Respiratory Gating System Research Articles

Dosimetric calibration of anatomy-specific ultra-high dose rate electron irradiation platform for preclinical FLASH radiobiology experiments.

FLASH radiation therapy (RT) offers a promising avenue for the broadening of the therapeutic index. However, to leverage the full potential of FLASH in the clinical setting, an improved understanding of the biological principles involved is critical. This requires the availability of specialized equipment optimized for the delivery of conventional (CONV) and ultra-high dose rate (UHDR) irradiation for preclinical studies. One method to conduct such preclinical radiobiological research involves adapting a clinical linear accelerator configured to deliver both CONV and UHDR irradiation. We characterized the dosimetric properties of a clinical linear accelerator configured to deliver ultra-high dose rate irradiation to two anatomic sites in mice and for cell-culture FLASH radiobiology experiments. Delivered doses of UHDR electron beams were controlled by a microcontroller and relay interfaced with the respiratory gating system. We also produced beam collimators with indexed stereotactic mouse positioning devices to provide anatomically specific preclinical treatments. Treatment delivery was monitored directly with an ionization chamber, and charge measurements were correlated with radiochromic film measurements at the entry surface of the mice. The setup for conventional dose rate irradiation utilized the same collimation system but at increased source-to-surface distance. Monte Carlo simulations and film dosimetry were used to characterize beam properties and dose distributions. The mean electron beam energies before the flattening filter were 18.8 MeV (UHDR) and 17.7 MeV (CONV), with corresponding values at the mouse surface of 17.2 and 16.2 MeV. The charges measured with an external ion chamber were linearly correlated with the mouse entrance dose. The use of relay gating for pulse control initially led to a delivery failure rate of 20% (±1 pulse); adjustments to account for the linac latency improved this rate to<1/20. Beam field sizes for two anatomically specific mouse collimators (4 × 4 cm2 for whole-abdomen and 1.5 × 1.5 cm2 for unilateral lung irradiation) were accurate within<5% and had low radiation leakage (<4%). Normalizing the dose at the center of the mouse (∼0.75cm depth) produced UHDR and CONV doses to the irradiated volumes with>95% agreement. We successfully configured a clinical linear accelerator for increased output and developed a robust preclinical platform for anatomically specific irradiation, with highly accurate and precise temporal and spatial dose delivery, for both CONV and UHDR irradiation applications.

High-speed bioimpedance-based gating system for radiotherapy: Prototype and proof of principle.

To investigate a novel bioimpedance-based respiratory gating system (BRGS) designed for external beam radiotherapy and to evaluate its technical characteristics in comparison with existing similar systems. The BRGS was tested on three healthy volunteers in free breathing and breath-hold patterns under laboratory conditions. Its parameters, including the time delay (TD) between the actual impedance change and the gating signal, temperature drift, root mean square (RMS) noise, and signal-to-noise ratio (SNR), were measured and analyzed. The gate-on TD and the gate-off TD were found to be 9.0±2.0ms [mean±standard deviation (M±SD)] and 7.2±1.3ms, respectively. The temperature drift of the BRGS output signal was 0.02 Ω after 30 min of operation. RMS noise averaged 0.14±0.05 Ω (M±SD) for all subjects and varied from 0.08 to 0.20 Ω with repeated measurements. A significant difference in SNR (p<0.001) was observed between subjects, ranging from 4 to 15. The evaluated bioimpedance-based gating system showed a high performance in real-time respiratory monitoring and may potentially be used as an external surrogate guidance for respiratory-gated external beam radiotherapy. Direct comparison with commercially available systems, 4D correlation studies, and expansion of the patient sample are goals for future preclinical studies.

Efficient EPID-based quality assurance of beam time delay for respiratory-gated radiotherapy with validation on Catalyst™ and AlignRT™ systems.

To propose a straightforward and time-efficient quality assurance (QA) approach of beam time delay for respiratory-gated radiotherapy and validate the proposed method on typical respiratory gating systems, Catalyst™ and AlignRT™. The QA apparatus was composed of a motion platform and a Winston-Lutz cube phantom (WL3) embedded with metal balls. The apparatus was first scanned in CT-Sim and two types of QA plans specific for beam on and beam off time delay, respectively, were designed. Static reference images and motion testing images of the WL3 cube were acquired with EPID. By comparing the position differences of the embedded metal balls in the motion and reference images, beam time delays were determined. The proposed approach was validated on three linacs with either Catalyst™ or AlignRT™ respiratory gating systems. To investigate the impact of energy and dose rate on beam time delay, a range of QA plans with Eclipse (V15.7) were devised with varying energy and dose rates. For all energies, the beam on time delays in AlignRT™ V6.3.226, AlignRT™ V7.1.1, and Catalyst™ were 92.13 5.79ms, 123.11 6.44ms, and 303.44 4.28ms, respectively. The beam off time delays in AlignRT™ V6.3.226, AlignRT™ V7.1.1, and Catalyst™ were 121.87 1.34ms, 119.33 0.75ms, and 97.69 2.02ms, respectively. Furthermore, the beam on delays decreased slightly as dose rates increased for all gating systems, whereas the beam off delays remained unaffected. The validation results demonstrate the proposed QA approach of beam time delay for respiratory-gated radiotherapy was both reproducible and time-efficient to practice for institutions to customize accordingly.

Impact of Respiratory-gated 4D PET/CT Scan for Motion Correction in Characterizing Lesions Adjacent to the Diaphragm - A Cross-sectional Study at a Tertiary Care Institute.

The blur introduced by breathing motion degrades the diagnostic accuracy of whole-body F-18 fluorodeoxyglucose positron emission tomography-computed tomography (18F-FDG PET-CT) in lesions adjacent to the diaphragm by increasing the apparent size and by decreasing their metabolic activity. This study aims to evaluate the efficacy of motion correction by four-dimensional phase-based respiratory-gated (RG) 18F-FDG PET-CT in improving metabolic parameters of lesions adjacent to the diaphragm (especially in the lungs or liver). Eighteen patients with known lung or liver lesions underwent conventional 18F-FDG PET-CT and respiratory-gated PET-CT acquisition of the desired region using a pressure-sensing, phase-based respiratory-gating system. Maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) were obtained for these lesions from gated and nongated PET-CT images for analysis. Furthermore, a visual analysis of lesions was done. Statistical significance of the RG image parameters was assessed by the two-tailed paired Student's t test and confirmed with the robust nonparametric Wilcoxon's signed-rank test (two-tailed asymptotic). There was an overall significant increase in SUVmax (P 0.001) in all gating methods with a percentage increase maximum of about 18.13%. On gating methods, MTV decreased significantly (P = 0.001) than that of nongating method (maximum reduction of about 32.9%). There was a significant difference (P = 0.02) in TLG between gated and nongated methods. Motion correction with phase-based respiratory gating improves the diagnostic value of 18F-FDG PET-CT imaging for lung and liver lesions by more accurate delineation of the lesion volume and quantitation of SUV and can thus impact staging, diagnosis as well as management in selected patients.

Comprehensive beam delivery latency evaluation for gated proton therapy system using customized multi-channel signal acquisition platform.

Beam delivery latency in respiratory-gated particle therapy systems is a crucial issue to dose delivery accuracy. The aim of this study is to develop a multi-channel signal acquisition platform for investigating gating latencies occurring within RPM respiratory gating system (Varian, USA) and ProBeam proton treatment system (Varian, USA) individually. The multi-channel signal acquisition platform consisted of several electronic components, including a string position sensor for target motion detection, a photodiode for proton beam sensing, an interfacing board for accessing the trigger signal between the respiratory gating system and the proton treatment system, a signal acquisition device for sampling and synchronizing signals from the aforementioned components, and a laptop for controlling the signal acquisition device and data storage. RPM system latencies were determined by comparing the expected gating phases extracted from the motion signal with the trigger signal's state turning points. ProBeam system latencies were assessed by comparing the state turning points of the trigger signal with the beam signal. The total beam delivery latencies were calculated as the sum of delays in the respiratory gating system and the cyclotron proton treatment system. During latency measurements, simulated sinusoidal motion were applied at different amplitudes and periods for complete beam delivery latency evaluation under different breathing patterns. Each breathing pattern was repeated 30 times for statistical analysis. The measured gating ON/OFF latencies in the RPM system were found to be 104.20±13.64ms and 113.60±14.98ms, respectively. The measured gating ON/OFF delays in the ProBeam system were 108.29±0.85ms and 1.20±0.04ms, respectively. The total beam ON/OFF latencies were determined to be 212.50±13.64ms and 114.80±14.98ms. With the developed multi-channel signal acquisition platform, it was able to investigate the gating lags happened in both the respiratory gating system and the proton treatment system. The resolution of the platform is enough to distinguish the delays at the millisecond time level. Both the respiratory gating system and the proton treatment system made contributions to gating latency. Both systems contributed nearly equally to the total beam ON latency, with approximately 100ms. In contrast, the respiratory gating system was the dominant contributor to the total beam OFF latency.

Chest Wall to Heart Distance Reproducibility in Postoperative Deep Inspiration Breath-Hold Radiotherapy for Left-Sided Breast Cancer Using an Anzai Laser Sensor With Visual Feedback.

Background Left-sided breast cancer radiotherapy may increase the risk of cardiovascular death due to possible heart irradiation. Thereproducibility of the chest wall to heart distance in deep inspiration breath-hold (DIBH) was studied using a laser sensor with visual feedback. Methodology A total of 10 consecutive postoperative left-sided breast cancer cases receiving DIBH radiotherapy between December 2022 and September 2023 were retrospectively investigated. The prescribed dose was 50 Gy in 25 fractions. An Anzai respiratory gating system, AZ-733VI (Anzai, Tokyo, Japan), was employed that has a laser displacement sensor and a visual feedback device. An Elekta linac with a cone-beam CT unit, Axesse (Elekta AB, Stockholm, Sweden), was used in this study. The interfractional changes in the chest wall to heart distance among 25 fractions were analyzed for each of the 10 patients in each coordinate axis. In addition, the median with the 95% confidence interval (CI) and interquartile range (IQR) for all 250 fractions were calculated in each axis to assess the reproducibility of our DIBH technique. Results The medians of the interfractional changes in the chest wall to heart distance in each of the 10 patients ranged from -2 mm to 3 mm, -1 mm to 3 mm, and -2 mm to 1 mm in the lateral (X), superior-inferior (Y), and anterior-posterior (Z) directions, respectively. For all 10 cases, the medians were 1 mm (95% CI = 0.72 to 1.28 mm) in X, 1 mm (95% CI = 0.76 to 1.24 mm) in Y, and 0 mm (95% CI = -0.20 to 0.20 mm) in Z directions, whereas the IQRs were 4 mm in X, 2 mm in Y and 2 mm in Z directions. The measured IQRs were two to three times smaller than those shown in a previous report without visual feedback, suggesting a clinical advantage of the visual feedback in DIBH for left-sided breast cancer radiotherapy. The DIBH solution shown in this study required approximately 10 minutes from room-in to room-out, thereby not reducing the daily number of patients. Conclusions Our DIBH approach with visual feedback achieved better distance reproducibility between the chest wall and heart by a factor of two to three in terms of IQR compared to the previously reported data without visual feedback. Patient throughput was also favorable. To our knowledge, this is the first report demonstrating the chest wall to heart distance reproducibility in DIBH with visual feedback.

Study on the Clinical Use of a Respiratory Navigator Combined with Breath-Hold for MRI- Guided Liver SBRT

Respiratory movement strongly affects the accuracy of stereotactic body radiation therapy (SBRT) of liver malignancies treated without the use of a respiratory gating system. This study investigates the feasibility and advantages of using a respiratory navigator-guided combined with patient breath-hold for liver SBRT in an adaptive magnetic-resonance guided workflow. Clinical datasets of 10 liver cancer patients treated with 1.5T MR-Linac with respiratory navigator-guided SBRT combined with patient breath-hold were retrospectively analyzed. All patients underwent simulation CT with and without contrast, and 4D-CT and 3D-T2w MRI without contrast. Patients received a prescription dose ranging from 36 to 50 Gy in 5 to 8 fractions and followed the adapt to shape (ATS) workflow including contours adjustment and a subsequent MR-based synthetic CT (sCT) calculation on the online MRI acquired. The reference treatment plan was optimized on the expiratory phase of the 4D-CT, and during the online session the contours and the adapted plans were performed using the 3D-T2w navigator MRI of the patient's end-expiratory signal; 2D-T2w real-time monitoring MRI was also used as support for the contour's definition. The radiation therapist instructed the patients to hold their breath at the end of the breathing cycle for the time of the beam on. A total of 59 fractions were analyzed. For each fraction the dosimetric parameters of the target and normal liver of the adaptive and reference plans were compared; particularly the volume, the conformity index (CI) and gradient index (GI) for the target, and V5, V10 and Dmean for the normal liver. T-student statistical analysis was performed; a p-value less than 0.05 was considered statistically significant. In the free breathing state, the 3D-T2w navigator MRI images enable a clear visualization of the tumor and its boundaries. The average target CI of the adaptive and reference plans is not significantly different (p = 0.448), while the GI is significantly higher (p = 0.043). Normal liver V10 and Dmean are lower and V5 is slightly increased, but without statistical differences. The mean values and standard deviation of the dosimetric parameters of the reference and adapted plans are shown in the Table below. The use of a respiratory navigator combined with the breath-hold for MRI- guided liver SBRT allows clear visualization of the tumor, ensures the accuracy of the delivered dose and may be considered an alternative when the respiratory gating system is not available during MRgART sessions.

Respiration-controlled radiotherapy in lung cancer: Systematic evaluation of the optimal application practice

Background and purposeDefinitive radiochemotherapy (RCT) for non-small cell lung cancer (NSCLC) in UICC/TNM I–IVA (singular, oligometastatic) is one of the treatment methods with a potentially curative concept. However, tumour respiratory motion during RT requires exact pre-planning. There are various techniques of motion management like creating internal target volume (ITV), gating, inspiration breath–hold and tracking. The primary goal is to cover the PTV with the prescribed dose while at the same time maximizing dose reduction of surrounding normal tissues (organs at risk, OAR). In this study, two standardized online breath–controlled application techniques used alternately in our department are compared with respect to lung and heart dose. Materials and methodsTwenty-four patients who were indicated for thoracic RT received planning CTs in voluntary deep inspiration breath-hold (DIBH) and in free shallow breathing, prospectively gated in expiration (FB-EH). A respiratory gating system by Varian (Real-time Position Management, RPM) was used for monitoring. OAR, GTV, CTV and PTV were contoured on both planning CTs. The PTV margin to the CTV was 5 mm in the axial and 6–8 mm in the cranio-caudal direction. The consistency of the contours was checked by elastic deformation (Varian Eclipse Version 15.5). RT plans were generated and compared in both breathing positions using the same technique, IMRT over fixed irradiation directions or VMAT. The patients were treated in a prospective registry study with the approval of the local ethics committee. ResultsThe PTV in expiration (FB-EH) was on average significantly smaller than the PTV in inspiration (DIBH): for tumours in the lower lobe (LL) 431.5 vs. 477.6 ml (Wilcoxon test for connected samples; p = 0.004), in the upper lobe (UL) 659.5 vs. 686.8 ml (p = 0.005). The intra-patient comparison of plans in DIBH and FB-EH showed superiority of DIBH for UL-tumours and equality of DIBH and FB-EH for LL-tumours. The dose for OAR in UL-tumours was lower in DIBH than in FB-EH (mean lung dose p = 0.011; lungV20, p = 0.002; mean heart dose p = 0.016). The plans for LL-tumours in FB-EH showed no difference in OAR compared to DIBH (mean lung dose p = 0.683; V20Gy p = 0.33; mean heart dose p = 0.929). The RT setting was controlled online for each fraction and was robustly reproducible in FB-EH. ConclusionRT plans for treating lung tumours implemented depend on the reproducibility of the DIBH and advantages of the respiratory situation with respect to OAR. The primary tumour localization in UL correlates with advantages of RT in DIBH, compared to FB-EH. For LL-tumours there is no difference between RT in FB-EH and RT in DIBH with respect to heart or lung exposure and therefore, reproducibility is the dominant criterion. FB-EH is recommended as a very robust and efficient technique for LL-tumours.

A sugárkezelés okozta cardiotoxicitas kockázatának csökkentése bal oldali emlőtumoros betegek kezelése során

Breast cancer is one of the most common malignancies affecting women. Treatment with drugs and radiotherapy increases the incidence of late cardiovascular disease. It is therefore particularly important to protect the heart from radiation exposure. We prepared an irradiation plan for 45 patients with left breast cancer using deep breathing and normal breathing techniques. The plans were compared and analyzed. The irradiation plans were created in the Philips Pinnacle v. 16 planning system. At the same target volume coverage, the use of the deep breathing technique leads to a reduction of the dose burden to the heart and to the left descending coronary branch, thus reducing the incidence of late cardiovascular complications. The results obtained show that the use of the deep breathing technique during adjuvant radiotherapy of left-sided breast cancer patients has a beneficial effect on the radiation exposure of the heart. Our results are in good agreement with similar data from national centres. We were not only able to maintain planning target volume coverage, but also to achieve an improvement of 1%. There is a significant difference in dose to the heart and coronary artery. By using the deep breathing technique, we were able to reduce the average cardiac dose by almost half (deep breathing: 2.87 Gy, normal breathing: 5.4 Gy). The coronary exposure was reduced from 19.5 Gy to 10.98 Gy. The accuracy of treatment can be further improved by using a respiratory gating system with a surface-guided radiotherapy system. The successful use of deep breathing technique requires professionalism of the treatment staff and good patient cooperation. It is less equipment intensive than a respiration-guided system. The deep breathing technique is no longer considered state-of-the-art in the era of breath-holding, but the experience gained in our department is worth describing because of its relevance to oncocardiology. Orv Hetil. 2023; 164(11): 420-425.

The Analysis of Correction Effect of Motion Artifacts in PET Images Using Respiratory Gating System

PET is used effectively for biochemical or pathological phenomena, disease diagnosis, prognosis determination after treatment, and treatment planning because it can quantify physiological indicators in the human body by imaging the distribution of various biochemical substances. However, since respiratory motion artifacts may occur due to the movement of the diaphragm due to breathing, we would like to evaluate the practical effect by using the a device-less data-driven gated technique called Motion Free (DDG) with the phase-based gating correction method called Q.static scan mode. In this study, images of changes in moving distance (0 cm, 1 cm, 2 cm, 3 cm) and degree of slope (0°, 2.5°, 5°, 10°) were acquired using a breathing-simulated moving phantom. The diameters of the six spheres in the phantom are 10 mm, 13 mm, 17 mm, 22 mm, 28 mm, and 37 mm, respectively. According to SUVmax and SUVmean measurements, when DDG was applied based on the moving distance, the average SUVmax of the correction effect by the moving distance was improved by 1.92, 2.48, 3.23 and 3.00, respectively, and the average SUVmean was improved by 0.04, 0.72, 1.36 and 1.49, respectively. When DDG was applied based on the diameter of the phantom spheres, the average SUVmax of the correction effect by the moving distance was improved by 2.37, 2.02, 1.44, 1.20, 0.42 and 0.52, and the average SUVmean was improved by 1.36, 1.23, 0.99, 0.82, 0.57 and 0.43, respectively. The correction effect by the degree of slope also improved the average SUVmax when DDG was applied to 2.93, 2.87, 1.61 and 1.45 respectively, and the average SUVmean to 1.61, 1.27, 0.8 and 0.95 respectively, based on the degree of slope. when DDG was applied based on the diameter of the phantom sphere, the average SUVmax was improved by 0.77, 1.73, 1.84, 2.56, 3.46 and 2.93 respectively and the average SUVmean was improved by 0.56, 0.44, 1.19, 0.98, 1.66 and 2.13, respectively. In the visual comparison due to the change of the moving distance and the degree of slope, it was found that the more the moving distance increases, the greater the degree of slope increases, the greater the correction effect of DDG. In the case of the area ratio, Based on the image with a moving distance of 0 cm, when moving distance was 1 cm, 2 cm and 3 cm, the difference between applying and not applying DDG was 5%, 12%, and 18%, respectively. Based on an image with degree of slope of 0°, when degree of slope was 2.5°, 5° and 10°, the difference between applying and not applying DDG was 6%, 7%, and 7%, respectively. In the case of the average density ratio, Based on an image with a moving distance of 0 cm, when moving distance was 1 cm, 2 cm and 3 cm, the difference between applying and not applying DDG was 3%, 6%, and 8%, respectively. Based on an image with degree of slope of 0°, when degree of slope was 2.5°, 5° and 10°, the difference between applying and not applying DDG was 3%, 4%, and 5%, respectively. In the comparison of FWM, FWHM, and FWTM, Based on the image with a moving distance of 0 cm, when moving distance was 1 cm, 2 cm and 3 cm, the difference between applying and not applying DDG was 1.6%, 9% and 9.4% in FWM, 4.4%, 7.6% and 6.4% in FWHM, 12.1%, 23.4% and 30.5% in FWTM respectively. Based on an image with degree of slope of 0°, when degree of slope was 2.5°, 5° and 10°, the difference between applying and not applying DDG was 3.0%, 3.2% and 11.7% in FWM, 2.7%, 5.0% and 2.3% in FWHM, 12.2%, 6.3%, and 7.5% in FWTM respectively. It means there is a quantitative correction effect when applying DDG. This shows that the overall experiment has a correction effect when applying DDG.

Measurement of the temporal latency of a respiratory gating system using two distinct approaches.

PurposeTo develop a methodology that can be used to measure the temporal latency of a respiratory gating system.MethodsThe gating system was composed of an automatic gating interface (Response) and an in‐house respiratory motion monitoring system featuring an optically tracked surface marker. Two approaches were used to measure gating latencies. A modular approach involved measuring separately the latency of the gating system's complementary metal–oxide–semiconductor tracking camera, tracking software, and a gating latency of the LINAC. Additionally, an end‐to‐end approach was used to measure the total latency of the gating system. End‐to‐end latencies were measured using the displacement of a radiographic target moving at known velocities during the gating process.ResultsSumming together the latencies of each of the modular components investigated yielded a total beam‐on latency of 1.55 s and a total beam‐off latency of 0.49 s. End‐to‐end beam‐on and beam‐off latency was found to be 1.49 and 0.34 s, respectively. In each case, no statistically significant differences were found between the end‐to‐end latency of the gating system and the summation of the individually measured components.ConclusionTwo distinct approaches to quantify gating latencies were presented. Measuring the end‐to‐end latency of the gating system provided an independent means of validating the modular approach. It is expected that the beam‐on latencies reported in this work could be reduced by altering the control system configuration of the LINAC. The modular approach can be used to decouple the individual latencies of the gating system, but future improvements in the temporal resolution of the service graphing feature are needed to reduce the uncertainty of LINAC‐related gating latencies measured using this approach. Both approaches are generalizable and can be used together when designing a quality assurance program for a respiratory gating system.

Monitoring Respiratory Motion during VMAT Treatment Delivery Using Ultra-Wideband Radar.

The goal of this paper is to evaluate the potential of a low-cost, ultra-wideband radar system for detecting and monitoring respiratory motion during radiation therapy treatment delivery. Radar signals from breathing motion patterns simulated using a respiratory motion phantom were captured during volumetric modulated arc therapy (VMAT) delivery. Gantry motion causes strong interference affecting the quality of the extracted respiration motion signal. We developed an artificial neural network (ANN) model for recovering the breathing motion patterns. Next, automated classification into four classes of breathing amplitudes is performed, including no breathing, breath hold, free breathing and deep inspiration. Breathing motion patterns extracted from the radar signal are in excellent agreement with the reference data recorded by the respiratory motion phantom. The classification accuracy of simulated deep inspiration breath hold breathing was 94% under the worst case interference from gantry motion and linac operation. Ultra-wideband radar systems can achieve accurate breathing rate estimation in real-time during dynamic radiation delivery. This technology serves as a viable alternative to motion detection and respiratory gating systems based on surface detection, and is well-suited to dynamic radiation treatment techniques. Novelties of this work include detection of the breathing signal using radar during strong interference from simultaneous gantry motion, and using ANN to perform adaptive signal processing to recover breathing signal from large interference signals in real time.

Performance Evaluation of Visual Guidance Patient-Controlled Respiratory Gating System for Respiratory-Gated Magnetic-Resonance Image-Guided Radiation Therapy

To evaluate the performance of visual guidance patient-controlled (VG-PC) respiratory gating system for respiratory-gated magnetic-resonance image-guided radiation therapy (MR-IGRT) and to investigate the relationship between patient specific factors and the performance of the system.The VG-PC respiratory gating system consists of a beam projector in the treatment room to project the near-real-time cine planar MR images inside the bore of the system in order for patients to monitor the images during treatment. With the visual information, patients voluntarily control their respiration to put the target volume into the gating boundary (gating window). A total of 15 patients with lung or liver tumors who were scheduled for stereotactic ablative radiotherapy (SABR) were selected for the study. A comprehensive instruction about the VG-PC gating system was given to patients before the first treatment. Some of the fractions were treated with the respiratory-gated MR-IGRT combined with the VG-PC gating system, while the remainder of the treatment was performed without the VG-PC gating system (free-breathing). For each fraction the total treatment time, beam-off time owing to the respiratory gating, and number of beam-off events during whole treatment session were analyzed.The average beam-off times due to respiratory gating with and without the VG-PC gating system were 806.0 ± 531.46 s and 1163.7 ± 773.9 s respectively (P < 0.05). Consequently, the average total treatment time was reduced from 2033.5 ± 928.0 s to 1674.7 ± 727.7 s by using the VG-PC gating system (P < 0.05). The average number of beam-off events during whole treatment session was reduced from 395 ± 213 times to 196 ± 127 times by using the VG-PC gating system (P < 0.001). The percent decrease in the average beam-off times due to respiratory gating, the average total treatment time, and the average number of beam-off events for patients with lung cancer are 22.5%, 37.6%, and 51.2% respectively and 3.5%, 6.9% and 47.2% respectively for patients with liver cancer.The VG-PC gating system could improve treatment efficiency when performing respiratory gated MR-IGRT for patients with lung or liver cancer. However, there were no evidences to suggest that other factors including patient's sex, age, and the exact location of the tumor have effect on the performance of the VG-PC gating system.H. Choun: None. H. An: None. H.Jin: None. J. Kim: None. C. Choi: None. J. Park: None.

Anatomical Predictors of Dosimetric Advantages for Deep-inspiration-breath-hold 3D-conformal Radiotherapy Among Women With Left Breast Cancer.

This study aimed to analyze the dosimetric gain of the deep-inspiration-breath-hold (DIBH) technique over the free-breathing (FB) one in left breast cancer (LBC) 3D-conformal-radiotherapy (3D-CRT), and simultaneously investigate the anatomical parameters related to heart RT-exposure. Treatment plans were generated in both DIBH and FB scenarios for 116 LBC patients monitored by the Varian RPM™ respiratory gating system for delivery of conventional or moderately hypofractionated schedules (±sequential boost). For comparison, we considered cardiac and ipsilateral lung doses and volumes. A significant reduction of cardiac and pulmonary doses using DIBH technique was achieved compared to FB plans. Larger clinical target volumes generally need longer distance between medial and lateral entrances of tangent fields at body surface, thus conditioning a worse heart RT-exposure. The DIBH technique reduces cardiac and pulmonary doses for LBC patients. Through easily detectable anatomical parameters, it is possible to predict which patients benefit most from DIBH-RT.

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 SUVmax and decreased the threshold-defined lesion volume. Compared with RPM-gated, DDG-retro gave an average increase in SUVmax 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.

Dosimetric Correlation Between The Depth of Chest Wall Expansion and Heart Dose in Left Breast Cancer Irradiation Using Deep Inspiratory Breath Hold Technique

Introduction and Objective: In adjuvant radiotherapy for left breast cancer, a significant heart volume may be included in the radiation field leading to long-term cardiac toxicities. Deep inspiratory breath hold technique (DIBH) leads to chest wall separation away from the heart and thus can reduce the heart dose compared to free breathing technique. The aim of this study is to correlate dosimetrically the degree of chest wall expansion measured on planning 4D-CT scan to the heart dose in left breast cancer irradiation using DIBH technique. Materials and Methods: Thirty four patients with left breast cancer planned for adjuvant radiotherapy were included. All patients were scanned by Varian RPM (Real Time Position Managment) respiratory gating system using infrared reflecting markers and a video camera to detect the respiratory motion. IMRT or VMAT plans were done for all patients with a prescribed dose 50Gy/25fr/5w with or without operative bed boost dose 10Gy/5fr/1w. The degree of chest wall expansion was identified by measuring the amplitude of DIBH breathing curve from baseline in planning 4D-CT scan in centimeters. The depth of expansion was correlated dosimetrically with the heart V20, V30, and mean heartdose. Results: The mean distance of chest wall expansion was 2.9cm. The mean left lung dose was 8.6Gy. The mean left lung V20 was 13.8%. The mean heart dose was 1.8Gy. The mean heart V30 was 0.6%. A statistically significant reduction of the mean heart dose and V30 was observed with chest wall expansion of 1.4cm or higher (p&lt;0.05). Conclusion: In DIBH technique, the depth of chest wall expansion in 4DCT planning is dosimetrically correlated with the cardiac dose reduction during adjuvant irradiation of left breast cancer. Further clinical studies are needed to translate this dosimetric advantage into clinical benefit.

Proceedings to the 6th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA): 14-16 October 2019, Hosted by Miami Cancer Institute, part of Baptist Health South Florida, Miami, FL, USA.

Proceedings to the 6th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA): 14-16 October 2019, Hosted by Miami Cancer Institute, part of Baptist Health South Florida, Miami, FL, USA.

A Retrospective Respiratory Gating System Based on Epipolar Consistency Conditions

A Retrospective Respiratory Gating System Based on Epipolar Consistency Conditions

Gated Radiotherapy Development and its Expansion.

One of the most important challenges in treatment of patients with cancerous tumors of chest and abdominal areas is organ movement. The delivery of treatment radiation doses to tumor tissue is a challenging matter while protecting healthy and radio sensitive tissues. Since the movement of organs due to respiration causes a discrepancy in the middle of planned and delivered dose distributions. The moderation in the fatalistic effect of intra-fractional target travel on the radiation therapy correctness is necessary for cutting-edge methods of motion remote monitoring and cancerous growth irradiancy. Tracking respiratory milling and implementation of breath-hold techniques by respiratory gating systems have been used for compensation of respiratory motion negative effects. Therefore, these systems help us to deliver precise treatments and also protect healthy and critical organs. It seems aspiration should be kept under observation all over treatment period employing tracking seed markers (e.g. fiducials), skin surface scanners (e.g. camera and laser monitoring systems) and aspiration detectors (e.g. spirometers). However, these systems are not readily available for most radiotherapy centers around the word. It is believed that providing and expanding the required equipment, gated radiotherapy will be a routine technique for treatment of chest and abdominal tumors in all clinical radiotherapy centers in the world by considering benefits of respiratory gating techniques in increasing efficiency of patient treatment in the near future. This review explains the different technologies and systems as well as some strategies available for motion management in radiotherapy centers.

An affordable custom phantom for measurement of linac time delay in gated treatments with irregular breathing.

Respiratory gated treatments are now common in order to reduce tumour motion uncertainties due to breathing. One issue associated with gated treatments is the time delay between the gating system and the linear accelerator. In this study we develop and characterise an affordable phantom to be used in routine and patient specific quality assurance (QA) of the Varian Real-Time Position Management™ (RPM) system. A photodiode has been incorporated into the phantom in order to estimate the time delay. A commercial Quasar phantom was customised to incorporate two stepper motors which independently control an anterior-posterior abdomen/thorax moving plate, and an inferior-superior moving lung insert. A photodiode placed in the path of the radiation is used to measure when beam on/off occurs. Two Arduino microcontroller boards have been utilised to control the motors, read the photodiode and write to an SD card. The measured beam on/off, correlated to the known positions of the phantom is compared to the gate window for RPM. The time delay was measured for sinusoidal movements with a period of 7.50s and 3.75s, and for three patient breathing traces. For the sinusoidal movements, time delays of 150 ± 34ms and 39 ± 34ms were measured, for 7.50s and 3.75s periods, respectively. In the case of the patients' breathing traces time delays of 135 ± 26ms, 137 ± 34ms and 129 ± 28ms were measured. An affordable motion phantom has been developed for routine and patient specific QA of respiratory gating systems. It is capable of reproducing a patient's breathing waveform and performing time delay measurements with a photodiode. Results indicate a time delay of the order of 0.1-0.2s for the RPM system.