFF and 6MV eqFFF varies from 0.9518 to 1.0619 and 0.9806 to 1.0206 respectively. From the measured values, we found that Sc, Sc,p and Sp factors of 6MV FFF less than 10 × 10cm2 field is similar to the 6MV eqFFF. For greater than 10 × 10 cm2 field size Sc, Sc,p and Sp factors higher for 6MV FFF than 6MV eqFFF.Conclusion:The energy matched 6MV FFF (6MV eqFFF) photon beam producing lesser Scatter radiation compare to the conventional 6MV FFF photon beams for field size more than 10 × 10 cm2.
SU‐E‐T‐691: Shielding Evaluation of a Treatment Room with An Electronic Brachytherapy System
Authors: Ibanez‐Rosello B , Bautista J , Candela‐Juan C , Villaescusa J , Ballester F , Perez‐Calatayud J 
Published: June 2015

Purpose:Esteya™ (Elekta) is a brachytherapy electronic system used for treating skin cancer lesions. This unit is based on a 69.5 kV X‐ray source and a surface applicator which produces a circular beam of a specific diameter, which varies from 1 to 3 cm. This study aims to establish the radiation protection measures for the system.Methods:A characterization of the scattered and leakage radiation of the system was implemented by means of experimental measurements. The scattered radiation measurements were performed with a Berthold LB133 ionization chamber, evaluating the dose rate for different distances from the applicator surface. The patient was simulated through water equivalent solid material of 9 cm thickness. Leakage was evaluated by setting 2 cm thick lead at the output of the radiation beam.From the obtained measurements, the necessary shielding has been estimated following the Report 147 by ICRP, and particularizing those values to a hypothetical installation. The dose received by a person who exceptionally would have to eventually stay inside the room with the patient was also analyzed.Results:The scattered dose rate ranges from 17.3 mSv/h at 0.25 m distance to 0.1 mSv/h at 2.5 m. Leakage represents 0.24% of the scattered dose rate. With these measurements and some assumptions on the workload and dimensions of a hypothetical treatment room it was estimated that the overall lead shielding for primary and secondary barriers was well below 1 mm, although it depends on each particular case. The overall absorbed dose to an eventual companion placed 0.5 m away from the patient is below 2 mSv after the complete treatment.Conclusion:Esteya shielding requirements are minimal, which facilitate its integration into conventional rooms. Furthermore, the presence of a companion during treatment is possible if absolutely necessary, recommending the use of a leaded apron and thyroid shielding.
SU‐E‐T‐699: Simulation of Bone Tissue Interface to Study Perturbation Effect in Gamma Knife Radiosurgery
Authors: Natanasabapathi Gopishankar , Vivekanandhan S , Kale SS , Rath GK , Bisht Raj Kishor , Sharma BS 
Published: June 2015

Purpose:To study perturbing effect of bone tissue interface in Gamma Knife dose distribution.Methods:PAGAT polymer gel was manufactured in‐house and poured into two PET cylinders for 3D measurement. Small vials were used for calibration.For 2D measurement EBT2 film was placed in mid portion of third gel filled PET cylinder. A bone material (+1400HU) of length 7cm and width 1.3cm was placed in the path of radiation beam at a distance of 4.5cm from measurement region to investigate its influence on dose distribution. For treatment planning each gel cylinder was fixed in Leksell frame and imaged in X‐Ray CT with scanning parameters: Tube Voltage — 120kVp, Tube Current — 130mAs, Slice Thickness — 1mm. Acquired images were transferred to Leksell Gamma Plan TPS (LGP Version 10.1). A treatment plan consisting of single 16mm collimator with coordinates x=100, y=100, z=100 was generated using convolution algorithm based planning (CABP). Each cylinder was positioned in treatment table and exposed to time calculated by the TPS. Irradiated gel was imaged with MRI (GE Medical Systems) to extract dose information from R2 maps and to determine subtle influence of bone material in the radiation path. Scanning parameter used: TE — 13.6ms, TR — 5000ms, slice thickness — 1.2mm, no of echoes — 8, FOV — 256×256mm2. Similarly exposed EBT2 film was scanned with EPSON scanner (Expression 10000XL) to measure dose.Results:3D and 2D measurement showed altered dose distribution in profile measurement, isodose overlay and dose volume histogram (DVH) comparison. For a gamma pass criteria of 1%/1mm voxel pass rate was around 76%.Conclusion:Presence of bone material in the radiation path perturbed the dose distribution unnoticeable in TPS calculation. Any HU value above +1024 is truncated by CABP hence need to incorporate higher HU values for accurate dose calculation in Gamma Knife TPS.The scientific resources used in this work were from the completed project N‐964 provided by AERB, Mumbai.
SU‐E‐T‐700: Single Isocenter Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiotherapy (IMRT) for Intact Left Breast Cancer Patients with Internal Mammary (IM) and Supraclavicular (S/C) Nodes ‐ a Treatment Planning Study
Authors: Lee G , Algan O , Keeling V , Higby C , Ahmad S , Hossain S 
Published: June 2015

Purpose:To investigate treatment plan quality and feasibility of VMAT for treatment delivery of intact left breast cancer patients with involved internal mammary (IM) and supraclavicular (S/C) nodes.Methods:Ten patients were selected for this retrospective study. All PTVs (Intact left breast, IM & S/C nodes) were contoured by a single radiation oncologist. Four 200° partial arcs with 2cm overlapping jaws (two clockwise and two counterclockwise; gantry angle 300°–140°) and ten fixed‐field equally spaced coplanar modulated fields were used to optimize single isocenter VMAT (RapidArc) and IMRT treatment plans, respectively, using Eclipse TPS. Prescribed dose to PTV was 46Gy in 23 fractions with prescription dose covering 95% of the PTV.Results:Four of the 10 patients had PTV > 1200cc. The mean PTV volume was 1200.17±571.51cc (findings are reported as mean ± 1 SD). All plans were judged clinically acceptable while satisfying dose‐volume constraints, with VMAT showing significantly better conformity than IMRT. The mean Paddick conformity index (PCI) was 0.88±0.03 for VMAT vs. 0.82±0.06 for IMRT plans (p=0.001). However, maximum doses were within ±1.0% of 111% of the prescription dose for both plans. The heart mean dose was 5.00±0.99Gy for VMAT vs. 7.09±1.70Gy for IMRT (p<0.001), heart volume receiving >30Gy was 0.18±0.29% for VMAT vs. 0.68±1.24% for IMRT (p=0.19), and V5Gy and V7Gy were 31.67±11.56% and 14.93±7.41% for VMAT vs. 67.15±17.66% and 36.55±16.59% for IMRT plans, respectively (p<0.001). The mean total lung dose was 8.95±0.52Gy vs. 8.48±0.81Gy (p=0.06) and V20Gy was 10.65±2.00% vs. 8.12±1.37% (p=0.055) for VMAT and IMRT plans, respectively. The right breast mean dose was 2.83±0.46Gy for VMAT vs. 4.06±0.61Gy for IMRT plans (p<0.001).Conclusion:VMAT plans achieved intended dose coverage to the intact left breast, IM & S/C nodes at ≥ 95% with significantly lower dose to critical structures, especially, to heart and contralateral breast compared to IMRT plans.
SU‐E‐T‐707: Soft‐Tissue / Bone Interface Backscatter Prediction by Two Commercial Electron Treatment Planning Algorithms
Authors: Catt B , Yudelev M 
Published: June 2015

Purpose:In this work, we investigate the accuracy of two commercial Monte Carlo algorithms used for electron treatment planning in their prediction of dose enhancement near a soft‐tissue / bone interface. The calculated doses at the interface of a heterogeneous phantom are compared with results obtained from measurements, simulations with EGSnrc, and calculations using an empirical formula.Methods:Phantoms were constructed and modeled in Eclipse 10.0 (Varian) and Monaco 5.0 (Elekta) treatment planning systems. Slabs of bone equivalent material (CIRS Inc.) were inserted into a stack of solid water and situated at 2.9 cm depth, equivalent to dmax for a 12 MeV electron beam. This setup was chosen as an exaggeration of any clinically relevant inconsistencies which may be seen near interfaces. Plans were run on these phantoms and doses at the interface were compared with results obtained using a similar phantom within EGSnrc. The measurements were performed in a 12 MeV electron beam, using a parallel plate ion chamber.Results:General agreement was observed between calculated and measured dose distributions along the beam's central axis in the regions away from the heterogeneity; however, Varian's eMC algorithm could not properly account for backscatter from higher density materials, instead predicting a decrease in dose just before the interface. This leads to an underestimation of dose by up to 9% at the interface, when compared with ion chamber measurements. Elekta's VMC++ algorithm was able to more accurately account for the presence of the backscatter material, demonstrating an agreement within 1.7% of ion chamber measurements at the interface.Conclusions:Although Monte Carlo algorithms are widely regarded as the gold standard for accuracy, care must still be taken when using implementations which have been optimized for calculation efficiency, especially within regions lacking electronic equilibrium such as those found near interfaces with bone.
SU‐E‐T‐708: Spatial Accuracy of Small‐Target SRS Using Conebeam CT Guidance and Static Arcs with MLC‐Defined Fields
Authors: Brezovich I , Popple R , Duan J , Wu X , Shen S , Huang M , Cardan R 
Published: June 2015

Purpose:To measure the spatial accuracy of dose delivery under conebeam CT guidance to small targets using static arcs with MLC‐defined fields.Methods:A plastic (PMMA) phantom simulating a small brain lesion was constructed. The lesion was a cylindrical air cavity having 3 mm length and 3.175 mm diameter. Gafchromic EBT 2 film passing through the cavity was pin pricked at the exact geometric cavity center. Following CT simulation treatment plans involving static arcs with MLC‐defined fields were designed, similar to radiotherapy with circular tertiary cones. 5×2 mm fields were generated by opening two centrally located leaf pairs of a high‐definition MLC to 2.0 mm. The target was irradiated with 6 MV photons on a STx linac under conebeam CT image guidance to 600 cGy at isocenter. Films from coronal and sagittal planes were scanned and evaluated using the ImageJ software. The distance between the centroid of the 50% isodose line and the center of the pin prick was the measure of geographic accuracy.Results:Single arcs resulted in ellipsoidal 50% isodose surfaces having diameters of 5.0 mm along the gantry axis and 7.7 mm in the cross‐sectional directions. 4‐arc delivery at couch angles of 0, 45, 90 and 315 degrees produced 50% isodose surfaces having diameters of 5.6, 5.7 and 7.5 mm diameters along the lateral, longitudinal and anterior‐posterior directions, respectively. In any of the experiments, the largest distance by which the centroid of the 50% isodose line missed the center of the target was 0.36 mm or less.Conclusion:MLC‐defined static arcs delivered under conebeam CT guidance provide precise irradiation of small targets. The method is very efficient since no special attachments or modifications of the accelerator are required. Since MLC leaves are stationary throughout the treatment, patient‐specific QA involving phantoms should not be required.
SU‐E‐T‐713: Study On Application of Beam Angle Optimization for Multiple Intracranial Metastases
Authors: Lin X , Sun T , Yin Y 
Published: June 2015

Purpose:To study the dosimetric impact of different angle fields IMRT and the feasibility of beam angle optimization (BAO) for multiple intracranial metastases.Methods:11 patients with multiple intracranial metastases were included in this analysis. In Varian Eclipse TPS two treatment techniques were designed for each patient: the 7 equal spaced fields and 7 fields by beam angle optimization IMRT. Two plans were designed for each patient with the same dose‐volume constraints and prescription dose. All plans were normalized to the mean dose to PTV. The dose distribution in the target, the dose to the organs at risk and normal brain tissues and total MU in two techniques were compared to explore the dosimetric differences.Results:For the target dose, conformity and homogeneity in PTV, no statistically differences were observed in the two plans. Compared to 7 equal spaced fields IMRT plans, IMRT plans with BAO reduced the maximum dose to left and right lens by an average of 45%, 37%, the mean dose to left and right eyes were reduced by an average of 42.6%,44.5% .The maximum dose of the right optic nerve and the mean dose of normal brain tissue were reduced by an average of 23%,3% respectively. The above data were statistically significant. IMRT plans with BAO reduced the maximum dose of the brainstem and the optic chiasm, the number of MU, but the Result were not statistically significant (p> 0.05).Conclusion:Compared to 7 equal spaced fields IMRT plans, IMRT plans with BAO showed the similar target dose and reduced the dose of the organs at risk. For multiple intracranial metastases, IMRT plans with BAO were feasible and beneficial.
SU‐E‐T‐716: Suitability Study of a Unique 3D Dosimeter for Commissioning Radiation Treatment Machines
Authors: Roed Y , Tailor R , Pinsky L , Ibbott G 
Published: June 2015

Purpose:To determine the suitability of a methacrylic acid‐based MAGAT gel dosimeter to serve as a 3D commissioning toolMethods:Different sized MAGAT gel dosimeters were fabricated in‐house to perform dose response, depth dose and dose rate measurements using an orthovoltage treatment unit. Dose response data were obtained by irradiating dosimeters to six dose levels at three different effective beam energies. Depth dose measurements were taken using one dose at one energy. Dose rate dependence was measured by varying only distances for the gel irradiations while dose level and energy remained unchanged. A Bruker Biospecs 4.7T MRI scanner was used to acquire spin‐spin relaxation rates on axial slices at different depths throughout each dosimeter 24h after irradiation.Results:The dose response curves exhibited a separation when compared for the measured energies. MAGAT depth dose data, normalized to ion chamber data at 2 cm depth, showed an increasing divergence with increasing depth. The dose rate decreased when distances were increased and demonstrated a significant dose rate dependence of the measurements. Consequently, dose rate corrections were applied to all measurements, thus, aligning the dose response curves for all three energies and reducing the divergence between MAGAT and ion chamber depth dose data.Conclusion:The MAGAT dosimeter was intended to serve as a 3D commissioning tool for testing radiation treatment plans of small fields with steep dose gradients and complex treatment volumes. A suitable detector for commissioning needs to be dependent on dose but independent of dose rate. This study, however, showed a dose rate dependence of up to 30% eliminating the current composition of MAGAT as a suitable dosimeter. Further investigations of chemical compositions need to be performed.
SU‐E‐T‐724: Testing the Limitations of a Photon Dose Algorithm in Commissioning
Authors: Xue J , Choi M , Park J , LaCouture T , Ibbott G 
Published: June 2015

Purpose:This work is to test the limitations of a photon dose algorithm during the commissioning of a treatment planning system.Methods:Commissioning tests for a model‐based dose calculation algorithm typically involve the verification of PDD, output and dose profiles, but often those tests are performed at one SSD, one depth and one nominal gantry position. Those tests are useful to validate the modeling of radiation beams, but they may not be sufficient to detect the limitations of an algorithm. Additional tests were performed at several SSDs, various depths, oblique gantry angles and off‐axis conditions to demonstrate the accuracy and limitations of the dose calculation algorithm. Dose profiles were measured by in‐water scanning with a three‐dimensional scanning system and calculated in the TPS using a virtual water phantom.Results:Dose profiles from both the measurement and the calculation were plotted for comparison. Also plotted were the difference in absolute dose between the measurement and the calculation. For the off‐axis MLC field tests, larger discrepancies were observed at the open portion and the far edge of the field, which became greater with short SSD and deep depth. In addition, the shape of the profile appeared different for the open portion of the field. For the oblique MLC field tests, the largest difference was seen around the high‐dose shoulder of the profile. Differences in some point doses were observed to be greater than 10% of the maximum field dose.Conclusion:We have learned the limitations of the superposition dose algorithm in the XiO planning system through some specific tests, which are related to the parallel kernel approximation and the simplified energy spectra employed by the algorithm to calculate field‐size dependent fluence.
SU‐E‐T‐736: The Impact of Beam Angle Optimization of Intensity‐Modulated Radiotherapy for Postoperative Radiotherapy of Cervical Cancer
Authors: Sun T , Yin Y , Lin X , Liu T , Zhang G 
Published: June 2015

Purpose:To evaluate the dosimetric characteristics of intensity‐modulated radiotherapy (IMRT) treatment plan with beam angle optimization.Methods:Ten post‐operation patients with cervical cancer were included in this analysis. Two IMRT plans using seven beams were designed in each patient. A standard coplanar equi‐space beam angles were used in the first plan (plan 1), whereas the selection of beam angle was optimized by beam angle optimization algorithm in Varian Eclipse treatment planning system for the same number of beams in the second plan (plan 2). Two plans were designed for each patient with the same dose‐volume constraints and prescription dose. All plans were normalized to the mean dose to PTV. The dose distribution in the target, the dose to the organs at risk and total MU were compared.Results:For conformity and homogeneity in PTV, no statistically differences were observed in the two plans. For the mean dose in bladder, plan 2 were significantly lower than plan 1(p<0.05). No statistically significant differences were observed between two plans for the mean doses in rectum, left and right femur heads. Compared with plan1, the average monitor units reduced 16% in plan 2.Conclusion:The IMRT plan based on beam angle optimization for cervical cancer could reduce the dose delivered to bladder and also reduce MU. Therefore there were some dosimetric advantages in the IMRT plan with beam angle optimization for cervical cancer.
SU‐E‐T‐738: The Limit of Detectability and Resolution of a Cylindrical Diode Array Phantom for VMAT and SRS Quality Assurance
Authors: Gray T , Pearson D 
Published: June 2015

Purpose:To determine the limit of detectability and resolution of a cylindrical QA phantom for quality assurance of VMAT and SRS procedures in small field sizes.Methods:Eight different square field sizes were delivered onto a cylindrical QA phantom with 1386 diodes at gantry angles of 0, 90, 180 and 270 degrees, using a 6 MV beam at a maximum dose rate of 600 MU/min on a dedicated stereotactic linear accelerator with 2.5mm and 5mm leaves. After verifying pass rates of normal square field sizes, errors were introduced into the quality‐assurance analysis, including an expansion of the field size by 1 mm for all jaws on all sides, an expansion of the field size by 1 mm on one side of the X and Y jaws,MLC errors, and a table shift by 1 mm vertically and longitudinally at 270 and 90 degrees and a table shift of 1mm laterally and longitudinally for angles of 0 and 180 degrees. Treatment planning system calculated dose distributions for measured square field size dose data was imported into the QA phantom software and compared against a treatment planning system calculated 3D dose distribution. Percent pass rates were computed using gamma analysis with 2mm/2% analysis criteria with a background threshold value of 30%.Results:QA software comparison between measured fields and treatment planning system calculations indicate that the passing rate of square fields decreases significantly when errors are induced in the quality assurance analysis. Adding two opposing MLC leaves on opposing sides of each square field in the treatment planning system produced a 31.2% average difference from normally measured square field sizes compared between the treatment planning system and what was measured by the QA software.Conclusion:This work indicates the potential for detecting errors in VMAT quality assurance in small field sizes using a cylindrical QA phantom.