Maximum Exhalation Research Articles

Can ultrasound be an assessment tool for sagittal spine mobility and chest expansion in patients with ankylosing spondylitis?

We aimed to examine whether ultrasound (US) is useful for evaluating spinal mobility and chest expansion in ankylosing spondylitis (AS) patients and determine a cutoff value to identify reduced sagittal lumbar mobility.Our cross-sectional study included 50 AS patients and 50 controls. Metric measurements and Bath AS indices were measured in AS patients. The distance between C6-C7, T11-T12, and L4-L5 vertebrae was measured, and the difference and percentage of difference between erect position and maximal cervical and lumbar flexion was calculated (T11-T12dif, T11-T12%, L4-L5dif, L4-L5%, T+L dif, T+L%). Intercostal divergence was measured 1.5 cm away on the left from the sternocostal space during maximum inhalation and maximum exhalation, and the difference and percentage of difference between them was calculated (ICdif, IC%).All metric measurements were lower in the AS group except for tragus-to-wall distance. T11-T12dif, T11-T12%, L4-L5dif, T+L dif, and T+L% values were higher in the control group, while other US measurements did not differ between the groups. All US measurements except ICdif and IC% correlated with the Bath AS Metrology Index.Thus, US may be used for assessing spinal mobility in patients with AS. T11-T12dif <0.79 cm may show decreased lumbar sagittal mobility.

The development of a 4D treatment planning methodology to simulate the tracking of central lung tumors in an MRI-linac.

PurposeTargeting and tracking of central lung tumors may be feasible on the Elekta MRI‐linac (MRL) due to the soft‐tissue visualization capabilities of MRI. The purpose of this work is to develop a novel treatment planning methodology to simulate tracking of central lung tumors with the MRL and to quantify the benefits in OAR sparing compared with the ITV approach.MethodsFull 4D‐CT datasets for five central lung cancer patients were selected to simulate the condition of having 4D‐pseudo‐CTs derived from 4D‐MRI data available on the MRL with real‐time tracking capabilities. We used the MRL treatment planning system to generate two plans: (a) with a set of MLC‐defined apertures around the target at each phase of the breathing (“4D‐MRL” method); (b) with a fixed set of fields encompassing the maximum inhale and exhale of the breathing cycle (“ITV” method). For both plans, dose accumulation was performed onto a reference phase. To further study the potential benefits of a 4D‐MRL method, the results were stratified by tumor motion amplitude, OAR‐to‐tumor proximity, and the relative OAR motion (ROM).ResultsWith the 4D‐MRL method, the reduction in mean doses was up to 3.0 Gy and 1.9 Gy for the heart and the lung. Moreover, the lung's V12.5 Gy was spared by a maximum of 300 cc. Maximum doses to serial organs were reduced by up to 6.1 Gy, 1.5 Gy, and 9.0 Gy for the esophagus, spinal cord, and the trachea, respectively. OAR dose reduction with our method depended on the tumor motion amplitude and the ROM. Some OARs with large ROMs and in close proximity to the tumor benefited from tracking despite small tumor amplitudes.ConclusionsWe developed a novel 4D tracking methodology for the MRL for central lung tumors and quantified the potential dosimetric benefits compared with our current ITV approach.

Efficient Interplay Effect Mitigation for Proton Pencil Beam Scanning by Spot-Adapted Layered Repainting Evenly Spread out Over the Full Breathing Cycle

To develop and implement a practical repainting method for efficient interplay effect mitigation in proton pencil beam scanning (PBS). A new flexible repainting scheme with spot-adapted numbers of repainting evenly spread out over the whole breathing cycle (assumed to be 4 seconds) was developed. Twelve fields from 5 thoracic and upper abdominal PBS plans were delivered 3 times using the new repainting scheme to an ion chamber array on a motion stage. One time was static and 2 used 4-second, 3-cm peak-to-peak sinusoidal motion with delivery started at maximum inhalation and maximum exhalation. For comparison, all dose measurements were repeated with no repainting and with 8 repaintings. For each motion experiment, the 3%/3-mm gamma pass rate was calculated using the motion-convolved static dose as the reference. Simulations were first validated with the experiments and then used to extend the study to 0- to 5-cm motion magnitude, 2- to 6-second motion periods, patient-measured liver tumor motion, and 1- to 6-fraction treatments. The effect of the proposed method was evaluated for the 5 clinical cases using 4-dimensional (4D) dose reconstruction in the planning 4D computed tomography scan. The target homogeneity index, HI = (D2 - D98)/Dmean, of a single-fraction delivery is reported, where D2 and D98 is the dose delivered to 2% and 98% of the target, respectively, and Dmean is the mean dose. The gamma pass rates were 59.6% ± 9.7% with no repainting, 76.5% ± 10.8% with 8 repaintings, and 92.4% ± 3.8% with the new repainting scheme. Simulations reproduced the experimental gamma pass rates with a 1.3% root-mean-square error and demonstrated largely improved gamma pass rates with the new repainting scheme for all investigated motion scenarios. One- and two-fraction deliveries with the new repainting scheme had gamma pass rates similar to those of 3-4 and 6-fraction deliveries with 8 repaintings. The mean HI for the 5 clinical cases was 14.2% with no repainting, 13.7% with 8 repaintings, 12.0% with the new repainting scheme, and 11.6% for the 4D dose without interplay effects. A novel repainting strategy for efficient interplay effect mitigation was proposed, implemented, and shown to outperform conventional repainting in experiments, simulations, and dose reconstructions. This strategy could allow for safe and more optimal clinical delivery of thoracic and abdominal proton PBS and better facilitate hypofractionated and stereotactic treatments.

Effects of collimator angle, couch angle, and starting phase on motion-tracking dynamic conformal arc therapy (4D DCAT).

PurposeThe aim of this study was to find an optimized configuration of collimator angle, couch angle, and starting tracking phase to improve the delivery performance in terms of MLC position errors, maximal MLC leaf speed, and total beam‐on time of DCAT plans with motion tracking (4D DCAT).Method and materialsNontracking conformal arc plans were first created based on a single phase (maximal exhalation phase) of a respiratory motion phantom with a spherical target. An ideal model was used to simulate the target motion in superior‐inferior (SI), anterior‐posterior (AP), and left‐right (LR) dimensions. The motion was decomposed to the MLC leaf position coordinates for motion compensation and generating 4D DCAT plans. The plans were studied with collimator angle ranged from 0° to 90°; couch angle ranged from 350°(−10°) to 10°; and starting tracking phases at maximal inhalation (θ=π/2) and exhalation (θ=0) phases. Plan performance score (PPS) evaluates the plan complexity including the variability in MLC leaf positions, degree of irregularity in field shape and area. PPS ranges from 0 to 1, where low PPS indicates a plan with high complexity. The 4D DCAT plans with the maximal and the minimal PPS were selected and delivered on a Varian TrueBeam linear accelerator. Gafchromic‐EBT3 dosimetry films were used to measure the dose delivered to the target in the phantom. Gamma analysis for film measurements with 90% passing rate threshold using 3%/3 mm criteria and trajectory log files were analyzed for plan delivery accuracy evaluation.ResultsThe maximal PPS of all the plans was 0.554, achieved with collimator angle at 87°, couch angle at 350°, and starting phase at maximal inhalation (θ=π/2). The maximal MLC leaf speed, MLC leaf errors, total leaf travel distance, and beam‐on time were 20 mm/s, 0.39 ± 0.16 mm, 1385 cm, and 157 s, respectively. The starting phase, whether at maximal inhalation or exhalation had a relatively small contribution to PPS (0.01 ± 0.05).ConclusionsBy selecting collimator angle, couch angle, and starting tracking phase, 4D DCAT plans with the maximal PPS demonstrated less MLC leaf position errors, lower maximal MLC leaf speed, and shorter beam‐on time which improved the performance of 4D motion‐tracking DCAT delivery.

Agreement Between Methods to Determine Procedure for Maximal Exhalation During Hydrostatic Weighing: A Methodological Investigation

Introduction: Current evidence suggests that there are many contentious issues that can impact significantly upon hydrostatic weighing assessments, for instance, obtaining reliable and precise data values within the testing environment [1,2]. Researchers such as Demura et al., [3] have addressed some of these issues, but there is still much uncertainty and significant challenges in terms of the procedure for maximal exhalation during hydrostatic weighing. Therefore, the due to some of these challenges, it was necessary to conduct a methodological investigation to reduce measurement error. Methods: (n = 22) students were recruited from the University of Gloucestershire BSc (Hons) Undergraduate programmes. All participants were over 18 years of age and all were free from disease, illness or injury ( s; age = 20.5  years, body mass = 68.7  kg and stretched stature = 172.0 8.3 cm). Results: When comparing body mass in water values between the two exhalation techniques, (pre-submersion and post-submersion exhalation) results indicated systematic bias (lower value for post-submersion technique). There was a significant difference in body mass values between pre-submersion technique (Mean  SD = 2.6 1.2 kg) and post-submersion technique (2.2 1.1 kg), t21 = 4.19 P < 0.01. Conclusion: When using hydrostatic weighing, the post-submersion exhalation technique was associated with greater measurement benefits thus resulting in a more reliable method.

Evaluation of reproducibility of tumor repositioning during multiple breathing cycles for liver stereotactic body radiotherapy treatment

AimTo evaluate the tumor repositioning during gated volumetric modulated arc therapy (VMAT) for liver stereotactic body radiotherapy(SBRT) treatment using implanted fiducial markers and intrafraction kilovoltage (kV) images acquired during dose delivery. Materials and methodsSince 2012, 47 liver cancer patients with implanted fiducial markers were treated using the gated VMAT technique with a Varian Truebeam STx linear accelerator. The fiducial markers were implanted inside or close to the tumor target before treatment simulation. They were defined at the maximum inhalation and exhalation phases on a 4-dimensionnal computed tomography (4DCT) acquisition. During the treatment, kV images were acquired just before the beam-on at each breathing cycle at maximum exhalation and inhalation phases to verify the fiducial markers positions. For the five first fractions of treatment in the first ten consecutive patients, a total of 2705 intrafraction kV images were retrospectively analyzed to assess the differences between expected and actual positions of the fiducial markers along the cranio-caudal (CC) direction during the exhalation phase. ResultsThe mean absolute intrafractional fiducial marker deviation along the CC direction was 1.0mm at the maximum exhalation phase. In 99%, 95% and 90% cases, the fiducial marker deviations were ≤4.5mm, 2.8mm and 2.2mm, respectively. ConclusionIntrafraction kV images allowed us to ensure the consistency of tumor repositioning during treatment. In 99% cases, the fiducial marker deviations were ≤4.5mm corresponding to our 5mm treatment margin. This margin seems to be well-adapted to the gated VMAT SBRT treatment in liver disease.

MO-FG-BRA-06: Electromagnetic Beacon Insertion in Lung Cancer Patients and Resultant Surrogacy Errors for Dynamic MLC Tumour Tracking

Purpose: To assess endo-bronchial electromagnetic beacon insertion and to quantify the geometric accuracy of using beacons as a surrogate for tumour motion in real-time multileaf collimator (MLC) tracking of lung tumours. Methods: The LIGHT SABR trial is a world-first clinical trial in which the MLC leaves move with lung tumours in real time on a standard linear accelerator. Tracking is performed based on implanted electromagnetic beacons (CalypsoTM, Varian Medical Systems, USA) as a surrogate for tumour motion. Five patients have been treated and have each had three beacons implanted endo-bronchially under fluoroscopic guidance. The centre of mass (C.O.M) has been used to adapt the MLC in real-time. The geometric error in using the beacon C.O.M as a surrogate for tumour motion was measured by measuring the tumour and beacon C.O.M in all phases of the respiratory cycle of a 4DCT. The surrogacy error was defined as the difference in beacon and tumour C.O.M relative to the reference phase (maximum exhale). Results: All five patients have had three beacons successfully implanted with no migration between simulation and end of treatment. Beacon placement relative to tumour C.O.M varied from 14 to 74 mm and in one patient spanned two lobes. Surrogacy error was measured in each patient on the simulation 4DCT and ranged from 0 to 3 mm. Surrogacy error as measured on 4DCT was subject to artefacts in mid-ventilation phases. Surrogacy error was a function of breathing phase and was typically larger at maximum inhale. Conclusion: Beacon placement and thus surrogacy error is a major component of geometric uncertainty in MLC tracking of lung tumours. Surrogacy error must be measured on each patient and incorporated into margin calculation. Reduction of surrogacy error is limited by airway anatomy, however should be taken into consideration when performing beacon insertion and planning. This research is funded by Varian Medical Systems via a collaborative research agreement.

SU-G-JeP1-14: Respiratory Motion Tracking Using Kinect V2

Purpose: Investigate capability and accuracy of Kinect v2 camera for tracking respiratory motion to use as a tool during 4DCT or in combination with motion management during radiotherapy treatments. Methods: Utilizing the depth sensor on the Kinect as well as code written in C#, the respiratory motion of a patient was tracked by recording the depth (distance) values obtained at several points on the patient. Respiratory traces were also obtained using Varian's RPM system, which traces the movement of a propriety marker placed on the patient's abdomen, as well as an Anzai belt, which utilizes a pressure sensor to track respiratory motion. With the Kinect mounted 60 cm above the patient and pointing straight down, 11 breathing cycles were recorded with each system simultaneously. Relative displacement values during this time period were saved to file. While RPM and the Kinect give displacement values in distance units, the Anzai system has arbitrary units. As such, displacement for all three are displayed relative to the maximum value for the time interval from that system. Additional analysis was performed between RPM and Kinect for absolute displacement values. Results: Analysis of the data from all three systems indicates the relative motion obtained from the Kinect is both accurate and in sync with the data from RPM and Anzai. The absolute displacement data from RPM and Kinect show similar displacement values throughout the acquisition except for the depth obtained from the Kinect during maximum exhalation (largest distance from Kinect). Conclusion: By simply utilizing the depth data of specific points on a patient obtained from the Kinect, respiratory motion can be tracked and visualized with accuracy comparable to that of the Varian RPM and Anzai belt.

FEV manoeuvre induced changes in breath VOC compositions: an unconventional view on lung function tests.

Breath volatile organic compound (VOC) analysis can open a non-invasive window onto pathological and metabolic processes in the body. Decades of clinical breath-gas analysis have revealed that changes in exhaled VOC concentrations are important rather than disease specific biomarkers. As physiological parameters, such as respiratory rate or cardiac output, have profound effects on exhaled VOCs, here we investigated VOC exhalation under respiratory manoeuvres. Breath VOCs were monitored by means of real-time mass-spectrometry during conventional FEV manoeuvres in 50 healthy humans. Simultaneously, we measured respiratory and hemodynamic parameters noninvasively. Tidal volume and minute ventilation increased by 292 and 171% during the manoeuvre. FEV manoeuvre induced substance specific changes in VOC concentrations. pET-CO2 and alveolar isoprene increased by 6 and 21% during maximum exhalation. Then they decreased by 18 and 37% at forced expiration mirroring cardiac output. Acetone concentrations rose by 4.5% despite increasing minute ventilation. Blood-borne furan and dimethyl-sulphide mimicked isoprene profile. Exogenous acetonitrile, sulphides, and most aliphatic and aromatic VOCs changed minimally. Reliable breath tests must avoid forced breathing. As isoprene exhalations mirrored FEV performances, endogenous VOCs might assure quality of lung function tests. Analysis of exhaled VOC concentrations can provide additional information on physiology of respiration and gas exchange.

SU‐F‐J‐132: Evaluation of CTV‐To‐PTV Expansion for Whole Breast Radiotherapy

Purpose:The current standard CTV‐to‐PTV expansion for whole breast radiotherapy (WBRT) is 7mm, as recommended by RTOG‐1005.This expansion is derived from the uncertainty due to patient positioning (±5mm) and respiratory motion (±5mm). We evaluated the expansion needed for respiratory motion uncertainty using 4DCT. After determining the appropriate expansion margins, RT plans were generated to evaluate the reduction in heart and lung dose.Methods:4DCT images were acquired during treatment simulation and retrospectively analyzed for 34 WBRT patients. Breast CTVs were contoured on the maximum inhale and exhale phase. Breast CTV displacement was measured in the L‐R, A‐P, and SUP‐INF directions using rigid registration between phase images. Averaging over the 34 patients, we determined the margin due to respiratory motion. Plans were generated for 10 left‐sided cases comparing the new expansion with the 7mm PTV expansion.Results:The results for respiratory motion uncertainty are shown in Table 1. Drawing on previous work by White et al at Princess Margaret Hospital (1) (see supporting document for reference) which studied the uncertainty due to patient positioning, we concluded that, in total, a 5mm expansion was sufficient. The results for our suggested PTV margin are shown in Table 2, combining the patient positioning results from White et al with our respiratory motion results. The planning results demonstrating the heart and lung dose differences in the 5mm CTV‐to‐PTV expanded plan compared to the 7mm plan are shown in Table 3.Conclusion:Our work evaluating the expansion needed for respiratory motion along with previous work evaluating the expansion needed for setup uncertainty shows that a CTV‐to‐PTV expansion of 5mm is acceptable and conservative. By reducing the PTV expansion, significant dose reduction to the heart and lung are achievable.

Lung motion estimation using dynamic point shifting: An innovative model based on a robust point matching algorithm.

Image-guided radiotherapy is an advanced 4D radiotherapy technique that has been developed in recent years. However, respiratory motion causes significant uncertainties in image-guided radiotherapy procedures. To address these issues, an innovative lung motion estimation model based on a robust point matching is proposed in this paper. An innovative robust point matching algorithm using dynamic point shifting is proposed to estimate patient-specific lung motion during free breathing from 4D computed tomography data. The correspondence of the landmark points is determined from the Euclidean distance between the landmark points and the similarity between the local images that are centered at points at the same time. To ensure that the points in the source image correspond to the points in the target image during other phases, the virtual target points are first created and shifted based on the similarity between the local image centered at the source point and the local image centered at the virtual target point. Second, the target points are shifted by the constrained inverse function mapping the target points to the virtual target points. The source point set and shifted target point set are used to estimate the transformation function between the source image and target image. The performances of the authors' method are evaluated on two publicly available DIR-lab and POPI-model lung datasets. For computing target registration errors on 750 landmark points in six phases of the DIR-lab dataset and 37 landmark points in ten phases of the POPI-model dataset, the mean and standard deviation by the authors' method are 1.11 and 1.11 mm, but they are 2.33 and 2.32 mm without considering image intensity, and 1.17 and 1.19 mm with sliding conditions. For the two phases of maximum inhalation and maximum exhalation in the DIR-lab dataset with 300 landmark points of each case, the mean and standard deviation of target registration errors on the 3000 landmark points of ten cases by the authors' method are 1.21 and 1.04 mm. In the EMPIRE10 lung registration challenge, the authors' method ranks 24 of 39. According to the index of the maximum shear stretch, the authors' method is also efficient to describe the discontinuous motion at the lung boundaries. By establishing the correspondence of the landmark points in the source phase and the other target phases combining shape matching and image intensity matching together, the mismatching issue in the robust point matching algorithm is adequately addressed. The target registration errors are statistically reduced by shifting the virtual target points and target points. The authors' method with consideration of sliding conditions can effectively estimate the discontinuous motion, and the estimated motion is natural. The primary limitation of the proposed method is that the temporal constraints of the trajectories of voxels are not introduced into the motion model. However, the proposed method provides satisfactory motion information, which results in precise tumor coverage by the radiation dose during radiotherapy.

Pharmacokinetic studies for proving bioequivalence of orally inhaled drug products-critical issues and concepts.

OPINION article Front. Pharmacol., 03 June 2015Sec. Experimental Pharmacology and Drug Discovery https://doi.org/10.3389/fphar.2015.00117

SU-E-J-59: Feasibility of Markerless Tumor Tracking by Sequential Dual-Energy Fluoroscopy On a Clinical Tumor Tracking System

Purpose: To evaluate the feasibility of markerless tumor tracking through the implementation of a novel dual-energy imaging approach into the clinical dynamic tracking (DT) workflow of the Vero SBRT system. Methods: Two sequential 20 s (11 Hz) fluoroscopy sequences were acquired at the start of one fraction for 7 patients treated for primary and metastatic lung cancer with DT on the Vero system. Sequences were acquired using 2 on-board kV imaging systems located at ±45° from the MV beam axis, at respectively 60 kVp (3.2 mAs) and 120 kVp (2.0 mAs). Offline, a normalized cross-correlation algorithm was applied to match the high (HE) and low energy (LE) images. Per breathing phase (inhale, exhale, maximum inhale and maximum exhale), the 5 best-matching HE and LE couples were extracted for DE subtraction. A contrast analysis according to gross tumor volume was conducted based on contrast-to-noise ratio (CNR). Improved tumor visibility was quantified using an improvement ratio. Results: Using the implanted fiducial as a benchmark, HE-LE sequence matching was effective for 13 out of 14 imaging angles. Overlying bony anatomy was removed on all DE images. With the exception of two imaging angles, the DE images showed no significantly improved tumor visibility comparedmore » to HE images, with an improvement ratio averaged over all patients of 1.46 ± 1.64. Qualitatively, it was observed that for those imaging angles that showed no significantly improved CNR, the tumor tissue could not be reliably visualized on neither HE nor DE images due to a total or partial overlap with other soft tissue. Conclusion: Dual-energy subtraction imaging by sequential orthogonal fluoroscopy was shown feasible by implementing an additional LE fluoroscopy sequence. However, for most imaging angles, DE images did not provide improved tumor visibility over single-energy images. Optimizing imaging angles is likely to improve tumor visibility and the efficacy of dual-energy imaging. This work was in part sponsored by corporate funding from BrainLAB AG.(BrainLAB AG, Feldkirchen, Germany)« less

Accuracy of Routine Treatment Planning 4-Dimensional and Deep-Inspiration Breath-Hold Computed Tomography Delineation of the Left Anterior Descending Artery in Radiation Therapy

To assess the feasibility of radiation therapy treatment planning 4-dimensional computed tomography (4DCT) and deep-inspiration breath-hold (DIBH) CT to accurately contour the left anterior descending artery (LAD), a primary indicator of radiation-induced cardiac toxicity for patients undergoing radiation therapy. Ten subjects were prospectively imaged with a cardiac-gated MRI protocol to determine cardiac motion effects, including the displacement of a region of interest comprising the LAD. A series of planar views were obtained and resampled to create a 3-dimensional (3D) volume. A 3D optical flow deformable image registration algorithm determined tissue displacement during the cardiac cycle. The measured motion was then used as a spatial boundary to characterize motion blurring of the radiologist-delineated LAD structure for a cohort of 10 consecutive patients enrolled prospectively on a breast study including 4DCT and DIBH scans. Coronary motion-induced blurring artifacts were quantified by applying an unsharp filter to accentuate the LAD structure despite the presence of motion blurring. The 4DCT maximum inhalation and exhalation respiratory phases were coregistered to determine the LAD displacement during tidal respiration, as visualized in 4DCT. The average 90th percentile heart motion for the region of interest was 0.7 ± 0.1 mm (left-right [LR]), 1.3 ± 0.6 mm (superior-inferior [SI]), and 0.6 ± 0.2 mm (anterior-posterior [AP]) in the cardiac-gated MRI cohort. The average relative increase in the number of voxels comprising the LAD contour was 69.4% ± 4.5% for the DIBH. The LAD volume overestimation had the dosimetric impact of decreasing the reported mean LAD dose by 23% ± 9% on average in the DIBH. During tidal respiration the average relative LAD contour increase was 69.3% ± 5.9% and 67.9% ± 4.6% for inhalation and exhalation respiratory phases, respectively. The average 90th percentile LAD motion was 4.8 ± 1.1 mm (LR), 0.9 ± 0.4 mm (SI), and 1.9 ± 0.6 mm (AP) for the 4DCT cohort, in the absence of cardiac gating. An anisotropic margin of 2.7 mm (LR), 4.1 mm (SI), and 2.4 mm (AP) was quantitatively determined to account for motion blurring and patient setup error while placing minimum constraint on the plan optimization.

Poster — Thur Eve — 30: 4D VMAT dose calculation methodology to investigate the interplay effect: experimental validation using TrueBeam Developer Mode and Gafchromic film

The interplay effect between the tumor motion and the radiation beam modulation during a VMAT treatment delivery alters the delivered dose distribution from the planned one. This work present and validate a method to accurately calculate the dose distribution in 4D taking into account the tumor motion, the field modulation and the treatment starting phase. A QUASAR™ respiratory motion phantom was 4D scanned with motion amplitude of 3 cm and with a 3 second period. A static scan was also acquired with the lung insert and the tumor contained in it centered. A VMAT plan with a 6XFFF beam was created on the averaged CT and delivered on a Varian TrueBeam and the trajectory log file was saved. From the trajectory log file 10 VMAT plans (one for each breathing phase) and a developer mode XML file were created. For the 10 VMAT plans, the tumor motion was modeled by moving the isocentre on the static scan, the plans were re‐calculated and summed in the treatment planning system. In the developer mode, the tumor motion was simulated by moving the couch dynamically during the treatment. Gafchromic films were placed in the QUASAR phantom static and irradiated using the developer mode. Different treatment starting phase were investigated (no phase shift, maximum inhalation and maximum exhalation). Calculated and measured isodose lines and profiles are in very good agreement. For each starting phase, the dose distribution exhibit significant differences but are accurately calculated with the methodology presented in this work.

Sci-Sat AM: Stereo - 04: Evaluation of VMAT interplay effect for lung SABR using TrueBeam 10XFFF beam

During a VMAT treatment delivery, the interplay effect between the moving target and varying machine parameters result in dose distributions that are different from those initially planned. In this work, we investigate this effect for lung SABR by using 4D dose calculation derived from the Varian TrueBeam trajectory log file. The impact of treatment start phase is also evaluated. A QUASAR™ respiratory motion phantom was scanned with motion amplitudes of 0.4, 1, 2 and 3 cm with a 4 second period. MIP and the average dataset were generated from the 4DCT. A static CT was also acquired with the tumor in its centre position. Plans were optimized with 10X FFF beam until PTV and fictitious critical structures met the dose constraints. Ten temporally interleaved plans were constructed with the temporal machine parameter information from the trajectory log file. Ten plans were calculated with isocentre shifts to simulate respiratory motion and then summed. For each motion amplitude, three separate sum plans were created with various phase shifts (no phase shift, maximum inhalation and maximum exhalation) to assess the impact of treatment start phase. For all the phase shifts investigated, the DVH for PTV demonstrated good dose coverage. However, a careful review of slice by slice plan comparison indicates dose “holes” are observed within PTV. The PTV dose difference between various treatment start phases can be as high as 19%. This assumes all treatment fractions have identical treatment start phase. Our future work includes evaluation of interplay effect for various breathing periods.

Augmenting interventional ultrasound using statistical shape model for guiding percutaneous nephrolithotomy: Initial evaluation in pigs

Successful percutaneous nephrolithotomy (PCNL) highly depends on an accurate needle puncture of the kidney. This puncture step is challenging and must be performed under intraoperative image guidance. This paper presents an image guidance method for PCNL by augmenting interventional ultrasound (US) using a 3D statistical kidney model. First, a 3D statistical kidney model is built aforehand from a collection of aligned training shapes. Intraoperatively, a patient-specific 3D kidney model is reconstructed in a fine-tune way using sparse manually picked points from calibrated US at maximum exhalation. The US images are then augmented with the kidney model and a real-time tracked virtual needle. Under the augmented-US guidance, percutaneous renal puncture can be performed. Experiments results based on Wuzhishan pig data have validated the accuracy and inter-operator repeatability of the presented kidney model reconstruction. The feasibility and efficiency of the proposed augmented US-guided puncture for PCNL have been demonstrated in pigs. With careful setup by trained surgeons, our proposed guidance has the potential to reduce the occurrence of complications such as PCS access failure and bleeding compared with a traditional US-guided method.

Use of 4D-CBCT to Assess Target and Organ Motion in Esophageal Cancer Patients

Radiotherapy for esophageal cancer is challenged by intra-fractional organ movement. Daily image guidance is used to assess patient set-up errors and correct for positional offsets of the target and organs at risk. There exists a paucity of published data on four-dimensional cone-beam computed tomography (4D-CBCT) as a method of image guidance for these patients. This study utilized 4D-CBCTs to compare the efficacy of different registration volumes (bone, internal target volume (ITV), carina) for image guidance with focus on whether carina is a useful ITV surrogate. The study also assessed our centre's current planning target volume (PTV) margins of 0.5 cm around the ITV. This retrospective study involved 17 esophageal cancer patients treated radically from July 2012-July 2013 using volumetric-modulated arc therapy. Daily CBCTs (402) were reconstructed into 4D Medium Resolution 8-phase 4D-CBCTs using Elekta XVI software and registered to the helical CT simulation scan in voluntary exhale. Two separate dual registration matches were done; the first registered a clipbox around the vertebrae and a mask around the ITV, and the second used carina as the mask. T-test was used to test for significant difference between X,Y,Z-offsets; means and standard deviations were calculated. For each directional shift, the average difference in amplitude (absolute value of maximum inhale plus maximum exhale) between 4DCT and 4D-CBCT was determined. In some comparisons of vertebrae/ITV/carina mean offsets, statistical significance was found (t-test, p=0.05). However, only comparison of vertebrae and ITV mean offsets revealed clinical significance for the Y-dimension with the magnitude being >0.2 cm. For 14 patients (3 excluded due to unavailable data), average difference in amplitude between 4DCT and 4D-CBCT in the X,Y,Z-directions were determined to be 0.12 cm, -0.05 cm, and 0.04 cm, respectively. In 8.4% of the cases, movement of the ITV in the Y-direction was greater than the PTV margin. Carina appears to be a better ITV surrogate versus vertebrae for image guidance on 4D-CBCTs in the Y-dimension. In the majority of cases, PTV margins are sufficient for target coverage. Future research on patient-specific indicators for significant ITV movement in the Y-direction is needed.

TU‐F‐BRF‐07: Accuracy of Routine Treatment Planning 4D and DIBH CT Delineation of the Left Anterior Descending Artery in Radiotherapy

Purpose:To assess the feasibility of routine treatment planning 4DCT and deep inspiration breath‐hold (DIBH) to accurately contour the left anterior descending artery (LAD), a primary indicator of cardiac toxicity, for radiotherapy treatment planning of breast cancer.Methods:Ten subjects were imaged with a cardiac‐gated MRI protocol to determine the displacement of a ROI that included the LAD. The subjects performed a series of breath‐hold maneuvers to obtain short‐axis and radial views, which were resampled to create a 3D‐volume. Tissue motion was determined using a multi‐resolution 3D optical flow deformable image registration algorithm. The ROI motion was then used as a spatial boundary to characterize the blurring motion of the LAD in ten patients during clinical 4DCT and DIBH protocols. A radiologist contoured the LAD. Coronary motion‐induced blurring artifacts were quantified by applying an unsharp filter to accentuate the LAD despite motion‐blurring. The 4DCT maximum inhalation and exhalation respiratory phases were co‐registered to determine the LAD displacement during tidal respiration, as visualized in 4DCT.Results:The average 90th percentile heart motion for the ROI was 0.7±0.1mm(LR), 1.3±0.6mm(SI), 0.6±0.2mm(AP) in the cardiac‐gated MRI cohort. The average relative increase in the number of voxels comprising the LAD contour was 69.4±4.5% for the DIBH. During tidal respiration, the average relative increase in the LAD contour was 69.3±5.9% and 67.9±4.6% for inhalation and exhalation respiratory phases respectively. The average 90th percentile LAD motion was 4.8±1.1mm(LR), 0.9±0.4mm(SI), 1.9±0.6mm(AP) for the 4DCT cohort, in the absence of cardiac‐gating.Conclusion:Uncompensated coronary motion was the dominant form of motion blurring present in the CT images due to the high frequency of the cardiac cycle relative to the respiratory cycle. The 4D and DIBH CT contour delineation of the LAD was consistently overestimated without cardiac‐gating, which could have led to inaccurate dose volume histogram indicators in clinical practice.

SU-E-T-179: Exploring Appropriate Offset Values for Pencil Beam and Monte Carlo Dose Optimization in Lung Stereotactic Body Radiotherapy Encompassing the Effects of Respiration and Tumor Location

Purpose: Exploring appropriate offset values in dose optimization with pencil beam (PB) algorithm to minimize dosimetric differences with plans calculated with Monte Carlo (MC) for lung cancer treatment with Stereotactic Body Radiotherapy (SBRT). Methods: 20 cases of Non-Small Cell Lung Cancer, treated with gated full motion range SBRT were selected. According to the proximity of the Gross Tumor Volume (GTV) to the chest wall, two groups are defined: peripherally located when GTV merges with the chest wall for at least 50% of the lesion diameter, and centrally located when the GTV is surrounded by lung tissue. Treatment plans were created on 4D average intensity projection (AIP) CT set with Brainlab iPlanDose 4.1.2 planning system. The D97 of PTV was normalized to 50Gy using the fast PB and compared with MC. The optimized plan was then recomputed over each 4D respiratory phase, and compared with MC using the same plan MU's. Results: The mean difference in the PB and MC D97 of the ITV was 10.5% (±0.8%) of the prescription dose (50Gy). PB algorithm showed 2.3–2.4% less overestimation to the D97 of the ITV, when comparing to MC, in the maximum exhalation phase than in the maximal inhalation phase. Significantly smallermore » dose difference between PB and MC is also shown in plans for peripheral lesions (7.7 ± 0.7%) versus for central lesions (12.7±0.8%) (p< 0.01). Conclusion: The dosimetric differences between PB and MC can be reasonably predicted depending on the location of lesion in the lung, and may be used as offset value in dose optimization with PB. Since the maximal exhalation phase demonstrates less dose discrepancy between the two algorithms than that in maximal inhalation phase, caution is suggested when the latter is included as a major phase portion in the respiration gated lung SBRT.« less