Respiration-induced movement of the upper abdominal organs: a pitfall for the three-dimensional conformal radiation treatment of pancreatic cancer

Respiration-Induced Organ Motion Compensation: A Review

PURPOSE

Motion of organs in the abdominal and thoracic cavity caused by respiration is a major issue that affects a wide range of clinical diagnoses or treatment outcomes, including radiotherapy, high-intensity focused ultrasound ablation, and many generalized percutaneous needle interventions. These motions pose significant challenges in accurately reaching the target even for the experienced clinician.

METHODS

This review was conducted through comprehensive search on IEEE Explore, Google Scholar, and PubMed.

RESULTS

Diverse methods have been proposed to compensate for this motion effect to enable effective surgical operations. This review paper aims to examine the current respiratory motion compensation techniques used across the clinical procedures of radiotherapy, high-intensity focused ultrasound, and percutaneous needle procedures.

CONCLUSION

The complexity of respiratory-induced organ motion and diversity of areas for which compensation can be applied allows for a variety of methods to be implemented. This review aims to serve as inspiration for the future development of new systems to achieve clinical relevance.

Data-driven gating (DDG)-based motion match for improved CTAC registration

BACKGROUND

Respiratory motion artefacts are a pitfall in thoracic PET/CT imaging. A source of these motion artefacts within PET images is the CT used for attenuation correction of the images. The arbitrary respiratory phase in which the helical CT ( CT helical ) is acquired often causes misregistration between PET and CT images, leading to inaccurate attenuation correction of the PET image. As a result, errors in tumour delineation or lesion uptake values can occur. To minimise the effect of motion in PET/CT imaging, a data-driven gating (DDG)-based motion match (MM) algorithm has been developed that estimates the phase of the CT helical , and subsequently warps this CT to a given phase of the respiratory cycle, allowing it to be phase-matched to the PET. A set of data was used which had four-dimensional CT (4DCT) acquired alongside PET/CT. The 4DCT allowed ground truth CT phases to be generated and compared to the algorithm-generated motion match CT (MMCT). Measurements of liver and lesion margin positions were taken across CT images to determine any differences and establish how well the algorithm performed concerning warping the CT helical to a given phase (end-of-expiration, EE).

RESULTS

Whilst there was a minor significance in the liver measurement between the 4DCT and MMCT ( p = 0.045 ), no significant differences were found between the 4DCT or MMCT for lesion measurements ( p = 1.0 ). In all instances, the CT helical was found to be significantly different from the 4DCT ( p < 0.001 ). Consequently, the 4DCT and MMCT can be considered equivalent with respect to warped CT generation, showing the DDG-based MM algorithm to be successful.

CONCLUSION

The MM algorithm successfully enables the phase-matching of a CT helical to the EE of a ground truth 4DCT. This would reduce the motion artefacts caused by PET/CT registration without requiring additional patient dose (required for a 4DCT).

Intraoperative liver deformation and organ motion caused by ventilation, laparotomy, and pneumoperitoneum in a porcine model for image-guided liver surgery

BACKGROUND

Image-guidance promises to make complex situations in liver interventions safer. Clinical success is limited by intraoperative organ motion due to ventilation and surgical manipulation. The aim was to assess influence of different ventilatory and operative states on liver motion in an experimental model.

METHODS

Liver motion due to ventilation (expiration, middle, and full inspiration) and operative state (native, laparotomy, and pneumoperitoneum) was assessed in a live porcine model (n = 10). Computed tomography (CT)-scans were taken for each pig for each possible combination of factors. Liver motion was measured by the vectors between predefined landmarks along the hepatic vein tree between CT scans after image segmentation.

RESULTS

Liver position changed significantly with ventilation. Peripheral regions of the liver showed significantly higher motion (maximal Euclidean motion 17.9 ± 2.7 mm) than central regions (maximal Euclidean motion 12.6 ± 2.1 mm, p < 0.001) across all operative states. The total average motion measured 11.6 ± 0.7 mm (p < 0.001). Between the operative states, the position of the liver changed the most from native state to pneumoperitoneum (14.6 ± 0.9 mm, p < 0.001). From native state to laparotomy comparatively, the displacement averaged 9.8 ± 1.2 mm (p < 0.001). With pneumoperitoneum, the breath-dependent liver motion was significantly reduced when compared to other modalities. Liver motion due to ventilation was 7.7 ± 0.6 mm during pneumoperitoneum, 13.9 ± 1.1 mm with laparotomy, and 13.5 ± 1.4 mm in the native state (p < 0.001 in all cases).

CONCLUSIONS

Ventilation and application of pneumoperitoneum caused significant changes in liver position. Liver motion was reduced but clearly measurable during pneumoperitoneum. Intraoperative guidance/navigation systems should therefore account for ventilation and intraoperative changes of liver position and peripheral deformation.

Accelerated respiratory-resolved 4D-MRI with separable spatio-temporal neural networks

BACKGROUND

Respiratory-resolved four-dimensional magnetic resonance imaging (4D-MRI) provides essential motion information for accurate radiation treatments of mobile tumors. However, obtaining high-quality 4D-MRI suffers from long acquisition and reconstruction times.

PURPOSE

To develop a deep learning architecture to quickly acquire and reconstruct high-quality 4D-MRI, enabling accurate motion quantification for MRI-guided radiotherapy (MRIgRT).

METHODS

A small convolutional neural network called MODEST is proposed to reconstruct 4D-MRI by performing a spatial and temporal decomposition, omitting the need for 4D convolutions to use all the spatio-temporal information present in 4D-MRI. This network is trained on undersampled 4D-MRI after respiratory binning to reconstruct high-quality 4D-MRI obtained by compressed sensing reconstruction. The network is trained, validated, and tested on 4D-MRI of 28 lung cancer patients acquired with a T1-weighted golden-angle radial stack-of-stars (GA-SOS) sequence. The 4D-MRI of 18, 5, and 5 patients were used for training, validation, and testing. Network performances are evaluated on image quality measured by the structural similarity index (SSIM) and motion consistency by comparing the position of the lung-liver interface on undersampled 4D-MRI before and after respiratory binning. The network is compared to conventional architectures such as a U-Net, which has 30 times more trainable parameters.

RESULTS

MODEST can reconstruct high-quality 4D-MRI with higher image quality than a U-Net, despite a thirty-fold reduction in trainable parameters. High-quality 4D-MRI can be obtained using MODEST in approximately 2.5 min, including acquisition, processing, and reconstruction.

CONCLUSION

High-quality accelerated 4D-MRI can be obtained using MODEST, which is particularly interesting for MRIgRT.

Characterization of motion dependent magnetic field inhomogeneity for DWI in the kidneys

PURPOSE

Diffusion-weighted imaging (DWI) of the abdomen has increased dramatically for both research and clinical purposes. Motion and static field inhomogeneity related challenges limit image quality of abdominopelvic imaging with the most conventional echo-planar imaging (EPI) pulse sequence. While reversed phase encoded imaging is increasingly used to facilitate distortion correction, it typically assumes one motion independent magnetic field distribution. In this study, we describe a more generalized workflow for the case of kidney DWI in which the field inhomogeneity at multiple respiratory phases is mapped and used to correct all images in a multi-contrast DWI series.

METHODS

In this HIPAA-compliant and IRB-approved prospective study, 8 volunteers (6 M, ages 28-51) had abdominal imaging performed in a 3 T MRI system (MAGNETOM Prisma; Siemens Healthcare, Erlangen, Germany) with ECG gating. Coronal oblique T2-weighted HASTE images were collected for anatomical reference. Sagittal phase-contrast (PC) MRI images through the left renal artery were collected to determine systolic and diastolic phases. Cardiac triggered oblique coronal DWI were collected at 10 b-values between 0 and 800 s/mm2 and 12 directions. DWI series were distortion corrected using field maps generated by forward and reversed phase encoded b = 0 images collected over the full respiratory cycle and matched by respiratory phase. Morphologic accuracy, intraseries spatial variability, and diffusion tensor imaging (DTI) metrics mean diffusivity (MD) and fractional anisotropy (FA) were compared for results generated with no distortion correction, correction with only one respiratory bin, and correction with multiple respiratory bins across the breathing cycle.

RESULTS

Computed field maps showed significant variation in static field with kidney laterality, region, and respiratory phase. Distortion corrected images showed significantly better registration to morphologic images than uncorrected images; for the left kidney, the multiple bin correction outperformed one bin correction. Line profile analysis showed significantly reduced spatial variation with multiple bins than one bin correction. DTI metrics were mostly similar between correction methods, with some differences observed in MD between uncorrected and corrected datasets.

CONCLUSIONS

Our results indicate improved morphology of kidney DWI and derived parametric maps as well as reduced variability over the full image series using the motion-resolved distortion correction. This work highlights some morphologic and quantitative metric improvements can be obtained for kidney DWI when distortion correction is performed in a respiratory-resolved manner.

Review of Robot-Assisted HIFU Therapy

This paper provides an overview of current robot-assisted high-intensity focused ultrasound (HIFU) systems for image-guided therapies. HIFU is a minimally invasive technique that relies on the thermo-mechanical effects of focused ultrasound waves to perform clinical treatments, such as tumor ablation, mild hyperthermia adjuvant to radiation or chemotherapy, vein occlusion, and many others. HIFU is typically performed under ultrasound (USgHIFU) or magnetic resonance imaging guidance (MRgHIFU), which provide intra-operative monitoring of treatment outcomes. Robot-assisted HIFU probe manipulation provides precise HIFU focal control to avoid damage to surrounding sensitive anatomy, such as blood vessels, nerve bundles, or adjacent organs. These clinical and technical benefits have promoted the rapid adoption of robot-assisted HIFU in the past several decades. This paper aims to present the recent developments of robot-assisted HIFU by summarizing the key features and clinical applications of each system. The paper concludes with a comparison and discussion of future perspectives on robot-assisted HIFU.

Real-time motion monitoring using orthogonal cine MRI during MR-guided adaptive radiation therapy for abdominal tumors on 1.5T MR-Linac

BACKGROUND

Real-time motion monitoring (RTMM) is necessary for accurate motion management of intrafraction motions during radiation therapy (RT).

PURPOSE

Building upon a previous study, this work develops and tests an improved RTMM technique based on real-time orthogonal cine magnetic resonance imaging (MRI) acquired during magnetic resonance-guided adaptive RT (MRgART) for abdominal tumors on MR-Linac.

METHODS

A motion monitoring research package (MMRP) was developed and tested for RTMM based on template rigid registration between beam-on real-time orthogonal cine MRI and pre-beam daily reference 3D-MRI (baseline). The MRI data acquired under free-breathing during the routine MRgART on a 1.5T MR-Linac for 18 patients with abdominal malignancies of 8 liver, 4 adrenal glands (renal fossa), and 6 pancreas cases were used to evaluate the MMRP package. For each patient, a 3D mid-position image derived from an in-house daily 4D-MRI was used to define a target mask or a surrogate sub-region encompassing the target. Additionally, an exploratory case reviewed for an MRI dataset of a healthy volunteer acquired under both free-breathing and deep inspiration breath-hold (DIBH) was used to test how effectively the RTMM using the MMRP can address through-plane motion (TPM). For all cases, the 2D T2/T1-weighted cine MRIs were captured with a temporal resolution of 200 ms interleaved between coronal and sagittal orientations. Manually delineated contours on the cine frames were used as the ground-truth motion. Common visible vessels and segments of target boundaries in proximity to the target were used as anatomical landmarks for reproducible delineations on both the 3D and the cine MRI images. Standard deviation of the error (SDE) between the ground-truth and the measured target motion from the MMRP package were analyzed to evaluate the RTMM accuracy. The maximum target motion (MTM) was measured on the 4D-MRI for all cases during free-breathing.

RESULTS

The mean (range) centroid motions for the 13 abdominal tumor cases were 7.69 (4.71-11.15), 1.73 (0.81-3.05), and 2.71 (1.45-3.93) mm with an overall accuracy of <2 mm in the superior-inferior (SI), the left-right (LR), and the anterior-posterior (AP) directions, respectively. The mean (range) of the MTM from the 4D-MRI was 7.38 (2-11) mm in the SI direction, smaller than the monitored motion of centroid, demonstrating the importance of the real-time motion capture. For the remaining patient cases, the ground-truth delineation was challenging under free-breathing due to the target deformation and the large TPM in the AP direction, the implant-induced image artifacts, and/or the suboptimal image plane selection. These cases were evaluated based on visual assessment. For the healthy volunteer, the TPM of the target was significant under free-breathing which degraded the RTMM accuracy. RTMM accuracy of <2 mm was achieved under DIBH, indicating DIBH is an effective method to address large TPM.

CONCLUSIONS

We have successfully developed and tested the use of a template-based registration method for an accurate RTMM of abdominal targets during MRgART on a 1.5T MR-Linac without using injected contrast agents or radio-opaque implants. DIBH may be used to effectively reduce or eliminate TPM of abdominal targets during RTMM.

Mixed reality navigation training system for liver surgery based on a high-definition human cross-sectional anatomy data set

OBJECTIVES

This study aims to use the three-dimensional (3D) mixed-reality model of liver, entailing complex intrahepatic systems and to deeply study the anatomical structures and to promote the training, diagnosis and treatment of liver diseases.

METHODS

Vascular perfusion human specimens were used for thin-layer frozen milling to obtain liver cross-sections. The 104-megapixel-high-definition cross sectional data set was established and registered to achieve structure identification and manual segmentation. The digital model was reconstructed and data was used to print a 3D hepatic model. The model was combined with HoloLens mixed reality technology to reflect the complex relationships of intrahepatic systems. We simulated 3D patient specific anatomy for identification and preoperative planning, conducted a questionnaire survey, and evaluated the results.

RESULTS

The 3D digital model and 1:1 transparent and colored model of liver established truly reflected intrahepatic vessels and their complex relationships. The reconstructed model imported into HoloLens could be accurately matched with the 3D model. Only 7.7% participants could identify accessory hepatic veins. The depth and spatial-relationship of intrahepatic structures were better understandable for 92%. The 100%, 84.6%, 69% and 84% believed the 3D models were useful in planning, safer surgical paths, reducing intraoperative complications and training of young surgeons respectively.

CONCLUSIONS

A detailed 3D model can be reconstructed using the higher quality cross-sectional anatomical data set. When combined with 3D printing and HoloLens technology, a novel hybrid-reality navigation-training system for liver surgery is created. Mixed Reality training is a worthy alternative to provide 3D information to clinicians and its possible application in surgery. This conclusion was obtained based on a questionnaire and evaluation. Surgeons with extensive experience in surgical operations perceived in the questionnaire that this technology might be useful in liver surgery, would help in precise preoperative planning, accurate intraoperative identification, and reduction of hepatic injury.

Clinical applicability of deep learning-based respiratory signal prediction models for four-dimensional radiation therapy

For accurate respiration gated radiation therapy, compensation for the beam latency of the beam control system is necessary. Therefore, we evaluate deep learning models for predicting patient respiration signals and investigate their clinical feasibility. Herein, long short-term memory (LSTM), bidirectional LSTM (Bi-LSTM), and the Transformer are evaluated. Among the 540 respiration signals, 60 signals are used as test data. Each of the remaining 480 signals was spilt into training and validation data in a 7:3 ratio. A total of 1000 ms of the signal sequence (T_s) is entered to the models, and the signal at 500 ms afterward (P_t) is predicted (standard training condition). The accuracy measures are: (1) root mean square error (RMSE) and Pearson correlation coefficient (CC), (2) accuracy dependency on T_s and P_t, (3) respiratory pattern dependency, and (4) error for 30% and 70% of the respiration gating for a 5 mm tumor motion for latencies of 300, 500, and 700 ms. Under standard conditions, the Transformer model exhibits the highest accuracy with an RMSE and CC of 0.1554 and 0.9768, respectively. An increase in T_s improves accuracy, whereas an increase in P_t decreases accuracy. An evaluation of the regularity of the respiratory signals reveals that the lowest predictive accuracy is achieved with irregular amplitude patterns. For 30% and 70% of the phases, the average error of the three models is <1.4 mm for a latency of 500 ms and >2.0 mm for a latency of 700 ms. The prediction accuracy of the Transformer is superior to LSTM and Bi-LSTM. Thus, the three models have clinically applicable accuracies for a latency <500 ms for 10 mm of regular tumor motion. The clinical acceptability of the deep learning models depends on the inherent latency and the strategy for reducing the irregularity of respiration.

Stereotactic Body Radiotherapy (SBRT) of Pancreatic Cancer-A Critical Review and Practical Consideration

Pancreatic cancer is the third leading cause of cancer death in the developed world and is predicted to become the second by 2030. A cure may be achieved only with surgical resection of an early diagnosed disease. Surgery for more advanced disease is challenging and can be contraindicated for many reasons. Neoadjuvant therapy may improve the probability of achieving R0 resection. It consists of systemic treatment followed by radiation therapy applied concurrently or sequentially with cytostatics. A novel approach to irradiation, stereotactic body radiotherapy (SBRT), has the potential to improve treatment results. SBRT can deliver higher doses of radiation to the tumor in only a few treatment fractions. It has attracted significant interest for pancreatic cancer patients, as it is completed quickly, requires less time away from full-dose chemotherapy, and is well-tolerated than conventional radiotherapy. In this review, we aim to provide the reader with a basic overview of current evidence for SBRT indications in the treatment of pancreatic tumors. In the second part of the review, we focus on practical information with respect to SBRT treatment plan preparation the performance of such therapy. Finally, we discuss future directions related to the use of magnetic resonance linear accelerators.

A phantom-based analysis for tracking intra-fraction pancreatic tumor motion by ultrasound imaging during radiation therapy

Purpose

In this study, we aim to further evaluate the accuracy of ultrasound tracking for intra-fraction pancreatic tumor motion during radiotherapy by a phantom-based study.

Methods

Twelve patients with pancreatic cancer who were treated with stereotactic body radiation therapy were enrolled in this study. The displacement points of the respiratory cycle were acquired from 4DCT and transferred to a motion platform to mimic realistic breathing movements in our phantom study. An ultrasound abdominal phantom was placed and fixed in the motion platform. The ground truth of phantom movement was recorded by tracking an optical tracker attached to this phantom. One tumor inside the phantom was the tracking target. In the evaluation of the results, the monitoring results from the ultrasound system were compared with the phantom motion results from the infrared camera. Differences between infrared monitoring motion and ultrasound tracking motion were analyzed by calculating the root-mean-square error.

Results

The 82.2% ultrasound tracking motion was within a 0.5 mm difference value between ultrasound tracking displacement and infrared monitoring motion. 0.7% ultrasound tracking failed to track accurately (a difference value &gt; 2.5 mm). These differences between ultrasound tracking motion and infrared monitored motion do not correlate with respiratory displacements, respiratory velocity, or respiratory acceleration by linear regression analysis.

Conclusions

The highly accurate monitoring results of this phantom study prove that the ultrasound tracking system may be a potential method for real-time monitoring targets, allowing more accurate delivery of radiation doses.

Dosimetric impact of intrafraction motion under abdominal compression during MR-guided SBRT for (Peri-) pancreatic tumors

Objective. Intrafraction motion is a major concern for the safety and effectiveness of high dose stereotactic body radiotherapy (SBRT) in the upper abdomen. In this study, the impact of the intrafraction motion on the delivered dose was assessed in a patient group that underwent MR-guided radiotherapy for upper abdominal malignancies with an abdominal corset. Approach. Fast online 2D cine MRI was used to extract tumor motion during beam-on time. These tumor motion profiles were combined with linac log files to reconstruct the delivered dose in 89 fractions of MR-guided SBRT in twenty patients. Aside the measured tumor motion, motion profiles were also simulated for a wide range of respiratory amplitudes and drifts, and their subsequent dosimetric impact was calculated in every fraction. Main results. The average (SD) D 99% of the gross tumor volume (GTV), relative to the planned D 99%, was 0.98 (0.03). The average (SD) relative D 0.5cc of the duodenum, small bowel and stomach was 0.99 (0.03), 1.00 (0.03), and 0.97 (0.05), respectively. No correlation of respiratory amplitude with dosimetric impact was observed. Fractions with larger baseline drifts generally led to a larger uncertainty of dosimetric impact on the GTV and organs at risk (OAR). The simulations yielded that the delivered dose is highly dependent on the direction of on baseline drift. Especially in anatomies where the OARs are closely abutting the GTV, even modest LR or AP drifts can lead to substantial deviations from the planned dose. Significance. The vast majority of the fractions was only modestly impacted by intrafraction motion, increasing our confidence that MR-guided SBRT with abdominal compression can be safely executed for patients with abdominal tumors, without the use of gating or tracking strategies.

Intrafractional accuracy and efficiency of a surface imaging system for deep inspiration breath hold during ablative gastrointestinal cancer treatment

PURPOSE

Beam gating with deep inspiration breath hold (DIBH) usually depends on some external surrogate to infer internal target movement, and the exact internal movement is unknown. In this study, we tracked internal targets and characterized residual motion during DIBH treatment, guided by a surface imaging system, for gastrointestinal cancer. We also report statistics on treatment time.

METHODS AND MATERIALS

We included 14 gastrointestinal cancer patients treated with surface imaging-guided DIBH volumetrically modulated arc therapy, each with at least one radiopaque marker implanted near or within the target. They were treated in 25, 15, or 10 fractions. Thirteen patients received treatment for pancreatic cancer, and one underwent separate treatments for two liver metastases. The surface imaging system monitored a three-dimensional surface with ± 3 mm translation and ± 3° rotation threshold. During delivery, a kilovolt image was automatically taken every 20° or 40° gantry rotation, and the internal marker was identified from the image. The displacement and residual motion of the markers were calculated. To analyze the treatment efficiency, the treatment time of each fraction was obtained from the imaging and treatment timestamps in the record and verify system.

RESULTS

Although the external surface was monitored and limited to ± 3 mm and ± 3°, significant residual internal target movement was observed in some patients. The range of residual motion was 3-21 mm. The average displacement for this cohort was 0-3 mm. In 19% of the analyzed images, the magnitude of the instantaneous displacement was > 5 mm. The mean treatment time was 17 min with a standard deviation of 4 min.

CONCLUSIONS

Precaution is needed when applying surface image guidance for gastrointestinal cancer treatment. Using it as a solo DIBH technique is discouraged when the correlation between internal anatomy and patient surface is limited. Real-time radiographic verification is critical for safe treatments.

Design of a 6-DoF Parallel Robotic Platform for MRI Applications

In this work, the design, analysis, and characterization of a parallel robotic motion generation platform with 6-degrees of freedom (DoF) for magnetic resonance imaging (MRI) applications are presented. The motivation for the development of this robot is the need for a robotic platform able to produce accurate 6-DoF motion inside the MRI bore to serve as the ground truth for motion modeling; other applications include manipulation of interventional tools such as biopsy and ablation needles and ultrasound probes for therapy and neuromodulation under MRI guidance. The robot is comprised of six pneumatic cylinder actuators controlled via a robust sliding mode controller. Tracking experiments of the pneumatic actuator indicates that the system is able to achieve an average error of 0.69 ± 0.14 mm and 0.67 ± 0.40 mm for step signal tracking and sinusoidal signal tracking, respectively. To demonstrate the feasibility and potential of using the proposed robot for minimally invasive procedures, a phantom experiment was performed in the benchtop environment, which showed a mean positional error of 1.20 ± 0.43 mm and a mean orientational error of 1.09 ± 0.57°, respectively. Experiments conducted in a 3T whole body human MRI scanner indicate that the robot is MRI compatible and capable of achieving positional error of 1.68 ± 0.31 mm and orientational error of 1.51 ± 0.32° inside the scanner, respectively. This study demonstrates the potential of this device to enable accurate 6-DoF motions in the MRI environment.

Applying the N-isopropylacrylamide gel dosimeter to quantify dynamic dose effects: A feasibility study

BACKGROUND:

The gel dosimeter is a chemical as well as a relative dosimeter.

OBJECTIVE:

To evaluate the feasibility of using N-isopropylacrylamide (NIPAM) gel dosimeter to observe the dynamic dose effects and quantification of the respiration, and to help determine the safety margins.

METHODS:

The NIPAM gel dosimeter combined with the dynamic phantom was used to simulate radiotherapy of lung or upper abdominal tumor. The field set to 4 × 5 cm2, simulate respiratory rate of 4 sec/cycle, and motion range 2 cm. MRI was used for reading, and MATLAB was used for analysis. The 3%/3 mm gamma passing rate > 95% was used as a clinical basis for evaluation.

RESULTS:

The dynamic dose curve was compared with 4 × 5, 4 × 4, 4 × 3 cm2 TPS, and gamma passing rates were 74.32%, 54.83%, 30.18%. Gamma mapping demonstrated that the highest dose region was similar to the result of the 4 × 4 cm2 TPS. After appropriate selection and comparing that the ⩾ 60% part of the dose curve with TPS, the gamma passing rate was 96.49%.

CONCLUSIONS:

Using the NIPAM gel dosimeter with dynamic phantom to simulate organ motion during respiration for dynamic dose measurement and quantified the dynamic dose effect is feasible. The results are consistent with clinical evaluation standards.

Using NIPAM gel dosimeter and concentric swing machine to simulate the dose distribution during breathing: A feasibility study

BACKGROUND:

Radiotherapy plays an important role in cancer treatment today. Successful radiotherapy includes precise positioning and accurate dosimetry.

OBJECTIVE:

To use NIPAM gel dosimeter and concentric swing machine to simulate and evaluate the feasibility of lung or upper abdominal tumor dose distribution during breathing.

METHODS:

We used a concentric swing machine to simulate actual radiotherapy for lung or upper abdomen tumors. A 4 × 4 cm2 irradiation field area was set and MRI was performed. Next, readout analysis was performed using MATLAB and the 3 mm, 3% gamma passing rate > 95% was used as a basis for evaluation.

RESULTS:

The concentric dynamic dose curve for a simulated respiratory rate of 3 seconds/breath and 4 × 4 cm2 field was compared with 4 × 4, 3 × 3, and 2 × 2 cm2 treatment planning systems (TPS), and the 3 mm, 3% gamma passing rate was 42.87%, 54.96%, and 49.92%, respectively. Pre-simulation showed that the high-dose region dose curve was similar to the 2 × 2 cm2 TPS result. After appropriate selection and comparison, we found that the 3 mm, 3% gamma passing rate was 97.92% on comparing the > 60% dose curve with the 2 × 2 cm2 TPS.

CONCLUSIONS:

NIPAM gel dosimeter and concentric swing machine use is feasible to simulate dose distribution during breathing and results conforming to clinical evaluation standards.

Intrafraction pancreatic tumor motion patterns during ungated magnetic resonance guided radiotherapy with an abdominal corset

Background

Stereotactic body radiotherapy (SBRT) has been shown to be a promising therapy for unresectable pancreatic tumors. However, intrafraction motion, caused by respiratory motion and organ drift, is one of the main concerns for efficient dose delivery in ungated upper abdominal radiotherapy. The aim of this study was to analyze the intrafraction gross tumor volume (GTV) motion in a clinical cohort.

Materials and methods

We included 13 patients that underwent online adaptive magnetic resonance (MR)-guided SBRT for malignancies in the pancreatic region (5 × 8 Gy). An abdominal corset was fitted in order to reduce the abdominal respiratory motion. Coronal and sagittal cine magnetic resonance images of the tumor region were made at 2 Hz during the entire beam-on time of each fraction. We used deformable image registration to obtain GTV motion profiles in all three directions, which were subsequently high-pass and low-pass filtered to isolate the motion caused by respiratory motion and baseline drift, respectively.

Results

The mean (SD) respiratory amplitudes were 4.2 (1.9) mm cranio-caudal (CC), 2.3 (1.1) mm ventral-dorsal (AP) and 1.4 (0.6) mm left–right (LR), with low variability within patients. The mean (SD) maximum baseline drifts were 1.2 (1.1) mm CC, 0.5 (0.4) mm AP and 0.5 (0.3) mm LR. The mean (SD) minimum baseline drifts were −0.7 (0.5) mm CC, −0.6 (0.5) mm AP and −0.5 (0.4) mm LR.

Conclusion

Overall tumor motion during treatment was small and interfractionally stable. These findings show that high-precision ungated MR-guided SBRT is feasible with an abdominal corset.

Improved Ultrasound Attenuation Measurement Method for the Non-invasive Evaluation of Hepatic Steatosis Using FibroScan

Controlled attenuation parameter (CAP) is a measurement of ultrasound attenuation used to assess liver steatosis non-invasively. However, the standard method has some limitations. This study assessed the performance of a new CAP method by ex vivo and in vivo assessments. The major difference with the new method is that it uses ultrasound data continuously acquired during the imaging phase of the FibroScan examination. Seven reference tissue-mimicking phantoms were used to test the performance. In vivo performance was assessed in two cohorts (in total 195 patients) of patients using magnetic resonance imaging proton density fat fraction (MRI-PDFF) as a reference. The precision of CAP was improved by more than 50% on tissue-mimicking phantoms and 22%-41% in the in vivo cohort studies. The agreement between both methods was excellent, and the correlation between CAP and MRI-PDFF improved in both studies (0.71 to 0.74; 0.70 to 0.76). Using MRI-PDFF as a reference, the diagnostic performance of the new method was at least equal or superior (area under the receiver operating curve 0.889-0.900, 0.835-0.873). This study suggests that the new continuous CAP method can significantly improve the precision of CAP measurements ex vivo and in vivo.

The feasibility of a noise elimination method using continuous wave response of therapeutic ultrasound signals for ultrasonic monitoring of high-intensity focused ultrasound treatment

Purpose

In this study, the robustness and feasibility of a noise elimination method using continuous wave response of therapeutic ultrasound signals were investigated when tissue samples were moved to simulate the respiration-induced movements of the different organs during actual high-intensity focused ultrasound (HIFU) treatment. In addition to that, the failure conditions of the proposed algorithm were also investigated.

Methods

The proposed method was applied to cases where tissue samples were moved along both the lateral and axial directions of the HIFU transducer to simulate respiration-induced motions during HIFU treatment, and the noise reduction level was investigated. In this experiment, the speed of movement was increased from 10 to 40 mm/s to simulate the actual movement of the tissue during HIFU exposure, with the intensity and driving frequency of HIFU set to 1.0–5.0 kW/cm² and 1.67 MHz, respectively. To investigate the failure conditions of the proposed algorithm, the proposed method was applied with the HIFU focus located at the boundary between the phantom and water to easily cause cavitation bubbles. The intensity of HIFU was set to 10 kW/cm².

Results

Almost all HIFU noise was constantly able to be eliminated using the proposed method when the phantom was moved along the lateral and axial directions during HIFU exposure. The noise reduction level (PRL in this study) at an intensity of 1.0, 3.0, and 5.0 kW/cm² was in the range of 28–32, 38–40, and 42–45 dB, respectively. On the other hand, HIFU noise was not basically eliminated during HIFU exposure after applying the proposed method in the case of cavitation generation at the HIFU focus.

Conclusions

The proposed method can be applicable even if homogeneous tissues or organs move axially or laterally to the direction of HIFU exposure because of breathing. A condition under which the proposed algorithm failed was when instantaneous tissue changes such as cavitation bubble generation occurred in the tissue, at which time the reflected continuous wave response became less steady.

Fiducial-based image-guided SBRT for pancreatic adenocarcinoma: Does inter-and intra-fraction treatment variation warrant adaptive therapy?

Purpose

Variation in target positioning represents a challenge to set-up reproducibility and reliability of dose delivery with stereotactic body radiation therapy (SBRT) for pancreatic adenocarcinoma (PDAC). While on-board imaging for fiducial matching allows for daily shifts to optimize target positioning, the magnitude of the shift as a result of inter- and intra-fraction variation may directly impact target coverage and dose to organs-at-risk. Herein, we characterize the variation patterns for PDAC patients treated at a high-volume institution with SBRT.

Methods

We reviewed 30 consecutive patients who received SBRT using active breathing coordination (ABC). Patients were aligned to bone and then subsequently shifted to fiducials. Inter-fraction and intra-fraction scans were reviewed to quantify the mean and maximum shift along each axis, and the shift magnitude. A linear regression model was conducted to investigate the relationship between the inter- and intra-fraction shifts.

Results

The mean inter-fraction shift in the LR, AP, and SI axes was 3.1 ± 1.8 mm, 2.9 ± 1.7 mm, and 3.5 ± 2.2 mm, respectively, and the mean vector shift was 6.4 ± 2.3 mm. The mean intra-fraction shift in the LR, AP, and SI directions were 2.0 ± 0.9 mm, 2.0 ± 1.3 mm, and 2.3 ± 1.4 mm, respectively, and the mean vector shift was 4.3 ± 1.8 mm. A linear regression model showed a significant relationship between the inter- and intra-fraction shift in the AP and SI axis and the shift magnitude.

Conclusions

Clinically significant inter- and intra-fraction variation occurs during treatment of PDAC with SBRT even with a comprehensive motion management strategy that utilizes ABC. Future studies to investigate how these variations could lead to variation in the dose to the target and OAR should be investigated. Strategies to mitigate the dosimetric impact, including real time imaging and adaptive therapy, in select cases should be considered.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13014-021-01782-w.

Effects of laparoscopy, laparotomy, and respiratory phase on liver volume in a live porcine model for liver resection

Background

Hepatectomy, living donor liver transplantations and other major hepatic interventions rely on precise calculation of the total, remnant and graft liver volume. However, liver volume might differ between the pre- and intraoperative situation. To model liver volume changes and develop and validate such pre- and intraoperative assistance systems, exact information about the influence of lung ventilation and intraoperative surgical state on liver volume is essential.

Methods

This study assessed the effects of respiratory phase, pneumoperitoneum for laparoscopy, and laparotomy on liver volume in a live porcine model. Nine CT scans were conducted per pig (N = 10), each for all possible combinations of the three operative (native, pneumoperitoneum and laparotomy) and respiratory states (expiration, middle inspiration and deep inspiration). Manual segmentations of the liver were generated and converted to a mesh model, and the corresponding liver volumes were calculated.

Results

With pneumoperitoneum the liver volume decreased on average by 13.2% (112.7 ml ± 63.8 ml, p < 0.0001) and after laparotomy by 7.3% (62.0 ml ± 65.7 ml, p = 0.0001) compared to native state. From expiration to middle inspiration the liver volume increased on average by 4.1% (31.1 ml ± 55.8 ml, p = 0.166) and from expiration to deep inspiration by 7.2% (54.7 ml ± 51.8 ml, p = 0.007).

Conclusions

Considerable changes in liver volume change were caused by pneumoperitoneum, laparotomy and respiration. These findings provide knowledge for the refinement of available preoperative simulation and operation planning and help to adjust preoperative imaging parameters to best suit the intraoperative situation.

Accuracy and efficiency of respiratory gating comparable to deep inspiration breath hold for pancreatic cancer treatment

Purpose

Deep inspiration breath hold (DIBH) and respiratory gating (RG) are widely used to reduce movement of target and healthy organs caused by breathing during irradiation. We hypothesized that accuracy and efficiency comparable to DIBH can be achieved with RG for pancreas treatment.

Methods and Materials

Twenty consecutive patients with pancreatic cancer treated with DIBH (eight) or RG (twelve) volumetric modulated arc therapy during 2017–2019 were included in this study, with radiopaque markers implanted near or in the targets. Seventeen patients received 25 fractions, while the other three received 15 fractions. Only patients who could not tolerate DIBH received RG treatment. While both techniques relied on respiratory signals from external markers, internal target motions were monitored with kV X‐ray imaging during treatment. A 3‐mm external gating window was used for DIBH treatment; RG treatment was centered on end‐expiration with a duty cycle of 40%, corresponding to an external gating window of 2–3 mm. During dose delivery, kV images were automatically taken every 20^◦ or 40^◦ gantry rotation, from which internal markers were identified. The marker displacement from their initial positions and the residual motion amplitudes were calculated. For the analysis of treatment efficiency, the treatment time of every session was calculated from the motion management waveform files recorded at the treatment console.

Results

Within one fraction, the displacement was 0–5 mm for DIBH and 0–6 mm for RG. The average magnitude of displacement for each patient during the entire course of treatment ranged 0–3 mm for both techniques. No statistically significant difference in displacement or residual motion was observed between the two techniques. The average treatment time was 15 min for DIBH and 17 min for RG, with no statistical significance.

Conclusions

The accuracy and efficiency were comparable between RG and DIBH treatment for pancreas irradiation. RG is a feasible alternative strategy to DIBH.

Dosimetric impact of baseline drift in volumetric modulated arc therapy with breath holding

BACKGROUND

We investigated the change of dose distributions in volumetric modulated arc therapy (VMAT) under baseline drift (BD) during breath holding.

MATERIALS AND METHODS

Ten VMAT plans recalculated to a static field at a gantry angle of 0° were prepared for measurement with a 2D array device and five original VMAT plans were prepared for measurement with gafchromic films. These measurement approaches were driven by a waveform reproducing breath holding with BD. We considered breath holding times of 15 and 10 s, and BD at four speeds; specifically, BD0 (0 mm/s), BD0.2 (0.2 mm/s), BD0.3 (0.3 mm/s), and BD0.4 (0.4 mm/s). The BD was periodically reproduced from the isocenter along the craniocaudal direction and the shift during breath holding (ShiftBH) ranged 0-6 mm.The dose distribution of BD0.2, BD0.3 and BD0.4 were compared to that of BD0 using gamma analysis with the criterion of 2%/2 mm.

RESULTS

The mean pass rates of each ShiftBH were 99.8% and 98.9% at 0 mm, 96.8% and 99.4% at 2 mm, 94.9% and 98.6% at 3 mm, 91.5% and 98.4% at 4 mm, 70.8% and 94.1% at 4.5 mm, and 55.0% and 83.6% at 6 mm for the array and film measurements, respectively.

CONCLUSION

We found significant differences in ShiftBH above 4 mm (ρ < 0.05). Hence, it is recommended that breath holding time should be shortened for patients to preserve the reproducibility of dose distributions.

Free-breathing liver fat and R 2 ∗ quantification using motion-corrected averaging based on a nonlocal means algorithm

PURPOSE

To propose a motion-robust chemical shift-encoded (CSE) method with high signal-to-noise (SNR) for accurate quantification of liver proton density fat fraction (PDFF) and R 2 ∗ .

METHODS

A free-breathing multi-repetition 2D CSE acquisition with motion-corrected averaging using nonlocal means (NLM) was proposed. PDFF and R 2 ∗ quantified with 2D CSE-NLM were compared to two alternative 2D techniques: direct averaging and single acquisition (2D 1ave) in a digital phantom. Further, 2D NLM was compared in patients to 3D techniques (standard breath-hold, free-breathing and navigated), and the alternative 2D techniques. A reader study and quantitative analysis (Bland-Altman, correlation analysis, paired Student's t-test) were performed to evaluate the image quality and assess PDFF and R 2 ∗ measurements in regions of interest.

RESULTS

In simulations, 2D NLM resulted in lower standard deviations (STDs) of PDFF (2.7%) and R 2 ∗ (8.2  s - 1 ) compared to direct averaging (PDFF: 3.1%, R 2 ∗ : 13.6  s - 1 ) and 2D 1ave (PDFF: 8.7%, R 2 ∗ : 33.2  s - 1 ). In patients, 2D NLM resulted in fewer motion artifacts than 3D free-breathing and 3D navigated, less signal loss than 2D direct averaging, and higher SNR than 2D 1ave. Quantitatively, the STDs of PDFF and R 2 ∗ of 2D NLM were comparable to those of 2D direct averaging (p>0.05). 2D NLM reduced bias, particularly in R 2 ∗ (-5.73 to -0.36  s - 1 ) that arises in direct averaging (-3.96 to 11.22  s - 1 ) in the presence of motion.

CONCLUSIONS

2D CSE-NLM enables accurate mapping of PDFF and R 2 ∗ in the liver during free-breathing.

Applicability of Augmented Reality in an Organ Transplantation

Augmented reality (AR) delivers virtual information or some of its elements to the real world. This technology, which has been used primarily for entertainment and military applications, has vigorously entered medicine, especially in radiology and surgery, yet has never been used in organ transplantation. AR could be useful in training transplant surgeons, promoting organ donations, graft retrieval and allocation, and microscopic diagnosis of rejection, treatment of complications, and post-transplantation neoplasms. The availability of AR display tools such as Smartphone screens and head-mounted goggles, accessibility of software for automated image segmentation and 3-dimensional reconstruction, and algorithms allowing registration, make augmented reality an attractive tool for surgery including transplantation. The shortage of hospital IT specialists and insufficient investments from medical equipment manufacturers into the development of AR technology remain the most significant obstacles in its broader application.

Data-Driven Respiratory Gating Outperforms Device-Based Gating for Clinical 18F-FDG PET/CT

A data-driven method for respiratory gating in PET has recently been commercially developed. We sought to compare the performance of the algorithm with an external, device-based system for oncologic ¹⁸F-FDG PET/CT imaging. Methods: In total, 144 whole-body ¹⁸F-FDG PET/CT examinations were acquired, with a respiratory gating waveform recorded by an external, device-based respiratory gating system. In each examination, 2 of the bed positions covering the liver and lung bases were acquired with a duration of 6 min. Quiescent-period gating retaining approximately 50% of coincidences was then able to produce images with an effective duration of 3 min for these 2 bed positions, matching the other bed positions. For each examination, 4 reconstructions were performed and compared: data-driven gating (DDG) (we use the term DDG-retro to distinguish that we did not use the real-time R-threshold-based application of DDG that is available within the manufacturer's product), external device-based gating (real-time position management (RPM)-gated), no gating but using only the first 3 min of data (ungated-matched), and no gating retaining all coincidences (ungated-full). Lesions in the images were quantified and image quality scored by a radiologist who was masked to the method of data processing. Results: Compared with the other reconstruction options, DDG-retro increased the SUV_max and decreased the threshold-defined lesion volume. Compared with RPM-gated, DDG-retro gave an average increase in SUV_max of 0.66 ± 0.1 g/mL (n = 87, P < 0.0005). Although the results from the masked image evaluation were most commonly equivalent, DDG-retro was preferred over RPM-gated in 13% of examinations, whereas the opposite occurred in just 2% of examinations. This was a significant preference for DDG-retro (P = 0.008, n = 121). Liver lesions were identified in 23 examinations. Considering this subset of data, DDG-retro was ranked superior to ungated-full in 6 of 23 (26%) cases. Gated reconstruction using the external device failed in 16% of examinations, whereas DDG-retro always provided a clinically acceptable image. Conclusion: In this clinical evaluation, DDG-retro provided performance superior to that of the external device-based system. For most examinations the performance was equivalent, but DDG-retro had superior performance in 13% of examinations, leading to a significant preference overall.

Impact of abdominal compression on setup error and image matching during radical abdominal radiotherapy

PURPOSE

To determine the impact of abdominal compression (AC) on setup error and image matching time.

MATERIALS AND METHODS

This study included 72 liver, pancreas and abdominal node patients treated radically from 2016 to 2019 in a single centre. Patients received either SBRT or conventional radical fractionation (CRF). Compressed patients were supine, arms up with kneefix and AC equipment. Uncompressed patients were supine, arms up with kneefix. All patients received daily online-matched CBCTs before treatment. Initial setup error was determined for all patients. Registration error was assessed for 10 liver and 10 pancreas patients. Image matching times were determined using beam on times. Statistical tests conducted were an F-test to compare variances in setup error, Student's t-tests for setup error and average image analysis, and a Wilcoxon Mann Whitney test for imaging matching time analysis.

RESULTS

Initial setup displacement was similar between compressed and uncompressed patients. Displacements > 1 cm occurred more frequently in the longitudinal direction for most patients. SBRT patients required more additional manual positioning following imaging. Mean absolute registration error in the SI direction was 5.4 mm and 3.3 mm for uncompressed and compressed pancreas patients respectively and 1.7 mm and 0.8 mm for uncompressed and compressed liver patients respectively. Compressed patients required less time for image matching and fewer images per fraction on average. Repeat imaging occurred more frequently in SBRT and uncompressed patients.

CONCLUSIONS

Although abdominal compression has no significant impact on setup error, it can reduce imaging matching times resulting in improved treatment accuracy.

Australasian Gastrointestinal Trials Group (AGITG) and Trans-Tasman Radiation Oncology Group (TROG) Guidelines for Pancreatic Stereotactic Body Radiation Therapy (SBRT)

PURPOSE

Nonrandomized data exploring pancreas stereotactic body radiation therapy (SBRT) has demonstrated excellent local control rates and low toxicity. Before commencing a randomized trial investigating pancreas SBRT, standardization of prescription dose, dose constraints, simulation technique, and clinical target volume delineation are required.

METHODS AND MATERIALS

Specialists in radiation oncology, medical oncology, hepatobiliary surgery, and gastroenterology attended 2 consecutive Australasian Gastrointestinal Trials Group workshops in 2017 and 2018. Sample cases were discussed during workshop contact with specifically invited international speakers highly experienced in pancreas SBRT. Furthermore, sample cases were contoured and planned between workshop contact to finalize dose constraints and clinical target volume delineation.

RESULTS

Over 2 separate workshops, consensus was reached on dose and simulation technique. The working group recommended a dose prescription of 40 Gy in 5 fractions. Treatment delivery during end-expiratory breath hold with triple-phase contrast enhanced computed tomography was recommended. In addition, dose constraints, stepwise contouring guidelines, and an anatomic atlas for pancreatic SBRT were developed.

CONCLUSIONS

Pancreas SBRT is emerging as a promising treatment modality requiring prospective evaluation in randomized studies. This work attempts to standardize dose, simulation technique, and volume delineation to support the delivery of high quality SBRT in a multicenter study.

Designing and validating a PVA liver phantom with respiratory motion for needle-based interventions

Purpose

The purpose is to design and validate an anthropomorphic polyvinyl alcohol (PVA) liver phantom with respiratory motion to simulate needle-based interventions. Such a system can, for example, be used as a validation tool for novel needles.

Methods

Image segmentations of CT scans of four patients during inspiration and expiration were used to measure liver and rib displacement. An anthropomorphic liver mold based on a CT scan was 3D printed and filled with 5% w/w PVA-to-water, undergoing two freeze–thaw cycles, in addition to a 3D-printed compliant rib cage. They were both held in place by a PVA abdominal phantom. A sinusoidal motion vector, based on the measured liver displacement, was applied to the liver phantom by means of a motion stage. Liver, rib cage and needle deflection were tracked by placing electromagnetic sensors on the phantom. Liver and rib cage phantom motion was validated by comparison with the CT images of the patients, whereas needle deflection was compared with the literature.

Results

CT analysis showed that from the state of expiration to inspiration, the livers moved predominantly toward the right (mean: 2 mm, range: − 11 to 11 mm), anterior (mean: 15 mm, range: 9–21 mm) and caudal (mean: 16 mm, range: 6–24 mm) direction. The mechatronic design of the liver phantom gives the freedom to set direction and amplitude of the motion and was able to mimic the direction of liver motion of one patient. Needle deflection inside the phantom increased from 1.6 to 3.8 mm from the initial expiration state to inspiration.

Conclusions

The developed liver phantom allows for applying different motion patterns and shapes/sizes and thus allows for patient-specific simulation of needle-based interventions. Moreover, it is able to mimic appropriate respiratory motion and needle deflection as observed in patients.

Electronic supplementary material

The online version of this article (10.1007/s11548-019-02029-6) contains supplementary material, which is available to authorized users.

Cardiac Pulsatility- and Respiratory-Induced Deformations of the Renal Arteries and Snorkel Stents After Snorkel Endovascular Aneurysm Sealing

Purpose: To quantify deformations of renal arteries and snorkel stents after snorkel endovascular aneurysm sealing (Sn-EVAS) resulting from cardiac pulsatility and respiration and compare these deformations to patients with untreated abdominal aortic aneurysms (AAA) and snorkel endovascular aneurysm repair (Sn-EVAR). Materials and Methods: Ten Sn-EVAS patients (mean age 75±6 years; 8 men) were scanned with cardiac-gated, respiration-resolved computed tomography angiography. From 3-dimensional geometric models, changes in renal artery and stent angulation and curvature due to cardiac pulsatility and respiration were quantified. Respiration-induced motions were compared with those of 16 previously reported untreated AAA patients and 11 Sn-EVAR patients. Results: Renal artery bending at the stent end was greater for respiratory vs cardiac influences (6°±7° vs -1°±2°, p<0.025). Respiration caused a 3-fold greater deformation on the left renal artery as compared with the right side. Maximum curvature change was higher for respiratory vs cardiac influences (0.49±0.29 vs 0.24±0.17 cm^-1, p<0.025), and snorkel renal stents experienced similar maximum curvature change due to cardiac pulsatility and respiration (0.14±0.10 vs 0.19±0.09 cm^-1, p=0.142). When comparing the 3 patient cohorts for respiratory-induced deformation, there was significant renal branch angulation in untreated AAAs, but not in Sn-EVAR or Sn-EVAS, and there was significant bending at the stent end in Sn-EVAR and Sn-EVAS. Maximum curvature change due to respiration was ~10-fold greater in Sn-EVAR and Sn-EVAS compared to untreated AAAs. Conclusion: The findings suggest that cardiac and respiratory influences may challenge the mechanical durability of snorkel stents of Sn-EVAS; similarly, however, respiration may be the primary culprit for tissue irritation, increasing the risk for stent-end thrombosis, especially in the left renal artery. The bending stiffness of snorkel stents in both the Sn-EVAR and Sn-EVAS cohorts damped renal branch angulation while it intensified bending of the artery distal to the snorkel stent. Understanding these device-to-artery interactions is critical as they may affect mechanical durability of branch stents and quality and durability of treatment.

Intrafraction tumor motion during deep inspiration breath hold pancreatic cancer treatment

Purpose

Beam 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 Materials

Eight 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.

Results

Even 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.

Conclusions

Internal 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.

Assessment of cardiac-driven liver movements with filtered harmonic phase image representation, optical flow quantification, and motion amplification

PURPOSE

To characterize cardiac-driven liver movements using a harmonic phase image representation (HARP) with an optical flow quantification and motion amplification method. The method was applied to define the cardiac trigger delay providing minimal signal losses in liver DWI images.

METHODS

The 16-s breath-hold balanced-SSFP time resolved 20 images/s were acquired at 3T in coronal and sagittal orientations. A peripheral pulse unit signal was recorded. Cardiac-triggered DWI images were acquired after different peripheral pulse unit delays. A steerable pyramid decomposition with multiple orientations and spatial frequencies was applied. The liver motion field-map was derived from temporal variations of the HARP representation filtered around the cardiac frequency. Liver displacements were quantified with an optical flow method; moreover the right liver motion was amplified.

RESULTS

The largest displacements were observed in the left liver (feet-head:3.70 ± 1.06 mm; anterior-posterior: 2.35 ± 0.51 mm). Displacements were statistically significantly weaker in the middle right liver (0.47 ± 0.11 mm; P = 0.0156). The average error was 0.013 ± 0.022 mm (coronal plane) and 0.021 ± 0.041 mm (sagittal plane). The velocity field demonstrated opposing movements of the right liver extremities during the cardiac cycle. DWI signal loss was minimized in regions and instants of smallest amplitude of both velocity and velocity gradient.

CONCLUSION

Cardiac-driven liver movements were quantified with combined cardiac frequency-filtered HARP and optical flow methods. A motion phase opposition between right liver extremities was demonstrated. Displacement amplitude and velocity were larger in the left liver especially along the vertical direction. Motion amplification visually emphasized cardiac-driven right liver displacements. The optimal cardiac timing minimizing signal loss in liver DWI images was derived.

The impact of 2D cine MR imaging parameters on automated tumor and organ localization for MR-guided real-time adaptive radiotherapy

2D cine MR imaging may be utilized to monitor rapidly moving tumors and organs-at-risk for real-time adaptive radiotherapy. This study systematically investigates the impact of geometric imaging parameters on the ability of 2D cine MR imaging to guide template-matching-driven autocontouring of lung tumors and abdominal organs. Abdominal 4D MR images were acquired of six healthy volunteers and thoracic 4D MR images were obtained of eight lung cancer patients. At each breathing phase of the images, the left kidney and gallbladder or lung tumor, respectively, were outlined as volumes of interest. These images and contours were used to create artificial 2D cine MR images, while simultaneously serving as 3D ground truth. We explored the impact of five different imaging parameters (pixel size, slice thickness, imaging plane orientation, number and relative alignment of images as well as strategies to create training images). For each possible combination of imaging parameters, we generated artificial 2D cine MR images as training and test images. A template-matching algorithm used the training images to determine the tumor or organ position in the test images. Subsequently, a 3D base contour was shifted to the determined position and compared to the ground truth via centroid distance and Dice similarity coefficient. The median centroid distance between adapted and ground truth contours was 1.56 mm for the kidney, 3.81 mm for the gallbladder and 1.03 mm for the lung tumor (median Dice similarity coefficient: 0.95, 0.72 and 0.93). We observed that a decrease in image resolution led to a modest decrease in localization accuracy, especially for the small gallbladder. However, for all volumes of interest localization accuracy varied substantially more between subjects than due to the different imaging parameters. Automated tumor and organ localization using 2D cine MR imaging and template-matching-based autocontouring is robust against variation of geometric imaging parameters. Future work and optimization efforts of 2D cine MR imaging for real-time adaptive radiotherapy is needed to characterize the influence of sequence- and anatomical site-specific imaging contrast.

MRI-guidance for motion management in external beam radiotherapy: current status and future challenges

High precision conformal radiotherapy requires sophisticated imaging techniques to aid in target localisation for planning and treatment, particularly when organ motion due to respiration is involved. X-ray based imaging is a well-established standard for radiotherapy treatments. Over the last few years, the ability of magnetic resonance imaging (MRI) to provide radiation-free images with high-resolution and superb soft tissue contrast has highlighted the potential of this imaging modality for radiotherapy treatment planning and motion management. In addition, these advantageous properties motivated several recent developments towards combined MRI radiation therapy treatment units, enabling in-room MRI-guidance and treatment adaptation. The aim of this review is to provide an overview of the state-of-the-art in MRI-based image guidance for organ motion management in external beam radiotherapy. Methodological aspects of MRI for organ motion management are reviewed and their application in treatment planning, in-room guidance and adaptive radiotherapy described. Finally, a roadmap for an optimal use of MRI-guidance is highlighted and future challenges are discussed.

Full Modeling of High-Intensity Focused Ultrasound and Thermal Heating in the Kidney Using Realistic Patient Models

OBJECTIVE

High-intensity focused ultrasound (HIFU) therapy can be used for noninvasive treatment of kidney (renal) cancer, but the clinical outcomes have been variable. In this study, the efficacy of renal HIFU therapy was studied using a nonlinear acoustic and thermal simulations in three patients.

METHODS

The acoustic simulations were conducted with and without refraction in order to investigate its effect on the shape, size, and pressure distribution at the focus. The values for the attenuation, sound speed, perfusion, and thermal conductivity of the kidney were varied over the reported ranges to determine the effect of variability on heating. Furthermore, the phase aberration was studied in order to quantify the underlying phase shifts using a second order polynomial function.

RESULTS

The ultrasound field intensity was found to drop on average 11.1 dB with refraction and 6.4 dB without refraction. Reflection at tissue interfaces was found to result in a loss less than 0.1 dB. Focal point splitting due to refraction significantly reduced the heating efficacy. Perfusion did not have a large effect on heating during short sonication durations. Small changes in temperature were seen with varying attenuation and thermal conductivity, but no visible changes were present with sound speed variations. The aberration study revealed an underlying trend in the spatial distribution of the phase shifts.

CONCLUSION

The results show that the efficacy of HIFU therapy in the kidney could be improved with aberration correction.

SIGNIFICANCE

A method is proposed by that patient specific pre-treatment calculations could be used to overcome the aberration and therefore make ultrasound treatment possible.

MRI guided stereotactic radiotherapy for locally advanced pancreatic cancer

OBJECTIVE:

We want to explore the safety and technical feasibility of MRI-guided stereotactic radiotherapy for locally advanced pancreatic cancer.

METHODS:

A custom-made abdominal corset was manufactured to reduce breathing induced tumour motion. Delineation of the tumour and organs at risk (OARs) was performed on CT and multiparametric MRI. Tumour motion was quantified with cine MRI. After treatment planning, the static dose distribution was convolved with the cine MRI-based motion trajectory to simulate the delivered dose to the tumour and OARs. Stereotactic body radiation therapy (SBRT) was carried out up to a dose of 24 G in three fractions in 1 week.

RESULTS:

From July 2013 to January 2016, 20 patients were included. Tumours and OARs were clearly visible with contrast-enhanced CT and MRI. After simulation of the delivered dose taking the motion into account, an adequate target coverage was achieved with acceptable dose in the OARs. No Grade3 or higher treatment related toxicity was observed.

CONCLUSION:

MRI-guided SBRT for pancreatic cancer is technical feasible and safe, with no treatment related grade ≥3 toxicity. New strategies are applied, including an individual corset to reduce breathing motion, MRI-based delineation and simulation of motion-integrated dose distributions.

ADVANCES IN KNOWLEDGE:

This article is the first to describe an MRI-integrated workflow in SBRT for locally advanced pancreatic cancer. In addition, it demonstrated that SBRT with an abdominal corset to reduce tumour motion is feasible and safe.

TRIAL REGISTRATION:

This trial was registered at www.clinicaltrials.gov (NCT01898741) on July 9, 2013.

Quantitative analysis of respiration-induced motion of each liver segment with helical computed tomography and 4-dimensional computed tomography

Background

To analyze the respiratory-induced motion of each liver segment using helical computed tomography (helical CT) and 4-dimensional computed tomography (4DCT), and to establish the individual segment expansion margin of internal target volume (ITV) to facilitate target delineation of tumors in different liver segments.

Methods

Twenty patients who received radiotherapy with CT-simulation scanning of the whole liver in both helical CT and 10-phase-gated 4DCT were investigated, including 2 patients with esophagus cancer, 4 with lung cancer, 10 with breast cancer, 2 with liver cancer, 1 with thymoma, and 1 with gastric diffuse large B-cell lymphoma (DLBCL). For each patient, 9 representative points were drawn on the helical CT images of liver segments 1, 2, 3, 4a, 4b, 5, 6, 7, and 8, respectively, and adaptively deformed to 2 phases of the 4DCT images at the end of inspiration (phase 0 CT) and expiration (phase 50 CT) in the treatment planning system. Using the amplitude of each point between phase 0 CT and phase 50 CT, we established quantitative data for the respiration-induced motion of each liver segment in 3-dimensional directions. Moreover, using the amplitude between the original helical CT and both 4DCT images, we rendered the individual segment expansion margin of ITV for hepatic target delineation to cover more than 95% of each tumor.

Results

The average amplitude (mean ± standard deviation) was 0.6 ± 3.0 mm in the left-right (LR) direction, 2.3 ± 2.4 mm in the anterior-posterior (AP) direction, and 5.7 ± 3.4 mm in the superior-inferior (SI) direction, respectively. All of the segments moved posteriorly and superiorly during expiration. Segment 7 had the largest amplitude in the SI direction, at 8.6 ± 3.4 mm. Otherwise, the segments over the lateral side, including segments 2, 3, 6, and 7, had greater excursion in the SI direction compared to the medial segments. To cover more than 95% of each tumor, the required expansion margin of ITV in the LR, AP, and SI directions were at least 2.5 mm, 2.5 mm, and 5.0 mm on average, respectively, with variations between different segments.

Conclusions

The greatest excursion occurred in liver segment 7, followed by the segments over the lateral side in the SI direction. The individual segment expansion margin of ITV is required to delineate targets for each segment and direction.

Evaluation of principal component analysis-based data-driven respiratory gating for positron emission tomography

Objective:

Respiratory motion can degrade PET image quality and lead to inaccurate quantification of lesion uptake. Such motion can be mitigated via respiratory gating. Our objective was to evaluate a data-driven gating (DDG) technique that is being developed commercially for clinical PET/CT.

Methods:

A data-driven respiratory gating algorithm based on principal component analysis (PCA) was applied to phantom and FDG patient data. An anthropomorphic phantom and a NEMA IEC Body phantom were filled with ¹⁸F, placed on a respiratory motion platform, and imaged using a PET/CT scanner. Motion waveforms were measured using an infrared camera [the Real-time Position Management™ system (RPM)] and also extracted from the PET data using the DDG algorithm. The waveforms were compared via calculation of Pearson’s correlation coefficients. PET data were reconstructed using quiescent period gating (QPG) and compared via measurement of recovery percentage and background variability.

Results:

Data-driven gating had similar performance to the external gating system, with correlation coefficients in excess of 0.97. Phantom and patient images were visually clearer with improved contrast when QPG was applied as compared to no motion compensation. Recovery coefficients in the phantoms were not significantly different between DDG- and RPM-based QPG, but were significantly higher than those found for no motion compensation (p < 0.05).

Conclusion:

A PCA-based DDG algorithm was evaluated and found to provide a reliable respiratory gating signal in anthropomorphic phantom studies and in example patients.

Advances in knowledge:

The prototype commercial DDG algorithm may enable reliable respiratory gating in routine clinical PET-CT.

Potential dosimetric benefits of adaptive tumor tracking over the internal target volume concept for stereotactic body radiation therapy of pancreatic cancer

BACKGROUND

Radiotherapy for pancreatic cancer has two major challenges: (I) the tumor is adjacent to several critical organs and, (II) the mobility of both, the tumor and its surrounding organs at risk (OARs). A treatment planning study simulating stereotactic body radiation therapy (SBRT) for pancreatic tumors with both the internal target volume (ITV) concept and the tumor tracking approach was performed. The two respiratory motion-management techniques were compared in terms of doses to the target volume and organs at risk.

METHODS AND MATERIALS

Two volumetric-modulated arc therapy (VMAT) treatment plans (5 × 5 Gy) were created for each of the 12 previously treated pancreatic cancer patients, one using the ITV concept and one the tumor tracking approach. To better evaluate the overall dose delivered to the moving tumor volume, 4D dose calculations were performed on four-dimensional computed tomography (4DCT) scans. The resulting planning target volume (PTV) size for each technique was analyzed. Target and OAR dose parameters were reported and analyzed for both 3D and 4D dose calculation.

RESULTS

Tumor motion ranged from 1.3 to 11.2 mm. Tracking led to a reduction of PTV size (max. 39.2%) accompanied with significant better tumor coverage (p<0.05, paired Wilcoxon signed rank test) both in 3D and 4D dose calculations and improved organ at risk sparing. Especially for duodenum, stomach and liver, the mean dose was significantly reduced (p<0.05) with tracking for 3D and 4D dose calculations.

CONCLUSIONS

By using an adaptive tumor tracking approach for respiratory-induced pancreatic motion management, a significant reduction in PTV size can be achieved, which subsequently facilitates treatment planning, and improves organ dose sparing. The dosimetric benefit of tumor tracking is organ and patient-specific.

Servoing Performance Enhancement via a Respiratory Organ Motion Prediction Model for a Non-Invasive Ultrasound Theragnostic System

[abstFig src='/00290002/15.jpg' width='300' text='Proposed method for tracking and following respiratory organ motion' ] High intensity focused ultrasound (HIFU) is potentially useful for treating stones and/or tumors. With respect to HIFU therapy, it is difficult to focus HIFU on the focal lesion due to respiratory organ motion, and this increases the risk of damaging the surrounding healthy tissues around the target focal lesion. Thus, this study proposes a method to cope with the fore-mentioned problem involving tracking and following the respiratory organ motion via a visual feedback and a prediction model for respiratory organ motion to realize highly accurate servoing performance for focal lesions. The prediction model is continuously updated based on the latest organ motion data. The results indicate that respiratory kidney motion of two healthy subjects is successfully tracked and followed with an accuracy of 0.88 mm by the proposed method and the constructed system.

Motion management strategies and technical issues associated with stereotactic body radiotherapy of thoracic and upper abdominal tumors: A review from NRG oncology

The efficacy of stereotactic body radiotherapy (SBRT) has been well demonstrated. However, it presents unique challenges for accurate planning and delivery especially in the lungs and upper abdomen where respiratory motion can be significantly confounding accurate targeting and avoidance of normal tissues. In this paper, we review the current literature on SBRT for lung and upper abdominal tumors with particular emphasis on addressing respiratory motion and its affects. We provide recommendations on strategies to manage motion for different, patient-specific situations. Some of the recommendations will potentially be adopted to guide clinical trial protocols.

Predictive factors of gastroduodenal bleeding after postoperative radiotherapy in biliary tract cancer

Objective

To identify predictive factors for gastroduodenal bleeding after postoperative radiation therapy in patients with biliary tract cancer.

Methods

We identified 186 patients with biliary tract cancer who completed scheduled postoperative radiation therapy from March 2000 to August 2013. To isolate the effects of radiation on gastroduodenal bleeding, patients with pylorus-preserving pancreaticoduodenectomy, pylorus-resecting pancreaticoduodenectomy or Whipple surgery (n = 67) were excluded from this analysis. Postoperative radiation therapy was started at a median 5 weeks (range: 4-12 weeks) after surgery with a median dose of 44 Gy (range: 44-54), and chemotherapy was also concurrently administered to 102 patients.

Results

The median age of the patients was 59 years (range: 36-76 years). Of the 119 patients, 26 had intrahepatic cholangiocarcinoma, 29 had hilar cholangiocarcinoma, while 64 had extrahepatic tumors (gallbladder cancer, n = 53; proximal bile duct cancer, n = 10; choledochal cyst cancer, n = 1). Of all, 11 patients (9%) developed gastroduodenal bleeding. In univariate analyses, hepatic artery resection and gastroduodenal wall thickening on postoperative radiation therapy simulation computed tomography were statistically significant factors for gastroduodenal bleeding. Multivariate analysis by a logistic regression model using those two variables revealed that both parameters were independent predictors for gastroduodenal bleeding.

Conclusions

Concomitant hepatic artery resection and presence of gastroduodenal wall thickening on postoperative radiation therapy simulation computed tomography were predictive factors for gastroduodenal bleeding after postoperative radiation therapy in biliary tract cancer. In such cases, patients should be informed of the high risk of gastroduodenal bleeding, and should be closely observed during and after postoperative radiation therapy.

The role of surgical clips in the evaluation of interfractional uncertainty for treatment of hepatobiliary and pancreatic cancer with postoperative radiotherapy

Purpose

To evaluate the utility of implanted surgical clips for detecting interfractional errors in the treatment of hepatobiliary and pancreatic cancer with postoperative radiotherapy (PORT).

Methods and Materials

Twenty patients had been treated with PORT for locally advanced hepatobiliary or pancreatic cancer, from November 2014 to April 2016. Patients underwent computed tomography simulation and were treated in expiratory breathing phase. During treatment, orthogonal kilovoltage (kV) imaging was taken twice a week, and isocenter shifts were made to match bony anatomy. The difference in position of clips between kV images and digitally reconstructed radiographs was determined. Clips were consist of 3 proximal clips (clip_p, ≤2 cm) and 3 distal clips (clip_d, >2 cm), which were classified according to distance from treatment center. The interfractional displacements of clips were measured in the superior-inferior (SI), anterior-posterior (AP), and right-left (RL) directions.

Results

The translocation of clip was well correlated with diaphragm movement in 90.4% (190/210) of all images. The clip position errors greater than 5 mm were observed in 26.0% in SI, 1.8% in AP, and 5.4% in RL directions, respectively. Moreover, the clip position errors greater than 10 mm were observed in 1.9% in SI, 0.2% in AP, and 0.2% in RL directions, despite respiratory control.

Conclusion

Quantitative analysis of surgical clip displacement reflect respiratory motion, setup errors and postoperative change of intraabdominal organ position. Furthermore, position of clips is distinguished easily in verification images. The identification of the surgical clip position may lead to a significant improvement in the accuracy of upper abdominal radiation therapy.