bluuebunny/crossref_metadata_2025_split huggingface dataset:
TH‐E‐BRE‐05: Analysis of Dosimetric Characteristics in Two Leaf Motion Calculator Algorithms for Sliding Window IMRT
Authors: Wu L , Huang B , Rowedder B , Ma B , Kuang Y 
Published: July 2014

Purpose:The Smart leaf motion calculator (SLMC) in Eclipse treatment planning system is an advanced fluence delivery modeling algorithm as it takes into account fine MLC features including inter‐leaf leakage, rounded leaf tips, non‐uniform leaf thickness, and the spindle cavity etc. In this study, SLMC and traditional Varian LMC (VLMC) algorithms were investigated, for the first time, in dosimetric characteristics and delivery accuracy of sliding window (SW) IMRT.Methods:The SW IMRT plans of 51 cancer cases were included to evaluate dosimetric characteristics and dose delivery accuracy from leaf motion calculated by SLMC and VLMC, respectively. All plans were delivered using a Varian TrueBeam Linac. The DVH and MUs of the plans were analyzed. Three patient specific QA tools – independent dose calculation software IMSure, Delta4 phantom, and EPID portal dosimetry were also used to measure the delivered dose distribution.Results:Significant differences in the MUs were observed between the two LMCs (p≤0.001).Gamma analysis shows an excellent agreement between the planned dose distribution calculated by both LMC algorithms and delivered dose distribution measured by three QA tools in all plans at 3%/3 mm, leading to a mean pass rate exceeding 97%. The mean fraction of pixels with gamma < 1 of SLMC is slightly lower than that of VLMC in the IMSure and Delta4 results, but higher in portal dosimetry (the highest spatial resolution), especially in complex cases such as nasopharynx.Conclusion:The study suggests that the two LMCs generates the similar target coverage and sparing patterns of critical structures. However, SLMC is modestly more accurate than VLMC in modeling advanced MLC features, which may lead to a more accurate dose delivery in SW IMRT. Current clinical QA tools might not be specific enough to differentiate the dosimetric discrepancies at the millimeter level calculated by these two LMC algorithms.NIH/NIGMS grant U54 GM104944, Lincy Endowed Assistant Professorship
TH‐E‐BRE‐06: Challenges in the Dosimetry of Flattening Filter Free Beams
Authors: Czarnecki D , von Voigts‐Rhetz P , Zink K 
Published: July 2014

Purpose:In current dosimetry protocols [AAPM TG51, IAEA TRS‐389] the beam quality correction factor kQ and the water‐to‐air restricted mass collision stopping‐power ratio SPR are related to beam quality specifiers %dd(10)x respectively TPR20,10 Determining kQ and SPR using these regular beam quality specifiers for conventional accelerators (WFF) and flattening filter free accelerators (FFF) similarly could lead to systemic bias. The influence of the flattening filter on the relationship between various beam quality specifiers and SPR respectively kQ was studied using Monte Carlo simulations with realistic beam sources.Methods:All Monte Carlo simulations were performed using the BEAMnrc/EGSnrc code system. Radiation transport through nine linear accelerator heads modeled according to technical drawings given by the manufactures and a 6 0 Co therapy source was simulated with BEAMnrc and then used as a radiation source for further simulations. FFF beam sources were implemented by removing the fattening filter from the WFF model. SPR was calculated applying the user code SPRRZnrc. The mean photon energy below the accelerator head and the mean energies of photons and electrons at the measuring point within the water phantom were calculated using FLURZnrc. Dose calculations within a small water voxel and the thimble ionization chamber PTW‐31010 in a water depth of 10 cm were made using the egs_chamber code.Results:SPR and kQ as a function of fluence spectra based beam quality specifiers as well as conventional beam quality specifiers differ systematically between FFF and WFF beams. According to the results the specifier %dd(10)x revealed the smallest deviation (max. 0.4%) between FFF and WFF beams.Conclusion:The results show that %dd(10)x is an acceptable beam quality specifier for FFF beams. Nevertheless the results confirm the expected bias between FFF and WFF beams which must by further investigated.
TH‐E‐BRF‐03: A Multivariate Interaction Model for Assessment of Hippocampal Vascular Dose‐Response and Early Prediction of Radiation‐Induced Neurocognitive Dysfunction
Authors: Farjam R , Pramanik P , Srinivasan A , Chapman C , Tsien C , Lawrence T , Cao Y 
Published: July 2014

Purpose:Vascular injury could be a cause of hippocampal dysfunction leading to late neurocognitive decline in patients receiving brain radiotherapy (RT). Hence, our aim was to develop a multivariate interaction model for characterization of hippocampal vascular dose‐response and early prediction of radiation‐induced late neurocognitive impairments.Methods:27 patients (17 males and 10 females, age 31–80 years) were enrolled in an IRB‐approved prospective longitudinal study. All patients were diagnosed with a low‐grade glioma or benign tumor and treated by 3‐D conformal or intensity‐modulated RT with a median dose of 54 Gy (50.4–59.4 Gy in 1.8− Gy fractions). Six DCE‐MRI scans were performed from pre‐RT to 18 months post‐RT. DCE data were fitted to the modified Toft model to obtain the transfer constant of gadolinium influx from the intravascular space into the extravascular extracellular space, Ktrans, and the fraction of blood plasma volume, Vp. The hippocampus vascular property alterations after starting RT were characterized by changes in the hippocampal mean values of, μh(Ktrans)τ and μh(Vp)τ. The dose‐response, Δμh(Ktrans/Vp)pre‐>τ, was modeled using a multivariate linear regression considering integrations of doses with age, sex, hippocampal laterality and presence of tumor/edema near a hippocampus. Finally, the early vascular dose‐response in hippocampus was correlated with neurocognitive decline 6 and 18 months post‐RT.Results:The μh(Ktrans) increased significantly from pre‐RT to 1 month post‐RT (p<0.0004). The multivariate model showed that the dose effect on Δμh(Ktrans)pre‐>1M post‐RT was interacted with sex (p<0.0007) and age (p<0.00004), with the dose‐response more pronounced in older females. Also, the vascular dose‐response in the left hippocampus of females was significantly correlated with memory function decline at 6 (r = − 0.95, p<0.0006) and 18 (r = −0.88, p<0.02) months post‐RT.Conclusion:The hippocampal vascular response to radiation could be sex and age dependent. The early hippocampal vascular dose‐response could predict late neurocognitive dysfunction.(Support: NIH‐RO1NS064973)
TH‐E‐17A‐06: Anatomical‐Adaptive Compressed Sensing (AACS) Reconstruction for Thoracic 4‐Dimensional Cone‐Beam CT
Authors: Shieh C , Kipritidis J , OBrien R , Cooper B , Kuncic Z , Keall P 
Published: July 2014

Purpose:The Feldkamp‐Davis‐Kress (FDK) algorithm currently used for clinical thoracic 4‐dimensional (4D) cone‐beam CT (CBCT) reconstruction suffers from noise and streaking artifacts due to projection under‐sampling. Compressed sensing theory enables reconstruction of under‐sampled datasets via total‐variation (TV) minimization, but TV‐minimization algorithms such as adaptive‐steepest‐descent‐projection‐onto‐convex‐sets (ASD‐POCS) often converge slowly and are prone to over‐smoothing anatomical details. These disadvantages can be overcome by incorporating general anatomical knowledge via anatomy segmentation. Based on this concept, we have developed an anatomical‐adaptive compressed sensing (AACS) algorithm for thoracic 4D‐CBCT reconstruction.Methods:AACS is based on the ASD‐POCS framework, where each iteration consists of a TV‐minimization step and a data fidelity constraint step. Prior to every AACS iteration, four major thoracic anatomical structures – soft tissue, lungs, bony anatomy, and pulmonary details – were segmented from the updated solution image. Based on the segmentation, an anatomical‐adaptive weighting was applied to the TV‐minimization step, so that TV‐minimization was enhanced at noisy/streaky regions and suppressed at anatomical structures of interest. The image quality and convergence speed of AACS was compared to conventional ASD‐POCS using an XCAT digital phantom and a patient scan.Results:For the XCAT phantom, the AACS image represented the ground truth better than the ASD‐POCS image, giving a higher structural similarity index (0.93 vs. 0.84) and lower absolute difference (1.1*104 vs. 1.4*104). For the patient case, while both algorithms resulted in much less noise and streaking than FDK, the AACS image showed considerably better contrast and sharpness of the vessels, tumor, and fiducial marker than the ASD‐POCS image. In addition, AACS converged over 50% faster than ASD‐POCS in both cases.Conclusions:The proposed AACS algorithm was shown to reconstruct thoracic 4D‐CBCT images more accurately and with faster convergence compared to ASD‐POCS. The superior image quality and rapid convergence makes AACS promising for future clinical use.
TH‐E‐17A‐09: High Quality and Artifact‐Free 4D Cone Beam CT and Its Application in Adaptive Treatment Planning
Authors: Niu K , Li K , Smilowitz J , Chen G 
Published: July 2014

Purpose:To develop a high quality 4D cone beam CT (4DCBCT) method that is immune to patient/couch truncations and to investigate its application in adaptive replanning of lung XRT.Methods:In this study, IRB‐approved human subject CBCT data was acquired using a Varian on‐board imager with 1 minute rotation time. The acquired projection data was retrospectively sorted into 20 respiratory phase bins, from which 4DCBCT images with high SNR and high temporal resolution were generated using Prior Image Constrained Compressed Sensing (PICCS). Couch and patient truncations generate strong data inconsistency in the projection data and artifacts in the 4DCBCT image. They were addressed using an adaptive PICCS method. The artifact‐free PICCS‐4DCBCT images were used to generate adaptive treatment plans for the same patient at the 10th (day 21) and 30th (day 47) fractions. Dosimetric impacts with and without PICCS‐ 4DCBCT were evaluated by isodose distributions, DVHs, and other dosimetric factors.Results:The adaptive PICCS‐4DCBCT method improves image quality by removing residue truncation artifacts; measured universal image quality increased 37%. The isodose lines and DVHs with PICCS‐4DCBCT‐based adaptive replanning were significantly more conformal to PTV than without replanning due to changes in patient anatomy caused by progress of the treatment. The mean dose to PTV at the 10th fraction was 63.1Gy with replanning and 64.2Gy without replanning, where the prescribed dose was 60Gy, in 2Gy × 30 fractions. The mean dose to PTV at the 30th fraction was 61.6Gy with replanning and 64.9Gy without replanning. Lung V20 was 37.1%, 41.9% and 43.3% for original plan, 10th fraction plan and 30th fraction plan; with re‐planning, Lung V20 was 37.1%, 32%, 27.8%.Conclusion:4DCBCT imaging using adaptive PICCS is able to generate high quality, artifact‐free images that potentially can be used to create replanning for improving radiotherapy of the lung. K Niu, K Li, J Smilowitz: Nothing to Disclose.G Chen: General Electric Company Research funded, Siemens AG Research funded, Varian Medical Systems Research funded, Hologic Research funded.
SU‐C‐16A‐01: In Vivo Source Position Verification in High Dose Rate (HDR) Prostate Brachytherapy Using a Flat Panel Imager: Initial Clinical Experience
Authors: Franich R , Smith R , Haworth A , Taylor M , McDermott L , Millar J 
Published: July 2014

Purpose:We report our initial clinical experience with a novel position‐sensitive source‐tracking system based on a flat panel imager. The system has been trialled with 4 prostate HDR brachytherapy patients (8 treatment fractions) in this initial study.Methods:The flat panel imaging system was mounted under a customised carbon fibre couch top assembly (Figure 1). Three gold fiducial markers were implanted into the prostate of each patient at the time of catheter placement. X‐ray dwell position markers were inserted into three catheters and a radiograph acquired to locate the implant relative to the imaging device. During treatment, as the HDR source dwells were delivered, images were acquired and processed to determine the position of the source in the patient. Source positions measured by the imaging device were compared to the treatment plan for verification of treatment delivery.Results:Measured dwell positions provided verification of relative dwell spacing within and between catheters, in the coronal plane. Measurements were typically within 2.0mm (0.2mm – 3.3mm, s.d. 0.8mm) of the planned positions over 60 dwells (Figure 2). Discrimination between larger dwell intervals and catheter differentiation were clear. This confirms important delivery attributes such as correct transfer tube connection, source step size, relative catheter positions and therefore overall correct plan selection and delivery. The fiducial markers, visible on the radiograph, provided verification of treatment delivery to the correct anatomical location. The absolute position of the dwells was determined by comparing the measured dwell positions with the x‐ray markers from the radiograph, validating the programmed treatment indexer length. The total impact on procedure time was less than 5 minutes.Conclusion:The novel, noninvasive HDR brachytherapy treatment verification system was used clinically with minor impact on workflow. The system allows verification of correct treatment delivery, free of most potential human related errors identified in ICRP 97.This research is supported by funding from the Australian Government Department of Health through Cancer Australia grant no. 616614.
SU‐C‐16A‐04: Dosimetric Validation of a Partially‐Shielded Gd‐153 Brachytherapy Concept
Authors: Li X , Adams Q , Flynn R 
Published: July 2014

Purpose:To demonstrate by measurement that using partially shielded Gd‐153 sources for rotating‐shield brachytherapy (RSBT) is feasible. RSBT is a potentially superior alternative to conventional high‐dose‐rate brachytherapy and provides the opportunity to dramatically improve tumor dose conformity for the treatment of, for example, prostate cancer.Methods:A custom‐built, stainless steel encapsulated 150 mCi Gd‐153 capsule with an outer length of 12.8 mm, outer diameter of 2.10 mm, active length of 9.98 mm, and active diameter of 1.53 mm was used. A partially shielded catheter was constructed with a 500 μm platinum shield and a 500 μm aluminum emission window, both with 180° azimuthal coverage. An acrylic phantom was constructed to measure the dose distributions from the shielded catheter in the transverse plane using Gafchromic EBT3 films. Film calibration curves were generated from 50, 70, and 100 kVp x‐ray beams with NIST‐traceable air kerma values to account for energy variation.Results:The transmission ratios of platinum to aluminum shielding at 1 cm off‐axis are 7.5% and 7.6% for Monte Carlo (MCNP5) predicted and experimental results, respectively. The predicted/measured relative dose rates at 1 cm, 2 cm and 3 cm off‐axis through the Al window were 100%/92.9%, 28.6%/27.0% and 13.8%/12.7%, respectively. Through the Pt shield, the predicted/measured relative dose rates were 7.5%/7.1%, 3.8%/3.0% and 2.4%/1.7%, respectively.Conclusion:Using partially‐shielded Gd‐153 sources for RSBT is a promising approach to improving brachytherapy dose distributions. The next step in making Gd‐153 based RSBT a reality is developing a Gd‐153 source that is small enough such that the source, shield, and catheter all fit within a 16 gauge needle, which has a 1.65 mm diameter.University of Iowa Research Foundation
SU‐C‐16A‐05: OAR Dose Tolerance Recommendations for Prostate and Cervical HDR Brachytherapy: Dose Versus Volume Metrics
Authors: Geneser S , Cunha J , Pouliot J , Hsu I 
Published: July 2014

Purpose:HDR brachytherapy consensus dose tolerance recommendations for organs at risk (OARs) remain widely debated. Prospective trials reporting metrics must be sufficiently data‐dense to assess adverse affects and identify optimally predictive tolerances. We explore the tradeoffs between reporting dose‐metrics versus volume‐metrics and the potential impact on trial outcome analysis and tolerance recommendations.Methods:We analyzed 26 prostate patients receiving 15 Gy HDR single‐fraction brachytherapy boost to 45 Gy external beam radiation therapy and 28 cervical patients receiving 28 Gy HDR brachytherapy monotherapy in 4 fractions using 2 implants. For each OAR structure, a robust linear regression fit was performed for the dose‐metrics as a function of the volume‐metrics. The plan quality information provided by recommended dose‐metric and volume‐metric values were compared.Results:For prostate rectal dose, D2cc and V75 lie close to the regression line, indicating they are similarly informative. Two outliers for prostate urethral dose are substantially different from the remaining cohort in terms of D0.1cc and V75, but not D1cc, suggesting the choice of reporting dose metric is essential. For prostate bladder and cervical bladder, rectum, and bowel, dose outliers are more apparent via V75 than recommended dose‐metrics. This suggests that for prostate bladder dose and all cervical OAR doses, the recommended volume‐metrics may be better predictors of clinical outcome than dose‐metrics.Conclusion:For plan acceptance criteria, dose and volume‐metrics are reciprocally equivalent. However, reporting dosemetrics or volume‐metrics alone provides substantially different information. Our results suggest that volume‐metrics may be more sensitive to differences in planned dose, and if one metric must be chosen, volumemetrics are preferable. However, reporting discrete DVH points severely limits the ability to identify planning tolerances most predictive of adverse effects. Thus, we recommend that full OAR DVH reporting be required for future prospective trials.
SU‐C‐19A‐03: Evaluation of Common Material Magnetic Susceptibility Effects for Immobilization Devices Used in MRI‐Guided Therapies
Authors: Paulson E , Jesmanowicz A 
Published: July 2014

Purpose:Phase variations induced by magnetic susceptibility differences of materials used for immobilization can result in localized signal dropout and spatial distortions on MR images. The goal of this study was to determine an optimal material for immobilization device construction that minimizes the effect of susceptibility on adjacent tissues.Methods:A total of 30 thermoset and thermoplastic material samples were included in the study. Each material sample was precision machined to dimensions of 11.1 × 23.8 × 123.8 mm3. During imaging, the samples were placed adjacent to a ball phantom with the long axis oriented parallel to the magnetic field. Imaging was performed at 3T using a GRE‐EPI sequence (FOV/matrix: 24cm2/128×128, TE/TR: 59/2000ms, rBW: 125 kHz, TH: 3mm). High order shimming was optimized once prior to acquisition. Phase images were reconstructed and unwrapped offline. Relative phase induced by the ith material was determined by subtracting the mean phase over a 3×3 kernel at the phantom center from the mean phase over a 3×3 kernel at a position of maximal phase‐induced change. Phase differences (Δϕ) induced by the ith material were determined by subtracting the relative phase with no sample from the relative phase with sample. Mann‐Whitney and Kruskal‐Wallis tests were used to determine whether significant differences in Δϕ existed between and among material categories.Results:In general, glass‐cloth resin reinforced materials produced the smallest phase differences, with G‐9 fiberglass producing the smallest phase difference of all materials studied. Significant phase differences were found between thermoset and thermoplastic materials (p=0.0002). Within the thermosets group, significant differences were found between glass‐cloth based materials relative to other thermosets (p=0.0157).Conclusions:Glass‐cloth resinreinforced thermosets, specifically G‐9 fiberglass, produced the smallest phase differences of all materials studied, and are recommended for construction of immobilization devices used in MR imaging and MRIguided therapies.Funding provided by Advancing a Healthier Wisconsin.
SU‐C‐19A‐04: Evaluation of Patient Positioning Reproducibility with Three Supine Breast Boards
Authors: Zhang Y , Brinkmann D , Pafundi D , Park S , Yan E , Choo R , Petersen I , Childs S , Pisansky T , Remmes N , Mutter R 
Published: July 2014

Purpose:To evaluate positioning reproducibility using three commercially available breast board immobilization systems for whole breast radiation therapy.Methods:Weekly pre‐treatment cone beam CT images from 18 free‐breathing breast radiotherapy patients, each immobilized with one of three breast boards, were retrospectively registered to the planning CT. Relative shifts between breast tissue and sternum/chest wall (CW), and breast tissue and spine compared to planning CT were obtained for each board. Positioning reproducibility, inter‐patient variation and intra‐patient variation were evaluated by group mean (M), standard deviation of group mean (Σ) and standard deviation of random shift (σ). Margins to account for setup uncertainties were calculated based on shift uncertainties in x, y, and z directions.Results:For breast positioning relative to sternum/CW, the average shift from planned positioning was 4.5mm (95% CI: 3.5 – 5.3), 3.3mm (CI: 2.9 – 3.8) and 2.6mm (CI: 1.8 – 3.5) for Breast Boards I, II, and III, respectively. The respective numbers for breast positioning relative to spine were 7.2 mm (CI: 4.1 – 10.3), 6.4 mm (CI: 4.3 – 8.3) and 4.3 mm (CI: 2.5 – 6.2). Localizing to the sternum/CW as a surrogate for the breast tissue, margins for setup uncertainties were 5.7mm, 5.5mm, and 6.0mm for Breast Board I, 5.0mm, 4.0mm and 4.3mm for Breast Board II, and 3.8mm, 3.5mm and 4.8mm for Breast Board III, in the lateral, anterior/posterior, and superior/inferior directions, respectively.Conclusion:Better patient positioning reproducibility was observed with Boards II and III compared to Board I. Inter‐ and intra‐patient set‐up uncertainties were also improved with Boards II and III, which requires smaller PTV margins. Independent of breast board, breast cancer patient positioning to the sternum/CW is a better surrogate than the spine. Our findings have potential dosimetric consequences from set‐up uncertainties when employing IMRT or proton treatments, and further analyses are on‐going.