bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐E‐108‐07: A Multi‐Institutional Evaluation of Multileaf Collimator Performance
Authors: Kerns J , Childress N , Kry S
Published: July 2013

Purpose: This study examined MLC positional accuracy via MLC logs from multiple institutions and multiple delivery techniques to evaluate typical positional accuracy and treatment and mechanical parameters that affect accuracy. Typical accuracy achieved was compared against TG‐142 recommendations for MLC performance; more appropriate recommendations are suggested. Methods: Over 85,000 Varian MLC treatment logs were collected from six institutions and analyzed with Fraction CHECK. Data were binned according to institution and treatment type to determine root mean square (RMS) and 95th percentile error values, and then to look for correlations between those errors and with mechanical and treatment parameters. Results: Results of treatment logs from six institutions found that leaf RMS error and 95th percentile leaf error were fairly consistent between institutions, but varied by treatment type. The step and shoot technique had very small errors: the mean RMS leaf error was 0.008 mm. For dynamic treatments the mean RMS leaf error was 0.32 mm, while VMAT showed the largest mean RMS leaf error at 0.46 mm. For the dynamic and VMAT techniques, the mean and maximum leaf speeds were significantly linked to the leaf RMS error. For dynamic delivery, the mean leaf error was correlated with RMS error, whereas for VMAT the average gantry speed was correlated. For all treatments, the RMS error and the 95th percentile leaf error were correlated. Conclusion: Restricting the maximum leaf speed can help improve MLC performance for dynamic and VMAT deliveries. Furthermore, the tolerances of leaf RMS and error counts for all treatment types should be tightened from the TG‐142 values to make them more appropriate for clinical performance. Values of 1 mm for the 95th percentile of leaf RMS error and 1.5 mm for the 95th percentile error are suggested as action levels for all treatment types.
TU‐E‐108‐08: EPID‐Based in Vivo Dosimetry: The Next Step in Patient‐Specific QA
Authors: Mijnheer B , Olaciregui‐Ruiz I , Rozendaal R , Sonke J‐J , Spreeuw H , Tielenburg R , van Herk M , Mans A
Published: July 2013

Purpose: To demonstrate that EPID‐based in vivo dosimetry can play an important role in the total chain of verification procedures in a radiotherapy department. Methods: In our institution a back‐projection algorithm has been implemented for the in vivo dose verification of all treatments, including IMRT and VMAT, using a‐Si EPIDs. For non‐IMRT plans the reconstructed dose is compared for each beam with the planned dose in a plane parallel to the EPID intersecting the isocenter. For IMRT and VMAT the total 3D dose distribution is reconstructed and compared with the planned dose distribution using 3D gamma evaluation. Dose‐reconstruction and gamma‐evaluation software runs automatically in the clinic; i.e. no user intervention is required for the analysis. Deviations outside the alert criteria are investigated by a medical physicist with respect to their clinical relevance. If necessary, additional phantom measurements are performed to separate patient‐related errors from planning or delivery errors. Results: With the current set of alert criteria, 63% of 3,839 patient treatments in 2012 were automatically approved without any human intervention. Most deviations were due to limitations of our back‐projection and dose evaluation software and could easily be recognized. Other sources of error were patient related: anatomical changes or deviations from the routine clinical procedure, and would not have been detected by pre‐treatment verification. Inspection of cone‐beam CT scans yielded information about anatomy changes such as shrinkage of the tumor and weight loss. Furthermore, 3D gamma‐evaluation of in vivo dose distributions obtained during verification of VMAT head‐and‐neck treatments showed a high correlation with DVH parameters. Conclusion: EPID‐based in vivo dosimetry as applied in our institution provides clinically more useful information and is less time consuming than patient‐specific pre‐treatment dose verification. In our opinion, large scale implementation of EPID‐based in vivo dosimetry is therefore the next step in patient‐specific QA.
TU‐E‐108‐09: Development of An Einzel Electron Focusing Lens for Microbeam Radiation Therapy Device
Authors: Zhang J , Lu J , Zhou O , Chang S
Published: July 2013

Purpose: The purpose of this work is to develop a novel Einzel electron focusing lens for carbon nanotube (CNT) field emission based microbeam radiation therapy (MRT). The CNT cathode used for the proposed microbeam radiation source has a unique linear cathode profile so that the focusing structure needs to be optimized in order to achieve the desired focal spot size for efficient generation of microbeam radiation. Methods: The proposed design of the MRT device has a square system configuration with four independent linear x‐ray tube modules. Each tube module includes a linear carbon nanotube field emission cathode array, which is the core component of the MRT device. The CNT cathode is comprised of 5 individually controlled CNT cathode segments, each of which has a dimension of 2.5mm×30mm. A commercial software package (Opera 3D, Cobham plc) was used to simulate and design the optimal focusing structure. A full scale computer model covering the entire electron beam path was constructed for the electron optical simulation. Results: Based on the simulation, the two‐stage electrostatic focusing lens is capable of providing the 102um focal spot size required for the proposed microbeam radiation therapy treatment with 100um beam width. Based on our simulation results, we are able to achieve over 65% electron beam transmission rate. Both results were verified experimentally using a small scale testing x‐ray chamber. Conclusion: We have designed a novel Einzel electron focusing lens to achieve the desired focal spot in order to improve the efficiency of microbeam generation, thus the dose rate. The simulation and experiment show the two‐stage electrostatic focusing lens is capable of providing a 102um effective focal spot size. Meanwhile we have also demonstrated reasonable electron beam transmission rate (>65%), which is critical in terms of achieving high x‐ray output.
TU‐E‐500‐01: Advanced Technologies for Breast RT
Authors: Li X , White J , Moran J
Published: July 2013

Breast conservation therapy (BCT) combining lumpectomy and post‐lumpectomy radiation therapy (RT) is a well established alternative to mastectomy for most patients with early stage breast cancer (ESBC). The fact that most of local recurrences occur in close proximity to the original tumor bed indicates that the whole breast irradiation (WBI) may not be necessary in all cases of ESBC. This led to the development of partial breast irradiation (PBI) which reduces the amount of irradiated normal tissue. Moreover, accelerated PBI can shorten the treatment time from 4–5 weeks for the current standard breast RT for ESBC to 5 days. In the current clinical practice of PBI, large CTV to PTV margins (e.g., 1.5 cm) are being used due to the variations in patient setup, anatomy change between treatment fractions, and respiratory motion during the treatment. These large margins limit the patient eligibility for PBI and lead to more normal tissue irradiated with high dose. Advanced technologies, including IMRT, IGRT, respiration motion management, and adaptive replanning, are being rapidly introduced in to the clinic to reduce these large margins and to enable conformal irradiation of either whole or partial breast. The purpose of this session is to review and update physicists on this exciting and rapidly developing area.

Learning Objectives:

1. Understanding rationale, indications and promise for using advanced RT Technologies for breast cancer

2. Review of recent advances in imaging, planning, and delivery technologies for breast RT

3. Discussing clinical implementation, and experience for using the advanced technologies for breast RT
TU‐E‐141‐02: Coverage‐Based Treatment Planning to Accommodate Deformable Organ Variations in Prostate Cancer Treatment
Authors: Xu H , Vile D , Sharma M , Gordon J , Siebers J
Published: July 2013

Purpose: To (1) investigate the dosimetric impact of interfraction deformable organ motion for high‐risk prostate cancer treatments and (2) compare two coverage‐based planning (CP) techniques with the fixed margin‐based planning (FM).Methods: 19 patients with 8–13 prostate CT images were used to model interfraction deformable organ changes using principal component analysis (PCA). Displacement vector fields (DVFs) that map from each of the 8–13 images to the reference image were analyzed with PCA to determine the dominant eigenmodes, which were then used to predict the synthetic patient geometries for virtual treatment course simulation. For each patient, an intensity modulated radiation therapy (IMRT) plan with zero PTV margin on target structures (CTVprostate and CTVseminalVesicles) was created, then evaluated by simulating 1000 30‐fraction virtual treatment courses. Each fraction was prostate centroid aligned. Probabilistic metrics, including 5% and 95% percentile DVHs (pDVH) and TCP/NTCP distributions, were computed. Patients whose D98 failed to achieve 95% coverage probability objective D98,95>=78Gy (CTVprostate) or D98,95>=66Gy (CTVseminalVesicles) were replanned using (1) FM (PTVprostate = CTVprostate + 5mm, PTVseminalVesicles = CTVseminalVesicles + 8mm), (2) CPOM which optimized uniform margins for CTVprostate and CTVseminalVesicles to meet the CP objective, and (3) CPCOP which directly optimized coverage‐based objectives for all structures of interest. Results: For zero‐PTV‐margin plans, 0/19 patients satisfied objective D98,95 for both CTVprostate and CTVseminalVesicles. The selected margins used in FM failed to ensure target coverage for 8/19 patients. 11 CPOM plans and 8 CPCOP plans were favored over the other plans by achieving desirable D98,95 while sparing more normal tissues. Conclusion: The dosimetric impact of deformable organ motions for prostate centroid alignment treatment is not insignificant. Coverage‐based treatment planning techniques can produce better plans than FM, while relative advantages of CPOM and CPCOP are patient specific. Supported by NIH P01‐CA‐116602 and Philips Medical Systems. Supported by NIH P01‐CA‐116602 and Philips Medical Systems; NIH P01‐CA‐116602 and Philips Medical Systems
TU‐E‐141‐05: Dosimetric and Anatomical Evaluation of Normal Tissue Changes During IMRT Radiotherapy for Head and Neck Cancer
Authors: Hunt M , Tyagi N , Tam M , Zhang P , Hu Y , Rao S , Lee N
Published: July 2013

Purpose: To measure changes to parotid, submandibular glands and oral cavity using weekly CBCT and to determine factors predictive of weekly volume and mean dose changes. Methods: Weekly CBCT images were reviewed for seven patients undergoing standard IMRT. Parotid, submandibular glands (SMG) and oral cavity were segmented both manually and through free‐form deformable registration of the CBCT to the planning CT. Structure volume, center‐of‐mass (COM) and manual/deformed similarity on each CBCT was recorded. All structures were then mapped back to the planning CT and weekly delivered mean doses were calculated. Temporal changes in volume, COM and dose were correlated to pre‐and on‐treatment anatomic and dosimetric parameters. Results: On average, 6.5 scans per patient were available for review. Mean decrease in parotid, submandibular gland and oral cavity volume by the end of treatment was 18.9% (σ=10.0), 21.9% (σ=13.1) and 3.1% (σ=7.8), respectively. Volume changes translated into an average 2.9 Gy (σ=2.8) increase in parotid gland mean dose. No significant change in mean dose to SMG or oral cavity was observed. Deformable registration commonly failed in areas of dental fillings requiring subsequent manual editing of parotid and oral cavity volumes. Average Dice Similarity Coefficients of 0.841 (σ=0.051), 0.752 (σ=0.089) and 0.892 (σ=0.037) for the parotids, submandibular glands and oral cavity were obtained. On multivariate analysis, factors correlated with volume and dose change during treatment included the planned dose‐to‐date, patient weight and changes in structure COMs. Conclusion: Dosimetric consequences of on‐treatment volume changes of normal tissues during head and neck IMRT treatment were limited to an increase in mean dose to the parotid glands. Planned dose‐to‐date, patient weight, and center‐of‐mass changes were all predictive of volume changes during treatment. Improvements in CBCT image quality are essential before these images can be used for treatment decisions or adaptive therapy.
TU‐E‐141‐09: Impact of Attenuation Correction Mode On 4D PET/CT for Target Definition in Lung Cancer Patients
Authors: Bowen SR , Nyflot MJ , Zeng J , Sandison GA , Patel SA , Kinahan PE
Published: July 2013

Purpose: The impact of attenuation correction on respiratory‐gated (4D) PET/CT images to define lung cancer targets, relative to 4D maximum intensity projection (MIP) or 3D static images, is poorly understood. Changes from 3DPET to 4DPET SUV metrics and target volumes were characterized in patients as a function of PET acquisition and CT attenuation correction (CTAC). Methods: Lung cancer patients underwent PET/CT list‐mode examinations spanning 3 bed positions. Static and respiratory phase‐gated sinograms were unlisted to generate 3DPET and 4DPET images. Emission data were attenuation‐corrected with phase‐averaged (4DAVG) or phase‐matched (4DMATCH) 4DCT and reconstructed with OSEM (2 iterations, 28 subsets, 5 mm post‐filter) on 2.0×2.0×3.3 mm3 voxel grids. PET target volumes were defined in MIM™5.6.3 using a gradient search method. Differences in SUVmax, SUVmean, SUVpeak, and defined volumes were compared between 3D, 4D MIP, and individual 4D phases by pairwise sign‐rank tests. 4DAVG and 4DMATCH CTAC‐PET image metrics were compared between respiratory phases using multi‐group non‐parametric ANOVA. Results: For 13 FDG‐PET avid lesions, SUVmax, SUVmean and SUVpeak were significantly higher in 4DMIP and 4D phase‐gated images relative to 3D images (9–11%, p<0.03). 4DMIP volumes were larger than 3D and 4D phase volumes (6–14%, p<0.01). 4DMATCH SUVmax was higher than 4DAVG SUVmax near end‐expiration phase and lower around peak‐inspiration phase (p=0.001). 4DMATCH SUVmean exceeded 4DAVG SUVmean at end‐expiration (p=0.02), while SUVpeak trended similarly but was insufficiently powered (p=0.06). 4D phase volumes were not significantly different between attenuation correction methods (p>0.37). Conclusion: 4DPET provides improved image quantification over 3DPET. 4DPET quantification near end‐expiration appears superior with phase‐matched CTAC, but may be less reliable during phase‐gates with residual motion and phase‐sorting CT artifacts. Optimization of CTAC from patient‐specific respiratory patterns may improve robustness of 4D PET/CT for lung cancer target definition and dose painting.
TU‐E‐103‐01: Image Quality Models in Advanced CT Applications
Authors: Siewerdsen J , Nishikawa R , Cunningham I , Chen G , Bochud F
Published: July 2013

The last decade saw the development of new x‐ray tomographic imaging technologies, such as flat‐panel detector cone‐beam CT and tomosynthesis, now prevalent in applications ranging from diagnostic imaging to image‐guided interventions. Such technologies proceeded in stride with models of imaging performance developed to provide a rigorous understanding of the factors governing image quality and help accelerate system design and translation. The decade ahead promises important advances ‐ for example: statistical and iterative model‐based image reconstruction; dual‐energy and spectral tomography; photon counting detectors; phase contrast tomography; and understanding the performance of model and real observers in the context of volumetric data. The theoretical models of imaging performance now developing alongside such advanced technologies are the topic of this symposium. Dr. Nishikawa will introduce the broad and challenging landscape of such technologies and applications. Dr. Siewerdsen will discuss image quality models for dual‐energy CT and the extension from conventional filtered backprojection to statistical / iterative reconstruction methods. Dr. Cunningham will describe the development of cascaded systems analysis for new photon counting detector systems. Dr. Chen will demonstrate how image quality models and performance measurement in x‐ray (absorption) CT can be extended to differential phase‐contrast CT. Finally, Dr. Bochud will address the performance of observers in volumetric data, highlighting newly appreciated factors that are distinct from conventional models and understanding in the context of 2D (or single slice) image interpretation.

Learning Objectivess:

1. Understand the growing landscape of advanced tomographic imaging technologies and applications.

2. Understand how image quality models developed over the last decade for CT, cone‐beam CT, and tomosynthesis can be extended to:

a.) dual‐energy / spectral CT

b.) statistical and iterative image reconstruction

c.) photon counting detectors

d.) differential phase contrast CT

3. Understand the distinctions and new considerations in observer performance and image quality assessment in volumetric data..

National Institutes of Health. Carestream Health. Siemens Healthcare.
TU‐E‐144‐01: Advanced Novel Technologies & Therapeutic Strategies
Authors: Ferrara K , Griffin R , Guha C , Holland C , Lafon C
Published: July 2013

A variety of novel techniques and treatment strategies have been developed and tested through preclinical trials for the clinical application of therapeutic ultrasound in recent years. This session features five invited presentations on the following topics: (1) ultrasound mediated drug delivery — the use of long circulation liposomes with ultrasound used to alter apparent vascular permeability and the use of temperature sensitive liposomes with ultrasound applied to release the drug, (2) high‐frequency ultrasound mapping of tumor vascular hypoxia as a targeting modality for focused ultrasound ablation to complement ionizing radiotherapy, (3) therapeutic ultrasound as an autologous in situ tumor vaccine — tumor‐specific cytotoxic immune response generated in mice receiving combined low energy focused ultrasound and high‐intensity focused ultrasound treatments, (4) sonothrombolysis and ultrasound‐mediated drug delivery for the treatment of cardiovascular disease, and (5) implantable ultrasound device for repeated opening of the blood brain barrier — a promising technology for drug delivery into the brain.

Learning Objectives:

1. To review the recent advances in therapeutic ultrasound techniques and their potential for clinical applications;

2. To understand the physical characteristics and biological effects of these novel therapeutic technologies;

3. To identify opportunities for medical physicists in development and assessment of practical treatment strategies utilizing these technologies
TU‐E‐144‐02: Dependence of Ultrasound Echo Decorrelation On Tissue Temperature During Radiofrequency Ablation of Ex Vivo Bovine Liver
Authors: Subramanian S , Schmidt DT , Fosnight TR , Rao MB , Mast TD
Published: July 2013

Purpose: Echo decorrelation imaging is a ultrasound imaging method that has been shown effective for mapping of thermal ablation effects on liver and tumor tissue, both ex vivo and in vivo. Quantification of tissue temperature during thermal ablation treatments would benefit treatment guidance and control. Here, the effect of tissue temperature on the mapped echo decorrelation parameter is assessed for ex vivo radiofrequency ablation (RFA). Methods: RFA treatments were performed on freshly acquired ex vivo bovine liver using a needle antenna with 500 kHz excitation for treatment voltages 30–40 V rms and durations 10–15 min. Throughout each treatment, beamformed ultrasound echo signals were recorded by a 7 MHz linear array and temperature was recorded by two thermocouples within the ultrasound image plane. Temperature maps were simulated by a finite element method, with tissue parameters determined using an unscented Kalman filter to best match measured ablation results. Echo decorrelation images were constructed from recorded echo data and correlated spatially with corresponding simulated temperature maps. Prediction of tissue temperatures over 60 °C, corresponding to local thermal ablation, was tested using receiver operating characteristic (ROC) curve analysis. Results: Strong correspondence was observed between time‐dependent echo decorrelation maps and corresponding temperature maps. Temperatures above 60 °C consistently corresponded to locally elevated echo decorrelation. Correlation coefficients between local temperature and echo decorrelation were weak but statistically significant. ROC curve analysis showed successful prediction of ablative tissue temperatures. Conclusion: Observed correspondence between local tissue temperature and echo decorrelation indicates that elevated tissue temperatures consistently cause elevated echo decorrelation. Although weak overall correlation between local echo decorrelation and tissue temperature suggests that temperature is not accurately predicted by echo decorrelation, ROC curve analysis indicates successful prediction of tissue ablation, suggesting the utility of echo decorrelation imaging as a tool for real‐time guidance and control of thermal ablation. This research was supported by NIH grants R01 CA158439 and R21 EB008483.
TU‐F‐137‐01: Writing and Reviewing Papers for Medical Physics
Authors: Hendee W , Slattery P , Karellas A , Rogers D
Published: July 2013

Writing and Reviewing Papers for Medical Physics There is an art to writing a scientific paper so that it communicates accurately, succinctly, and comprehensively. Developing this art comes with experience, and sharing that experience with younger physicists is an obligation of senior scientists, especially those with editorial responsibilities for the journal. In this workshop, the preparation of a scientific manuscript will be dissected so participants can appreciate how each part is developed and then assembled into a complete paper. Then the review process for the paper will be discussed, including how to examine a paper and write an insightful and constructive review. Finally, we will consider the challenge of accommodating the concerns and recommendations of a reviewer in preparing a revision of the paper. A second feature of the workshop will be a discussion of the process of electronic submission of a paper for consideration by Medical Physics. The web‐based PeerX‐Press engine for manuscript submission and management will be examined, with attention to special features such as epaps and line‐referencing. Finally, new features of Medical Physics will be explained, such as Vision 20/20 manuscripts, Physics Letters and the standardized formatting of book reviews.

Learning Objectives:

1. Improve the participants' abilities to write a scientific manuscript.

2. Understand the review process for Medical Physics manuscripts and how to participate in and benefit from it.

3. Appreciate the many features of the PeerX‐Press electronic management process for Medical Physics manuscripts.

4. Develop a knowledge of new features of Medical Physics.
TU‐G‐137‐01: New Member Symposium
Authors: Sherouse G , Clements J
Published: July 2013

As a new member of the AAPM, it's easy to feel overwhelmed by the size and complexity of the association and to be unaware of the benefits and opportunities available to members. At this year's AAPM national meeting in Indianapolis, we will host a New Member Symposium where you can learn more about the organization, member resources, opportunities to get involved, and about topics of particular interest to new professionals. We encourage you to take advantage of this great opportunity to learn valuable information and to grow your professional network. Following an introduction from Dr. John Hazle, the AAPM President; Jessica Clements, chair of the Professional Services Committee, will speak on, “How and Why You Should Volunteer With a Professional Organization.” Next will be Dr. George Sherouse sharing invaluable information in his talk, “Things You Won' t Be Able to Say Somebody Should' ve Told You.” The session will be followed by a social for all the new members, and also invited are chairs from all the AAPM committees. Registered attendees will receive a raffle ticket for entry in a drawing to win a complimentary registration for the 2014 Annual Meeting in Austin, Texas. In addition, all new members who register for the Symposium will receive a drink ticket good for one complimentary beer served at the social after the New Member Symposium.
TU‐G‐108‐03: Small Lung Size Increases the Risk of Radiation Pneumonitis in Lung Cancer Patients
Authors: Briere TM , Tucker SL , Liao Z , Martel MK
Published: July 2013

Purpose: There may be certain populations of lung cancer patients who are especially sensitive to radiation pneumonitis. We have examined the relationship of lung size with the risk of pneumonitis. Methods: A total of 509 non‐small cell carcinoma patients were included in this study. Patients received normally fractionated radiation (180 ‐ 225 cGy per fraction) with a minimum total dose of 50 Gy. Patients were planned with either 3D conformal (296 pts) or intensity modulated radiation therapy (IMRT, 213 pts). Radiation pneumonitis was graded by the treating physician according to the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE) 3.0. Univariate analysis was performed considering mean lung dose, percentage DVH, lung size, and spared lung. The Lyman‐Kutcher‐Burman (LKB) method was used to fit the normal tissue complication probability (NTCP) curve to the data with respect to effective dose. Results: Overall 20% of patients developed Grade 3 or higher pneumonitis, including 24% of the 3D patients and 15% of the IMRT patients. Univariate analysis showed lung size, mean lung dose, percentage treated and spared lung volumes to be significant. An LKB fit to the effective dose showed that it is important to take the volume parameter into account. The risk of pneumonitis predicted by NTCP analysis is underestimated for patients with small total lung sizes (< 2550 cc), where 40% of patients developed Grade 3 or higher pneumonitis. Conclusion: Patients with small lung sizes may be especially vulnerable to radiation pneumonitis. This new finding could be used during treatment planning to reduce the risk of pneumonitis in patients with small lungs.
TU‐G‐108‐04: Lack of Differentiation in Performance of Predictive Radiation Pneumonitis Models
Authors: Krafft S , Court L , Briere T , Martel M
Published: July 2013

Purpose: Numerous normal tissue complication probability (NTCP) models for radiation pneumonitis (RP) have been published in the literature, but minimal consideration is given to their predictive performance. Using several published model parameters, we quantified the range of model performance metrics to differentiate between and assess clinical utility of predictive RP models. Methods: Clinical, demographic, and dosimetric data was collected for 453 NSCLC patients treated with definitive photon radiotherapy. A series of logistic NTCP models were developed to assess overall performance. A baseline mean lung dose (MLD) model was considered in addition to our institutions best model, which incorporates MLD and smoking status. The model parameters from several publications were identified and incorporated in the analysis. The considered endpoint was CTCAEv3.0 grade>=3. Metrics of model performance including area under the curve (AUC) and Spearmans rank correlation (rs) were calculated for each of the models to facilitate comparison. Results: The MLD plus smoking status model performed best in terms of observed AUC (0.685) and rs (0.337); however, model performance was similar to that achieved by all of the other tested models (AUC range=[0.663‐0.685] and rs range=[0.263‐0.337]). In all considered models, predictive performance was poor (i.e. AUC<0.7 and rs<0.4). Additionally, the narrow range of AUC/rs values indicates that there is marginal difference in the performance of any one model over another. Conclusion: The range of quantitative performance metrics indicates that there is minimal ability to differentiate between the selected models. The achieved values for AUC and rs indicate poor overall model accuracy, which limits the practical utility of NTCP models for RP prediction. Furthermore, model parameters from the literature cannot by applied to our dataset to improve RP prediction. Other model formulations and still unidentified patient factors should be considered to develop more applicable and clinically useful NTCP models for treatment personalization.
TU‐G‐108‐07: Development and QA of a Novel Framework to Quantify Normal Tissue Toxicity Using the Jacobian Map
Authors: Niedzielski J , Yang J , Zhang L , Martel M , Briere T , Gomez D , Court L
Published: July 2013

Purpose: To develop and validate a novel computational method that quantifies the dose‐response of tissues on a voxel‐to‐voxel level. Methods: An algorithm was created to calculate the Jacobian Map (JM) from the deformation computed between a planning CT image and treatment image. This Jacobian Map represents local volume change at the voxel level. The relationship between the JM and the local radiation dose can be used to investigate the dose‐response of tissues on a voxel level. To validate the algorithm, a mathematical phantom simulating swelling of known quantities was used. The algorithm was then used to investigate esophageal swelling associated with grade 3 esophagitis for five non‐small cell lung cancer patients previously treated with external beam radiotherapy. The JM was calculated for CT images of the first and final week of treatment, deformed from the planning CT image. The JM for the first week is a control to assess patient specific uncertainties in this framework. The mean JM of the final week and dose to the esophagus for each axial slice were analyzed for each patient. Results: The phantom test showed the accuracy and precision of the algorithm to calculate the JM. The five patients analyzed showed a similar behavior as the phantom: an increasing JM corresponds to increasing dose. Week 1 mean JM values were 0.95–1.1 with standard deviations of 0.08–0.12, indicating no quantifiable swelling. Final week JM values showed a quadratic trend with dose with a mean correlation coefficient of 0.78 (range 0.70–0.85). The amount of expansion was patient dependent (range 40%–200%) and greatest at maximal doses. Conclusion: The computational framework developed in this study shows viability to quantify esophageal expansion throughout the course of radiotherapy as an objective test for normal tissue toxicity. This method may be applied to other organs as well as tumor response.
TU‐G‐108‐09: Can NTCP Models Derived From 3D‐CRT Data Be Used to Predict Gastrointestinal Toxicities for IMRT Prostate Cancer Patients?
Authors: Troeller A , Soehn M , Yan D
Published: July 2013

Purpose: It is unclear whether NTCP models derived from one treatment modality are applicable to patients receiving a different treatment technique. In this large prostate cancer patient cohort study, we compare the model parameters of patients treated with 3D‐CRT vs. IMRT, for EUD‐based and a dose‐volume‐based NTCP model. Methods: Rectal‐wall DVHs of 1116 patients treated for prostate cancer under an adaptive radiotherapy protocol were used to model gastrointestinal (GI) toxicity grade>=2, as defined by CTCAE v.3. Of the total cohort, 458 patients were treated with 3D‐CRT, the remaining 658 with IMRT. Three NTCP models were investigated: the Lyman‐gEUD model, the Lyman‐EUDlog model, and a dose‐volume‐based cutoff‐dose logistic regression model. All parameter estimates and their standard‐errors were determined using maximum‐likelihood‐estimation. Models were fit to the whole group, as well as to the 3D‐CRT and IMRT sub‐groups separately. Results: 128 (27.9%) of the patients who received 3D‐CRT, and 48 (7.3%) of IMRT patients experienced GI toxicities grade>=2. Median follow‐up was 5.8 years (2.0–12.5 years). For all models, parameter estimates derived from conformal data were in agreement with values found in the literature, but did not predict IMRT data well (p>0.05). Models developed for the whole population overestimate the NTCP for IMRT patients and underestimate the NTCP for 3D‐CRT patients. The Lyman‐EUDlog model converged to the Lyman‐gEUD model for all three patient groups. Conclusion: Our study suggests that using the NTCP models investigated here, it is not possible to predict toxicities for IMRT and 3D‐CRT patients with the same model. This holds for both the EUD‐based as well as the dose‐volume‐based models. The reason for these findings have yet to be investigated. Since IMRT is increasingly utilized clinically, it is of high importance that appropriate NTCP model parameters are determined for this treatment modality, especially when using NTCP models in practice.
TU‐G‐500‐01: The Science of Clinical Medical Physics D Jaffray1*, E Roelofs2*, T
Authors: Purdie  , Bortfeld T
Published: July 2013

Medical physicists have a unique role in the clinical setting. In many medical centers, they are often the only individuals with formal research training. The rapid advance in technological innovation within the radiation oncology community has resulted in medical physicists being immersed in the role of technology manager with activities dominated by implementation. When combined with the rising challenges with respect to access to peer‐reviewed funding and changes in the pathway to professional certification, this situation has created open debate in the medical physics community regarding the role of medical physicists as a scientist. In parallel, the emerging trends of personalized cancer medicine, medical informatics, automation, and the drive to establish evidence to support innovative treatments are all highlighting the need for greater scientific engagement in the advancement of medicine. Medical physicists could be positioned to play a key role in the progression of these trends, however, this requires us to take a broader perspective on our talents and unique environment within medicine. In this session, these concepts and issues will be expanded upon and speakers will highlight examples of medical physics research that push the conventional domain. A lively discussion should emerge that will facilitate the further engagement of medical physicists in clinical science.

Learning Objectives:

1. Understand the challenges related to medical physicists contributing to the science of medicine

2. Learn of new frontiers where clinical medical physicists are making important contributions

3. Learn of the emerging opportunities for clinical science for medical physicists

4. Become aware of the efforts within the medical physics community to facilitate greater engagement
TU‐G‐141‐06: Deformation Vector Fields (DVF)‐Driven Image Reconstruction for 4D‐CBCT
Authors: Dang J , Ouyang L , Gu X , Wang J
Published: July 2013

Purpose: High‐quality four dimensional cone‐beam CT (4D‐CBCT) can be obtained by deforming the planning CT in radiotherapy, where the deformation vector fields (DVF) is estimated by matching the forward projection of the deformed planning CT and measured 4D‐CBCT projections. Due to the presence of scatter signal in CBCT projection images, the accuracy of DVF estimation is degraded when the sum of squared intensity difference (SSID) is used as the matching criterion. The goal of this work is to improve the estimation accuracy of DVF by using normalized correlation coefficient (NCC) as the matching criterion to obtain high quality on‐treatment 4D‐CBCT of lung cancer patients in radiation therapy. Methods: The DVF used to deform the planning CT is estimated by maximizing the NCC between the projections of on‐treatment 4D‐CBCT and the forward projection of the deformed planning CT. A non‐linear conjugate gradient (NLCG) algorithm was used for the optimization. To obtain better initial DVF for NLCG optimization, demons registration was first performed between planning CT and 4D‐CBCT reconstructed by total variation (TV) minimization. A 4D NCAT phantom was used to quantitatively evaluate the performance of the algorithm, where the reconstruction error is calculated as the sum of squared difference between the reconstructed 4D‐CBCT and the phantom image. Results: NCC based DVF estimation improves the image reconstruction accuracy as compared to the results obtained using SSID criterion. The image reconstruction error of 4D‐CBCT obtained by NCC criterion is 61.5% smaller than that is obtained by SSID criterion. Conclusion: The accuracy DVF estimation and image reconstruction is substantially improved by using the NCC criterion, as compared to the results obtained by SSID criterion. High quality 4D‐CBCT can be a valuable tool in image‐guided radiation therapy for lung cancer patients. Cancer Prevention and Research Institute of Texas (RP110562)
TU‐G‐103‐02: Clinical Evaluation of VirtualDose — a Software for Tracking and Reporting CTDI, DLP, Organ and Effective Dose for Adult and Pediatric Patient
Authors: Ding A , Gao Y , Caracappa P , Long D , Bolch W , Liu B , Kalra M , Xu X
Published: July 2013

Purpose: To update the development and clinical testing of a new Software as a Service (SaaS) ‐ VirtualDose for tracking and reporting CT doses. Methods: Incorporating SaaS technology and the comprehensive original dose data derived from Monte Carlo simulations on a family of adult and pediatric computational phantoms, covering 50th‐percentile adults and children at different ages, pregnant females at three gestational stages, and a set of overweight and obese phantoms, VirtualDose is being designed as a Web based CT dose reporting platform. For the client‐and server‐side scripting, JavaScript, Hypertext Markup Language, Cascading Style Sheets, and C# were used. A JSON (JavaScript Object Notation) is used as a request‐response interaction pattern to connect both the client‐and server‐side. Organ doses and effective doses are computed using ICRP Publication 60 and 103. Patient‐specific dosimetry capabilities are included by integrating a DICOM reader function module which could automatically extract dose, patient, and CT scanner (e.g., CTDI, DLP, kVp, mAs, weight, age, gender, etc.) information. Results: VirtualDose has been developed as a CT dose reporting SaaS by offering a web‐based dynamic user‐friendly interface. Based on the user‐specified scanning parameters, VirtualDose rapidly report the organ dose data from the remote server‐side database and interactively tabulate and plot the results of interest within a web browser. Clinical testing found the dose up to 24% different as compared to those derived from the stylized MIRD‐type phantoms. The morbidly obese phantom received up to 60% smaller CT dose than that of the normal weight phantomConclusion: VirtualDose is now available in the following website: http://www.virtualphantoms.com and being tested at more than 20 medical centers nationwide. Using a large library of adult and pediatric phantoms, it provides more accurate dose data and is expected to improve both the accuracy and usability in CT dose reporting in the future.
TU‐G‐103‐03: Validation of a Novel CT Breast Dosimetry Method in Post Mortem, Unembalmed Female Subjects
Authors: Sandoval D , Hatch G , Gerrard C , Heintz P
Published: July 2013

Purpose: Validate breast dose from CT in post mortem subjects, as measured by implanted dosimeters, for later comparison to currently accepted calculation methods. Methods: The study population consisted of 22 female decedents, referred to the New Mexico Office of the Medical Investigator and scheduled for autopsy. Exclusion criteria were: postmortem interval greater than 24hours, significant trauma to the thorax, large pleural or vascular gas collections and significant external or internal decomposition. Under CT guidance, using a Philips large bore 16 slice CT scanner, a microMOSFET detector was implanted in the glandular tissue of the decedent's left breast using plastic flexi‐needles under CT guidance. The implanted dosimeter was placed in the subaereolar breast, at a depth midway between nipple and the posterior margin of glandular tissue. An additional MOSFET and Unfors PSD detector (for cross comparison) were placed on the skin surface, over the nipple of the contralateral breast. Each decedent was scanned using our standard clinical chest and clinical CTA protocol.Breast dose calculations were performed using ImpactCT dose calculator and PCXMCrotation software packages for comparison to measured data. Results: Results demonstrate good agreement between the implanted microMOSFET detector, PSD, and the surface microMOSFET detector. Additionally, there is poor agreement between measured doses and the Impact CT calculations, which are limited by the assumption of a single standard patient size. Calculations using PCXMCrotation, which allows for some patient size specifications, are in progress. Conclusion: The agreement between the implanted surface dosimeters suggests that 1) an accurate surface measurement may be sufficient to determine the breast dose, and 2) as employed, the method of measuring dose using an implanted microMOSFET is accurate. The postmortem microMOSFET model presented here may, in future, produce more meaningful dose estimates and patient specific dose models and be used for measuring dose in other radiosensitive organs.
TU‐G‐103‐05: Affordable Supercomputer‐Based Monte Carlo CT Dose Calculations: A Hardware Comparison Between Nvidia M2090 GPU and Intel Xeon Phi 5110p Coprocessor
Authors: Liu T , Du X , Xu X
Published: July 2013

Purpose: To develop a fast Monte Carlo code ARCHER (a testbed for Accelerated Radiation‐transport Computation in Heterogeneous EnviRonments) to calculate CT imaging organ doses on heterogeneous computing systems. Methods: ARCHER simulates the transport of low‐energy (1∼140keV) photons in heterogeneous media using two selectable interaction models, simple and detailed. It includes an extensive library of voxelized human phantoms such as RPI‐Pregnant women with 3, 6, 9 month gestation, extended RPI‐Adult male and female phantoms representing patients of different obesity level. It contains a validated scanner model based on a GE LightSpeed third‐generation 16‐multi‐detector CT. A series of scan protocols are predefined, including a combination of scan mode (helical or axial), beam collimation (5, 10, or 20 mm) and kVp (80, 100, 120 or 140). ARCHER is targeted for three platforms, CPU (an Intel Xeon X5650 6‐core processor), GPU (Nvidia M2090 GPU), and coprocessor (Intel Xeon Phi 5110p coprocessor), and correspondingly has three code variants developed in MPI‐OpenMP, CUDA and offload OpenMP respectively. Results: Absorbed doses to 28 organs/tissues of dosimetric interest were calculated. MCNPX was used as the accuracy benchmark. The average difference of the organ doses calculated by MCNPX and ARCHER were found to be less than 5% and 0.5% for simple and detailed interaction models respectively, indicating an excellent agreement. While ARCHER's three variants were 63∼1207x faster than MCNPX, the GPU and coprocessor codes were 1.6∼3.4x faster than the CPU (6 core) code. Conclusion: The accelerator‐based new Monte Carlo code ARCHER is developed for accurate and fast CT imaging organ dose calculations. Its full capability to simulate patients of different genders and body sizes receiving different scan protocols exhibits high clinical value.
TU‐G‐103‐07: Quantifying the Dose Distribution of OBI CBCT Using Monte Carlo Simulations with a Measurement‐Based Source Model
Authors: McMillan K , DeMarco J , Tenn S , Chow P , McNitt‐Gray M , Ruan D
Published: July 2013

Purpose: To test the feasibility of using a measurement‐based source model in Monte Carlo simulations to calculate in‐phantom 3D dose distributions, with the application to kV‐CBCT dose quantification on a Varian OBI platform. Methods: A 3‐part nested CTDI phantom was used in this investigation. It contains 7 tracks in the x‐y plane that can be probed. The central reference point of the phantom was aligned at machine isocenter, and using standard head and pelvis CBCT protocols, point dose measurements were made at various 3D locations with a 0.6cc thimble ionization chamber by moving the phantom along the z‐direction and changing the ionization chamber position among the tracks under repetitive scans. We have generated a measurement‐based source model for the OBI system and incorporated it with the Monte Carlo software MCNPX to model each CBCT protocol under examination. The in‐phantom CBCT dose (mGy per particle) was simulated at all 3D measurement locations and converted to absolute dose (mGy) by normalizing with the ratio between measured and Monte Carlo simulated dose at the reference center. The calculated results were compared with the physical measurement and their discrepancies were assessed quantitatively. Results: Agreement was observed between Monte Carlo simulation results and in‐phantom measurements for both the OBI CBCT head and pelvis protocols. For the head protocol, the average agreement was 3.40% with a maximum and minimum disagreement of 5.72% and 1.61%, respectively. For the pelvis protocol, the average agreement was 3.18% with a maximum and minimum disagreement of 4.29% and 1.87%, respectively. Conclusion: We have demonstrated the accuracy of a measurement‐based OBI source model to reproduce an array of measured point doses in phantom when using the CBCT mode of operation. These results serve as the basis for using this source model to investigate OBI dosimetry with anthropomorphic phantoms and patient specific models. (a) Dr. McNitt‐Gray: Institutional research agreement, Siemens AG;Recipient research support Siemens AG; Consultant, Flaherty Sensabaugh Bonasso PLLC; Consultant, Fulbright and Jaworski, LLC; (b) Dr. Dan Ruan: Recipient research support AACR; Recipient research support TRDRP; (c) K McMillan: Research partially supported by a grant from Siemens AG; Research partially supported by a grant from AACR; Research partially supported by a grant from TRDRP