bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐134: Optimizing Technical Parameters for Using Atlas Based Automatic Segmentation for Evaluation of Contour Accuracy Experience with Cardiac Structures From NRG Oncology/RTOG 0617
Authors: Yu J , Gong Y , Bar‐Ad V , Giaddui T , Hu C , Gore E , Wheatley M , Witt J , Robinson C , Kong F , Bradley J , Galvin J , Xiao Y
Published: June 2015

Purpose:

Accurate contour delineation is crucial for radiotherapy. Atlas based automatic segmentation tools can be used to increase the efficiency of contour accuracy evaluation. This study aims to optimize technical parameters utilized in the tool by exploring the impact of library size and atlas number on the accuracy of cardiac contour evaluation.

Methods:

Patient CT DICOMs from RTOG 0617 were used for this study. Five experienced physicians delineated the cardiac structures including pericardium, atria and ventricles following an atlas guideline. The consistency of cardiac structured delineation using the atlas guideline was verified by a study with four observers and seventeen patients. The CT and cardiac structure DICOM files were then used for the ABAS technique.To study the impact of library size (LS) and atlas number (AN) on automatic contour accuracy, automatic contours were generated with varied technique parameters for five randomly selected patients. Three LS (20, 60, and 100) were studied using commercially available software. The AN was four, recommended by the manufacturer. Using the manual contour as the gold standard, Dice Similarity Coefficient (DSC) was calculated between the manual and automatic contours. Five‐patient averaged DSCs were calculated for comparison for each cardiac structure.In order to study the impact of AN, the LS was set 100, and AN was tested from one to five. The five‐patient averaged DSCs were also calculated for each cardiac structure.

Results:

DSC values are highest when LS is 100 and AN is four. The DSC is 0.90±0.02 for pericardium, 0.75±0.06 for atria, and 0.86±0.02 for ventricles.

Conclusion:

By comparing DSC values, the combination AN=4 and LS=100 gives the best performance.

This project was supported by NCI grants U24CA12014, U24CA180803, U10CA180868, U10CA180822, PA CURE grant and Bristol‐Myers Squibb and Eli Lilly.
SU‐E‐J‐135: Feasibility of Using Quantitative Cone Beam CT for Proton Adaptive Planning
Authors: Jingqian W , Tsui T , Wei J , Wang Q , Zhang X , Wen Z , Zhu X , Frank S , Li H , Zhu L
Published: June 2015

Purpose:

To investigate the feasibility of using scatter corrected cone beam CT (CBCT) for proton adaptive planning.

Methods:

Phantom study was used to evaluate the CT number difference between the planning CT (pCT), quantitative CBCT (qCBCT) with scatter correction and calibrated Hounsfield units using adaptive scatter kernel superposition (ASKS) technique, and raw CBCT (rCBCT). After confirming the CT number accuracy, prostate patients, each with a pCT and several sets of weekly CBCT, were investigated for this study. Spot scanning proton treatment plans were independently generated on pCT, qCBCT and rCBCT. The treatment plans were then recalculated on all images. Dose‐volume‐histogram (DVH) parameters and gamma analysis were used to compare between dose distributions.

Results:

Phantom study suggested that Hounsfield unit accuracy for different materials are within 20 HU for qCBCT and over 250 HU for rCBCT. For prostate patients, proton dose could be calculated accurately on qCBCT but not on rCBCT. When the original plan was recalculated on qCBCT, tumor coverage was maintained when anatomy was consistent with pCT. However, large dose variance was observed when patient anatomy change. Adaptive plan using qCBCT was able to recover tumor coverage and reduce dose to normal tissue.

Conclusion:

It is feasible to use qu antitative CBCT (qCBCT) with scatter correction and calibrated Hounsfield units for proton dose calculation and adaptive planning in proton therapy.

Partly supported by Varian Medical Systems.
SU‐E‐J‐139: One Institution's Experience with Surface Imaging in Proton Therapy
Authors: Zhao L , Singh H , Zheng Y
Published: June 2015

Purpose:

X‐ray system is commonly used for IGRT in proton therapy, however image acquisition not only increases treatment time but also adds imaging dose. We studied a 3D surface camera system (AlignRT) performance for proton therapy.

Methods:

System accuracy was evaluated with rigid phantom under two different camera location configurations. For initial clinical applications, post mastectomy chest wall and partial breast treatments were studied. X‐ray alignment was used as our ground truth. Our studies included: 1) comparison of daily patient setup shifts between X‐ray alignment and SI calculation; 2) interfractional breast surface position variation when aligning to bony landmark on X‐ray; 3) absolute positioning using planning CT DICOM data; 4) shifts for multi‐isocenter treatment plan; 5) couch isocentric rotation accuracy.

Results:

Camera locations affected the system performance. After camera relocation, the accuracy of the system for the rigid phantom was within 1 mm (fixed couch), and 1.5 mm (isocentric rotation). For intrafractional patient positioning, X‐ray and AlignRT shifts were highly correlated (r=0.99), with the largest difference (mean ± SD) in the longitudinal direction (2.14 ± 1.02 mm). For interfractional breast surface variation and absolute positioning, there were still larger disagreements between the two modalities due to different focus on anatomical landmarks, and 95% of the data lie within 5mm with some outliers at 7 mm–9 mm. For multi‐isocenter shifts, the difference was 1 ± 0.56 mm over an 11 cm shift in longitudinal direction. For couch rotation study, the differences was 1.36 ± 1.0 mm in vertical direction, 3.04 ± 2.11 mm in longitudinal direction, and 2.10 ± 1.66 mm in lateral direction, with all rotation differences < 1.5 degree.

Conclusion:

Surface imaging is promising for intrafractional treatment application in proton therapy to reduce X‐ray frequency. However the interfractional discrepancy between the X‐ray and SI requires future validation.
SU‐E‐J‐140: Simulation Study Using Thermoacoustics to Image Proton Dose and Range in Water and Skull Phantom
Authors: Stantz K , Moskvin V
Published: June 2015

Purpose:

In this study, thermoacoustic pressure signals generated from a proton beam were simulated in water and currently within a skull phantom to investigate the sensitivity of radioacoustic CT imaging in the brain.

Methods:

Thermoacoustically generated pressure signals from a pulse pencil proton beam (12, 15, 20, and 27cm range) were simulated in water. These simulated pressure signal are detected using a (71) transducer array placed along the surface of a cylinder (30cm × 40cm) and rotated over 2π (in 2 degree increments), where the normal vector to the surface of each transducer intersects the isocenter of the scanner. Currently, a software skull phantom is positioned at isocenter, where the scattering, absorption and speed of dispersion of the thermoacoustic signal through a three layer cortical‐trabecular‐cortical structure is being simulated. Based on data obtained from the literature, the effects of acoustic attenuation and speed‐of‐sound (dispersion) will be applied within the 3D FBP algorithm to obtain dosimetric images.

Results:

Based on hydrophone detector specifications, a 0.5MHz bandwidth and 50dB re 1μPa per Hz^1/2, a 1.6cGy sensitivity at the Bragg peak was demonstrated while maintaining a 1.0 mm (FWHM) range resolution along the central axis of the beam. Utilizing this same information, the integral dose within the Bragg peak and distal edge compared to MC had a 2% (statistical) and 5% voxel‐based RMS at this same dose sensitivity. We plan to present preliminary data determining the range sensitivity for a head phantom for this scanner design and the feasibility of imaging the proton dose in patients with a brain tumor undergoing therapy.

Conclusion:

RACT scanner provides 3D dosimetric images with 1.6cGy (Bragg peak) sensitivity with 1mm range sensitivity. Simulations will be performed to determine feasibility to treat brain cancer patients.
SU‐E‐J‐150: Four‐Dimensional Cone‐Beam CT Algorithm by Extraction of Physical and Motion Parameter of Mobile Targets Retrospective to Image Reconstruction with Motion Modeling
Authors: Ali I , Alsbou N , Ahmad S
Published: June 2015

Purpose:

To develop 4D‐cone‐beam CT (CBCT) algorithm by motion modeling that extracts actual length, CT numbers level and motion amplitude of a mobile target retrospective to image reconstruction by motion modeling.

Methods:

The algorithm used three measurable parameters: apparent length and blurred CT number distribution of a mobile target obtained from CBCT images to determine actual length, CT‐number value of the stationary target, and motion amplitude. The predictions of this algorithm were tested with mobile targets that with different well‐known sizes made from tissue‐equivalent gel which was inserted into a thorax phantom. The phantom moved sinusoidally in one‐direction to simulate respiratory motion using eight amplitudes ranging 0–20mm.

Results:

Using this 4D‐CBCT algorithm, three unknown parameters were extracted that include: length of the target, CT number level, speed or motion amplitude for the mobile targets retrospective to image reconstruction. The motion algorithms solved for the three unknown parameters using measurable apparent length, CT number level and gradient for a well‐defined mobile target obtained from CBCT images. The motion model agreed with measured apparent lengths which were dependent on the actual target length and motion amplitude. The gradient of the CT number distribution of the mobile target is dependent on the stationary CT number level, actual target length and motion amplitude. Motion frequency and phase did not affect the elongation and CT number distribution of the mobile target and could not be determined.

Conclusion:

A 4D‐CBCT motion algorithm was developed to extract three parameters that include actual length, CT number level and motion amplitude or speed of mobile targets directly from reconstructed CBCT images without prior knowledge of the stationary target parameters. This algorithm provides alternative to 4D‐CBCT without requirement to motion tracking and sorting of the images into different breathing phases which has potential applications in diagnostic CT imaging and radiotherapy.
SU‐E‐J‐152: Synthetic Gated CBCT Imaging for Lung SBRT
Authors: Li X , Zhang P , Gewanter R , Chan M , Tang X , Hunt M
Published: June 2015

Purpose:

Due to slow scanning speed, when free breathing CBCT (FBCBCT) is used to localize target in lung SBRT treatment, respiratory motion induced image artifacts may degrade the image quality and compromise the target positioning accuracy. The purpose of this study is to investigate the feasibility of synthetic gated CBCT (SGCBCT) imaging for lung SBRT treatment.

Methods:

Two Lung SBRT patients were selected for this study. The amplitudes of tumor respiratory motion were 1.2cm and 3.0cm (Superior‐Inferior).Each Lung SBRT patient underwent FBCBCT scan, and then the acquired projection images were exported to an in‐house program for off‐line analysis. Firstly a semi‐automatic algorithm was used to trace the diaphragm movement from those projection images in order to correlate respiratory phases with each projection image. Secondly, a Feldkamp‐Davis‐Kress (FDK) algorithm was utilized to reconstruct the gated CBCT (GCBCT) images based on the projection images within the gating windows (35∼65% for exhale; 85∼15% for inhale). Thirdly, the bony structures were automatically segmented from FBCBCT images using Fuzzy C‐mean segmentation method. Finally, the SGCBCT was generated by replacing the HU value of the GCBCT image with the value of FBCBCT image for the voxels that belong to the bony structure based on the above segmentation results.

Results:

Due to the respiratory motion effect, the targets determined by FBCBCT have reduced image contrast and blurred boundary between tumor and surrounding normal lung tissues. Compared to FBCBCT, the SGCBCT images at exhale and inhale not only delineate the target with enhanced image contrast and much clearer boundary with less motion artifacts, but also determine the amplitudes of tumor respiratory motion.

Conclusion:

SGCBCT provides better representation of the moving lung tumor with less motion artifacts, and has a potential to improve the positioning accuracy in lung SBRT treatment.
SU‐E‐J‐153: Reconstructing 4D Cone Beam CT Images for Clinical QA of Lung SABR Treatments
Authors: Beaudry J , Cropp R , Bergman A
Published: June 2015

Purpose:

To verify that the planned Primary Target Volume (PTV) and Internal Gross Tumor Volume (IGTV) fully enclose a moving lung tumor volume as visualized on a pre‐SABR treatment verification 4D Cone Beam CT.

Methods:

Daily 3DCBCT image sets were acquired immediately prior to treatment for 10 SABR lung patients using the on‐board imaging system integrated into a Varian TrueBeam (v1.6: no 4DCBCT module available). Respiratory information was acquired during the scan using the Varian RPM system. The CBCT projections were sorted into 8 bins offline, both by breathing phase and amplitude, using in‐house software. An iterative algorithm based on total variation minimization, implemented in the open source reconstruction toolkit (RTK), was used to reconstruct the binned projections into 4DCBCT images. The relative tumor motion was quantified by tracking the centroid of the tumor volume from each 4DCBCT image. Following CT‐CBCT registration, the planning CT volumes were compared to the location of the CBCT tumor volume as it moves along its breathing trajectory. An overlap metric quantified the ability of the planned PTV and IGTV to contain the tumor volume at treatment.

Results:

The 4DCBCT reconstructed images visibly show the tumor motion. The mean overlap between the planned PTV (IGTV) and the 4DCBCT tumor volumes was 100% (94%), with an uncertainty of 5% from the 4DCBCT tumor volume contours. Examination of the tumor motion and overlap metric verify that the IGTV drawn at the planning stage is a good representation of the tumor location at treatment.

Conclusion:

It is difficult to compare GTV volumes from a 4DCBCT and a planning CT due to image quality differences. However, it was possible to conclude the GTV remained within the PTV 100% of the time thus giving the treatment staff confidence that SABR lung treatements are being delivered accurately.
SU‐E‐J‐157: Comparison Between Internal Respiratory Signal and External Respiratory Signal in 4D CT
Authors: Suh Y , Hui C , Robertson D , Pan T , Das P , Crane C , Beddar S
Published: June 2015

Purpose:

To investigate the effectiveness of using a Fourier transformbased internal respiratory signal (IRS) to sort four‐dimensional (4D) CT images, compared to images sorted using the external respiratory signal from the real‐time position management (RPM) system.

Methods:

80 patients with abdominal or thoracic cancers were retrospectively selected for this study. The IRS were computed using an algorithm previously described by our group. 4D images were then sorted using the end inspiration times calculated from the IRS. We compared the IRS to the RPM signals by assessing their similarities using the normalized cross correlation (NCC), and the end inspiration times identified from the respective signals. The IRS‐sorted 4D images were also compared to the RPM‐sorted clinical images using a correlation‐based metric to compare their image qualities.

Results:

In 90% of the data sets, the IRS matched with the RPM signal with NCC >= 0.5. In this cohort of matching signals, the average difference between end inspiration times from the IRS and RPM signal was 0.11 s. In the remaining 10% of the data sets, the IRS did not match the RPM signal in at least one couch position (NCC < 0.5). The average difference between end inspiration times was 0.73 s in the non‐matching couch positions. The correlation‐based metric indicated poorer matching of neighboring couch positions in the RPM‐sorted images. This implied that, when the IRS did not match the RPM signal, the images sorted using the IRS showed fewer artifacts than the clinical images sorted using the RPM signal.

Conclusion:

The IRS is in good agreement with the RPM signal in most cases. In some cases, the IRS provides better sorting than the RPM signal, especially when the RPM system fails. The IRS can therefore be a viable complementary tool or even a replacement for the RPM system.
SU‐E‐J‐158: Audiovisual Biofeedback Reduces Image Artefacts in 4DCT: A Digital Phantom Study
Authors: Pollock S , Kipritidis J , Lee D , Bernatowicz K , Keall P
Published: June 2015

Purpose:

Irregular breathing motion has a deleterious impact on 4DCT image quality. The breathing guidance system: audiovisual biofeedback (AVB) is designed to improve breathing regularity, however, its impact on 4DCT image quality has yet to be quantified. The purpose of this study was to quantify the impact of AVB on thoracic 4DCT image quality by utilizing the digital eXtended Cardiac Torso (XCAT) phantom driven by lung tumor motion patterns.

Methods:

2D tumor motion obtained from 4 lung cancer patients under two breathing conditions (i) without breathing guidance (free breathing), and (ii) with guidance (AVB). There were two breathing sessions, yielding 8 tumor motion traces. This tumor motion was synchronized with the XCAT phantom to simulate 4DCT acquisitions under two acquisition modes: (1) cine mode, and (2) prospective respiratory‐gated mode. Motion regularity was quantified by the root mean square error (RMSE) of displacement. The number of artefacts was visually assessed for each 4DCT and summed up for each breathing condition. Inter‐session anatomic reproducibility was quantified by the mean absolute difference (MAD) between the Session 1 4DCT and Session 2 4DCT.

Results:

AVB improved tumor motion regularity by 30%. In cine mode, the number of artefacts was reduced from 61 in free breathing to 40 with AVB, in addition to AVB reducing the MAD by 34%. In gated mode, the number of artefacts was reduced from 63 in free breathing to 51 with AVB, in addition to AVB reducing the MAD by 23%.

Conclusion:

This was the first study to compare the impact of breathing guidance on 4DCT image quality compared to free breathing, with AVB reducing the amount of artefacts present in 4DCT images in addition to improving inter‐session anatomic reproducibility. Results thus far suggest that breathing guidance interventions could have implications for improving radiotherapy treatment planning and interfraction reproducibility.
SU‐E‐J‐160: Motion Analysis and 3D Plane Fit Through the Tumor Center of Mass Positions in the 4DCT Data Set
Authors: Jurkovic I , Stathakis S , Li Y , Patel A , Vincent J , Papanikolaou N , Mavroidis P
Published: June 2015

Purpose:

To model GTV's center of mass (COM) motion planes based on 4DCT lung data sets and establish possible correlation with the GTV's size and/or location as an aid in defining adequate GTV margins based on the most prominent motion amplitude in the 3D space.

Methods:

For the modeling of the COM motion throughout the respiratory phases, eleven lung cancer patients were used and the least square fitting was applied. The least square fitting generally involves either data smoothening or apparent trend identification. Quadratic minimization, singular value decomposition, orthogonal projections (orthogonal regression), are ways to find a least square solution. The linear least squares method was initially used for the planar fitting of the 3D point data. Evaluation of the goodness of fit was performed through the root mean square deviations (root mean square error, RMSE) and normalized RMSE (NRMSE) values.

Results:

The summed square of residuals of the fit method varied from 0.02 to 0.26 cm and the coefficient of determination from 0.04 to 0.89, while RMSE ranged from 0.05 to 0.13 and NRMSE from 0.11 to 0.29. The most prominent motion was in the transverse and sagittal planes. A correlation was found between the best fit motion plane and the GTV size and/or location. In the lower GTVs, when maximum SI was 1.5, AP and RL motions were 0.87 and 1.0 cm, respectively. This Result confirms the need for margins larger than 0.5 cm for these GTVs.

Conclusion:

The lower RMSE and NRMSE values showed that for each patient a good planar fit can be achieved for the COM motion path. Knowing the GTV size and location, a good estimate of the motion plane in the 3D space can be made. The required dosimetric margins can be easily calculated knowing only one motion extent and motion plane angle.
SU‐E‐J‐164: Estimation of DVH Variation for PTV Due to Interfraction Organ Motion in Prostate VMAT Using Gaussian Error Function
Authors: Lewis C , Jiang R , Chow J
Published: June 2015

Purpose:

We developed a method to predict the change of DVH for PTV due to interfraction organ motion in prostate VMAT without repeating the CT scan and treatment planning. The method is based on a pre‐calculated patient database with DVH curves of PTV modelled by the Gaussian error function (GEF).

Methods:

For a group of 30 patients with different prostate sizes, their VMAT plans were recalculated by shifting their PTVs 1 cm with 10 increments in the anterior‐posterior, left‐right and superior‐inferior directions. The DVH curve of PTV in each replan was then fitted by the GEF to determine parameters describing the shape of curve. Information of parameters, varying with the DVH change due to prostate motion for different prostate sizes, was analyzed and stored in a database of a program written by MATLAB.

Results:

To predict a new DVH for PTV due to prostate interfraction motion, prostate size and shift distance with direction were input to the program. Parameters modelling the DVH for PTV were determined based on the pre‐calculated patient dataset. From the new parameters, DVH curves of PTVs with and without considering the prostate motion were plotted for comparison. The program was verified with different prostate cases involving interfraction prostate shifts and replans.

Conclusion:

Variation of DVH for PTV in prostate VMAT can be predicted using a pre‐calculated patient database with DVH curve fitting. The computing time is fast because CT rescan and replan are not required. This quick DVH estimation can help radiation staff to determine if the changed PTV coverage due to prostate shift is tolerable in the treatment. However, it should be noted that the program can only consider prostate interfraction motions along three axes, and is restricted to prostate VMAT plan using the same plan script in the treatment planning system.
SU‐E‐J‐167: Dosimetric Consequences From Minimal Displacements in APBI with SAVI Applicators
Authors: Chandrasekara S , Dumitru N , Hyvarinen M , Pella S
Published: June 2015

Purpose:

To determine the importance of providing proper solid immobilization in every fraction of treatment in APBI with brachytherapy.

Methods:

125 patients treated with APBI brachytherapy with SAVI applicators at SFRO Boca Raton, from 2013–2015 were considered for this retrospective study. The CT scans of each patient, which were taken before each treatment, were imported in to the Oncentra treatment planning system. Then they were compared with the initial CT scan which was used for the initial plan. Deviation in displacements in reference to ribs and skin surface was measured and dosimetric evaluations respective to the initial image were performed.

Results:

Small deviations in displacements were observed from the SAVI applicator to the ribs and the skin surface. Dosimetric evaluations revealed, very small changes in the inter‐fractionation position make significant differences in the maximum dose to critical organs. Additionally, the volume of the cavity also changed between fractions. As a Result, the maximum dose manifested variance between 10% and 32% in ribs and skin surface respectively.

Conclusion:

It appears that taking a CT scan before each treatment is necessary to minimize the risk of delivering undesired high doses to the critical organs. This study indicates, in 30% of the cases re‐planning was necessary between treatments. We conclude that, treatment planning teams should evaluate the placement of the device by analyzing the CT images before each treatment and they must be prepared for re‐planning if needed. This study also reveals the urgent need of improving the immobilization methods with APBI when treating with the SAVI applicator.
SU‐E‐J‐168: Investigation of the Effect of Modulation Factor and Treatment Delivery Time for Liver VMAT SBRT
Authors: Hubley E , Pierce G , Ecclestone G
Published: June 2015

Purpose:

To investigate the effect on PTV target coverage of liver VMAT SBRT treatment plans by varying the IMRT modulation factor (MF) and length of delivery time in the presence of induced respiratory motion.

Methods:

Four different VMAT SBRT plans (MFs 2.1 to 3.5) were created for a liver phantom within the treatment planning system (Eclipse, Varian Oncology Systems). For each plan, the dose prescription was set to 5 different values (1000cGy to 5000cGy in 5 fractions); these variations force a change in the treatment delivery time due to reduce gantry speed required to deliver higher doses. To simulate respiratory motion, an in‐house program was developed that shifts the positions of the MLC leaves at each control point according to population‐based respiratory curves. This was done for 4 respiratory traces of comparable peak‐to‐peak amplitudes and breathing cycle lengths, with one trace exhibiting a baseline drift. A PTV margin of 5mm was used for all treatment plans.

Results:

A two‐way repeatedmeasures ANOVA looked at changes in PTV V95 and GTV V95 coverage, based on IMRT factor and treatment time. The GTV V95 coverage and mean liver dose showed no significant difference (p values >0.05). The PTV V95 coverage showed a significant decrease with increasing IMRT factor and decreasing treatment time (p values < 0.01 for both). The patient curve with baseline drift exhibited a decrease in PTV coverage with increasing delivery time.

Conclusion:

Decreased PTV coverage was seen with increasing modulation factor and decreasing treatment times for patients with regular breathing curves. With the advent of faster treatment times it is recommended that lower modulation factors for SBRT treatment plans be utilized to mitigate the possibility of interplay. Additionally, longer treatment times could be advantageous to blur out the interplay effect for SBRT treatments. Further investigation is required in patient plans.
SU‐E‐J‐170: Dosimetric Consequences of Uncorrected Rotational Setup Errors During Stereotactic Body Radiation Therapy (SBRT) Treatment of Pancreatic Cancers
Authors: Di Maso L , Forbang R Teboh , Zhang Y , Herman J , Lee J
Published: June 2015

Purpose:

To explore the dosimetric consequences of uncorrected rotational setup errors during SBRT for pancreatic cancer patients.

Methods:

This was a retrospective study utilizing data from ten (n=10) previously treated SBRT pancreas patients. For each original planning CT, we applied rotational transformations to derive additional CT images representative of possible rotational setup errors. This resulted in 6 different sets of rotational combinations, creating a total of 60 CT planning images. The patients’ clinical dosimetric plans were then applied to their corresponding rotated CT images. The 6 rotation sets encompassed a 3, 2 and 1‐degree rotation in each rotational direction and a 3‐degree in just the pitch, a 3‐degree in just the yaw and a 3‐degree in just the roll. After the dosimetric plan was applied to the rotated CT images, the resulting plan was then evaluated and compared with the clinical plan for tumor coverage and normal tissue sparing.

Results:

PTV coverage, defined here by V33 throughout all of the patients’ clinical plans, ranged from 92–98%. After an n degree rotation in each rotational direction that range decreased to 68–87%, 85–92%, and 88– 94% for n=3, 2 and 1 respectively. Normal tissue sparing defined here by the proximal stomach V15 throughout all of the patients’ clinical plans ranged from 0–8.9 cc. After an n degree rotation in each rotational direction that range increased to 0–17 cc, 0–12 cc, and 0–10 cc for n=3, 2, and 1 respectively.

Conclusion:

For pancreatic SBRT, small rotational setup errors in the pitch, yaw and roll direction on average caused under dosage to PTV and over dosage to proximal normal tissue. The 1‐degree rotation was on average the least detrimental to the normal tissue and the coverage of the PTV. The 3‐degree yaw created on average the lowest increase in volume coverage to normal tissue.

This research was sponsored by the AAPM Education Council through the AAPM Education and Research Fund for the AAPM Summer Undergraduate Fellowship Program.
SU‐E‐J‐177: A Computational Approach for Determination of Anisotropic PTV Margins Based On Statistical Shape Analysis for Prostate Cancer Radiotherapy
Authors: Shibayama Y , Arimura H , Hirose T , Nakamura K , Umezu Y , Nakamura Y , Honda H , Toyofuku F
Published: June 2015

Purpose:

Our aim of this study was to propose a computational approach for determination of anisotropic planning target volume (PTV) margins based on statistical shape analysis with taking into account time variations of clinical target volume (CTV) shapes for the prostate cancer radiation treatment planning (RTP).

Methods:

Systematic and random setup errors were measured using orthogonal projection and cone beam computed tomography (CBCT) images for data of 20 patients, who underwent the intensity modulated radiation therapy for prostate cancer. The low‐risk, intermediate‐risk, and high‐risk CTVs were defined as only a prostate, a prostate plus proximal 1‐cm seminal vesicles, and a prostate plus proximal 2‐cm seminal vesicles, respectively. All CTV regions were registered with a reference CTV region with a median volume to remove the effect of the setup errors, and converted to a point distribution models. The systematic and random errors for translations of CTV regions were automatically evaluated by analyzing the movements of centroids of CTV regions. The random and systematic errors for shape variations of CTV regions were obtained from covariance matrices based on point distributions for the CTV contours on CBCT images of 72 fractions of 10 patients. Anisotropic PTV margins for 6 directions (right, left, anterior, posterior, superior and inferior) were derived by using Yoda's PTV margin model.

Results:

PTV margins with and without shape variations were 5.75 to 8.03 mm and 5.23 to 7.67 mm for low‐risk group, 5.87 to 8.33 mm and 5.23 to 7.67 mm for intermediate‐risk group, and 5.88 to 8.25 mm and 5.29 to 7.82 mm for highrisk group, respectively.

Conclusion:

The proposed computational approach could be feasible for determination of the anisotropic PTV margins with taking into account CTV shape variations for the RTP.
SU‐E‐J‐178: Towards ART ‐ Bootstrap Based Estimation of Cumulated Dose Distribution
Authors: Gizynska M , Blatkiewicz D , Cichonski A , Czyzew B , Galecki M , Gil‐Ulkowska M , Kaminski M , Lukomska S , Piziorska M , Zaleska A , Ziemek M , Zygierewicz J , Kukolowicz P
Published: June 2015

Purpose:

A lot of effort is put into diminishing the CTV‐PTV margin and providing Adaptive RT in order to spare normal structures adjacent to the PTV. The purpose of this work was to test the hypothesis that bootstrap method can be used to estimate cumulated dose distribution, representing the whole treatment and that the quality of this estimation is independent on the CTV‐PTV margin.

Methods:

For 25 prostate patients treated in our clinic daily set‐up errors were recorded. For each patient treatment plans for three techniques were prepared: 3D‐CRT, IMRT and VMAT. We prepared plans for different CTV‐PTV margins, for asymmetric margin (0.4, 0.7, and 0.7 cm for lateral, cranial‐caudal, and AP respectively) and than for several symmetric ones of 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 cm. For each treatment plan and each fraction the dose distribution was calculated with the isocenter corrected for the set‐up error. Cumulated Dose Distribution (CDDall) was calculated as the sum of all dose distributions for each single fraction. Estimated Dose Distribution (EDDn) was calculated with bootstrap methodology. The EDDn and CDDall were compared using the 3D gamma concept (2mm and 2%) for each pair of dose distributions. The Result was treated as acceptable if at least 95% of voxels with gamma index ≤ 1 were obtained.

Results:

For 3D and IMRT EDDn calculated from at least 8 (3D) and 7 (IMRT) first fractions (EDDn>7 and EDDn>6), for all patients, but one, acceptable results were obtained. For VMAT our requirement was fulfilled for all patients and EDDn>2. Statistical tests show no significant difference between gamma results for different CTV‐PTV margins.

Conclusion:

The cumulated dose distribution CDDall can be estimated from at least 8 fractions regardless of the technique and CTV‐PTV margin. For VMAT technique the cumulated dose distribution may be estimated with 3 fractions.
SU‐E‐J‐185: A Systematic Review of Breathing Guidance in Radiation Oncology and Radiology
Authors: Pollock S , Keall R , Keall P
Published: June 2015

Purpose:

The advent of image‐guided radiation therapy (IGRT) has led to dramatic improvements in the accuracy of treatment delivery in radiotherapy. Such advancements have highlighted the deleterious impact tumor motion can have on both image quality and radiation treatment delivery. One approach to reducing tumor motion is the use of breathing guidance systems during imaging and treatment. A review of such research had not yet been performed, it was therefore our aim to perform a systematic review of breathing guidance interventions within the fields of radiation oncology and radiology.

Methods:

Results of online database searches were filtered in accordance to a set of eligibility criteria. The search, filtration, and analysis of articles were conducted in accordance with the PRISMAStatement reporting standard (Preferred Reporting Items for Systematic reviews and Meta‐Analyses) utilizing the PICOS approach (Participants, Intervention, Comparison, Outcome, Study design).

Participants:

Cancer patients, healthy volunteers.

Intervention:

Biofeedback breathing guidance systems.

Comparison:

No breathing guidance of the same breathing type.

Outcome:

Regularity of breathing signal and anatomic/tumor motion, medical image quality, radiation treatment margins and coverage, medical imaging and radiation treatment times.

Study design:

Quantitative and controlled prospective or retrospective trials.

Results:

The systematic search yielded a total of 479 articles, which were filtered down to 27 relevant articles in accordance to the eligibility criteria. The vast majority of investigated outcomes were significantly positively impacted by the use of breathing guidance; however, this was dependent upon the nature of the breathing guidance system and study design. In 25/27 studies significant improvements from the use of breathing guidance were observed.

Conclusion:

The results found here indicate that further clinical studies are warranted which quantify more comprehensively the clinical impact of The results found here indicate that further clinical studies are warranted which quantify more comprehensively the clinical impact of breathing guidance interventions.
SU‐E‐J‐196: Implementation of An In‐House Visual Feedback System for Motion Management During Radiation Therapy
Authors: Nguyen V , Ellerbusch D , James J , Wang B
Published: June 2015

Purpose:

To describe an in‐house video goggle feedback system for motion management during simulation and treatment of radiation therapy patients.

Methods:

This video goggle system works by splitting and amplifying the video output signal directly from the Varian Real‐Time Position Management (RPM) workstation or TrueBeam imaging workstation into two signals using a Distribution Amplifier. The first signal S[1] gets reconnected back to the monitor. The second signal S[2] gets connected to the input of a Video Scaler. The S[2] signal can be scaled, cropped and panned in real time to display only the relevant information to the patient. The output signal from the Video Scaler gets connected to an HDMI Extender Transmitter via a DVI‐D to HDMI converter cable. The S[2] signal can be transported from the HDMI Extender Transmitter to the HDMI Extender Receiver located inside the treatment room via a Cat5e/6 cable. Inside the treatment room, the HDMI Extender Receiver is permanently mounted on the wall near the conduit where the Cat5e/6 cable is located. An HDMI cable is used to connect from the output of the HDMI Receiver to the video goggles.

Results:

This video goggle feedback system is currently being used at two institutions. At one institution, the system was just recently implemented for simulation and treatments on two breath‐hold gated patients with 8+ total fractions over a two month period. At the other institution, the system was used to treat 100+ breath‐hold gated patients on three Varian TrueBeam linacs and has been operational for twelve months. The average time to prepare the video goggle system for treatment is less than 1 minute.

Conclusion:

The video goggle system provides an efficient and reliable method to set up a video feedback signal for radiotherapy patients with motion management.
SU‐E‐J‐197: Investigation of Microsoft Kinect 2.0 Depth Resolution for Patient Motion Tracking
Authors: Silverstein E , Snyder M
Published: June 2015

Purpose:

Investigate the use of the Kinect 2.0 for patient motion tracking during radiotherapy by studying spatial and depth resolution capabilities.

Methods:

Using code written in C#, depth map data was abstracted from the Kinect to create an initial depth map template indicative of the initial position of an object to be compared to the depth map of the object over time. To test this process, simple setup was created in which two objects were imaged: a 40 cm × 40 cm board covered in non reflective material and a 15 cm × 26 cm textbook with a slightly reflective, glossy cover. Each object, imaged and measured separately, was placed on a movable platform with object to camera distance measured. The object was then moved a specified amount to ascertain whether the Kinect's depth camera would visualize the difference in position of the object.

Results:

Initial investigations have shown the Kinect depth resolution is dependent on the object to camera distance. Measurements indicate that movements as small as 1 mm can be visualized for objects as close as 50 cm away. This depth resolution decreases linearly with object to camera distance. At 4 m, the depth resolution had decreased to observe a minimum movement of 1 cm.

Conclusion:

The improved resolution and advanced hardware of the Kinect 2.0 allows for increase of depth resolution over the Kinect 1.0. Although obvious that the depth resolution should decrease with increasing distance from an object given the decrease in number of pixels representing said object, the depth resolution at large distances indicates its usefulness in a clinical setting.
SU‐E‐J‐199: A Software Tool for Quality Assurance of Online Replanning with MR‐Linac
Authors: Chen G , Ahunbay E , Li X
Published: June 2015

Purpose:

To develop a quality assurance software tool, ArtQA, capable of automatically checking radiation treatment plan parameters, verifying plan data transfer from treatment planning system (TPS) to record and verify (R&V) system, performing a secondary MU calculation considering the effect of magnetic field from MR‐Linac, and verifying the delivery and plan consistency, for online replanning.

Methods:

ArtQA was developed by creating interfaces to TPS (e.g., Monaco, Elekta), R&V system (Mosaiq, Elekta), and secondary MU calculation system. The tool obtains plan parameters from the TPS via direct file reading, and retrieves plan data both transferred from TPS and recorded during the actual delivery in the R&V system database via open database connectivity and structured query language. By comparing beam/plan datasets in different systems, ArtQA detects and outputs discrepancies between TPS, R&V system and secondary MU calculation system, and delivery. To consider the effect of 1.5T transverse magnetic field from MR‐Linac in the secondary MU calculation, a method based on modified Clarkson integration algorithm was developed and tested for a series of clinical situations.

Results:

ArtQA is capable of automatically checking plan integrity and logic consistency, detecting plan data transfer errors, performing secondary MU calculations with or without a transverse magnetic field, and verifying treatment delivery. The tool is efficient and effective for pre‐ and post‐treatment QA checks of all available treatment parameters that may be impractical with the commonly‐used visual inspection.

Conclusion:

The software tool ArtQA can be used for quick and automatic pre‐ and post‐treatment QA check, eliminating human error associated with visual inspection. While this tool is developed for online replanning to be used on MR‐Linac, where the QA needs to be performed rapidly as the patient is lying on the table waiting for the treatment, ArtQA can be used as a general QA tool in radiation oncology practice.

This work is partially supported by Elekta Inc.
SU‐E‐J‐202: Performance of the Patient QA Systems in a Hybrid MRI‐Linac
Authors: Houweling A , Vries W de , Wolthaus J , Woodings S , van Asselen B , Kok J , Lagendijk J , Raaymakers B
Published: June 2015

Purpose:

The first clinical MR‐linac will soon become operational, therefore patient plan QA procedures and equipment have to become MRcompatible. Reference dosimetry is affected by the magnetic field, however, relative dosimetry using patient QA systems haven't been investigated extensively. The purpose of this study was to examine the performance characteristics of the MR‐compatible ArcCHECK and Delta4 systems in a transverse 1.5 T magnetic field.

Methods:

Recently MR‐compatible versions of both ArcCheck (Sun Nuclear) and Delta4 (Scandidos) have been developed. To examine the performance characteristics within the magnetic field, the reproducibility, dose linearity, dose rate dependence, field size and angular dependence were evaluated on the MR‐linac (8 MV FFF beam, SAD of 142 cm) and a conventional linac (Elekta, 6MV). To allow comparison of the measurements with and without magnetic field, the measurement setup for the conventional linac is adapted to mimic the setup at the MR‐linac if possible (e.g. SAD, dose rate). The results from the MR‐linac were benchmarked to the results from the conventional linac as being the clinical reference.

Results:

At the moment of writing, measurements for the Delta4 are still running. Therefore, only the results of the ArcCheck are presented in this abstract. No significant difference was observed in the reproducibility of the ArcCheck (<0.06%) between both linacs. The maximum dose response difference when measuring the dose linearity was less than 0.4% and the varying dose rate resulted in maximal dose differences of 1.0% for both linacs. Response variation for varying field sizes was <2.6% at the conventional linac, and <1.0% at the MR‐linac. Angular response was similar for both linacs.

Conclusion:

The reproducibility, dose linearity, dose rate dependence, field size and angular dependence of the MR compatible ArcCheck were not influenced by the presence of a transverse 1.5 T magnetic field. The results for the Delta4 are about to follow.

Equipment is generously provided by Sun Nuclear Corporation (Melbourne, USA) and Scandidos (Uppsala, Sweden)
SU‐E‐J‐207: Effect of Pulse Sequence Parameters On Geometric Distortions Induced by a Titanium Brachytherapy Applicator
Authors: Shea S , Diak A , Surucu M , Harkenrider M , Yacoub J , Roeske J , Small W
Published: June 2015

Purpose:

To investigate the effect of readout bandwidth and voxel size on the appearance of distortion artifacts caused by a titanium brachytherapy applicator.

Methods:

An acrylic phantom was constructed to rigidly hold a MR conditional, titanium Fletcher‐Suit‐Delclos‐style applicator set (Varian Medical Systems) for imaging on CT (Philips Brilliance) and 1.5T MRI (Siemens Magnetom Aera). Several variants of MRI parameters were tried for 2D T2‐weighted turbo spin echo imaging in comparison against the standard clinical protocol with the criteria to keep relative SNR loss less than 20% and imaging time as short as possible. Two 3D sequences were also used for comparison with similar parameters. The applicator tandem was segmented on axial CT images (0.4×0.4×1.5mm 3 resolution) and the CT images were registered to the 3D MR images in Eclipse (Varian). The applicator volume was then overlaid on all MRI sets in 3D‐Slicer and distances were measured from the tandem tip to the MRI artifact edge in right/left/superior and anterior/posterior/superior directions from coronal and sagittal 2D acquisitions, respectively, or 3D data reformats. Artifact regions were also manually contoured in coronal/sagittal orientations for area measurements.

Results:

As would be expected, reductions in voxel size and increases in readout bandwidth reduced artifact size (average max artifact length decreased by 0.95 mm and average max area decrease by 0.27 cm2). Interestingly, bandwidth increases yielded reductions in area (0.19 cm2) and in distance measurements (1 mm) even with voxel increases, as compared to a standard protocol. This could be useful when high performance protocols are not feasible due to long imaging times.

Conclusion:

We have characterized artifacts caused by cervical brachytherapy applicator across multiple sequence parameters at 1.5T. Future work will focus on finalizing an optimal protocol that balances artifact reduction with imaging time and then testing this new protocol in patients.
SU‐E‐J‐211: Assessing the Consistency of the ViewRay 0.35 T MRI System
Authors: Yan Y , Saenz D , Bayouth J , Paliwal B
Published: June 2015

Purpose:

ViewRay is a novel image‐guided radiotherapy approach with an integrated 0.35 T MR unit and three Cobalt‐60 heads. In order to continuously ensure the high resolution and high soft tissue contrast available in MR images, we quantified a multitude of relevant imaging parameters over a period of six months to establish its stability and imaging quality. In the assessment process, consideration is also given to the need to establish the number of tests required to have confidence in the performance of the system for radiation therapy planning applications.

Methods:

Daily, weekly, monthly and annual imaging tests were performed over a period of six months using standardized phantoms (a 24 cm diameter sphere and the ACR phantom) to quantify the performance of the system. In addition to the ACR and NEMA recommended tests, we also included element testing, spatial integrity, Eddy current and magnetic field inhomogeneity measurements. The ACR test is used for assessing the following parameters for T1 and T2: geometric accuracy, high contrast spatial resolution, slice thickness accuracy, slice position accuracy, percent signal ghosting, low contrast object detectability. It also includes percent image uniformity (PIU) for T1. The NEMA test is primarily designed to check SNR and PIU.

Results:

Over the period of six months, all the parameters were maintained within the recommendations provided in the ACR and NEMA standards. PIU and SNR were found to be sensitive to malfunctions in the components of the multileaf collimators. Details of the findings will be presented.

Conclusion:

The data suggests that ViewRay imaging system has functioned in a consistent and reliable manner. MR imaging from ViewRay 0.35T system complies with the ACR and NEMA recommended acceptance standards.