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Early Experience in Cone Beam Projection Image Streaming for Real-Time Intrafractional Motion Monitoring Using a Conventional Linear Accelerator
Oral Scientific Sessions S115
Volume 93 Number 3S Supplement 2015 Results: Percussion-assisted RT offered a high level of success in chest stabilization with excellent tolerability. The mean duration time for breathing stabilization was 10.4 minutes in 10 healthy volunteers, 28 tests (each subject tested 3 times), and 380 measures. We had 100% success on first and second tests, and 80% success on the third tests. Transferred into clinic, PART was applied with good tolerance for patients included so far, without treatment breaks during the overall fractionated RT; PART offered better dosimetric profiles when compared to MI or FB. For lung cancer patients, the volume of normal lung tissue irradiated by the 95% isodose was divided by a factor of two in the first two cases. Until now, we treated one patient with left breast cancer (50 Gy in 25 fractions, 100% success rate, mean stabilization for beam-on time 5.68 min, range 3.12e7.18 min), one patient treated with lung SBRT (60 Gy in 8 fractions, 100% success rate, mean stabilization for beam-on time 10.00 min, range 8.55e12.68 min), and one patient with locally advanced lung cancer (51 Gy in 17 fractions, 100% success rate, mean stabilization for beam-on time 9.35 min, range 8.17e11.58 min). In addition to this, percussive ventilation assistance markedly improved FDG PET image quality in detecting pulmonary lesions. Conclusion: Percussion-assisted RT was tolerable and applicable in clinical practice with a dosimetric gain for patients in comparison to other breath hold gating techniques. This pilot study is ongoing, and updated data will be presented at the meeting. Author Disclosure: E. Ozsahin: None. N. Peguret: None. M. Zeverino: None. B. Belmondo: None. F. Duclos: None. J. Simons: None. O. Long: None. J.O. Prior: None. R. Moeckli: None. J. Bourhis: None.
261 Implementation of Real-Time, Real-Anatomy Tracking and Radiation Beam Control on the First MR-IGRT Clinical System O.L. Green, L.J. Rankine, B. Cai, R. Kashani, L. Santanam, S.M. Goddu, C.G. Robinson, P.J. Parikh, J.R. Olsen, J.D. Bradley, and S. Mutic; Washington University School of Medicine, St. Louis, MO Purpose/Objective(s): We reported on the geometric and dosimetric results, quality assurance, and workflow process for the first clinical implementation of real-time, real-anatomy tracking and beam control for free-breathing patients. Materials/Methods: The first clinically implemented magnetic resonance imaging guided radiation therapy (MR-IGRT) system used for over a year at our institution has the capability for sagittal cine imaging at 4 frames per second, while tracking a chosen anatomical organ at the same time. The tracking algorithm implemented in the delivery system deformed an initial contour on every subsequent cine frame and compared it to a predetermined boundary contour. If the anatomy of interest was determined via the deformed contour to be outside the boundary, the radiation delivery was stopped until it returned to within the boundary. To understand the system performance and derive appropriate treatment margins and gating boundaries, the following components were characterized: overall system latency, shutter dose, spatial integrity of the magnetic field, output constancy, and absolute spatial dosimetric accuracy. Motion phantoms compatible with the magnetic field were used with radiographic film to establish the spatial accuracy of the gated dose distributions; MR-compatible ionization chambers were used to confirm an implemented shutter dose correction. The overall goal of these tests was to determine parameters such that the PTV margins remained comparable to Linac-based deliveries, while delivering doses to targets visualized within treatment boundaries. Results: Gated output measurements showed a 1.28% average difference as compared to static delivery, demonstrating that the shutter dose correction was appropriate. The spatial distribution of dose was within 2 mm of the planned distribution when delivered to a motion phantom with the tracking capability implemented. The overall latency of the system (500 msec on average) contributed the most to the spatial dose error. The spatial integrity of the magnetic field was within 2 mm for a 24 cm diameter field of view, and 1 mm at 10. Coupled with inherent imaging resolution, it was determined that a 3 mm boundary around the anatomy of interest allowed for a 5 mm GTV to PTV expansion, identical to standard of care for fiducial-based tracking in our clinic. The expected duty cycles will be about 50% for the recommended
parameters, used with an exhale-based volumetric MR image for initial setup. Five tracking-enabled deliveries with larger PTV expansions showed good tracking and beam control so far at duty cycles of 80e90%. Conclusion: The goal of clinical real-time anatomy tracking has now been achieved in radiation therapy. By characterizing system performance in relation to adjustable parameters, accurate dose distributions were achieved while having ongoing monitoring of anatomy position during delivery. Author Disclosure: O.L. Green: Honoraria; ViewRay, Inc. L.J. Rankine: None. B. Cai: None. R. Kashani: None. L. Santanam: None. S. Goddu: None. C.G. Robinson: None. P.J. Parikh: Research Grant; Varian, Philips. J.R. Olsen: Research Grant; ViewRay, Inc. J.D. Bradley: Research Grant; ViewRay, Inc. S. Mutic: Honoraria; ViewRay.
262 Early Experience in Cone Beam Projection Image Streaming for Real-Time Intrafractional Motion Monitoring Using a Conventional Linear Accelerator Y.K. Park,1 G.C. Sharp,1 S.J. Ye,2 and B. Winey1; 1Massachusetts General Hospital, Boston, MA, 2Seoul National University Hospital, Seoul, Korea, Republic of Korea Purpose/Objective(s): Kilovoltage x-ray image streaming capability has been recently designed and enabled for linear accelerators, which potentially enables real-time tumor localization and tracking on conventional linear accelerators. This study aimed to investigate the feasibility and performance of real-time fiducial tracking during cone beam CT acquisition with or without simultaneous treatment delivery. Materials/Methods: A client computer was connected to an imaging system via a Gigabit Ethernet switch. The imaging system streamed out projection image data to the client computer immediately after image acquisition with fluoroscopy or CBCT. A performance test was conducted to investigate imaging frequency, latency and tracking feasibility. Three gold fiducial markers with a length of 3 mm were implanted in solid water slabs that constituted a pelvis-shaped phantom with a thickness of 36 cm. The phantom was placed on a motion platform oscillating with amplitudes of 1.4 cm and 3 cm in anterior-posterior and superior-inferior direction simultaneously, at a cycle of 4 s. In-house marker tracking software based on FFT normalized cross-correlation was developed and installed in the client computer. The marker motion was tracked in real-time for two different imaging scenarios: (1) a kV-only CBCT scan with treatment beam off; (2) a kV CBCT scan during a 6 MV VMAT delivery. In total, 345 and 154 consecutive projections, respectively, from kV-only and kV-VMAT scans were analyzed. Results: The projection streaming system successfully transferred projection images to the client computer with a frequency of 5.8 +/- 1.8 Hz in kVonly mode. In the kV-VMAT case, on the other hand, the frequency varied according to the MV beam-on state. The system latency was found to be 231.2 +/- 9.8ms, including panel read-out time (w182ms). In addition, w150ms was required for image processing and marker detection algorithms. Using an in-house fiducial marker tracking algorithm, the detection rate was >95% in the kV-only scan and 85.1% in the kV-VMAT scan. Conclusion: Our early experience in projection streaming service demonstrated promising results supporting the feasibility of real-time intrafractional motion monitoring using a conventional linear accelerator. Further research is ongoing to improve tracking accuracy, MV-scatter suppression and processing speed. Author Disclosure: Y. Park: Research Grant; Elekta. G.C. Sharp: Research Grant; Elekta. S. Ye: None. B. Winey: Research Grant; Elekta.
263 Interfractional and Immobilization Related Respiratory Motion Variability for Treatment of Liver Tumors B. Lavajo Vieira,1,2 T.K. Kosak,2 Y. Belkacemi,1,3 J.Y. Wo,2 A.X. Zhu,2 T.S. Hong,2 and J.A. Wolfgang2; 1(AROME) Association of Radiotherapy and Oncology of the Mediterranean Area, Paris, France, 2Massachusetts General Hospital, Harvard Medical School, Boston, MA, 3Henri Mondor University Hospital, Cre´teil, France
Volume 93 Number 3S Supplement 2015 Results: Percussion-assisted RT offered a high level of success in chest stabilization with excellent tolerability. The mean duration time for breathing stabilization was 10.4 minutes in 10 healthy volunteers, 28 tests (each subject tested 3 times), and 380 measures. We had 100% success on first and second tests, and 80% success on the third tests. Transferred into clinic, PART was applied with good tolerance for patients included so far, without treatment breaks during the overall fractionated RT; PART offered better dosimetric profiles when compared to MI or FB. For lung cancer patients, the volume of normal lung tissue irradiated by the 95% isodose was divided by a factor of two in the first two cases. Until now, we treated one patient with left breast cancer (50 Gy in 25 fractions, 100% success rate, mean stabilization for beam-on time 5.68 min, range 3.12e7.18 min), one patient treated with lung SBRT (60 Gy in 8 fractions, 100% success rate, mean stabilization for beam-on time 10.00 min, range 8.55e12.68 min), and one patient with locally advanced lung cancer (51 Gy in 17 fractions, 100% success rate, mean stabilization for beam-on time 9.35 min, range 8.17e11.58 min). In addition to this, percussive ventilation assistance markedly improved FDG PET image quality in detecting pulmonary lesions. Conclusion: Percussion-assisted RT was tolerable and applicable in clinical practice with a dosimetric gain for patients in comparison to other breath hold gating techniques. This pilot study is ongoing, and updated data will be presented at the meeting. Author Disclosure: E. Ozsahin: None. N. Peguret: None. M. Zeverino: None. B. Belmondo: None. F. Duclos: None. J. Simons: None. O. Long: None. J.O. Prior: None. R. Moeckli: None. J. Bourhis: None.
261 Implementation of Real-Time, Real-Anatomy Tracking and Radiation Beam Control on the First MR-IGRT Clinical System O.L. Green, L.J. Rankine, B. Cai, R. Kashani, L. Santanam, S.M. Goddu, C.G. Robinson, P.J. Parikh, J.R. Olsen, J.D. Bradley, and S. Mutic; Washington University School of Medicine, St. Louis, MO Purpose/Objective(s): We reported on the geometric and dosimetric results, quality assurance, and workflow process for the first clinical implementation of real-time, real-anatomy tracking and beam control for free-breathing patients. Materials/Methods: The first clinically implemented magnetic resonance imaging guided radiation therapy (MR-IGRT) system used for over a year at our institution has the capability for sagittal cine imaging at 4 frames per second, while tracking a chosen anatomical organ at the same time. The tracking algorithm implemented in the delivery system deformed an initial contour on every subsequent cine frame and compared it to a predetermined boundary contour. If the anatomy of interest was determined via the deformed contour to be outside the boundary, the radiation delivery was stopped until it returned to within the boundary. To understand the system performance and derive appropriate treatment margins and gating boundaries, the following components were characterized: overall system latency, shutter dose, spatial integrity of the magnetic field, output constancy, and absolute spatial dosimetric accuracy. Motion phantoms compatible with the magnetic field were used with radiographic film to establish the spatial accuracy of the gated dose distributions; MR-compatible ionization chambers were used to confirm an implemented shutter dose correction. The overall goal of these tests was to determine parameters such that the PTV margins remained comparable to Linac-based deliveries, while delivering doses to targets visualized within treatment boundaries. Results: Gated output measurements showed a 1.28% average difference as compared to static delivery, demonstrating that the shutter dose correction was appropriate. The spatial distribution of dose was within 2 mm of the planned distribution when delivered to a motion phantom with the tracking capability implemented. The overall latency of the system (500 msec on average) contributed the most to the spatial dose error. The spatial integrity of the magnetic field was within 2 mm for a 24 cm diameter field of view, and 1 mm at 10. Coupled with inherent imaging resolution, it was determined that a 3 mm boundary around the anatomy of interest allowed for a 5 mm GTV to PTV expansion, identical to standard of care for fiducial-based tracking in our clinic. The expected duty cycles will be about 50% for the recommended
parameters, used with an exhale-based volumetric MR image for initial setup. Five tracking-enabled deliveries with larger PTV expansions showed good tracking and beam control so far at duty cycles of 80e90%. Conclusion: The goal of clinical real-time anatomy tracking has now been achieved in radiation therapy. By characterizing system performance in relation to adjustable parameters, accurate dose distributions were achieved while having ongoing monitoring of anatomy position during delivery. Author Disclosure: O.L. Green: Honoraria; ViewRay, Inc. L.J. Rankine: None. B. Cai: None. R. Kashani: None. L. Santanam: None. S. Goddu: None. C.G. Robinson: None. P.J. Parikh: Research Grant; Varian, Philips. J.R. Olsen: Research Grant; ViewRay, Inc. J.D. Bradley: Research Grant; ViewRay, Inc. S. Mutic: Honoraria; ViewRay.
262 Early Experience in Cone Beam Projection Image Streaming for Real-Time Intrafractional Motion Monitoring Using a Conventional Linear Accelerator Y.K. Park,1 G.C. Sharp,1 S.J. Ye,2 and B. Winey1; 1Massachusetts General Hospital, Boston, MA, 2Seoul National University Hospital, Seoul, Korea, Republic of Korea Purpose/Objective(s): Kilovoltage x-ray image streaming capability has been recently designed and enabled for linear accelerators, which potentially enables real-time tumor localization and tracking on conventional linear accelerators. This study aimed to investigate the feasibility and performance of real-time fiducial tracking during cone beam CT acquisition with or without simultaneous treatment delivery. Materials/Methods: A client computer was connected to an imaging system via a Gigabit Ethernet switch. The imaging system streamed out projection image data to the client computer immediately after image acquisition with fluoroscopy or CBCT. A performance test was conducted to investigate imaging frequency, latency and tracking feasibility. Three gold fiducial markers with a length of 3 mm were implanted in solid water slabs that constituted a pelvis-shaped phantom with a thickness of 36 cm. The phantom was placed on a motion platform oscillating with amplitudes of 1.4 cm and 3 cm in anterior-posterior and superior-inferior direction simultaneously, at a cycle of 4 s. In-house marker tracking software based on FFT normalized cross-correlation was developed and installed in the client computer. The marker motion was tracked in real-time for two different imaging scenarios: (1) a kV-only CBCT scan with treatment beam off; (2) a kV CBCT scan during a 6 MV VMAT delivery. In total, 345 and 154 consecutive projections, respectively, from kV-only and kV-VMAT scans were analyzed. Results: The projection streaming system successfully transferred projection images to the client computer with a frequency of 5.8 +/- 1.8 Hz in kVonly mode. In the kV-VMAT case, on the other hand, the frequency varied according to the MV beam-on state. The system latency was found to be 231.2 +/- 9.8ms, including panel read-out time (w182ms). In addition, w150ms was required for image processing and marker detection algorithms. Using an in-house fiducial marker tracking algorithm, the detection rate was >95% in the kV-only scan and 85.1% in the kV-VMAT scan. Conclusion: Our early experience in projection streaming service demonstrated promising results supporting the feasibility of real-time intrafractional motion monitoring using a conventional linear accelerator. Further research is ongoing to improve tracking accuracy, MV-scatter suppression and processing speed. Author Disclosure: Y. Park: Research Grant; Elekta. G.C. Sharp: Research Grant; Elekta. S. Ye: None. B. Winey: Research Grant; Elekta.
263 Interfractional and Immobilization Related Respiratory Motion Variability for Treatment of Liver Tumors B. Lavajo Vieira,1,2 T.K. Kosak,2 Y. Belkacemi,1,3 J.Y. Wo,2 A.X. Zhu,2 T.S. Hong,2 and J.A. Wolfgang2; 1(AROME) Association of Radiotherapy and Oncology of the Mediterranean Area, Paris, France, 2Massachusetts General Hospital, Harvard Medical School, Boston, MA, 3Henri Mondor University Hospital, Cre´teil, France