bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐720: Surface Electronic Brachytherapy Dosimetry: Comparison and Uncertainty Evaluation of Different Calibration Protocols and Ionization Chambers
Authors: Candela‐Juan C , Garcia‐Martinez T , Niatsetski Y , Schuurman J , Nauta G , Vijande J , Ouhib Z , Ballester F , Perez‐Calatayud J 
Published: June 2015

Purpose:The Esteya electronic brachytherapy system (Elekta Brachytherapy, The Netherlands) has been recently developed for HDR brachytherapy treatment of skin lesions, using a 69.5 kVp x‐ray source and a set of applicators that generate beams of 1 to 3 cm diameter. The purpose of this study was to evaluate the surface dose rate of the Esteya (and its estimated uncertainty) by using different detectors and calibration protocols.Methods:The surface dose rates for the different applicators were measured with the plane parallel ionization chamber T34013 (PTW‐Freiburg, Germany) and the parallel plate ionization chamber Exradin A20 (Standard Imaging Inc., USA). The first one was calibrated in both air and water, whereas the second one was provided with calibration in air. Two different chambers of each type were used to evaluate detector reproducibility. Measurements in air were performed according to dosimetric protocol established by the TG‐61 of the AAPM, whereas measurements in water were performed in a CIRS Plastic Water LR phantom, using the methodology proposed by the TRS‐398 of IAEA. The correction factors of each protocol and ionization chamber were carefully evaluated.Results:Differences between surface dose rates measured in‐air and in‐water using the T34013 chamber range from 1.6% to 3.3%. Differences are below 3.7% when measurements with the A20 and the T34013 chambers calibrated in air are compared. However, absorbed dose rates measured with the A20 chamber in air and the T34013 chamber in water differ up to 6%. Estimated uncertainties are of the order of 2.5% (with coverage factor k=1). The output factors measured with the PTW chambers differ by less than 1.1% when compared to the values measured with the A20 chamber.Conclusion:The two ionization chambers and the two dosimetric protocols provide consistent results considering the combined uncertainties. Both chambers have negligible stem effect.This study was supported in part by Generalitat Valenciana under Project PROMETEOII/2013/010 and by Spanish Government under Project No. FIS2013‐42156. Funding was also received by Elekta and PTW.
SU‐E‐T‐721: Systematic Dose Discrepancy of Diode Based In‐Vivo Dosimetry Due to Short Source‐To‐Surface Distance and Oblique Beam Angle Incidence
Authors: Chen F , Rao M , Cao D , Wu J , Ye J 
Published: June 2015

Purpose:The diode detectors for photon beam In‐Vivo dose (IVD) measurement are usually manufactured with intrinsic buildup, which may cause the IVD respond differently from the predicted dose when the source‐to‐surface distance (SSD) and/or the beam incident angle changes, such as that in breast or chest wall irradiations. This work is to evaluate this systematic discrepancy.Methods:In‐Vivo dose was measured on a solid water phantom as a function of varying SSD and beam oblique incidence. The cylindrical IVD detectors were calibrated to 100cGy at nominal gantry angle, 100MU, 10×10cm field, 100 SAD with isocenter at dmax. To study SSD dependence, beams were delivered from nominal gantry angle at SSDs from 105 to 75cm. Doses calculated at the dmax were used as the predicted values. To study the oblique incidence responses, measurements were performed at fixed 100 SSD with gantry angles ranging from the nominal angle (0 degree) to horizontal (90 degree). Two calculation points were used for comparison, one at dmax from nominal angle, a second one at dmax along the oblique beam ray. For both setup, IVD was positioned at the beam CAX on the phantom surface.Results:Dose discrepancy increases with decreasing SSD and is more pronounced with high photon energy. This discrepancy is as high as 4.6% for an 18MV beam at 75SSD. For oblique measurements, both calculated values decrease as the oblique angle increases; however, the measured IVD doses exhibited little changes, which introduce significant systematic errors (∼20% at 80 degree) for incident angles larger than 60 degrees.Conclusion:Significant systematic dose discrepancies are observed between IVD measurements and the predicted values for short SSD and oblique incident angles. Cautions must be taken in evaluating IVD results at short SSD and at oblique incidence angles larger than 60 degrees.
SU‐E‐T‐723: Testing Critical Structure Avoidance: End‐To‐End Verification Using the MAX‐HD Phantom
Authors: Shay K , Myers D , Gersh J 
Published: June 2015

Purpose:End‐to‐end tests should be performed prior to implementation of any major component in the treatment workflow. Each facet of the workflow should be tested; simulation, planning, image‐guided alignment, and delivery. This study demonstrates the use of the MAX‐HD Phantom (Integrated Medical Technologies, Troy, NY) for multi‐system QA prior to clinical implementation of a new LINAC. This anthropomorphic cranial phantom contains multiple targets which can be localized during simulation and planning. During delivery, the dose to these targets can be measured using detectors and dose distribution measured using radiochromic film. While dose to the PTV is an important test, as‐important is the verification of critical structure avoidance. This phantom allows for placement of detectors in several critical structure regions, yielding a subsequent verification of the fidelity of avoidance algorithms.Methods:The described end‐to‐end tests evaluate cranial RapidArc treatments planned using Eclipse (AAA and Acuros) delivered using a Varian TrueBeam (Varian Medical Systems, Palo Alto, CA). A 2.5cm‐diameter spherical volume serves as the PTV while a peripherally‐located region (3cm‐offset) serves as the avoidance structure. The planning CT was performed with an “imaging insert,” which is identical to the “detector insert,” however lacks detector bore holes. Prior to delivery, CBCT is used for alignment. Two deliveries were performed for each plan; one with the detector placed within the PTV and the other within the avoidance structure.Results:Ten plans were tested; varying the energy, fluence mode, and algorithm. The dose to the PTV differed on average by 0.66% while the dose to the avoidance structure differed by 0.27%.Conclusion:The MAX‐HD allowed for the verification of treatment workflow (simulation, treatment planning, image‐guided alignment, and delivery), concentrating not only on absolute dose to the PTV, but the dose to an avoidance structure.Presenting author is the President/Owner of Spectrum Medical Physics, LLC, a company which maintains contracts with Siemens Healthcare and Standard Imaging, Inc.
SU‐E‐T‐727: The Application of Regularization‐Based Multi‐Channel Radiochromic Film Dosimetry for Patient‐Specific QA of Stereotactic Body Radiation Therapy (SBRT) Treatment
Authors: Li Darrell T H , Chan Kenny S K , Lee Louis K Y , Chan Anthony T C 
Published: June 2015

Purpose:To examine the feasibility of using radiochromic film with advanced calibration techniques for absolute and relative dose measurement in patient‐specific SBRT QA.Methods:Ten SBRT cases were randomly selected. The treatment plans were mapped to a cylindrical Perspex phantom for QA measurement. A radiochromic film of 8”x10” was cut into a large piece of 20×21cm2 and 2 small pieces of 4×4cm2 each. The large piece was inserted in the mid‐plane of the phantom which was irradiated with the treatment beam. One of the small pieces was irradiated with known dose. All irradiated films were allowed to stabilize for 24 hours before scanning. The protocol of single‐scan with recalibration was followed and the 2 small films were used to adjust the calibration curve. The treatment film was calibrated with the dose gradient regularization method by an in‐house developed MATLab program. The calculated dose planes were then exported to RIT113V4.4. Both treatment films and planned dose planes were normalized to the corresponding prescribed fractional dose for analysis.Results:The analysis was performed by normalizing both the treatment film and the planned dose planes to the prescribed fractional dose. Isodose line comparison was performed to visually check the alignment of the isodose level of steep dose gradient regions. Good agreements were observed in all 10 cases. Gamma index analysis with tolerance of 3% and 2mm was also carried out for quantitative analysis. All 10 cases were reported with a gamma index passing percentage of at least 98.9%, which were higher than the institute's passing criteria of over 95%.Conclusion:By employing recalibration and regularization‐based calibration techniques, radiochromic film can measure both the absolute and relative dose of SBRT treatment plans. This study suggested that radiochromic film, with proper application of advanced calibration methods, can be a promising tool for patient‐specific SBRT QA.
SU‐E‐T‐728: The Comparison of Risk of Secondary Malignancies Arising From Five Different Whole Breast Radiation Treatments
Authors: Kim D , Han E , Paudel N , Hardee M , Chung W , Sung J , Yoon M 
Published: June 2015

Purpose:This study aimed to compare estimates of secondary cancer risks using five radiotherapy modalities to treat breast cancer: intensity‐modulated radiotherapy (IMRT), 3‐dimensional conformal radiation therapy (3D‐CRT), field‐in‐field forward‐planned intensity‐modulated radiation (FinF), volumetric modulated arc therapy (VMAT), and TomoHDA (TOMO).Methods:Each of 10 selected breast patients was re‐planned with the five different modalities. The planning target volume (PTV) was defined as the contoured breast subtracted 5 mm from the skin, and lungs, heart, and contralateral breast were contoured as OARs. The prescription (Rx) was 50.4 Gy in 28 fractions, which covered 95% of the PTV. Dose constraints for the contralateral lung of volumes receiving 20 Gy and 10 Gy (V20Gy and V10Gy) were less than 20% and 40%, respectively, a maximum cord dose less than 45 Gy and for the rest. Qrgan equivalent doses (OEDs), dose characteristics, and lifetime attributable risks (LARs) were derived from dose‐volume histograms for in‐field regions and radio‐photoluminescence glass dosimeter (RPLGD) measurements for out‐of‐field regions.Results:TOMO had a better target dose distribution than 3D‐CRT and FinF. OEDs for TOMO were similar to those of 3D‐CRT in in‐field region but increased as distance from the field boundary increased. LARs of the lung and contralateral breast were highest for VMAT, followed by IMRT, FinF, 3D‐CRT, and TOMO. IMRT and VMAT had a 40–50% lower in V20Gy than 3D‐CRT.Conclusion:Our results indicate that TOMO provides comparable plan quality for breast cancer radiotherapy compared to IMRT/VMAT, and, at the same time, the lowest cancer risk in in‐field regions among all studied treatment modalities. Therefore TOMO could be a better alternative treatment modality than 3D‐CRT for breast cancer patients.
SU‐E‐T‐733: The Effects of Duty Cycle On Gated VMAT Delivery
Authors: Song C , Xue C , Li R , Xue T 
Published: June 2015

Purpose:When delivering gated VMAT treatments, the gantry moves back and forth after each beam interruption. There are more beam interruptions with smaller duty cycles. This is a study of the effects of gating and duty cycle on the dose output from the treatment machine.Methods:5 previously‐treated SBRT lung patients with 6X FFF RapidArc plans and 4 previously‐treated lung patients with 6X RapidArc plans are used for this study. The treatment machine is a TrueBeam STx with HD‐MLC. A sinusoidal motion generator is used to gate the beam. A MapCheck, and a 0.6 cc ion chamber sandwiched in solid water phantom are used for dose measurements. The MapCheck is used to measure non‐gated, gated with 50% and 30% duty cycles. The ion chamber is used to measure non‐gated and gated with 30% duty cycles.Results:For the 5 SBRT lung plans with 6X FFF, the average percentage of diodes with dose difference less than 0.1% is 99.5% between non‐gated and 50% duty cycle, and 99.7% between non‐gated and 30% duty cycle. For the 4 lung plans with 6X, the average percentage of diodes with dose difference less than 0.1% is 99.5% between non‐gated and 50% duty cycle, and 98.9% between non‐gated and 30% duty cycle. Using the ion chamber, the measured dose difference between non‐gated and 30% duty cycle is within 0.1% for all 10 SBRT arcs and within 0.2% for all 10 non‐SBRT arcs.Conclusion:On a TrueBeam machine, the VMAT dose delivery difference is within 0.2% between non‐gated and gated treatments. This difference decreases with the increase of duty cycle, also decreases with the decrease of target volume.
SU‐E‐T‐734: The Feasibility of Using Polymer Gel Dosimetry to Measure the Dose Around Thin High Z Materials Irradiated with High Energy Photon Beams
Authors: Warmington L , Watanabe Y 
Published: June 2015

Purpose:The purpose of this study is to investigate the feasibility of 3D dose measurements near thin high z materials using high energy photon beams.Methods:A MAGAT‐type polymer gel was manufactured in‐house. Lead foils of dimensions 1cm × 1cm × 0.5mm were encapsulated in 0.06mm thick tape and placed in two foil supports with 4cm depth and 0.7cm separation. The foils and supports were placed in a 500ml polystyrene container and the gel was poured into the phantom. The phantom was irradiated with a 18MV photon beam of 5cm × 5cm field size perpendicular to the foil at 100cm SSD. The gel was imaged with a Siemens 3T MRI scanner using the CPMG pulse sequence. DOSXYZnrc was used to calculate the expected dose and the Monte Carlo dose was compared with the gel. Enough histories were simulated so that the average error was less than 1%. The percentage difference of the dose between the heterogeneous gel and the homogeneous water was computed along and perpendicular to the beam axis.Results:Depth dose measurements made on the central axis showed increased dose upstream and between the foils, but had a decreased dose downstream. The range of increased dose was 1.8cm above and 0.7cm below the foils. The minimum dose point between the foils had an enhancement of 7.4%. The dose reduction downstream averaged around 5%. There was very good agreement between the Monte Carlo measurements and the gel doses. The gel and Monte Carlo results were within 2% at the minimum point.Conclusion:It was demonstrated that the MAGAT polymer‐gel can be used to measure the fine structures around small metallic objects. The results suggest that the dose of a 18MV photon beam can be increased in between thin high Z foils while reducing the dose downstream.
SU‐E‐T‐735: The Feasibility of Using A Knowledge Base of Prior Treatment Plans in Cervical Cancer: A Dosimetric Comparision with Original Plans
Authors: Ma C , Yin Y 
Published: June 2015

Purpose:To demonstrate the feasibility of using a knowledge base of prior treatment plans to generate new cervical intensity modulated radiation therapy (IMRT) plans. Dosimetric diffeerences were investigated between knowledge‐based IMRT rapidplans and original plans.Methods:A database of 20 cervical IMRT treatment plans were assembled to create a knowledge‐based IMRT rapidplan model. Another 19 clinical cases were randomly selected to test the model. A comparision of the difference in the dose‐volume histograms(DVH) between the semiautomated treatment plans and the original treatment plans were analyzed.Results:On average, the new knowledge‐based rapidplans are capable of achieving very comparable planning target volume coverage as the original plan, to within 1% as evaluated for D98, D95, and D1. For the rectum, the mean and standard deviation of the dose percentage differences for D20, D30, and D50 are3.79%±8.31%, 4.00%±9.87%, and 1.52±10.89%, respectively. For the bladder, the mean and standard deviation of the dose percentage differences for D20, D30, and D50 are −2.43%±9.40%, −2.03%±10.17% and −2.94%±12.30%, respectively. For the femoral heads, the mean and standard deviation of the dose percentage differences for the left and right are 3.15%±18.29% and −3.18%±13.79%. A negative percentage difference indicates that the new plan has greater dose sparing as compared to the original plan.Conclusion:We demonstrate a knowledge‐based IMRT model in cervical cancer can generate clinically acceptable treatment plans of high quality. This semiautomated approach can improve the efficiency of the treatment planning process while ensuring that high quality plans are developed.
SU‐E‐T‐740: The Optimization in Segment Numbers for Nasopharyngeal Carcinoma (NPC) Treated by Intensity Modulated
Authors: Qiu R , Wang Y , Chi Z 
Published: June 2015

Purpose:In premise of uninfluenced to dose distribution of tumor target and organ at risk(OAR) in Nasopharyngeal carcinoma (NPC),the number of segment was changed to increase efficacy and optimize treatment method by designing different plan of intensity modulated radiotherapy(IMRT).Methods:10 cases of NPC were confirmed in pathology and treated with step and shoot IMRT. The target volumes were defined: GVT‐T (the primary tumor); GVT‐N (the metastasis lymph nodes in neck); CTV‐T and CTV‐N (the clinical targets of GVT‐T and GTV‐N); and PTV (incidental lymph nodal region). Dose of GTV/CTV/PTV was 70/64/54Gy for 30 fractions.Every patient was designed 7 treatment plans of IMRT by Pinnacle 8.0m planning system,each plan was used with 9 beams of uniform distribution and fixing incidence direction(200°,240°,280°,320°,0°,40°,80°,120°and 160°respectively),and designed for delivery on Elekta Synergy linear accelerator.All plans were optimized with the direct machine parameter optimization(DMPO) algorithm.Minimum MU in each segment was defined at 4MU,and minimal segment area was 4cm2.Number of maximum segment field was defined at 120,110,100,90,80,70,60, respectively.Coverage and conformity of GTV/CTV/PTV,sparing of OARs(spinal cord, brain, parotids, lens and optic nerves) were compared.Results:In this group,mean volume of GTV(GTV‐T+GTV‐N),CTV(CTV‐T+CTV‐N)and PTV were 91.39±71.13cm3,177.27±92.16cm3 and 1028.05±167.03cm3,.respectively. Compared with the number of segment decreased from 120 to 60, there were no difference in MU(p>0.05),and the dose distribution of targets(GTV/CTV/PTV),OARs and CI were not different too(p>0.05).But when the segment number was <60, CI of PTV was changed compared with others(p<0.05).Conclusion:The minimal segment number of IMRT plan designed by Pinnacle 8.0m planning system in NPC should be decreased reasonably and the limit of minimal segment number was recommended by 70.
SU‐E‐T‐745: The Use of Electron Dense Materials for Quality Assurance Testing in a Magnetic Field
Authors: van Zijp H , van Asselen B , de Vries W , Ishakoglu K , Beld E , Kok J , Wolthaus J , Lagendijk J , Raaymakers B 
Published: June 2015

Purpose:Due to the effect of the magnetic field on the dose deposition (skewing the beam), machine quality assurance (QA) tests for the MR‐linac (MRI combined with a linear accelerator) need to be redesigned. In this work we focus on the redesign of QA tests that address geometrical accuracy of the system.Methods:Using electron dense materials (e.g. copper in our experiment) the dose kernel is minimized and thereby the effect of the magnetic field on the dose distribution. This approach is supported by Monte‐Carlo simulations and can be used in practice with film measurements. Two examples of QA tests are presented: beam profile and star‐shot measurements.Results:The novel method was verified by performing both measurements on a conventional linac and the MR‐linac with a film that was sandwiched between copper layers. Measurements were compared with a reference setup which was similar to setup used in clinical practice. On a conventional linac the experimental outcome showed good agreement between the reference and the new setup for both QA tests. The results from the MR‐linac showed that the symmetry of the beam profile was restored in presence of the copper layers in the setup and that the isocenter size can be determined accurately with the introduced star‐shot setup (see supporting material).Conclusion:The use of electron dense materials for QA tests was shown to be a simple and effective method to remove the effects on the dose distribution enabling assessment of geometrical accuracy of a MR‐linac system. The use of high dense materials is not limited to the presented QA tests only, but has a broad applicability for beam specific QA tests in presence of a magnetic field.
SU‐E‐T‐746: The Use of Radiochromic Film Analyzed with Three Channel Dosimetry as a Secondary Patient‐Specific QA Tool for Small SBRT Fields
Authors: Hadsell M , Holcombe C , Chin E , Hsu A 
Published: June 2015

Introduction:As diagnostic techniques become more sensitive and targeting methods grow in accuracy, target volumes continue to shrink and SBRT becomes more prevalent. Due to this fact, patient‐specific QA must also enhance resolution and accuracy in order to verify dose delivery in these volumes. It has been suggested that when measuring small fields at least two separate detectors be used to verify delivered dose. Therefore, we have instituted a secondary patient QA verification for small (<3cm) SBRT fields using Gafchromic EBT2 film.Methods:Films were cross‐calibrated using a Farmer chamber in plastic water at reference conditions as defined by TG‐51. Films were scanned, and an RGB calibration curve was created according to best practices published by Ashland, Inc. Four SBRT cases were evaluated both with the Scandidos Delta4 and with EBT2 films sandwiched in plastic water. Raw values obtained from the film were converted to dose using an in‐house algorithm employing all three color channels to increase accuracy and dosimetric range. Gamma and dose profile comparisons to Eclipse dose calculations were obtained using RIT and compared to values obtained with the Delta4.Results:Film gamma pass rates at 2% and 2mm were similar to those obtained with the Delta4. However, dose difference histograms showed better absolute dose agreement, with the average mean film dose agreeing with calculation to 0.3% and the Delta4 only agreeing to 3.1% across the cases. Additionally, films provided more resolution than the Delta4 and thus their dose profiles better succeeded in diagnosing dose calculation inaccuracies.Conclusion:We believe that the implementation of secondary patient QA using EBT2 film analyzed with all three color channels is an invaluable tool for evaluation of small SBRT fields. Furthermore, we have shown that this method can sometimes provide a more detailed and faithful reproduction of plan dose than the Delta4.