bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐76: Incorporation of Ultrasound Elastography in Target Volume Delineation for Partial Breast Radiotherapy Planning: A Comparative Study
Authors: Juneja P , Harris E , Bamber J
Published: July 2014

Purpose:

There is substantial observer variability in the delineation of target volumes for post‐surgical partial breast radiotherapy because the tumour bed has poor x‐ray contrast. This variability may result in substantial variations in planned dose distribution. Ultrasound elastography (USE) has an ability to detect mechanical discontinuities and therefore, the potential to image the scar and distortion in breast tissue architecture. The goal of this study was to compare USE techniques: strain elastography (SE), shear wave elastography (SWE) and acoustic radiation force impulse (ARFI) imaging using phantoms that simulate features of the tumour bed, for the purpose of incorporating USE in breast radiotherapy planning.

Methods:

Three gelatine‐based phantoms (10% w/v) containing: a stiff inclusion (gelatine 16% w/v) with adhered boundaries, a stiff inclusion (gelatine 16% w/v) with mobile boundaries and fluid cavity inclusion (to mimic seroma), were constructed and used to investigate the USE techniques. The accuracy of the elastography techniques was quantified by comparing the imaged inclusion with the modelled ground‐truth using the Dice similarity coefficient (DSC). For two regions of interest (ROI), the DSC measures their spatial overlap. Ground‐truth ROIs were modelled using geometrical measurements from B‐mode images.

Results:

The phantoms simulating stiff scar tissue with adhered and mobile boundaries and seroma were successfully developed and imaged using SE and SWE. The edges of the stiff inclusions were more clearly visible in SE than in SWE. Subsequently, for all these phantoms the measured DSCs were found to be higher for SE (DSCs: 0.91–0.97) than SWE (DSCs: 0.68–0.79) with an average relative difference of 23%. In the case of seroma phantom, DSC values for SE and SWE were similar.

Conclusion:

This study presents a first attempt to identify the most suitable elastography technique for use in breast radiotherapy planning. Further analysis will include comparison of ARFI with SE and SWE.

This work is supported by the EPSRC Platform Grant, reference number EP/H046526/1.
SU‐E‐J‐77: Inter‐Fractional Variations in Internal Tumor Volumes Using Multiple 4DCTs and CBCTs
Authors: Xue M , Feigenberg S , Tan S , Reese A , Yi B , D' Souza W , Lu W
Published: July 2014

Purpose:

To quantitatively evaluate the inter‐fractional variations in ITVs over the course of treatment using multiple 4DCTs and CBCTs for patients treated with SBRT for lung targets. To compare using ITV generated from all phases of a 4D or average intensity projection (ITV‐AIP) as reference contours for image guidance.

Methods:

An IRB approved study included five patients who received SBRT for a lung target using daily image guidance with a CBCT. Three 4DCTs were acquired before (simulation), during and at the end of treatment. ITV‐4Ds (on all 10 phases) and ITV‐CBCTs were contoured manually. All CT images and contours were registered to the reference image – AIP1 from 4D1. The registration consists of intensity‐based image registration followed by manual soft‐tissue alignment, where physicians manually make shift to ensure that the tumor seen on CBCT is encompassed in ITV‐4D1 or ITV‐AIP1. The relationship between two ITVs was quantified by centroid distance, volume inclusion, and volume overlap (Dice Coefficient).

Results:

The average volume for ITV‐4D, ITV‐AIP, and ITV‐CBCT were 23.1, 17.2, and 14.1 cm3, respectively. When using ITV‐4D1 as a reference contour in the manual soft‐tissue alignment, an average of 93% of ITV‐CBCTs was included in ITV‐4D1, with a centroid distance of 2.0 mm. Only 81% of ITV‐4Ds were included in ITV‐4D1. The Dice Coefficient between ITV‐4D1 and ITV‐4Ds was only 0.68, suggesting that the two ITVs were not highly overlapping. For all comparisons, the results were similar using either ITV‐AIP1 or ITV‐4D1 as a reference contour in the manual soft‐tissue alignment.

Conclusions:

There were noteworthy inter‐fractional variations in ITV‐4Ds. Compared to ITV‐4D, ITV‐AIP was much similar to ITV‐CBCT. However, there was no significant difference between using ITV‐4D1 and using ITV‐AIP1 as a reference contour for image guidance. Further dosimetric studies are required to evaluate actual tumor coverage.

This study was supported in part by Philips Healthcare.
SU‐E‐J‐81: Interplay Effect in Non‐Gated Dynamic Treatment Delivery of a Lung Phantom with Simulated Respiratory Motion
Authors: Desai V , Fagerstrom J , Bayliss A , Kissick M
Published: July 2014

Purpose:

To quantify the interplay effect in non‐gated VMAT external beam delivery using realistic, clinically relevant 3D motion in an anthropomorphic lung phantom, and to determine if adding margins is sufficient to account for motion or if gating is required in all cases.

Methods:

A 4D motion stage was used to move a Virtual Water (VW) lung target containing a piece of radiochromic EBT3 film in an anthropomorphic chest phantom. A five‐arc stereotactic body radiation therapy (SBRT) treatment was planned using a CT scan of the phantom in its stationary position, using planning parameters chosen to push the optimizer to achieve a highly‐modulated plan. Two scenarios were delivered using a Varian TrueBeam: the first was delivered with the phantom and target both stationary and the second was delivered with the phantom stationary but the target moving in a realistic, irregular 3D elliptical pattern. A single piece of 4×4 cm2 film was used per fraction, located in the central coronal plane of the target. Film was calibrated on a 6 MV beam with dose values from 0.20 to 20 Gy.

Results:

Preliminary test films were analyzed in ImageJ and MatLab software. Dose maps were calculated on a central region of interest (ROI) delineated on both the motion‐induced and stationary films. Both static and dynamic film dose maps agreed with planning values within acceptable uncertainty.

Conclusion:

Including a large number of arcs in a clinically realistic SBRT treatment could reduce the effect of motion interplay due to averaging. Because all clinics do not employ multiple arcs for SBRT lung treatments, it is still important to consider the effects of motion on treatment delivery. Further analysis on the treatment films, as well as a broader investigation other planning parameters, will be conducted.
SU‐E‐J‐87: Lung Deformable Image Registration Using Surface Mesh Deformation for Dose Distribution Combination
Authors: Labine A , Chav R , Carrier J , DeGuise J , Bedwani S
Published: July 2014

Purpose:

To allow a reliable deformable image registration (DIR) method for dose calculation in radiation therapy. This work proposes a performance assessment of a morphological segmentation algorithm that generates a deformation field from lung surface displacements with 4DCT datasets.

Methods:

From the 4DCT scans of 15 selected patients, the deep exhale phase of the breathing cycle is identified as the reference scan. Varian TPS EclipseTM is used to draw lung contours, which are given as input to the morphological segmentation algorithm. Voxelized contours are smoothed by a Gaussian filter and then transformed into a surface mesh representation. Such mesh is adapted by rigid and elastic deformations to match each subsequent lung volumes. The segmentation efficiency is assessed by comparing the segmented lung contour and the TPS contour considering two volume metrics, defined as Volumetric Overlap Error (VOE) [%] and Relative Volume Difference (RVD) [%] and three surface metrics, defined as Average Symmetric Surface Distance (ASSD) [mm], Root Mean Square Symmetric Surface Distance (RMSSD) [mm] and Maximum Symmetric Surface Distance (MSSD) [mm]. Then, the surface deformation between two breathing phases is determined by the displacement of corresponding vertices in each deformed surface. The lung surface deformation is linearly propagated in the lung volume to generate 3D deformation fields for each breathing phase.

Results:

The metrics were averaged over the 15 patients and calculated with the same segmentation parameters. The volume metrics obtained are a VOE of 5.2% and a RVD of 2.6%. The surface metrics computed are an ASSD of 0.5 mm, a RMSSD of 0.8 mm and a MSSD of 6.9 mm.

Conclusion:

This study shows that the morphological segmentation algorithm can provide an automatic method to capture an organ motion from 4DCT scans and translate it into a volume deformation grid needed by DIR method for dose distribution combination.
SU‐E‐J‐88: Margin Reduction of Level II/III Planning Target Volume for Image‐Guided Simultaneous Integrated Boost Head‐And‐Neck Treatment
Authors: Can S , Neylon J , Qi S , Santhanam A , Low D
Published: July 2014

Purpose:

To investigate the feasibility of improved normal tissue sparing for head‐and‐neck (H' N) image‐guided radiotherapy (IGRT) by employing tighter CTV‐to‐PTV margins for target level II/III though a GPU‐based deformable image registration and dose accumulation framework.

Methods:

Ten H' N simultaneous integrated boost cases treated on TomoTherapy were retrospectively analyzed. Weekly kVCT scans in addition to daily MVCT scans were acquired for each patient. Reduced margin plans were generated with 0‐ mm margin for level II and III PTV (while 3‐5 mm margin for PTV1) and compared with the standard margin plan using 3‐5mm margin to all CTV1‐3 (reference plan). An in‐house developed GPU‐based 3D image deformation tool was used to register and deform the weekly KVCTs with the planning CT and determine the delivered mean/minimum/maximum dose, dose volume histograms (DVHs), etc.

Results:

Compared with the reference plans, the averaged cord maximum, the right and left parotid doses reduced by 22.7 %, 16.5 %, and 9 % respectively in the reduced margin plans. The V95 for PTV2 and PTV3 were found within 2 and 5% between the reference and tighter margin plans. For the reduced margin plans, the averaged cumulative mean doses were consistent with the planned dose for PTV1, PTV2 and PTV3 within 1.5%, 1.7% and 1.4%. Similar dose variations of the delivered dose were seen for the reference and tighter margin plans. The delivered maximum and mean doses for the cord were 3.55 % and 2.37% higher than the planned doses; a 5 % higher cumulative mean dose for the parotids was also observed for the delivered dose than the planned doses in both plans.

Conclusion:

By imposing tighter CTV‐to‐PTV margins for level II and III targets for H' N irradiation, acceptable cumulative doses were achievable when coupled with weekly kVCT guidance while improving normal structure sparing.
SU‐E‐J‐90: MRI‐Based Treatment Simulation and Patient Setup for Radiation Therapy of Brain Cancer
Authors: Yang Y , Cao M , Han F , Santhanam A , Neylon J , Gomez C , Kaprealian T , Sheng K , Agazaryan N , Low D , Hu P
Published: July 2014

Purpose:

Traditional radiation therapy of cancer is heavily dependent on CT. CT provides excellent depiction of the bones but lacks good soft tissue contrast, which makes contouring difficult. Often, MRIs are fused with CT to take advantage of its superior soft tissue contrast. Such an approach has drawbacks. It is desirable to perform treatment simulation entirely based on MRI. To achieve MR‐based simulation for radiation therapy, bone imaging is an important challenge because of the low MR signal intensity from bone due to its ultra‐short T2 and T1, which presents difficulty for both dose calculation and patient setup in terms of digitally reconstructed radiograph (DRR) generation. Current solutions will either require manual bone contouring or multiple MR scans. We present a technique to generate DRR using MRI with an Ultra Short Echo Time (UTE) sequence which is applicable to both OBI and ExacTrac 2D patient setup.

Methods:

Seven brain cancer patients were scanned at 1.5 Tesla using a radial UTE sequence. The sequence acquires two images at two different echo times. The two images were processed using in‐house software. The resultant bone images were subsequently loaded into commercial systems to generate DRRs. Simulation and patient clinical on‐board images were used to evaluate 2D patient setup with MRI‐DRRs.

Results:

The majority bones are well visualized in all patients. The fused image of patient CT with the MR bone image demonstrates the accuracy of automatic bone identification using our technique. The generated DRR is of good quality. Accuracy of 2D patient setup by using MRI‐DRR is comparable to CT‐based 2D patient setup.

Conclusion:

This study shows the potential of DRR generation with single MR sequence. Further work will be needed on MR sequence development and post‐processing procedure to achieve robust MR bone imaging for other human sites in addition to brain.
SU‐E‐J‐91: Novel Epitaxial Silicon Array for Quality Assurance in Photon and Proton Therapy
Authors: Talamonti C , Menichelli D , Zani M , Friedl F , Scaringella M , Bruzzi M , Bucciolini M
Published: July 2014

Purpose:

to demonstrate suitability of a novel silicon array for measuring the dose properties of highly conformal photon and proton beams.

Methods:

prototype under test is a 24cm long linear array prototype, although the underlying technology is suitable to construct 2D arrays as well. It is based on a 64pixels monolithic sensor with 1mm pixel pitch, made of epitaxial ptype silicon. Thanks to design modularity, more sensors can be placed side by side without breaking pixel pitch. Flattened and unflattened photon beams, as well as proton radiation from a cyclotron in pencil beam scanning mode, were considered. Measurements of beam characteristics as percentage depth doses, dose profiles, output factors and energy response, which are necessary to deliver radiation with high precision and reliability, were performed.

Results:

Dose rate independence with photons was verified in the dose per pulse range 0.03 to 2mGy. Results clearly indicate nondependence of the detector sensitivity both for flattened and unflattened beams, with a variation of at most 0.5percentage. OFs were obtained for field with a lateral size ranging from 0.8cm to 16cm and the results are in good agreement with ion chamber A1SL, max difference less than 1.5percentage. Field sizes and beam penumbra were measured and compared to EBT film results. Concerning proton beams, sensitivity independence on dose rate was verified by changing the beam current in the interval 2‐130Gy/s. Field sizes and beam penumbra measurements are in agreement with data taken with a scintillating 2D array with 0.5mm resolution IBA Lynx, and a better penumbra definition than an array of ionization chambers IBA MatriXX is reached.

Conclusion:

The device is a novel and valuable tool for QA both for photon and proton dose delivery. All measurements demonstrated its capability to measure with high spatial resolution many crucial properties of the RT beam.
SU‐E‐J‐92: On‐Line Cone Beam CT Based Planning for Emergency and Palliative Radiation Therapy
Authors: Held M , Morin O , Pouliot J
Published: July 2014

Purpose:

To evaluate and develop the feasibility of on‐line cone beam CT based planning for emergency and palliative radiotherapy treatments.

Methods:

Subsequent to phantom studies, a case library of 28 clinical megavoltage cone beam CT (MVCBCT) was built to assess dose‐planning accuracies on MVCBCT for all anatomical sites. A simple emergency treatment plan was created on the MVCBCT and copied to its reference CT. The agreement between the dose distributions of each image pair was evaluated by the mean dose difference of the dose volume and the gamma index of the central 2D axial plane. An array of popular urgent and palliative cases was also evaluated for imaging component clearance and field‐of‐view.

Results:

The treatment cases were categorized into four groups (head and neck, thorax/spine, pelvis and extremities). Dose distributions for head and neck treatments were predicted accurately in all cases with a gamma index of >95% for 2% and 2 mm criteria. Thoracic spine treatments had a gamma index as low as 60% indicating a need for better uniformity correction and tissue density calibration. Small anatomy changes between CT and MVCBCT could contribute to local errors. Pelvis and sacral spine treatment cases had a gamma index between 90% and 98% for 3%/3 mm criteria. The limited FOV became an issue for large pelvis patients. Imaging clearance was difficult for cases where the tumor was positioned far off midline.

Conclusion:

The MVCBCT based dose planning and delivery approach is feasible in many treatment cases. Dose distributions for head and neck patients are unrestrictedly predictable. Some FOV restrictions apply to other treatment sites. Lung tissue is most challenging for accurate dose calculations given the current imaging filters and corrections. Additional clinical cases for extremities need to be included in the study to assess the full range of site‐specific planning accuracies.

This work is supported by Siemens.
SU‐E‐J‐102: Separation of Metabolic Supply and Demand: From Power Grid Economics to Cancer Metabolism
Authors: Epstein T , Xu L , Gillies R , Gatenby R
Published: July 2014

Purpose:

To study a new model of glucose metabolism which is primarily governed by the timescale of the energetic demand and not by the oxygen level, and its implication on cancer metabolism (Warburg effect)

Methods:

1) Metabolic profiling of membrane transporters activity in several cell lines, which represent the spectrum from normal breast epithelium to aggressive, metastatic cancer, using Seahorse XF reader.2) Spatial localization of oxidative and non‐oxidative metabolic components using immunocytochemical imaging of the glycolytic ATP‐producing enzyme, pyruvate kinase and mitochondria. 3) Finite element simulations of coupled partial differential equations using COMSOL and MATLAB.

Results:

Inhibition or activation of pumps on the cell membrane led to reduction or increase in aerobic glycolysis, respectively, while oxidative phosphorylation remained unchanged. These results were consistent with computational simulations of changes in short‐timescale demand for energy by cell membrane processes. A specific model prediction was that the spatial distribution of ATP‐producing enzymes in the glycolytic pathway must be primarily localized adjacent to the cell membrane, while mitochondria should be predominantly peri‐nuclear. These predictions were confirmed experimentally.

Conclusion:

The results in this work support a new model for glucose metabolism in which glycolysis and oxidative phosphorylation supply different types of energy demand. Similar to power grid economics, optimal metabolic control requires the two pathways, even in normoxic conditions, to match two different types of energy demands. Cells use aerobic metabolism to meet baseline, steady energy demand and glycolytic metabolism to meet short‐timescale energy demands, mainly from membrane transport activities, even in the presence of oxygen. This model provides a mechanism for the origin of the Warburg effect in cancer cells. Here, the Warburg effect emerges during carcinogenesis is a physiological response to an increase in energy demands from membrane transporters, required for cell division, growth, and migration.

This work is supported by the NIH Physical Sciences in Oncology Center grant 1U54CA143970‐03 and NIH R01 CA077575‐10.
SU‐E‐J‐103: Setup Errors Analysis by Cone‐Beam CT (CBCT)‐Based Imaged‐Guided Intensity Modulated Radiotherapy for Esophageal Cancer
Authors: Yang H , Wang W , Hu W , Chen X , Wang X , Yu C
Published: July 2014

Purpose:

To quantify setup errors by pretreatment kilovolt cone‐beam computed tomography(KV‐CBCT) scans for middle or distal esophageal carcinoma patients.

Methods:

Fifty‐two consecutive middle or distal esophageal carcinoma patients who underwent IMRT were included this study. A planning CT scan using a big‐bore CT simulator was performed in the treatment position and was used as the reference scan for image registration with CBCT. CBCT scans(On‐Board Imaging v1. 5 system, Varian Medical Systems) were acquired daily during the first treatment week. A total of 260 CBCT scans was assessed with a registration clip box defined around the PTV‐thorax in the reference scan based on(nine CBCTs per patient) bony anatomy using Offline Review software v10.0(Varian Medical Systems). The anterior‐posterior(AP), left‐right(LR), superiorinferior(SI) corrections were recorded. The systematic and random errors were calculated. The CTV‐to‐PTV margins in each CBCT frequency was based on the Van Herk formula (2.5Σ+0.7σ).

Results:

The SD of systematic error (Σ) was 2.0mm, 2.3mm, 3.8mm in the AP, LR and SI directions, respectively. The average random error (σ) was 1.6mm, 2.4mm, 4.1mm in the AP, LR and SI directions, respectively. The CTV‐to‐PTV safety margin was 6.1mm, 7.5mm, 12.3mm in the AP, LR and SI directions based on van Herk formula.

Conclusion:

Our data recommend the use of 6 mm, 8mm, and 12 mm for esophageal carcinoma patient setup in AP, LR, SI directions, respectively.
SU‐E‐J‐105: Stromal‐Epithelial Responses to Fractionated Radiotherapy
Authors: Qayyum M
Published: July 2014

Purpose:

The stromal‐epithelial‐cell interactions that are responsible for directing normal breast‐tissue development and maintenance play a central role in the progression of breast cancer. In the present study, we developed three‐dimensional (3‐D) cell co‐cultures used to study cancerous mammary cell responses to fractionated radiotherapy. In particular, we focused on the role of the reactive stroma in determining the therapeutic ratio for postsurgical treatment.

Methods:

Cancerous human mammary epithelial cells were cultured in a 3‐D collagen matrix with human fibroblasts stimulated by various concentrations of transforming growth factor beta 1 (TGF‐β1). These culture samples were designed to model the post‐lumpectomy mammary stroma in the presence of residual cancer cells. We tracked over time the changes in medium stiffness, fibroblast‐cell activation (conversion to cancer activated fibroblasts (CAF)), and proliferation of both cell types under a variety of fractionated radiotherapy protocols. Samples were exposed to 6 MV X‐rays from a linear accelerator in daily fraction sizes of 90, 180 and 360 cGy over five days in a manner consistent with irradiation exposure during radiotherapy.

Results:

We found in fractionation studies with fibroblasts and CAF that higher doses per fraction may be more effective early on in deactivating cancer‐harboring cellular environments. Higher‐dose fraction schemes inhibit contractility in CAF and prevent differentiation of fibroblasts, thereby metabolically uncoupling tumor cells from their surrounding stroma. Yet, over a longer time period, the higher dose fractions may slow wound healing and increase ECM stiffening that could stimulate proliferation of surviving cancer cells.

Conclusion:

The findings suggest that dose escalation to the region with residual disease can deactivate the reactive stroma, thus minimizing the cancer promoting features of the cellular environment. Large‐fraction irradiation may be used to sterilize residual tumor cells and inhibit activation of intracellular transduction pathways that are promoted during the post‐surgical woundhealing period.

NIH award R01CA138882
SU‐E‐J‐106: Study of Variation of Internal Taget Volume Between 4DCT and Slow‐CT in Respiratory Patterns Using Respiratory Motion Phantom
Authors: Lee S , Choi S , Min C , Ji Y , Jung H , Kim M , Yoo H , Kim C , Yi C , kim K
Published: July 2014

Purpose:

The objective of this study is to investigate the difference of ITV lengths and ITVs between 4DCT and Slow‐CT images according to respiratory patterns using a respiratory motion phantom.

Methods:

The respiratory periods 1∼4s and target motion 1∼3 cm were applied on each respiratory pattern. 4DCT and Slow‐CT images were acquired for 3 times. 4DCT and Slow‐CT ITVs were measured with contouring the target in the Eclipse RTP system. The measured ITV lenghts and ITVs in 4DCT and Slow‐CT images were compared to the known values.

Results:

For the ITV lengths and ITVs in the 4DCT, the difference of them were reduced as the respiratory period is longer and target motion is shorter. For the Slow‐CT, there was same tendency with change in 4DCT ITV lengths and ITVs about target motion. According to the respiratory patterns, pattern A had the highest reproducibility. Pattern B, C and D were showed the difference similar to each other. However, for pattern E, the reproducibility was the lowest compared with other four patterns. The difference of ITV lengths and ITVs between Slow‐CT and 4DCT was increased by increasing the respiratory periods and target motion for all respiratory patterns. In case of pattern A, B and C, length difference was 3 mm at S(superior) and I(inferior) direction, and the length difference of pattern D was 1.45 cm at only “I” direction whereas the length difference of pattern E was 5 mm longer in “S” direction than “I” direction.

Conclusion:

The margin in SI directions should be determined by considering the respiratory patterns when the margin of Slow‐CT is compensated for 4DCT ITV lengths. Afterward, we think that the Resultof this study will be useful to analyze the ITV lengths and ITVs from the CT images on the basis of the patient respiratory signals.
SU‐E‐J‐135: An Investigation of Ultrasound Imaging for 3D Intra‐Fraction Prostate Motion Estimation
Authors: O' Shea T , Harris E , Evans P , Bamber J
Published: July 2014

Purpose:

This study investigates the use of a mechanically swept 3D ultrasound (US) probe to estimate intra‐fraction motion of the prostate during radiation therapy using an US phantom and simulated transperineal imaging.

Methods:

A 3D motion platform was used to translate an US speckle phantom while simulating transperineal US imaging. Motion patterns for five representative types of prostate motion, generated from patient data previously acquired with a Calypso system, were using to move the phantom in 3D. The phantom was also implanted with fiducial markers and subsequently tracked using the CyberKnife kV x‐ray system for comparison. A normalised cross correlation block matching algorithm was used to track speckle patterns in 3D and 2D US data. Motion estimation results were compared with known phantom translations.

Results:

Transperineal 3D US could track superior‐inferior (axial) and anterior‐posterior (lateral) motion to better than 0.8 mm root‐mean‐square error (RMSE) at a volume rate of 1.7 Hz (comparable with kV x‐ray tracking RMSE). Motion estimation accuracy was poorest along the US probe's swept axis (right‐left; RL; RMSE < 4.2 mm) but simple regularisation methods could be used to improve RMSE (< 2 mm). 2D US was found to be feasible for slowly varying motion (RMSE < 0.5 mm). 3D US could also allow accurate radiation beam gating with displacement thresholds of 2 mm and 5 mm exhibiting a RMSE of less than 0.5 mm.

Conclusion:

2D and 3D US speckle tracking is feasible for prostate motion estimation during radiation delivery. Since RL prostate motion is small in magnitude and frequency, 2D or a hybrid (2D/3D) US imaging approach which also accounts for potential prostate rotations could be used. Regularisation methods could be used to ensure the accuracy of tracking data, making US a feasible approach for gating or tracking in standard or hypo‐fractionated prostate treatments.
SU‐E‐J‐136: Multimodality‐Image‐Based Target Delineation for Dose Painting of Pancreatic Cancer
Authors: Dalah E , Paulson E , Erickson B , Li X
Published: July 2014

Purpose:

Dose escalated RT may provide improved disease local‐control for selected unresectable pancreatic cancer. Accurate delineation of the gross tumor volume (GTV) inside pancreatic head or body would allow safe dose escalation considering the tolerances of adjacent organs at risk (OAR). Here we explore the potential of multi‐modality imaging (DCE‐MRI, ADC‐MRI, and FDG‐PET) to define the GTV for dose painting of pancreatic cancer. Volumetric variations of DCE‐MRI, ADC‐MRI and FDG‐PET defined GTVs were assessed in comparison to the findings on CT, and to pathology specimens for resectable and borderline reseactable cases of pancreatic cancer.

Methods:

A total of 19 representative patients with DCE‐MRI, ADC‐MRI and FDG‐PET data were analyzed. Of these, 8 patients had pathological specimens. GTV, inside pancreatic head/neck, or body, were delineated on MRI (denoted GTVDCE, and GTVADC), on FDG‐PET using SUV of 2.5, 40% SUVmax, and 50% SUVmax (denoted GTV2.5, GTV40%, and GTV50%). A Kruskal‐Wallis test was used to determine whether significant differences existed between GTV volumes.

Results:

Significant statistical differences were found between the GTVs defined by DCE‐MRI, ADC‐MRI, and FDG‐PET, with a mean and range of 4.73 (1.00–9.79), 14.52 (3.21–25.49), 22.04 (1.00–45.69), 19.10 (4.84–45.59), and 9.80 (0.32–35.21) cm3 (p<0.0001) for GTVDCE, GTVADC, GTV2.5, GTV40%, and GTV50%, respectively. The mean difference and range in the measurements of maximum dimension of GTVs based on DCE‐MRI, ADC‐MRI, SUV2.5, 40% SUVmax, and 50% SUVmax compared with pathologic specimens were −0.84 (−2.24 to 0.9), 0.41 (−0.15 to 2.3), 0.58 (−1.41 to 3.69), 0.66 (−0.67 to 1.32), and 0.15 (−1.53 to 2.38) cm, respectively.

Conclusion:

Differences exists between DCE, ADC, and PET defined target volumes for RT of pancreatic cancer. Further studies combined with pathological specimens are required to identify the optimal imaging modality and/or acquisition method to define the GTV.
SU‐E‐J‐137: Incorporating Tumor Regression Into Robust Plan Optimization for Head and Neck Radiotherapy
Authors: Zhang P , Hu J , Tyagi N , Mageras G , Lee N , Hunt M
Published: July 2014

Purpose:

To develop a robust planning paradigm which incorporates a tumor regression model into the optimization process to ensure tumor coverage in head and neck radiotherapy.

Methods:

Simulation and weekly MR images were acquired for a group of head and neck patients to characterize tumor regression during radiotherapy. For each patient, the tumor and parotid glands were segmented on the MR images and the weekly changes were formulated with an affine transformation, where morphological shrinkage and positional changes are modeled by a scaling factor, and centroid shifts, respectively. The tumor and parotid contours were also transferred to the planning CT via rigid registration. To perform the robust planning, weekly predicted PTV and parotid structures were created by transforming the corresponding simulation structures according to the weekly affine transformation matrix averaged over patients other than him/herself. Next, robust PTV and parotid structures were generated as the union of the simulation and weekly prediction contours. In the subsequent robust optimization process, attainment of the clinical dose objectives was required for the robust PTV and parotids, as well as other organs at risk (OAR). The resulting robust plans were evaluated by looking at the weekly and total accumulated dose to the actual weekly PTV and parotid structures. The robust plan was compared with the original plan based on the planning CT to determine its potential clinical benefit.

Results:

For four patients, the average weekly change to tumor volume and position was −4% and 1.2 mm laterally‐posteriorly. Due to these temporal changes, the robust plans resulted in an accumulated PTV D95 that was, on average, 2.7 Gy higher than the plan created from the planning CT. OAR doses were similar.

Conclusion:

Integration of a tumor regression model into target delineation and plan robust optimization is feasible and may yield improved tumor coverage.

Part of this research is supported by Varian Medical System
SU‐E‐J‐141: Comparison of Dose Calculation On Automatically Generated MRBased ED Maps and Corresponding Patient CT for Clinical Prostate EBRT Plans
Authors: Schadewaldt N , Schulz H , Helle M , Frantzen‐Steneker M , Heide U , Renisch S
Published: July 2014

Purpose:

To analyze the effect of computing radiation dose on automatically generated MR‐based simulated CT images compared to true patient CTs.

Methods:

Six prostate cancer patients received a regular planning CT for RT planning as well as a conventional 3D fast‐field dual‐echo scan on a Philips 3.0T Achieva, adding approximately 2 min of scan time to the clinical protocol. Simulated CTs (simCT) where synthesized by assigning known average CT values to the tissue classes air, water, fat, cortical and cancellous bone. For this, Dixon reconstruction of the nearly out‐of‐phase (echo 1) and in‐phase images (echo 2) allowed for water and fat classification. Model based bone segmentation was performed on a combination of the DIXON images. A subsequent automatic threshold divides into cortical and cancellous bone. For validation, the simCT was registered to the true CT and clinical treatment plans were re‐computed on the simCT in pinnacle3. To differentiate effects related to the 5 tissue classes and changes in the patient anatomy not compensated by rigid registration, we also calculate the dose on a stratified CT, where HU values are sorted in to the same 5 tissue classes as the simCT.

Results:

Dose and volume parameters on PTV and risk organs as used for the clinical approval were compared. All deviations are below 1.1%, except the anal sphincter mean dose, which is at most 2.2%, but well below clinical acceptance threshold. Average deviations are below 0.4% for PTV and risk organs and 1.3% for the anal sphincter. The deviations of the stratifiedCT are in the same range as for the simCT. All plans would have passed clinical acceptance thresholds on the simulated CT images.

Conclusion:

This study demonstrated the clinical usability of MR based dose calculation with the presented Dixon acquisition and subsequent fully automatic image processing.

N. Schadewaldt, H. Schulz, M. Helle and S. Renisch are employed by Phlips Technologie Innovative Techonologies, a subsidiary of Royal Philips NV.
SU‐E‐J‐143: Short‐ and Near‐Term Effects of Proton Therapy On Cerebral White Matter
Authors: Uh J , Merchant T , Ogg R , Sabin N , Indelicato D , Hua C
Published: July 2014

Purpose:

To assess early effects of proton therapy on the structural integrity of cerebral white matter in relation to the subsequent near‐term development of such effects.

Methods:

Sixteen children (aged 2–19 years) with craniopharyngioma underwent proton therapy of 54 Cobalt Gray Equivalent (CGE) in a prospective therapeutic trial. Diffusion tensor imaging (DTI) was performed at baseline before proton therapy and every 3 months thereafter. Tract‐based spatial statics analysis of DTI data was performed to derive the fractional anisotropy (FA) and radial diffusivity (RD) in 26 volumes of interest (VOIs). The dose distributions were spatially normalized to identify VOIs prone to high doses. The longitudinal percentage changes of the FA and RD in these VOIs at 3 and 12 months from the baseline were calculated, and their relationships were evaluated.

Results:

The average dose was highest to the cerebral peduncle (CP), corticospinal tract (CST) in the pons, pontine crossing tract (PCT), anterior/posterior limbs of the internal capsule (ALIC/PLIC), and genu of the corpus callosum (GCC). It ranged from 33.3 GCE (GCC) to 49.7 GCE (CP). A mild but statistically significant (P<0.05) decline of FA was observed 3 months after proton therapy in all VOIs except the PLIC and ranged from −1.7% (ALIC) to −2.8% (PCT). A significant increase of RD was found in the CP (3.5%) and ALIC (2.1%). The average longitudinal change from the baseline was reduced at 12 months for most VOIs. However, the standard deviation increased, indicating that the temporal pattern varied individually. The follow‐up measurements at 3 and 12 months correlated for the CP, CST, PCT, and GCC (P < 0.04).

Conclusion:

DTI data suggest early (3 months) effects of proton therapy on microstructures in the white matter. The subsequent follow‐up indicated individual variation of the changes, which was partly implied by the early effects.
SU‐E‐J‐144: MRI Visualization of a Metallic Fiducial Marker Used for Image Guided Prostate Radiotherapy
Authors: Yee S , Krauss D , Yan D
Published: July 2014

Purpose:

Unlike on the daily CBCT used for the image‐guided radiation therapy, the visualization of an implantable metallic fiducial marker on the planning MRI images has been a challenge due to the inherent insensitivity of metal in MRI, and very thin (∼ 1 mm or less) diameter. Here, an MRI technique to visualize a marker used for prostate cancer radiotherapy is reported.

Methods:

During the MRI acquisitions, a multi‐shot turbo spin echo (TSE) technique (TR=3500 ms, TE=8.6 ms, ETL=17, recon voxel=0.42×0.42×3.5 mm3) was acquired in Philips 3T Ingenia together with a T2‐weighted multi‐shot TSE (TR=5381 ms, TE=110 ms, ETL=17, recon voxel=0.47×0.47×3 mm3) and a balanced turbo field echo (bTFE, flip angle 60, TR=2.76 ms, TE=1.3 ms, 0.85×0.85×3 mm3, NSA=4). In acquiring the MRI to visualize the fiducial marker, a particular emphasis was made to improve the spatial resolution and visibility in the generally dark, inhomogeneous prostate area by adjusting the slice profile ordering and TE values of TSE acquisition (in general, the lower value of TE in TSE acquisition generates a brighter signal but at the cost of high spatial resolution since the k‐space, responsible for high spatial resolution, is filled with noisier data).

Results:

While clearly visible in CT, the marker was not visible in either T2‐weighted TSE or bTFE, although the image qualities of both images were superior. In the new TSE acquisition (∼ a proton‐density weighted image) adjusted by changing the profile ordering and the TE value, the marker was visible as a negative (but clear) contrast in the magnitude MRI, and as a positive contrast in the imaginary image of the phase‐sensitive MRI.

Conclusion:

A metallic fiducial marker used for image guidance before prostate cancer radiotherapy can be made visible in MRI, which may facilitate more use of MRI in planning and guiding such radiation therapy.
SU‐E‐J‐146: Spatial Accuracy QA of An MR System
Authors: Hwang K , Illerstam F , Torfeh T , Maier J , Shave S , Hoang M
Published: July 2014

Purpose:

To develop a phantom and measurement protocol for quantifying spatial accuracy of an MR imaging system over its entire imaging volume.

Methods:

The measurement protocol is comprised of a phantom, a set of MR sequence parameters for imaging the phantom, and analysis software for calculating spatial errors in the acquired phantom images. The phantom covers the entire imaging volume of the scanner above the patient table, and consists of layers of foam embedded with a matrix of spherical markers. To account for possible spatial errors in the construction of the phantom, the phantom may be imaged with CT to create a gold standard data set. On MR scanners, the phantom is acquired with a 3D FGRE sequence that covers the full imaging volume. Error measurements are performed by detecting markers in the image sets and identifying them based on their known locations on the phantom. The spatial error of a marker is defined as the difference between its locations on the MR and CT image sets. The phantom, protocol, and analysis program may also be adapted to different applications by allowing for differences in phantom size and region of analysis within the scanner.

Results:

Three copies of the phantom were constructed and the measurement protocol was successfully executed on several MR scanners at multiple sites. Submillimeter precision and repeatability of the marker detection was also confirmed with manual measurements and repeated acquisitions on a single scanner.

Conclusion:

The proposed phantom and protocol can be an effective tool for verifying the spatial accuracy of an MR system, which in turn can improve the accuracy and confidence of MR guided therapies. Data from this protocol may also serve as a basis for a specification for spatial accuracy or be used in the development of advanced distortion correction algorithms.

Hwang, Illerstam, Maier, and Hoang are employees of GE Healthcare.
SU‐E‐J‐149: Establishing the Relationship Between Pre‐Treatment Lung Ventilation, Dose, and Toxicity Outcome
Authors: Mistry N , D' Souza W , Sornsen de Koste J , Senan S
Published: July 2014

Purpose:

Recently, there has been an interest in incorporating functional information in treatment planning especially in thoracic tumors. The rationale is that healthy lung regions need to be spared from radiation if possible to help achieve better control on toxicity. However, it is still unclear whether high functioning regions need to be spared or have more capacity to deal with the excessive radiation as compared to the compromised regions of the lung. Our goal with this work is to establish the tools by which we can establish a relationship between pre‐treatment lung function, dose, and radiographic outcomes of lung toxicity.

Methods:

Treatment planning was performed using a single phase of a 4DCT scan, and follow‐up anatomical CT scans were performed every 3 months for most patients. In this study, we developed the pipeline of tools needed to analyze such a large dataset, while trying to establish a relationship between function, dose, and outcome. Pre‐treatment lung function was evaluated using a recently published technique that evaluates Fractional Regional Ventilation (FRV). All images including the FRV map and the individual follow‐up anatomical CT images were all spatially matched to the planning CT using a diffusion based Demons image registration algorithm. Change in HU value was used as a metric to capture the effects of lung toxicity. To validate the findings, a radiologist evaluated the follow‐up anatomical CT images and scored lung toxicity.

Results:

Initial experience in 1 patient shows a relationship between the pre‐treatment lung function, dose and toxicity outcome. The results are also correlated to the findings by the radiologist who was blinded to the analysis or dose.

Conclusion:

The pipeline we have established to study this enables future studies in large retrospective studies. However, the tools are dependent on the fidelity of 4DCT reconstruction for accurate evaluation of regional ventilation.

Patent Pending for the technique presented in this work to evaluate FRV incorporating mass correction.
SU‐E‐J‐152: Evaluation of TrueBeam OBI V. 1.5 CBCT Performance in An Adaptive RT Environment
Authors: Gardner S , Studenski M , Giaddui T , Cui Y , Galvin J , Yu Y , Xiao Y
Published: July 2014

Purpose:

To evaluate the image quality and imaging dose of the Varian TrueBeam OBIv.1.5 CBCT system in a clinical adaptive radiation therapy environment, simulated by changing phantom thickness.

Methods:

Various OBI CBCT protocols(Head, Pelvis, Thorax, Spotlight) were used to acquire images of Catphan504 phantom(nominal phantom thickness and 10 cm additional phantom thickness). The images were analyzed for low contrast detectability(CNR), uniformity(UI), and HU sensitivity. These results were compared to the same image sets for planning CT(pCT)(GE LightSpeed 16‐ slice). Imaging dose measurements were performed with Gafchromic XRQA2 film for various OBI protocols (Pelvis, Thorax, Spotlight) in a pelvic‐sized phantom(nominal thickness and 4cm additional thickness). Dose measurements were acquired in the interior and at the surface of the phantom.

Results:

The nominal CNR[additional thickness CNR] for OBI was—Pelvis:1.45[0.81],Thorax:0.86[0.48], Spotlight:0.67[0.39],Head:0.28 [0.10]. The nominal CNR[additional thickness CNR] for pCT was— Pelvis:0.87[0.41],Head:0.60[0.22]. The nominal UI[additional thickness UI] for OBI was—Pelvis:11.5[24.1],Thorax:17.0[20.6], Spotlight:23.2[23.2], Head:15.6[59.9]. The nominal UI[additional thickness UI] for pCT was— Pelvis:9.2[8.6],Head:2.1[2.9]. The HU difference(averaged over all material inserts) between nominal and additional thickness scans for OBI: 8.26HU(Pelvis), 33.39HU(Thorax), 178.98HU(Head), 108.20HU (Spotlight); for pCT: 16.00HU(Pelvis), 19.85HU(Head). Uncertainties in electron density were calculated based on HU values with varying phantom thickness. Average electron‐density deviations (ρ(water)=1)for GE‐Pelvis, GE‐Head, OBI‐Pelvis, OBI‐Thorax, OBI‐Spotlight, and OBI‐Head were: 0.0182, 0.0180, 0.0058, 0.0478, 0.2750, and 0.3115, respectively. The average phantom interior dose was(OBI‐nominal):2.35cGy(Pelvis), 0.60cGy(Thorax), 1.87cGy(Spotlight); OBI‐increased thickness: 1.77cGy(Pelvis), 0.43cGy(Thorax), 1.53cGy (Spotlight). Average surface dose(OBI‐nominal): 2.29cGy(Pelvis), 0.56cGy(Thorax), 1.79cGy (Spotlight); OBI‐increased thickness: 1.94cGy(Pelvis), 0.48cGy(Thorax), 1.47cGy (Spotlight).

Conclusion:

The OBI‐Pelvis protocol offered comparable CNR and HU constancy to pCT for each geometry; other protocols, particularly Spotlight and Head, exhibited lower HU constancy and CNR. The uniformity of pCT was superior to OBI for all protocols. CNR and UI were degraded for both systems/scan types with increased thickness. The OBI interior dose decreased by approximately 30% with additional thickness.

This work was funded, in part, under a grant with the Pennsylvania Department of Health. The Department of Health specifically declaims responsibility for any analyses, interpretations, or conclusions.
SU‐E‐J‐153: MRI Based, Daily Adaptive Radiotherapy for Rectal Cancer: Contour Adaptation
Authors: Kleijnen J , Burbach M , Verbraeken T , Weggers R , Zoetelief A , Reerink O , Lagendijk J , Raaymakers B , Asselen B
Published: July 2014

Purpose:

A major hurdle in adaptive radiotherapy is the adaptation of the planning MRI's delineations to the daily anatomy. We therefore investigate the accuracy and time needed for online clinical target volume (CTV) adaptation by radiation therapists (RTT), to be used in MRI‐guided adaptive treatments on a MRI‐Linac (MRL).

Methods:

Sixteen patients, diagnosed with early stage rectal cancer, underwent a T2‐weighted MRI prior to each fraction of short‐course radiotherapy, resulting in 4–5 scans per patient. On these scans, the CTV was delineated according to guidelines by an experienced radiation oncologist (RO) and considered to be the gold standard. For each patient, the first MRI was considered as the planning MRI and matched on bony anatomy to the 3–4 daily MRIs. The planning MRI's CTV delineation was rigidly propagated to the daily MRI scans as a proposal for adaptation. Three RTTs in training started the adaptation of the CTV conform guidelines, after a two hour training lecture and a two patient (n=7) training set. To assess the inter‐therapist variation, all three RTTs altered delineations of 3 patients (n=12). One RTT altered the CTV delineations (n=53) of the remaining 11 patients. Time needed for adaptation of the CTV to guidelines was registered.As a measure of agreement, the conformity index (CI) was determined between the RTTs' delineations as a group. Dice similarity coefficients were determined between delineations of the RTT and the RO.

Results:

We found good agreement between RTTs' and RO's delineations (average Dice=0.91, SD=0.03). Furthermore, the inter‐observer agreement between the RTTs was high (average CI=0.94, SD=0.02). Adaptation time reduced from 10:33 min (SD= 3:46) to 2:56 min (SD=1:06) between the first and last ten delineations, respectively.

Conclusion:

Daily CTV adaptation by RTTs, seems a feasible and safe way to introduce daily, online MRI‐based plan adaptation for a MRL.