Reduction of Respiratory Motion During PET/CT by Pulsatile-Flow Ventilation: A First Clinical Evaluation

A review of the clinical introduction of 4D particle therapy research concepts

Background and purpose

Many 4D particle therapy research concepts have been recently translated into clinics, however, remaining substantial differences depend on the indication and institute-related aspects. This work aims to summarise current state-of-the-art 4D particle therapy technology and outline a roadmap for future research and developments.

Material and methods

This review focused on the clinical implementation of 4D approaches for imaging, treatment planning, delivery and evaluation based on the 2021 and 2022 4D Treatment Workshops for Particle Therapy as well as a review of the most recent surveys, guidelines and scientific papers dedicated to this topic.

Results

Available technological capabilities for motion surveillance and compensation determined the course of each 4D particle treatment. 4D motion management, delivery techniques and strategies including imaging were diverse and depended on many factors. These included aspects of motion amplitude, tumour location, as well as accelerator technology driving the necessity of centre-specific dosimetric validation. Novel methodologies for X-ray based image processing and MRI for real-time tumour tracking and motion management were shown to have a large potential for online and offline adaptation schemes compensating for potential anatomical changes over the treatment course. The latest research developments were dominated by particle imaging, artificial intelligence methods and FLASH adding another level of complexity but also opportunities in the context of 4D treatments.

Conclusion

This review showed that the rapid technological advances in radiation oncology together with the available intrafractional motion management and adaptive strategies paved the way towards clinical implementation.

Lung CT stabilization with high-frequency non-invasive ventilation (HF-NIV) and breath-hold (BH) in lung nodule assessment by PET/CT

PURPOSE

To evaluate the effect of lung stabilization using high-frequency non-invasive ventilation (HF-NIV) and breath-hold (BH) techniques on lung nodule detection and texture assessment in PET/CT compared to a free-breathing (FB) standard lung CT acquisition in PET/CT.

MATERIALS AND METHODS

Six patients aged 65 ± 7 years, addressed for initial assessment of at least one suspicious lung nodule with 18F-FDG PET/CT, underwent three consecutive lung PET/CT acquisitions with FB, HF-NIV and BH. Lung nodules were assessed on all three CT acquisitions of the PET/CT and characterized for any size, volume and solid/sub-solid nature.

RESULTS

BH detected a significantly higher number of nodules (n = 422) compared to HF-NIV (n = 368) and FB (n = 191) (p < 0.001). The mean nodule size (mm) was 2.4 ± 2.1, 2.6 ± 1.9 and 3.2 ± 2.4 in BH, HF-NIV and FB, respectively, for long axis and 1.5 ± 1.3, 1.6 ± 1.2 and 2.1 ± 1.7 in BH, HF-NIV and FB, respectively, for short axis. Long- and short-axis diameters were significantly different between BH and FB (p < 0.001) and between HF-NIV and FB (p < 0.001 and p = 0.008), but not between BH and HF-NIV. A trend for higher volume was shown in FB compared to BH (p = 0.055) and HF-NIV (p = 0.068) without significant difference between BH and HF-NIV (p = 1). We found a significant difference in detectability of sub-solid nodules between the three acquisitions, with BH showing a higher number of sub-solid nodules (n = 128) compared to HF-NIV (n = 72) and FB (n = 44) (p = 0.002).

CONCLUSION

We observed a higher detection rate of pulmonary nodules on CT under BH or HF-NIV conditions applied to PET/CT than with FB. BH and HF-NIV demonstrated comparable texture assessment and performed better than FB in assessing size and volume. BH showed a better performance for detecting sub-solid nodules compared to HF-NIV and FB. The addition of BH or HF-NIV to PET/CT can help improve the detection and texture characterization of lung nodules by CT, therefore improving the accuracy of oncological lung disease assessment. The ease of use of BH and its added value should prompt its use in routine practice.

Impact of opioid free Anaesthesia versus opioid Anaesthesia on the immediate postoperative oxygenation after bariatric surgery: a prospective observational study

Introduction: Opioid induced respiratory depression (OIRD) is a preventable aetiology of postoperative respiratory depression with 85% of the episodes taking place in the first 24 postoperative hours. Due to altered respiratory functional metrics and frequently coexisting comorbidities, obese patients are at a particularly higher risk for such complications. The present study aimed to assess if an opioid-free anesthesia (OFA) was associated with a reduced immediate postoperative OIRD when compared to Opiod-based anesthesia (OA). Methods: Obese patients presenting for bariatric surgery were consecutively included in a non-randomized fashion. Lung protective ventilation strategies applied in both groups. In the OA group, Sufentanil was used for intraoperative analgesia in a liberal fashion. In the OFA group, patients received a pre-induction dexmedetomidine loading, followed by a lidocaine, ketamine and dexmedetomidine bolus immediately before induction, further maintained throughout the intraoperative period. Plethysmographic saturations were obtained before induction as well as after extubation and in the Post-anesthesia care unit (PACU). Opioid requirement and Postoperative Nausea and Vomiting incidence were similarly registered. Results: Thirty-four patients were included in the OFA group, and 30 in the OA group. No significant anthropometric and comorbidity differences were found between both groups. OFA patients had significantly lower pre-induction saturations after dexmedetomidine loading. No difference was found for post-extubation saturations as well as well as pre-PACU discharge. The need for supplemental oxygen at the PACU was higher in the OA group. Opioid requirement and cumulative consumption (MEDs) were significantly higher with OA. Conclusion: OFA was not associated with significant postoperative saturation changes but led to a lower need of postoperative supplemental oxygen therapy. OA led to higher opioid rescue need. No fatal respiratory complications were registered in both groups in the immediate postoperative period.

Impact of low injected activity on data driven respiratory gating for PET/CT imaging with continuous bed motion

Data driven respiratory gating (DDG) in positron emission tomography (PET) imaging extracts respiratory waveforms from the acquired PET data obviating the need for dedicated external devices. DDG performance, however, degrades with decreasing detected number of coincidence counts. In this paper, we assess the clinical impact of reducing injected activity on a new DDG algorithm designed for PET data acquired with continuous bed motion (CBM_DDG) by evaluating CBM_DDG waveforms, tumor quantification, and physician's perception of motion blur in resultant images. Forty patients were imaged on a Siemens mCT scanner in CBM mode. Reduced injected activity was simulated by generating list mode datasets with 50% and 25% of the original data (100%). CBM_DDG waveforms were compared to that of the original data over the range between the aortic arch and the center of the right kidney using the Pearson correlation coefficient (PCC). Tumor quantification was assessed by comparing the maximum standardized uptake value (SUVmax) and peak SUV (SUVpeak) of reconstructed images from the various list mode datasets using elastic motion deblurring (EMDB) reconstruction. Perceived motion blur was assessed by three radiologists of one lesion per patient on a continuous scale from no motion blur (0) to significant motion blur (3). The mean PCC of the 50% and 25% dataset waveforms was 0.74 ± 0.18 and 0.59 ± 0.25, respectively. In comparison to the 100% datasets, the mean SUVmax increased by 2.25% (p = 0.11) for the 50% datasets and by 3.91% (p = 0.16) for the 25% datasets, while SUVpeak changes were within ±0.25%. Radiologist evaluations of motion blur showed negligible changes with average values of 0.21, 0.3, and 0.28 for the 100%, 50%, and 25% datasets. Decreased injected activities degrades the resultant CBM_DDG respiratory waveforms; however this decrease has minimal impact on quantification and perceived image motion blur.

Percussion assisted radiation therapy in Hodgkin lymphoma allows a marked reduction in heart dose

BACKGROUND AND PURPOSE

Early-stage Hodgkin lymphoma (HL) is a highly curable disease but the treatment can induce late complications many years later. Irradiation of the healthy heart is inevitable during radiation treatment of mediastinal sites. We developed a novel method to induce a prolonged apnea-like state that can help decrease the dose to organs at risk during radiation therapy. We present the results of the first 8 HL patients treated routinely with percussion assisted radiation therapy (PART) in our clinic.

MATERIAL AND METHODS

We used a newly developed high-frequency non-invasive ventilation system to suppress respiratory motion for prolonged periods and push the heart away from the treated volume.

RESULTS

All 8 patients were able to rapidly learn the technique and had an advantage to be treated by PART. We lowered the mean heart dose by an average of 3 Gy with similar target coverage compared to a classical free breathing treatment plan. They were all treated for 15 radiotherapy sessions by PART without any notable side effects.

CONCLUSIONS

Percussion assisted radiation therapy can be used routinely to reduce the dose to the heart in Hodgkin lymphoma.

Mechanically-assisted and non-invasive ventilation for radiation therapy: A safe technique to regularize and modulate internal tumour motion

BACKGROUND AND PURPOSE

Current motion mitigation strategies, like margins, gating, and tracking, deal with geometrical uncertainties in the tumour position, induced by breathing during radiotherapy (RT). However, they often overlook motion variability in amplitude, respiratory rate, or baseline position, when breathing spontaneously. Consequently, this may negatively affect the delivered dose conformality in comparison to the plan. We previously demonstrated on volunteers that 3 different modes of mechanically-assisted and non-invasive ventilation (MANIV) may reduce variability in breathing motion. The volume-controlled mode (VC) constraints the amplitude and respiratory rate (RR) in physiologic condition. The shallow-controlled mode (SH), derived from VC, increases the RR and decreases amplitude. The slow-controlled mode (SL) induces repeated breath holds with constrained ventilation pressure. In this study, we compared these mechanical ventilation modes to spontaneous breathing or breath hold and assessed their tolerance and effects on internal tumour motion in patients receiving RT.

MATERIAL AND METHODS

The VC and SH modes were evaluated in ten patients with lung or liver cancers (cohort A). The SL mode was evaluated in 12 left breast cancer patients (cohort B). After a training and simulation session, the patients underwent 2 MRI sessions to analyze the internal motion of breast and tumour.

RESULTS

MANIV was well tolerated, without any adverse events or oxymetric changes, even in patients with respiratory comorbidities. In cohort A, when compared to spontaneous breathing (SP), VC reduced significantly inter-session variations of the tumour motion amplitude (p = 0.01), as well as intra- and inter-session variations of the RR (p < 0.05). As to SH, the RR increased, while its variations within and across sessions decreased when compared to SP (p < 0.001). SH reduced the median amplitude of the tumour motion by 6.1 mm or 38.2% (p ≤ 0.01) compared to VC. In cohort B, breast position stability over the end-inspiratory plateaus obtained spontaneously or with SL remained similar. Median duration of the plateaus in SL was 16.6 s.

CONCLUSION

MANIV is a safe and well tolerated ventilation technique for patients receiving radiotherapy. MANIV could thus make current motion mitigation strategies less critical and more robust. Clinical implementation might be considered, provided the ventilation mode is carefully selected with respect to the treatment indication and patient individualities.

Ultrashort echo time imaging of the lungs under high-frequency noninvasive ventilation: A new approach to lung imaging

Background

Although ultrashort echo time (UTE) sequences allow excellent assessment of lung parenchyma, image quality remains lower than that of computed tomography (CT).

Purpose

To investigate a high‐frequency noninvasive ventilation (HF‐NIV) technique allowing a stabilized inspiration and to compare image quality with current dedicated MR sequences.

Study Type

Prospective.

Population

Ten healthy volunteers.

Field Strength/Sequence

3D radial UTE sequence at 1.5T.

Assessment

UTE‐HF‐NIV sequence was compared with UTE‐free‐breathing (UTE‐FB), reconstructed at end expiration (UTE‐Exp) and average (UTE‐Avg), and breath‐hold VIBE sequences. The distance from lung apex to the dome of the right hemidiaphragm was measured. Visual assessment of the visibility and sharpness of normal anatomical structures was carried out. Dedicated software also quantitatively evaluated vessel–lung and right lung–liver interface sharpness. Apparent signal ratio (Sr) and contrast ratios (Cr) were quantitatively evaluated.

Statistical Tests

Wilcoxon signed rank test for visual scores, paired t‐test for continuous variables, significance at P < 0.05.

Results

The distance between apex and the right hemidiaphragmatic dome was significantly larger (P < 0.001) with UTE‐HF‐NIV compared with UTE‐FB and VIBE acquisitions. Vessel and airway visibility had identical median visual scores with all UTE methods. Median visual scores for sharpness of vessels and airways were significantly higher (P < 0.001) with HF‐NIV (vessels = 3; airways = 2) than in UTE‐FB (vessels = 2; airways = 1) and VIBE (vessels = 1; airways = 1). Software‐based vessel sharpness evaluation resulted in larger values in 8/10 volunteers with UTE‐HF‐NIV (67.3 ± 9.8) compared with UTE‐Avg (62.3 ± 12.6) but the average difference was not significant (P = 0.28). The sharpness of the lung–liver interface was significantly higher (P < 0.001) with HF‐NIV (17.3 ± 5.3) compared with UTE‐Avg (14.1 ± 3.9). Significantly higher values (P < 0.01) of Sr and Cr were observed with UTE‐HF‐NIV compared with UTE‐FB and VIBE.

Data Conclusion

HF‐NIV allowing acquisition at full inspiration significantly improves image quality for lung imaging. This could offer the option to alternate some follow‐up CT studies by using this technique.

Level of Evidence: 2

Technical Efficacy: Stage 1

J. Magn. Reson. Imaging 2019;50:1789–1797.

High frequency percussive ventilation for respiratory immobilization in radiotherapy

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HFPV maybe a tool for immobilizing thoracic targets in radiotherapy.

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The procedure itself was well tolerated and well complied.

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Chest wall motion was significantly reduced by greater than 60%.

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HFPV can be greatly advantageous, particularly for SBRT and PBS proton therapy.

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Duty cycle under HFPV was significantly higher than conventional methods.

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The appropriate interface can lead to extensive HFPV prolonged times.

High frequency percussive ventilation (HFPV) employs high frequency low tidal volumes (100–400 bursts/min) to provide respiration in awake patients while simultaneously reducing respiratory motion. The purpose of this study is to evaluate HFPV as a technique for respiratory motion immobilization in radiotherapy. In this study fifteen healthy volunteers (age 30–75 y) underwent HFPV using three different oral interfaces. We evaluated each HFPV oral interface device for compliance, ease of use, comfort, geometric interference, minimal chest wall motion, duty cycle and prolonged percussive time. Their chest wall motion was monitored using an external respiratory motion laser system. The percussive ventilations were delivered via an air driven pneumatic system. All volunteers were monitored for PO₂ and tc-CO₂ with a pulse oximeter and CO₂ Monitoring System. A total of N = 62 percussive sessions were analyzed from the external respiratory motion laser system. Chest-wall motion was well tolerated and drastically reduced using HFPV in each volunteer evaluated. As a result, we believe HFPV may provide thoracic immobilization during radiotherapy, particularly for SBRT and pencil beam scanning proton therapy.

Quantification of Lung PET Images: Challenges and Opportunities

Millions of people are affected by respiratory diseases, leading to a significant health burden globally. Because of the current insufficient knowledge of the underlying mechanisms that lead to the development and progression of respiratory diseases, treatment options remain limited. To overcome this limitation and understand the associated molecular changes, noninvasive imaging techniques such as PET and SPECT have been explored for biomarker development, with ¹⁸F-FDG PET imaging being the most studied. The quantification of pulmonary molecular imaging data remains challenging because of variations in tissue, air, blood, and water fractions within the lungs. The proportions of these components further differ depending on the lung disease. Therefore, different quantification approaches have been proposed to address these variabilities. However, no standardized approach has been developed to date. This article reviews the data evaluating ¹⁸F-FDG PET quantification approaches in lung diseases, focusing on methods to account for variations in lung components and the interpretation of the derived parameters. The diseases reviewed include acute respiratory distress syndrome, chronic obstructive pulmonary disease, and interstitial lung diseases such as idiopathic pulmonary fibrosis. Based on review of prior literature, ongoing research, and discussions among the authors, suggested considerations are presented to assist with the interpretation of the derived parameters from these approaches and the design of future studies.