bluuebunny/crossref_metadata_2025_split huggingface dataset:
WE‐AB‐BRB‐04: Cherenkov Imaging for Radiation Therapy Dose Verification On Patients
Authors: Pogue B. 
Published: July 2016

Despite widespread IMRT treatments at modern radiation therapy clinics, precise dosimetric commissioning of an IMRT system remains a challenge. In the most recent report from the Radiological Physics Center (RPC), nearly 20% of institutions failed an end‐to‐end test with an anthropomorphic head and neck phantom, a test that has rather lenient dose difference and distance‐to‐agreement criteria of 7% and 4 mm. The RPC report provides strong evidence that IMRT implementation is prone to error and that improved quality assurance tools are required. At the heart of radiation therapy dosimetry is the multidimensional dosimeter. However, due to the limited availability of water‐equivalent dosimetry materials, research and development in this important field is challenging. In this session, we will review a few dosimeter developments that are either in the laboratory phase or in the pre‐commercialization phase. 1) Radiochromic plastic. Novel formulations exhibit light absorbing optical contrast with very little scatter, enabling faster, broad beam optical CT design. 2) Storage phosphor. After irradiation, the dosimetry panels will be read out using a dedicated 2D scanning apparatus in a non‐invasive, electro‐optic manner and immediately restored for further use. 3) Liquid scintillator. Scintillators convert the energy from x‐rays and proton beams into visible light, which can be recorded with a scientific camera (CCD or CMOS) from multiple angles. The 3D shape of the dose distribution can then be reconstructed. 4) Cherenkov emission imaging. Gated intensified imaging allows video‐rate passive detection of Cherenkov emission during radiation therapy with the room lights on.

Learning Objectives:
To understand the physics of a variety of dosimetry techniques based upon optical imaging
To investigate the strategies to overcome respective challenges and limitations
To explore novel ideas of dosimeter designSupported in part by NIH Grants R01CA148853, R01CA182450, R01CA109558. Brian Pogue is founder and president of the company DoseOptics LLC, dedicated to developing and commercializing the first dedicated Cerenkov imaging camera and system for radiation dose imaging. Work reported in this talk does not involve the use of DoseOptics technology.; H. Li, this work was supported in part by NIH Grant No. R01CA148853; S. Beddar, NIH funding R01‐CA182450
WE‐AB‐BRA‐04: Investigation of MRI Derived Thermal Dose Models
Authors: MacLellan C , Fuentes D , Espinoza H , Prabhu S , Rao G , Weinberg J , Stafford R 
Published: July 2016

Purpose:To develop and investigate a novel thermal dose model methodology using MR temperature imaging (MRTI) and post‐treatment MRI changes as a surrogate of tissue damage in clinical laser ablation of the brain.Methods:Post‐treatment contrast enhanced T1‐weighted images were registered to MRTI acquired during two MR‐guided thermal ablation procedures. The non‐enhancing central region and hyperintense ring of vascular disruption characteristic of the thermal lesion were segmented manually and resampled into the 2D geometry of the MRTI. Regions immediately inside and outside the ring were classified as nonviable and viable tissue, respectively (N=1860). Logistic regression was performed on these classifications using thermal dose (Ω) calculated via four Arrhenius dose models from the literature (Henriques (H), Weaver & Stoll (WS), Diller & Klutke (DK), and Brown (B)). The optimal (O) Arrhenius dose model was found by iteratively changing the parameters of the Arrhenius model, Ea and A, until logistic model deviance was minimized.Results:Deviance of the Henriques model was closest to the optimized model (360 (H), 630 (WS), 438 (DK), 803(B), 330(O)). The thermal dose required to achieve a 90% probability of nonviability was 1.4 (H), 2.65 (WS), 1.8 (D), 4.5 (B), 1.1 (O) for each model. Agreement between the area of >90% nonviability between each model and the optimal model was 0.97 (H), 0.89(WS), 0.94(DK), and 0.88(B) using the Dice Similarity Coefficient.Conclusion:A methodology for deriving new thermal dose models from clinically used surrogates of tissue damage has been developed and tested. The logistic model suggests that the common dose threshold of Ω=1 may overestimate tissue damage. Good agreement is observed between the nonviable regions predicted by the optimized model and literature models. However, agreement between models is expected to decrease for longer ablation procedures designed to create larger thermal lesions and is an opportunity for further study.
WE‐AB‐BRA‐05: PET‐Guided Delivery Quality Evaluation of Yttrium‐90 Microsphere Radioembolizaton for Hepatocellular Carcinoma Patients: The Optimal Sequence of Radioembolizaton and Chemoembolization Treatments
Authors: Lin M , Saboury B 
Published: July 2016

Purpose:Selective‐internal‐radiation‐therapy (SIRT) and transarterial‐chemoembolization (TACE) are commonly used for treatment of liver tumors. The use of TACE, which is macroembolic, prior to SIRT may cause hemodynamic changes in tumor vasculature that impair yttrium‐90 (90Y) microsphere delivery to the targeted lesions. This work aims to quantify dosimetric tumor coverage using 90Y positron emission tomography (PET) dosimetry after SIRT alone compared to TACE followed by SIRT.Methods:A total of 40 consecutive hepatocellular carcinoma (HCC) SIRT patients who had a post‐SIRT 90Y PET/CT scan were evaluated. The patient‐specific‐3D‐dose was reconstructed from the PET images. Patients were categorized into two groups: patients received TACE prior SIRT procedure (n=18) and patient received SIRT alone (n=22). The lesions and liver were delineated by a senior radiologist. We evaluated both the lesion‐specific dose‐volume‐histogram (DVH) and the selectivity index (SI) defined as the ratio of the average dose inside the total lesion(s) and the average dose of the normal liver. The SI values of patients were compared based on whether TACE was previously used.Results:A wide spectrum was observed in the lesion‐specific DVH‐evaluation and SI appeared to be suitable of evaluating the quality of each SIRT infusion. The average SI of the entire patient group was 3.0, i.e. targeted lesion receiving three times higher dose than normal liver. The average SI was 1.8 for patients who had prior TACE and 3.9 for patients who did not have prior TACE (p=0.008). 85% of the patients with prior TACE demonstrated poor 90Y‐microsphere delivery (SI <2) while none demonstrated excellent delivery (SI >4). On the other hand, the incidence SI >4 among patients with no prior TACE was 37%.Conclusion:3D dose evaluation using post‐SIRT PET suggests that 90Y microsphere delivery to liver tumors is impaired among patients who received prior TACE compared to those who receive SIRT alone.
WE‐AB‐BRA‐11: Improved Imaging of Permanent Prostate Brachytherapy Seed Implants by Combining an Endorectal X‐Ray Sensor with a CT Scanner
Authors: Steiner J , Matthews K , Jia G 
Published: July 2016

Purpose:To test feasibility of the use of a digital endorectal x‐ray sensor for improved image resolution of permanent brachytherapy seed implants compared to conventional CT.Methods:Two phantoms simulating the male pelvic region were used to test the capabilities of a digital endorectal x‐ray sensor for imaging permanent brachytherapy seed implants. Phantom 1 was constructed from acrylic plastic with cavities milled in the locations of the prostate and the rectum. The prostate cavity was filled a Styrofoam plug implanted with 10 training seeds. Phantom 2 was constructed from tissue‐equivalent gelatins and contained a prostate phantom implanted with 18 strands of training seeds. For both phantoms, an intraoral digital dental x‐ray sensor was placed in the rectum within 2 cm of the seed implants. Scout scans were taken of the phantoms over a limited arc angle using a CT scanner (80 kV, 120–200 mA). The dental sensor was removed from the phantoms and normal helical CT and scout (0 degree) scans using typical parameters for pelvic CT (120 kV, auto‐mA) were collected. A shift‐and add tomosynthesis algorithm was developed to localize seed plane location normal to detector face.Results:The endorectal sensor produced images with improved resolution compared to CT scans. Seed clusters and individual seed geometry were more discernable using the endorectal sensor. Seed 3D locations, including seeds that were not located in every projection image, were discernable using the shift and add algorithm.Conclusion:This work shows that digital endorectal x‐ray sensors are a feasible method for improving imaging of permanent brachytherapy seed implants. Future work will consist of optimizing the tomosynthesis technique to produce higher resolution, lower dose images of 1) permanent brachytherapy seed implants for post‐implant dosimetry and 2) fine anatomic details for imaging and managing prostatic disease compared to CT images.Funding: LSU Faculty Start‐up Funding. Disclosure: XDR Radiography has loaned our research group the digital x‐ray detector used in this work. CoI: None.
WE‐AB‐207A‐02: John's Equation Based Consistency Condition and Incomplete Projection Restoration Upon Circular Orbit CBCT
Authors: Ma J , Qi H , Wu S , Yan H , Xu Y , Zhou L 
Published: July 2016

Purpose:In transmitted X‐ray tomography imaging, projections are sometimes incomplete due to a variety of reasons, such as geometry inaccuracy, defective detector cells, etc. To address this issue, we have derived a direct consistency condition based on John's Equation, and proposed a method to effectively restore incomplete projections based on this consistency condition.Methods:Through parameter substitutions, we have derived a direct consistency condition equation from John's equation, in which the left side is only projection derivative of view and the right side is projection derivative of other geometrical parameters. Based on this consistency condition, a projection restoration method is proposed, which includes five steps: 1) Forward projecting reconstructed image and using linear interpolation to estimate the incomplete projections as the initial result; 2) Performing Fourier transform on the projections; 3) Restoring the incomplete frequency data using the consistency condition equation; 4) Performing inverse Fourier transform; 5) Repeat step 2)∼4) until our criteria is met to terminate the iteration.Results:A beam‐blocking‐based scatter correction case and a bad‐pixel correction case were used to demonstrate the efficacy and robustness of our restoration method. The mean absolute error (MAE), signal noise ratio (SNR) and mean square error (MSE) were employed as our evaluation metrics of the reconstructed images. For the scatter correction case, the MAE is reduced from 63.3% to 71.7% with 4 iterations. Compared with the existing Patch's method, the MAE of our method is further reduced by 8.72%. For the bad‐pixel case, the SNR of the reconstructed image by our method is increased from 13.49% to 21.48%, with the MSE being decreased by 45.95%, compared with linear interpolation method.Conclusion:Our studies have demonstrated that our restoration method based on the new consistency condition could effectively restore the incomplete projections, especially for their high frequency component.
WE‐AB‐206‐01: Diagnostic Ultrasound Imaging Quality Assurance
Authors: Zagzebski J. 
Published: July 2016

The involvement of medical physicists in diagnostic ultrasound imaging service is increasing due to QC and accreditation requirements. The goal of this ultrasound hands‐on workshop is to demonstrate quality control (QC) testing in diagnostic ultrasound and to provide updates in ACR ultrasound accreditation requirements. The first half of this workshop will include two presentations reviewing diagnostic ultrasound QA/QC and ACR ultrasound accreditation requirements. The second half of the workshop will include live demonstrations of basic QC tests. An array of ultrasound testing phantoms and ultrasound scanners will be available for attendees to learn diagnostic ultrasound QC in a hands‐on environment with live demonstrations and on‐site instructors. The targeted attendees are medical physicists in diagnostic imaging.

Learning Objectives:
Gain familiarity with common elements of a QA/QC program for diagnostic ultrasound imaging
dentify QC tools available for testing diagnostic ultrasound systems and learn how to use these tools
Learn ACR ultrasound accreditation requirementsJennifer Walter is an employee of American College of Radiology on Ultrasound Accreditation.
WE‐AB‐209‐01: A Monte Carlo‐Based Method to Include Random Errors in Robust Optimization
Authors: Barragan Montero A , Souris K , Lee J , Sterpin E 
Published: July 2016

Purpose:To develop an efficient method to implement random set‐up errors and organ motion in robust optimization for proton therapy treatment planning.Methods:The plans were created with an in‐house robust optimizer, coupled with a super‐fast Monte Carlo (MC) engine (less than 1 minute for final dose). MC simulates random errors by shifting randomly the starting point of each particle, according to their probability distribution. Such strategy assumes a sufficient number of treatment fractions. Two strategies are presented: 1) Full robust optimization with beamlets that already include the effect of random errors and 2) Mixed robust optimization, where the nominal beamlets are involved but a correction term C modifies the prescription. Starting from C=0, the method alternates optimization of the spot weights with the nominal beamlets and updates of C, with C=Drandom‐Dnominal and where Drandom results from a regular MC computation (without pre‐computed beamlets) that simulates random errors. Updates of C can be triggered as often as necessary by running the MC engine with the last corrected values for the spot weights as input. The method was applied to lung and prostate cases. For both patients the range error was set to 3%, systematic setup error to 5mm and standard deviation for random errors to 5 mm. Comparison between full robust optimization and the mixed strategy (with 3 updates of C) is presented.Results:Target coverage was far below the clinical constraints (D95 > 95% of the prescribed dose) for plans where random errors were not simulated, especially for lung case. However, by using the proposed strategies the plans achieved a target coverage above clinical constraints.Conclusion:Full robust optimization gives better results than the mixed strategy, but the latter can be useful in cases where a MC engine is not available or too computationally intensive for beamlets calculation.
WE‐AB‐209‐02: A New Inverse Planning Framework with Principle‐Based Modeling of Inter‐Structural Dosimetric Tradeoffs
Authors: Liu H , Dong P , Xing L 
Published: July 2016

Purpose:Traditional radiotherapy inverse planning relies on the weighting factors to phenomenologically balance the conflicting criteria for different structures. The resulting manual trial‐and‐error determination of the weights has long been recognized as the most time‐consuming part of treatment planning. The purpose of this work is to develop an inverse planning framework that parameterizes the inter‐structural dosimetric tradeoff among with physically more meaningful quantities to simplify the search for a clinically sensible plan.Methods:A permissible dosimetric uncertainty is introduced for each of the structures to balance their conflicting dosimetric requirements. The inverse planning is then formulated as a convex feasibility problem, which aims to generate plans with acceptable dosimetric uncertainties. A sequential procedure (SP) is derived to decompose the model into three submodels to constrain the uncertainty in the planning target volume (PTV), the critical structures, and all other structures to spare, sequentially. The proposed technique is applied to plan a liver case and a head‐and‐neck case and compared with a conventional approach.Results:Our results show that the strategy is able to generate clinically sensible plans with little trial‐and‐error. In the case of liver IMRT, the fractional volumes to liver and heart above 20Gy are found to be 22% and 10%, respectively, which are 15.1% and 33.3% lower than that of the counterpart conventional plan while maintaining the same PTV coverage. The planning of the head and neck IMRT show the same level of success, with the DVHs for all organs at risk and PTV very competitive to a counterpart plan.Conclusion:A new inverse planning framework has been established. With physically more meaningful modeling of the inter‐structural tradeoff, the technique enables us to substantially reduce the need for trial‐and‐error adjustment of the model parameters and opens new opportunities of incorporating prior knowledge to facilitate the treatment planning process.
WE‐AB‐209‐04: Biological Evaluation of Universal Multi‐Criteria Optimization VMAT Prostate Plans
Authors: Guerrero M , Chen S 
Published: July 2016

Purpose:In recent years Multi‐Criteria Optimization (MCO) has become commercially available as a potential optimization method for intensity modulated and volumetric arc therapies (IMRT and VMAT). The purpose of our work is to develop a universal set of objectives and constraints to generate prostate cancer MCO plans with VMAT and evaluate them using biological metrics.Methods:We randomly selected ten prostate plans (two‐arc VMAT) for patients with intermediate risk prostate cancer prescribed 75.6–79.2Gy to the prostate and seminal vesicles. We compared the plan scores to our clinical plans generated with standard IMRT optimization techniques. The planning target volumes (PTV) were 5–10 mm set‐up margin expansion of the gross target volume. Using the same two arcs we generated MCO plans with a standard set of constraints and objectives using Raystation v4.5. The dose‐volume histograms (DVH) for the (PTV), rectum and bladder were exported and used to calculate tumor control probability (TCP) and the complication‐free tumor control probability P+ using biological models from the literature. We classified the plans by their level of difficulty based on the rectum‐PTV overlap and develop MCO plans with similar levels of conformality as the clinical plans.Results:The P+ values of the MCO plans had an average of 86.4%±2.3% and were equivalent to the clinical plans (P+ average of 85.0%±2.1%, p‐value=0.33). The MCO NTCP values for the rectum ranged from 0.7% to 20% and were highly correlated with rectum‐PTV overlap. NTCP values for the bladder were less than 1% for all MCO plans.Conclusion:MCO VMAT prostate plans obtained with standardized objectives and constraints generate biologically equivalent plans to the clinical plans generated with standard optimization techniques.
WE‐AB‐209‐06: Dynamic Collimator Trajectory Algorithm for Use in VMAT Treatment Deliveries
Authors: MacDonald L , Thomas C , Syme A 
Published: July 2016

Purpose:To develop advanced dynamic collimator positioning algorithms for optimal beam's‐eye‐view (BEV) fitting of targets in VMAT procedures, including multiple metastases stereotactic radiosurgery procedures.Methods:A trajectory algorithm was developed, which can dynamically modify the angle of the collimator as a function of VMAT control point to provide optimized collimation of target volume(s). Central to this algorithm is a concept denoted “whitespace”, defined as area within the jaw‐defined BEV field, outside of the PTV, and not shielded by the MLC when fit to the PTV. Calculating whitespace at all collimator angles and every control point, a two‐dimensional topographical map depicting the tightness‐of‐fit of the MLC was generated. A variety of novel searching algorithms identified a number of candidate trajectories of continuous collimator motion. Ranking these candidate trajectories according to their accrued whitespace value produced an optimal solution for navigation of this map.Results:All trajectories were normalized to minimum possible (i.e. calculated without consideration of collimator motion constraints) accrued whitespace. On an acoustic neuroma case, a random walk algorithm generated a trajectory with 151% whitespace; random walk including a mandatory anchor point improved this to 148%; gradient search produced a trajectory with 137%; and bi‐directional gradient search generated a trajectory with 130% whitespace. For comparison, a fixed collimator angle of 30° and 330° accumulated 272% and 228% of whitespace, respectively. The algorithm was tested on a clinical case with two metastases (single isocentre) and identified collimator angles that allow for simultaneous irradiation of the PTVs while minimizing normal tissue irradiation.Conclusion:Dynamic collimator trajectories have the potential to improve VMAT deliveries through increased efficiency and reduced normal tissue dose, especially in treatment of multiple cranial metastases, without significant safety concerns that hinder immediate clinical implementation.
WE‐AB‐209‐09: Optimization of Rotational Arc Station Parameter Optimized Radiation Therapy
Authors: Dong P , Ungun B , Boyd S , Xing L 
Published: July 2016

Purpose:To develop a fast optimization method for station parameter optimized radiation therapy (SPORT) and show that SPORT is capable of improving VMAT in both plan quality and delivery efficiency.Methods:The angular space from 0° to 360° was divided into 180 station points (SPs). A candidate aperture was assigned to each of the SPs based on the calculation results using a column generation algorithm. The weights of the apertures were then obtained by optimizing the objective function using a state‐of‐the‐art GPU based Proximal Operator Graph Solver (POGS) within seconds. Apertures with zero or low weight were thrown out. To avoid being trapped in a local minimum, a stochastic gradient descent method was employed which also greatly increased the convergence rate of the objective function. The above procedure repeated until the plan could not be improved any further. A weighting factor associated with the total plan MU also indirectly controlled the complexities of aperture shapes. The number of apertures for VMAT and SPORT was confined to 180. The SPORT allowed the coexistence of multiple apertures in a single SP. The optimization technique was assessed by using three clinical cases (prostate, H&N and brain).Results:Marked dosimetric quality improvement was demonstrated in the SPORT plans for all three studied cases. Prostate case: the volume of the 50% prescription dose was decreased by 22% for the rectum. H&N case: SPORT improved the mean dose for the left and right parotids by 15% each. Brain case: the doses to the eyes, chiasm and inner ears were all improved. SPORT shortened the treatment time by ∼1 min for the prostate case, ∼0.5 min for brain case, and ∼0.2 min for the H&N case.Conclusion:The superior dosimetric quality and delivery efficiency presented here indicates that SPORT is an intriguing alternative treatment modality.