bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐D‐18A‐04: Quantifying the Ability of Tumor Tracking to Spare Normal Tissue
Authors: Burger A , Buzurovic I , Hurwitz M , Mishra P , Williams C , Seco J , Lewis J
Published: July 2014

Purpose:

Tumor tracking allows for smaller tissue volumes to be treated, potentially reducing normal tissue damage. However, tumor tracking is a more complex treatment and has little benefit in some scenarios. Here we quantify the benefit of tumor tracking for a range of patients by estimating the dose of radiation to organs at risk and the normal tissue complication probability (NTCP) for both standard and tracking treatment plans. This comparison is performed using both patient 4DCT data and extended Cardiac‐Torso (XCAT) digital phantoms.

Methods:

We use 4DCT data for 10 patients. Additionally, we generate digital phantoms with motion derived from measured patient long tumor trajectories to compare standard and tracking treatment plans. The standard treatment is based on the average intensity projection (AIP) of 4DCT images taken over a breath cycle. The tracking treatment is based on doses calculated on images representing the anatomy at each time point. It is assumed that there are no errors in tracking the target. The NTCP values are calculated based on RTOG guidelines.

Results:

The mean reduction in the mean dose delivered was 5.5% to the lungs (from 7.3 Gy to 6.9 Gy) and 4.0% to the heart (from 12.5 Gy to 12.0 Gy). The mean reduction in the max dose delivered was 13% to the spinal cord (from 27.6 Gy to 24.0 Gy), 2.5% to the carina (from 31.7 Gy to 30.9 Gy), and 15% to the esophagus (from 69.6 Gy to 58.9 Gy). The mean reduction in the probability of 2nd degree radiation pneumonitis (RP) was 8.7% (3.1% to 2.8%) and the mean reduction in the effective volume was 6.8% (10.8% to 10.2%).

Conclusions:

Tumor tracking has the potential to reduce irradiation of organs at risk, and consequentially reduce the normal tissue complication probability. The benefits vary based on the clinical scenario.

This study is supported by Varian Medical Systems, Inc.
SU‐D‐18A‐05: Assessing Elekta MLC Tracking Performance
Authors: Glitzner M , Crijns S , Lagendijk J , Raaymakers B
Published: July 2014

Purpose:

To investigate the technical feasibility of using Elekta MLCs in tracked radiotherapy, specifically to show the capability of an Agility MLC to follow model tumor trajectories using object tracking. The system performance of the MLC is to be assessed via dosimetric experiments and temporal response measures.

Methods:

The system observer in the tracking cascade consisted of a camera serving for this proof of concept; Images of a moving object were acquired continuously and decorrelated for the position information, which was fed forward to the RT computer controlling the MLC via an interface provided by Elekta. The 1D motion (in the direction of the leaves) was induced by a CIRS motion controller. Additionally, the aperture position was observed by means of the light field of the linac. Calculating the phase between aperture and object yielded the mean aperture lag for the current setup. The object was restricted to sinusoidal motion with a period of 10s. For dosimetry, GafChromic radiosensitive film was irradiated with a total dose of 1000MU using an aperture size of 40mm and a motion range of 30mm.

Results:

Object tracking can substantially reconstruct the geometric dose response of a static target. In the dynamic case, dose is smeared out into the legs of the static distribution, leading to a reduced plateau and increased FWHM of 5mm, compared to the static width of 38mm. The time‐lag between object and aperture was determined to be approximately 300ms for the current set‐up.

Conclusion:

We demonstrated a tracking experiment performed on a clinical Elekta linear accelator for the first time. Observed profile variations show the dosimetric impact of tracked delivery. The determined lag is a valuable descriptor for a future tracking cascade employing predictor filters. The performed experiments are generic and possible predecessors for future applications with MR‐Linac or ultrasound probes.

Conflict of interest: this project is partly funded by Elekta.
SU‐D‐18A‐07: Towards 6‐Degree‐Of‐Freedom Real‐Time Motion Management in Cancer Radiotherapy
Authors: Huang C.Y. , Nasehi Tehrani J , Booth J , Keall P
Published: July 2014

Purpose:

Lung tumor motion has been identified as a major issue that deteriorates treatment efficacy for radiotherapy, especially for SBRT. As tighter PTV margins are applied due to translational compensation, tumor rotation will become the dominant factor limiting tumor targeting accuracy. This is the world‐first study quantifies lung tumor rotation by utilizing kV images with fiducial markers and a step towards 6‐degree‐of‐freedom real‐time cancer radiotherapy.

Methods:

Three or four gold coils were implanted as tumor surrogates in 3 lung cancer patients. 50 fractions of 8‐ minute, 10 Hz 4D CBCT projections were acquired for the patients immediately prior or after radiotherapy. The fiducial marker positions are segmented, reconstructed and used to determine tumour rotation by the iterative closest point algorithm. Different data acceptance and filtering methods were applied to accept data or smooth the marker trajectory.

Results:

The average rotation angles around the left/ right (LR), superior/inferior (SI), anterior/posterior (AP) rotations were found to be 0.8±4.2, ‐0.8±4.5 and 1.7±3.1 degrees respectively. For 28% of the treatment time, the lung tumors rotated more than 5° around the SI axis. Respiration‐induced rotational motion was detected in 2 of the 3 lung patients. This can be explained by the patient developed atelectasis during the treatment period. Interestingly, no heart beating component of rotation was observed in the power spectrum. Different rotational types were observed within the patient cohort with large variations in the magnitude of the rotation between patients.

Conclusions:

For the first time, continuous tumor rotation has been measured for lung patients with gold fiducial markers. Tumors were found to undergo rotations of more than 5° for almost a third of the total treatment time. The study also demonstrated the feasibility of using continuously kV images for real‐time lung tumour motion adaptive radiotherapy which can potentially reduce treatment margins and side effects.

The authors acknowledge the financial support of an NHMRC Australia Fellowship.
SU‐D‐18C‐05: Variable Bolus Arterial Spin Labeling MRI for Accurate Cerebral Blood Flow and Arterial Transit Time Mapping
Authors: Johnston M , Jung Y
Published: July 2014

Purpose:

Arterial spin labeling (ASL) is an MRI perfusion imaging method from which quantitative cerebral blood flow (CBF) maps can be calculated. Acquisition with variable post‐labeling delays (PLD) and variable TRs allows for arterial transit time (ATT) mapping and leads to more accurate CBF quantification with a scan time saving of 48%. In addition, T1 and M0 maps can be obtained without a separate scan. In order to accurately estimate ATT and T1 of brain tissue from the ASL data, variable labeling durations were invented, entitled variable‐bolus ASL.

Methods:

All images were collected on a healthy subject with a 3T Siemens Skyra scanner. Variable‐bolus Psuedo‐continuous ASL (PCASL) images were collected with 7 TI times ranging 100‐4300ms in increments of 700ms with TR ranging 1000‐5200ms. All boluses were 1600ms when the TI allowed, otherwise the bolus duration was 100ms shorter than the TI. All TI times were interleaved to reduce sensitivity to motion. Voxel‐wise T1 and M0 maps were estimated using a linear least squares fitting routine from the average singal from each TI time. Then pairwise subtraction of each label/control pair and averaging for each TI time was performed. CBF and ATT maps were created using the standard model by Buxton et al. with a nonlinear fitting routine using the T1 tissue map.

Results:

CBF maps insensitive to ATT were produced along with ATT maps. Both maps show patterns and averages consistent with literature. The T1 map also shows typical T1 contrast.

Conclusion:

It has been demonstrated that variablebolus ASL produces CBF maps free from the errors due to ATT and tissue T1 variations and provides M0, T1, and ATT maps which have potential utility. This is accomplished with a single scan in a feasible scan time (under 6 minutes) with low sensivity to motion.
SU‐D‐9A‐01: Listmode‐Driven Optimal Gating (OG) Respiratory Motion Management: Potential Impact On Quantitative PET Imaging
Authors: Lee K , Hristov D
Published: July 2014

Purpose:

To evaluate the potential impact of listmode‐driven amplitude based optimal gating (OG) respiratory motion management technique on quantitative PET imaging.

Methods:

During the PET acquisitions, an optical camera tracked and recorded the motion of a tool placed on top of patients' torso. PET event data were utilized to detect and derive a motion signal that is directly coupled with a specific internal organ. A radioactivity‐trace was generated from listmode data by accumulating all prompt counts in temporal bins matching the sampling rate of the external tracking device. Decay correction for 18F was performed. The image reconstructions using OG respiratory motion management technique that uses 35% of total radioactivity counts within limited motion amplitudes were performed with external motion and radioactivity traces separately with ordered subset expectation maximization (OSEM) with 2 iterations and 21 subsets. Standard uptake values (SUVs) in a tumor region were calculated to measure the effect of using radioactivity trace for motion compensation. Motion‐blurred 3D static PET image was also reconstructed with all counts and the SUVs derived from OG images were compared with SUVs from 3D images.

Results:

A 5.7 % increase of the maximum SUV in the lesion was found for optimal gating image reconstruction with radioactivity trace when compared to a static 3D image. The mean and maximum SUVs on the image that was reconstructed with radioactivity trace were found comparable (0.4 % and 4.5 % increase, respectively) to the values derived from the image that was reconstructed with external trace.

Conclusion:

The image reconstructed using radioactivity trace showed that the blurring due to the motion was reduced with impact on derived SUVs. The resolution and contrast of the images reconstructed with radioactivity trace were comparable to the resolution and contrast of the images reconstructed with external respiratory traces.

Research supported by Siemens
SU‐D‐9A‐02: Relative Effects of Threshold Choice and Spatial Resolution Modeling On SUV and Volume Quantification in F18‐FDG PET Imaging of Anal Cancer Patients
Authors: Zhao F , Bowsher J , Palta M , Czito B , Willett C , Yin F
Published: July 2014

Purpose:

PET imaging with F18‐FDG is utilized for treatment planning, treatment assessment, and prognosis. A region of interest (ROI) encompassing the tumor may be determined on the PET image, often by a threshold T on the PET standard uptake values (SUVs). Several studies have shown prognostic value for relevant ROI properties including maximum SUV value (SUVmax), metabolic tumor volume (MTV), and total glycolytic activity (TGA). The choice of threshold T may affect mean SUV value (SUVmean), MTV, and TGA. Recently spatial resolution modeling (SRM) has been introduced on many PET systems. SRM may also affect these ROI properties. The purpose of this work is to investigate the relative influence of SRM and threshold choice T on SUVmean, MTV, TGA, and SUVmax.

Methods:

For 9 anal cancer patients, 18F‐FDG PET scans were performed prior to treatment. PET images were reconstructed by 2 iterations of Ordered Subsets Expectation Maximization (OSEM), with and without SRM. ROI contours were generated by 5 different SUV threshold values T: 2.5, 3.0, 30%, 40%, and 50% of SUVmax. Paired‐samples t tests were used to compare SUVmean, MTV, and TGA (a) for SRM on versus off and (b) between each pair of threshold values T. SUVmax was also compared for SRM on versus off.

Results:

For almost all (57/60) comparisons of 2 different threshold values, SUVmean, MTV, and TGA showed statistically significant variation. For comparison of SRM on versus off, there were no statistically significant changes in SUVmax and TGA, but there were statistically significant changes in MTV for T=2.5 and T=3.0 and in SUVmean for all T.

Conclusion:

The near‐universal statistical significance of threshold choice T suggests that, regarding harmonization across sites, threshold choice may be a greater concern than choice of SRM. However, broader study is warranted, e.g. other iterations of OSEM should be considered.
SU‐D‐9A‐03: STAMP: Simulator for Texture Analysis in MRI/PET
Authors: Laberge S , Vallieres M , Levesque I R. , El Naqa I
Published: July 2014

Purpose:

To develop a convenient simulation platform to facilitate PET/MR image analysis with the prospect of gaining a better understanding of the influence of acquisition parameters on PET/MRI textural features. The simulation platform is demonstrated by showing textural variations of a representative case study using different image acquisition parameters.

Methods:

The simulation platform is composed of MRI simulators JEMRIS and SIMRI to achieve simulations of customized MRI sequences on sample tumor models. The PET simulator GATE is used to get 2D and 3D Monte Carlo acquisitions of voxelized PET sources using a phantom geometry and a customized scanner architecture. The platform incorporates a series of graphical user interfaces written in Matlab. Two GUIs are used to facilitate communication with the simulation executables installed on a computer cluster. A third GUI is used to collect and display the clinical and simulated images, as well as fused PET/MRI images, and perform computation of textural features. To illustrate the capabilities of this platform, one FDG‐PET and T1‐weighted (T1w) digitized tumor models were generated from clinical images of a soft‐tissue sarcoma patient. Numerically simulated MR images were produced using 3 different echo times (TE) and 5 different repetition times (TR). PET 2D images were simulated using an OSEM algorithm with 1 to 32 iterations and a post‐reconstruction Gaussian filter of 0, 2, 4 or 6 mm width.

Results:

STAMP was successfully used to produce numerically simulated FDG‐PET and MRI images, and to calculate their corresponding textures. Three typical textures (GLCM‐Contrast, GLSZM‐ZSV and NGTDM‐Coarseness) were found to vary by a range of 45% on average compared to reference scanning conditions in the case of FDG‐PET, and by a range of 40% in the case of T1w MRI.

Conclusion:

We have successfully developed a Matlab‐based simulation platform to facilitate PET/MRI texture image analysis for outcome prediction.
SU‐D‐9A‐04: Brain PET/CT Imaging On a Scanner with a Large Axial Field‐Of‐View
Authors: Park M , Gerbaudo V , Hamberg L , Seaver K , Kijewski M
Published: July 2014

Purpose:

Large axial field‐of‐view (FOV) PET/CT scanners are valued for high sensitivity. Brain PET image quality may depend on the head position within the FOV. We investigated the precision of activity estimation for brain PET imaging when the brain was positioned at the end (END) and in the middle (CEN) of the FOV. The additional CT dose for the CEN position was recorded.

Methods:

An image quality (Jaszczak) phantom and a striatal phantom were filled with F‐18 and positioned in END and CEN locations. For each phantom and each location, we acquired a ∼1‐hr listmode PET, rebinned the data into 10 frames with equal number of coincidence events, and reconstructed each frame using an iterative algorithm. For the striatal phantom, END and CEN were compared by drawing on each image three regions of interest (ROI) in axially separated uniform areas. The standard deviation of the activity estimation within each ROI was averaged over the 10 images. The coefficient of variation (CV) for activity estimation was calculated at each position. Image quality was assessed by inspecting the resolution bar pattern in the Jaszczak phantom at two different head positions.

Results:

The CV was the lowest for ROIs near the center of the FOV. For slices near the end, not only was the CV highest, but also the resolution pattern was degraded. CTDIvol summarized in the dose report indicated that the CT dose was ∼ 10% higher for CEN as compared to END position.

Conclusion:

Positioning the brain in the middle of the FOV in a large FOV PET/CT scanner allows more precise measurement of tracer uptake and better image quality at the cost of increased CT dose. For the end location longer scan times may minimize image quality degradation without any additional CT dose.
SU‐D‐9A‐06: 3D Localization of Neurovascular Bundles Through MR‐TRUS Registration in Prostate Radiotherapy
Authors: Yang X , Rossi P , Ogunleye T , Jani A , Curran W , Liu T
Published: July 2014

Purpose:

Erectile dysfunction (ED) is the most common complication of prostate‐cancer radiotherapy (RT) and the major mechanism is radiation‐induced neurovascular bundle (NVB) damage. However, the localization of the NVB remains challenging. This study's purpose is to accurately localize 3D NVB by integrating MR and transrectal ultrasound (TRUS) images through MR‐TRUS fusion.

Methods:

T1 and T2‐weighted MR prostate images were acquired using a Philips 1.5T MR scanner and a pelvic phase‐array coil. The 3D TRUS images were captured with a clinical scanner and a 7.5 MHz biplane probe. The TRUS probe was attached to a stepper; the B‐mode images were captured from the prostate base to apex at a 1‐mm step and the Doppler images were acquired in a 5‐mm step. The registration method modeled the prostate tissue as an elastic material, and jointly estimated the boundary condition (surface deformation) and the volumetric deformations under elastic constraint. This technique was validated with a clinical study of 7 patients undergoing RT treatment for prostate cancer. The accuracy of our approach was assessed through the locations of landmarks, as well as previous ultrasound Doppler images of patients.

Results:

MR‐TRUS registration was successfully performed for all patients. The mean displacement of the landmarks between the post‐registration MR and TRUS images was 1.37±0.42 mm, which demonstrated the precision of the registration based on the biomechanical model; and the NVB volume Dice Overlap Coefficient was 92.1±3.2%, which demonstrated the accuracy of the NVB localization.

Conclusion:

We have developed a novel approach to improve 3D NVB localization through MR‐TRUS fusion for prostate RT, demonstrated its clinical feasibility, and validated its accuracy with ultrasound Doppler data. This technique could be a useful tool as we try to spare the NVB in prostate RT, monitor NBV response to RT, and potentially improve post‐RT potency outcomes.
SU‐D‐12A‐02: DeTECT, a Method to Enhance Soft Tissue Contrast From Mega Voltage CT
Authors: Sheng K , Gou S , Qi S
Published: July 2014

Purpose:

MVCT images have been used on TomoTherapy system to align patients based on bony anatomies but its usefulness for soft tissue registration, delineation and adaptive radiation therapy is severely limited due to minimal photoelectric interaction and prominent presence of noise resulting from low detector quantum efficiency of megavoltage x‐rays. We aim to utilize a non‐local means denoising method and texture analysis to recover the soft tissue information for MVCT.

Methods:

A block matching 3D (BM3D) algorithm was adapted to reduce the noise while keeping the texture information of the MVCT images. BM3D is an imaging denoising algorithm developed from non‐local means methods. BM3D additionally creates 3D groups by stacking 2D patches by the order of similarity. 3D denoising operation is then performed. The resultant 3D group is inversely transformed back to 2D images. In this study, BM3D was applied to MVCT images of a CT quality phantom, a head and neck and a prostate patient. Following denoising, imaging texture was enhanced to create the denoised and texture enhanced CT (DeTECT).

Results:

The original MVCT images show prevalent noise and poor soft tissue contrast. By applying BM3D denoising and texture enhancement, all MVCT images show remarkable improvements. For the phantom, the contrast to noise ratio for the low contrast plug was improved from 2.2 to 13.1 without compromising line pair conspicuity. For the head and neck patient, the lymph nodes and vein in the carotid space inconspicuous in the original MVCT image becomes highly visible in DeTECT. For the prostate patient, the boundary between the bladder and the prostate in the original MVCT is successfully recovered. Both results are visually validated by kVCT images of the corresponding patients.

Conclusion:

DeTECT showed the promise to drastically improve the soft tissue contrast of MVCT for image guided radiotherapy and adaptive radiotherapy.
SU‐D‐12A‐07: Optimization of a Moving Blocker System for Cone‐Beam Computed Tomography Scatter Correction
Authors: Ouyang L , Yan H , Zhang H , Jia X , Jiang S , Wang J
Published: July 2014

Purpose:

A moving blocker based strategy has shown promising results for scatter correction in cone‐beam computed tomography (CBCT). Different parameters of the system design affect its performance in scatter estimation and image reconstruction accuracy. The goal of this work is to optimize the geometric design of the moving block system.

Methods:

In the moving blocker system, a blocker consisting of lead strips is inserted between the x‐ray source and imaging object and moving back and forth along rotation axis during CBCT acquisition. CT image of an anthropomorphic pelvic phantom was used in the simulation study. Scatter signal was simulated by Monte Carlo calculation with various combinations of the lead strip width and the gap between neighboring lead strips, ranging from 4 mm to 80 mm (projected at the detector plane). Scatter signal in the unblocked region was estimated by cubic B‐spline interpolation from the blocked region. Scatter estimation accuracy was quantified as relative root mean squared error by comparing the interpolated scatter to the Monte Carlo simulated scatter. CBCT was reconstructed by total variation minimization from the unblocked region, under various combinations of the lead strip width and gap. Reconstruction accuracy in each condition is quantified by CT number error as comparing to a CBCT reconstructed from unblocked full projection data.

Results:

Scatter estimation error varied from 0.5% to 2.6% as the lead strip width and the gap varied from 4mm to 80mm. CT number error in the reconstructed CBCT images varied from 12 to 44. Highest reconstruction accuracy is achieved when the blocker lead strip width is 8 mm and the gap is 48 mm.

Conclusions:

Accurate scatter estimation can be achieved in large range of combinations of lead strip width and gap. However, image reconstruction accuracy is greatly affected by the geometry design of the blocker.
SU‐E‐E‐01: ABR Diagnostic Radiology Core Exam: Was Our Redesigned Physics Course Successful in Teaching Physics to Radiology Residents?
Authors: Kanal K , Hoff M , Dickinson R , Zamora D , Stewart B
Published: July 2014

Purpose:

Our purpose is to evaluate the effectiveness of our two year physics course in preparing radiology residents for the American Board of Radiology (ABR) diagnostic radiology exam.

Methods:

We designed a new two‐year physics course that integrates radiology clinical content and practice and is primarily based on the AAPM curriculum and RSNA/AAPM physics modules. Biweekly classes focus on relevant concepts from assigned reading and use audience response systems to encourage participation. Teaching efficiency is optimized through lecturer rotations of physicists, radiologists, and guest speakers. An emphasis is placed on clinical relevance by requiring lab work and providing equipment demonstrations. Periodic quiz were given during the course. The course website was also redesigned for usability, and physics review lectures were conducted two weeks before the board exam to refresh key concepts. At the completion of our first two‐year course, we conducted a confidential evaluation of the faculty and course. The evaluation assessed metrics such as overall organization, clinical relevance of content, and level of difficulty, with a rating scale from poor to excellent.

Results:

Our evaluation indicated that the redesigned course provided effective board exam preparation, with most responses between good and excellent. There was some criticism on the course length and on chronological discontinuity, but the review lectures were appreciated by the residents. All of our residents passed the physics component of the ABR exam with scores exceeding the minimum passing score by a significant margin.

Conclusion:

The course evaluation and board exam results indicate that our new two‐year course format provides valuable board exam preparation. This is possible thanks to the time and effort taken by the physics faculty on ensuring the residents get quality physics education.
SU‐E‐E‐02: Dashboard for Tracking Physics Resident Progress
Authors: Becker SJ
Published: July 2014

Purpose:

Design a system to easily and securely track the progress of medical physics residents through their residency. Paper sign‐offs while offering a real signature are not easily updated or summarized. A resident or mentor needs to be able to quickly assess what the current assignments are, what are overdue, and whether the resident is on track to complete all the tasks in a timely fashion. An electronic version can accomplish all these goals.

Methods:

An electronic dashboard was created in excel to not only house the tasks and sign‐off but to succinctly summarize the residents progress. The first tab contains the dashboard which displays tables of the progress of the residents in each rotation, their current task, and overdue tasks. It also displays the last meetings with the residents, and timeline of important items, and a burn‐down chart of the remaining tasks. This are all tied to the data and current date which auto fills the tables. The second tab contains the data. This is comprised of lists of rotations and their associated tasks along with their due dates. A signature column was also created which is password protected but allows special subset users i.e. mentors to alter without using a password.

Results:

The dashboard has allowed residents to better track their progress and tells them what they should be working on. It has also allowed the mentors and the program director to rapid assess their progress.

Conclusion:

The dashboard is successful and has been created to allow easy addition and subtraction of required tasks as the residency evolves. The next step is to create a web app version of the excel sheet with logins.
SU‐E‐E‐05: Initial Experience On Physics Rotation of Radiological Residents
Authors: Zhang J , Williams D , DiSantis D , Hardy P , Oates M
Published: July 2014

Purpose:

The new ABR core exam integrates physics into clinical teaching, with an emphasis on understanding image quality, image artifacts, radiation dose and patient safety for each modality and/or sub‐specialty. Accordingly, physics training of radiological residents faces a challenge. A traditional teaching of physics through didactic lectures may not fully fulfill this goal. It is also difficult to incorporate physics teaching in clinical practice due to time constraints. A dedicated physics rotation may be a solution. This study is to evaluate a full week physics workshop developed for the first year radiological residents.

Methods:

The physics rotation took a full week. It included three major parts, introduction lectures, hand‐on experiences and observation of technologist operation. An introduction of basic concepts was given to each modality at the beginning. Hand‐on experiments were emphasized and took most of time. During hand‐on experiments, residents performed radiation measurements, studied the relationship between patient dose and practice (i.e., fluoroscopy), investigated influence of acquisition parameters (i.g., kV, mAs) on image quality, and evaluated image quality using phantoms A physics test before and after the workshop was also given but not for comparison purpose.

Results:

The evaluation shows that the physics rotation during the first week of residency in radiology is preferred by all residents. The length of a full week of physics workshop is appropriate. All residents think that the intensive workshop can significantly benefit their coming clinical rotations. Residents become more comfortable regarding the use of radiation and counseling relevant questions such as a pregnant patient risk from a CE PE examination.

Conclusion:

A dedicated physics rotation, assisting with didactic lectures, may fulfill the requirements of physics of the new ABR core exam. It helps radiologists deeply understand the physics concepts and more efficiently use the medical physics in practice.
SU‐E‐P‐02: Imaging and Radiation Oncology Core (IROC) Houston QA Center (RPC) Credentialing
Authors: Amador C , Keith T , Nguyen T , Molineu A , Followill D
Published: July 2014

Purpose:

To provide information pertaining to IROC Houston QA Center's (RPC) credentialing process for institutions participating in NCI‐sponsored clinical trials.

Methods:

IROC Houston issues credentials for NCI sponsored study groups. Requirements for credentialing might include any combination of questionnaires, knowledge assessment forms, benchmarks, or phantom irradiations. Credentialing requirements for specific protocols can be found on IROC Houston's website (irochouston.mdanderson.org). The website also houses the credentialing status inquiry (CSI) form. Once an institution has reviewed the protocol's credentialing requirements, a CSI form should be completed and submitted to IROC Houston. This form is used both to request whether requirements have been met as well as to notify IROC Houston that the institution requests credentialing for a specific protocol. IROC Houston will contact the institution to discuss any delinquent requirements. Once the institution has met all requirements IROC Houston issues a credentialing letter to the institution and will inform study groups and other IROC offices of the credentials. Institutions can all phone the IROC Houston office to initiate credentialing or ask any credentialing related questions.

Results:

Since 2010 IROC has received 1313 credentialing status inquiry forms. We received 317 in 2010, 266 in 2011, 324 in 2012, and 406 in 2013. On average we receive 35 phone calls per week with multiple types of credentialing questions. Decisions regarding credentialing status are based on the protocol specifications and previous completed credentialing by the institution. In some cases, such as for general IMRT credentialing, up to 5 sites may be credentialed based on the credentialing of one main center. Each of these situations is handled individually.

Conclusion:

IROC Houston will issue radiation therapy credentials for the NCI trials in the National Clinical Trials Network. Credentialing requirements and the CSI form can be found online at the IROC Houston's website.

Work supported by PHS grant CA10953 and CA081647 (NCI, DHHS).
SU‐E‐P‐03: Implementing a Low Dose Lung Screening CT Program Meeting Regulatory Requirements
Authors: LaFrance M , Marsh S , O' Donnell G
Published: July 2014

Purpose:

To provide information pertaining to IROC Houston QA Center's (RPC) credentialing process for institutions participating in NCI‐sponsored clinical trials.

Purpose:

Provide guidance to the Radiology Departments with the intent of implementing a Low Dose CT Screening Program using different CT Scanners with multiple techniques within the framework of the required state regulations.

Method:

State Requirements for the purpose of implementing a Low Dose CT Lung Protocol required working with the Radiology and Pulmonary Department in setting up a Low Dose Screening Protocol designed to reduce the radiation burden to the patients enrolled. Radiation dose measurements (CTDIvol) for various CT manufacturers (Siemens16, Siemens 64, Philips 64, and Neusoft128) for three different weight based protocols. All scans were reviewed by the Radiologist. Prior to starting a low dose lung screening protocol, information had to be submitted to the state for approval. Performing a Healing Arts protocol requires extensive information. This not only includes name and address of the applicant but a detailed description of the disease, the x‐ray examination and the population to be examined. The unit had to be tested by a qualified expert using the technique charts. The credentials of all the operators, the supervisors and the Radiologists had to be submitted to the state.

Results:

All the appropriate documentation was sent to the state for review. The measured results between the Low Dose Protocol versus the default Adult Chest Protocol showed that there was a dose reduction of 65% for small (100‐150 lb.) patient, 75% for the Medium patient (151‐250 lbs.), and a 55% reduction for the Large patient (over 250 lbs.).

Conclusion:

Measured results indicated that the Low Dose Protocol indeed lowered the screening patient's radiation dose and the institution was able to submit the protocol to the State's regulators.
SU‐E‐P‐07: Evaluation of Productivity Systems for Radiation Therapy
Authors: Ramsey C , Usynin A
Published: July 2014

Purpose:

Health systems throughout the United States are under increased financial pressure to reduce operating cost. As a result, productivity models developed by third‐party consultants are being used to optimize staff to treatment volumes. The purpose of this study was to critically evaluate productivity systems for radiation oncology.

Methods:

Staffing efficiency was evaluated using multiple productivity models. The first model evaluated staffing levels using equal weighting of procedure codes and hours worked. A second productivity model was developed using hours worked by job class and relative value units for each procedure code. A third model was developed using the measured procedure times extracted from the electronic medical record, which tracks the wait and treatment times for each patient for each treatment fraction. A MatLab program was developed to query and analyze the daily treatment data. A model was then created to determine any theoretical gains in treatment productivity.

Results:

Productivity was evaluated for six radiation therapy departments operating nine linear accelerators delivering over 40,000 treatment fractions per year. Third party productivity models that do not take into consideration the unique nature of radiation therapy can be counterproductive. For example, other outpatient departments can compress their daily schedule to decrease the worked hours. This approach was tested using the treatment schedule evaluation tool developed as part of this study. It was determined that the maximum possible savings for treatment schedule compression was $32,000 per year per linac. All annual cost savings would be lost if only two patients per year choose to be treated elsewhere because of limited or restricted appointment times.

Conclusion:

The use of productivity models in radiation therapy can easily result in a loss of treatment revenue that is greater than any potential cost savings in reduced hours worked by staff.
SU‐E‐P‐08: Alarming Range of Seed Activities Ordered for I‐125 Plaque Brachytherapy
Authors: Merz B
Published: July 2014

Purpose:

To investigate the variation in I‐125 seed activities ordered by various clinics for their plaque brachytherapy cases under a standardized set of assumptions.

Methods:

A majority of the plaque programs in North America were contacted and a survey was designed to give a few standardized cases to allow inter‐comparison of seed activities ordered. Tumor dose, treatment duration, number of seeds, plaque, and tumor apex were held constant in order to reveal differences in prescription point, seed type, and seed activity.

Results:

While the survey is presently underway, preliminary results show alarmingly wide variations between centers. Differences up to 45% have been found with 15% differences being common.

Conclusion:

Though knowledge of the TG‐43 dose calculation formalism is common, a number of factors in the field of plaque brachytherapy lead to alarming differences in activity of I‐125 seeds being ordered for a given tumor. Knowledge of the present reality of widely varying treatment activities, and thus doses to tumor and normal structures, should serve as motivation for centers involved in this modality to review their programs with others in the community and share their experiences.
SU‐E‐I‐02: A Framework to Perform Batch Simulations of Computational Voxel Phantoms to Study Organ Doses in Computed Tomography Using a Commercial Monte Carlo Software Package
Authors: Bujila R , Nowik P , Poludniowski G
Published: July 2014

Purpose:

ImpactMC (CT Imaging, Erlangen, Germany) is a Monte Carlo (MC) software package that offers a GPU enabled, user definable and validated method for 3D dose distribution calculations for radiography and Computed Tomography (CT). ImpactMC, in and of itself, offers limited capabilities to perform batch simulations. The aim of this work was to develop a framework for the batch simulation of absorbed organ dose distributions from CT scans of computational voxel phantoms.

Methods:

The ICRP 110 adult Reference Male and Reference Female computational voxel phantoms were formatted into compatible input volumes for MC simulations. A Matlab (The MathWorks Inc., Natick, MA) script was written to loop through a user defined set of simulation parameters and 1) generate input files required for the simulation, 2) start the MC simulation, 3) segment the absorbed dose for organs in the simulated dose volume and 4) transfer the organ doses to a database. A demonstration of the framework is made where the glandular breast dose to the adult Reference Female phantom, for a typical Chest CT examination, is investigated.

Results:

A batch of 48 contiguous simulations was performed with variations in the total collimation and spiral pitch. The demonstration of the framework showed that the glandular dose to the right and left breast will vary depending on the start angle of rotation, total collimation and spiral pitch.

Conclusion:

The developed framework provides a robust and efficient approach to performing a large number of user defined MC simulations with computational voxel phantoms in CT (minimal user interaction). The resulting organ doses from each simulation can be accessed through a database which greatly increases the ease of analyzing the resulting organ doses. The framework developed in this work provides a valuable resource when investigating different dose optimization strategies in CT.
SU‐E‐I‐06: A Robust and Improved Method of Analysis for Dose Calibrator Linearity Data Based On First Principles
Authors: Gress DA , Kappadath SC
Published: July 2014

Purpose:

Identify shortcomings in the common mathematical methods of dose calibrator linearity analysis, then propose an improved and more robust method.

Methods:

Precision of activity measurements using attenuator sleeves was measured using inter‐user (several users) & intra‐user (single user) measurements. We performed retrospective follow‐up investigation of several reported dose calibrator linearity failures at our institution. Common methods of linearity analysis generate best‐fits without using the known decay constant, no‐weighting of data points, and/or compare scaled values to the “zero” measurement (inherently assumed to be error‐free).Fixing the known slope (‐λ) of our data on a semilog plot, we then use least‐squares methodology to find y‐intercept of data's best fit line, against which linearity is assessed.

Results:

Two‐sigma precision ranges of attenuator sleeve measurements were ±0.4–1.2% for inter‐user measurements, and ±0.4–2.1% for intra‐user measurements. Retrospective analysis of all reported dose calibrator linearity failures from previous four years showed that robust least squares method of analysis would have prevented all repeat testing. Trending data using different methods shows more consistent data ranges (max. deviation 4.9–6.7% versus 3.2–4.2% for select datasets) i.e. more consistent device performance (as anecdotally expected) is demonstrated when analyzed with least squares method. Lower absolute maximum variation values are also calculated across nearly all linearity data sets when using least squares method of analysis.

Conclusion:

Precision of attenuator sleeve measurements confirm signal averaging must be used in analysis. Dose calibrator performance specification for accuracy is 1%. Linearity tolerance for heightened scrutiny, and arguably a best practice action limit, is 5%. Thus a considerable fraction of the allowed tolerance for the test can be occupied by measurement error. Proposed method of analysis is improvement over other common methods based on first principles, and is demonstrated to be robust.
SU‐E‐I‐12: Characterization of Edge Effects in a Commercial Low‐Dose Image Processing System
Authors: Marsh R , Silosky M
Published: July 2014

Purpose:

Minimizing radiation dose while preserving image quality is critical in fluoroscopic imaging. One recent development is a noise reduction system (Allura Clarity) offered by Philips. Others have reported approximately 50% reduction in air kerma when using Clarity. These studies, however, provide only a cursory look at how the Clarity system affects image quality. The purpose of this work was to evaluate the effect of Clarity on the appearance of high‐frequency image information.

Methods:

A lead attenuator with a smooth edge was imaged on two Philips Allura FD20 detectors: one with Clarity and one without. The edge was positioned in the center of the field of view and images were obtained under the following conditions: 40cm and 11cm fields of view, single shot and continuous fluoroscopy modes, and using abdomen and cardiac protocols, for a total of sixteen imaging conditions. Profiles were drawn perpendicular to the edge across 80% of its length, averaged to reduce noise, normalized to the maximum pixel value, and plotted as a function of distance.

Results:

For all single‐shot acquisitions and most fluoroscopic images, overshoot of the edge was observed. This effect was more substantial for single‐shot acquisitions (∼20%) than for fluoroscopic images (∼50%). For fluoroscopic acquisition, the overshoot decayed more quickly with the Clarity system. However, the system with Clarity introduced a ringing effect for both single‐shot and fluoroscopic images that is not present on the non‐Clarity system.

Conclusion:

Previous reports have demonstrated a substantial dose reduction when using Clarity but the impact this has on image appearance has not been characterized. One demonstrated difference is the change in appearance of high‐frequency image information. It remains to be determined whether this effect may impact clinical images adversely.
SU‐E‐I‐13: Comparison of CCD and CMOS Micro‐Angiographic Fluoroscope (MAF) Detector Systems Using Contrast Measurements for Specific Imaging Tasks Related to Neuro‐Endovascular Image‐Guided Interventional (EIGI) Procedures
Authors: Rana R , Jain A , Setlur Nagesh S , Bednarek D , Rudin S
Published: July 2014

Purpose:

To compare the performance of two high‐resolution detector systems for use during neuro‐EIGI procedures.

Methods:

The task‐specific performance of custom high‐resolution CCD and CMOS micro‐angiographic fluoroscopes (MAF) was compared. To simulate the attenuation of x‐rays by a patient in neuro‐EIGIs, a modified ANSI head phantom was used. A bar phantom with 0.05‐mm thick lead was used to simulate the contrast and size of EIGI devices used in neuro EIGIs. The bar phantom, placed at an angle of 6.5 degrees relative to the pixel rows of both detectors, was imaged for 88kVp using the small 0.3mm focal spot in order to decrease the geometric unsharpness and preserve the high‐resolution capabilities of both detectors. The resultant images have a geometric object magnification of 1.25, similar to that of a clinical neuro‐EIGI, and a fixed field size was used to keep the scatter the same for both detectors. For images obtained using each detector, we calculated and compared the contrast of the averaged line profiles for the 5.0, 5.6 and 6.3 lp/mm bar pattern groups, which have lead‐line widths of 100, 89, and 79 microns, respectively.

Results:

For the MAF‐CCD, the measured contrasts were 0.020, 0.019 and 0.013 for the 5.0, 5.6 and 6.3 line pair groups, respectively, and for the MAF‐CMOS the contrasts were 0.025, 0.019 and 0.014 for the 5.0, 5.6 and 6.3 line pair groups, respectively.

Conclusion:

For the very small lines of the bar pattern, the MAF‐CMOS appears to provide almost the same contrast as compared to the MAF‐CCD, within the measurement error; however, noise and dynamic range characteristics remain to be studied before concluding that the MAF‐CMOS can replace the MAF‐CCD during task‐specific neuro‐EIGI procedures where high spatial resolution is required.

Supported by NIH Grant: 2R01EB002873 and an equipment grant from Toshiba Medical Systems Corporation.
SU‐E‐I‐18: CT Scanner QA Using Normalized CTDI Ratio
Authors: Randazzo M , Tambasco M , Russell B
Published: July 2014

Purpose:

To create a ratio of weighted computed tomography dose index (CTDIw) data normalized to in‐air measurements (CTDIair) as a function of beam quality to create a look‐up table for frequent, rapid quality assurance (QA) checks of CTDI.

Methods:

The CTDIw values were measured according to TG‐63 protocol using a pencil ionization chamber (Unfors Xi CT detector) and head and body Polymethyl methacrylate (PMMA) phantoms (16 and 32 cm diameter, respectively). Single scan dose profiles were measured at each clinically available energy (80,100,120,140 kVp) on three different CT scanners (two Siemens SOMATOM Definition Flash and one GE Optima), using a tube current of 400 mA, a one second rotation time, and the widest available beam width (32 × 0.6 mm and 16 × 1.25 mm, respectively). These values were normalized to CTDIair measurements using the same conditions as CTDIw. The ratios (expressed in cGy/R) were assessed for each scanner as a function of each energy's half value layer (HVL) paired with the phantom's appropriate bow tie filter measured in mmAl.

Results:

Normalized CTDI values vary linearly with HVL for both the head and body phantoms. The ratios for the two Siemens machines are very similar at each energy. Compared to the GE scanner, these values vary between 10–20% for each kVp setting. Differences in CTDIair contribute most to the deviation of the ratios across machines. Ratios are independent of both mAs and collimation.

Conclusion:

Look‐up tables constructed of normalized CTDI values as a function of HVL can be used to derive CTDIw data from only three in‐air measurements (one for CTDIair and two with added filtration for HVL) to allow for simple, frequent QA checks without CT phantom setup. Future investigations will involve comparing results with Monte Carlo simulations for validation.