bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐496: Influence of the Intrafraction Patient Repositioning On Spot Scanning Proton Therapy for Prostate Cancer
Authors:   Proton Therapy for Prostate Cancer, Fujii Y , Matsuura T , Takao S , Matsuzaki Y , Yamada T , Miyamoto N , Shimizu S , Umegaki K , Shirato H 
Published: June 2015

PurposeTo verify the effect of intrafraction patient repositioning based on real time image guidance on the proton dose distribution for prostate cancer.MethodsDose distributions were simulated using CT images of prostate cancer patients. Treatment plans were prepared using proton beam from left side of the patient with 3 and 6 mm lateral margins. During the beam delivery, prostate position was assumed to be shifted by 5 mm in anterior, posterior, superior and inferior directions. The dose distributions were calculated for two scenarios; (i) the patient position was readjusted by 5 mm just after the prostate shift occurs (ii) the patient position was not adjusted. Such a real time readjustment can be realized with real time image guidance. The differences of the values D5 and D95 in CTV (D5–95) were compared between different sizes of the lateral margins and different scenarios.ResultsD5–95 values in the case of scenario (i) are smaller than scenario (ii). The differences between scenario (i) and (ii) were not depend on the directions of the prostate shift. In the case of scenario (ii), margin expansion makes D5–95 values small. In the case of scenario (i), margin size is uncorrelated to D5–95 values.ConclusionThese results indicate that the intrafraction patient repositioning is effective to minimize dose deterioration when the prostate moves during the irradiation. In the case without intrafraction patient repositioning, margin expansion is effective to reduce dose deterioration. In the case with intrafraction patient repositioning, 3 mm margin is enough to minimize dose deterioration.
SU‐E‐T‐497: Initial Characterization of a Novel 2D Computed Radiography (CR) Dosimeter for SBRT
Authors: Crijns W , Ramaekers S , Leblans P , Defraene G , Maes F , Haustermans K , Depuydt T 
Published: June 2015

PurposeFor 2D, sub‐mm resolution dose measurements Gafchromic™ film is currently a standard in radiotherapy; mainly because of its energy independence and water equivalence. However, EBT film is disposable. Therefore, the dosimetric and uniformity characteristics needs to be estimated from a second, possibly different, (calibration) film. Moreover, EBT has a post‐irradiation coloration and a non‐linear dose dependence with saturation, which limits the applicable time interval and dose range. CR technology forms an interesting alternative for EBT. Dose dependent CRplates have a sub‐mm resolution, and additionally a linear dose dependence over decades of dose. But, CR has an inherent signal fading and energy dependence. Here, for the first time, a radiotherapy 2D CR prototype was characterized for an extended dose range (up to 35Gy), signal fading, and basic energy dependence.MethodsThe prototype was irradiated with a standard 10×10cm 6MV photon beam, and scanned with a commercial CR 15‐X(R) scanner. The time between the start of irradiation and scanning (T_Scan) was monitored. The linearity of the dose response was evaluated between 0 and 35Gy using a fixed T_Scan of 4min, if possible (i.e. ≤10Gy). Next, the signal fading was characterized for a T_Scan‐range of 4 to 20min. The energy dependence was assessed by a comparison of out‐of‐field measurements of CR, EBT, and TLD.ResultsThe radiotherapy CR prototype has a linear response over the complete SBRT dose range (0– 35Gy). The prototype had a small (5%), but linear signal fading over the time interval of interest (4–20min). Out‐of‐field, the prototype has a 8% over response due to an increased amount of low energy photons. The impact of the over response on intensity modulated radiotherapy remains to be evaluated.ConclusionCR technology is promising for SBRT dose measurements up to 35Gy. It is a reusable linear alternative for film dosimetry.
SU‐E‐T‐501: Initial Orthovoltage Beam Profile Analysis of a Small Brass MLC
Authors: Loughery B , Snyder M 
Published: June 2015

PurposeTo create brass leaves for an orthovoltage MLC and take initial beam profile measurements.MethodsThe low‐energy MLC was designed in previous work. Brass was chosen for its self‐lubrication and low cost. Stock brass rectangles (30cm × 1.0cm × 0.5cm) were ordered with pre‐cut gear rack along the topmost long edges. Leaf designs were translated into G‐code, then cut with a Tormach CNC‐1100 mill. Intense bowing was observed in the beam direction, which required straightening via an in‐house jig. Straightened leaves were placed into MLC assembly and mounted to a 320 kVp orthovoltage tube. EDR2 film was irradiated in four situations: MLC open so one edge was isocentric, and MLC open more than isocentric, completely closed MLC, and an open field shot with the MLC removed. The first two scans tested penumbra for our rectangular edges due to unfocused design. The final two scans tested transmission and interleaf leakage. All four experiments were set to 120 kVp and 10 mA for two minutes.ResultsTransmission and interleaf leakage were found to be zero. Interleaf leakage is faintly visible on film, but undetected by our film scanner despite high spatial resolution. Penumbra at isocenter was found to be 0.72mm, which matched the penumbras of true field edges. Penumbra off‐isocenter was 1.1mm. Mechanically, leaves are moving smoothly once straightened.ConclusionBeam profiles through our brass MLC are acceptable. Leaves attenuate and move as designed. Looking forward, we intend to animate our MLC to deliver more complicated treatment plans.
SU‐E‐T‐505: Inter‐Comparison of Clinical Plans Created On Truebeam with Trilogy and Clinac
Authors: Sharma M , Wu Y , Kim S 
Published: June 2015

PurposeThe purpose of this study is to investigate the dosimetric differences in clinical treatment plans when machine parameters are switched from Varian Truebeam to older Varian models and vice‐versa. This is used to determine the clinically‐safe limits to directly transfer patients from Truebeam to Trilogy or Clinac.MethodsThirty‐two patients with cancer of different treatment sites such as lung, head‐and‐neck, prostate and breast were studied. The clinically approved IMRT, VMAT or 3D conformal treatment plans were delivered either on Truebeam or Clinac/Trilogy. Keeping the monitor units, fraction size and other machine parameters the same, the plans were recomputed on a different Varian linear accelerator (e.g., Truebeam plans were recomputed on Trilogy and vice‐versa). The plans comparison was done using the target D98 and normal organ D2, D10, D20, D30, D50 and D70 dose metrics.ResultsThe perfraction dose‐difference in the PTV‐D98 for all 32 patients varied from 0.01 to −0.06 Gy with median being −0.04 Gy. For a 2Gy/fraction treatment course, this would be maximum PTV‐D98 dose‐difference of 6 cGy/fraction or 30 cGy/5fractions. For organs‐at‐risks the maximum per‐fraction dosedifference in D2, D5, D10, D20, D30, D50 and D70 between Truebeam and Trilogy/Clinac plans varied from 0.06 to −0.07 Gy with median being with — 0.02 Gy. The 3D‐CRT plans had relatively lower dose‐difference in comparison to IMRT and VMAT plans. The dose computed on Truebeam was systematically lower than the dose computed on Trilogy/ Clinac.Conclusionsfor conventional fractionation schedules, assuming the maximum uncertainty of <2%, it is clinically safe to switch the treatment machine for 5 fractions. For hypo‐fractionated treatments with higher dose per‐fraction, plans may need to be revisited before switching the linear accelerator from Truebeam to Clinac/Trilogy or vice‐versa.
SU‐E‐T‐506: Intercomparison Study On Small Field Output Factor Measurements
Authors: Talamonti C , Casati M , Compagnucci A , Arilli C , Greto D , Marrazzo L , Pallotta S , Zani M , Marinelli M , Menichelli D , Scotti L , Verona G 
Published: June 2015

PurposeIn radiotherapy, uncertainties due to small field measurements (SFM) introduce systematic errors to the treatment process and the development of new dosimeters for quality assurance programs is a challenge. In this work we analyze the behavior of seven detectors measuring output factors of 6MV photon beam.MethodsThe dosimeters employed are: a single cristal diamond detector (SCCD) developed at the University of Rome Tor Vergata, a silicon diode developed within the project MAESTRO, a IBA Razor silicon diode, A1SL and A26 Exradin ion chambers, an EBT3 Gafchromic film and the Exradin W1 Scintillator.Diamond sensitive volume is a cylinder 2.2mm in diameter and 1μm thick. MAESTRO diode is 2×2mm2 active area. Razor sensitive volume is a cylinder 0.6 mm in diameter and 0.02 mm thick. A16 and A1Sl have a collecting volume of 0,015cc and 0,053cc. The W1 is an optical fiber with an active volume of 0.002cc. All measurements were performed in a water phantom, with detector positioned at the isocenter (SSD=90cm, d=10cm), MAESTRO diode being sandwiched in solid water to obtain an equivalent experimental setup.ResultsThese measurements are challenging due to the absence of charged particle equilibrium conditions, detector size and positioning problems. They are in good agreement among each other, especially GAF, Razor, W1 and SCDD. Maximum deviations reported are related to the field 0.8×0.8cm2 for MAESTRO and chambers data with respect to EBT3: around 15% (A1SLvsEBT3), 16% (MAESTROvsEBT3). Razor and W1 show a deviation around 3% with respect to SCDD.ConclusionIn this work measurements made with a variety of detectors are compared. These study show the possibility to choose different detectors for SFM and that smaller ion chambers are still not competitive with solid state detectors. Silicon, diamond and optical fiber dosimeters show a similar behavior with minor discrepancies for the smallest field.
SU‐E‐T‐508: Internal Organ Motion Effect On Radiation Dose to a Point Under Half‐Beam Block Match Line
Authors: Zhou S , Zhu X , Zhang M , Zheng D , Lei Y , Zhang Q , Li S , Driewer J , Wang S , Enke C 
Published: June 2015

PurposeHalf‐beam block is a field matching technique frequently used in radiotherapy. With no setup error, a well calibrated linac, and no internal organ motion, two photon fields can be matched seamlessly dosimetry‐wise with their central axes passing the match line. However, in actual clinical situations, internal organ motion is often inevitable. This study was conducted to investigate its influence on radiation dose to patient internal points directly under the matching line.MethodsA clinical setting is modeled as two half‐space (x<0 and x<0) radiation fields that are turned on sequentially with a time gap of integer times of the patient internal organ motion period (T0). Our point of interest moves with patient internal organs periodically and evenly in and out of the radiation fields, resulting in an average location at x=0. When the fields are delivered without any motion management, the initial phase of the point's movement is unknown. Statistical methods are used to compute the expected value (<D>) and variance (σ) of the point dose given the uncertainty.ResultsAnalytical solutions are obtained for <D> and s of dose received by a point directly under the match line. <D> is proportional to the total beam‐on time (T1), and σ demonstrates previously unknown periodic behavior. <D>/<Dσ has local maximums (minimums) when T1 is 2n*T0 ((2n+1)*T0) (n is an integer) with an upper envelope scales as 1/T1. Worst case scenario the point dose can be zero or double of the expected value.ConclusionWe have analytically analyzed the internal organ motion effect on radiation dose received by a patient internal point directly under a half‐beam block match line. Our results help us to better understand this phenomenon and facilitate the reduction of point dosimetric uncertainties in our clinical practice.
SU‐E‐T‐513: Investigating Dose of Internal Target Volume After Correcting for Tissue Heterogeneity in SBRT Lung Plans with Homogeneity Calculation
Authors: Qi P , Zhuang T , Magnelli A , Djemil T , Shang Q , Balik S , Andrews M , Stephans K , Videtic G , Xia P 
Published: June 2015

PurposeIt was recommended to use the prescription of 54 Gy/3 with heterogeneity corrections for previously established dose scheme of 60 Gy/3 with homogeneity calculation. This study is to investigate dose coverage for the internal target volume (ITV) with and without heterogeneity correction.MethodsThirty patients who received stereotactic body radiotherapy (SBRT) to a dose of 60 Gy in 3 fractions with homogeneous planning for early stage non‐small‐cell lung cancer (NSCLC) were selected. ITV was created either from 4DCT scans or a fusion of multi‐phase respiratory scans. Planning target volume (PTV) was a 5 mm expansion of the ITV. For this study, we recalculated homogeneous clinical plans using heterogeneity corrections with monitor units set as clinically delivered. All plans were calculated with 3 mm dose grids and collapsed cone convolution algorithm. To account for uncertainties from tumor delineation and image‐guided radiotherapy, a structure ITV2mm was created by expanding ITV with 2 mm margins. Dose coverage to the PTV, ITV and ITV2mm were compared with a student paired t‐test.ResultsWith heterogeneity corrections, the PTV V60Gy decreased by 10.1% ± 18.4% (p<0.01) while the maximum dose to the PTV increased by 3.7 ± 4.3% (p<0.01). With and without corrections, D99% was 65.8 ± 4.0 Gy and 66.7 ± 4.8 Gy (p=0.15) for the ITV, and 63.9 ± 3.4 Gy and 62.9 ± 4.6 Gy for the ITV2mm (p=0.22), respectively. The mean dose to the ITV and ITV2mm increased 3.6% ± 4.7% (p<0.01) and 2.3% ± 5.2% (p=0.01) with heterogeneity corrections.ConclusionAfter heterogeneity correction, the peripheral coverage of the PTV decreased to approximately 54 Gy, but D99% of the ITV and ITV2mm was unchanged and the mean dose to the ITV and ITV2mm was increased. Clinical implication of these results requires more investigation.
SU‐E‐T‐517: Investigation of Factors Contributing to Extracranial Radiation Doses From Leksell Gamma Knife
Authors: Kon D , Nakano M , Nawa K , Haga A , Nakagawa K 
Published: June 2015

PurposeThe purpose of this study is to investigate dominant factors for doses to extracranial sites in treatment with Leksell Gamma Knife (LGK).MethodsMonte Carlo simulation was implemented using EGS5 version 1.4.401. The simulation was divided into two major steps for the purpose of efficiency. As the first step, phase‐space files were obtained at a scoring plane located just below patient‐side surface of the collimator helmet of LGK. Scored particles were classified into three groups, primary, leakage and scatter, using their history information until their arrival to the scoring plane. Then classification was used at the following second step simulation to investigate which type of particle is dominant in the deposited energy at extra‐cranial sites. In the second stage, a cylindrical phantom with a semisphere shaped head was modeled such that the geometrical center of the phantom's head corresponds to the unit center point (UCP) of LGK. Scoring regions were arranged at 10 cm intervals from the UCP to 70 cm away on the central axis of the phantom. Energy deposition from each type of particles and location of interaction were recorded.ResultsThe dominant factor of deposited energy depended on the collimator size. In the case of smaller collimator size, leakage was dominant. However, contribution of leakage was relatively small in the case of larger collimator size. The contribution of internal scatter varied with the distance from the UCP. In the proximal areas, internal scatter was dominant, whereas in the distal areas, particles interacting with machine components became dominant factor.ConclusionThe Result of this study indicates that the dominant factor to dose to an extracranial site can vary with the distance from UCP and with collimator size. This means that the variation of this contribution must be considered for modeling of the extracranial dose especially in the distal area.This work was partly supported by the JSPS Core‐to‐Core Program (No. 23003).
SU‐E‐T‐522: Investigation of Underdosage of Total Body Irradiation with Bilateral Irradiation Scheme
Authors: Lin T , Eldib A , Hossain M , Price R , Ma C 
Published: June 2015

Purpose:Patient in‐vivo measurements report lower readings than those predicted from TMR‐based treatment planning on TBI patient knees and ankles where rice was placed to fill the gap between patient's legs. This study is to understand and correct the under dosage of Total Body Irradiation(TBI) with rice tissue equivalent bolus placement at TBI treatment patient setup.Methods:Bilateral TBI scheme was investigated with rice bags bolus placing between patient's two legs acting as missing tissue. In‐house TMR based treatment planning system was commissioned with measurements under TBI condition at 10MV, i.e. source‐to‐reference distance 383.4cm with 40×40cm field size with 1cm thickness Lucite. Predictions of patient specific dose points are reported at different sites with 200cGy prescription at patient umbilicus point. Solid water and rice bag phantoms are used at TBI conditions for the attenuation factor verification and CT scanned to verify the CT number and electron density.Results:We found that the rice bag bolus overall density is 11% lower than the water; however, the attenuation factor of rice bags could become 15% lower than that of water at TBI condition. This overestimate of rice bag electron density could cause the lack of lateral scatter and the lack of backscatter. This could Result in an overestimate of dose at in‐vivo dosimeter measurement points with TMR‐based treatment planning systems. Observations of patient specific optically stimulated luminescent dosimeters(OSLDs) were used to confirm this overestimation. Measurements of setups with increasing the rice bag filled patient leg separation were performed to demonstrate eliminating the overdose issue.Conclusion:Rice bolus has a lower electron density than water does(11%) but results in 15% lower in attenuation factor at TBI condition. This effect was observed in patient delivery with OSLD measurements and can be corrected by increasing the filling rice bolus thickness with 15% longer of separation.
SU‐E‐T‐524: In‐Vivo Diode Dosimetry Proton Therapy Range Verification Validation Study for Pediatric CSI
Authors: Toltz A , Hoesl M , Schuemann J , Seuntjens J , Lu H , Paganetti H 
Published: June 2015

Purpose:With the aim of reducing acute esophageal radiation toxicity in pediatric patients receiving craniospinal irradiation (CSI), we investigated the implementation of an in‐vivo, adaptive proton therapy range verification methodology. Simulation experiments and in‐phantom measurements were conducted to validate the range verification technique for this clinical application.Methods:A silicon diode array system has been developed and experimentally tested in phantom for passively scattered proton beam range verification for a prostate treatment case by correlating properties of the detector signal to the water equivalent path length (WEPL). We propose to extend the methodology to verify range distal to the vertebral body for pediatric CSI cases by placing this small volume dosimeter in the esophagus of the anesthetized patient immediately prior to treatment. A set of calibration measurements was performed to establish a time signal to WEPL fit for a “scout” beam in a solid water phantom. Measurements are compared against Monte Carlo simulation in GEANT4 using the Tool for Particle Simulation (TOPAS).Results:Measurements with the diode array in a spread out Bragg peak of 14 cm modulation width and 15 cm range (177 MeV passively scattered beam) in solid water were successfully validated against proton fluence rate simulations in TOPAS. The resulting calibration curve allows for a sensitivity analysis of detector system response with dose rate in simulation and with individual diode position through simulation on patient CT data.Conclusion:Feasibility has been shown for the application of this range verification methodology to pediatric CSI. An in‐vivo measurement to determine the WEPL to the inner surface of the esophagus will allow for personalized adjustment of the treatment plan to ensure sparing of the esophagus while confirming target coverage.A Toltz acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering Research Council (Grant number: 432290).
SU‐E‐T‐535: Linac Based Multiple SRS Targets Plan Evaluation: Understanding Conformity Index Generated Form BrainLab IPlan RT Dose 4.1 SRS Planning System
Authors: Workie D , Hasson B , Geraghty C , Torano A , Dad L , Mary Y 
Published: June 2015

Purpose:The study intent is to provide a practical method of extracting Conformity Index for multiple Stereotactic Radiosurgery (SRS) target plans generated from BrainLab iPlan RT Dose 4.1 planning system (CIiPlan).Methods:CIiPlan is the ratio between normal tissue volume (VN, IDL) and target volume (VPTV, IDL) encompassed by the prescription isodose line (IDL). BrainLab iPlan RT Dose 4.1 planning and physics documents lack details on how to retrieve and interpret CIiPlan parameters of multiple SRS targets. The CIiPlan values for multiple lesions are misleading and in most cases gave bigger values than what is reflected from the plan. To understand and demonstrate the underlying issues CIiPlan values of patient plans with multiple SRS targets were extracted using two different methods. Method 1: CIiPlan values were directly obtained with all target plans present (CITN,iPlan). Method 2: CIiPlan values were extracted by assigning 100% weighting for one of the targets and 0 weighting for the rest of the targets (CIIN,iPlan). This process was t repeated for each target. In both cases CIiPlan were read from DVH graphs at the prescription IDL.Results:CITN,iPlan values from Method 1 were larger than CIIN,iPlan values obtained using Method 2. The difference was pronounced for smaller lesions. Even though targets were far apart and were not covered with the same prescription IDL, CIiPlan values from Method 1 were based on normal tissue volume encompassed by 5 treatment IDL from all targets. Carefully analyzing CIiPlan values from the two methods we were able to provide appropriate CIiPlan formulas that gave good estimate of both methods values.Conclusion:CIiPlan for multiple SRS targets need be analyzed with great caution; especially if small lesions and big lesions are part of same plan. CIIN,iPlan values based on each target normal tissue volume encompassed by the prescription IDL should be used.