Respiratory-gated Radiotherapy Research Articles

Clinical Implementation and Initial Validation of Respiratory-Gated Stereotactic Body Radiotherapy for Thoracoabdominal Tumors Under Abdominal Compression Using an Anzai Laser-Based Gating Device With Visual Guidance on an Elekta Linear Accelerator

Clinical Implementation and Initial Validation of Respiratory-Gated Stereotactic Body Radiotherapy for Thoracoabdominal Tumors Under Abdominal Compression Using an Anzai Laser-Based Gating Device With Visual Guidance on an Elekta Linear Accelerator

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.

Benefit of respiratory gating in the Danish Breast Cancer Group partial breast irradiation trial

Background and purposePartial breast irradiation (PBI)has beenthe Danish Breast Cancer Group(DBCG) standard for selected breast cancer patients since 2016 based onearlyresults from the DBCG PBI trial.During trial accrual, respiratory-gated radiotherapy was introduced in Denmark. This study aims to investigate the effect of respiratory-gating on mean heart dose (MHD). Patients and methodsFrom 2009 to 2016 the DBCG PBI trial included 230 patientswith left-sided breast cancer receiving external beam PBI, 40 Gy/15 fractions/3 weeks.Localization of the tumor bed on the planning CT scan, the use of respiratory-gating, coverage of the clinical target volume (CTV), and doses to organs at risk were collected. ResultsRespiratory-gating was used in 123 patients (53 %). In 176 patients (77 %) the tumor bed was in the upper and in 54 patients (23 %) in the lower breast quadrants. The median MHD was 0.37 Gy (interquartile range 0.26–0.57 Gy), 0.33 Gy (0.23–0.49 Gy) for respiratory-gating, and 0.49 Gy (0.31–0.70 Gy) for free breathing, p < 0.0001. MHD was < 1 Gy in 206 patients (90 %) and < 2 Gy in 221 patients (96 %).Respiratory-gating led to significantly lower MHD for upper-located, but not for lower-located tumor beds, however, all MHD were low irrespective of respiratory-gating. Respiratory-gating did not improve CTV coverage or lower lung doses. ConclusionsPBI ensured a low MHD for most patients. Adding respiratory-gating further reduced MHD for upper-located but not for lower-located tumor beds but did not influence target coverage or lung doses. Respiratory-gating is no longer DBCG standard for left-sided PBI.

Impact of intrafraction motion in pancreatic cancer treatments with MR-guided adaptive radiation therapy.

The total time of radiation treatment delivery for pancreatic cancer patients with daily online adaptive radiation therapy (ART) on an MR-Linac can range from 50 to 90min. During this period, the target and normal tissues undergo changes due to respiration and physiologic organ motion. We evaluated the dosimetric impact of the intrafraction physiological organ changes. Ten locally advanced pancreatic cancer patients were treated with 50 Gy in five fractions with intensity-modulated respiratory-gated radiation therapy on a 0.35-T MR-Linac. Patients received both pre- and post-treatment volumetric MRIs for each fraction. Gastrointestinal organs at risk (GI-OARs) were delineated on the pre-treatment MRI during the online ART process and retrospectively on the post-treatment MRI. The treated dose distribution for each adaptive plan was assessed on the post-treatment anatomy. Prescribed dose volume histogram metrics for the scheduled plan on the pre-treatment anatomy, the adapted plan on the pre-treatment anatomy, and the adapted plan on post-treatment anatomy were compared to the OAR-defined criteria for adaptation: the volume of the GI-OAR receiving greater than 33 Gy (V33Gy) should be ≤1 cubic centimeter. Across the 50 adapted plans for the 10 patients studied, 70% were adapted to meet the duodenum constraint, 74% for the stomach, 12% for the colon, and 48% for the small bowel. Owing to intrafraction organ motion, at the time of post-treatment imaging, the adaptive criteria were exceeded for the duodenum in 62% of fractions, the stomach in 36%, the colon in 10%, and the small bowel in 48%. Compared to the scheduled plan, the post-treatment plans showed a decrease in the V33Gy, demonstrating the benefit of plan adaptation for 66% of the fractions for the duodenum, 95% for the stomach, 100% for the colon, and 79% for the small bowel. Post-treatment images demonstrated that over the course of the adaptive plan generation and delivery, the GI-OARs moved from their isotoxic low-dose region and nearer to the dose-escalated high-dose region, exceeding dose-volume constraints. Intrafraction motion can have a significant dosimetric impact; therefore, measures to mitigate this motion are needed. Despite consistent intrafraction motion, plan adaptation still provides a dosimetric benefit.

Development of a Breath Control Training System for Breath-Hold Techniques and Respiratory-Gated Radiation Therapy

Development of a Breath Control Training System for Breath-Hold Techniques and Respiratory-Gated Radiation Therapy

End-to-end test of respiratory gating radiation therapy for lung stereotactic body radiation therapy treatments.

In this paper, a dosimetric end-to-end test of respiratory gated radiation therapy (RGRT) applied in lung cancer stereotactic body radiation therapy (SBRT) was performed. The test was performed from treatment simulation to treatment delivery using a QUASAR phantom, for regular, slightly irregular and irregular breathing patterns in phase- and amplitude-gated modes. A mechanical and dosimetric verification was performed to evaluate all steps of the proposed treatment workflow. Dose measurements were performed using a PinPoint ion chamber and GafChromic EBT3 films. Mechanical verification confirmed good function of the chosen systems. Dosimetric verification showed good agreement between planned and measured doses, for the phase-gated versus amplitude-gated modes: 1.4 ± 0.4% versus 1.2 ± 0.2% for regular, 2.8 ± 0.3% versus 3.0 ± 0.3% for slightly irregular, and 6.2 ± 0.7% versus 7.4 ± 0.5% for irregular breathing patterns. The gamma passing rates for 3%/3mm and 2%/2mm criteria, comparing phase- versus amplitude-gated modes, were 99.0 ± 0.3% versus 99.5 ± 0.2% and 95.2 ± 0.2% versus 96.1 ± 0.2% for the regular, 97.4 ± 0.8% versus 98.0 ± 0.6% and 91.7 ± 0.5% versus 92.4 ± 0.4% for the slightly irregular, and 96.4 ± 0.5% versus 95.3 ± 0.7% and 86.4 ± 0.5% versus 84.6 ± 0.7% for the irregular breathing patterns, respectively. It is concluded that using equipment and workflow for the treatment of lung cancer by means of SBRT in RGRT mode is safe and efficient, for regular and slightly irregular breathing patterns.

Stability and Reliability of Enhanced External-Internal Motion Correlation via Dynamic Phase-Shift Corrections Over 30-min Timeframe for Respiratory-Gated Radiotherapy.

To assess the stability of patient-specific phase shifts between external- and internal-respiratory motion waveforms, the reliability of enhanced external–internal correlation with phase-shift correction, and the feasibility of guiding respiratory-gated radiotherapy (RGRT) over 30 min. In this clinical feasibility investigation, external bellows and internal-navigator waveforms were simultaneously and prospectively acquired along with two four-dimensional magnetic resonance imaging (4DMRI) scans (6–15 m each) with 15–20 m intervals in 10 volunteers. A bellows was placed 5 cm inferior to the xiphoid to monitor abdominal motion, and an MR navigator was used to track the diaphragmatic motion. The mean phase-domain (MPD) method was applied, which combines three individual phase-calculating methods: phase-space oval fitting, principal component analysis, and analytic signal analysis, weighted by the reciprocal of their residual errors (RE) excluding outliers (RE >2σ). The time-domain cross-correlation (TCC) analysis was applied for comparison. Dynamic phase-shift correction was performed based on the phase shift detected on the fly within two 10 s moving datasets. Simulating bellows-triggered gating, the median and 95% confidence interval for the navigator's position at beam-on/beam-off and %harm (percentage of beam-on time outside the safety margin) were calculated. Averaged across all subjects, the mean phase shifts are found indistinguishable (p > .05) between scan 1 (55˚ ± 9˚) and scan 2 (59˚ ± 11˚). Using the MPD method the averaged correlation increases from 0.56 ± 0.22 to 0.85 ± 0.11 for scan 1 and from 0.47 ± 0.30 to 0.84 ± 0.08 for scan 2. The TCC correction results in similar results. After phase-shift correction, the number of cases that were suitable for amplitude gating (with <10%harm) increased from 2 to 17 out of 20 cases. A patient-specific, stable phase-shift between the external and internal motions was observed and corrected using the MPD and TCC methods, producing long-lasting enhanced motion correlation over 30m. Phase-shift correction offers a feasible strategy for improving the accuracy of tumor-motion prediction during RGRT.

Does irregular breathing impact on respiratory gated radiation therapy of lung stereotactic body radiation therapy treatments?

The impact of irregular breathing on respiratory gated radiation therapy (RGRT) was evaluated for lung stereotactic body radiation therapy (SBRT) treatments. Measurements in the static mode were performed with different field sizes, depths of the measurements, breathing periods and duty cycles, using the Farmer ion chamber, PinPoint ion chamber, and microDiamond detector. The output constancy (OC) was evaluated between gated and nongated beams. Measurements in the dynamic mode for regular and irregular breathing in phase- and amplitude-gated modes, were performed with the amplitude of target motion from 5 mm to 25 mm, and breathing period from 3 to 6 s, for ion chamber, and film inserts. The dose discrepancy was evaluated for the ion chamber insert. The gamma passing rate was evaluated with film dosimetry. In the static mode, the maximum obtained OC was 0.8% using the Farmer ion chamber, 1% (p < 0.001) using the microDiamond detector, and 1.4% (p < 0.001) using the PinPoint ion chamber. In the dynamic mode, good agreement between planned and measured doses was obtained for regular breathing, 2.08 ± 0.48% (1.57 to 2.74%), which increased to 3.42 ± 1.24% (1.58 to 6.69%) for irregular breathing. The gamma passing rate of 3mm/3%, 3mm/2%, 3mm/1% and 2mm/2% was 99.4% ± 0.3, 98.2 ± 0.8%, 88.2 ± 3.0% and 96.4 ± 1.0% for regular and 97.2% ± 1.6%, 95.1 ± 2.6%, 85.6 ± 3.0% and 92.9 ± 2.9% for irregular breathing patterns (p < 0.01), respectively. For a slightly irregular breathing amplitude, lung SBRT cancer patients can be treated in the phase-gated mode.

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.

Interfractional diaphragmatic position variation according to stomach volume change during respiratory-gated radiotherapy for hepatocellular carcinoma.

We evaluated the correlation between stomach volume change and interfractional baseline shifts of the diaphragm in image-guided radiotherapy (IGRT) for hepatocellular carcinoma (HCC). Twenty-four patients with HCC underwent ten fractions of IGRT, and a total of 240 cone beam computed tomography (CBCT) and on-board imager (OBI) kV image sets were acquired. These image sets were retrospectively analyzed. Baseline shifts of the diaphragm relative to bone and stomach volume change ratios were evaluated using four-dimensional simulation CT, kV image, and CBCT images. Associations between baseline shifts and patient physiologic factors were investigated. The average baseline shift of the diaphragm in the superior-inferior (SI) direction was 1.5mm (standard deviation 4.6mm), which was higher than the shift in other directions (0.7, 2.0mm and 0.9, 2.6mm in right-left (RL) and anterior-posterior (AP) directions, respectively). Interfractional baseline shifts of the diaphragm in the SI and AP directions were positively correlated with the stomach volume change ratio (Pearson's r: 0.416 and 0.302, p-value: <0.001 and <0.001, respectively). The interfractional baseline shifts of the diaphragm in the SI and AP directions correlated well with stomach volume changes. Efforts to maintain a constant stomach volume before the simulation and each treatment, such as fasting, may reduce interfractional baseline shifts of liver tumors.

Late Sequelae of Radiotherapy

Approximately half of all patients with tumors need radiotherapy. Long-term survivors may suffer from late sequelae of the treatment. The existing radiotherapeutic techniques are being refined so that radiation can be applied more precisely, with the goal of limiting the radiation exposure of normal tissue and reducing late sequelae.This review is based on the findings of a selective search in PubMed for publications on late sequelae of conventional percutaneous radiotherapy, January 2000 to May 2020. Late sequelae affecting the central nervous system, lungs, and heart and the development of second tumors are presented, and radiobiological mechanisms and the relevant technical and conceptual considerations are discussed.The current standard of treatment involves the use of linear accelerators, intensity-modulated radiotherapy (IMRT), image-guided and respiratory-gated radiotherapy, and the integration of positron emission tomography combined with computed tomography (PET-CT) in radiation treatment planning. Cardiotoxicity has been reduced with regard to the risk of coronary heart disease after radiotherapy for Hodgkin's lymphoma (hazard ratio [HR] 0.44 [0.23; 0.85]). It was also found that the rate of radiation- induced pneumonitis dropped from 7.9% with conformal treatment to 3.5% with IMRT in a phase III lung cancer trial. It is hoped that neurocognitive functional impairment will be reduced by hippocampal avoidance in modern treatment planning: an initial phase III trial yielded a hazard ratio of 0.74 [0.58; 0.94]. It is estimated that 8% of second solid tumors in adults are induced by radiotherapy (3 additional tumors per 1000 patients at 10 years).Special challenges for research in this field arise from the long latency of radiation sequelae and the need for largescale, well-documented patient collectives in order to discern dose-effect relationships, and take account of cofactors, when the overall number of events is small. It is hoped that further technical and conceptual advances will be made in the areas of adaptive radiotherapy, proton and heavy-ion therapy, and personalized therapy.

End-to-End Test of Respiratory Gated Radiation Therapy for Lung Stereotactic Body Radiation Therapy Treatments

End-to-End Test of Respiratory Gated Radiation Therapy for Lung Stereotactic Body Radiation Therapy Treatments

Residual Set Up Errors of the Surrogate-guided Registration Using Four-dimensional CT Images and Breath Holding Ones in Respiratory Gated Radiotherapy for Liver Cancer.

To evaluate the surrogate-guided registration accuracy of two computed tomography (CT) image sets, expiratory phase four-dimensional (Ex4D) CT and breath-holding CT (BHCT), in respiratory-gated radiotherapy for liver cancer. The surrogate-guided registration errors were defined as the differences between the diaphragm- and fiducial-guided registrations or the differences between upper and lower fiducial registrations in three directions: left-right (LR), anterior-posterior (AP), and cranio-caudal (CC). The mean±SDs of the absolute errors for diaphragm-guided registration were 1.9±1.3, 2.7±1.8, and 2.6±1.7 mm with Ex4D and 1.8±1.8, 2.6±1.9, and 1.8±1.7 mm with BHCT in the LR, AP and CC directions, respectively (CC direction, p<0.01). In the fiducial-guided registration, there were no significant differences in any direction. In registration with Ex4D, there were positive correlations between registration errors and the respiratory irregularity during 4D scanning (correlation coefficient; diaphragm: 0.65, fiducial: 0.54). BHCT has the advantage of accurate surrogate-guided registration compared with Ex4D.

Abstract 16347: Simplified Workflow to Improve the Precision of Non-invasive Radio-ablation of Ventricular Tachycardia Storm

Background: Stereotactic ablative radiotherapy (SAbR) is an emerging therapy for ventricular tachycardia (VT) storm, but the feasibility and outcomes guided by computational 12-lead ECG mapping and respiratory-gated radiation delivery have not been reported. Hypothesis: We hypothesized that a novel 12-lead ECG-based mapping system and respiratory-gated radiotherapy delivery may simplify the workflow and improve precision of SAbR in critically ill patients with VT storm. Methods: We enrolled patients with VT storm who were not candidates for catheter ablation. VT was induced using non-invasive stimulation and recorded on 12-lead ECGs. Computational ECG mapping was performed to localize VT exit sites. Target volumes were contoured onto an averaged free-breathing CT. Ionizing radiation (25 Gy) was delivered using a linear accelerator (Varian, Palo Alto). In patients with significant respiratory motion, radiotherapy was delivered at end-expiration, guided by ICD lead fiducials. Results: In 5 patients (age 74±6.1 years, EF 29±14%) refractory to 2±1 ablation procedures, 1.5±0.6 VT morphologies were localized on 3D models (Fig 1A) using ECG-based mapping (mapping time 1.2±0.3 min). In patients whom respiratory gating (Fig 1B) was used prospectively due to respiratory variation, the planned target volume (PTV) was smaller compared to patients who were not gated (71 ± 7 vs 153 ± 35 cc, p&lt;0.01). These patients also had VT targets (crux or inferior LV) close to the stomach, and did not experience adverse events. ICD shocks were decreased after SAbR compared to before (0.25±0.5 vs 26±19 shocks, p&lt;0.001) at 4.4±3.4 months follow-up. Conclusion: Non-invasive computational mapping based upon the 12-lead ECG alone simplifies radioablation workflow in critically ill VT storm patients and reduces the burden of ICD shocks. Respiratory gated radiotherapy ablation appears feasible and may help reduce target volume of therapy. Studies with longer follow-up are ongoing.

Real-time Linear Fiducial Marker Tracking in Respiratory-gated Radiotherapy With a Deep Neural Network

To achieve high treatment accuracy in respiratory-gated radiotherapy, it is important to obtain a mobile tumor position in 3D space. Instead of tracking a tumor, Mylonas et al. proposed the method of detecting linear fiducial markers in fluoroscopic images with convolutional neural network (CNN) models (Mylonas et al. Med Phys. 2019; 46 2286-97). However, it is difficult to prepare the many marker images required for training the model. Therefore, we propose a method to train a CNN model with 3D simulated training marker images. Furthermore, the proposed model tracks the markers in a pair of orthogonal fluoroscopic images. Owing to no need of taking fluoroscopic images of implanted markers, our method can build the model for the arbitrary-shaped marker more efficiently. To make training images, we cropped patch images, whose size was 31x31x2 pixels, from the position such that 3D points were projected onto the paired fluoroscopic images of non-implanted patients. These patch images were labeled “not-marker images”. The simulated “marker images” were generated by drawing the shape of the marker, which was virtually put at the 3D points with any posture, projected onto the patch images. We built a CNN model by training 1000 marker and not-marker images. The model consisted of four convolutional layers with two max-pooling layers and lastly a fully connected layer to output the marker likelihood. Each convolutional layer has a batch normalization layer and a rectified linear unit. For tracking the marker, the trained model calculated the likelihood of each 3D point by inputting the cropped image from where the 3D point was projected onto the fluoroscopic images and the marker position in 3D space was determined with the likelihood-weighted average of the positions. To reduce the number of calculated 3D points, we used a particle filter. The method was evaluated using three liver fluoroscopic image datasets with an implanted linear fiducial marker 0.5 mm in diameter by 3.0 mm in length. Each dataset consisted of at least one respiratory phase. The positional error of each marker was calculated between the tracked position and the ground truth position in 3D space. In addition, the calculation time was measured on a workstation (Intel Xeon® CPU @ 3.6 GHz). The mean positional error for three patients was measured to be 0.32 mm with a standard deviation of 0.17 mm. The worst positional error was 1.1 mm. For the first, second and third patient, the mean errors were 0.38, 0.26 and 0.32 mm with a standard deviation of 0.16, 0.13 and 0.16 mm, respectively. The calculation time was within 50.4 milliseconds per frame. We presented real-time linear fiducial marker tracking for respiratory-gated radiotherapy with a DNN framework. We performed experiments involving three live patients with our proposed method and obtained high accuracy and short computation time.

Assessment of Internal and External Surrogates for Lung Stereotactic Body Radiation Therapy

Purpose: To evaluate internal (lung, heart and diaphragm) and external (nine glass marbles) marker motion in correlation with lung tumor motion, to determine potential surrogate for respiratory gating radiation therapy (RGRT) depending on tumor localization, upper lobe (UL) vs lower lobe (LL).Methods: This study included 58 patients (34 male and 24 female) with small lung cancer (≤ 5cm), who underwent Stereotactic Body Radiation Therapy (SBRT). All patients were scanned and contoured in all ten phases (Varian Eclipse 13.7) after four-dimensional computed tomography simulation (4D-CT). The motion of internal markers and external markers were analyzed and correlated with tumor motion. The Pearson correlation coefficient (PCC) was used to evaluate the correlation between internal and external marker motion with tumor motion. Results: The median (range) values of tumor motion were 3.2 (0.6-11.0) vs 8.6 (4.0-24.0) mm in the UL vs LL. The median (range) values of organs motion and PCC comparing UL vs LL were: 2.0 (0.3-9.1) vs 6.0 (2.8-13.9) mm and 0.46 (0.30-0.95) vs 0.79 (0.50-0.94) to the lung; 11.9 (2.5-16.3) vs 12.5 (5.0-22.5) mm and 0.68 (0.11-0.93) vs 0.89 (0.30-0.99) to the diaphragm; and 3.9 (2.5-6.3) vs 7.6 (4.5-8.6) mm and 0.49 (0.20-0.70) vs 0.59 (0.36-0.83) to the heart. The external marker motion and correlation coefficient for UL and LL were 2.5 (0.9-7.4) vs 2.3 (1.0-5.9) mm and 0.54 (0.09-0.96) vs 0.73 (0.27-0.94).Conclusion: Lung and diaphragm motion correlate better with tumor motion than the external marker. Diaphragm motion can be an excellent indicator for treatment based on RGRT.

Analysis of dosimetric impact of intrafraction translation and rotation during respiratory-gated stereotactic body radiotherapy with real-time tumor monitoring of the lung using a novel six degrees-of-freedom robotic moving phantom.

This study aimed to develop a six degrees-of-freedom (6DoF) robotic moving phantom for evaluating the dosimetric impact of intrafraction rotation during respiratory-gated radiotherapy with real-time tumor monitoring in the lung. Fifteen patients who had undergone respiratory-gated stereotactic body radiotherapy (SBRT) with the SyncTraX system for lung tumors were enrolled in this study. A water-equivalent phantom (WEP) was set at the tip of the robotic arm. A log file that recorded the three-dimensional positions of three fiducial markers implanted near the lung tumor was used as the input to the 6DoF robotic moving phantom. Respiratory-gated radiotherapy was performed for the WEP, which was driven using translational and rotational motions of the lung tumor. The accuracy of the 6DoF robotic moving phantom was calculated as the difference between the actual and the measured positions. To evaluate the dosimetric impact of intrafraction rotation, the absolute dose distributions under conditions involving gating and movement were compared with those under static conditions. For the sinusoidal patterns, the mean±standard deviation (SD) of the root mean square errors (RMSEs) of the translation and rotation positional errors was <0.40mm and 0.30°, respectively, for all directions. For the respiratory motion patterns of 15 patients, the mean±SD of the RMSEs of the translation and rotation positional errors was <0.55mm and 0.85°, respectively, for all directions. The γ3%/2mm values under translation with/without gating were 97.6±2.2%/80.9±18.1% and 96.8±2.3%/80.0±17.0% in the coronal and sagittal planes, respectively. Further, the γ3%/2mm values under rotation with/without gating were 91.5±6.5%/72.8±18.6% and 90.3±6.1%/72.9±15.7% in the coronal and sagittal planes, respectively. The developed 6DoF robotic phantom system could determine the translational and rotational motions of lung tumors with high accuracy. Further, respiratory-gating radiotherapy with real-time tumor monitoring using an internal surrogate marker was effective in compensating for the translational motion of lung tumors but not for correcting their rotational motion.

Accuracy of real-time respiratory motion tracking and time delay of gating radiotherapy based on optical surface imaging technique

BackgroundSurface-guided radiation therapy (SGRT) employs a non-invasive real-time optical surface imaging (OSI) technique for patient surface motion monitoring during radiotherapy. The main purpose of this study is to verify the real-time tracking accuracy of SGRT for respiratory motion and provide a fitting method to detect the time delay of gating.MethodsA respiratory motion phantom was utilized to simulate respiratory motion using 17 cosine breathing pattern curves with various periods and amplitudes. The motion tracking of the phantom was performed by the Catalyst™ system. The tracking accuracy of the system (with period and amplitude variations) was evaluated by analyzing the adjusted coefficient of determination (A_R2) and root mean square error (RMSE). Furthermore, 13 actual respiratory curves, which were categorized into regular and irregular patterns, were selected and then simulated by the phantom. The Fourier transform was applied to the respiratory curves, and tracking accuracy was compared through the quantitative analyses of curve similarity using the Pearson correlation coefficient (PCC). In addition, the time delay of amplitude-based respiratory-gating radiotherapy based on the OSI system with various beam hold times was tested using film dosimetry for the Elekta Versa-HD and Varian Edge linacs. A dose convolution-fitting method was provided to accurately measure the beam-on and beam-off time delays.ResultsA_R2 and RMSE for the cosine curves were 0.9990–0.9996 and 0.110–0.241 mm for periods ranging from 1 s to 10 s and 0.9990–0.9994 and 0.059–0.175 mm for amplitudes ranging from 3 mm to 15 mm. The PCC for the actual respiratory curves ranged from 0.9955 to 0.9994, which was not significantly affected by breathing patterns. For gating radiotherapy, the average beam-on and beam-off time delays were 1664 ± 72 and 25 ± 30 ms for Versa-HD and 303 ± 45 and 34 ± 25 ms for Edge, respectively. The time delay was relatively stable as the beam hold time increased.ConclusionsThe OSI technique provides high accuracy for respiratory motion tracking. The proposed dose convolution-fitting method can accurately measure the time delay of respiratory-gating radiotherapy. When the OSI technique is used for respiratory-gating radiotherapy, the time delay for the beam-on is considerably longer than the beam-off.

Feasibility of markerless fluoroscopic real-time tumor detection for adaptive radiotherapy: development and end-to-end testing

Respiratory-gated radiotherapy treatments of lung tumors reduce the irradiated normal tissue volume and potentially lower the risk of side effects. However, in clinical routine, the gating signal is usually derived from external markers or other surrogate signals and may not always correlate well with the actual tumor position. This study uses the kV-imaging system of a LINAC in combination with a multiple template matching algorithm for markerless real-time detection of the tumor position in a dynamic anthropomorphic porcine lung phantom. The tumor was realized by a small container filled with polymer dosimetry gel, the so-called gel tumor. A full end-to-end test for a gated treatment was performed and the geometric and dosimetric accuracy was validated. The accuracy of the tumor detection algorithm in SI- direction was found to be mm and the gel tumor was automatically detected in 98 out of 100 images. The measured 3D dose distribution showed a uniform coverage of the gel tumor and comparison with the treatment plan revealed a high 3D -passing rate of (). The simulated treatment confirmed the employed margin sizes for residual motion within the gating window and serves as an end-to-end test for a gated treatment based on a markerless fluoroscopic real-time tumor detection.

A machine learning-based real-time tumor tracking system for fluoroscopic gating of lung radiotherapy

To improve respiratory-gated radiotherapy accuracy, we developed a machine learning approach for markerless tumor tracking and evaluated it using lung cancer patient data. Digitally reconstructed radiography (DRR) datasets were generated using planning 4DCT data. Tumor positions were selected on respective DRR images to place the GTV center of gravity in the center of each DRR. DRR subimages around the tumor regions were cropped so that the subimage size was defined by tumor size. Training data were then classified into two groups: positive (including tumor) and negative (not including tumor) samples. Machine learning parameters were optimized by the extremely randomized tree method. For the tracking stage, a machine learning algorithm was generated to provide a tumor likelihood map using fluoroscopic images. Prior probability tumor positions were also calculated using the previous two frames. Tumor position was then estimated by calculating maximum probability on the tumor likelihood map and prior probability tumor positions.We acquired treatment planning 4DCT images in eight patients. Digital fluoroscopic imaging systems on either side of the vertical irradiation port allowed fluoroscopic image acquisition during treatment delivery. Each fluoroscopic dataset was acquired at 15 frames per second. We evaluated the tracking accuracy and computation times.Tracking positional accuracy averaged over all patients was 1.03 ± 0.34 mm (mean ± standard deviation, Euclidean distance) and 1.76 ± 0.71 mm ( percentile). Computation time was 28.66 ± 1.89 ms/frame averaged over all frames. Our markerless algorithm successfully estimated tumor position in real time.