bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐108: Template Matching Based On Multiple Templates Can Improve the Tumor Tracking Performance When There Is Large Tumor Deformation
Authors: Shi X , Lin J , Diwanji T , Mooney K , D' Souza W , Mistry N
Published: July 2014

Purpose:

Recently, template matching has been shown to be able to track tumor motion on cine‐MRI images. However, artifacts such as deformation, rotation, and/or out‐of‐plane movement could seriously degrade the performance of this technique. In this work, we demonstrate the utility of multiple templates derived from different phases of tumor motion in reducing the negative effects of artifacts and improving the accuracy of template matching methods.

Methods:

Data from 2 patients with large tumors and significant tumor deformation were analyzed from a group of 12 patients from an earlier study. Cine‐MRI (200 frames) imaging was performed while the patients were instructed to breathe normally. Ground truth tumor position was established on each frame manually by a radiation oncologist. Tumor positions were also automatically determined using template matching with either single or multiple (5) templates. The tracking errors, defined as the absolute differences in tumor positions determined by the manual and automated methods, when using either single or multiple templates were compared in both the AP and SI directions, respectively.

Results:

Using multiple templates reduced the tracking error of template matching. In the SI direction where the tumor movement and deformation were significant, the mean tracking error decreased from 1.94 mm to 0.91 mm (Patient 1) and from 6.61 mm to 2.06 mm (Patient 2). In the AP direction where the tumor movement was small, the reduction of the mean tracking error was significant in Patient 1 (from 3.36 mm to 1.04 mm), but not in Patient 2 (from 3.86 mm to 3.80 mm).

Conclusion:

This study shows the effectiveness of using multiple templates in improving the performance of template matching when artifacts like large tumor deformation or out‐of‐plane motion exists. Accurate tumor tracking capabilities can be integrated with MRI guided radiation therapy systems.

This work was supported in part by grants from NIH/NCI CA 124766 and Varian Medical Systems, Palo Alto, CA.
SU‐E‐J‐111: The Contouring Error of the Parotids Based On the CT and MRI Images in Radiotherapy Planning for Nasopharyngeal Carcinoma
Authors: Gong G , Liu C
Published: July 2014

Purpose:

To analyze the variation of sketching the parotid for patients with nasopharyngeal carcinoma who underwent radiotherapy based on computed tomography (CT) and magnetic resonance(MR) images.

Methods:

41 nasopharyngeal cancer patients were randomly selected. Each patient underwent MR and CT scanning. The Gross Tumor Volume and Organs at risk were contoured on both contrasted CT and T1‐MR images. For each patient, one radiotherapist sketched the parotid on CT and MR images for 10 times, and 10 different radiotherapists were asked to sketching the parotid on CT and MR images only one time. The inter‐ and intra‐observers volumes and outline variations were compared.

Results:

The volumes of parotid contoured by inter‐observer on CT and MR images were 34.6±12.1cm3(left),34.3±9.0cm3(right) and 24.6±7.6cm3(L),23.2±8.1cm3(R); In the same way, for intra‐observer on CT and MR images the volumes were 28.2±7.6cm3(L),29.4±9.4cm3(R) and 24.4±7.6cm3(L),22.5±7.4cm3(R), respectively. The variable ratios of volume on MR images were 4.7±0.7%(L),5.0±0.6%(R) for inter‐observer and 2.3±0.4%(L),2.1±0.7%(R) for intra‐observer. Similarly, The inter‐ and intra‐observer ratios for contouring on CT images reached 18.0±4.8%(L),17.4±4.6%(R) and 6.3±1.5%(L),6.8±1.5%(R), respectively.

Conclusion:

Contouring the parotids on MR images was more accurate and reproducible than that on CT images.
SU‐E‐J‐114: Towards Integrated CT and Ultrasound Guided Radiation Therapy Using A Robotic Arm with Virtual Springs
Authors: Ding K , Zhang Y , Sen H , Lediju Bell M , Goldstein S , Kazanzides P , Iordachita I , Wong J
Published: July 2014

Purpose:

Currently there is an urgent need in Radiation Therapy for noninvasive and nonionizing soft tissue target guidance such as localization before treatment and continuous monitoring during treatment. Ultrasound is a portable, low cost option that can be easily integrated with the LINAC room. We are developing a cooperatively controlled robot arm that has high intrafraction reproducibility with repositioning of the ultrasound probe. In this study, we introduce virtual springs (VS) to assist with interfraction probe repositioning and we compare the soft tissue deformation introduced by VS to the deformation that would exist without them.

Methods:

Three metal markers were surgically implanted in the kidney of one dog. The dog was anesthetized and immobilized supine in an alpha cradle. The reference ultrasound probe position and force to ideally visualize the kidney was defined by an experienced ultrasonographer using the Clarity ultrasound system and robot sensor. For each interfraction study, the dog was removed from the cradle and re‐setup based on CBCT with bony anatomy alignment to mimic regular patient setup. The ultrasound probe was automatically returned to the reference position using the robot. To accommodate the soft tissue anatomy changes between each setup the operator used the VS feature to adjust the probe and obtain an ultrasound image that matched the reference image. CBCT images were acquired and each interfraction marker location was compared with the first interfraction

Result. Results:

Analysis of the marker positions revealed that the kidney was displaced by 18.8 ± 6.4 mm without VS and 19.9 ± 10.5 mm with VS. No statistically significant differences were found between two procedures.

Conclusion:

The VS feature is necessary to obtain matching ultrasound images, and they do not introduce further changes to the tissue deformation. Future work will focus on automatic VS based on ultrasound feedback.

Supported in part by: NCI R01 CA161613; Elekta Sponsored Research
SU‐E‐J‐120: X‐Ray Imaging System with Scattering Reduction and Phase Contrast
Authors: Feng Y
Published: July 2014

Purpose:

To improve X‐ray quality, we proposed an optimization method and a design of imaging system that combine the capabilities of suppressing scattering and enhancing phase contrast. The images were reconstructed by combing both temporal and spatial multiplexing approaches.

Methods:

Numerical calculation methods were applied to obtain the angle distraction X‐Ray emerging from an object. The geometrical parameters of the imaging system was optimized to achieve high scattering suppress and high angle resolution, in order to obtain high definition imaging enhanced by phase contrast. Numerical method was used to simulate this system to image a phantom with density variations. The Expectation‐maximization algorithm was used to reconstruct images.

Results:

A primary design of the imaging system was accomplished. The simulation of the imaging system showed high efficiency in suppressing scattering and high sensitivity in phase contrast.

Conclusion:

The innovated collimation system showed promising in high definition X‐ray imaging with phase contrast.
SU‐E‐J‐122: Detecting Treatment‐Induced Metabolic Abnormalities in Craniopharyngioma Patients Undergoing Surgery and Proton Therapy
Authors: Hua C , Shulkin B , Indelicato D , Boop F , Li Y , LI X , Merchant T
Published: July 2014

Purpose:

To identify treatment‐induced defects in the brain of children with craniopharyngioma receiving surgery and proton therapy using fluorodeoxyglucose positron emission tomography (FDG PET).

Methods:

Forty seven patients were enrolled on a clinical trial for craniopharyngioma with serial imaging and functional evaluations. Proton therapy was delivered using the double‐scattered beams with a prescribed dose of 54 Cobalt Gray Equivalent. FDG tracer uptake in each of 63 anatomical regions was computed after warping PET images to a 3D reference template in Talairach coordinates. Regional uptake was deemed significantly low or high if exceeding two standard deviations of normal population from the mean. For establishing the normal ranges, 132 children aged 1–20 years with noncentral nervous system related diseases and normal‐appearing cerebral PET scans were analyzed. Age‐ and gender‐dependent regional uptake models were developed by linear regression and confidence intervals were calculated.

Results:

Most common PET abnormality before proton therapy was significantly low uptake in the frontal lobe, the occipital lobe (particularly in cuneus), the medial and ventral temporal lobe, cingulate gyrus, caudate nuclei, and thalamus. They were related to injury from surgical corridors, tumor mass effect, insertion of a ventricular catheter, and the placement of an Ommaya reservoir. Surprisingly a significantly high uptake was observed in temporal gyri and the parietal lobe. In 13 patients who already completed 18‐month PET scans, metabolic abnormalities improved in 11 patients from baseline. One patient had persistent abnormalities. Only one revealed new uptake abnormalities in thalamus, brainstem, cerebellum, and insula.

Conclusion:

Postoperative FDG PET of craniopharyngioma patients revealed metabolic abnormalities in specific regions of the brain. Proton therapy did not appear to exacerbate these surgery‐ and tumor‐induced defects. In patients with persistent and new abnormalities, continued investigation on clinical symptoms and cognitive outcomes is ongoing to establish the association and predictive values of metabolic imaging.
SU‐E‐J‐125: Classification of CBCT Noises in Terms of Their Contribution to Proton Range Uncertainty
Authors: Brousmiche S , Orban de Xivry J , Macq B , Seco J
Published: July 2014

Purpose:

This study assesses the potential use of CBCT images in adaptive protontherapy by estimating the contribution of the main sources of noise and calibration errors to the proton range uncertainty.

Methods:

Measurements intended to highlight each particular source have been achieved by adapting either the testbench configuration, e.g. use of filtration, fan‐beam collimation, beam stop arrays, phantoms and detector reset light, or the sequence of correction algorithms including water precorrection. Additional Monte‐Carlo simulations have been performed to complement these measurements, especially for the beam hardening and the scatter cases. Simulations of proton beams penetration through the resulting images have then been carried out to quantify the range change due to these effects. The particular case of a brain irradiation is considered mainly because of the multiple effects that the skull bones have on the internal soft tissues.

Results:

On top of the range error sources is the undercorrection of scatter. Its influence has been analyzed from a comparison of fan‐beam and full axial FOV acquisitions. In this case, large range errors of about 12 mm can be reached if the assumption is made that the scatter has only a constant contribution over the projection images. Even the detector lag, which a priori induces a much smaller effect, has been shown to contribute for up to 2 mm to the overall error if its correction only aims at reducing the skin artefact. This last result can partially be understood by the larger interface between tissues and bones inside the skull.

Conclusion:

This study has set the basis of a more systematical analysis of the effect CBCT noise on range uncertainties based on a combination of measurements, simulations and theoretical results. With our method, even more subtle effects such as the cone‐beam artifact or the detector lag can be assessed.

SBR and JOR are financed by iMagX, a public‐private partnership between the region Wallone of Belgium and IBA under convention #1217662
SU‐E‐J‐127: Real‐Time Dosimetric Assessment for Adaptive Head‐And‐Neck Treatment Via A GPU‐Based Deformable Image Registration Framework
Authors: Qi S , Neylon J , Chen A , Low D , Kupelian P , Steinberg M , Santhanam A
Published: July 2014

Purposes:

To systematically monitor anatomic variations and their dosimetric consequences during head‐and‐neck (H' N) radiation therapy using a GPU‐based deformable image registration (DIR) framework.

Methods:

Eleven H' N IMRT patients comprised the subject population. The daily megavoltage CT and weekly kVCT scans were acquired for each patient. The pre‐treatment CTs were automatically registered with their corresponding planning CT through an in‐house GPU‐based DIR framework. The deformation of each contoured structure was computed to account for non‐rigid change in the patient setup. The Jacobian determinant for the PTVs and critical structures was used to quantify anatomical volume changes. Dose accumulation was performed to determine the actual delivered dose and dose accumulation. A landmark tool was developed to determine the uncertainty in the dose distribution due to registration error.

Results:

Dramatic interfraction anatomic changes leading to dosimetric variations were observed. During the treatment courses of 6–7 weeks, the parotid gland volumes changed up to 34.7%, the center‐of‐mass displacement of the two parotids varied in the range of 0.9–8.8mm. Mean doses were within 5% and 3% of the planned mean doses for all PTVs and CTVs, respectively. The cumulative minimum/mean/EUD doses were lower than the planned doses by 18%, 2%, and 7%, respectively for the PTV1. The ratio of the averaged cumulative cord maximum doses to the plan was 1.06±0.15. The cumulative mean doses assessed by the weekly kVCTs were significantly higher than the planned dose for the left‐parotid (p=0.03) and right‐parotid gland (p=0.006). The computation time was nearly real‐time (∼ 45 seconds) for registering each pre‐treatment CT to the planning CT and dose accumulation with registration accuracy (for kVCT) at sub‐voxel level (<1.5mm).

Conclusions:

Real‐time assessment of anatomic and dosimetric variations is feasible using the GPU‐based DIR framework. Clinical implementation of this technology may enable timely plan adaption and potentially lead to improved outcome.
SU‐E‐J‐128: 3D Surface Reconstruction of a Patient Using Epipolar Geometry
Authors: Kotoku J , Nakabayashi S , Haga A , Kumagai S , Ishibashi T , Arai N , Saotome N , Kobayashi T
Published: July 2014

Purpose:

To obtain a 3D surface data of a patient in a non‐invasive way can substantially reduce the effort for the registration of patient in radiation therapy. To achieve this goal, we introduced the multiple view stereo technique, which is known to be used in a “photo tourism” on the internet.

Methods:

70 Images were taken with a digital single‐lens reflex camera from different angles and positions. The camera positions and angles were inferred later in the reconstruction step. A sparse 3D reconstruction model was locating by SIFT features, which is robust for rotation and shift variance, in each image. We then found a set of correspondences between pairs of images by computing the fundamental matrix using the eight‐point algorithm with RANSAC. After the pair matching, we optimized the parameter including camera positions to minimize the reprojection error by use of bundle adjustment technique (non‐linear optimization). As a final step, we performed dense reconstruction and associate a color with each point using the library of PMVS.

Results:

Surface data were reconstructed well by visual inspection. The human skin is reconstructed well, althogh the reconstruction was time‐consuming for direct use in daily clinical practice.

Conclusion:

3D reconstruction using multi view stereo geometry is a promising tool for reducing the effort of patient setup.

This work was supported by JSPS KAKENHI(25861128).
SU‐E‐J‐129: A Strategy to Consolidate the Image Database of a VERO Unit Into a Radiotherapy Management System
Authors: Yan Y , Medin P , Yordy J , Zhao B , Jiang S
Published: July 2014

Purpose:

To present a strategy to integrate the imaging database of a VERO unit with a treatment management system (TMS) to improve clinical workflow and consolidate image data to facilitate clinical quality control and documentation.

Methods:

A VERO unit is equipped with both kV and MV imaging capabilities for IGRT treatments. It has its own imaging database behind a firewall. It has been a challenge to transfer images on this unit to a TMS in a radiation therapy clinic so that registered images can be reviewed remotely with an approval or rejection record. In this study, a software system, iPump‐VERO, was developed to connect VERO and a TMS in our clinic. The patient database folder on the VERO unit was mapped to a read‐only folder on a file server outside VERO firewall. The application runs on a regular computer with the read access to the patient database folder. It finds the latest registered images and fuses them in one of six predefined patterns before sends them via DICOM connection to the TMS. The residual image registration errors will be overlaid on the fused image to facilitate image review.

Results:

The fused images of either registered kV planar images or CBCT images are fully DICOM compatible. A sentinel module is built to sense new registered images with negligible computing resources from the VERO ExacTrac imaging computer. It takes a few seconds to fuse registered images and send them to the TMS. The whole process is automated without any human intervention.

Conclusion:

Transferring images in DICOM connection is the easiest way to consolidate images of various sources in your TMS. Technically the attending does not have to go to the VERO treatment console to review image registration prior delivery. It is a useful tool for a busy clinic with a VERO unit.
SU‐E‐J‐132: Sensitivity Evaluation of Organ Based Registration for Pancreatic IGRT
Authors: Yang P , Tuli R , Sandler H , Fraass B
Published: July 2014

Purpose:

Soft‐tissue‐based CBCT registration is not always straightforward. Typical image guidance is based on use of generic registration criteria that may not be adequately sensitive to PTV and critical organ positioning errors. This work presents a novel organ‐based registration criterion to help quantify registration results and guidance.

Methods:

Ten pancreatic cancer patients treated using IGRT were included. Five individual CBCTs for each patient were manually registered to the planning CT by an expert. Instead of calculating the cross‐correlation (CC) for the entire imaging volume, the CC values of the PTV and critical normal tissue (limited to a 1‐cm ring around the PTV), were calculated as references. The CBCT images were then intentionally shifted in three axes by 1, 3, 5, 8, and 10 mm. New CC values were computed between the shifted CBCT and planning CT. The organ based CC was called sensitive to a given shift size when the p‐value between new and reference CC values for the 5 CBCTs was <0.05.

Results:

The average reference CC was 0.23 (0.06–0.41). Despite the low correlation values, the CC‐PTV is sensitive to average registration errors ≥ 5, 3 and 5 mm in the sup/inf, ant/post and right/left directions, respectively. Critical organ cross‐correlation is sensitive to registration errors ≥ 7, 4 and 6 mm in these directions. 3/10 patients showed particularly poor sensitivity (≥ 8 mm) due to low reference CC, heavy contrast presence in the planning CT or small PTV volume.

Conclusion:

CBCT of upper abdomen tends to have very low similarity to the planning CT, affecting registration accuracy and reliability. This organ‐based registration method focuses on the PTV and the most critical tissues, and shows improved sensitivity to positioning errors that may not be easily resolved by visual inspection.

This work supported in part by grant 1R03CA173273‐01
SU‐E‐J‐133: Evaluation of Inter‐ and Intra‐Fractional Pancreas Tumor Residual Motions with Abdominal Compression
Authors: Li Y , Shi F , Tian Z , Jia X , Meyer J , Jiang S , Mao W
Published: July 2014

Purpose:

Abdominal compression (AC) has been widely used to reduce pancreas motion due to respiration for pancreatic cancer patients undergoing stereotactic body radiotherapy (SBRT). However, the inter‐fractional and intra‐fractional patient motions may degrade the treatment. The purpose of this work is to study daily CBCT projections and 4DCT to evaluate the inter‐fractional and intra‐fractional pancreatic motions.

Methods:

As a standard of care at our institution, 4D CT scan was performed for treatment planning. At least two CBCT scans were performed for daily treatment. Retrospective studies were performed on patients with implanted internal fiducial markers or surgical clips. The initial motion pattern was obtained by extracting marker positions on every phase of 4D CT images. Daily motions were presented by marker positions on CBCT scan projection images. An adaptive threshold segmentation algorithm was used to extract maker positions. Both marker average positions and motion ranges were compared among three sets of scans, 4D CT, positioning CBCT, and conformal CBCT, for inter‐fractional and intra‐fractional motion variations.

Results:

Data from four pancreatic cancer patients were analyzed. These patients had three fiducial markers implanted. All patients were treated by an Elekta Synergy with single fraction SBRT. CBCT projections were acquired by XVI. Markers were successfully detected on most of the projection images. The inter‐fractional changes were determined by 4D CT and the first CBCT while the intra‐fractional changes were determined by multiple CBCT scans. It is found that the average motion range variations are within 2 mm, however, the average marker positions may drift by 6.5 mm.

Conclusion:

The patients respiratory motion variation for pancreas SBRT with AC was evaluated by detecting markers from CBCT projections and 4DCT, both the inter‐fraction and intra‐fraction motion range change is small but the drift of marker positions may be comparable to motion ranges.
SU‐E‐J‐138: An IGRT QA Device for Measuring with Tenths‐Millimeter Accuracy KV and MV Isocenter Congruence, Couch Travel and Laser Alignment of Accelerators Used for SRS and SBRT
Authors: Brezovich I , Popple R , Duan J , Huang M , Benhabib S , Shen S , Cardan R , Wu X
Published: July 2014

Purpose:

To develop a practical device having sufficient accuracy for daily QA tests of accelerators used for SRS and SBRT.

Methods:

The UAB (Universal Alignment Ball) consists of a 6.35 mm (1/4 inch) diameter tungsten sphere located concentrically within a 25.4 mm (1 inch) diameter acrylic plastic (PMMA) sphere. The spheres are embedded in polystyrene foam, which, in turn, is surrounded by a cylindrical PMMA shell. The UAB is placed on the couch and aligned with wall lasers according to marks that have known positions in relation to the center of the spheres. Using planar and cone beam images the couch is shifted till the surface of the PMMA sphere matches Eclipse‐generated circular contours. Anterior and lateral MV images taken with small MLC openings allow measurement of distance between kV and MV isocenter, laser and MLC alignment. Measurements were taken over a one‐month period.

Results:

Artifacts from the tungsten sphere were confined within the PMMA sphere and did not affect cone beam localization of the sphere boundary, allowing 0.1 mm precise alignment with a computer‐generated circle centered at kV isocenter. In tests extending over a one‐month period, the distance between kV and MV isocenters along the vertical, longitudinal and lateral directions was 0.125 +/−0.06, 0.19 +/−0.08, and 0.02 +/−0.08 mm, respectively. Laser misalignment along these directions was 0.34 +/‐ 0.15, 0.74 +/−0.29, and 0.49 +/−0.22 mm. Automated couch shifts moved the spheres to within 0.1 mm of the selected position. The center of a 1cmx1cm MLC‐defined field remained within +/−0.2 mm of the tungsten sphere center as the gantry was rotated.

Conclusion:

The UAB is practical for daily end‐to‐end QA tests of accelerator alignment. It provides tenths‐mm accuracy for measuring agreement of kV and MV isocenters, couch motions, gantry flex and laser alignment.
SU‐E‐J‐145: Geometric Uncertainty in CBCT Extrapolation for Head and Neck Adaptive Radiotherapy
Authors: Liu C , Kumarasiri A , Chetvertkov M , Gordon J , Chetty I , Siddiqui F , Kim J
Published: July 2014

Purpose:

One primary limitation of using CBCT images for H' N adaptive radiotherapy (ART) is the limited field of view (FOV) range. We propose a method to extrapolate the CBCT by using a deformed planning CT for the dose of the day calculations. The aim was to estimate the geometric uncertainty of our extrapolation method.

Methods:

Ten H' N patients, each with a planning CT (CT1) and a subsequent CT (CT2) taken, were selected. Furthermore, a small FOV CBCT (CT2short) was synthetically created by cropping CT2 to the size of a CBCT image. Then, an extrapolated CBCT (CBCTextrp) was generated by deformably registering CT1 to CT2short and resampling with a wider FOV (42mm more from the CT2short borders), where CT1 is deformed through translation, rigid, affine, and b‐spline transformations in order. The geometric error is measured as the distance map ||DVF|| produced by a deformable registration between CBCTextrp and CT2. Mean errors were calculated as a function of the distance away from the CBCT borders. The quality of all the registrations was visually verified.

Results:

Results were collected based on the average numbers from 10 patients. The extrapolation error increased linearly as a function of the distance (at a rate of 0.7mm per 1 cm) away from the CBCT borders in the S/I direction. The errors (μ±σ) at the superior and inferior boarders were 0.8 ± 0.5mm and 3.0 ± 1.5mm respectively, and increased to 2.7 ± 2.2mm and 5.9 ± 1.9mm at 4.2cm away. The mean error within CBCT borders was 1.16 ± 0.54mm . The overall errors within 4.2cm error expansion were 2.0 ± 1.2mm (sup) and 4.5 ± 1.6mm (inf).

Conclusion:

The overall error in inf direction is larger due to more large unpredictable deformations in the chest. The error introduced by extrapolation is plan dependent. The mean error in the expanded region can be large, and must be considered during implementation.

This work is supported in part by Varian Medical Systems, Palo Alto, CA.
SU‐E‐J‐147: Quantitative Analysis of 2.5 MV Portal Imaging Performance Compared to KV and 6MV Portal Imaging On the Novel Edge LINAC
Authors: Song K , Kim J , Wen N , Li H , Snyder K , Zhong H , Gordon J , Chetty I
Published: July 2014

Purpose:

To quantitatively evaluate the performance of 2.5 MV imaging compared to traditional kV and 6MV imaging on the new Edge LINAC (Varian

Methods:

The high and low contrast resolution and contrast‐tonoise ratios of kV, 2.5MV, and 6MV portal imaging were evaluated using Las Vegas, Leeds, CIRS torso, Rando torso, and BrainLab pelvis phantoms. Different thicknesses of solid water were added at both sides of phantom to simulate and assess the imaging characteristics associated with increased scatter in larger patients. The contrast‐to‐noise ratios of bone‐to‐soft tissue were obtained from aforementioned phantoms.

Results:

The 2.5 MV portal imaging resolved all objects in the Las Vegas phantom except the smallest object. 6 MV imaging couldn' t image three smallest objects. From the Leeds phantom, kV, 2.5 MV, and 6 MV imaging achieve 2.24, 1.4, and 1.25 LP/mm with no additional slabs, respectively. With 10 cm slabs added, resolutions deteriorate to 1.6, 1.25, and 0.7 LP/mm. In low contrast detectability, kV, 2.5 MV, and 6 MV imaging visualize 18, 18, and 15 different‐contrast objects in total. With 10cm slab added, they imaged 12, 15, and 8 objects. CIRS phantom CNRs of bone‐to‐soft tissue were 10, 27, and 17 for KV, 2.5 MV, and 6 MV, respectively with no slab added. Rando phantom CNRs were 11, 8, and 7 and similarly CNRs from the BrainLab pelvis phantom were 9, 13, and 11. With additional slab, KV imaging CNRs degraded much more than those of 2.5 MV and 6 MV imaging.

Conclusion:

In this study, we evaluated kV, 2.5 MV and 6 MV imaging using various phantoms. The 2.5 MV imaging shows better imaging performance at large phantom configurations in terms of high and low contrast resolutions and CNRs. We believe that the 2.5 MV portal imaging will be the next trend in portal imaging, especially for SRS/SBRT patient localization.
SU‐E‐J‐151: Dosimetric Evaluation of DIR Mapped Contours for Image Guided Adaptive Radiotherapy with 4D Cone‐Beam CT
Authors: Balik S , Weiss E , Jan N , Zhang L , Roman N , Christensen G , Williamson J , Hugo G
Published: July 2014

Purpose:

To estimate dosimetric errors resulting from using contours deformably mapped from planning CT to 4D cone beam CT (CBCT) images for image‐guided adaptive radiotherapy of locally advanced non‐small cell lung cancer (NSCLC).

Methods:

Ten locally advanced non‐small cell lung cancer (NSCLC) patients underwent one planning 4D fan‐beam CT (4DFBCT) and weekly 4DCBCT scans. Multiple physicians delineated the gross tumor volume (GTV) and normal structures in planning CT images and only GTV in CBCT images. Manual contours were mapped from planning CT to CBCTs using small deformation, inverse consistent linear elastic (SICLE) algorithm for two scans in each patient. Two physicians reviewed and rated the DIR‐mapped (auto) and manual GTV contours as clinically acceptable (CA), clinically acceptable after minor modification (CAMM) and unacceptable (CU). Mapped normal structures were visually inspected and corrected if necessary, and used to override tissue density for dose calculation. CTV (6mm expansion of GTV) and PTV (5mm expansion of CTV) were created. VMAT plans were generated using the DIR‐mapped contours to deliver 66 Gy in 33 fractions with 95% and 100% coverage (V66) to PTV and CTV, respectively. Plan evaluation for V66 was based on manual PTV and CTV contours.

Results:

Mean PTV V66 was 84% (range 75% – 95%) and mean CTV V66 was 97% (range 93% – 100%) for CAMM scored plans (12 plans); and was 90% (range 80% – 95%) and 99% (range 95% – 100%) for CA scored plans (7 plans). The difference in V66 between CAMM and CA was significant for PTV (p = 0.03) and approached significance for CTV (p = 0.07).

Conclusion:

The quality of DIR‐mapped contours directly impacted the plan quality for 4DCBCT‐based adaptation. Larger safety margins may be needed when planning with auto contours for IGART with 4DCBCT images.

Reseach was supported by NIH P01CA116602.
SU‐E‐J‐161: Inverse Problems for Optical Parameters in Laser Induced Thermal Therapy
Authors: Fahrenholtz SJ , Stafford RJ , Fuentes DT
Published: July 2014

Purpose:

Magnetic resonance‐guided laser‐induced thermal therapy (MRgLITT) is investigated as a neurosurgical intervention for oncological applications throughout the body by active post market studies. Real‐time MR temperature imaging is used to monitor ablative thermal delivery in the clinic. Additionally, brain MRgLITT could improve through effective planning for laser fiber's placement. Mathematical bioheat models have been extensively investigated but require reliable patient specific physical parameter data, e.g. optical parameters. This abstract applies an inverse problem algorithm to characterize optical parameter data obtained from previous MRgLITT interventions.

Methods:

The implemented inverse problem has three primary components: a parameter‐space search algorithm, a physics model, and training data. First, the parameter‐space search algorithm uses a gradient‐based quasi‐Newton method to optimize the effective optical attenuation coefficient, μ_eff. A parameter reduction reduces the amount of optical parameter‐space the algorithm must search. Second, the physics model is a simplified bioheat model for homogeneous tissue where closed‐form Green's functions represent the exact solution. Third, the training data was temperature imaging data from 23 MRgLITT oncological brain ablations (980 nm wavelength) from seven different patients.

Results:

To three significant figures, the descriptive statistics for μ_eff were 1470 m−1 mean, 1360 m−1 median, 369 m−1 standard deviation, 933 m−1 minimum and 2260 m−1 maximum. The standard deviation normalized by the mean was 25.0%. The inverse problem took <30 minutes to optimize all 23 datasets.

Conclusion:

As expected, the inferred average is biased by underlying physics model. However, the standard deviation normalized by the mean is smaller than literature values and indicates an increased precision in the characterization of the optical parameters needed to plan MRgLITT procedures. This investigation demonstrates the potential for the optimization and validation of more sophisticated bioheat models that incorporate the uncertainty of the data into the predictions, e.g. stochastic finite element methods.
SU‐E‐J‐171: Surface Imaging Based Intrafraction Motion Assessments for Whole Brain Radiotherapy
Authors: Wiant D , Vanderstraeten C , Maurer J , Pursley J , Terrell J , Sintay B
Published: July 2014

Purpose:

To quantify and characterize intrafraction motion for whole brain radiotherapy treatments in open face masks using 3D surface imaging.

Methods:

Fifteen whole brain patients were monitored with 3D surface imaging over a total of 202 monitoring sessions. Mean translations and rotations were calculated over each minute, each session, and over all sessions combined. The percentage of each session that the root mean square (RMS) of the linear translations were outside of 2 mm, 3 mm, 4 mm, and 5 mm were determined for each patient. Correlations between mean translations per minute and time and between standard deviation per minute and time were evaluated using Pearson's r value.

Results:

The mean RMS translation averaged over all patients was 1.45 mm +/− 1.52 mm. The patients spent an average of 18%, 10%, 6%, and 3% of the monitoring time outside of 2 mm, 3 mm, 4 mm, and 5 mm RMS tolerances, respectively. The RMS values averaged over all patients were 1.31 mm +/− 0.98 mm, 1.52 +/‐ 1.04, and 1.30 mm +/− 0.71 mm over the 1th, 5th, and 10th minutes of monitoring, respectively. Neither, the RMS values (p = 0.15) or the standard deviations of the RMS values (p = 0.16) showed significant correlations with time.

Conclusion:

The patients were positioned within 2 mm of isocenter, which was the initial set‐up tolerance, for the majority of their treatments. The average position changed by < 0.3 mm over 10 minutes of monitoring. Short term movements, reflected by the standard deviations, where on the order of 1 mm. This immobilization system provides adequate immobilization over a course of treatment for whole brain radiotherapy. This system may also be suitable for head and neck or stereotactic radiosurgery treatments as well.
SU‐E‐J‐174: Adaptive PET‐Based Dose Painting with Tomotherapy
Authors: Darwish N , Mackie T , Thomadsen B
Published: July 2014

Purpose:

PET imaging can be converted into dose prescription directly. Due to the variability of the intensity of PET the image, PET prescription maybe superior over uniform dose prescription. Furthermore, unlike the case in image reconstruction of not knowing the image solution in advance, the prescribed dose is known from a PET image a priori. Therefore, optimum beam orientations are derivable.

Methods:

We can assume the PET image to be the prescribed dose and invert it to determine the energy fluence. The same method used to reconstruct tissue images from projections could be used to solve the inverse problem of determining beam orientations and modulation patterns from a dose prescription [10]. Unlike standard tomographic reconstruction of images from measured projection profiles, the inversion of the prescribed dose results in photon fluence which may be negative and therefore unphysical. Two‐dimensional modulated beams can be modelled in terms of the attenuated or exponential radon transform of the prescribed dose function (assumed to be the PET image in this case), an application of a Ram‐Lak filter, and inversion by backprojection. Unlike the case in PET processing, however, the filtered beam obtained from the inversion represents a physical photon fluence. Therefore, a positivity constraint for the fluence (setting negative fluence to zero) must be applied (Brahme et al 1982, Bortfeld et al 1990)

Results:

Truncating the negative profiles from the PET data results in an approximation of the derivable energy fluence. Backprojection of the deliverable fluence is an approximation of the dose delivered. The deliverable dose is comparable to the original PET image and is similar to the PET image.

Conclusion:

It is possible to use the PET data or image as a direct indicator of deliverable fluence for cylindrical radiotherapy systems such as TomoTherapy.
SU‐E‐J‐186: Acquiring and Assessing Upright CBCT Images for Future Treatment Planning
Authors: Fave X , Yang J , Balter P , Court L
Published: July 2014

Purpose:

To acquire upright CBCT images using the onboard imager of a Varian TrueBeam. An easy to implement upright imaging protocol could allow for widespread upright radiation therapy which would greatly benefit certain patients. These include thoracic cancer patients (because lung volume increases in a seated position) and patients who experience substantial discomfort during supine treatment.

Methods:

To acquire upright CBCT images, the gantry head remained stationary at 0 degrees with the KV imager arms extended to their lateral positions. Phantoms were placed upright at the end of the treatment couch. During a scan, the couch rotated from 270 to 90 degrees while continuous fluoroscopic projections were taken by the onboard imager. To extend the field‐of‐view, this sequence was performed twice: once with the KV detector longitudinally offset +14.5cm and once with it longitudinally offset −14.5cm. The resulting two image sets were stitched together before reconstruction. The imaging beam parameters were chosen to deliver a dose similar to that given during a simulation CT. Image quality was evaluated for spatial linearity, high and low contrast resolution, and HU linearity using CatPhan and anthropomorphic phantoms. A deformable registration technique was used to evaluate HU mapping from a simulation CT.

Results:

Spatial linearity and high contrast resolution were maintained in upright CBCT when compared to simulation CT. However, low contrast resolution and HU linearity degraded. Streak artifacts were caused by the limited 180 degree arc of the couch, and the stitching process created a sharp artifact at the center of the reconstruction. The deformable registration was robust in the HU mapping even with these artifacts and the loss of HU linearity.

Conclusions:

The image quality obtained from upright CBCT was sufficient for treatment planning. The success of this novel technique is an important step towards a future clinical protocol.

This project was funded in part by Varian Medical Systems, Inc.
SU‐E‐J‐188: Impact of Unexpected Dose Warping with Deformable Image Registration in Lung Cancer
Authors: Moriya S , Tachibana H , Sugawara Y , Sato M , Sawant A
Published: July 2014

Purpose:

In our previous study of dose warping validation, four cases in twenty lung SBRT patients shows unexpected result. We clarify the impact of dose warping with a free‐downloadable deformable image registration (DIR) program and a commercially‐available DIR software program.

Methods:

Our in‐house software was implemented with the blockmatching algorithm for rigid registration and the free‐form deformation algorithm for non‐rigid registration from the NiftyReg. The deformation algorithm implemented in the MIM software was also based on the freeform deformation algorithm. In order to assess the accuracy of dose warping from the two software programs, generalized equivalent uniformed dose (gEUD) of the deformed dose distribution for peak inhale phase was compared with the gEUD of the dose distribution for peak inhale phase base on a assumption that a radiobiological equivalent dose would be stable before and after the deformation. The peak‐inhale deformed dose distribution was superimposed on peak‐exhale phase CT and structure datasets.

Results:

The in‐house software shows that the difference of gEUD for the tumor was less than 1% in the previous study. The difference was 21.4% on average in the four cases (Max: 51.2%). In the four cases in the MIM, the result was improved, however was still more than 1% (Average: 7.3%, Max: 24.3%). In the visual evaluation of the case with large gEUD difference, the shape of dose distribution from dose warping was not in nature from the motion of the tumor. The CT images of a case, which have large difference of gEUD, shows that the tumor was surrounded by the structure with the similar CT values, which were the chest wall or the diaphragm.

Conclusion:

A commissioning test of not only a freedownloadable DIR program but also a commercial software is essential and we should understand pitfalls of dose warping from the DIR.
SU‐E‐J‐198: Evaluation of a Free‐Form Intensity‐Based Deformable Registration Method Using the POPI Model
Authors: Nelson AS , Duchateau M , Piper JW , Verellen D , Ridder M De
Published: July 2014

Purpose:

Our goal is to evaluate the accuracy of a free‐form intensity‐based deformable registration method using the POPI model.

Methods:

Five subjects with 4DCT datasets from the POPI model (Vandemeulebrouke Med Phys 2011) were used to assess deformable registration accuracy. Each subject contained 100 or more identified landmark points that corresponded between the end‐inspiratory and end‐expiratory phases. The 0% phase was registered to the 50% phase first using a rigid alignment followed by a freeform intensity‐based deformable registration. Landmark displacement was measured after the rigid registration (initial displacement) and the deformable registration (residual error). A single subject (POPI2) with significant initial displacement was also registered using an interactive tool to influence the deformation by locking local alignments to help guide the deformation. Error was measured with and without using the tool for this subject.

Results:

The average initial displacement prior to deformable registration ranged from 5.7 mm to 14.0 mm. The mean (SD) residual error after deformation ranged from 1.0 mm (0.9) to 1.7 mm (3.3) for four of the five subjects. For POPI2 the initial residual deformable error was 4.6 mm (6.8). Using seven local alignments to guide the deformation the error for POPI2 decreased to 1.2 mm (1.0). The average error across all 5 subjects was 1.3 mm (2.0).

Conclusion:

A free‐form intensity‐based deformable registration method was found to provide good accuracy with an average error of 1.3 mm. A method for locally guided deformation allowed for the accurate registration of a challenging case with significant respiratory motion. References1. Vandemeulebrouke et al. Med Phys 2011.2. http://www.creatis.insa‐lyon.fr/rio/popi‐model/

AS Nelson is an employee with ownership at MIM Software, Inc. JW Piper is an employee with ownership at MIM Software, Inc.
SU‐E‐J‐200: A Dosimetric Analysis of 3D Versus 4D Image‐Based Dose Calculation for Stereotactic Body Radiation Therapy in Lung Tumors
Authors: Ma M , Rouabhi O , Bayouth J , Flynn R , Xia J
Published: July 2014

Purpose:

To evaluate the dosimetric difference between 3D and 4Dweighted dose calculation using patient specific respiratory trace and deformable image registration for stereotactic body radiation therapy in lung tumors.

Methods:

Two dose calculation techniques, 3D and 4D‐weighed dose calculation, were used for dosimetric comparison for 9 lung cancer patients. The magnitude of the tumor motion varied from 3 mm to 23 mm. Breath‐hold exhale CT was used for 3D dose calculation with ITV generated from the motion observed from 4D‐CT. For 4D‐weighted calculation, dose of each binned CT image from the ten breathing amplitudes was first recomputed using the same planning parameters as those used in the 3D calculation. The dose distribution of each binned CT was mapped to the breath‐hold CT using deformable image registration. The 4D‐weighted dose was computed by summing the deformed doses with the temporal probabilities calculated from their corresponding respiratory traces. Dosimetric evaluation criteria includes lung V20, mean lung dose, and mean tumor dose.

Results:

Comparing with 3D calculation, lung V20, mean lung dose, and mean tumor dose using 4D‐weighted dose calculation were changed by −0.67% ± 2.13%, −4.11% ± 6.94% (−0.36 Gy ± 0.87 Gy), −1.16% ± 1.36%(−0.73 Gy ± 0.85 Gy) accordingly.

Conclusion:

This work demonstrates that conventional 3D dose calculation method may overestimate the lung V20, MLD, and MTD. The absolute difference between 3D and 4D‐weighted dose calculation in lung tumor may not be clinically significant.

This research is supported by Siemens Medical Solutions USA, Inc and Iowa Center for Research By Undergraduates
SU‐E‐J‐205: Monte Carlo Modeling of Ultrasound Probes for Real‐Time Ultrasound Image‐Guided Radiotherapy
Authors: Hristov D , Schlosser J , Chen J , Bazalova M
Published: July 2014

Purpose:

To quantify the effect of ultrasound (US) probe beam attenuation for radiation therapy delivered under real‐time US image guidance by means of Monte Carlo (MC) simulations.

Methods:

MC models of two Philips US probes, an X6‐1 matrix‐array transducer and a C5‐2 curved‐array transducer, were built based on their CT images in the EGSnrc BEAMnrc and DOSXYZnrc codes. Due to the metal parts, the probes were scanned in a Tomotherapy machine with a 3.5 MV beam. Mass densities in the probes were assigned based on an electron density calibration phantom consisting of cylinders with mass densities between 0.2–8.0 g/cm3. Beam attenuation due to the probes was measured in a solid water phantom for a 6 MV and 15 MV 15×15 cm2 beam delivered on a Varian Trilogy linear accelerator. The dose was measured with the PTW‐729 ionization chamber array at two depths and compared to MC simulations. The extreme case beam attenuation expected in robotic US image guided radiotherapy for probes in upright position was quantified by means of MC simulations.

Results:

The 3.5 MV CT number to mass density calibration curve was found to be linear with R2 > 0.99. The maximum mass densities were 4.6 and 4.2 g/cm3 in the C5‐2 and X6‐1 probe, respectively. Gamma analysis of the simulated and measured doses revealed that over 98% of measurement points passed the 3%/3mm criteria for both probes and measurement depths. The extreme attenuation for probes in upright position was found to be 25% and 31% for the C5‐2 and X6‐1 probe, respectively, for both 6 and 15 MV beams at 10 cm depth.

Conclusion:

MC models of two US probes used for real‐time image guidance during radiotherapy have been built. As a Result, radiotherapy treatment planning with the imaging probes in place can now be performed.

J Schlosser is an employee of SoniTrack Systems, Inc. D Hristov has financial interest in SoniTrack Systems, Inc.