Simulated Respiratory Motion Research Articles

Direct Comparison of Respiration-Correlated Four-Dimensional Magnetic Resonance Imaging Reconstructed Using Concurrent Internal Navigator and External Bellows

To compare the image quality of amplitude-binned 4-dimensional magnetic resonance imaging (4DMRI) reconstructed using 2 concurrent respiratory (navigator and bellows) waveforms. A prospective, respiratory-correlated 4DMRI scanning program was used to acquire T2-weighted single-breath 4DMRI images with internal navigator and external bellows. After a 10-second training waveform of a surrogate signal, 2-dimensional MRI acquisition was triggered at a level (bin) and anatomic location (slice) until the bin-slice table was completed for 4DMRI reconstruction. The bellows signal was always collected, even when the navigator trigger was used, to retrospectively reconstruct a bellows-rebinned 4DMRI. Ten volunteers participated in this institutional review board-approved 4DMRI study. Four scans were acquired for each subject, including coronal and sagittal scans triggered by either navigator or bellows, and 6 4DMRI images (navigator-triggered, bellows-rebinned, and bellows-triggered) were reconstructed. The simultaneously acquired waveforms and resulting 4DMRI quality were compared using signal correlation, bin/phase shift, and binning motion artifacts. The consecutive bellows-triggered 4DMRI scan was used for indirect comparison. Correlation coefficients between the navigator and bellows signals were found to be patient-specific and inhalation-/exhalation-dependent, ranging from 0.1 to 0.9 because of breathing irregularities (>50% scans) and commonly observed bin/phase shifts (-1.1±0.6 bin) in both 1-dimensional waveforms and diaphragm motion extracted from 4D images. Navigator-triggered 4DMRI contained many fewer binning motion artifacts at the diaphragm than did the bellows-rebinned and bellows-triggered 4DMRI scans. Coronal scans were faster than sagittal scans because of the fewer slices and higher achievable acceleration factors. Navigator-triggered 4DMRI contains substantially fewer binning motion artifacts than bellows-rebinned and bellows-triggered 4DMRI, primarily owing to the deviation of the external from the internal surrogate. The present study compared 2 concurrent surrogates during the same 4DMRI scan and their resulting 4DMRI quality. The navigator-triggered 4DMRI scanning protocol should be preferred to the bellows-based, especially for coronal scans, for clinical respiratory motion simulation.

Evaluation of Dose Distribution in Intensity Modulated Radiosurgery for Lung Cancer under Condition of Respiratory Motion.

The dose of a real tumor target volume and surrounding organs at risk (OARs) under the effect of respiratory motion was calculated for a lung tumor plan, based on the target volume covering the whole tumor motion range for intensity modulated radiosurgery (IMRS). Two types of IMRS plans based on simulated respiratory motion were designed using humanoid and dynamic phantoms. Delivery quality assurance (DQA) was performed using ArcCHECK and MapCHECK2 for several moving conditions of the tumor and the real dose inside the humanoid phantom was evaluated using the 3DVH program. This evaluated dose in the tumor target and OAR using the 3DVH program was higher than the calculated dose in the plan, and a greater difference was seen for the RapidArc treatment than for the standard intensity modulated radiation therapy (IMRT) with fixed gantry angle beams. The results of this study show that for IMRS plans based on target volume, including the whole tumor motion range, tighter constraints of the OAR should be considered in the optimization process. The method devised in this study can be applied effectively to analyze the dose distribution in the real volume of tumor target and OARs in IMRT plans targeting the whole tumor motion range.

Sci‐Fri PM: Radiation Therapy, Planning, Imaging, and Special Techniques ‐ 05: A novel respiratory motion simulation program for VMAT treatment plans: a phantom validation study

Purpose:To develop and validate a computational method to simulate craniocaudal respiratory motion in a VMAT treatment plan.Methods:Three 4DCTs of the QUASAR respiratory motion phantom were acquired with a 2cm water‐density spherical tumour embedded in cedar to simulate lung. The phantom was oscillating sinusoidally with an amplitude of 2cm and periods of 3, 4, and 5 seconds. An ITV was contoured and 5mm PTV margin was added. High and a low modulation factor VMAT plans were created for each scan. An in‐house program was developed to simulate respiratory motion in the treatment plans by shifting the MLC leaf positions relative to the phantom. Each plan was delivered to the phantom and the dose was measured using Gafchromic film. The measured and calculated plans were compared using an absolute dose gamma analysis (3%/3mm).Results:The average gamma pass rate for the low modulation plan and high modulation plans were 91.1% and 51.4% respectively. The difference between the high and low modulation plans gamma pass rates is likely related to the different sampling frequency of the respiratory curve and the higher MLC leaf speeds in the high modulation plan. A high modulation plan has a slower gantry speed and therefore samples the breathing cycle at a coarser frequency leading to inaccuracies between the measured and planned doses.Conclusion:A simple program, including a novel method for increasing sampling frequency beyond the control point frequency, has been developed to simulate respiratory motion in VMAT plans by shifting the MLC leaf positions.

SU-G-BRB-17: Dosimetric Evaluation of the Respiratory Interplay Effect During VMAT Delivery Using IPAGAT Polymer Gel Dosimeter

Purpose: To evaluate the dosimetric impact of the interplay effect between multileaf collimator (MLC) movement and tumor respiratory motion during delivery of volumetric modulate arc therapy (VMAT) by using customized polymer gel dosimeter. Methods: Polyacrylamide-based gel dosimeter contained magnesium chloride as a sensitizer (iPAGAT) was used in this study. An excellent gas barrier PAN (BAREX) techno bottle (φ8 cm, 650 mL) filled with iPAGAT was set to the QUASAR™ respiratory motion phantom, and was moved with motion amplitudes of 1 and 2 cm with a 4 second period during VMAT delivery by the Novalis Tx linear accelerator (Varian/BrainLAB). Two spherical tumors with a 2 cm diameter (GTV1 and GTV2) were defined, and ITV1 (GTV1+1 cm) and ITV2 (GTV2+2 cm) with expansion in the superior-inferior (S-I) direction were also defined with simulated respiratory motion. PTV margin was 2 mm around the ITV considering the setup uncertainty. Two single arc VMAT plans with 30 Gy at 3 Gy per fraction (GTV: D98>100%, PTV: D95=100%) were generated by the Varian Eclipse treatment planning system. Three-dimensional dose distribution in iPAGAT was read out by the Signa 1.5T MRI system (GE), and was evaluated by dose-volume histogram (DVH) using in-house developed software. Results: According to DVH analysis by iPAGAT, D98 of GTV1 and GTV2 were more than 100% of the prescribed dose. In contrast, D95 of PTV1 and PTV2 were about 85% and 65%, respectively. Furthermore, low-to-intermediate dose was widespread with motion amplitude of 2 cm. Conclusion: DVH analysis using iPAGAT polymer gel dosimeter was performed in this study. As a result, interplay effect was negligible, since dose coverage of GTV was sufficient during VMAT delivery with simulated respiratory motion. However, the dose reduction of PTV and the spread of low-to-intermediate dose compared to the planned dose require scrupulous attention for large tumor respiratory motion.

SU‐F‐I‐15: Evaluation of a New MR‐Compatible Respiratory Motion Device at 3T

Purpose:Recent advances in MRI‐guided radiotherapy has inspired the development of MRI‐compatible motion devices that simulate patient periodic motion in the scanner, particularly respiratory motion. Most commercial devices rely on non MR‐safe ferromagnetic stepper motors which are not practical for regular QA testing. This work evaluates the motion performance of a new fully MRI compatible respiratory motion device at 3T.Methods:The QUASAR™ MRI‐compatible respiratory motion phantom has been recently developed by Modus QA Inc., London, ON, Canada. The prototype is constructed from diamagnetic materials with linear motion generated using MRI‐compatible piezoelectric motors that can be safely inserted in the scanner bore. The tumor was represented by a fillable sphere and is attached to the linear motion generator. The spherical tumor‐representative and its surroundings were filled with different concentrations of MnCl2 to produce realistic relaxation times. The motion was generated along the longitudinal (H/F) axis of the bore using sinusoidal reference waveform (amplitude = 15 mm, frequency 0.25 Hz). Imaging was then performed on 3T Philips Achieva using a 32‐channel cardiac coil. Fast 2D spoiled gradient‐echo was used with a spatial resolution of 1.8 × 1.8 mm2 and slice thickness of 4 mm. The motion waveform was then measured on the resultant image series by tracking the centroid of the sphere through the time series. This image‐derived measured motion was compared to the software‐generated reference waveform.Results:No visible distortions from the device were observed on the images. Excellent agreement between the measured and the reference waveforms were obtained. Negligible motion was observed in the lateral (R/L) direction.Conclusion:Our investigation demonstrates that this piezo‐electric motor design is effective at simulating periodic motion and is a potential candidate for MRI‐radiotherapy respiratory motion simulation. Future work should focus on evaluating non‐sinusoidal waveforms, fast 3D pulse sequences, and perform dosimetric QA.

Evaluation of the Accuracy of Liver Lesion DCEUS Quantification With Respiratory Gating.

Confidence in the accuracy of dynamic contrast enhanced ultrasound (DCEUS) quantification parameters is imperative for the correct diagnosis of liver lesion perfusion characteristics. An important source of uncertainty in liver DCEUS acquisitions is artifacts introduced by respiratory motion. The objective of this study is to construct a respiratory motion simulation model (RMSM) of dual contrast imaging mode acquisitions of liver lesions in order to evaluate an algorithm for automatic respiratory gating (ARG). The respiratory kinetics as well as the perfusion models of the liver lesion and parenchyma used by the RMSM were solely derived from clinical data. The quality of fit (of the DCEUS data onto the bolus kinetics model) depends on the respiration amplitude. Similar trends in terms of quality of fit as a function of respiration amplitude were observed from RMSM and clinical data. The errors introduced on the DCEUS quantification under the influence of respiration were evaluated. The RMSM revealed that the error in the liver lesion DCEUS quantification parameters significantly decreased (p < 0.001) from a maximum of 32.3% to 6.2% when ARG was used. The use of RMSM clearly demonstrates the capability of the ARG algorithm in significantly reducing errors introduced from both in-plane and out-of-plane respiratory motion.

O.14 - Theoretical modelling of γ-H2AX foci kinetics in human lymphocytes after exposure to fast neutrons

Introduction and Aim: Respiratory motion results in reduction of quali- tative and quantitative accuracy in PET imaging of the heart, muscles of the diaphragm, liver, spleen, pancreas and imaging of the lung area. It causes blurring of the images and thus a loss of sensitivity in lesion detection. The aim was to determine the importance of respiratory motion on SUV ac- curacy in pulmonary lesions through simulation of respiratory motion. Materials and Methods: The XCAT Phantom was used to assess the influ- ence of breathing on SUV quantification in a human-like simulation model. Six spherical lesions were introduced into the lungs of the model, three in the left lung and three in the right lung. Activity concentrations as- signed to the lesions were varied to create a range of different lesions: background ratios, thus creating a range of contrasts. The simulations were repeated for various lesion sizes. GATE software was used to perform Monte Carlo simulations during breathing. True-, scattered-, random- and total coincidences were extracted from the simulated data and reconstructed using OPL-EM and corrected for attenuation. Results: The % trues-to-total coincidences generally followed a down- ward trend with a decrease in contrast. Scattered coincidences had a more significant contribution at low contrast and when the lesion was closer to the diaphragm. This was greater in 3D simulations than in 2D simula- tions. Random coincidences were relatively greater in the apical region than in the other lung regions, particularly at low contrast large lesions. This increased for 3D compared to 2D acquisitions. The fraction of true coincidences-to-total coincidences increased when the lesions became smaller, but the relative amount of scattered events also increased. Conclusion: Breathing plays a significant role when determining the SUV of pulmonary lesions after accounting for the size, location, and the amount of activity within the simulated lesions compared to the background activity. ,a , O.V. Belov

O.12 - Determination of the influence of respiratory motion on the SUV accuracy in pulmonary lesions

Introduction and Aim: Respiratory motion results in reduction of qualitative and quantitative accuracy in PET imaging of the heart, muscles of the diaphragm, liver, spleen, pancreas and imaging of the lung area. It causes blurring of the images and thus a loss of sensitivity in lesion detection. The aim was to determine the importance of respiratory motion on SUV accuracy in pulmonary lesions through simulation of respiratory motion. Materials and Methods: The XCAT Phantom was used to assess the influence of breathing on SUV quantification in a human-like simulation model. Six spherical lesions were introduced into the lungs of the model, three in the left lung and three in the right lung. Activity concentrations assigned to the lesions were varied to create a range of different lesions: background ratios, thus creating a range of contrasts. The simulations were repeated for various lesion sizes. GATE software was used to performMonte Carlo simulations during breathing. True-, scattered-, randomand total coincidences were extracted from the simulated data and reconstructed using OPL-EM and corrected for attenuation. Results: The % trues-to-total coincidences generally followed a downward trend with a decrease in contrast. Scattered coincidences had a more significant contribution at low contrast and when the lesion was closer to the diaphragm. This was greater in 3D simulations than in 2D simulations. Random coincidences were relatively greater in the apical region than in the other lung regions, particularly at low contrast large lesions. This increased for 3D compared to 2D acquisitions. The fraction of true coincidences-to-total coincidences increased when the lesions became smaller, but the relative amount of scattered events also increased. Conclusion: Breathing plays a significant role when determining the SUV of pulmonary lesions after accounting for the size, location, and the amount of activity within the simulated lesions compared to the background activity.

SU-E-J-60: Evaluation of Temporal Lag in Radiotherapy Gating for Tumor Motion Trajectories

Purpose: Evaluating timing differences between LINAC beam ON/OFF and the estimation of tumor positioning using gating systems is essential for establishing confidence when treating with gating during radiotherapy, and is an annual requirement of TG-142. Temporal discrepancies between the trajectories of external marker surrogates and beam delivery may vary depending upon the type of external marker motion, which is quantified in this work for several trajectories. Methods: A precise robotic 3D motion stage performed several trajectories typically used for gating phantoms, including sinusoidal and Lujan-type motion; a commercial respiratory motion simulator was also employed. The true motions were monitored using variable resistors. The beam ON/OFF was controlled separately by two RPM (Varian) systems, an integrated version delivered by a Varian Truebeam LINAC and version 1.6 delivered by a Varian Trilogy, and measured using a diode. The resistor and diode signals were read by a multichannel digital oscilloscope, and timing differences between beam ON/OFF as measured by the diode and the phantom motion were determined using a peak detection algorithm. Results: Timing differences between beam ON/OFF and 3D stage motion peaks (diode—true motion timing) were computed to be 79.4 & 57.7ms for sinusoidal motion and 109.1 & 63.6ms for Lujan-type motion on the Truebeam LINAC, for beam ON and OFF, respectively. Timing differences for the Trilogy LINAC were 34.4 & 55.2ms for the sinusoidal motion and 29.0 & 26.3ms for the Lujan-type motion, for beam ON and OFF, respectively. With the commercial motion simulator, the timing differences were found to be −9ms and −78ms for beam ON/OFF, respectively, with the Truebeam, and −97.6ms and −60.9ms for beam ON/OFF, respectively, with the Trilogy. Conclusion: Setup-dependent temporal lags were found using this methodology. These discrepancies have the potential to influence quality assurance on gating systems and ultimately the treatment dose during radiotherapy. NIH National Institute of Biomedical Imaging and Bioengineering grant T32 EB002103-21

Pose-independent surface matching for intra-operative soft-tissue marker-less registration

One of the main challenges in computer-assisted soft tissue surgery is the registration of multi-modal patient-specific data for enhancing the surgeon's navigation capabilities by observing beyond exposed tissue surfaces. A new approach to marker-less guidance involves capturing the intra-operative patient anatomy with a range image device and doing a shape-based registration. However, as the target organ is only partially visible, typically does not provide salient features and underlies severe non-rigid deformations, surface matching in this context is extremely challenging. Furthermore, the intra-operatively acquired surface data may be subject to severe systematic errors and noise. To address these issues, we propose a new approach to establishing surface correspondences, which can be used to initialize fine surface matching algorithms in the context of intra-operative shape-based registration. Our method does not require any prior knowledge on the relative poses of the input surfaces to each other, does not rely on the detection of prominent surface features, is robust to noise and can be used for overlapping surfaces. It takes into account (1) similarity of feature descriptors, (2) compatibility of multiple correspondence pairs, as well as (3) the spatial configuration of the entire correspondence set. We evaluate the algorithm on time-of-flight (ToF) data from porcine livers in a respiratory liver motion simulator. In all our experiments the alignment computed from the established surface correspondences yields a registration error below 1cm and is thus well suited for initializing fine surface matching algorithms for intra-operative soft-tissue registration.

SU‐E‐J‐81: Interplay Effect in Non‐Gated Dynamic Treatment Delivery of a Lung Phantom with Simulated Respiratory Motion

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‐155: Utilizing Varian TrueBeam Developer Mode for the Quantification of Mechanical Limits and the Simulation of 4D Respiratory Motion

Purpose:Use Varian TrueBeam Developer mode to quantify the mechanical limits of the couch and to simulate 4D respiratory motion.Methods:An in‐house MATLAB based GUI was created to make the BEAM XML files. The couch was moved in a triangular wave in the S/I direction with varying amplitudes (1mm, 5mm, 10mm, and 50mm) and periods (3s, 6s, and 9s). The periods were determined by specifying the speed. The theoretical positions were compared to the values recorded by the machine at 50 Hz. HD videos were taken for certain tests as external validation. 4D Respiratory motion was simulated by an A/P MV beam being delivered while the couch moved in an elliptical manner. The ellipse had a major axis of 2 cm (S/I) and a minor axis of 1 cm (A/P).Results:The path planned by the TrueBeam deviated from the theoretical triangular form as the speed increased. Deviations were noticed starting at a speed of 3.33 cm/s (50mm amplitude, 6s period). The greatest deviation occurred in the 50mm‐ 3s sequence with a correlation value of −0.13 and a 27% time increase; the plan essentially became out of phase. Excluding these two, the plans had correlation values of 0.99. The elliptical sequence effectively simulated a respiratory pattern with a period of 6s. The period could be controlled by changing the speeds or the dose rate.Conclusion:The work first shows the quantification of the mechanical limits of the couch and the speeds at which the proposed plans begin to deviate. These limits must be kept in mind when programming other couch sequences. The methodology can be used to quantify the limits of other axes. Furthermore, the work shows the possibility of creating 4D respiratory simulations without using specialized phantoms or motion‐platforms. This can be further developed to program patient‐specific breathing patterns.

A non-axisymmetric, elongated pressure distribution in the lithotripter focal plane enhances stone comminution in vitro during simulated respiratory motion

A challenge in clinical shock wave lithotripsy (SWL) is stone translation due to a patient’s respiratory motion, in a direction perpendicular to shockwave propagation, which may negatively affect stone comminution while increasing the risk of tissue injury. We have developed a method using external masks and a modified lens geometry to transform the axisymmetric pressure distribution in the focal plane of an electromagnetic lithotripter into a non-axisymmetric elliptical distribution. At equivalent acoustic pulse energy (46 mJ), the peak pressure was reduced from 44 MPa to 38 MPa while the −6 dB focal width was increased from 7.4 mm for the original to 11.7 mm (major axis) and 7.9 mm (minor axis) of the modified field. In vitro stone comminution was performed in a tube holder (d = 14 mm) using a translation pattern with 12 breaths per minute and 15 mm in excursion distance. Stone comminution after 1000 shocks are 71.2 ± 4.4% and 65.2 ±8.3% (p &amp;lt; 0.05) along the major- and minor-axis of the modified field, respectively, compared to 62.6 ± 7.2% for the original axisymmetric field. These results suggest that an elongated pressure field aligned along the direction of stone motion may enhance stone comminution in SWL. [Work supported by the NIH and the NSF GRFP.]

A heuristic model of stone comminution in shock wave lithotripsy

A heuristic model is presented to describe the overall progression of stone comminution in shock wave lithotripsy (SWL), accounting for the effects of shock wave dose and the average peak pressure, P+(avg), incident on the stone during the treatment. The model is developed through adaptation of the Weibull theory for brittle fracture, incorporating threshold values in dose and P+(avg) that are required to initiate fragmentation. The model is validated against experimental data of stone comminution from two stone types (hard and soft BegoStone) obtained at various positions in lithotripter fields produced by two shock wave sources of different beam width and pulse profile both in water and in 1,3-butanediol (which suppresses cavitation). Subsequently, the model is used to assess the performance of a newly developed acoustic lens for electromagnetic lithotripters in comparison with its original counterpart both under static and simulated respiratory motion. The results have demonstrated the predictive value of this heuristic model in elucidating the physical basis for improved performance of the new lens. The model also provides a rationale for the selection of SWL treatment protocols to achieve effective stone comminution without elevating the risk of tissue injury.

Externally Navigated Bronchoscopy Using 2-D Motion Sensors: Dynamic Phantom Validation

The paper presents a new endoscope motion tracking method that is based on a novel external endoscope tracking device and our modified stochastic optimization method for boosting endoscopy navigation. We designed a novel tracking prototype where a 2-D motion sensor was introduced to directly measure the insertion-retreat linear motion and also the rotation of the endoscope. With our developed stochastic optimization method, which embeds traceable particle swarm optimization in the Condensation algorithm, a full six degrees-of-freedom endoscope pose (position and orientation) can be recovered from 2-D motion sensor measurements. Experiments were performed on a dynamic bronchial phantom with maximal simulated respiratory motion around 24.0 mm. The experimental results demonstrate that our proposed method provides a promising endoscope motion tracking approach with more effective and robust performance than several current available tracking techniques. The average tracking accuracy of the position improved from 6.5 to 3.3 mm, which further approaches the clinical requirement of 2.0 mm in practice.

Respiratory Motion and Correction Simulation Platform for Coronary MR Angiography

Respiratory Motion and Correction Simulation Platform for Coronary MR Angiography

Simulation of respiratory motion during IMRT dose delivery

Background. When intensity modulated radiation therapy (IMRT) is realised with dynamic multi-leaf collimators (MLC) and given under respiratory motion, dosimetric errors may occur. These errors are a consequence of the dose blurring and the interplay between the organ motion and the leaf motion. In the present study, a model for evaluating these dosimetric effects for patient-specific cases has been developed and tested. Material and methods. In the purpose written software, three dimensional (3D) dose distributions can be calculated both with and without a generated breathing cycle. To validate the presented model and illustrate its application, periodic breathing cycles were generated, where the starting phase was set randomly for each field during the calculations. Respiration in the anterior-posterior (AP), superior-inferior (SI) and left-right (LR) direction was tested and verified. To illustrate the application of the presented model, two 5-fields IMRT plans with different complexity were calculated with a 2 cm peak-to-peak motion in the AP direction for one fraction and for 25 fractions. Results. The results showed that the calculation method is of good accuracy, in particular for IMRT plans consisting of several fields, where 97% of the pixels within the body fulfilled a tolerance set to 4% dose difference and 4 mm distance to agreement (DTA). For the two IMRT plans with different complexity, pronounced respiratory induced dose errors, which increased with increasing complexity, were found for both one fraction and 25 fractions, but due to the random stating phase the interplay effect was considerably reduced for the plans consisting of 25 fractions. This illustrates how the dosimetric effects will vary depending on the dose plan and on the number of fractions investigated. Conclusion. For patient specific cases, the model can with good accuracy calculate 3D dose distributions both with and without respiratory motion, and evaluate the dosimetric effects.

CT Fluoroscopy-Guided Lung Biopsy with Novel Steerable Biopsy Canula: Ex-Vivo Evaluation in Ventilated Porcine Lung Explants

The purpose was to evaluate ex-vivo a prototype of a novel biopsy canula under CT fluoroscopy-guidance in ventilated porcine lung explants in respiratory motion simulations. Using an established chest phantom for porcine lung explants, n = 24 artificial lesions consisting of a fat-wax-Lipiodol mixture (approx. 70HU) were placed adjacent to sensible structures such as aorta, pericardium, diaphragm, bronchus and pulmonary artery. A piston pump connected to a reservoir beneath a flexible silicone reconstruction of a diaphragm simulated respiratory motion by rhythmic inflation and deflation of 1.5 L water. As biopsy device an 18-gauge prototype biopsy canula with a lancet-like, helically bended cutting edge was used. The artificial lesions were punctured under CT fluoroscopy-guidance (SOMATOM Sensation 64, Siemens, Erlangen, Germany; 30mAs/120 kV/5 mm slice thickness) implementing a dedicated protocol for CT fluoroscopy-guided lung biopsy. The mean-diameter of the artificial lesions was 8.3 +/- 2.6 mm, and the mean-distance of the phantom wall to the lesions was 54.1 +/- 13.5 mm. The mean-displacement of the lesions by respiratory motion was 14.1 +/- 4.0 mm. The mean-duration of CT fluoroscopy was 9.6 +/- 5.1 s. On a 4-point scale (1 = central; 2 = peripheral; 3 = marginal; 4 = off target), the mean-targeted precision was 1.9 +/- 0.9. No misplacement of the biopsy canula affecting adjacent structures could be detected. The novel steerable biopsy canula proved to be efficient in the ex-vivo set-up. The chest phantom enabling respiratory motion and the steerable biopsy canula offer a feasible ex-vivo system for evaluating and training CT fluoroscopy-guided lung biopsy adapted to respiratory motion.

Validation of a computational method for assessing the impact of intra-fraction motion on helical tomotherapy plans

In this work, a method for direct incorporation of patient motion into tomotherapy dose calculations is developed and validated. This computational method accounts for all treatment dynamics and can incorporate random as well as cyclical motion data. Hence, interplay effects between treatment dynamics and patient motion are taken into account during dose calculation. This allows for a realistic assessment of intra-fraction motion on the dose distribution. The specific approach entails modifying the position and velocity events in the tomotherapy delivery plan to accommodate any known motion. The computational method is verified through phantom and film measurements. Here, measured prostate motion and simulated respiratory motion tracks were incorporated in the dose calculation. The calculated motion-encoded dose profiles showed excellent agreement with the measurements. Gamma analysis using 3 mm and 3% tolerance criteria showed over 97% and 96% average of points passing for the prostate and breathing motion tracks, respectively. The profile and gamma analysis results validate the accuracy of this method for incorporating intra-fraction motion into the dose calculation engine for assessment of dosimetric effects on helical tomotherapy dose deliveries.

Evaluation of Dynamic Volume Scanning on a 320-slice CT for Routine Assessment of Respiratory-induced Lung Tumor Motion

A novel volumetric CT scanner (Aquilion One, Toshiba) has been installed at the Princess Margaret Hospital for implementation into routine CT simulation. This 320-slice technology offers great advantages for dynamic imaging in terms of speed and coverage as conventional 4D CT studies are limited in cradio-caudal extent during dynamic acquisition and rely on respiratory correlation between couch positions. The aim of this work is to evaluate the dynamic volume capabilities in the presence of simulated respiratory motion.