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EP-1633: Respiratory Motion Analysis using a Surface Guided Radiation Therapy System for Lung SBRT Patients
S885 ESTRO 36 _______________________________________________________________________________________________
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Conclusion This low-cost, computer-vision system for real-time motion monitoring of the irradiation of breast cancer patients showed submillimetric accuracy and acceptable latency. It allowed the authors to highlight differences in surface motion that may be correlated to tumor motion. Madibreast detects and tracks accurately external motion on the breast using low-cost material and accessible opensource, high-level computer vision libraries. It allows immediate monitoring by visually displaying an immediate trace, which can alert that substantial motion could have occurred. Limitations include some remaining failures of the apparatus under low-exposure conditions, as well as considerable CPU occupation. EP-1633 Respiratory Motion Analysis using a Surface Guided Radiation Therapy System for Lung SBRT Patients M. Jermoumi1, D. Cao1, V. Mehta1, D. Shepard1 1 Swedish Cancer Institute, Radiation Oncology, Seattle, USA Purpose or Objective Surface guided radiation therapy (SGRT) uses a camera/projector pair to create a 3D map of a patient’s surface. SGRT can be used to assist in patient set up, real time motion monitoring, and respiratory motion management. In this work, we used SGRT to track the respiratory breathing pattern for lung SBRT patients. An excursion gating approach was employed where the beam delivery was interrupted if the breathing deviated from the expected pattern. The purpose of this work is to evaluate the patients breathing motion during SBRT treatment. Material and Methods To date, 10 NSCLC patients have been enrolled in this study and treated with stereotactic body radiation therapy (SBRT) using a 12Gyx4 fractionation. Prior to each fraction, each patient was aligned using SGRT. Next, a 4DCBCT scan was acquired to align based on internal anatomy. A virtual respiratory tracking point was then placed close on the patient’s surface close to the sternum. The patient’s gating window was set based on the end-toend amplitude measured during the acquisition of the CT at the time of simulation. The gating window was expanded 5 mm beyond the upper level window and 5 mm below the lower level window. In-house developed code was used to evaluate the respiratory data collected from all 40 fractions. The evaluation included an examination of the end-to end amplitude, the breathing period, and baseline drift. The correlation between baseline drift and the treatment time was assessed over the course of treatment. Results The mean (± SD) treatment time was 5.3 (± 1.34) minutes. The mean (± SD) end-to-end amplitude observed due to inter-fraction and intra-fraction motion were 6.79(±2.51) mm and 6.79(±2.86) mm respectively and the mean (± SD)
breathing period was 4.08(±0.44) s. The coefficient of variance (CV) of the end-to-end amplitude was less than 10% for 50% of the patients and greater than 20 % for 40% of the patients. In 80% of the treatments, the CV of the breathing period was less than 10%. A baseline drift of greater than 2 mm, 3 mm, and 5 mm was observed for 85%, 4%, and 1% of the total treatment times, respectively. The variability (1SD) of baseline drift was within a range of 0.49 to 1.34 mm. The baseline drift versus time showed no correlation (r=0.009, p=0.24). Conclusion SGRT provides an excellent tool to track the respiratory signal of lung SBRT patients. The amplitude variability is less than 5 mm which is consistent with other reported studies. These results can be considered as reference data for decision making for subsequent SBRT lung patients. EP-1634 Combined 4D and 3D cone beam CT protocol for lung SBRT for reliable and fast position verification W. Woliner-van der Weg1, N. Gelens2, V.H.J. LeijserKersten1, P.M. Braam1, J. Bussink1, M. Wendling1 1 UMC St Radboud Nijmegen, Radiation Oncology, Nijmegen, The Netherlands 2 Fontys Paramedische Hogeschool, Medisch Beeldvormende en Radiotherapeutische Technieken MBRT, Eindhoven, The Netherlands Purpose or Objective In our standard lung SBRT position verification protocol, the use of online 3D or 4D cone beam CT (CBCT) is based on the amplitude of tumor motion as measured on 4D planning CT. This results in about 60% of the patients having 4D CBCT position verification. While 3D CBCT takes only 1 min, 4D CBCT lasts about 4 min. With repetitive imaging, this difference considerably contributes to the time needed for position verification, and the time the patient lies on the treatment couch. We reconsidered our position verification protocol, to expand the use of 3D CBCT while maintaining reliable position verification for all patients. Therefore, we developed a decision protocol, in which 4D CBCTs of the first treatment fraction are used for further stratification. Material and Methods For both 3D and 4D CBCT, the first CBCT has to be within 1 mm in all 3 directions compared to the planning CT, otherwise the positioning error is corrected with the treatment couch and a second CBCT is made for verification. The verification CBCT has to be within 2 mm in all 3 directions, otherwise the procedure is repeated. Initial selection for 3D or 4D position verification in our department is based on the 3D amplitude of tumor motion measured on 4D planning CT. Patients with a tumor motion vector length >5 mm are positioned based on 4D CBCT. In the new protocol the choice for 4D CBCT is reconsidered during the treatment course. After the first fraction, the 4D CBCTs are also matched in 3D with the planning CT. Corrections resulting from this match are compared to the corrections resulting from the initial 4D match. If the difference is within 0.5 mm in all 3 directions, for the second and third fraction only the first CBCT is made in 4D, and verification CBCTs are made in 3D. If during the second and third fraction the difference between the 4D and 3D match remain within 0.5 mm in all 3 directions, for the remainder of fractions only 3D online CBCTs are made
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Conclusion This low-cost, computer-vision system for real-time motion monitoring of the irradiation of breast cancer patients showed submillimetric accuracy and acceptable latency. It allowed the authors to highlight differences in surface motion that may be correlated to tumor motion. Madibreast detects and tracks accurately external motion on the breast using low-cost material and accessible opensource, high-level computer vision libraries. It allows immediate monitoring by visually displaying an immediate trace, which can alert that substantial motion could have occurred. Limitations include some remaining failures of the apparatus under low-exposure conditions, as well as considerable CPU occupation. EP-1633 Respiratory Motion Analysis using a Surface Guided Radiation Therapy System for Lung SBRT Patients M. Jermoumi1, D. Cao1, V. Mehta1, D. Shepard1 1 Swedish Cancer Institute, Radiation Oncology, Seattle, USA Purpose or Objective Surface guided radiation therapy (SGRT) uses a camera/projector pair to create a 3D map of a patient’s surface. SGRT can be used to assist in patient set up, real time motion monitoring, and respiratory motion management. In this work, we used SGRT to track the respiratory breathing pattern for lung SBRT patients. An excursion gating approach was employed where the beam delivery was interrupted if the breathing deviated from the expected pattern. The purpose of this work is to evaluate the patients breathing motion during SBRT treatment. Material and Methods To date, 10 NSCLC patients have been enrolled in this study and treated with stereotactic body radiation therapy (SBRT) using a 12Gyx4 fractionation. Prior to each fraction, each patient was aligned using SGRT. Next, a 4DCBCT scan was acquired to align based on internal anatomy. A virtual respiratory tracking point was then placed close on the patient’s surface close to the sternum. The patient’s gating window was set based on the end-toend amplitude measured during the acquisition of the CT at the time of simulation. The gating window was expanded 5 mm beyond the upper level window and 5 mm below the lower level window. In-house developed code was used to evaluate the respiratory data collected from all 40 fractions. The evaluation included an examination of the end-to end amplitude, the breathing period, and baseline drift. The correlation between baseline drift and the treatment time was assessed over the course of treatment. Results The mean (± SD) treatment time was 5.3 (± 1.34) minutes. The mean (± SD) end-to-end amplitude observed due to inter-fraction and intra-fraction motion were 6.79(±2.51) mm and 6.79(±2.86) mm respectively and the mean (± SD)
breathing period was 4.08(±0.44) s. The coefficient of variance (CV) of the end-to-end amplitude was less than 10% for 50% of the patients and greater than 20 % for 40% of the patients. In 80% of the treatments, the CV of the breathing period was less than 10%. A baseline drift of greater than 2 mm, 3 mm, and 5 mm was observed for 85%, 4%, and 1% of the total treatment times, respectively. The variability (1SD) of baseline drift was within a range of 0.49 to 1.34 mm. The baseline drift versus time showed no correlation (r=0.009, p=0.24). Conclusion SGRT provides an excellent tool to track the respiratory signal of lung SBRT patients. The amplitude variability is less than 5 mm which is consistent with other reported studies. These results can be considered as reference data for decision making for subsequent SBRT lung patients. EP-1634 Combined 4D and 3D cone beam CT protocol for lung SBRT for reliable and fast position verification W. Woliner-van der Weg1, N. Gelens2, V.H.J. LeijserKersten1, P.M. Braam1, J. Bussink1, M. Wendling1 1 UMC St Radboud Nijmegen, Radiation Oncology, Nijmegen, The Netherlands 2 Fontys Paramedische Hogeschool, Medisch Beeldvormende en Radiotherapeutische Technieken MBRT, Eindhoven, The Netherlands Purpose or Objective In our standard lung SBRT position verification protocol, the use of online 3D or 4D cone beam CT (CBCT) is based on the amplitude of tumor motion as measured on 4D planning CT. This results in about 60% of the patients having 4D CBCT position verification. While 3D CBCT takes only 1 min, 4D CBCT lasts about 4 min. With repetitive imaging, this difference considerably contributes to the time needed for position verification, and the time the patient lies on the treatment couch. We reconsidered our position verification protocol, to expand the use of 3D CBCT while maintaining reliable position verification for all patients. Therefore, we developed a decision protocol, in which 4D CBCTs of the first treatment fraction are used for further stratification. Material and Methods For both 3D and 4D CBCT, the first CBCT has to be within 1 mm in all 3 directions compared to the planning CT, otherwise the positioning error is corrected with the treatment couch and a second CBCT is made for verification. The verification CBCT has to be within 2 mm in all 3 directions, otherwise the procedure is repeated. Initial selection for 3D or 4D position verification in our department is based on the 3D amplitude of tumor motion measured on 4D planning CT. Patients with a tumor motion vector length >5 mm are positioned based on 4D CBCT. In the new protocol the choice for 4D CBCT is reconsidered during the treatment course. After the first fraction, the 4D CBCTs are also matched in 3D with the planning CT. Corrections resulting from this match are compared to the corrections resulting from the initial 4D match. If the difference is within 0.5 mm in all 3 directions, for the second and third fraction only the first CBCT is made in 4D, and verification CBCTs are made in 3D. If during the second and third fraction the difference between the 4D and 3D match remain within 0.5 mm in all 3 directions, for the remainder of fractions only 3D online CBCTs are made