bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐A‐18C‐10: Dynamic Intensity Weighted Region of Interest Imaging
Authors: Pearson E , Pan X , Pelizzari C
Published: July 2014

Purpose:

For image guidance tasks full image quality is not required throughout the entire image. With dynamic filtration of the kV imaging beam the noise properties of the CT image can be locally controlled, providing a high quality image around the target volume with a lower quality surrounding region while providing substantial dose sparing to the patient as well as reduced scatter fluence on the detector.

Methods:

A dynamic collimation device with 3mm copper blades has been designed to mount in place of the bowtie filter on the On‐Board Imager (Varian Medical Systems). The beam intensity is reduced by 95% behind the copper filters and the aperture is controlled dynamically to conformally illuminate a given ROI during a standard cone‐beam CT scan. A data correction framework to account for the physical effects of the collimator prior to reconstruction was developed. Furthermore, to determine the dose savings and scatter reduction a monte carlo model was built in BEAMnrc with specifics from the Varian Monte Carlo Data Package. The MC model was validated with Gafchromic film.

Results:

The reconstructed image shows image quality comparable to a standard scan in the specified ROI, with higher noise and streaks in the outer region but still sufficient information for alignment to high contrast structures. The monte carlo modeling showed that the scatter‐to‐primary ratio was reduced from 1.26 for an unfiltered scan to 0.45 for an intensity weighted scan, suggesting that image quality may be improved in the inner ROI. Dose in the inner region was reduced 10–15% due to reduced scatter and by as much as 75% in the outer region.

Conclusion:

Dynamic intensity‐weighted ROI imaging allows reduction of imaging dose to sensitive organs away from the target region while providing images that retain their utility for patient setup and procedure guidance.

Funding was provided in part by Varian Medical Systems and NIH Grants 1RO1CA120540, T32EB002103, S10 RR021039 and P30 CA14599.

The contents of this work are solely the responsibility of the authors and do not necessarily represent the official views of any of the supporting organizations.
TH‐A‐9A‐02: BEST IN PHYSICS (THERAPY) – 4D IMRT Planning Using Highly‐ Parallelizable Particle Swarm Optimization
Authors: Modiri A , Gu X , Sawant A
Published: July 2014

Purpose:

We present a particle swarm optimization (PSO)‐based 4D IMRT planning technique designed for dynamic MLC tracking delivery to lung tumors. The key idea is to utilize the temporal dimension as an additional degree of freedom rather than a constraint in order to achieve improved sparing of organs at risk (OARs).

Methods:

The target and normal structures were manually contoured on each of the ten phases of a 4DCT scan acquired from a lung SBRT patient who exhibited 1.5cm tumor motion despite the use of abdominal compression. Corresponding ten IMRT plans were generated using the Eclipse treatment planning system. These plans served as initial guess solutions for the PSO algorithm. Fluence weights were optimized over the entire solution space i.e., 10 phases × 12 beams × 166 control points. The size of the solution space motivated our choice of PSO, which is a highly parallelizable stochastic global optimization technique that is well‐suited for such large problems. A summed fluence map was created using an in‐house B‐spline deformable image registration. Each plan was compared with a corresponding, internal target volume (ITV)‐based IMRT plan.

Results:

The PSO 4D IMRT plan yielded comparable PTV coverage and significantly higher dose—sparing for parallel and serial OARs compared to the ITV‐based plan. The dose‐sparing achieved via PSO‐4DIMRT was: lung Dmean = 28%; lung V20 = 90%; spinal cord Dmax = 23%; esophagus Dmax = 31%; heart Dmax = 51%; heart Dmean = 64%.

Conclusion:

Truly 4D IMRT that uses the temporal dimension as an additional degree of freedom can achieve significant dose sparing of serial and parallel OARs. Given the large solution space, PSO represents an attractive, parallelizable tool to achieve globally optimal solutions for such problems. This work was supported through funding from the National Institutes of Health and Varian Medical Systems.

Amit Sawant has research funding from Varian Medical Systems, VisionRT Ltd. and Elekta
TH‐C‐9A‐01: Lean Tools and Methods
Authors: Rangaraj D , Chan K , Boddu S , Pawlicki T , Dieterich S
Published: July 2014

Lean thinking has revolutionized the manufacturing industry. Toyota has pioneered and leveraged this aspect of Lean thinking. Application of Lean thinking and Lean Six Sigma techniques into Healthcare and in particular in Radiation Oncology has its merits and challenges. To improve quality, safety and patient satisfaction with available resources or reducing cost in terms of time, staff and resources is demands of today's healthcare. Radiation oncology treatment involves many processes and steps, identifying and removing the non‐value added steps in a process can significantly improve the efficiency. Real projects undertaken in radiation oncology department in cutting down the procedure time for MRI guided brachytherapy to 40% less using lean thinking will be narrated. Simple Lean tools and techniques such as Gemba walk, visual control, daily huddles, standard work, value stream mapping, error‐proofing, etc. can be applied with existing resources and how that improved the operation in a Radiation Oncology department's two year experience will be discussed. Lean thinking focuses on identifying and solving the root‐cause of a problem by asking “Why” and not “Who” and this requires a culture change of no blame. Role of leadership in building lean culture, employee empowerment and trains and develops lean thinkers will be presented. Why Lean initiatives fail and how to implement lean successfully in your clinic will be discussed.

Learning Objectives:

Concepts of lean management or lean thinking.

Lean tools and techniques applied in Radiation Oncology.

Implement no blame culture and focus on system and processes.

Leadership role in implementing lean culture.

Challenges for Lean thinking in healthcare
TH‐E‐19A‐01: Quality and Safety in Radiation Therapy
Authors: Ford E , Ezzell G , Miller B , Yorke E
Published: July 2014

Clinical radiotherapy data clearly demonstrate the link between the quality and safety of radiation treatments and the outcome for patients. The medical physicist plays an essential role in this process. To ensure the highest quality treatments, the medical physicist must understand and employ modern quality improvement techniques. This extends well beyond the duties traditionally associated with prescriptive QA measures. This session will review the current best practices for improving quality and safety in radiation therapy.

General elements of quality management will be reviewed including: what makes a good quality management structure, the use of prospective risk analysis such as FMEA, and the use of incident learning. All of these practices are recommended in society‐level documents and are incorporated into the new Practice Accreditation program developed by ASTRO. To be effective, however, these techniques must be practical in a resource‐limited environment. This session will therefore focus on practical tools such as the newly‐released radiation oncology incident learning system, RO‐ILS, supported by AAPM and ASTRO.

With these general constructs in mind, a case study will be presented of quality management in an SBRT service. An example FMEA risk assessment will be presented along with incident learning examples including root cause analysis.

As the physicist's role as “quality officer” continues to evolve it will be essential to understand and employ the most effective techniques for quality improvement. This session will provide a concrete overview of the fundamentals in quality and safety.

Learning Objectives:

Recognize the essential elements of a good quality management system in radiotherapy.

Understand the value of incident learning and the AAPM/ASTRO ROILS incident learning system.

Appreciate failure mode and effects analysis as a risk assessment tool and its use in resource‐limited environments.

Understand the fundamental principles of good error proofing that extends beyond traditional prescriptive QA measures.
TH‐E‐16A‐01: Building, Maintaining and Improving Physics Residency Program
Authors: Klein E , Nye J
Published: July 2014

In this session we will discuss the key steps for building, maintaining and improving a physics residency program. The initial momentum starts with a secure commitment of; a program director, physics faculty, physicians, key technical personnel, and, of course, administration. The ultimate goal is to build a strong clinical physicist who practice independently and/or work in an interdisciplinary team. Part of the initiation is to find out the right balance of training, resident empowerment, and service contributed back to the clinic. Funding of residencies will be discussed including obstacles and benefits to residents participating in clinical service and establishing hub and spoke training collaborations. Another key step that will be discussed is the recruitment of resident candidates. Namely, where the residents are coming from, what their educational background is, and most importantly during interviews, how to gauge what makes an ideal resident. The key to maintenance of a residency program is to not allow stagnation, but rather to constantly update. Examples will be given of evolution of programs in terms of the didactic and clinical rotational components. In addition, how to allocate the resident developmental work, whether it be clinical or benchmark, without disrupting training. We will also discuss how to evaluate faculty on the ownership they take regarding resident training. We will discuss both therapy and imaging programs. Finally, we will share experiences on steps to continually improve one's program.

Learning Objectives:

To obtain from the experience of long standing programs the lessons learned.

To find out what historically has worked out to be ideal resident candidates.

Guidelines for continually improving a program.
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.
SU‐C‐19A‐06: A Robust and Affordable Table Indexing Approach for Total Lymphoid Irradiation Treatment
Authors: Yu S , Fahimian B , Kenyon M , Hsu A
Published: July 2014

Purpose:

Total lymphoid irradiation (TLI) is conventionally delivered through the dosimetric matching of mantle, spleen, and pelvis fields, necessitating multiple isocenters delivered through a combination of couch shifts and sliding of patients relative to the couch rendering the technique susceptible to shifting errors. To address this challenge, a novel technique for the couch indexing of TLI treatments is developed and evaluated through a multi‐patient pilot trial.

Methods:

An immobilization device was designed consisting of a movable indexed slide board with an Exact Lok‐Bar drilled into it. A Timo headrests were used fixate the head of the patient relative to the slide board. For the Varian Exact Couch™, the immobilization board was connected to the H3 notch to avoid the metal infrastructure of the couch for the delivery of the mantle and spleen fields. For tall patients the required shift for the pelvis isocenter reaches the shifting limit and the board was slid from H3 to H4 (a fixed distance of 14 cm). A total 22 patients were stratified in two groups of 11, one consisting of the conventional setup, and one group with the proposed immobilization technique.

Results:

The standard deviations (SD) of the couch positions in lateral, longitudinal, and vertical directions for 10 fractions for each patient in both groups were calculated. In the non‐indexed group, the positioning SD ranged from 0.9 to 4.7 cm. Using our device, the positioning SD was reduced to a range of 0.2 to 0.9 cm, with the longitudinal direction showing the largest improvement.

Conclusion:

Matched field TLI remains error prone to geometrical misses. The feasibility of full indexing TLI treatments was validated and shown to result in a significant reduction of positioning errors.
SU‐C‐BRE‐01: 3D Conformal Micro Irradiation Results of Four Treatment Sites for Preclinical Small Animal and Clinical Treatment Plans
Authors: Price S , Yaddanapudi S , Rangaraj D , Izaguirre E
Published: July 2014

Purpose:

Small animal irradiation can provide preclinical insights necessary for clinical advancement. In order to provide clinically relevant data, these small animal irradiations must be designed such that the treatment methods and results are comparable to clinical protocols, regardless of variations in treatment size and modality.

Methods:

Small animal treatments for four treatment sites (brain, liver, lung and spine) were investigated, accounting for change in treatment energy and target size. Up to five orthovoltage (300kVp) beams were used in the preclinical treatments, using circular, square, and conformal tungsten apertures, based on the treatment site. Treatments were delivered using the image guided micro irradiator (microIGRT). The plans were delivered to a mouse sized phantom and dose measurements in axial and coronal planes were performed using radiochromic film. The results of the clinical and preclinical protocols were characterized in terms of conformality number, CTV coverage, dose nonuniformity ratio, and organ at risk sparing.

Results:

Preclinical small animal treatment conformality was within 1–16% of clinical results for all treatment sites. The volume of the CTV receiving 100% of the prescription dose was typically within 10% of clinical values. The dose non‐uniformity was consistently higher for preclinical treatments compared to clinical treatments, indicating hot spots in the target. The ratios of the mean dose in the target to the mean dose in an organ at risk were comparable if not better for preclinical versus clinical treatments. Finally, QUANTEC dose constraints were applied and the recommended morbidity limits were satisfied in each small animal treatment site.

Conclusion:

We have shown that for four treatment sites, preclinical 3D conformal small animal treatments can be clinically comparable if clinical protocols are followed. Using clinical protocols as the standard, preclinical irradiation methods can be altered and iteratively improved to achieve a clinically relevant irradiation model.
SU‐C‐BRE‐07: Sensitivity Analysis of the Threshold Energy for the Creation of Strand Breaks and of Single and Double Strand Break Clustering Conditions
Authors: Pater P
Published: July 2014

Purpose:

To analyse the sensitivity of the creation of strand breaks (SB) to the threshold energy (Eth) and thresholding method and to quantify the impact of clustering conditions on single strand break (SSB) and double strand break (DSB) yields.

Methods:

Monte Carlo simulations using Geant4‐DNA were conducted for electron tracks of 280 eV to 220 keV in a geometrical DNA model composed of nucleosomes of 396 phospho‐diester groups (PDGs) each. A strand break was created inside a PDG when the sum of all energy deposits (method 1) or energy transfers (method 2) was higher than Eth or when at least one interaction deposited (method 3) or transferred (method 4) an energy higher than Eth. SBs were then clustered into SSBs and DSBs using clustering scoring criteria from the literature and compared to our own.

Results:

The total number of SBs decreases as Eth is increased. In addition, thresholding on the energy transfers (methods 2 and 4) produces a higher SB count than when thresholding on energy deposits (methods 1 and 3). Method 2 produces a step‐like function and should be avoided when attempting to optimize Eth. When SBs are grouped into damage patterns, clustering conditions can underestimated SSBs by up to 18 % and DSBs can be overestimated by up to 12 % compared to our own implementation.

Conclusion:

We show that two often underreported simulation parameters have a non‐negligible effect on overall DNA damage yields. First more SBs are counted when using energy transfers to the PDG rather than energy deposits. Also, SBs grouped according to different clustering conditions can influence reported SSB and DSB by as much as 20%. Careful handling of these parameters is required when trying to compare DNA damage yields from different authors.

Research funding from the governments of Canada and Quebec. PP acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering Research Council (Grant number: 432290)
SU‐C‐BRD‐01: A Statistical Modeling Method for Quality Control of Intensity‐ Modulated Radiation Therapy Planning
Authors: Gao S , Meyer R , Shi L , D' Souza W , Zhang H
Published: July 2014

Purpose:

To apply a statistical modeling approach, threshold modeling (TM), for quality control of intensity‐modulated radiation therapy (IMRT) treatment plans.

Methods:

A quantitative measure, which was the weighted sum of violations of dose/dose‐volume constraints, was first developed to represent the quality of each IMRT plan. Threshold modeling approach, which is is an extension of extreme value theory in statistics and is an effect way to model extreme values, was then applied to analyze the quality of the plans summarized by our quantitative measures. Our approach modeled the plans generated by planners as a series of independent and identically distributed random variables and described the behaviors of them if the plan quality was controlled below certain threshold. We tested our approach with five locally advanced head and neck cancer patients retrospectively. Two statistics were incorporated for numerical analysis: probability of quality improvement (PQI) of the plans and expected amount of improvement on the quantitative measure (EQI).

Results:

After clinical planners generated 15 plans for each patient, we applied our approach to obtain the PQI and EQI as if planners would generate additional 15 plans. For two of the patients, the PQI was significantly higher than the other three (0.17 and 0.18 comparing to 0.08, 0.01 and 0.01). The actual percentage of the additional 15 plans that outperformed the best of initial 15 plans was 20% and 27% comparing to 11%, 0% and 0%. EQI for the two potential patients were 34.5 and 32.9 and the rest of three patients were 9.9, 1.4 and 6.6. The actual improvements obtained were 28.3 and 20.5 comparing to 6.2, 0 and 0.

Conclusion:

TM is capable of reliably identifying the potential quality improvement of IMRT plans. It provides clinicians an effective tool to assess the trade‐off between extra planning effort and achievable plan quality.

This work was supported in part by NIH/NCI grant CA130814.
SU‐C‐BRD‐03: Analysis of Accelerator Generated Text Logs for Preemptive Maintenance
Authors: Able CM , Baydush AH , Nguyen C , Gersh J , Ndlovu A , Rebo I , Booth J , Perez M , Sintay B , Munley MT
Published: July 2014

Purpose:

To develop a model to analyze medical accelerator generated parameter and performance data that will provide an early warning of performance degradation and impending component failure.

Methods:

A robust 6 MV VMAT quality assurance treatment delivery was used to test the constancy of accelerator performance. The generated text log files were decoded and analyzed using statistical process control (SPC) methodology. The text file data is a single snapshot of energy specific and overall systems parameters. A total of 36 system parameters were monitored which include RF generation, electron gun control, energy control, beam uniformity control, DC voltage generation, and cooling systems. The parameters were analyzed using Individual and Moving Range (I/MR) charts. The chart limits were calculated using a hybrid technique that included the use of the standard 3σ limits and the parameter/system specification. Synthetic errors/changes were introduced to determine the initial effectiveness of I/MR charts in detecting relevant changes in operating parameters. The magnitude of the synthetic errors/changes was based on: the value of 1 standard deviation from the mean operating parameter of 483 TB systems, a small fraction (≤ 5%) of the operating range, or a fraction of the minor fault deviation.

Results:

There were 34 parameters in which synthetic errors were introduced. There were 2 parameters (radial position steering coil, and positive 24V DC) in which the errors did not exceed the limit of the I/MR chart. The I chart limit was exceeded for all of the remaining parameters (94.2%). The MR chart limit was exceeded in 29 of the 32 parameters (85.3%) in which the I chart limit was exceeded.

Conclusion:

Statistical process control I/MR evaluation of text log file parameters may be effective in providing an early warning of performance degradation or component failure for digital medical accelerator systems.

Research is Supported by Varian Medical Systems, Inc.
SU‐C‐BRD‐06: Results From a 5 Patient in Vivo Rectal Wall Dosimetry Study Using Plastic Scintillation Detectors
Authors: Wootton L , Kudchadker R , Lee A , Beddar S
Published: July 2014

Purpose:

To evaluate the performance characteristics of plastic scintillation detectors (PSDs) in an in vivo environment for external beam radiation, and to establish the usefulness and ease of implementation of a PSD based in vivo dosimetry system for routine clinical use.

Methods:

A five patient IRB approved in vivo dosimetry study was performed. Five patients with prostate cancer were enrolled and PSDs were used to monitor rectal wall dose and verify the delivered dose for approximately two fractions each week over the course of their treatment (approximately fourteen fractions), resulting in a total of 142 in vivo measurements. A set of two PSDs was fabricated for each patient. At each monitored fraction the PSDs were attached to the anterior surface of an endorectal balloon used to immobilize the patient's prostate during treatment. A CT scan was acquired with a CTon‐ rails linear accelerator to localize the detectors and to calculate the dose expected to be delivered to the detectors. Each PSD acquired data in 10 second intervals for the duration of the treatment. The deviation between expected and measured cumulative dose was calculated for each detector for each fraction, and averaged over each patient and the patient population as a whole.

Results:

The average difference between expected dose and measured dose ranged from ‐3.3% to 3.3% for individual patients, with standard deviations between 5.6% and 7.1% for four of the patients. The average difference for the entire population was ‐0.4% with a standard deviation of 2.8%. The detectors were well tolerated by the patients and the system did not interrupt the clinical workflow.

Conclusion:

PSDs perform well as in vivo dosimeters, exhibiting good accuracy and precision. This, combined with the practicability of using such a system, positions the PSD as a strong candidate for clinical in vivo dosimetry in the future.

This work supported in part by the National Cancer Institute through an R01 grant (CA120198‐01A2) and by the American Legion Auxiliary through the American Auxiliary Fellowship in Cancer Research.
Complete Genome Sequences of Two Porcine Circovirus Type 2 Field Isolates Bearing an Unusual Sequence Duplication in the
rep
Gene
Authors: Willems Hermann , Hofmeister Regina , Reiner Gerald
Published: July 2014

Porcine circovirus type 2 (PCV-2) is the etiologic agent of porcine circovirus-associated disease (PCVAD). PCV-2 is classified into three genotypes. Here, we present the complete genomic sequences of two PCV-2 isolates (KM and H026) with an unusual sequence duplication in the
rep
gene coding for viral replicase proteins.
Draft Whole-Genome Sequences of Nine Non-O157 Shiga Toxin-Producing Escherichia coli Strains
Authors: Lindsey Rebecca L. , Trees Eija , Sammons Scott , Loparev Vladimir , Frace Mike , Strockbine Nancy , Sabol Ashley L. , Sowers Evan , Stripling Devon , Martin Haley , Knipe Kristen , Rowe Lori , Gerner-Smidt Peter
Published: July 2014

Shiga toxin-producing
Escherichia coli
(STEC) is an important food-borne pathogen. Here, we report the draft whole-genome sequences of nine STEC strains isolated from clinical cases in the United States. This is the first report of such information for STEC of serotypes O69, H11, O145:H25, O118:H16, O91:H21, O146:H21, O45:H2, O128:H2, and O121:H19.
Complete Genome Sequence of the
Streptococcus
sp. Strain VT 162, Isolated from the Saliva of Pediatric Oncohematology Patients
Authors: Vecherkovskaya Maria F. , Tetz George V. , Tetz Victor V.
Published: July 2014

Streptococcus
sp. strain VT 162 was isolated from the saliva of pediatric oncohematology patients. Its full genome is 2,045,418 bp. The availability of this genome will provide insights into the composition of microbial flora among pediatric oncohematology patients and the host interaction and pathogenicity of this species.