bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐440: Gain Calibration Stability Study of a MV Flat‐Panel‐Detector (FPD) On Siemens ARTISTE Linac
Authors: Lei Y , Zheng D , Wang S , Zhu X , Zhang Q , Li S , Driewer J , Zhou S 
Published: June 2015

Purpose:To study gain calibration variation over time for an MV flat‐panel‐detector (FPD).Methods:Gain calibration images (1024×1024 pixels) of a FPD (PerkinElmer AN‐9 on a Siemens ARTISTE) acquired in 40 consecutive months were studied. Using Python programming language, the images were processed to analyze the central 900×900 pixels with a threshold applied to exclude dead pixels. Month1 was set as the base image, then the difference images between it and the following months were calculated. The pixel intensity mean and standard deviation of the difference images were used to study the gain variation over time. Two other months’ images were also randomly selected as the base image and the above analyses were repeated. Finally, to investigate the equivalence of monthly calibration and quarterly calibration, the results from comparing neighboring months’ images, such as (month2‐month1), (month3 ‐month2) et al, were compared with those from comparing images taken in 3‐month intervals, such as (month4‐month1), (month7‐month4) et al, using Welch's t‐test.Results:For most months’ gain calibration images, the differences (mean and standard deviation) from base images were constant. In three months, the differences were relatively larger compared to other months but seemed instantaneous without any worsening trend. In those 3 months no clinical portal image quality degradation was observed. The difference between monthly and quarterly calibration tested by Welch's t‐test were insignificant for both means (p=0.9) and standard deviations (p=0.8).Conclusion:Long term stability of the FPD gain calibration images was observed. Therefore, the vendor‐recommended calibration frequency of 2–4 weeks is unnecessary. Less frequent, such as quarterly, calibration is sufficient.
SU‐E‐T‐447: Growth of Metal Whiskers Under External Beam Irradiation: Experimental Evidence and Implications in Medical Electronic Devices for Radiation Therapy Treatments
Authors: Shvydka D , Warrell G , Parsai E , Karpov V , Vasko A 
Published: June 2015

Purpose:Thin metallic protrusions, termed “whiskers,” have been identified as a cause of failure in devices ranging from satellites to pacemakers. For decades, lead was used in tin‐based soldering alloys to suppress whisker formation. With the adoption of the Restriction of Hazardous Substances act and the expiration of its exemption on medical devices, including implanted medical devices (IMDs), electronic circuits are required to be lead‐free as of July 2014. The effect of radiation on such soldering components remains unknown.Methods:We have irradiated a thin (150 nm) tin metal layer, deposited on a 3 mm thick glass substrate, with a 6 MeV medical linac (Varian TrueBeam) electron beam in five 2‐hour long sessions. After receiving ∼10 kGy, whisker growth on the sample was assessed with scanning electron microscopy and compared to a reference sample not exposed to radiation.Results:After 10 hours of irradiation, the sample was found to develop intense whisker infestation, while the reference sample remained in its pristine as‐deposited condition. Repeating the same irradiation schedule generated more and longer whiskers. The observed phenomenon can be explained through charge accumulation in the glass substrate, generating an electric field that promotes whisker growth. The observed substrate glass darkening under irradiation points towards development of color centers related to charge trapping. Experiments on the same type of samples with direct application of the external field in a capacitor‐like setting also resulted in intense whisker growth.Conclusion:Extreme care should be taken in dealing with all electronic devices, especially IMDs, produced with lead‐free solder and components, subject to radiation exposure. While in our experiments strong electric fields were intentionally generated to accelerate whisker growth over hours, in everyday use the circuit soldering may cause problems in a matter of days or months. Designated reliability testing under radiation must be conducted.This work is partially supported by NRC grant No. NRC‐HQ‐12‐G‐38‐0042
SU‐E‐T‐454: Impact of Air Gap On PDDs of 6 MV Photon Beam for Various Field Sizes in Inhomogeneous Phantoms
Authors: Oyewale S , Pokharel  , Singh H , Islam M , Rana S 
Published: June 2015

Purpose:To investigate how the shape of air gap and its size will impact the percent depth doses (PDDs) of a 6MV photon beam for various field sizes.Methods:Two in‐house phantoms were manufactured containing rectangular (phantom A) and circular (phantom B) air gaps. Both phantoms A and B were composed of same top layer (solid‐water; 30×30cm2,5cm thickness) and bottom layer (solid‐water; 30×30cm 2,8cm thickness), but middle layer was varied to observe air gap effects and scatter contribution to the measurement point. In phantom A, a rectangular shaped air gap (30×30cm2,7cm thickness) was created by placing Styrofoam blocks between top and bottom layers of the phantom. In phantom B, middle layer was replaced by “inhomogenous block”, composed of acrylic plate (30×30cm2, 4cm thickness) followed by PVC(30×30cm2,3cm thickness). Additionally, circular air gap was created by drilling a hole (diameter=2.8cm, length=7cm) at the center of “inhomogenous block”. In both phantoms, measurement readings were obtained at 13cm depth (i.e., 1cm after air gap) and depth of maximum dose(6MV energy; 100 MUs; field sizes ranged from 3×3cm2 to 10×10cm2). The PDDs at 13cm depth were compared in both phantoms.Results:The measurements in both phantoms A and B showed an almost linear increase in PDDs with increasing field size, especially for smaller field sizes (from 3×3 to 7×7cm2). For each field size, the PDD in phantom A was smaller compared to the one in phantom B. The difference in PDDs between two phantoms decreased with an increase in field size as the PDD difference decreased from 9.0% to 6.4%.Conclusion:The shape and size of air gap affect the PDD measurements in secondary build‐up region as 6 MV primary beam traverses through the center of air gap. The scatter contribution due to increase in field size was more noticeable for field sizes ≤7×7cm2.
SU‐E‐T‐455: Impact of Different Independent Dose Verification Software Programs for Secondary Check
Authors: Itano M , Yamazaki T , Yamashita M , Ishibashi S , Higuchi Y , Kosaka M , Kobayashi N , Tachibana H 
Published: June 2015

Purpose:There have been many reports for different dose calculation algorithms for treatment planning system (TPS). Independent dose verification program (IndpPro) is essential to verify clinical plans from the TPS. However, the accuracy of different independent dose verification programs was not evident. We conducted a multi‐institutional study to reveal the impact of different IndpPros using different TPSs.Methods:Three institutes participated in this study. They used two different IndpPros (RADCALC and Simple MU Analysis (SMU), which implemented the Clarkson algorithm. RADCALC needed the input of radiological path length (RPL) computed by the TPSs (Eclipse or Pinnacle3). SMU used CT images to compute the RPL independently from TPS). An ion‐chamber measurement in water‐equivalent phantom was performed to evaluate the accuracy of two IndpPros and the TPS in each institute. Next, the accuracy of dose calculation using the two IndpPros compared to TPS was assessed in clinical plan.Results:The accuracy of IndpPros and the TPSs in the homogenous phantom was +/−1% variation to the measurement. 1543 treatment fields were collected from the patients treated in the institutes. The RADCALC showed better accuracy (0.9 ± 2.2 %) than the SMU (1.7 ± 2.1 %). However, the accuracy was dependent on the TPS (Eclipse: 0.5%, Pinnacle3: 1.0%). The accuracy of RADCALC with Eclipse was similar to that of SMU in one of the institute.Conclusion:Depending on independent dose verification program, the accuracy shows systematic dose accuracy variation even though the measurement comparison showed a similar variation. The variation was affected by radiological path length calculation. IndpPro with Pinnacle3 has different variation because Pinnacle3 computed the RPL using physical density. Eclipse and SMU uses electron density, though.
SU‐E‐T‐458: Impact of Parameters for Volumetric Modulated Arc Therapy (VMAT) for Rectal Cancer
Authors: Runxiao L , Yankun C , Rong Q , Yuzhi S , Kai S , Mingchang M 
Published: June 2015

Purpose:Different parameters Result in different plans. As the developing of volumetric modulated arc therapy for rectal cancer, the purpose of this study was to work out appropriate parameters for the optimization of rectal cancer.Methods:For ten cases which were optimized using Oncentra4.3 version, varying systematically the number of arcs, collimator angle and the delivery time to create different plans. Homogeneity in planning target volume, median dose in the organs at risk and number of monitor units were evaluated for statistical analysis. Measurements were performed with Delt4, taking the delivery time, and compared to the calculation by the gamma method.Results:Plans with collimator 45° were little superior to plans with collimator 0°. Single arc achieved lower homogeneous indices in the planning target volume compared with dual arc, but also requiring less monitor units per fraction dose than dual arc. Single arc needs less monitor units for the treatment; the measured delivery time was reduced from 4 min of dual arc to 2.5 min of single arc. All the plans could achieve good pass rate with gamma method.Conclusion:Some of the parameters have been found as the appropriate sets which can be used as standard for volumetric modulated arc therapy of rectal cancer.
SU‐E‐T‐462: Impact of the Radiochromic Film Energy Response On Dose Measurements of Low Energy Electronic Brachytherapy Sources
Authors: Liang L , Bekerat H , Tomic N , DeBlois F , Devic S , Morcos M , Popovic M , Watson P , Seuntjens J 
Published: June 2015

Purpose:We investigated the effect of the EBT3 GafChromicTM film model absorbed dose energy response when used for percent depth dose (PDD) measurements in low‐energy photon beams.Methods:We measured PDDs in water from a Xoft 50 kVp source using EBT3 film, and compared them to PDD measurements acquired with a PTW‐TN34013 parallel‐plate ionization chamber. For the x‐ray source, we simulated spectra using the EGSnrc (BEAMnrc) Monte Carlo code, and calculated Half Value Layer (HVL) at different distances from the source in water. Pieces of EBT3 film were irradiated in air and calibration curves were created in terms of air‐kerma in air ((Kair)air) for different beam qualities. Pieces of EBT3 film were positioned at distances of 2–6 cm from the Xoft source in a water phantom using a custom‐made holder, and irradiated at the same time. As scatter is incorporated in the measured film signal in water, measured (Kair)wat was subsequently converted into absorbed dose to water by the ratio of mass energy absorption coefficients following the AAPM TG‐61 dosimetry protocol.Results:Our results show that film calibration curves obtained at beam qualities near the effective energy of the Xoft 50 kVp source in water lead to variation in absorbed dose energy dependence of the response of around 3%. However, if the calibration curve was established at MV beam quality, the error in absorbed dose could be as large as 15%. We observed agreement within 1% between PDD measurements using EBT3 film model (using a calibration curve obtained at 80 kVp, HVL=2.18 mm Al, Eeff=29.5 keV) and the parallel‐plate ionization chamber.Conclusion:Accurate dose measurements using radiochromic films at low photon energies require that the radiochromic film dosimetry system be calibrated at corresponding low energies, as large absorbed dose errors are expected for calibrations performed at MV beam qualities.
SU‐E‐T‐463: Impact to Total Scatter Factors On the Calculated Dose Distribution in Radiosurgery
Authors: Garcia O , Larraga‐Gutierrez J 
Published: June 2015

Purpose:To assess the impact of relative measurements: off axis ratios (OAR), tissue phantom ratios (TPR) and especially total scatter factor (TSF) on the calculated dose distribution in stereotactic radiosurgery with circular cones.Methods:Six detectors were employed to characterize circular collimated photon beams of 6 MV: three diodes (SFD, E, SRS), one ionization chamber (CC01) and two radiochromic films (EBT, EBT2). The relative measurements were incorporated in the treatment planning system (TPS) in order to compare and analyze the calculated dose distributions (DD). Each dose distribution was re‐scaled by the TSF to observe its effect in the final dose distribution. The comparison was performed by using the gamma index. A Monte Carlo generated dosimetry was used as reference.Results:The results showed that in terms of relative dosimetry all the detectors have a good agreement within 2%, with the exception of the CC01 and EBT2 film. However, the analysis performed with the dose distributions re‐scaled relative to the TSF for each detector showed that the impact it was not only to the isocenter dose. The dose to the PTV and normal tissue showed differences up to 13% depending of the dosimeter used for TSF measurements.Conclusion:With the exception of the CC01 ionization chamber and EBT2 radiochromic film, all the studied dosimeters were adequate for the measurement of OAR and TPR. However, attention must be put in the measurement of TSF. The use of the wrong detector does not only affect the isocenter dose, it may have an impact in the PTV and normal tissue dose.
SU‐E‐T‐464: Implementation and Validation of 4D Acuros XB Dose Calculations
Authors: Thomas S , Huang V , Milette M , Yuen C , Teke T 
Published: June 2015

Purpose:In this abstract we implement and validate a 4D VMAT Acuros XB dose calculation using Gafchromic film. Special attention is paid to the physical material assignment in the CT dataset and to reported dose to water and dose to medium.Methods:A QUASAR phantom with a 3 cm sinusoidal tumor motion and 5 second period was scanned using 4D computed tomography. A CT was also obtained of the static QUASAR phantom with the tumor at the central position. A VMAT plan was created on the average CT dataset and was delivered on a Varian TrueBeam linear accelerator. The trajectory log file from this treatment was acquired and used to create 10 VMAT subplans (one for each portion of the breathing cycle). Motion for each subplan was simulated by moving the beam isocentre in the superior/inferior direction in the Treatment Planning System on the static CT scan. The 10 plans were calculated (both dose to medium and dose to water) and summed for 1) the original HU values from the static CT scan and 2) the correct physical material assignment in the CT dataset. To acquire a breathing phase synchronized film measurements the trajectory log was used to create a VMAT delivery plan which includes dynamic couch motion using the Developer Mode. Three different treatment start phases were investigated (mid inhalation, full inhalation and full exhalation).Results:For each scenario the coronal dose distributions were measured using Gafchromic film and compared to the corresponding calculation with Film QA Pro Software using a Gamma test with a 3%/3mm distance to agreement criteria. Good agreement was found between calculation and measurement. No statistically significant difference in agreement was found between calculations to original HU values vs calculations to over‐written (material‐assigned) HU values.Conclusion:The investigated 4D dose calculation method agrees well with measurement.
SU‐E‐T‐465: Implementation of An Automated Collision Detection Program Using Open Source Software for the Pinnacle Treatment Planning System
Authors: Tanny S , Bogue J , Parsai E , Sperling N 
Published: June 2015

Purpose:Potential collisions between the gantry head and the patient or table assembly are difficult to detect in most treatment planning systems. We have developed and implemented a novel software package for the representation of potential gantry collisions with the couch assembly at the time of treatment planning.Methods:Physical dimensions of the Varian Edge linear accelerator treatment head were measured and reproduced using the Visual Python display package. A script was developed for the Pinnacle treatment planning system to generate a file with the relevant couch, gantry, and isocenter positions for each beam in a planning trial. A python program was developed to parse the information from the TPS and produce a representative model of the couch/gantry system. Using the model and the Visual Python libraries, a rendering window is generated for each beam that allows the planner to evaluate the possibility of a collision.Results:Comparison against heuristic methods and direct verification on the machine validated the collision model generated by the software. Encounters of <1 cm between the gantry treatment head and table were visualized as collisions in our virtual model. Visual windows were created depicting the angle of collision for each beam, including the anticipated table coordinates. Visual rendering of a 6 arc trial with multiple couch positions was completed in under 1 minute, with network bandwidth being the primary bottleneck.Conclusion:The developed software allows for quick examination of possible collisions during the treatment planning process and helps to prevent major collisions prior to plan approval. The software can easily be implemented on future planning systems due to the versatility and platform independence of the Python programming language. Further integration of the software with the treatment planning system will allow the possibility of patient‐gantry collision detection for a range of treatment machines.
SU‐E‐T‐473: Improvements of GPU Based Calculations Over CPU Based Calculations and the Effects of Variable Computer Hardware
Authors: Donaghue J , Gajdos S 
Published: June 2015

Purpose:To compare the calculation times in Raystation treatment planning system (TPS) for different graphical processor units (GPU). Also, to determine the amount of time saved by using a GPU based calculation.Methods:Four different hardware configurations were utilized. (DC1) – Intel Xeon E5‐2650 dual CPU with 64 GB RAM and nVidia Quadro K4000 GPU. (DC1 Titan Black) – Same configuration as (DC1) but with nVidia Titan Black GPU. (RVW1) – Intel Xeon E5‐2650 CPU with 32 GB RAM and nVidia Quadro K4000 GPU. (RVW2) – Intel Xeon E5‐2650 CPU with 16 GB of RAM and Quadro K2000 GPU. Dose calculation was also performed without the GPU on DC1 and RVW2. Seven clinically delivered treatment plans were elected. The plans were picked with varying IMRT complexities. Each plan was calculated consecutively eleven times, and each plan had a uniform dose grid voxel size of 2 mm3.Results:When compared to non‐GPU calculation, the average time on DC1 with GPU improved by 21.8% (range: 9.4%–38.9%). Similarly, the average time on RVW2 with GPU improved by 42.3% (range: 35.3%–50.5%). Also, the DC1 Titan Black average calculation time was 48.6% faster (range: 13.1%–73.4%) than the nVidia Quadro GPU models. Overall, the DC1 Titan Black calculation times outperformed DC1 non‐GPU by an average of 58.3% (range: 32.9%–77.5%) For the prostate and nodes study, the DC1 Titan Black reduced times from 724±2.5 seconds 205±1.0 seconds.Conclusion:Dose calculation time is reduced with the addition of a GPU. Also, the nVidia Titan Black GPU provided better time savings than the nVidia Quadro GPU models. Available RAM also plays a role in calculation time due to system lag when the memory reaches capacity. The clinical user must determine the best hardware specifications for his or her institution based on speed but also on monetary cost.
SU‐E‐T‐477: IMPT Vs. VMAT: A Treatment Planning Study for High‐Risk Prostate Cancer
Authors: Rana S , Zheng Y , Cheng C 
Published: June 2015

Purpose:The purpose of this study was to compare the dosimetric results between intensity modulated proton therapy (IMPT) and volumetric modulated arc therapy (VMAT) plans for a high‐risk prostate cancer.Methods:Six high‐risk prostate cancer cases were included in this retrospective study. For each case, IMPT plans were generated using multiple field optimization (MFO) technique (2 fields) with XiO treatment planning system (TPS), whereas VMAT plans were generated using RapidArc technique (2 full arcs) with Eclipse TPS. IMPT and VMAT plans were optimized for a total prescription dose of 79.2 Gy[RBE] and 79.2 Gy, respectively. IMPT and VMAT plans were compared using physical dose‐volume parameters. The absolute differences in a dosimetric parameter between IMPT and VMAT plans were calculated. The results were averaged over six cases.Results:For the planning target volume (PTV), the mean dose was comparable between IMPT (80.65 Gy[RBE]) and VMAT (80.33 Gy) plans, whereas the PTV coverage was slightly better in IMPT (97.41%) than in VMAT (95.00%) plans. The mean dose to the rectum and bladder were lower in IMPT (17.68 Gy[RBE] and 15.70 Gy[RBE], respectively) when compared to VMAT (42.17 Gy and 30.29 Gy, respectively) plans. The rectal V₇₀, V5₀, and V₃₀ were lower in IMPT plans than in VMAT plans by 4.91%, 28.34%, and 46.74%, respectively. For bladder, V₇₀ was comparable (8.92 Gy(RBE) vs. 9.03 Gy), whereas V5₀ and V₃₀ were lower in IMPT plans by 6.25% and 25.92%, respectively, when compared to VMAT plans. The mean doses to the left and right femoral heads were lower in VMAT plans (18.08 Gy and 21.91 Gy, respectively) than in VMAT plans (31.35 Gy[RBE] and 29.52 Gy[RBE], respectively)Conclusion:Both IMPT and VMAT plans provided excellent target coverage and acceptable femoral head dose. IMPT provided better tissue sparing for the rectum and bladder compared to VMAT.
SU‐E‐T‐478: IMRT Delivery Parameter Dependence of Dose‐Mass Optimization
Authors: Couto M , Mihaylov I 
Published: June 2015

Purpose:To compare DMH and DVH optimization sensitivity to changes in IMRT delivery parameters.Methods:Two lung and two head and neck (HN) cases were retrospectively optimized using DVH and DMH optimization. For both optimization approaches, changes to two parameters were studied: number of IMRT segments (5 and 10 per beam) and the minimum segment area (2 and 6 cm2). The number of beams, beam angles, and minimum MUs per segment were the same for both optimizations approaches for each patient. During optimization, doses to the organs at risk (OARs) were iteratively lowered until the standard deviation across the PTV was above ∼3.0%. For each patient DVH and DMH plans were normalized such that 95% of the PTV received the same dose. Plan quality was evaluated by dose indices (DIs), which represent the dose delivered to a certain anatomical structure volume. For the lung cases, DIs assessed included: 1% cord, 33% heart, both lungs 20% and 30%, and 50% esophagus. In the HN cases: 1% cord, 1% brainstem, left/right parotids 50%, 50% larynx, and 50% esophagus.Results:When increasing the number of segments, while keeping a small segment area (2cm2), the average percent change of all DIs for DVH/DMH optimizations for each patient were: −4.66/4.71, 3.21/3.46, −9.62/21.69 and −3.28/−7.62. For a large segment area (6cm2): −0.26/−1.46, −5.04/−1.92, −5.23/−2.19 and 4.12/19.63. Results from increasing segment area while keeping a small number of segments (5segments/beam) were: 1.41/7.90, 8.17/11.66, 0.09/33.58 and −4.83/−11.60 for each case. For large number of segments (10 segments/beam): 8.35/1.30, −0.91/5.77, 6.29/7.08 and 2.62/5.16.Conclusion:This preliminary study showed case dependent results. Changes in IMRT parameters did not show consistent DI changes for either optimization approach. A larger population of patients is warranted for such comparison.