bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐G‐BRA‐11: Tumor Tracking in An Iterative Volume of Interest Based 4D CBCT Reconstruction
Authors: Martin R , Ahmad M , Pan T
Published: July 2016

Purpose:

4D CBCT can allow evaluation of tumor motion immediately prior to radiation therapy, but suffers from heavy artifacts that limit its ability to track tumors. Various iterative and compressed sensing reconstructions have been proposed to reduce these artifacts, but are costly time‐wise and can degrade the image quality of bony anatomy for alignment with regularization. We have previously proposed an iterative volume of interest (I4D VOI) method which minimizes reconstruction time and maintains image quality of bony anatomy by focusing a 4D reconstruction within a VOI. The purpose of this study is to test the tumor tracking accuracy of this method compared to existing methods.

Methods:

Long scan (8–10 mins) CBCT data with corresponding RPM data was collected for 12 lung cancer patients. The full data set was sorted into 8 phases and reconstructed using FDK cone beam reconstruction to serve as a gold standard. The data was reduced in way that maintains a normal breathing pattern and used to reconstruct 4D images using FDK, low and high regularization TV minimization (λ=2,10), and the proposed I4D VOI method with PTVs used for the VOI. Tumor trajectories were found using rigid registration within the VOI for each reconstruction and compared to the gold standard.

Results:

The root mean square error (RMSE) values were 2.70mm for FDK, 2.50mm for low regularization TV, 1.48mm for high regularization TV, and 2.34mm for I4D VOI. Streak artifacts in I4D VOI were reduced compared to FDK and images were less blurred than TV reconstructed images.

Conclusion:

I4D VOI performed at least as well as existing methods in tumor tracking, with the exception of high regularization TV minimization. These results along with the reconstruction time and outside VOI image quality advantages suggest I4D VOI to be an improvement over existing methods.

Funding support provided by CPRIT grant RP110562‐P2‐01
SU‐G‐BRA‐16: Target Dose Comparison for Dynamic MLC Tracking and Mid‐ Ventilation Planning in Lung Radiotherapy Subject to Intrafractional Baseline Drifts
Authors: Menten MJ , Fast MF , Nill S , Oelfke U
Published: July 2016

Purpose:

Lung tumor motion during radiotherapy can be accounted for by expanded treatment margins, for example using a mid‐ventilation planning approach, or by localizing the tumor in real‐time and adapting the treatment beam with multileaf collimator (MLC) tracking. This study evaluates the effect of intrafractional changes in the average tumor position (baseline drifts) on these two treatment techniques.

Methods:

Lung stereotactic treatment plans (9‐beam IMRT, 54Gy/3 fractions, mean treatment time: 9.63min) were generated for three patients: either for delivery with MLC tracking (isotropic GTV‐to‐PTV margin: 2.6mm) or planned with a mid‐ventilation approach and delivered without online motion compensation (GTV‐to‐PTV margin: 4.4‐6.3mm). Delivery to a breathing patient was simulated using DynaTrack, our in‐house tracking and delivery software. Baseline drifts in cranial and posterior direction were simulated at a rate of 0.5, 1.0 or 1.5mm/min. For dose reconstruction, the corresponding 4DCT phase was selected for each time point of the delivery. Baseline drifts were accounted for by rigidly shifting the CT to ensure correct relative beam‐to‐target positioning. Afterwards, the doses delivered to each 4DCT phase were accumulated deformably on the mid‐ventilation phase using research RayStation v4.6 and dose coverage of the GTV was evaluated.

Results:

When using the mid‐ventilation planning approach, dose coverage of the tumor deteriorated substantially in the presence of baseline drifts. The reduction in D98% coverage of the GTV in a single fraction ranged from 0.4‐1.2, 0.6‐3.3 and 4.5‐6.2Gy, respectively, for the different drift rates. With MLC tracking the GTV D98% coverage remained unchanged (+/− 0.1Gy) regardless of drift.

Conclusion:

Intrafractional baseline drifts reduce the tumor dose in treatments based on mid‐ventilation planning. In rare, large target baseline drifts tumor dose coverage may drop below the prescription, potentially affecting clinical outcome in hypofractionated treatment protocols. Dynamic MLC tracking preserves tumor dose coverage even in the presence of extreme baseline drifts.

We acknowledge financial and technical support of the MLC tracking research from Elekta AB. Research at ICR is supported by CRUK under Programme C33589/A19727 and NHS funding to the NIHR Biomedical Research Centre at RMH and ICR. MFF is supported by CRUK under Programme C33589/A19908.
SU‐G‐IeP1‐02: Automated SNR Analysis of MR Images Using Model‐Based Noise Determination
Authors: Krugh K
Published: July 2016

Purpose:

To develop a robust automated method of signal‐to‐noise (SNR) analysis from MR images using a single image acquisition approach and model‐based noise determination.

Methods:

Three consecutive MRI phantom scans were performed according to the SNR test procedures in the 2015 ACR MRI Quality Control Manual. This was repeated for several different RF coils and on MRI scanners from two different vendors. The three images from each RF coil were analyzed by the single‐image (SNR‐ACR1) and two‐image (SNR‐ACR2) SNR analysis methods also described in the ACR QC Manual. In addition the images were analyzed by the automated method (SNR‐AUTO). The SNR‐AUTO method utilizes an ImageJ macro file that was developed to 1) segment the phantom from the background region by means of a simple histogram‐based thresholding algorithm, 2) measure the signal from a ROI encompassing 80% of the phantom area, and 3) determine noise by fitting the histogram of the background region (devoid of the phase encode direction) to a noise distribution model established in the literature.

Results:

The accuracy of the SNR‐AUTO analysis method is demonstrated by it yielding SNR results that on average were −0.8% ± 6.7% of the SNR‐ACR1 method and 7.5% ± 8.6% of the SNR‐ACR2 method. The SNR‐AUTO method demonstrated a higher level of reproducibility (average COV = 0.32%) than that of the other two methods (average COV = 1.01% and 1.69% for SNR‐ACR1 and SNRACR2 respectively) both of which require manual placement of ROIs. An additional finding is that the model‐based noise determination is relatively insensitive to the presence of minor artifacts in the background region.

Conclusion:

The SNR‐AUTO method proved to be an accurate, highly reproducible, time‐efficient method for analysis of SNR in MR images and is insensitive to minor artifacts in the noise‐measuring region.
SU‐G‐IeP1‐04: Comparison of Cerebral Blood Volume Estimated by DSC‐ and DCEMRI
Authors: Aryal M , Cao Y
Published: July 2016

Purpose:

The cerebral blood volume (CBV) is commonly estimated from T2*/T2‐weighted dynamic susceptibility contrast (DSC) MRI acquired by an EPI sequence. There are several challenges with DSC imaging, including geometric distortion, limited brain spatial coverage, and unreliable arterial input function (AIF) due to the partial volume effect. However, CBV can be estimated from T1‐weighted dynamic contrast enhanced (DCE) MRI. This study aimed to examine whether CBV estimated from DCE‐MRI is comparable to one from DSC‐MRI. Methods and Materials: Of 16 patients with brain metastases, both DCE and DSC series were acquired on a 3T scanner. 3D T1‐weighted DCE images were acquired using a gradient‐echo (GRE) sequence, while 2D multi‐slice DSC (14–19 slices) were obtained using a GRE EPI sequence. CBV maps were generated from DCE images by the modified Toft model and from DSC images by a pharmacokinetic model with leakage correction. After image registration, CBV values estimated by the two methods were compared in two volumes of interest (VOIs) of normal appearing gray matter and white matter (NAGMWM) and in metastatic lesions at both voxel‐level and the VOI‐level.

Results:

In the two normal tissue VOIs, means (±std) of CBV were 2.04(±0.45)% and 1.86(±0.45)% from DCE imaging and 1.95(±0.46)% and 1.82(±0.44)% from DSC imaging, which were not significantly different in either VOIs. The voxel‐by‐voxel correlations within the two normal tissue VOIs led to averaged R=0.53 and 0.59 across 16 patients, suggesting high correlation between the two methods.

Conclusion:

The CBV estimated from DCE imaging was highly comparable to one from DSC imaging. The CBV estimated from DCE imaging is less affected by the susceptibility effect, and can cover the whole brain, which could be an alternative approach for the CBV estimation.

This research work was supported by NIH grant: U01 CA183848
SU‐G‐IeP1‐06: Estimating Relative Tissue Density From Quantitative MR Images: A Novel Perspective for MRI‐Only Heterogeneity Corrected Dose Calculation
Authors: Soliman A , Hashemi M , Safigholi H , Tchistiakova E , Song W
Published: July 2016

Purpose:

To explore the feasibility of extracting the relative density from quantitative MRI measurements as well as estimate a correlation between the extracted measures and CT Hounsfield units.

Methods:

MRI has the ability to separate water and fat signals, producing two separate images for each component. By performing appropriate corrections on the separated images, quantitative measurement of water and fat mass density can be estimated. This work aims to test this hypothesis on 1.5T.Peanut oil was used as fat‐representative, while agar as water‐representative. Gadolinium Chloride III and Sodium Chloride were added to the agar solution to adjust the relaxation times and the medium conductivity, respectively. Peanut oil was added to the agar solution with different percentages: 0%, 3%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%. The phantom was scanned on 1.5T GE Optima 450W with the body coil using a multigradient echo sequences. Water/fat separation were performed while correcting for main field (B0) inhomogeneity and T2* relaxation time. B1+ inhomogeneities were ignored. The phantom was subsequently scanned on a Philips Brilliance CT Big Bore. MR‐corrected fat signal from all vials were normalized to 100% fat signal. CT Hounsfield values were then compared to those obtained from the normalized MR‐corrected fat values as well as to the phantom for validation.

Results:

Good agreement were found between CT HU and the MR‐extracted fat values (R2 = 0.98). CT HU also showed excellent agreement with the prepared fat fractions (R2=0.99). Vials with 70%, 80%, and 90% fat percentages showed inhomogeneous distributions, however their results were included for completion.

Conclusion:

Quantitative MRI water/fat imaging can be potentially used to extract the relative tissue density. Further in‐vivo validation are required.
SU‐G‐IeP1‐09: MRI Evaluation of a Direction‐Modulated Brachytherapy (DMBT) Tandem Applicator for Cervical Cancer On 3T
Authors: Soliman A , Han D , Elzibak A , Safigholi H , Mashouf S , Owrangi A , Ravi A , Song W
Published: July 2016

Purpose:

To assess image quality and artifact extent of a novel direction modulated brachytherapy (DMBT) tandem applicator on a 3T MRI using various clinical imaging sequences.

Methods:

The tandem applicator is composed of a tungsten alloy with 6 peripheral grooves covered with a PEEK tip. An MR‐compatible phantom with similar dimensions to the female pelvis was manufactured. To visually assess the spatial shift of the applicator's tip, a mountable radial‐fiducial with 4 plastic rods, each of 3mm diameter, was designed to tightly fit on the applicator. The rods are separated by 16 mm and mounted at 90‐degree relative to one another. The pelvis phantom was filled with a solution of MnCl2 to mimic T2 relaxation time of the cervix (60‐80 ms at 3T).Imaging was performed on a 3T Philips Achieva using a 16‐channel Torso coil array. Four MR sequences were tested: T2‐weighted fast spin‐echo (T2w‐FSE), proton density weighted FSE (PDw‐FSE), T1‐weighted FSE (T1w‐FSE) and T1 weighted spoiled gradient echo (T1w‐GE). The spatial resolution was kept the same between all sequences: 0.6 × 0.6 × 3 mm3 with no slice gaps. Para‐sagittal images were acquired with the applicator fixed at a 30‐degree angle anterior to the B0‐ field to mimic clinical settings.

Results:

Minimal artifacts were observed on T2w‐FSE, PDw‐FSE and T1‐FSE, while significant artifacts were seen on T1w‐GE images. Artifacts induced in all 3 FSE sequences did not hinder accurate localisation of the tip and the applicator boundaries. The drift of the applicator's centreline from the radial fiducials was measured and found to be < 1 mm for the 3 FSE sequences.

Conclusion:

The tungsten–based DMBT applicator can be potentially used on 3T with various clinical sequences without inducing significant artifacts. Further validation on patients as well as the evaluation of relative SNR among the different sequences is required.
SU‐G‐JeP1‐03: Automatic Motion Tracking Reset in Ultrasound Liver Image Sequences
Authors: Xu Kele , W Ruixing , Zhu Li , Liu Chang , Zhao Yi
Published: July 2016

Purpose:

We explore an automatic anatomical landmarks tracking reset method in the ultrasound liver sequences, with the goal to improve the robustness and accuracy of the tracking.

Methods:

The proposed tracking failure re‐initialization method works as follows: before anatomic landmarks tracking is carried out, the image similarity coefficient is calculated (In our method, the complex wavelet structural similarity is used), between the region of interest (ROI) selected in current frame and the ROI in the first frame. If this similarity coefficient exceeds a set threshold, the positions of anatomical landmarks are reset to those which were input for the first frame. This provides a method to prevent accumulation of errors over long sequences, which can lead to erroneous tracking, and amounts to a sort of “automatic reset” of the tracking starting points based on initial a priori information.

Results:

The experiments are conducted to track the landmarks in the 5 volunteer B‐mode ultrasound liver sequences. The results were evaluated by comparison with manual annotations of liver feature (vessels) throughout each image sequence which were provided after automated tracking was complete. Tracking accuracy was evaluated using the Euclidean distance between tracked points and manually annotated points which was summarized by the mean. The mean error for all ROIs in different sequences are about 1–1.5 mm with the proposed automatic reset method, while the error is about 2 mm without the automatic reset method.

Conclusion:

Due to the periodic motion of the anatomical landmarks, the proposed image similarity‐based automatic re‐initialization method can improve the accuracy and robustness of the motion tracking in the ultrasound liver sequences. It may also be applied to other organs’ tracking problem using ultrasound imaging.
SU‐G‐JeP1‐05: Clinical Impact of MLC Tracking for Lung SABR
Authors: Caillet V , Colvill E , Szymura K , Stevens M , Booth J , Keall P
Published: July 2016

Purpose:

The objective of this study was to investigate the dosimetric benefits of multi‐leaf collimator (MLC) tracking for lung SABR treatments in end‐to‐end clinically realistic planning and delivery scenarios.

Methods:

The clinical benefits of MLC tracking were assessed using previously delivered treatment plans and physical experiments. The 10 most recent single lesion lung SABR patients were re‐planned following a 4D‐GTV‐based real‐time adaptive protocol (PTV defined as the end‐of‐exhalation GTV plus 5.0 mm margins). The plans were delivered on a Trilogy Varian linac. Electromagnetic transponders (Calypso, Varian Medical Systems, USA) were embedded into a programmable moving phantom (HexaMotion platform) tracked with the Varian Calypso system. For each physical experiment, the MLC positions were collected and used as input for dose reconstruction. For both planned and physical experiments, the OAR dose metrics from the conventional and real‐time adaptive SABR plans (Mean Lung Dose (MLD), V20 for lung, and near‐maximum dose (D2%) for spine and heart) were statistically compared. The Wilcoxon test was used to compare plan and physical experiment dose metrics.

Results:

While maintaining target coverage, percentage reductions in dose metrics to the OARs were observed for both planned and physical experiments. Comparing the two plans showed MLD percentage reduction (MLDr) of 25.4% (absolute differences of 1.41 Gy) and 28.9% (1.29%) for the V20r. D2% percentage reduction for spine and heart were respectively 27.9% (0.3 Gy) and 20.2% (0.3 Gy). For the physical experiments, MLDr was 23.9% (1.3 Gy), and V20r 37.4% (1.6%). D2% reduction for spine and heart were respectively 27.3% (0.3 Gy) and 19.6% (0.3 Gy). For both plans and physical experiments, significant OAR dose differences (p<0.05) were found between the conventional SABR and real‐time adaptive plans.

Conclusion:

Application of MLC tracking for lung SABR patients has the potential to reduce the dose to OARs during radiation therapy.
SU‐G‐TeP2‐12: IROCHouston and MDAPL SRS Anthropomorphic Phantom Results
Authors: Molineu A , Kry S , Alvarez P , Hernandez N , Nguyen T , Followill D
Published: July 2016

Purpose:

To report the results of SRS phantom irradiations

Methods:

Anthropomorphic SRS head phantoms were sent to institutions participating in NCI sponsored SRS clinical trials and institutions interested in verifying SRS treatment delivery. The phantom shell was purchased from Phantom Laboratory and altered to house dosimetry and imaging inserts. The imaging insert has 1.9 cm diameter spherical target. The dosimetry insert holds two TLD capsules and radiochromic film in the coronal and sagittal planes through the center of the target. Institutions were asked to image, plan and treat the phantom as they would an SRS patient. GammaKnife, CyberKnife and c‐arm accelerator institutions were asked to cover the target with 15 Gy, 20 Gy and 25 Gy, respectively. Following these guidelines and typical planning protocols for these three types of machines gives roughly 30 Gy to the center of the target for all units. Submission of the DICOM digital data set was required for analysis. Criteria of 5% for TLD results and 85% of pixels passing 5%/3mm gamma analysis were applied beginning in 2013.

Results:

The phantom was analyzed 269 times between the beginning of 2013 to present. The pass rate is 81%. Nineteen of the irradiation results failed only the TLD criteria, 19 failed only the film criteria and 12 failed both. Irradiations included 32 CyberKnife 23 GammaKnife, 3 TomoTherapy and 211 c‐arm units. Planning systems included Eclipse, Ergo, GammaPlan, Hi‐Art, iPlan, Monaco, MultiPlan, Pinnacle, RayStation, XiO and XKnife. Irradiations that were not accompanied with DICOM data were not included in this analysis.

Conclusion:

The phantom is a valuable end‐to‐end test used to independently verify the accuracy of SRS treatment delivery.

This investigation was supported by IROC grant CA180803 awarded by the NCI.
SU‐G‐IeP3‐01: Better Kerma‐Area‐Product (KAP) Estimation Using the System Parameters in Radiography and Fluoroscopy
Authors: Kim D , MacDougall R
Published: July 2016

Purpose:

Accurate values for Kerma‐Area‐Product (KAP) are needed for patient dosimetry and quality control for exams utilizing radiographic and/or fluoroscopic imaging. The KAP measured using a typical direct KAP meter built with parallel‐plate transmission ionization chamber is not precise and depends on the energy spectrum of diagnostic x‐rays. This study compared the accuracy and reproducibility of KAP derived from system parameters with values measured with a direct KAP meter.

Methods:

IEC tolerance for displayed KAP is specified up to ± 35% above 2.5 Gy‐cm2 and manufacturer's specifications are typically ± 25%. KAP values from the direct KAP meter drifts with time leading to replacement or re‐calibration. More precise and consistent KAP is achievable utilizing a database of known radiation output for various system parameters. The integrated KAP meter was removed from a radiography system. A total of 48 measurements of air kerma were acquired at x‐ray tube potential from 40 to 150 kVp with 10 kVp increment using ion chamber type external dosimeter at free‐in‐air geometry for four different types of filter combinations following the manufacturer's service procedure. These data were used to create updated correction factors that determine air kerma computationally for given system parameters. Results of calculated KAP were evaluated against results using a calibrated ion chamber based dosimeter and a computed radiography imaging plate to measure x‐ray field size.

Results:

The accuracy of calculated KAP from the system parameters was better within 4% deviation in all diagnostic x‐ray tube potentials tested from 50 to 140 kVp. In contrast, deviations of up to 25% were measured from KAP displayed from the direct KAP meter.

Conclusion:

The “calculated KAP” approach provides the nominal advantage of improved accuracy and precision of displayed KAP as well as reduced cost of calibrating or replacing integrated KAP meters.
SU‐G‐IeP3‐02: Characteristics of In‐Vivo MOSFET Dosimeters for Diagnostic X‐Ray Low‐Dose Measurements
Authors: Li S , Ali S , Harper K , Liang Q , Serratore D
Published: July 2016

Purpose:

To correct in‐vivo metal‐oxide‐semiconductor field‐effect transistor (MOSFET) dosimeters dependence on X‐ray energy, dose and dose rate, and temperature in order to measure doses or exposures on several anatomic points of interest undergoing some routine radiographs.

Methods:

A mobile MOSFET system (BEST Medical) was carefully calibrated with X‐ray at kVp of 70, 80, 100, 120, and 138 kVp, phantom temperatures at 0, 21, and 43 oC, and exposure range from 0.01 to 10 R confirmed with Raysafe and RadCal dosimeters. The MOSFETS were placed on the midline bladder or uterus, left pelvic iliac artery, left abdominal above iliac crest, abdominal midline anterior at inferior margin of stomach, and left pectoral of a large and a small body‐size cadavers undergoing AP/PA chest and lumber spine radiographs using manual and automatic exposure control (AEC) with and without lead shielding. MOSTFETs and TLD chips were also placed on the stomach, sigmoid, pubic symphysis, left and right pelvic walls of another cadaver for AP pelvic manual or AEC radiography prior to and after a left hip metal implant.

Results:

Individual MOSFET detectors had various low‐dose limits in ranged from 0.03 to 0.08 R, nonlinear response to X‐ray energy, and significant temperature effect of 15%. By accumulating 10 manual exposures and 20 AEC exposures, we achieved dose measured accuracy of 6%. There were up to 8 fold increases for AEC exposure of spine and chest X‐ray procedure from no shielding to with shielding. For pelvic radiography, exposure to public symphysis was the highest even higher than that of the skin. After hip implant, AEC pelvic radiograph increase exposure by 30 to 200% consistent with results of TLDs.

Conclusion:

Dependence of energy, temperature and dose limit were accurately corrected. We have found significant exposure for those clinical pr°ocedures and the study provided evidences for developing new clinical procedures.
SU‐G‐IeP3‐09: Investigating the Interplay of Antiscatter Grids with Modern Detectors and Image Processing in Digital Radiography
Authors: Sanchez A , Little K , Baad M , Reiser I , Lu ZF , Feinstein K
Published: July 2016

Purpose:

To use phantom and simulation experiments to relate technique factors, patient size and antiscatter grid use to image quality in portable digital radiography (DR), in light of advancements in detector design and image processing.

Methods:

Image contrast‐to‐noise ratio (CNR) on a portable DR system (MobileDaRt Evolution, Shimadzu) was measured by imaging four aluminum inserts of varying thickness, superimposed on a Lucite slab phantom using a pediatric abdominal protocol. Three thicknesses of Lucite were used: 6.1cm, 12cm, and 18.2cm, with both 55 and 65 kVp beams. The mAs was set so that detector entrance exposure (DEE) was matched between kVp values. Each technique and phantom was used with and without an antiscatter grid (focused linear grid embedded in aluminum with an 8:1 ratio). The CNR‐improvement‐factor was then used to determine the thickness‐ and technique‐dependent appropriateness of grid use. Finally, the same experiment was performed via Monte Carlo simulation, integrating incident energy fluence at each detector pixel, so that effects of detector design and image processing could be isolated from physical factors upstream of the detector.

Results:

The physical phantom experiment demonstrated a clear improvement for the lower tube voltage (55kVp), along with substantial CNR benefits with grid use for 12–18cm phantoms. Neither trend was evident with Monte Carlo, suggesting that suboptimal quantum‐detection‐efficiency and automated grid‐removal could explain trends in kVp and grid use, respectively.

Conclusion:

Physical experiments demonstrate marked improvement in CNR when using a grid for phantoms of 12 and 18cm Lucite thickness (above ∼10cm soft‐tissue equivalent). This benefit is likely due to image processing, as this result was not seen with Monte Carlo. The impact of image processing on image resolution should also be investigated, and the CNR benefit of low kVp and grid use should be weighed against the increased exposure time necessary to achieve adequate DEE.
SU‐G‐JeP3‐10: Update On a Real‐Time Treatment Guidance System Using An IR Navigation System for Pleural PDT
Authors: Kim M , Penjweini R , Zhu T
Published: July 2016

Purpose:

Photodynamic therapy (PDT) is used in conjunction with surgical debulking of tumorous tissue during treatment for pleural mesothelioma. One of the key components of effective PDT is uniform light distribution. Currently, light is monitored with 8 isotropic light detectors that are placed at specific locations inside the pleural cavity. A tracking system with real‐time feedback software can be utilized to improve the uniformity of light in addition to the existing detectors.

Methods:

An infrared (IR) tracking camera is used to monitor the movement of the light source. The same system determines the pleural geometry of the treatment area. Software upgrades allow visualization of the pleural cavity as a two‐dimensional volume. The treatment delivery wand was upgraded for ease of light delivery while incorporating the IR system. Isotropic detector locations are also displayed. Data from the tracking system is used to calculate the light fluence rate delivered. This data is also compared with in vivo data collected via the isotropic detectors. Furthermore, treatment volume information will be used to form light dose volume histograms of the pleural cavity.

Results:

In a phantom study, the light distribution was improved by using real‐time guidance compared to the distribution when using detectors without guidance. With the tracking system, 2D data can be collected regarding light fluence rather than just the 8 discrete locations inside the pleural cavity. Light fluence distribution on the entire cavity can be calculated at every time in the treatment.

Conclusion:

The IR camera has been used successfully during pleural PDT patient treatment to track the motion of the light source and provide real‐time display of 2D light fluence. It is possible to use the feedback system to deliver a more uniform dose of light throughout the pleural cavity.
SU‐G‐JeP3‐13: Use of Volumetric Indices to Study the Viability of Respiratory Gating in Conjunction with Abdominal Compression in the Management of Non‐Small Cell Lung Cancer Tumors Using Stereotactic Body Radiation Therapy Under the Conditions of Controlled Breathing
Authors: Malhotra H , Gomez J
Published: July 2016

Purpose:

AAPM TG‐76 report advises lung patients experiencing tumor motion >5mm to use some form of motion management with even smaller limit for complex/special procedures like SBRT. Generally, either respiratory gating or abdominal compression is used for motion management. In this retrospective study, we are using an innovative index, Volumetric Indices (VI) = (GTVnn AND GTV50+Xmm)/(GTVnn) to quantify how much of the tumor remains within 1, 2, and 3mm margins throughout the breathing cycle using GTV50+Xmm margin on GTV50[nn=0,10,20,…90]. Using appropriate limits, VI can provide tumor motion information and to check if RPM gates could have been used in conjunction with abdominal compression to better manage tumor motion.

Methods:

64 SBRT patients with a total of 67 lung tumors were studied. 4DCT scans were taken, fully capturing tumor motion throughout the 10 phases of the breathing cycle. For each phase, Gross Tumor Volume (GTV) was segmented and appropriates structures were defined to determine VI values. For the 2mm margin, VI values less than 0.95 for peripheral lesions and 0.97 for central lesions indicate tumor movement greater than 4mm. VI values for 1mm and 3mm margins were also analyzed signifying tumor motion of 2mm & 6mm, respectively.

Results:

Of the 64 patients, 35 (55%) had motion greater than 4mm & could have benefited from respiratory gating. For 5/8 (63%) middle lobe lesions, 21/27 (78%) lower lobe lesions, and 10/32 (31%) upper lobe lesions, gating could have resulted in smaller ITV. 32/55 (58%) peripheral lesions and 4/12 (33%) central lesions could have had gating. Average ITV decreased by 1.25cc (11.43%) and average VI increased by 0.11.

Conclusion:

Out of 64 patients, 55% exhibited motion greater than 4mm even with abdominal compression. Even with abdominalcompression, lung tumors can move >4mm as the degree of pressure which a patient can tolerate, is patient specific.
SU‐G‐JeP3‐14: Positioning and Dosimetric Uncertainties in Image‐Guided Radiation Therapy with Respiratory Gating
Authors: Ali I , Hossain S , Algan O , Syzek E , Ahmad S
Published: July 2016

Purpose:

To investigate quantitatively positioning and dosimetric uncertainties due to 4D‐CT intra‐phase motion in the internal‐target‐volume (ITV) associated with radiation therapy using respiratory‐gating for patients setup with image‐guidance‐radiation‐therapy (IGRT) using free‐breathing or average‐phase CT‐images.

Methods:

A lung phantom with an embedded tissue‐equivalent target is imaged with CT while it is stationary and moving. Four‐sets of structures are outlined: (a) the actual target on CT‐images of the stationary‐target, (b) ITV on CT‐images for the free‐moving phantom, (c) ITV's from the ten different phases (10–100%) and (d) ITV on the CT‐images generated from combining 3 phases: 40%–50%–60%. The variations in volume, length and center‐position of the ITV's and their effects on dosimetry during dose delivery for patients setup with image‐guidance are investigated.

Results:

Intra‐phase motion due to breathing affects the volume, center position and length of the ITVs from different respiratory‐phases. The ITV's vary by about 10% from one phase to another. The largest ITV is measured on the free breathing CT images and the smallest is on the stationary CT‐images. The ITV lengths vary by about 4mm where it may shrink or elongated depending on the motion‐phase. The center position of the ITV varies between the different motion‐phases which shifts upto 10mm from the stationary‐position which is nearly equal to motion‐amplitude. This causes systematic shifts during dose delivery with beam gating using certain phases (40%–50%–60%) for patients setup with IGRT using free‐breathing or average‐phase CT‐images. The dose coverage of the ITV depends on the margins used for treatment‐planning‐volume where margins larger than the motion‐amplitudes are needed to ensure dose coverage of the ITV.

Conclusion:

Volume, length, and center position of the ITV's change between the different motion phases. Large systematic shifts are induced by respiratory‐gating with ITVs on certain phases when patients are setup with IGRT using free‐breathing or average‐phase CT‐images.
SU‐G‐TeP3‐07: On the Development of Mechano‐Biological Assessment of Leukemia Cells Using Optical Tweezers
Authors: Brost E , Brooks J , Piepenburg J , Chakraborty S , Das T , Green A , Watanabe Y , Hui S
Published: July 2016

Purpose:

Patients with BCR‐ABL (Ph +ve) acute lymphoblastic leukemia are at very high risk of relapse and mortality. In line with the NIH mission to understand the physical and biological processes, we seek to report mechano‐biological method to assessment and distinguish treated/untreated leukemia cells.

Methods:

BCR‐ABL leukemia cell populations and silica microspheres were trapped in a 100x magnification optical trapping system (λ=660 nm, 70 mW). Light refracted through the trapped sample was collected in the back focal plane by a quadrant detector to measure the positions of individual cells. The sample was driven at a known frequency and amplitude with a flexure translation stage, and the target's response was recorded. The measured response was calibrated using the known driving parameters, and information about cell movements due to mechano‐biological effects was extracted. Two leukemia cell populations were tested: a control group and a group treated with 2 Gy.

Results:

The mechano‐biological movements of 10 microspheres, control cells, and treated cells were tracked over a ∼30 minute window at 1 minute intervals. The microsphere population did not see significant change in mechano‐biological movements over the testing interval and remained constant. The control cell population saw a two‐fold rise in activity that peaked around 1200 seconds, then dropped off sharply. The treated cell population saw a two‐fold rise in activity that peaked at 400 seconds, and dropped off slowly.

Conclusion:

The investigated technique allows for direct measurement the movements of a trapped object due to mechano‐biological effects such as thermal and extracellular motion. When testing microspheres, the mechano‐biological activity remained constant over time due to the lack of biological factors. In both the control and treated cell populations, the mechano‐biological activity was increased, possibly due to mitochondrial activation. This extra activity decreased over time, possibly due to cellular damage from trapping radiation.
SU‐G‐TeP3‐11: Radiobiological‐Cum‐Dosimetric Quality Assurance of Complex Radiotherapy Plans
Authors: Paudel N , Narayanasamy G , Zhang X , Penagaricano J , Mavroidis P , Pyakuryal A , Han E , Liang X , Kim D , Morrill S
Published: July 2016

Purpose:

Dosimetric gamma‐analysis used for QA of complex radiotherapy plans tests the dosimetric equivalence of a delivered plan with the treatment planning system (TPS) optimized plan. It does not examine whether a dosimetric difference results in any radiobiological difference. This study introduces a method to test the radiobiological and dosimetric equivalence between a delivered and the TPS optimized plan.

Methods:

Six head and neck and seven lung cancer VMAT or IMRT plans optimized for patient treatment were calculated and delivered to an ArcCheck phantom. ArcCheck measured dose distributions were compared with the TPS calculated dose distributions using a 2‐D gamma‐analysis. Dose volume histograms (DVHs) for various patient structures were obtained by using measured data in 3DVH software and compared against the TPS calculated DVHs using 3‐D gamma analysis. DVH data were used in the Poisson model to calculate tumor control probability (TCP) for the treatment targets and in the sigmoid dose response model to calculate normal tissue complication probability (NTCP) for the normal structures.

Results:

Two‐D and three‐D gamma passing rates among six H&N patient plans differed by 0 to 2.7% and among seven lung plans by 0.1 to 4.5%. Average ± SD TCPs based on measurement and TPS were 0.665±0.018 and 0.674±0.044 for H&N, and 0.791±0.027 and 0.733±0.031 for lung plans, respectively. Differences in NTCPs were usually negligible. The differences in dosimetric results, TCPs and NTCPs were insignificant.

Conclusion:

The 2‐D and 3‐D gamma‐analysis based agreement between measured and planned dose distributions may indicate their dosimetric equivalence. Small and insignificant differences in TCPs and NTCPs based on measured and planned dose distributions indicate the radiobiological equivalence between the measured and optimized plans. However, patient plans showing larger differences between 2‐D and 3‐D gamma‐analysis can help us make a more definite conclusion through our ongoing research with a larger number of patients.
SU‐G‐IeP4‐01: A Simple Doppler Flow Phantom Design for Evaluation of Doppler Ultrasound Systems
Authors: Ozus B , Chen J , Beeson J , Feng J
Published: July 2016

Purpose:

There are a number of commercially available flow phantoms for evaluating Doppler ultrasound systems. However, it may be hard to justify purchasing these phantoms if a hospital has a small number of ultrasound units to evaluate. In this study, we developed a simple flow phantom with parts available in a hospital to evaluate Doppler ultrasound systems.

Methods:

To create a flow reserve, one end of an IV line was connected to a 100 ml saline bag and the line was filled with saline. 20 ml of glycerin was injected into the saline bag to simulate blood like flow characteristics. The other end of the IV line was also connected to the saline bag to create a loop. The IV line was fed into an infusion pump (programmable up to 999 ml/hr) and was also placed between a uniform ultrasound phantom and a standoff gel pad. To minimize impedance differences, acoustic gel was used between the phantom and the gel pad. Doppler measurements were performed on two Philips iU22 ultrasound units using the L12‐5 probes.

Results:

The pulsatile flow of the solution in the IV line could be seen in the Doppler mode when the infusion pump was running. The color Doppler also indicated the direction of the flow via overlaid red or blue color on the grayscale B‐mode ultrasound image of the IV line. The directionality of the flow could be confirmed by reversing the direction of the probe. The peak flow rates (cm/s) observed on the waveforms were reproducible within %10 when the measurements were repeated.

Conclusion:

A simple flow phantom can be developed from materials available in a hospital for routine evaluation of Doppler ultrasound systems.
SU‐G‐IeP4‐12: Performance of In‐111 Coincident Gamma‐Ray Counting: A Monte Carlo Simulation
Authors: Pahlka R , Kappadath S , Mawlawi O
Published: July 2016

Purpose:

The decay of In‐111 results in a non‐isotropic gamma‐ray cascade, which is normally imaged using a gamma camera. Creating images with a gamma camera using coincident gamma‐rays from In‐111 has not been previously studied. Our objective was to explore the feasibility of imaging this cascade as coincidence events and to determine the optimal timing resolution and source activity using Monte Carlo simulations.

Methods:

GEANT4 was used to simulate the decay of the In‐111 nucleus and to model the gamma camera. Each photon emission was assigned a timestamp, and the time delay and angular separation for the second gamma‐ray in the cascade was consistent with the known intermediate state half‐life of 85ns. The gamma‐rays are transported through a model of a Siemens dual head Symbia “S” gamma camera with a 5/8‐inch thick crystal and medium energy collimators. A true coincident event was defined as a single 171keV gamma‐ray followed by a single 245keV gamma‐ray within a specified time window (or vice versa). Several source activities (ranging from 10uCi to 5mCi) with and without incorporation of background counts were then simulated. Each simulation was analyzed using varying time windows to assess random events. The noise equivalent count rate (NECR) was computed based on the number of true and random counts for each combination of activity and time window. No scatter events were assumed since sources were simulated in air.

Results:

As expected, increasing the timing window increased the total number of observed coincidences albeit at the expense of true coincidences. A timing window range of 200–500ns maximizes the NECR at clinically‐used source activities. The background rate did not significantly alter the maximum NECR.

Conclusion:

This work suggests coincident measurements of In‐111 gamma‐ray decay can be performed with commercial gamma cameras at clinically‐relevant activities. Work is ongoing to assess useful clinical applications.
SU‐G‐IeP4‐14: Prostate Brachytherapy Activity Measurement and Source Localization by Using a Dual Photon Emission Computed Tomography System: A Feasibility Study
Authors: Lin C , Tsai Y , Lin H , Chuang K , Chiang C
Published: July 2016

Purpose:

To monitor the activity distribution and needle position during and after implantation in operating rooms.

Methods:

Simulation studies were conducted to assess the feasibility of measurement activity distribution and seed localization using the DuPECT system. The system consists of a LaBr3‐based probe and planar detection heads, a collimation system, and a coincidence circuit. The two heads can be manipulated independently. Simplified Yb‐169 brachytherapy seeds were used. A water‐filled cylindrical phantom with a 40‐mm diameter and 40‐mm length was used to model a simplified prostate of the Asian man. Two simplified seeds were placed at a radial distance of 10 mm and tangential distance of 10 mm from the center of the phantom. The probe head was arranged perpendicular to the planar head. Results of various imaging durations were analyzed and the accuracy of the seed localization was assessed by calculating the centroid of the seed.

Results:

The reconstructed images indicate that the DuPECT can measure the activity distribution and locate the seeds dwelt in different positions intraoperatively. The calculated centroid on average turned out to be accurate within the pixel size of 0.5 mm. The two sources were identified when the duration is longer than 15 s. The sensitivity measured in water was merely 0.07 cps/MBq.

Conclusion:

Preliminary results show that the measurement of the activity distribution and seed localization are feasible using the DuPECT system intraoperatively. It indicates the DuPECT system has potential to be an approach for dose‐distribution‐validation. The efficacy of acvtivity distribution measurement and source localization using the DuPECT system will evaluated in more realistic phantom studies (e.g., various attenuation materials and greater number of seeds) in the future investigation.
SU‐G‐JeP4‐04: Commissioning and Acceptance Testing of Optical Surface Monitoring System On TrueBEAM STx as Per Task Group 147
Authors: Mhatre V , Patwe P , Dandekar P
Published: July 2016

Purpose:

Optical Surface Monitoring system (OSMS) have been recently introduced by Varian for initial patient positioning and real‐time monitoring during complex radiotherapy treatment. The purpose of this work was to implement TG 147 with OSMS.

Methods:

Recently we installed OSMS first of its kind in India on trueBEAM STx at our Institue. The OSMS is composed of a three cameras ceiling mounted and a Workstation. The following tests were performed to validate the system a. Calibration b. System reproducibility and drift c. Static localization displacement accuracy and d. Dynamic radiation gating delivery. The Calibration procedure consists of Daily,Monthly and MV Radiation Isocenter Calibration. The reproducibility of system was tested by monitoring the varian gating phantom test pattern for at least 120 min. Each recorded pattern was registered to the reference surface to calculate the required couch adjustment. To measure the static localization displacement accuracy of the system to detect and quantify patient shift relative to a reference image,we compared the shift detected by the surface imaging system with known couch transitions in a phantom study. The phantom was set in a motion and the radiation beam was holded by changing the threshold in the software for different clinical setups to test the dynamic radiation gating capability.

Results:

Daily calibration was within ±0.5 mm. The MV radiation isocentre with respect to cameras was less than 1 mm in translational axis and less than 0.5° for rotational axis. The reproducibility was found to be 0.4 mm. The maximum static displacement accuracy was 0.75 mm for the three translational axis, and less than 0.5° for rotational axis. The system was able to hold the beam with a minimum threshold of 1 mm.

Conclusion:

A quality assurance process has been developed as per TG 147 for the clinical implementation of an OSMS in radiation therapy.
SU‐G‐JeP4‐07: Evaluation of Intrafraction Motion Using 3D Surface Guided Radiation Therapy in Lung SBRT
Authors: Jermoumi M , Cao D , Mehta V , Shepard D
Published: July 2016

Purpose:

Surface guided radiation therapy (SGRT) uses stereoscopic video images in combination with patterns projected onto the patient's surface to dynamically capture and reconstruct a 3D surface map. In this work, we used a C‐RAD Catalyst HD system (C‐RAD) to evaluate intrafraction motion in the delivery of lung SBRT.

Methods:

The surface acquired from the 4DCT images from our preliminary cohort of eight lung cancer patients treated with SBRT were matched to the surface images acquired prior to each treatment. Additionally, a CBCT image set was acquired. A linear regression model was established between the external and internal motion of tumor during pretreatment and used to predict the CBCT deviation during treatment. The shifts determined from CBCT and the shifts from surface map imaging were compared and assessed using Bland‐Altman method. For intrafraction motion, we assessed the percentage of mean errors that fell outside of the threshold of 2 mm, 3 mm, and 5 mm along the translational directions. The required PTV margin was quantified over the course of treatment. The correlation between intrafraction treatment time and mean error of 3D displacement was evaluated using the Pearson coefficient, r

Results:

A total of 7971 data points were analyzed. Deviations of 2mm, 3mm, and 5mm were observed less than 7%, 2 %, and 0 % of the time along the translational direction. CBCT and Catalyst showed close agreement during patient positioning. Furthermore, the calculated PTV margins were less than our clinical tolerance of 5 mm. Using the Pearson coefficient r,the mean error of 3D displacement showed significant correlation with treatment time (r=0.69, p= 0.000002).

Conclusion:

SGRT can be used to ensure accurate patient positioning during treatment without an additional delivery of dose to the patient. This study shows that importance of treatment time as a consideration during the treatment planning process.