Mm In Anterior-posterior Directions Research Articles

Intrafraction tumor motion monitoring and dose reconstruction for liver pencil beam scanning proton therapy

Pencil beam scanning (PBS) proton therapy can provide highly conformal target dose distributions and healthy tissue sparing. However, proton therapy of hepatocellular carcinoma (HCC) is prone to dosimetrical uncertainties induced by respiratory motion. This study aims to develop intra-treatment tumor motion monitoring during respiratory gated proton therapy and combine it with motion-including dose reconstruction to estimate the delivered tumor doses for individual HCC treatment fractions. Three HCC-patients were planned to receive 58 GyRBE (n=2) or 67.5 GyRBE (n=1) of exhale respiratory gated PBS proton therapy in 15 fractions. The treatment planning was based on the exhale phase of a 4-dimensional CT scan. Daily setup was based on cone-beam CT (CBCT) imaging of three implanted fiducial markers. An external marker block (RPM) on the patient's abdomen was used for exhale gating in free breathing. This study was based on 5 fractions (patient 1), 1 fraction (patient 2) and 6 fractions (patient 3) where a post-treatment control CBCT was available. After treatment, segmented 2D marker positions in the post-treatment CBCT projections provided the estimated 3D motion trajectory during the CBCT by a probability-based method. An external-internal correlation model (ECM) that estimated the tumor motion from the RPM motion was built from the synchronized RPM signal and marker motion in the CBCT. The ECM was then used to estimate intra-treatment tumor motion. Finally, the motion-including CTV dose was estimated using a dose reconstruction method that emulates tumor motion in beam's eye view as lateral spot shifts and in-depth motion as changes in the proton beam energy. The CTV homogeneity index (HI) The CTV homogeneity index (HI) was calculated as . The tumor position during spot delivery had a root-mean-square error of 1.3mm in left-right, 2.8mm in cranio-caudal and 1.7mm in anterior-posterior directions compared to the planned position. On average, the CTV HI was larger than planned by 3.7%-points (range: 1.0-6.6%-points) for individual fractions and by 0.7%-points (range: 0.3-1.1%-points) for the average dose of 5 or 6 fractions. A method to estimate internal tumor motion and reconstruct the motion-including fraction dose for PBS proton therapy of HCC was developed and demonstrated successfully clinically.

Vector coding reveals the underlying balance control strategies used by humans during translational perturbation

Postural control research has focused on standing balance experiments on platforms moving with relatively large amplitudes (0.1–0.2 m). This study investigated balance strategies while standing on a platform moving 4 mm in anterior-posterior direction with frequency scaled linearly from 0.4 to 6 Hz. Platform motion and kinematic and kinetic information for nine healthy participants were recorded using motion capture and force plate systems. Coordination between hip, knee and ankle joint torque, and centre of mass (COM) and centre of pressure (COP) motion was quantified by vector coding. Significant main effect of platform frequency for knee-ankle and COP-COM phase relationship was observed (p = 0.023, p = 0.016). At frequencies below 2.11 and 2.34 Hz, ankle strategy was recruited. With ankle strategy, in-phase COP-COM motion with COP dominancy occurred at frequencies below 2.19 and 2.23 Hz during scaling up and down, respectively. As platform frequency passed these values, COM dominated over COP which was followed by anti-phase knee-ankle torque, called a knee strategy, and anti-phase motion between the COP and COM that allowed COP to regain dominance over COM. Collectively, we reveal knee strategy as a new and relevant strategy in real-life settings, and transition between ankle and knee strategies that underpinned transition between COP-COM relative motion.

A Prospective, Randomized, Controlled Clinical Study of Cervical Muscle Group Training Improving Radiotherapy Setup Accuracy Repeatability for Head and Neck Tumors

<h3>Purpose/Objective(s)</h3> Studies have shown that head and neck tumors are impossible to achieve an ideal match over the entire length of the neck due to the wide range of radiotherapy target areas. Previous studies have shown random deformation errors of 0.5 to 3.6 mm in the head and neck, the difference between any two different matched areas can reach 2 to 6 mm. we aimed to evaluate the role of neck muscle group training on the repeatability of the pose in patients treated with radiotherapy for head and neck tumors. <h3>Materials/Methods</h3> Patients treated with radiotherapy for head and neck tumors were randomly assigned (1:1) to a study group and a control group. The study group started cervical spine exercises+massage training one week before the start of radiotherapy until the end of radiotherapy. In the control group, conventional treatment without specific interventions was performed. The primary endpoint was the difference in the reproducibility of cervical spine set-up between the two groups, and the secondary endpoints were the differences in cervical curvature changes on lateral cervical radiographs before and after treatment between the two groups, and the differences in the timing and extent of side effects before, during, and after treatment between the two groups. <h3>Results</h3> A total of 947 CBCT scans were performed in 166 patients, including 479 CBCTs in 83 patients in the study group and 468 CBCTs in 83 patients in the control group. 26.51% (22/83) of the study group and 33.73% (28/83) of the control group had an error of ≥3 mm during the first treatment, (P=0.31). Patients with clivus and neck error >3mm in anterior-posterior direction during treatment accounted for 8.43% (7/83) of the study group and 26.51% (22/83) of the control group(P=0.002). The number of repeated setups except the first treatment was 2.42% in the study group and 7.02% in the control group (P=0.01). The error range from clivus to neck was (7, 3, 7) mm. setup error: in the clivus position of the two groups in the X, Y, Z three directions of the Setup error were (0.95 ± 0.89, 1.09 ± 0.94, 1.62 ± 1.18) mm vs (1.02 ± 0.94, 1.14 ± 0.96, 1.82 ± 1.21) mm, p in the z-direction is statistically significant (p = 0.01); The position of the 4,7th cervical vertebra also had statistical significance in the Z direction. Comparison between the surgical study group and non-surgical study group, the errors in the x and Z directions of the clivus and the 7th cervical vertebra were (0.99±0.96, 1.65±1.36 and 1.64±1.23, 1.61±1.37) mm vs (0.80±0.77, 1.85±1.44 and 1.67±1.07, 1.95±1.60) mm, P = 0.02, 0.11, 0.77, 0.01; the results were similar to it when comparing surgical controls to non-surgical controls. It can be seen from the data that in the X and Z directions from the clivus to the neck, the error change of the surgical group is smaller than that of the non-surgical group. There was no difference in toxicity and side effects. <h3>Conclusion</h3> The results show that neck muscle training can improve the anterior and posterior neck deformation error, improve the radiotherapy accuracy and setup efficiency.

Pilot tone-based motion correction for prospective respiratory compensated cardiac cine MRI.

To evaluate prospective motion correction using the pilot tone (PT) as a quantitative respiratory motion signal with high temporal resolution for cardiac cine images during free breathing. Before cine data acquisition, a short prescan was performed, calibrating the PT to the respiratory-induced heart motion using respiratory-resolved real-time images. The calibrated PT was then applied for nearly real-time prospective motion correction of cine MRI through slice tracking (ie, updating the slice position before every readout). Additionally, in-plane motion correction was performed retrospectively also based on the calibrated PT data. The proposed method was evaluated in a moving phantom and 10 healthy volunteers. The PT showed very good correlation to the phantom motion. In volunteer studies using a long-term scan over 7.96 ± 1.40 min, the mean absolute error between registered and predicted motion from the PT was 1.44 ± 0.46 mm in head-feet and 0.46 ± 0.07 mm in anterior-posterior direction. Irregular breathing could also be corrected well with the PT. The PT motion correction leads to a significant improvement of contrast-to-noise ratio by 68% (P ≤ .01) between blood pool and myocardium and sharpness of endocardium by 24% (P = .04) in comparison to uncorrected data. The image score, which refers to the cine image quality, has improved with the utilization of the proposed PT motion correction. The proposed approach provides respiratory motion-corrected cine images of the heart with improved image quality and a high scan efficiency using the PT. The PT is independent of the MR acquisition, making this a very flexible motion-correction approach.

Adaptive radiotherapy and the dosimetric impact of inter- and intrafractional motion on the planning target volume for prostate cancer patients

PurposeTo investigate the dosimetric influence of daily interfractional (inter) setup errors and intrafractional (intra) target motion on the planning target volume (PTV) and the possibility of an offline adaptive radiotherapy (ART) method to correct larger patient positioning uncertainties in image-guided radiotherapy for prostate cancer (PCa).Materials and methodsA CTV (clinical target volume)-to-PTV margin ranging from 15 mm in LR (left-right) and SI (superior-inferior) and 5–10 mm in AP (anterior-posterior) direction was applied to all patients. The dosimetric influence of this margin was retrospectively calculated by analysing systematic and random components of inter and intra errors of 31 consecutive intermediate- and high-risk localized PCa patients using daily cone beam computed tomography and kV/kV (kilo-Voltage) imaging. For each patient inter variation was assessed by observing the first 4 treatment days, which led to an offline ART-based treatment plan in case of larger variations.Results:Systematic inter uncertainties were larger (1.12 in LR, 2.28 in SI and 1.48 mm in AP) than intra systematic errors (0.44 in LR, 0.69 in SI and 0.80 mm in AP). Same findings for the random error in SI direction with 3.19 (inter) and 2.30 mm (intra), whereas in LR and AP results were alike with 1.89 (inter) and 1.91 mm (intra) and 2.10 (inter) and 2.27 mm (intra), respectively. The calculated margin revealed dimensions of 4–5 mm in LR, 8–9 mm in SI and 6–7 mm in AP direction. Treatment plans which had to be adapted showed smaller variations with 1.12 (LR) and 1.72 mm (SI) for Σ and 4.17 (LR) and 3.75 mm (SI) for σ compared to initial plans with 1.77 and 2.62 mm for Σ and 4.46 and 5.39 mm for σ in LR and SI, respectively.ConclusionThe currently clinically used margin of 15 mm in LR and SI and 5–10 mm in AP direction includes inter and intra uncertainties. The results show that offline ART is feasible which becomes a necessity with further reductions in PTV margins.

No need for frame-wise attenuation correction in dynamic Rubidium-82 PET for myocardial blood flow quantification

BackgroundRegadenoson-induced stress causes a repositioning of the heart, myocardial creep, in half of the patients undergoing Rubidium-82 (Rb-82) positron emission tomography (PET). As a result, misalignment of dynamic PET and computer tomography (CT) may occur, possibly affecting CT-based attenuation correction (AC) and thereby PET-based myocardial blood flow (MBF) quantification. Our aim was to determine the need for frame-wise PET-CT AC to obtain reliable MBF measurements. Methods31 Out of 64 consecutive patients had myocardial creep during regadenoson-induced stress Rb-82 PET-CT and were included. Prior to PET image reconstruction, we applied two AC methods; single PET-CT alignment and frame-wise alignment in which PET time-frames with myocardial creep were individually co-registered with CT. The PET-CT misalignment was then quantified and MBFs for the three vascular territories and whole myocardium were calculated and compared between both methods. ResultsThe magnitude of misalignment due to myocardial creep was 13.8 ± 4.5 mm in caudal-cranial direction, 1.8 ± 2.1 mm in medial-lateral and 2.5 ± 1.8 mm in anterior-posterior direction. Frame-wise PET-CT registration did not result in different MBF measurements (P ≥ .07) and the magnitude of misalignment and MBF differences did not correlate (P ≥ .58). ConclusionThere is no need for frame-wise AC in dynamic Rb-82 PET for MBF quantification. Single alignment seems sufficient in patients with myocardial creep.

Visualizing the Invisible in Prostate Radiation Therapy: Markerless Prostate Target Localization Via a Deep Learning Model and Monoscopic Kv Projection X-Ray Image

Current image guided prostate radiotherapy often relies on the use of implanted fiducial markers (FMs) or transducers for online/offline target localization. Fiducial or transducer insertion requires an invasive procedure that adds cost and risks for bleeding, infection and discomfort to the patient. We are developing a novel markerless prostate localization strategy using a pre-trained deep learning model to interpret routine projection kV X-ray images without the need for daily cone-beam computed tomography (CBCT). We trained a deep learning model to recognize prostate treatment target location from over 800 annotated projection X-ray images using data augmentation to enhance the learning process. The end point of the deep learning was a model capable of identifying the location of the prostate target for a given input X-ray projection image. To assess the accuracy of the approach, we retrospectively studied images from four patients who received volumetric modulated arc therapy (VMAT)for prostate cancer. In each case, the daily patient setup anterior-posterior (AP) and lateral images were used as the input for analysis by our deep learning model to derive the prostate target location. We quantitatively compared the results obtained from the deep learning model with the annotations. A comparison of the results with that defined by fiducial localization and with location derived from the on-board CBCT imaging was also done. Training the deep learning model took about one hour for each view angle. After training, the model identified the prostate location on a projection kV image within 200 ms. The deviations between the target positions obtained by the deep learning model and the corresponding annotations ranged from 0.7 mm to 2.21 mm for AP direction, and from 1.23 mm to 2.20 mm for lateral direction. Oblique images may be useful for online tracking. The deviations for images obtained at oblique angles ranged from 0.67 mm to 2.88 mm. Target position provided by deep learning model for the kV images acquired using OBI is found to be consistent that derived from the implanted FMs. This study demonstrates that highly accurate markerless prostate localization based on deep learning is achievable. The strategy provides a clinically valuable solution for image guided radiotherapy of the prostate and should be adaptable to other soft tissue tumor targets. The proposed method may be useful for daily patient positioning and real-time target tracking during prostate radiotherapy.

Set-up errors in head and neck cancer treated with IMRT technique assessed by cone-beam computed tomography: a feasible protocol.

PurposeTo investigate set-up errors, suggest the adequate planning target volume (PTV) margin and image-guided radiotherapy frequency in head and neck (H&N) cancer treated with intensity-modulated radiotherapy (IMRT) assessed by kV cone-beam computed tomography (CBCT).MethodsWe analyzed 360 CBCTs in 60 patients with H&N cancer treated with IMRT. The target delineation was contoured according to ICRU62. PTVs were generated by adding a 3–5 mm margin in all directions to the respective clinical target volumes. The kV CBCT images were obtained at first three days of irradiation and weekly thereafter. The overall mean displacement, range, systematic (∑) and random (σ) errors were calculated. Adequate PTV margins were calculated according to the van Herk formula (2.5∑ + 0.7r).ResultsThe mean of set-up errors was less than 2 mm in any direction. The overall frequency of set-up displacements greater than 3 mm was 3.9% in medial-lateral (ML) direction, 8% in superior-inferior (SI) direction, and 15.5% in anterior-posterior (AP) direction. The range of translations shifts was 0–9 mm in ML direction, 0–5 mm in SI direction and 0–10 mm in AP direction, respectively. After systematic set-up errors correction, the adequate margin to overcome the problem of set-up errors was found to be less than 3 mm.ConclusionImage-guided kV CBCT was effective for the evaluation of set-up accuracy in H&N cancer. The kV CBCT at first three fractions and followed-by weekly appears adequate for reducing significantly set-up errors in H&N cancer treated with IMRT technique. Finally, 3–5 mm PTV margins appear adequate and safe to overcome the problem of set-up errors.

TU‐F‐CAMPUS‐J‐01: Inference of Prostate PTV Margins in VMAT Delivery From Intra‐Fraction Prostate Motion During SBRT Delivery

Purpose:To retrospectively quantify the intra‐fraction prostate motion during stereotactic body radiation therapy (SBRT) treatment using CyberKnife's target tracking system, which may provide insight into expansion margins from GTV to PTV used in gantry‐based treatments. CyberKnife is equipped with an active tracking system (InTempo) that tracks the four fiducials placed in the prostate gland. The system acquires intra‐fraction orthogonal kV images at 45° and 315° in a sequential fashion.Methods:A total of 38 patients treated with SBRT using CyberKnife between 2011 and 2013 were studied. Dose‐regime was 36.25 Gy in 5 fractions (7.25 Gy/fraction, twice per week) as per RTOG 0938 guidelines. The CyberKnife image tracking logs for all SBRT treatments using InTempo were examined. A total of 13663 images were examined for the superior/inferior (SI), anterior/posterior (AP) and left/right (LR) translation as well as roll, pitch and yaw rotations for the target position relative to the last known model position.Results:The mean ± 2 SD of intra‐fraction motion was contained within 3 mm for SI and LR and 4.5 mm for AP directions at 5 minutes into the treatment delivery. It was contained within 4 mm for SI and LR and 5 mm for AP at 10 minutes. At 15 minutes into delivery, all translations were contained within 5 mm. The mean ± 2 SD of prostate roll, pitch and yaw increased with time but were contained within 5 degree at 5, 10 and 15 minutes into treatment. Additionally, target translations and rotations were within ± 1 mm and ± 1 degree for 90% and 78% of the time.Conclusion:The organ motion component of PTV margin for 10 minute VMAT delivery is contained within 4 mm in SI and LR direction and within 5 mm in the AP direction.

A novel respiratory gating method for oncologic positron emission tomography based on bioimpedance approach.

Respiratory motion causes loss of image quality and inaccuracy of quantification in oncologic positron emission tomography (PET) imaging. This study introduces a bioimpedance-based gating method for compensation of respiratory motion artefacts. The bioimpedance-based respiratory gating method was studied parallel to a clinically used respiratory gating method [Real-time Position Management by Varian Medical Systems] in 4D PET/CT acquisition of 9 oncologic patients. The quantitative analysis consisted of the evaluation of tumour SUVpeak, SUVmax and volume. Additionally, target-to-background ratios as well as motion in cranial-caudal and anterior-posterior directions were measured. The evaluation was performed with amplitude- and time-based gating using averaged attenuation correction maps. Bioimpedance gating resulted in 17.7-18.9% increase in mean SUVpeak and 20.0-21.4% decrease in mean volume compared to non-gated images. The maximum motion measured from the bioimpedance-gated images was 19mm in cranial-caudal direction and 9mm in anterior-posterior direction. Bioimpedance-based respiratory gating compensates the adverse effects of motion in oncologic PET imaging.

WE-G-213CD-09: Quality Assurance of the Surrogate Signal-Based Dynamic Tumor-Tracking Irradiation with Vero4DRT (MHI-TM2000).

To perform the quality assurance for the dynamic tumor-tracking (DTT) irradiation with Vero4DRT (MHI-Tm2 000). Vero4DRT swings its gimbaled 6-MV C-band x-ray head along the pan and tilt direction to track a moving tumor. Surrogate signal-based DTT system implemented in Vero4DRT was used. Before DTT irradiation, the correlation model (4D-model) between motion of the IR markers on the abdominal wall and the tumor position was created with synchronously monitoring by the IR camera and orthogonal kV x-ray imaging subsystem. During beam delivery, the 4D-model predicted the future tumor position from the displacement of the IR markers in real-time, and then contentiously transferred the corresponding tracking orientation to the gimbaled x-ray head.Water-equivalent phantoms were set on a 1D motor-driven base with IR markers. A film placed at a depth of 10 cm in the phantom was irradiated under the following conditions: stationary state, and tracking and non- tracking state for sinusoidal patterns. In addition, the geometric accuracy was evaluated using a 3D moving phantom and Polaris Spectra for the previously-acquired patient's respiratory pattern. Compared to the stationary conditions, reductions in lateral distance between 95% doses of the dose profile were 1.2 mm for tracking and 29.6 mm for non-tracking state for (amplitude [A], period [T]) = (20 mm, 2 s); and 0.2 mm and 29.4 mm for (A, T) = (20 mm, 4 s); and 0.0 mm and 11.2 mm for (A, T) = (10 mm, 2 s), respectively. In the geometric accuracy testing, 95th percentile of the tracking error was 0.5 mm in left-right, 1.0 mm in superior-inferior, and 0.5 mm in anterior-posterior direction. We demonstrated that Vero4DRT substantially reduced the blurring effects on dose distribution with high tracking accuracy, and confirmed the safety of the DTT irradiation for a clinical application. This research was supported by the Japan Society for the Promotion of Science (JSPS) through its Funding Program for World-Leading Innovation R&D on Science and Technology (FIRST Program), and sponsored in part by Mitsubishi Heavy Industries, Ltd.

Hypofractionated radiotherapy for lung tumors with online cone beam CT guidance and active breathing control

BackgroundTo study the set-up errors, PTV margin and toxicity of cone beam CT (CBCT) guided hypofractionated radiotherapy with active breathing control (ABC) for patients with non-small cell lung cancer (NSCLC) or metastatic tumors in lung.Methods32 tumors in 20 patients were treated. Based on the location of tumor, dose per fraction given to tumor was divided into three groups: 12 Gy, 8 Gy and 6 Gy. ABC is applied for every patient. During each treatment, patients receive CBCT scan for online set-up correction. The pre- and post-correction setup errors between fractions, the interfractional and intrafractional, set-up errors, PTV margin as well as toxicity are analyzed.ResultsThe pre-correction systematic and random errors in the left-right (LR), superior-inferior (SI), anterior-posterior (AP) directions were 3.7 mm and 5.3 mm, 3.1 mm and 2.1 mm, 3.7 mm and 2.8 mm, respectively, while the post-correction residual errors were 0.6 mm and 0.8 mm, 0.8 mm and 0.8 mm, 1.2 mm and 1.3 mm, respectively. There was an obvious intrafractional shift of tumor position. The pre-correction PTV margin was 9.5 mm in LR, 14.1 mm in SI and 8.2 mm in AP direction. After CBCT guided online correction, the PTV margin was markedly reduced in all three directions. The post-correction margins ranged 1.5 to 2.1 mm. The treatment was well tolerated by patients, of whom there were 4 (20%) grade1-2 acute pneumonitis, 3 (15%) grade1 acute esophagitis, 2 (10%) grade1 late pneumonitis and 1 (5%) grade 1 late esophagitis.ConclusionThe positioning errors for lung SBRT using ABC were significant. Online correction with CBCT image guidance should be applied to reduce setup errors and PTV margin, which may reduce radiotherapy toxicity of tissues when ABC was used.

Clinical Accuracy of the Respiratory Tumor Tracking System of the CyberKnife: Assessment by Analysis of Log Files

To quantify the clinical accuracy of the respiratory motion tracking system of the CyberKnife treatment device. Data in log files of 44 lung cancer patients treated with tumor tracking were analyzed. Errors in the correlation model, which relates the internal target motion with the external breathing motion, were quantified. The correlation model error was compared with the geometric error obtained when no respiratory tracking was used. Errors in the prediction method were calculated by subtracting the predicted position from the actual measured position after 192.5 ms (the time lag to prediction in our current system). The prediction error was also measured for a time lag of 115 ms and a new prediction method. The mean correlation model errors were less than 0.3 mm. Standard deviations describing intrafraction variations around the whole-fraction mean error were 0.2 to 1.9 mm for cranio-caudal, 0.1 to 1.9 mm for left-right, and 0.2 to 2.5 mm for anterior-posterior directions. Without the use of respiratory tracking, these variations would have been 0.2 to 8.1 mm, 0.2 to 5.5 mm, and 0.2 to 4.4 mm. The overall mean prediction error was small (0.0 +/- 0.0 mm) for all directions. The intrafraction standard deviation ranged from 0.0 to 2.9 mm for a time delay of 192.5 ms but was halved by using the new prediction method. Analyses of the log files of real clinical cases have shown that the geometric error caused by respiratory motion is substantially reduced by the application of respiratory motion tracking.

Extracranial stereotactic radiation therapy: set-up accuracy of patients treated for liver metastases

Purpose: Patients with liver metastases might benefit from high-dose conformal radiation therapy. A high accuracy of repositioning and a reduction of target movement are necessary for such an approach. The set-up accuracy of patients with liver metastases treated with stereotactic single dose radiation was evaluated. Methods and Materials: Twenty-four patients with liver metastases were treated with single dose radiation therapy on 26 occasions using a self-developed stereotactic frame. Liver movement was reduced by abdominal pressure. The effectiveness was evaluated under fluoroscopy. CT scans were performed on the planning day and directly before treatment. Representative reference marks were chosen and the coordinates were calculated. In addition, the target displacement was quantitatively evaluated after treatment. Results: Diaphragmal movement was reduced to median 7 mm (range: 3–13 mm). The final set-up accuracy of the body was limited to all of median 1.8 mm in latero-lateral direction (range: 0.3–5.0 mm) and 2.0 mm in anterior-posterior direction (0.8–3.8 mm). Deviations of the body in cranio-caudal direction were always less than the thickness of one CT slice (<5 mm). However, a repositioning was necessary in 16 occasions. The final target shift was median 1.6 mm (0.2–7.0 mm) in latero-lateral and 2.3 mm in anterior-posterior direction (0.0–6.3 mm). The median shift in cranio-caudal direction was 4.4 mm (0.0–10.0 mm). Conclusions: In patients with liver metastases, a high set-up accuracy of the body and the target can be achieved. This allows a high-dose focal radiotherapy of these lesions. However, a control CT scan should be performed directly before therapy to confirm set-up accuracy and possibly prompt necessary corrections.