bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐40: Exploring the Reproducibility of Tumor Volumes Measured by Radiologist, Computer‐Aided Radiologist and Computer Alone
Authors: Zhao B , Tan Y , Li Y , Guo P , Schwartz L 
Published: November 2011

Purpose: The use of volumetric CT as an imaging metric to better assess cancer response to treatment requires knowledge of measurement reproducibility. This study was designed to explore the reproducibility of tumor volumes obtained by radiologist manual delineation (MAN), computer‐aided method (CAM) and computer alone (CA) using a same‐day repeat CT dataset of 32 non‐small cell lung cancer (NSCLC) patients. Methods: We used a publicly accessible repeat CT dataset aimed at studying cancer treatment response. Briefly, each patient was scanned twice within 15 minutes using the same imaging protocol and CT scanner (16‐ or 64‐row). Patients were repositioned before the second scan. Thin‐sectional images of 1.25mm slice interval were reconstructed using a shaper filter. Thirty‐two lesions (one per patient) were analyzed using the following three Methods: (1) MAN‐an experienced radiologist manually drew tumor contours on two repeat scans in a side‐by‐side mode, (2) CAM‐an operator applied a home‐grown algorithm to segment the tumors and the computer‐generated contours were reviewed/edited by the same radiologist, also in a side‐by‐side mode, and (3) CA‐an operator applied a different, also homegrown, algorithm to delineate tumor contours (no edit). Bland‐Altman plots were constructed to assess the agreement between volumes measured by each method on the two repeat scans. Volume difference between MAN and CA on each patientˈs first scan was analyzed using a paired t‐test. Results: The 95% limits of agreements for the tumor volumes made by MAN, CAM and CA on two repeat scans were (−19.9%, 19.6%), (−12.1%, 13.4%) and (−11.8%, 16.0%), respectively. The difference between tumor volumes measured by MAN and CA was not statistically significant (p=0.497). Conclusions: MAN is the least reproducible method for measuring tumor volumes compared to CAM and CA. The recommended way to obtain tumor volumes is to use a computer algorithm to segment tumors followed by radiologistˈs supervision.This work is supported in part by R01CA125143 from National Cancer Institute
SU‐E‐T‐108: EBT2 Film Based Dosimetry Incorporating Correction for Spatial‐Temporal Dose Response Variation
Authors: Tenn S , Ruan D , Dou T , Low D 
Published: November 2011

Purpose: Implementation of radiochromic film, such as GafChromic EBT2 film, as a quantitative 2‐dimensional dosimeter requires an array of equipment calibrations and corrections. We have developed a holistic model‐based calibration/correction mechanism for radiochromic film dosimetry. Methods: One challenge of using radiochromic film is that most of the densitometry scanners in use are designed for qualitative, not quantitative use. We performed careful characterization and quantification of the systematic and random components of all temporal and spatial optical density variations. In the proposed workflow, the spatial‐dependent dose response is estimated in the calibration stage under a novel model‐based optimization framework. A benchmark calibration process has been developed for the full (optical density, space) calibration map. For improved robustness, a simplified model that assumes separability of spatial variation and dose dependence was developed. The corresponding QA tool utilizes a consistent correction principle and maps the observed pixel intensity value based on the estimated spatially varying calibration map. The developed method has been tested on seven plans (both IMRT and VMAT) and compared with commercial software correction results. Dosimetry accuracy was validated against EDR2 film by comparison with treatment planning system calculated dose distribution using 3%‐3mm gamma criterion.Results: Under equivalent test conditions, the proposed method achieves gamma passing rates with EBT2 that are comparable to or better than a correction method of a commercial counterpart. Such corroboration is consistent for both IMRT and VMAT plans under gamma tests Conclusions: We have developed a systematic approach to comprehensively calibrate and use EBT2 film, accounting for temporal and spatial dose response variations. Specifically, a formal generative model and an estimation methodology was developed to achieve good balance between measurement sensitivity and robustness. This process has been implemented with in‐house software.Research supported in part by AACR career development award.
SU‐E‐T‐112: 18 MV X‐Ray Beam Commissioning with the IC Profiler: A Fast 3D Relative Dosimetry Technique Using An Ion Chamber Array in a Solid Tissue‐Equivalent Phantom
Authors: Leduc V , Furstoss C , Pater P , Munger P , Wierzbicki W 
Published: November 2011

Purpose: To devise a technique of 3D relative dosimetry using an ion chamber array with solid phantom to significantly reduce overall measurement time needed for photon beam modeling. Methods: Measurement setup of the array was determined by comparison of acquired profiles in the array and in a water tank. Software was developed to queue measurements in step‐and‐shoot sequences and process the resulting IC array data. Beam profiles and PDDs necessary for beam modeling were acquired with the IC array for 18 MV. A model was created with the IC array data using the Pinnacle TPS and compared to a model created from water tank measurements. Both models were first compared by measuring differences between profiles and PDDs. Secondly, 3D dose distributions predicted by both models were compared using a gamma metric for a pair of treatment plans. Results: The IC array model was found to match the water tank model for most profiles. Due to fixed chamber depth in the IC array, PDDs near the surface differed in the IC array model from the water tank model. For a prostate case treatment plan, comparison of 3D dose distributions from both models showed that 90.4 % of voxels agreed within a gamma of (1%, 1 mm). This tolerance was violated near air‐tissue interfaces due to differences in the measured PDDs between both models. The devised technique allowed most measurements necessary for beam modeling, except for output factors, to be made for a single energy in under 8 hours. Conclusions: The IC array with solid phantom setup allows substantially faster beam acquisition than a water tank. Further investigation is required for measuring exact PDDs in the IC array setup. Future work will study lower photon energies and electron beam modeling with IC array acquisitions.Funding for the presenting author was provided for this study by Sun Nuclear Corporation during the summer of 2010.
SU‐E‐T‐139: Note on the Underestimation of the Dosimetrical Significance of Detected IMRT Verification Deviations Using the Gamma‐Index Method and a Global Acceptance Criterion Based on the Number of Passing Points
Authors: Poppe B , Looe H , Luellau T , Willborn K , Allgaier B , Harder D 
Published: November 2011

Purpose: Possible underestimations of the dosimetrical impact of Gamma‐Index detected dose deviations due to the choice of the maximum dose in the analysis plane as the reference value are analyzed. It is shown that clinical relevant deviations can be thereby missed in possible projections of organs‐at‐risk as low dose regions. Furthermore global criteria based on the number of points passing a verification procedure may be not sufficient to guarantee the detection of dose deviations within relevant areas of the patient. Methods: Clinical relevant dose deviations are introduced in some IMRT plans. Measurements are performed with the 2D‐ARRAY and analyzed by the Gamma Index method by normalization to the maximum and local dose in the plane. The acceptance procedure is performed according to guidelines recommending a fraction of approximately 95% accepted points to accept the plan. A point‐by‐point evaluation is performed to further analyze if the failing chambers may have a relevant impact on organs‐at‐risk. Results: Referencing relative doses to the “maximum dose in plane” tends to underestimate the deviations in the low dose regions. These regions are often in the beam projection of organs‐at‐risk, therefore possible impacts may be overseen. Even under tight acceptance criteria for the “global fraction” of points failing the analysis, relying on only this criterium may not be sufficient. We have started to re‐evaluate the dose deviations on a chamber‐by‐chamber basis, regarding them as screening values for detection of relevant deviations. Conclusions: In situations in which deviations in low dose regions may indicate a dosimetrical impact on critical structures, a local normalization procedure should be used. In addition to the global acceptance criterion of an IMRT treatment plan verification, we consider the single‐chamber failings of the Gamma‐Index analysis as screening values for actual dosimetrical impacts in the patient.One of the co‐authors works for PTW. However there was no funding for this study.
SU‐E‐T‐187: A Dedicated Phantom for Electron Density Calibration and Image QA of Linac Cone Beam CT Options
Authors: Cossmann P 
Published: November 2011

Purpose: In order to use linac Cone‐Beam‐CT (CBCT) data for dosimetric planning an electron density calibration is compulsory. Studies on available phantoms for CT performance checks/QA have shown that these are not sufficient for an adequate HU calibration. Therefore we designed a new dedicated phantom and carried out a planning study to determine the usability of such calibrated CBCT data in comparison with diagnostic CT data. Methods: Available linac CBCT options acquire in a single gantry rotation a volumetric CT data set. In order to 3D‐calibrate the system with regard to HU a special phantom has been designed to include the whole imager area. Removable inserts allow flexible positioning of the probes in x‐z as well as z‐direction. Furthermore a performance and image QA part according AAPM recommendations No. 1 has been integrated and evaluated. We compared 20 plan setups (10 in the pelvic and 10 in the thoracic region). Results: Within the field of view the HU variation is up to 5%. Towards the imager edges hounsfield units show small deviations relative to the imager center (max. 8%). Relative dose distributions in CBCT‐based plans show minor differences to plans calculated using a diagnostic CT image dataset (p=0.002) and absolute dosage deviations are within 1% (p=0.001). Image quality comparisons using the performance and image QA part showed that CBCT images are of lower quality than diagnostic images, i.e. spatial and low contrast resolution are 2–3 levels below. Conclusions: The newly designed phantom allows real 3D‐calibration of linac CBCT. It is made of water equivalent material and consists of probes with tissue equivalent materials. The phantom has additional scatter material to simulate a real patientsˈ situation. CBCT data can be used for treatment planning. Furthermore the image QA part allows to carry out recommended constancy checks in straightforward approach.We received financial support from Varian Medical Systems to manufacture the prototypes.
SU‐E‐T‐197: Normoxic Polymer Gel Dosimetry for Intensity Modulated Radiation Therapy
Authors: Kwon S , Cho Y , Cho K , Lee S , Ji Y , Jung H , Kim K B , Kim K M 
Published: November 2011

Purpose: To evaluate a tissue equivalent normoxic polymer gel dosimeter as a tool for 3‐dimensional dose quality assurance for intensity modulated radiation therapy (IMRT) by measuring the dose characteristics of therapeutic radiation by Magnetic Resonance Imaging (MRI). Methods: Polymer gel under normoxic conditions was synthesized using gelatin, methyacrylic acid (MAA), hydroquinone (HQ) and tetrakis hydroxymethyl phosphonium chloride (THPC), and polymer gel dosimeter was fabricated by placing it into each phantom for the appropriate experiments. Co‐60 gamma‐rays and a 6 MV photon beam were used for the dose reaction experiments. The dose range was 0∼20 Gy. The dose characteristics of the polymer gel dosimeter were compared with those of the ion chamber and Gafchromic EBT2 film using 3.0T MRI. Results: The linear correlation coefficient was r2=0.970, r2=0.999 and r2=0.972 for the polymer gel dosimeter, ion chamber and film, respectively. The percentage depth dose at a depth of 50 mm was 85.8% and 84.6% for the polymer gel dosimeter and ion chamber, respectively. The flatness and symmetry of the gel dosimeter on the cross‐plane were 3.80% and 3.58%, respectively. After applying the gel dosimeter to IMRT, the dosages measured in the 100% dose domain of therapeutic planning for the axial, sagittal and coronal planes were 96.2%, 103.0% and 100%, respectively. Conclusions: The results show a relatively high level of precision in the high dose range in IMRT, which is important in clinic sites. The possibility of this as a 3‐dimensional dose quality assurance tool of a polymer gel dosimeter was confirmedThis work was supported by National Research Foundation of Korea Grant funded by the Korean Government.
SU‐E‐T‐246: Practical Quality Assurance for Image‐Guided Robotic Brachytherapy System
Authors: Buzurovic I , Podder T , Yu Y 
Published: November 2011

Purpose: To establish device‐specific daily quality assurance procedure for image‐guided brachytherapy robotic system. To recommend sufficient tests and tolerance levels which would be acceptable for readily identifying and localizing possible deviations from normal system functionalities.Methods: Image‐guided brachytherapy robot consists of three mutually paired functional modules: robotic hardware with sensors, control and planning software, and image acquisition subsystem. Therefore, daily QA procedure should ensure mechanical and software functionality, appropriate system calibration, clinical image acquisition and quality, and verification of system accuracy. Recommended daily QA tests can be summarized into three basic groups: mechanical screening, robotic system functionality, and overall calibration test. Mechanical screening test includes visual check of connectors, controllers, wires, sensors and motors, connectivity test for controllers, motors, encoders and moving parts, sensors readings and sensitivity, and emergency subsystem functionality test, such as emergency button or manual takeover check. Robotic system functionality test incorporates automatic hardware detection and mobility of moving parts, such as probe stage, gantry and insertion mechanism. It also includes image upload and acquisition test. Purpose of overall calibration test is to simulate seed placement into predefined position using captured image sets. Specially designed tool with three markers should be attached to the robot. Tip of each marker has different coordinates. System should drive needle, touch and stop next to each marker. Difference between needle and marker tip should be recorded.Results: First and the second groups of tests are designed to have pass/fail outcome. Tolerance values for third test are ±0.5 mm. Daily QA procedure was developed to minimize test time which is 20min on average Conclusions: Routine daily QA procedure plays crucial role in ensuring overall safety of brachytherapy robotic system for clinical implementation. Recommended procedures are intended to support and supplement development of comprehensive brachytherapy robotic QA program.Acknowledgement: Supported by NCI‐R01‐CA091763.
SU‐E‐T‐278: Volume Based Comparison of Deformable Image Registration Algorithms Using Spatial Discrepancy Volume Histograms
Authors: Fatyga M , Dogan N , Wijesooriya K , Sleeman W , Zhang B , Christensen G 
Published: November 2011

Purpose: Accurate Deformable Image Registration (DIR) algorithms are essential to clinical implementation of adaptive planning strategies hence finding validation strategies for DIR algorithms remains a pressing concern. Most validation efforts are based on contour or landmark tracking, thus sampling the Deformable Vector Field (DVF) relatively sparsely. The primary purpose of this work is to assess interchangeability of DIR algorithms in dose accumulation, and assess if contour based methods are sufficient to validate the equivalence of DIR algorithms. Methods: We registered peak inhale and peak exhale phases of thirteen lung patients using three DIR algorithms. The DVF maps were pairwise compared through voxel‐by‐voxel subtraction of vector fields. The vector difference maps were analyzed by building volume histograms on regions of interest. This method of analysis is directly relevant to the Dose Volume Histogram accumulation, as vector difference between the maps will be translated into a distance between dose interpolation points. We further compared Jacobian distributions for the three maps, as local derivatives of DVF maps would be important to any algorithm that attempts local density corrections. We performed contour based comparison of the three algorithms, to connect this validation method to prior work. Results: The volume histogram analysis shows that differences between DVFs in 2% tails of volume histogram are in the 1cm – 4cm range, although the contour‐based analysis using Diceˈs Similarity Coefficient (DSC) would suggest that the three algorithms are nearly equivalent. For most structures, spatial differences between maps are below 0.5cm over approximately 70% of structure volume, and exceed 0.5cm over the remainder. Jacobian distributions differ significantly, implying that local density corrections are strongly algorithm dependent. Conclusions: Differences between algorithms are potentially significant for dose accumulation, and such differences are not revealed by contour based comparisons.Acknowledgments: Supported by NIH Grant P01 CA11602
SU‐E‐T‐293: Accuracy of Elekta ‐ Image Guided Radiation Therapy
Authors: Sutton M , Matthews K , Parker B 
Published: November 2011

Purpose: Frameless Stereotactic Radiosurgery requires <1mm positional accuracy. We quantified the accuracy and precision of the IGRT treatment process for the Elekta Infinity using a comprehensive phantom‐based QA procedure. The IGRT process was evaluated for both MV planar imaging and kilovoltage cone beam computed tomography (kVCBCT). Methods: A CIRS Radiosurgery head phantom with a film dosimetry insert was used to measure dose distributions in three anatomic planes. Once the phantom was properly aligned on the treatment couch, a series of offsets were applied to the position of the phantom; intentional misalignments of ±5mm in the lateral, longitudinal, and axial directions were applied. Prior to treatment, one of the IGRT modalities was used, and the calculated realignment values were applied to the phantom position. An isocentric seven‐field treatment plan with a prescription of 3Gy per fraction was delivered to the phantom. The delivered dose distributions were analyzed and compared to the calculated dose distributions from the Pinnacle(v.8.0m) treatment planning system. Two metrics were analyzed from the film: (1) dose profile positional alignment error at the 70% dose level and (2) directional mismatch of dose profile edges at the 80% dose points. Results: The largest positional alignment errors occurred along the inferior‐superior axis [0.64 ± 1.01mm]. This was possibly due to slack in the couch along this direction — the couch tended to shake slightly along this axis. Similarly, the shifts in the 80% dose points were worst along the inferior‐superior axis [80%(Inf) = −0.71 ± 0.91mm; 80%(Sup) = −0.89 ± 1.17mm]. Conclusions: Our evaluation indicates the Elekta Infinity does not have sufficient positional accuracy for frameless Stereotactic Radiosurgery, but its positional accuracy is more than suitable for conventional radiotherapy. For all cases, using kVCBCT for phantom alignment resulted in more conformal dose coverage than using MV Planar imaging.This work is supported by a research contract from Elekta
SU‐E‐T‐311: Comparison of Two Imaging Setups for Small Animal Cone Beam CT
Authors: Yang Y , Armour M , Siewerdsen J , Iordachita I , Wong J 
Published: November 2011

Purpose: To support non‐coplanar irradiation, cone beam CT (CBCT) on our small animal radiation research platform (SARRP) is acquired in a “pancake” setup where the prone animal is rotated between the stationary x‐ray source and flat‐panel detector. This study compares the performance of the pancake setup with conventional CBCT of a stationary animal. Methods: CBCT images were acquired on the SARRP using the pancake and a “tubular” setup with upright phantoms to mimic conventional CBCT. PMMA cylindrical phantoms of mouse dimension (3‐cm wide and 7.5‐cm long) embedded with 5‐mm wide rods of teflon, delrin, acrylic and polyethylene inhomogeneities were employed. The study included a single phantom, three side‐by‐side phantoms, and a euthanized mouse. Images were acquired at 65 kVp, 0.1‐mm brass filtration for: (1) imaging dose at 1x, 2x, and 4x of 1.6 cGy; (2) inclined “pancake” object at 14 degree and 28 degree. Comparison of zero‐frequency signal‐to‐noise ratio (SNR) and contrast‐to‐nose ratio (CNR) were made. Results: At 1.6 cGy, both SNR (19.4–23.0 vs 23.2–48.5) and CNR (−0.11%–0.57% vs −0.15%–0.88%) of the pancake setup were lower than those of the tubular setup for the 4 inhomogeneities. Similar results were obtained for the 3‐phantom study. Doubling the dose for the pancake setup improved these metrics and approached those of tubular setup at 1x dose. The difference in SNR and CNR between the pancake and tubular setups were reduced with increasing inclination. Pancake CBCT of an inclined mouse at 28 degree was virtually identical to that of the tubular setup. Conclusions: CBCT image quality of the pancake setup is compromised in favor of the ease of non‐coplanar irradiation. Image quality can be recovered with a modest increase in imaging dose to 3 cGy. Notwithstanding, pancake CBCT is adequate to support image guidance, while providing other irradiation advantages.John Wong has a sponsored research agreement with Xstrahl Ltd. Xstrahl Ltd. has a technology transfer agreement with Johns Hopkins University on the SARRP.
SU‐E‐T‐426: Assessment of the Limitations of Intensity Modulated Radiation Therapy Quality Control Procedure
Authors: Girard F , Lacroix F 
Published: November 2011

Purpose: To determine the impact of dose delivery errors due to multileaf collimator bank offset and gantry angle offset on the resulting gamma value of an IMRT Quality Control (QC) test as determined by a planar 2D dosimeter. Also to determine the impact of the planar 2D dosimeter array resolution on the gamma. Methods: Systematic errors such as MLC leaf bank offset and gantry angle offset were numerically introduced in IM verification plans. The dose received by a phantom was calculated using anisotropic analytical algorithm with a grid size of 1 mm. A corona plane (30×30 cm2) was selected for each modified plan and compared t original using the geometric gamma approach in absolute or relative using a 3%/3 mm criteria. The plans were then irradiated in a phan composed of 20×20 cm2 slabs of plastic water. The phantom was im using a CT scan and imported into the treatment planning system Ec (Varian inc.). A radiochromic EBT2 (ISP Corp. inc.) film was placed depth of 4 cm. Results: Absolute dose measurements are much m sensitive to MLC bank offsets than relative measurements. In con modifying the gantry angle by 1 degree has little effect on the relativ absolute gamma value. There is a clear increase in the variance of gamma value as the detector spacing is increased beyond 2–3 Conclusions: Absolute dose measurements should be performed maximize QC sensitivity. Ideally, the detector spacing in a 2D planar a should be less than 2–3 mm in order to minimize the uncertainty on gamma.This work has been supported by the Ministère de la Santé et des Ser Sociaux and Natural Sciences and Engineering Research Council Disco Grant No. 357402.