Varian Real-time Position Management Research Articles

Imaging investigation of small motion target for lung stereotactic body radiotherapy (SBRT)

Purpose: Motion management is important in lung tumor SBRT. Small target four-dimensional computed tomography (4DCT) imaging could give significant target motion information. In this study, Quality of 4DCT for small target was investigated to provide information for treatment planning in SBRT of small target, which is in favor of magnifying the target margin characteristics during 4DCT scan. Method and Materials: A Real Time Position Management (RPM) phantom from Varian Medical System and 6 CT-spot pellets from Beekley Medical were employed for this study. Each pellet was equivalent to a 4mm diameter ball. The CT spot pellets were attached to the RPM phantom. Two pellet set planes formed 8cm distance and generated two speeds which were 0.2cm and 0.4mm per second given a period with 5.0 seconds. With a GE LightSpeedTM RT CT scanner, the phantom was executed with helical scan with 1.25mm slice thickness with and without motion. Then a 4D CT scan in axial cine mode was carried on at the same phantom. The image exams were exported the GE Advantage Workstation for process. The exams were reviewed and sorted into 10 phases retrospectively. The 0% phase image set, 50% phase image set, maximum intensity projection (MIP) image set, and average intensity projection (Ave-IP) image set were exported to the Eclipse treatment planning system for analysis. In image sets, multi-dimensional variables such as center coordinate of pellets, distance between pellets, and volume of the pellets were used for analysis. Results: At 350 HU window width and 40HU window level, image sets from helical scan for the static phantom is used as reference, comparing to helical scan from moving phantom, retrospective MIP, average intensity projection, 0% phase and 50% phase, for pellets moving at 0.4 cm per second, the average coordinate deviation are 0.49cm, 0.22cm, 0.19cm, 0.59cm and 0.06cm with standard deviation 0.83cm, 0.29cm, 0.32cm, 0.69cm, and 0.07cm, the percentage distance differences are 10.2%, 3.3%, 7.3%, 0.1%, and 0.1% with standard deviation of 13.2%, 4.4%, 9.6%, 0.1%, and 0.1%. and the percentage volumes changes are 17.4%, 171.5%, 18.4%, 14.2% and 7.8% with standard deviation at 25.4%, 201.8%, 23.7%, 19.85% and 10%. Conclusions: A simple and sensitive 4DCT quality assurance method was developed by combining Varian RPM phantom and CT-spot pellets from Beekley Medical and it shows that the 50% phase image set is better for SBRT planning. Further study will include dosimetric effect on the small target moving in different directions.

Surface Guided Radiotherapy (SGRT) vs Varian RPM for deep inspiration breathhold (DIBH) breast treatments

DIBH for breast treatments allows for the reduction of irradiated heart volume, reduces tumour bed motion and increases lung sparing. Since 2007, we have treated breast patients in DIBH using Varian real time position management (RPM), which comprises a marker block with two reflective infrared markers placed on the patients’ abdomen. This is tracked during treatment to allow for reproducible breathhold.

Intrafraction tumor motion during deep inspiration breath hold pancreatic cancer treatment.

PurposeBeam gating with deep inspiration breath hold (DIBH) has been widely used for motion management in radiotherapy. Normally it relies on some external surrogate for estimating the internal target motion, while the exact internal motion is unknown. In this study, we used the intrafraction motion review (IMR) application to directly track an internal target and characterized the residual motion during DIBH treatment for pancreatic cancer patients through their full treatment courses.Methods and MaterialsEight patients with pancreatic cancer treated with DIBH volumetric modulated arc therapy in 2017 and 2018 were selected for this study, each with some radiopaque markers (fiducial or surgical clips) implanted near or inside the target. The Varian Real‐time Position Management (RPM) system was used to monitor the breath hold, represented by the anterior‐posterior displacement of an external surrogate, namely reflective markers mounted on a plastic block placed on the patient's abdomen. Before each treatment, a cone beam computed tomography (CBCT) scan under DIBH was acquired for patient setup. For scan and treatment, the breath hold reported by RPM had to lie within a 3 mm window. IMR kV images were taken every 20° or 40° gantry rotation during dose delivery, resulting in over 5000 images for the cohort. The internal markers were manually identified in the IMR images. The residual motion amplitudes of the markers as well as the displacement from their initial positions located in the setup CBCT images were analyzed.ResultsEven though the external markers indicated that the respiratory motion was within 3 mm in DIBH treatment, significant residual internal target motion was observed for some patients. The range of average motion was from 3.4 to 7.9 mm, with standard deviation ranging from 1.2 to 3.5 mm. For all patients, the target residual motions seemed to be random with mean positions around their initial setup positions. Therefore, the absolute target displacement relative to the initial position was small during DIBH treatment, with the mean and the standard deviation 0.6 and 2.9 mm, respectively.ConclusionsInternal target motion may differ from external surrogate motion in DIBH treatment. Radiographic verification of target position at the beginning and during each fraction is necessary for precise RT delivery. IMR can serve as a useful tool to directly monitor the internal target motion.

P256] The effect of different breathing stages on treatment plans prepared using VMAT technique in early stage left breast irradiation

Purpose Volumetric Arc Therapy (VMAT) has become one of the most frequently used techniques in the treatment of left breast cancer radiotherapy due to its ability to reduce critical organ doses.In patients with left breast cancer, it is very important to reduce the amount of irradiated heart dose-volume in order to prevent possible cardiovascular morbidity associated with radiotherapy. Deep inspiration breath-hold (DIBH) is a technique that delivered the radiotherapy to the left breast patients in a deep breath hold position.In this study, VMAT plans on computed tomography (CT) images taken at different breath phases for left sided breast cancer patients were compared in terms of plan quality and risky organ doses. Methods In the study, VMAT plans were prepared on the CT images taken both free-breathing (FB) and DIBH modes. Eclipse treatment planning system (TPS) was used in order to prepare radiotherapy plans. The Varian Real Time Position Management System (RPM) was used for the DIBH technique.The dose was defined as 50 Gy/25 fractions. For all plans, 95% of the CTV breast volume was targeted to receive 46 Gy. In both techniques, target volume homogeneity index (HI) and conformity index (CI), critical organ doses and MU values were compared. Result CI values of VMAT plans prepared for both FB and DIBH CT images was found as 1.02 ± 0.04 and 1.014 ± 0.03; HI was found as 0.101 ± 0.018 and 0.113 ± 0.016, respectively. In terms of dose homogeneity, DIBH-VMAT plans were found to be better than FB-VMAT plans; the difference is statistically significant. The LAD mean doses were found to be lower in the DIBH-VMAT technique (p Conclusion DIBH-VMAT technique should be preferred instead of FB-VMAT technique for early stage left breast cancer irradiation. This work was supported by Scientific Research Projects Coordination Unit of Istanbul University (Project Number: I.U.BAP-23057).

A novel dual gating approach using joint inertial sensors: implications for cardiac PET imaging

Positron emission tomography (PET) is a non-invasive imaging technique which may be considered as the state of art for the examination of cardiac inflammation due to atherosclerosis. A fundamental limitation of PET is that cardiac and respiratory motions reduce the quality of the achieved images. Current approaches for motion compensation involve gating the PET data based on the timing of quiescent periods of cardiac and respiratory cycles. In this study, we present a novel gating method called microelectromechanical (MEMS) dual gating which relies on joint non-electrical sensors, i.e. tri-axial accelerometer and gyroscope. This approach can be used for optimized selection of quiescent phases of cardiac and respiratory cycles. Cardiomechanical activity according to echocardiography observations was investigated to confirm whether this dual sensor solution can provide accurate trigger timings for cardiac gating. Additionally, longitudinal chest motions originating from breathing were measured by accelerometric- and gyroscopic-derived respiratory (ADR and GDR) tracking. The ADR and GDR signals were evaluated against Varian real-time position management (RPM) signals in terms of amplitude and phase. Accordingly, high linear correlation and agreement were achieved between the reference electrocardiography, RPM, and measured MEMS signals. We also performed a Ge-68 phantom study to evaluate possible metal artifacts caused by the integrated read-out electronics including mechanical sensors and semiconductors. The reconstructed phantom images did not reveal any image artifacts. Thus, it was concluded that MEMS-driven dual gating can be used in PET studies without an effect on the quantitative or visual accuracy of the PET images. Finally, the applicability of MEMS dual gating for cardiac PET imaging was investigated with two atherosclerosis patients. Dual gated PET images were successfully reconstructed using only MEMS signals and both qualitative and quantitative assessments revealed encouraging results that warrant further investigation of this method.

Three-Year Outcome Evaluation of Deep Inspiration Breath Hold Technique in Post–Radiation Therapy Patients After Left-Sided Breast-Conserving Surgery by Echocardiography With Quantitative Tissue Velocity Imaging

This study aims to evaluate the benefits of deep inspiration breath hold (DIBH) technique over free breathing (FB) by quantitative tissue velocity imaging(QTVI) in patients with left-sided breast cancer. Between 2012 and 2014, 68 patients with T1–2N0 breast cancer (BC) received whole breast radiotherapy (RT) after breast-conserving surgery (BCS) in our hospital. Patients treated with adjuvant chemotherapy were excluded. 30 patients treated with FB（A group and 38 patients took the DIBH technique (B group) using Varian real-time position management (RPM) system. The prescribed dose was 46 Gy in 23 fractions for the whole breast and 14Gy in 7 fractions for resection cavity. Each patient received the QTVI in the initial day of RT and 3 years after RT. The following data are acquired: The diameter of left atrial and late diastolic left ventricle (LV), the thickness of interventricular septum and LV posterior wall, LV ejection fraction, the peak velocity of mitral inflow (E/A). Regional velocity profiles of 6 walls of LV. The peak velocity of systolic (Vs), early diastolic velocity (Ea), late diastolic velocity(Aa) and the ratio of Ea and Aa(Ea/Aa). Parameters of interest about RT plan, cardiac V5, mean LAD dose, maximum LAD dose, and mean heart dose were calculated and analyzed. All enrolled patients completed the study. The cardiac V5, mean LAD dose, maximum LAD dose, and mean heart dose in RT plan of A group were always significant lower than those of B group (P<0.05). The differences of all parameters about QTVI between A and B group were not significant before radiotherapy. Compared with A group after radiotherapy, E/A、Vs、Ea/Aa were significantly reduced in B group after radiotherapy (P<0.05). This study shows that there is markedly reduced cardiac exposure in patients with DIBH as compared to FB. At the end of 3rd year, radioactive heart damage was significantly less in patients using DIBH technique than FB. The DIBH is a clinically useful heart protection for radiation therapy of left-sided breast cancer after BCS. Keyword: DIBH; radioactive heart damage; echocardiography; QTVI.

A Tool for Characterizing Randomness and Irregularity in Patient Respiratory Motion

Patient random irregular breathing undermines the fundamental assumption for 4DCT and radiotherapy based on it, either ITV-based or gated treatments. During patient’s 4DCT simulation, Respiratory Gating Signal Waveform (RGSW) is usually collected over a duration much longer than one breathing cycle. Therefore, RGSW may contain valuable information on irregularities in the patient breathing cycles and help to improve imaging and delivery in 4D radiation therapy. In this study, we developed a RGSW based tool for quantitatively accessing the randomness and irregularity level in patient respiratory motion. Totally 242 clinical RGSWs obtained with Varian Real-time Position Management (RPM) system were included in this study. For each RGSW, firstly we constructed its unwrapped phase φ(t) using Hilbert transform. Secondly, we computed the phase differences, i.e., φ(t+τ)-φ(t), between any two points along the waveform with a fixed time interval τ. Thirdly, we estimated the standard deviation σ of the phase differences. Finally, we calculated volatility (i.e., σ ⁄√τ) of the RGSW's phase in the given time interval τ. Sixteen intervals (i.e., τ=1s, 2s, 3s, …, 16s) were selected for volatility’s computation to examine if it was stable over different time intervals. The relative standard deviation of the acquired volatility values at all 16 time-intervals was computed for each RGSW. Fittings were performed on the histograms formed by observed volatility over a fixed time interval (e.g., 4s) and the relative standard deviation in its measured values with all 16 intervals from all patient RPM RGSWs. A stochastic random walk phase model was utilized to interpret the results. The unwrapped phase of an ideal periodic RGSW always has zero volatility. For our clinical RGSWs, the volatility is non-zero but reasonably stable over the selected time intervals. The observed volatility at 4s interval from the 242 RGSWs (∈ [0.07, 3.7] (1⁄√s), median=0.78 (1⁄√s)) could be approximated by a Gamma distribution Γ(3.0, 0.3). The population histogram of the relative standard deviation in volatility for the investigated time intervals (∈[2%, 35%], median=11.5%) could be fitted with a Gamma distribution Γ(3.5, 0.04). The stochastic random walk phase model, which yields a fixed volatility value over any given time interval, might serve as a useful tool in explaining our observations on phase volatility in patient's RGSW. We proposed a new application of patient’s RGSW for measuring the randomness and irregularity in patient respiratory motion. The volatility in RPM RGSW phase has a potential correlation to the eligibility and treatment response of a given patient to a given clinical procedure. Further studies are needed to explore its potential clinical role in patient 4D image acquisition and patient radiotherapy delivery.

A software platform for statistical evaluation of patient respiratory patterns in radiation therapy

AimThe aim of this work was to design and evaluate a software tool for analysis of a patient’s respiration, with the goal of optimizing the effectiveness of motion management techniques during radiotherapy imaging and treatment. Materials and methodsA software tool which analyses patient respiratory data files (.vxp files) created by the Varian Real-Time Position Management System (RPM) was developed to analyse patient respiratory data. The software, called RespAnalysis, was created in MATLAB and provides four modules, one each for determining respiration characteristics, providing breathing coaching (biofeedback training), comparing pre and post-training characteristics and performing a fraction-by-fraction assessment. The modules analyse respiratory traces to determine signal characteristics and specifically use a Sample Entropy algorithm as the key means to quantify breathing irregularity. Simulated respiratory signals, as well as 91 patient RPM traces were analysed with RespAnalysis to test the viability of using the Sample Entropy for predicting breathing regularity. ResultsRetrospective assessment of patient data demonstrated that the Sample Entropy metric was a predictor of periodic irregularity in respiration data, however, it was found to be insensitive to amplitude variation. Additional waveform statistics assessing the distribution of signal amplitudes over time coupled with Sample Entropy method were found to be useful in assessing breathing regularity. ConclusionsThe RespAnalysis software tool presented in this work uses the Sample Entropy method to analyse patient respiratory data recorded for motion management purposes in radiation therapy. This is applicable during treatment simulation and during subsequent treatment fractions, providing a way to quantify breathing irregularity, as well as assess the need for breathing coaching. It was demonstrated that the Sample Entropy metric was correlated to the irregularity of the patient’s respiratory motion in terms of periodicity, whilst other metrics, such as percentage deviation of inhale/exhale peak positions provided insight into respiratory amplitude regularity.

TH-CD-207A-04: Optimized Respiratory Gating for Abnormal Breathers in Pancreatic SBRT

Purpose: Pancreatic SBRT is uniquely challenging due to both the erratic/unstable motion of the pancreas and the close proximity of the radiosensitive small bowel. Respiratory gating can mitigate this effect, but the irregularity of motion severely affects traditional phase-based gating. The purpose of this study was to analyze real-time motion data of pancreatic tumors to optimize the efficacy and accuracy of respiratory gating, with the overall goal of enabling dose escalated pancreatic SBRT. Methods: Fifteen pancreatic SBRT patients received 30–33 Gy in 5 fractions on a Varian TrueBeam STx unit. Abdominal compression was used to reduce the amplitude of tumor motion, and daily cone-beam computed tomography (CBCT) scans were acquired prior to each treatment for target localization purposes. For this study, breathing data (phase and amplitude) were collected during each CBCT scan using Varian's Real-Time Position Management system. An in-house template matching technique was used to track the superior-inferior motion of implanted fiducial markers in CBCT projection images. Using tumor motion and breathing data, phase-based or amplitude-based respiratory gating was simulated for all 75 fractions, targeting either end-exhalation or end-inhalation phases of breathing. Results: For the average patient, gating at end-exhalation offered the best reductions in effective motion for equal duty cycles. However, optimal central phase angle varied widely (range: 0–92%, mean±SD: 49±12%), and phase-based gating windows typically associated with end-exhalation (i.e., “30–70%”) were rarely ideal. Amplitude-based gating significantly outperformed phase-based gating, with average effective ranges for amplitude-based gating 25% lower than phase-based gating ranges (as much as 73% lower). Amplitude-based gating was consistently better suited to accommodate abnormal breathing patterns. For both phase-based and amplitude-based gating, end-exhalation provided significantly better results than end-inhalation. Conclusion: Amplitude-based gating reliably outperformed phase-based gating, and end-exhalation was more suitable than end-inhalation. These results will be used to guide future dose-escalation trials. Research funding provided by Varian Medical Systems to Miften and Jones.

The benefit of deep inspiration breath hold: evaluating cardiac radiation exposure in patients after mastectomy and after breast-conserving surgery.

This study aims to evaluate the reduction of cardiac radiation dose and volume with deep inspiration breath hold (DIBH) technique compared to free breathing (FB) in patients with left-sided breast cancer. The study also aims to evaluate whether the benefits of DIBH vary in patients who had whole breast radiotherapy (RT) after breast-conserving surgery (BCS) and those who had chest wall RT post-mastectomy (M). FB and DIBH plans were generated for 15 consecutive post-BCS patients and 17 post-M patients who underwent RT with DIBH using varian real-time position management (RPM) system. Cardiac shields were used in all post-BCS plans, provided that clinical treatment volume coverage was not compromised, while chest wall coverage took priority in post-M plans. The prescribed dose was 50Gy in 25 fractions for the whole breast or the chest wall. Parameters of interest were cardiac V5, mean LAD dose, maximum LAD dose, and mean heart dose. The impact of DIBH was compared in post-BCS and post-M patients using paired t tests. To gauge clinically meaningful outcome, the proportion of patients with V5<5% and mean cardiac dose <2Gy were compared using McNemar's test. DIBH decreased V5 by an absolute 4.5% (2.3 vs. 6.8%; p<0.0001) in post-M group, and by an absolute 2.4% (1.3 vs. 3.7%; p=0.0028) in post-BCS group. DIBH decreased the mean heart dose by 107.0cGy (127.4 vs. 234.4cGy; p=0.0002) in post-M group, and by 58.9cGy (82.2 vs. 141.1cGy; p=0.0012) in post-BCS group. DIBH decreased mean LAD by 1201.6cGy (670 vs. 1872.5cGy; p=0.0006) in post-M group, and by 799.0cGy (425.3 vs. 1224.3cGy; p=0.0003) in post-BCS group. DIBH also decreased max LAD dose by 1244.3cGy (2776.0 vs. 4020.3cGy; p=0.0014) in post-M group, and by 1856.3cGy (1898.7 vs. 3754.9cGy; p=0.0005) in post-BCS group. In post-BCS group, cardiac V5<5% was achieved in 10/15 (67%) FB patients, and in 15/15 (100%) DIBH patients (p=0.002), and mean heart dose <2Gy was achieved in 12/15 (80%) FB patients and in 15/15 (100%) DIBH patients (p<0.001). This compares with post-M group, in which V5<5% was achieved in 6/17 (35%) FB patients and in 16/17 (94%) DIBH patients (p=0.05), and mean heart dose <2Gy was achieved in 7/17 FB (41%) an 16/17 DIBH patients (94%) (p=0.03). The results of this study suggest that there is considerable reduction in cardiac exposure in most patients with DIBH compared to FB, although less reduction is observed in the post-BCS patients. The use of cardiac shields and collimators/gantry adjustments, more readily applicable for post-BCS cases, may limit the additional benefits of DIBH. In an environment where DIBH availability is limited, the result of this study supports the preferential use of DIBH in post-M patients over post-BCS patients.

Accuracy Verification of Respiratory-gated Radiotherapy that Combines the Respiration-Monitoring Device and Respiratory-gated System.

The purpose of this study is to evaluate the mechanical accuracy of a respiratory-gated radiation system that combines the Linear Indicator-equipped Abches respiration-monitoring device and the Varian Real-time Position Management system (LI-RPM system). This combined configuration, implemented for the first time in Japan, was compared with the stand-alone Varian RPM system (RPM system). The delay times, dose profiles, and output waveforms of the LI-RPM and RPM systems were evaluated using a self-produced dynamic phantom. The delay times for the LI-RPM and RPM systems were both 0.1 s for 4 s and 8 s test periods. The corresponding output waveform correlation factors (R2) for the 4 s and 8 s test periods were 0.9981 and 0.9975, respectively. No difference was observed in the dose profiles of the two systems. Thus, the present results indicate that the proposed LI-RPM combined respiratory-gated radiation system has similar properties to the RPM system. However, it offers several advantages in terms of its versatility, including its alignment assistance capabilities for non-coplanar treatments.

SU‐E‐J‐159: Analysis of Total Imaging Uncertainty in Respiratory‐Gated Radiotherapy

Purpose:In respiratory‐gated radiotherapy, the gating phase during treatment delivery needs to coincide with the corresponding phase determined during the treatment plan. However, because radiotherapy is performed based on the image obtained for the treatment plan, the time delay, motion artifact, volume effect, and resolution in the images are uncertain. Thus, imaging uncertainty is the most basic factor that affects the localization accuracy. Therefore, these uncertainties should be analyzed. This study aims to analyze the total imaging uncertainty in respiratory‐gated radiotherapy.Methods:Two factors of imaging uncertainties related to respiratory‐gated radiotherapy were analyzed. First, CT image was used to determine the target volume and 4D treatment planning for the Varian Realtime Position Management (RPM) system. Second, an X‐ray image was acquired for image‐guided radiotherapy (IGRT) for the BrainLAB ExacTrac system. These factors were measured using a respiratory gating phantom. The conditions applied during phantom operation were as follows: respiratory wave form, sine curve; respiratory cycle, 4 s; phantom target motion amplitude, 10, 20, and 29 mm (which is maximum phantom longitudinal motion). The target and cylindrical marker implanted in the phantom coverage of the CT images was measured and compared with the theoretically calculated coverage from the phantom motion. The theoretical position of the cylindrical marker implanted in the phantom was compared with that acquired from the X‐ray image. The total imaging uncertainty was analyzed from these two factors.Results:In the CT image, the uncertainty between the target and cylindrical marker's actual coverage and the coverage of CT images was 1.19 mm and 2.50mm, respectively. In the Xray image, the uncertainty was 0.39 mm. The total imaging uncertainty from the two factors was 1.62mm.Conclusion:The total imaging uncertainty in respiratory‐gated radiotherapy was clinically acceptable. However, an internal margin should be added to account for the total imaging uncertainty.

Feasibility study of deep inspiration breath-hold based volumetric modulated arc therapy for locally advanced left sided breast cancer patients.

The purpose of this study was to assess the feasibility of deep inspiration breath-hold (DIBH) based volumetric modulated arc therapy (VMAT) for locally advanced left sided breast cancer patients undergoing radical mastectomy. DIBH immobilizes the tumor bed providing dosimetric benefits over free breathing (FB). Ten left sided post mastectomy patients were immobilized in a supine position with both the arms lifted above the head on a hemi-body vaclock. Two thermoplastic masks were prepared for each patient, one for normal free breathing and a second made with breath-hold to maintain reproducibility. DIBH CT scans were performed in the prospective mode of the Varian real time position management (RPM) system. The planning target volume (PTV) included the left chest wall and supraclavicular nodes and PTV prescription dose was 5000cGy in 25 fractions. DIBH-3DCRT planning was performed with the single iso-centre technique using a 6MV photon beam and the field-in-field technique. VMAT plans for FB and DIBH contained two partial arcs (179o-300oCCW/CW). Dose volume histograms of PTV and OAR's were analyzed for DIBH-VMAT, FB-VMAT and DIBH-3DCRT. In DIBH mode daily orthogonal (0o and 90o) KV images were taken to determine the setup variability and weekly twice CBCT to verify gating threshold level reproducibility. DIBH-VMAT reduced the lung and heart dose compared to FB-VMAT, while maintaining similar PTV coverage. The mean heart V30Gy was 2.3% ±2.7, 5.1% ±3.2 and 3.3% ±7.2 and for left lung V20Gy was 18.57% ±2.9, 21.7% ±3.9 and 23.5% ±5.1 for DIBH-VMAT, FB-VMAT and DIBH-3DCRT respectively. DIBH-VMAT significantly reduced the heart and lung dose for left side chest wall patients compared to FB-VMAT. PTV conformity index, homogeneity index, ipsilateral lung dose and heart dose were better for DIBH-VMAT compared to DIBH-3DCRT. However, contralateral lung and breast volumes exposed to low doses were increased with DIBH-VMAT.

Motion Freeze for Respiration Motion Correction in PET/CT: A Preliminary Investigation With Lung Cancer Patient Data

Purpose. Respiratory motion presents significant challenges for accurate PET/CT. It often introduces apparent increase of lesion size, reduction of measured standardized uptake value (SUV), and the mismatch in PET/CT fusion images. In this study, we developed the motion freeze method to use 100% of the counts collected by recombining the counts acquired from all phases of gated PET data into a single 3D PET data, with correction of respiration by deformable image registration. Methods. Six patients with diagnosis of lung cancer confirmed by oncologists were recruited. PET/CT scans were performed with Discovery STE system. The 4D PET/CT with the Varian real-time position management for respiratory motion tracking was followed by a clinical 3D PET/CT scan procedure in the static mode. Motion freeze applies the deformation matrices calculated by optical flow method to generate a single 3D effective PET image using the data from all the 4D PET phases. Results. The increase in SUV and decrease in tumor size with motion freeze for all lesions compared to the results from 3D and 4D was observed in the preliminary data of lung cancer patients. In addition, motion freeze substantially reduced tumor mismatch between the CT image and the corresponding PET images. Conclusion. Motion freeze integrating 100% of the PET counts has the potential to eliminate the influences induced by respiratory motion in PET data.

SU‐E‐J‐172: A Quantitative Assessment of Lung Tumor Motion Using 4DCT Imaging Under Conditions of Controlled Breathing in the Management of Non‐Small Cell Lung Cancer (NSCLC) Using Stereotactic Body Radiation Therapy (SBRT)

Purpose:To study breathing related tumor motion amplitudes by lung lobe location under controlled breathing conditions used in Stereotactic Body Radiation Therapy (SBRT) for NSCLC.Methods:Sixty‐five NSCLC SBRT patients since 2009 were investigated. Patients were categorized based on tumor anatomic location (RUL‐17, RML‐7, RLL‐18, LUL‐14, LLL‐9). A 16‐slice CT scanner [GE RT16 Pro] along with Varian Realtime Position Management (RPM) software was used to acquire the 4DCT data set using 1.25 mm slice width. Images were binned in 10 phases, T00 being at maximum inspiration ' T50 at maximum expiration phase. Tumor volume was segmented in T50 using the CT‐lung window and its displacement were measured from phase to phase in all three axes; superiorinferior, anterior‐posterior ' medial‐lateral at the centroid level of the tumor.Results:The median tumor movement in each lobe was as follows: RUL= 3.8±2.0 mm (mean ITV: 9.5 cm3), RML= 4.7±2.8 mm (mean ITV: 9.2 cm3), RLL=6.6±2.6 mm (mean ITV: 12.3 cm3), LUL=3.8±2.4 mm (mean ITV: 18.5 cm3), ' LLL=4.7±2.5 mm (mean ITV: 11.9 cm3). The median respiratory cycle for all patients was found to be 3.81 ± 1.08 seconds [minimum 2.50 seconds, maximum 7.07 seconds]. The tumor mobility incorporating breathing cycle was RUL = 0.95±0.49 mm/s, RML = 1.35±0.62 mm/s, RLL = 1.83±0.71 mm/s, LUL = 0.98 ±0.50 mm/s, and LLL = 1.15 ±0.53 mm/s.Conclusion:Our results show that tumor displacement is location dependent. The range of motion and mobility increases as the location of the tumor nears the diaphragm. Under abdominal compression, the magnitude of tumor motion is reduced by as much as a factor of 2 in comparison to reported tumor magnitudes under conventional free breathing conditions. This study demonstrates the utility of abdominal compression in reducing the tumor motion leading to reduced ITV and planning tumor volumes (PTV).

Motion freeze for respiration motion correction in PET/CT: a preliminary investigation with lung cancer patient data.

Purpose. Respiratory motion presents significant challenges for accurate PET/CT. It often introduces apparent increase of lesion size, reduction of measured standardized uptake value (SUV), and the mismatch in PET/CT fusion images. In this study, we developed the motion freeze method to use 100% of the counts collected by recombining the counts acquired from all phases of gated PET data into a single 3D PET data, with correction of respiration by deformable image registration. Methods. Six patients with diagnosis of lung cancer confirmed by oncologists were recruited. PET/CT scans were performed with Discovery STE system. The 4D PET/CT with the Varian real-time position management for respiratory motion tracking was followed by a clinical 3D PET/CT scan procedure in the static mode. Motion freeze applies the deformation matrices calculated by optical flow method to generate a single 3D effective PET image using the data from all the 4D PET phases. Results. The increase in SUV and decrease in tumor size with motion freeze for all lesions compared to the results from 3D and 4D was observed in the preliminary data of lung cancer patients. In addition, motion freeze substantially reduced tumor mismatch between the CT image and the corresponding PET images. Conclusion. Motion freeze integrating 100% of the PET counts has the potential to eliminate the influences induced by respiratory motion in PET data.

Evaluation of two synchronized external surrogates for 4D CT sorting

The purpose of this study was to quantify the performance and agreement between two different external surrogate acquisition systems: Varian's Real‐Time Position Management (RPM) and Philips Medical Systems' pneumatic bellows, in the context of waveform and 4D CT image analysis. Eight patient displacement curves derived from RPM data were inputted into a motion platform with varying amplitudes (0.5 to 3 cm) and patterns. Simultaneous 4D CT acquisition, with synchronized X‐ray on detection, was performed with the bellows and RPM block placed on the platform. Bellows data were used for online retrospective phase‐based sorting, while RPM data were used for off‐line reconstruction of raw 4D CT data. RPM and bellows breathing curves were resampled, normalized, and analyzed to determine associations between different external surrogates, relative amplitude differences, and system latency. Maximum intensity projection (MIP) images were generated, phantom targets were delineated, and volume differences, overlap index, and Dice similarity coefficient differences were evaluated. A prospective patient study of ten patients was performed and waveforms were evaluated for latency (i.e., absolute time differences) and overall agreement. 4D CT sorting quality and subtraction images were assessed. Near perfect associations between the RPM and bellows‐acquired breathing traces were found (Pearson′sr=0.987−0.999). Target volumes were 200.4±12ccand199.8±12.6cc for RPM and bellows targets, respectively, which was not significantly different (U=33,p>0.05). Negligible centroid variations were observed between bellows and RPM‐contoured MIP targets (largest discrepancy=−0.24±0.31mm in superior‐inferior direction). The maximum volume difference was observed for an RPM target 2.5 cc (1%) less than bellows, yielding the largest difference in centroid displacement (0.9 mm). Strong correlations in bellows and RPM waveforms were observed for all patients (0.947±0.037). Latency between external surrogates was <100ms for phantom and patient data. Negligible differences were observed between MIP, end‐exhale, and end‐inhale phase images for all cases, with delineated RPM and bellows lung volumes demonstrating a mean difference of −0.3±0.51%. Dice similarity coefficients and overlap indices were near unity for phantom target volumes and patient lung volumes. Slight differences were observed in waveform and latency analysis between Philips bellows and Varian's RPM, although these did not translate to differences in image quality or impact delineations. Therefore, the two systems were found to be equivalent external surrogates in the context of 4D CT for treatment planning purposes.PACS numbers: 87.57.Q‐, 07.07.Df

External respiratory motion analysis and statistics for patients and volunteers

We analyzed a large patient and volunteer study of external respiratory motion in order to develop a population database of respiratory information. We analyzed 120 lung, liver, and abdominal patients and 25 volunteers without lung disease to determine the extent of motion using the Varian Real‐Time Position Management system. The volunteer respiratory motion was measured for both abdominal and thoracic placement of the RPM box. Evaluation of a subset of 55 patients demonstrates inter‐ and intrafraction variation over treatment. We also calculated baseline drift and duty cycle for patients and volunteers. The mean peak‐to‐peak amplitude (SD) for the patients was 1.0 (0.5) cm, and for the volunteers it was abdomen 0.8 (0.3) cm and thoracic 0.2 (0.2) cm. The mean period (SD) was 3.6 (1.0) s, 4.2 (1.1) s, and 4.1 (0.8) s, and the mean end exhale position (SD) was 60% (6), 58% (7), and 56% (7) for patient, volunteer abdomen, and volunteer thoracic, respectively. Baseline drift was greater than 0.5 cm for 40% of patients. We found statistically significant differences between the patient and volunteer groups. Peak‐to‐peak amplitude was significantly larger for patients than the volunteer abdominal measurement and the volunteer abdominal measurement is significantly larger than the volunteer thoracic measurement. The patient group also exhibited significantly larger baseline drift than the volunteer group. We also found that peak‐to‐peak amplitude was the most variable parameter for both intra‐ and interfraction motion. This database compilation can be used as a resource for expected motion when using external surrogates in radiotherapy applications.PACS number: 87.19.Wx, 87.55.Km

SU-E-J-165: Development of a Low-Cost and Clinically Available Patient Intrafraction Motion Monitoring System.

We have developed a flexible system in order to monitor the intrafraction motion. The purpose of our study is to extend the monitoring system to clinically available system with low cost. Our system is composed of a standard web camera with a low-cost and 8x magnitude telescope, a personal computer with our in-house software and a specific marker box. The telescopic lens was attached with the web camera to extend more effective distance of the measurement in order to avoid patient's interference. The dynamic calibration algorithm was developed to take into account patient's rotation during treatment in order to measure the intrafraction motion more accurately. Tracking three markers simultaneously based on a template matching technique using parallel CPU computing was performed to measure the intrafraction motion with dynamic calibration. To evaluate our new system, a respiratory motion QA phantom with 10 mm-amplitude was used in order to measure the amplitudes under the different angles of web camera setting (0 to 50 degree, 5 degree step) using our system and Varian Real-Time Position Management Respiratory Gating (Varian-RPM) System. The results of our system were compared with the results of Varian-RPM System. The result of the amplitudes measured by our system and Varian RPM-System are 10.2±0.3 mm and 10.3±0.1mm at the angle of 0 deg., respectively. The values of both systems were within the tolerance value of AAPM Task group 142. The results of the amplitude of our system and Varian-RPM system were 10.2±0.3mm and 10.4±0.1mm, respectively, while the angle was changed. Under the parallel CPU computing, the calculation time to measure the position of the marker was about 50msec including the latency. Our proposed system could have clinically acceptable accuracies. The system would be contributed broadly to improve the treatment accuracy because of low-cost installation of it.

A programmable motion phantom for quality assurance of motion management in radiotherapy

A commercially available motion phantom (QUASAR, Modus Medical) was modified for programmable motion control with the aim of reproducing patient respiratory motion in one dimension in both the anterior-posterior and superior-inferior directions, as well as, providing controllable breath-hold and sinusoidal patterns for the testing of radiotherapy gating systems. In order to simulate realistic patient motion, the DC motor was replaced by a stepper motor. A separate 'chest-wall' motion platform was also designed to accommodate a variety of surrogate marker systems. The platform employs a second stepper motor that allows for the decoupling of the chest-wall and insert motion. The platform's accuracy was tested by replicating patient traces recorded with the Varian real-time position management (RPM) system and comparing the motion platform's recorded motion trace with the original patient data. Six lung cancer patient traces recorded with the RPM system were uploaded to the motion platform's in-house control software and subsequently replicated through the phantom motion platform. The phantom's motion profile was recorded with the RPM system and compared to the original patient data. Sinusoidal and breath-hold patterns were simulated with the motion platform and recorded with the RPM system to verify the systems potential for routine quality assurance of commercial radiotherapy gating systems. There was good correlation between replicated and actual patient data (P 0.003). Mean differences between the location of maxima in replicated and patient data-sets for six patients amounted to 0.034 cm with the corresponding minima mean equal to 0.010 cm. The upgraded motion phantom was found to replicate patient motion accurately as well as provide useful test patterns to aid in the quality assurance of motion management methods and technologies.