bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐288: Root Cause Analysis for a Wrong Isocenter Error
Authors: Cao N , Sponseller P , Yang F , Kim E , Ford E 
Published: July 2014

Purpose:This study is to explore root cause analysis (RCA) in the context of a departmental incident reporting system through a case report of a wrong isocenter. RCA of this incident provides a means to undercover and address underlying causal factors to prevent such an event in the future.Methods:The wrong isocenter error was detected on port films, making it a near‐miss, but the potential impact was severe. Following the modified London Protocol for RCA, we interviewed all the staff involved, including the simulation and treatment therapists, the dosimetrist, the physicist and the physician. A timeline of events leading up to the incident and its discovery was created. We then generated a list of care delivery problems and associated contributing factors. Finally, solutions were identified to address the contributing factors and prevent future recurrences of such an incident.Results:Though not obvious at the outset of this RCA, the main care delivery problem turned out to be a misidentification of the ball‐bearing (BB) location on the treatment planning CT. A metal wire used to mark a drain site was identified as an isocenter mark rather than the BB on the AP surface as intended. Contributing factors include: 1)no policy implemented regarding the location of BBs and metal wire; 2) wires with similar diameter and feature as BBs in CT images; 3)lack of communication when confusion and uncertainties exist. A solution was chosen to help visualize the drain site. When drain site needs to be marked, a marker different from the regular wire will be used (e.g. plastic washer).Conclusion:Through RCA of an incorrect isocenter placement case, we identified the causal factors and also proposed solutions. RCA is a crucial tool for incident learning. This case study serves as valuable guidance for this particular problem and for RCA more generally.
SU‐E‐T‐290: Secondary Dose Monitoring Using Scintillating Fibers in Proton Therapy of Prostate Cancer: A Geant4 Monte Carlo Simulation
Authors: Tesfamicael B , Gueye P , Lyons D , Avery S , Mahesh M 
Published: July 2014

Purpose:To monitor the secondary dose distribution originating from a water phantom during proton therapy of prostate cancer using scintillating fibers.Methods:The Geant4 Monte Carlo toolkit version 9.6.p02 was used to simulate prostate cancer proton therapy based treatments. Two cases were studied. In the first case, 8 × 8 = 64 equally spaced fibers inside three 4 × 4 × 2.54 cmm3 DuPont™ Delrin blocks were used to monitor the emission of secondary particles in the transverse (left and right) and distal regions relative to the beam direction. In the second case, a scintillating block with a thickness of 2.54 cm and equal vertical and longitudinal dimensions as the water phantom was used. Geometrical cuts were used to extract the energy deposited in each fiber and the scintillating block.Results:The transverse dose distributions from secondary particles in both cases agree within <5% and with a very good symmetry. The energy deposited not only gradually increases as one moves from the peripheral row fibers towards the center of the block (aligned with the center of the prostate) but also decreases as one goes from the frontal to distal region of the block. The ratio of the doses from the prostate to the ones in the middle two rows of fibers showed a linear relationship with a slope (−3.55±2.26) × 10−5 MeV per treatment Gy. The distal detectors recorded a very small energy deposited due to water attenuation.Conclusion:With a good calibration and the ability to define a good correlation between the dose to the external fibers and the prostate, such fibers can be used for real time dose verification to the target.
SU‐E‐T‐292: Sensitivity of Fractionated Lung IMPT Treatments to Setup Uncertainties and Motion Effects
Authors: Dowdell S , Grassberger C , Paganetti H 
Published: July 2014

Purpose:Evaluate the sensitivity of intensity‐modulated proton therapy (IMPT) lung treatments to systematic and random setup uncertainties combined with motion effects.Methods:Treatment plans with single‐field homogeneity restricted to ±20% (IMPT‐20%) were compared to plans with no restriction (IMPT‐full). 4D Monte Carlo simulations were performed for 10 lung patients using the patient CT geometry with either ±5mm systematic or random setup uncertainties applied over a 35 × 2.5Gy(RBE) fractionated treatment course. Intra‐fraction, inter‐field and inter‐fraction motions were investigated. 50 fractionated treatments with systematic or random setup uncertainties applied to each fraction were generated for both IMPT delivery methods and three energy‐dependent spot sizes (big spots – BS σ=18‐9mm, intermediate spots – IS σ=11‐5mm, small spots – SS σ=4‐2mm). These results were compared to a Monte Carlo recalculation of the original treatment plan, with results presented as the difference in EUD (ΔEUD), V95 (ΔV95) and target homogeneity (ΔD1–D99) between the 4D simulations and the Monte Carlo calculation on the planning CT.Results:The standard deviations in the ΔEUD were 1.95±0.47(BS), 1.85±0.66(IS) and 1.31±0.35(SS) times higher in IMPT‐full compared to IMPT‐20% when ±5mm systematic setup uncertainties were applied. The ΔV95 variations were also 1.53±0.26(BS), 1.60±0.50(IS) and 1.38±0.38(SS) times higher for IMPT‐full. For random setup uncertainties, the standard deviations of the ΔEUD from 50 simulated fractionated treatments were 1.94±0.90(BS), 2.13±1.08(IS) and 1.45±0.57(SS) times higher in IMPTfull compared to IMPT‐20%. For all spot sizes considered, the ΔD1‐D99 coincided within the uncertainty limits for the two IMPT delivery methods, with the mean value always higher for IMPT‐full. Statistical analysis showed significant differences between the IMPT‐full and IMPT‐20% dose distributions for the majority of scenarios studied.Conclusion:Lung IMPT‐full treatments are more sensitive to both systematic and random setup uncertainties compared to IMPT‐20%.This work was supported by the NIH R01 CA111590.
SU‐E‐T‐293: Simplifying Assumption for Determining Sc and Sp
Authors: King R , Cheung A , Anderson R , Thompson G , Fletcher M 
Published: July 2014

Purpose:Scp(mlc,jaw) is a two‐dimensional function of collimator field size and effective field size. Conventionally, Scp(mlc,jaw) is treated as separable into components Sc(jaw) and Sp(mlc). Scp(mlc=jaw) is measured in phantom and Sc(jaw) is measured in air with Sp=Scp/Sc. Ideally, Sc and Sp would be able to predict measured values of Scp(mlc,jaw) for all combinations of mlc and jaw. However, ideal Sc and Sp functions do not exist and a measured two‐dimensional Scp dataset cannot be decomposed into a unique pair of one‐dimensional functions.If the output functions Sc(jaw) and Sp(mlc) were equal to each other and thus each equal to Scp(mlc=jaw)^0.5, this condition would lead to a simpler measurement process by eliminating the need for in‐air measurements. Without the distorting effect of the buildup‐cap, small‐field measurement would be limited only by the dimensions of the detector and would thus be improved by this simplification of the output functions. The goal of the present study is to evaluate an assumption that Sc=Sp.Methods:For a 6 MV x‐ray beam, Sc and Sp were determined both by the conventional method and as Scp(mlc=jaw)^0.5. Square field benchmark values of Scp(mlc,jaw) were then measured across the range from 2×2 to 29×29. Both Sc and Sp functions were then evaluated as to their ability to predict these measurements.Results:Both methods produced qualitatively similar results with <4% error for all cases and >3% error in 1 case. The conventional method produced 2 cases with >2% error, while the squareroot method produced only 1 such case.Conclusion:Though it would need to be validated for any specific beam to which it might be applied, under the conditions studied, the simplifying assumption that Sc = Sp is justified.
SU‐E‐T‐294: Simulations to Investigate the Feasibility of ‘dry’ Optical‐CT Imaging for 3D Dosimetry
Authors: Chisholm K , Rankine L , Oldham M 
Published: July 2014

Purpose:To perform simulations investigating the feasibility of “dry” optical‐CT, and determine optimal design and scanning parameters for a novel dry tank telecentric optical‐CT 3D dosimetry system. Such a system would have important advantages in terms of practical convenience and reduced cost.Methods:A Matlab based ray‐tracing simulation platform, ScanSim, was used to model a telecentric system with a polyurethane dry tank, cylindrical dosimeter, and surrounding fluid. This program's capabilities were expanded for the geometry and physics of dry scanning. To categorize the effects of refractive index (RI) mismatches, simulations were run for several dosimeter (RI = 1.5−1.48) and fluid (RI = 1.55−1.33) combinations. Additional simulations examined the effect of increasing gap size (1–5mm) between the dosimeter and tank wall, and of changing the telecentric lens tolerance (0.5°−5°). The evaluation metric is the usable radius; the distance from the dosimeter center where the measured and true doses differ by less than 2%.Results:As the tank/dosimeter RI mismatch increases from 0–0.02, the usable radius decreases from 97.6% to 50.2%. The fluid RI for matching is lower than either the tank or dosimeter RI. Changing gap sizes has drastic effects on the usable radius, requiring more closely matched fluid at large gap sizes. Increasing the telecentric tolerance through a range from 0.5°–5.0° improved the usable radius for every combination of media.Conclusion:Dry optical‐CT with telecentric lenses is feasible when the dosimeter and tank RIs are closely matched (<0.01 difference), or when data in the periphery is not required. The ScanSim tool proved very useful in situations when the tank and dosimeter have slight differences in RI by enabling estimation of the optimal choice of RI of the small amount of fluid still required. Some spoiling of the telecentric beam and increasing the tolerance helps recover the usable radius.
SU‐E‐T‐296: Single Field Per Day Vs. Multiple Fields Per Day and the Impact On BED in Proton Therapy Treatment
Authors: Grantham K , Wooten H , Zhao T , Klein E 
Published: July 2014

Purpose:A common practice, in proton therapy, is to deliver a rotating subset of fields from the treatment plan for the daily fractions. This study compares the impact this practice has on the biological effective dose (BED) versus delivering all planned fields daily.Methods:For two scenarios (a phantom with a geometry approximating the anatomy of a prostate treatment with opposing lateral beams, and a clinical 3‐field brain treatment), treatment plans were produced in Eclipse (Varian) to simulate delivery of one, two, and three fields per fraction. The RT‐Dose file, structure set, and α/β ratios were processed using in‐house MATLAB code to return a new RT‐Dose file containing the BED (including a proton RBE of 1.1) which was imported back into Eclipse for analysis.Results:For targets and regions of field overlap in the treatment plan, BED is not affected by delivery regimen. In the phantom, BED in the femoral heads showed increased by 20% when a single field was used rather than two fields. In the brain treatment, the minimum BED to the left optic nerve and the pituitary gland increased by 13% and 10% respectively, for a one‐field regime compared to three‐fields per fraction. Comparing the two‐field and threefield regimes, the optic nerve BED was not significantly affected and the minimum pituitary BED was 4% higher for two fields per day.Conclusion:Hypo‐fractionation effects, in regions of non‐overlap of fields, significantly increase the BED to the involved tissues by as much as 20%. Care should be taken to avoid inadvertently sacrificing plan effectiveness in the interest of reduced treatment time.
SU‐E‐T‐299: Small Fields Profiles Correction Through Detectors Spatial Response Functions and Field Size Dependence Analysis
Authors: Filipuzzi M , Garrigo E , Germanier A , Venencia C 
Published: July 2014

Purpose:To calculate the spatial response function of various radiation detectors, to evaluate the dependence on the field size and to analyze the small fields profiles corrections by deconvolution techniques.Methods:Crossline profiles were measured on a Novalis Tx 6MV beam with a HDMLC. The configuration setup was SSD=100cm and depth=5cm. Five fields were studied (200×200mm2,100×100mm2, 20×20mm2, 10×10mm2and 5×5mm2) and measured were made with passive detectors (EBT3 radiochromic films and TLD700 thermoluminescent detectors), ionization chambers (PTW30013, PTW31003, CC04 and PTW31016) and diodes (PTW60012 and IBA SFD). The results of passive detectors were adopted as the actual beam profile. To calculate the detectors kernels, modeled by Gaussian functions, an iterative process based on a least squares criterion was used. The deconvolutions of the measured profiles were calculated with the Richardson‐Lucy method.Results:The profiles of the passive detectors corresponded with a difference in the penumbra less than 0.1mm. Both diodes resolve the profiles with an overestimation of the penumbra smaller than 0.2mm. For the other detectors, response functions were calculated and resulted in Gaussian functions with a standard deviation approximate to the radius of the detector in study (with a variation less than 3%). The corrected profiles resolve the penumbra with less than 1% error. Major discrepancies were observed for cases in extreme conditions (PTW31003 and 5×5mm2 field size).Conclusion:This work concludes that the response function of a radiation detector is independent on the field size, even for small radiation beams. The profiles correction, using deconvolution techniques and response functions of standard deviation equal to the radius of the detector, gives penumbra values with less than 1% difference to the real profile. The implementation of this technique allows estimating the real profile, freeing from the effects of the detector used for the acquisition.
SU‐E‐T‐300: Spatial Variations of Multiple Off‐Axial Targets for a Single Isocenter SRS Treatment Plan in ExacTrac 6D Robotic Couch System
Authors: Kim S , Tseng T 
Published: July 2014

Purpose:To evaluate the spatial variations of multiple off‐axial targets for a single isocenter stereotactic radiosurgery (SRS) treatment plan in ExacTrac 6D robotic couch system (BrainLab AG).Methods:Five metallic ball bearing (BB) markers were placed sparsely in 3D off‐axial locations (non‐coplanar) inside a skull phantom as the representatives of multiple targets mimicking multiple brain metastases. The locations of the BB markers were carefully chosen to minimize overlapping of each other in a port imaging detector plane. The skull phantom was immobilized by a frameless mask and CT scanned with a BrainLab Head&Neck Localizer using a GE Optima MDCT scanner. The CT images were exported to iPlan software (BrainLab AG) and a multiple target PTV was drawn by combining all the contours of the BBs. The margin of the MLC opening was selected as 3 mm expansion outward. Two coplanar arc beams were placed to generate a single isocenter SRS plan to treat the PTV. The arc beams were delivered using Novalis Tx system with portal imaging acquisition mode per 10% temporal resolution. The locations of the BBs were visualized and analyzed with respect to the MLC aperture in the treatment plan similar to the Winston‐Lutz test.Results:All the BBs were clearly identified inside the MLC openings. The positional errors for the BBs were overall less than 1 mm along the rotational path of the two arcs.Conclusion:This study verified that the spatial deviations of multiple off‐axial targets for a single isocenter SRS treatment plan is within sub‐millimeter range in ExacTrac 6D robotic couch system. Accompanied with the Winston‐Lutz test, this test will quality‐assure the spatial accuracies of the isocenter as well as the positions of multiple off‐axial targets for the SRS treatment using a single isocenter multiple target treatment plan.
SU‐E‐T‐302: Spine SBRT Planning for Patients with Spinal Hardware
Authors: Meyer J , Hendrickson K , Bowen S , Nyflot M , Patel S , Halasz L 
Published: July 2014

Purpose:To investigate the effects of different imaging artifact correction strategies and susceptibility to setup errors for multiple spinal SBRT planning approaches in treating a patient with titanium hardware.Methods:Two‐step‐IMRT, IMRT and two arc VMAT plans were created for a C‐spine SBRT case with titanium hardware. The plans were normalized to the maximum point dose to the thecal sac. Density overrides for the planning CT were applied to mitigate imaging artifacts. All plans were recalculated on CTs with no density overrides and with the density of all structures set to 1g/cm^3. Setup errors up to 2mm toward the spinal cord were simulated.Results:The 2‐step IMRT plans achieved a mean dose to the cord of 6.5Gy compared to 8.0 and 8.7Gy for the IMRT and VMAT plans. The PTV coverage was comparable for both the 2‐step‐IMRT and the IMRT plan. The VMAT plan achieved a higher mean dose, but had hot spots >130%. If no density overrides were applied for the same MUs the increase in maximum dose to the cord was 0.3, 1.2 and 0.0% for 2‐step‐IMRT, IMRT and VMAT plans, respectively, compared to an increase of 2.3, 2.0 and 1.0% for unit density override.An isocenter shift of 2mm toward the cord resulted in an increase in maximum dose to the cord of 10.7, 8.0 and 5.0% for the 2‐step IMRT, IMRT and VMAT plan, respectively, with the absolute dose to the cord still being lowest for the 2‐step‐IMRT plan compared to the other plans without simulated setup errors.Conclusion:The 2‐step‐IMRT plan achieved the clinically most acceptable dose distribution. The plan quality was relatively insensitive to density overrides. The 2‐step‐IMRT plan was the most sensitive to setup errors due to the steep gradient but this was offset by the initial improvement in sparing of the cord.
SU‐E‐T‐304: Study of Secondary Neutrons From Uniform Scanning Proton Beams
Authors: Islam M , Zheng Y , Benton E 
Published: July 2014

Purpose:Secondary neutrons are unwanted byproducts from proton therapy and exposure from secondary radiation during treatment could increase risk of developing a secondary cancer later in a patient's lifetime. The purpose of this study is to investigate secondary neutrons from uniform scanning proton beams under various beam conditions using both measurements and Monte Carlo simulations.Methods:CR‐39 Plastic Track Nuclear Detectors (PNTD) were used for the measurement. CR‐39 PNTD has tissue like sensitivity to the secondary neutrons but insensitive to the therapeutic protons. In this study, we devised two experimental conditions: a) hollow‐phantom; phantom is bored with a hollow cylinder along the direction of the beam so that the primary proton passes through the phantom without interacting with the phantom material, b) cylindrical‐phantom; a solid cylinder of diameter close to the beam diameter is placed along the beam path. CR‐39 PNTDs were placed laterally inside a 60×20×35 cm3 phantom (hollow‐phantom) and in air (cylindrical‐phantom) at various angles with respect to the primary beam axis. We studied for three different proton energies (78 MeV, 162 MeV and 226 MeV), using a 4 cm modulation width and 5cm diameter brass aperture for the entire experiment and simulation. A comparison of the experiment was performed using the Monte Carlo code FLUKA.Results:The measured secondary neutron dose equivalent per therapeutic primary proton dose (H/D) ranges from 2.1 ± 0.2 to 25.42 ± 2.3 mSv/Gy for the hollow phantom study, and 2.7 ± 0.3 to 46.4 ± 3.4 mSv/Gy for the cylindrical phantom study. Monte Carlo simulations predicated neutron dose equivalent from measurements within a factor of 5.Conclusion:The study suggests that the production of external neutrons is significantly higher than the production of internal neutrons.
SU‐E‐T‐306: Study of the Reduction Technique for the Secondary Cancer Risk Due to Cone Beam CT in Image Guided Radiotherapy
Authors: Sung J , Kim D , Kim D , Baek T , Lee H , Chung W , Yoon M 
Published: July 2014

Purpose:This study evaluated the effectiveness of a thin lead sheet based simple shielding method for imaging doses from cone beam computed tomography (CBCT) in image‐guided radiotherapy (IGRT).Methods:The entire body, except for the region scanned by CBCT, was shielded by wrapping in a 2 mm lead sheet. Reduction of secondary doses from CBCT was measured using a radio‐photoluminescence glass dosimeter (RPLGD) placed inside an anthropomorphic phantom and changes in secondary cancer risk due to the shielding effect were estimated using BEIR VII model.Results:Doses to out‐of‐field organs for head‐and‐neck, chest, and pelvis scans were decreased 15∼100 %, 23∼90 %, and 23∼98 %, respectively, and the average reductions in lifetime secondary cancer risk due to the 2 mm lead shielding were 1.61, 10.4, and 12.8 persons per 100,000, respectively.Conclusion:This study suggests that a simple thin lead sheet based shielding method results in a non‐negligible reduction of secondary doses to out‐of‐field regions for CBCT.
SU‐E‐T‐307: Susceptibility of SBRT to Delivery Uncertainties Using RapidArc Or Dynamic IMRT
Authors: Betzel G , Tejani M , Dhabaan A 
Published: July 2014

Purpose:To determine if SBRT is more susceptible to delivery uncertainties when using either RapidArc or dynamic IMRT.Methods:Systematic or random uncertainties in MLC leaf positions, gantry position and dose rate were incorporated into RapidArc (RA) and sliding‐window IMRT (SW) treatment plans for retrospective SBRT lung and liver cases, which also included the use of FFF or SRS energies and therefore higher dose rates. Initial plan comparisons included homogeneity and conformity indices. Dose distributions and dose‐value histograms of original and modified plans were compared using Gamma analysis and dose indices of planned treatment volumes (PTV) and organs at risk (OAR).Results:SBRT lung PTVs using RA were more susceptible to systematic MLC delivery errors than SW (∼6%/mm vs. ∼4%/mm), in contrast to a previous study examining hyperfractionated prostate and head‐and‐neck treatments; esophagus and cord Dmin and Dmax values changed proportionately for both techniques; RA plans were superior globally but not locally (PTV) using Gamma analyses. Uniformly distributed random variations of 2 mm for active MLC leaves had a negligible effect on all PTV dose distributions (Dmin, Dmax < 0.4%). PTV coverage was affected equally when incorporating systematic gantry errors.Conclusion:RapidArc deliveries were found to be more sensitive to systematic errors in MLC leaf positions, in contrast to a previous study on hyperfractionated treatments. However, this is reasonable as both studies correlate average segmental field size or mean leaf gap with adverse dosimetric effects due to such uncertainties; mean leaf gaps for either technique in this study were similar. Gantry angle variations had similar effects on both techniques.