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EP-1640: Can pre-treatment 4DCT-based motion margins estimates be trusted for proton radiotherapy?
ESTRO 33, 2014
S221
the new monitoring system was detected to be ≤ 1 mm and ≤ 1° with threshold values of three sensors in real-time.The threshold values of sensor pressures with 87% of detection accuracy were +4.1 kPa at superior side, -4.3 kPa and +4.9 kPa at left side, and -6.4 kPa and +5.5 kPa at right side, respectively. In addition, there was a statistical significant difference between the groups of the RSS values > 1 mm and ≤ 1 mm in the values of absolute pressures at left and right side of the sensor, and the mean values of absolute pressure of all sensors. The pressures in the RSS values ≤ 1 mm were smaller than those values > 1 mm (falling12.2 kPa vs. exceeding 12.4 kPa).
tumor motionis based on real patient lung tumor trajectories recorded over multiple days.Using 'Day 1' patient data, 100 ITVs were generated with 1 s interval betweenconsecutive scan start times. Each ITV was made up by the union of 10 tumor positions obtained from 6 s scan time. Two ITV volumes were chosen for treatment planning: ITVmean-σ and ITVmean+σ. The delivered dose was computed on i) 10phases forming the planning ITV ('10-phase' - simulating dose calculation basedon 4D-CT) and ii) 50 phantoms produced from 100 s of data from any other day with tumor positions sampled every 2 s('dynamic' - simulating the dose that would actually be delivered).
Conclusions: The dedicated real-time monitoring system using patient surface pressure can detect intra-fractional motion in intracranial treatment with high precision of 1 mm and 1°. Intra-fractional head motion could be reduced by using the pressure within 12 kPa given to the head.
Results: For similar breathing patterns between 'Day 1' and any other 'DayN(>1)', the 95% volume coverage (D95) for 'dynamic' case was 8.13% lower than the '10-phase' case for ITVmean+σ. For breathing patterns that were very different between 'Day 1' and any other 'Day N(>1)', this difference was as high as 24.5% for ITVmean-σ.
EP-1639 Fast evaluation of interplay effects in proton scanning therapy for mobile targets in free breathing patients A. Protik1, M. Van Herk1, J.J. Sonke1, Y. Szeto1 1 The Netherlands Cancer Institute, Radiation Oncology, Amsterdam, The Netherlands
Conclusions: Proton treatment planning based on pre-treatment 4DCT can lead to under-dosage of the tumor and over-dosage of the surrounding tissues, because of inadequate estimate of the range of motion of the tumor. This is due to the shift of the Bragg peak compared to photon therapy in which the tumor is surrounded by an electron bath.
Purpose/Objective: To compare Single Field Uniform Dose (SFUD) and Intensity ModulatedProton Therapy (IMPT) treatment plans for lung cancer patients in terms of dose inhomogeneity introduced by interplay and range effects under realistic respiration motion. Materials and Methods: We analyzed three patients with an isolated lung tumor with motion amplitudes of 2cm, 1.8cm and 1.7cm in craniocaudal direction. SFUD and IMPTplans with two beams were optimized with Pinnacle v 9.2 on the mid-position CT with IGTV density override. The 3D dose distributions were recreated from a single spot dose with inhouse software utilizing spot position and weight data from the pinnacle plan. Interplay effects occur due to the scanning beam delivery, respiration motion and breathing irregularities. To take these effects into account in the dose reconstruction process each single spot is synchronously deformed with previously developed instantaneous motion model.The model has two components: 1) a 4D CT motion model that tracks the anatomical changes due to the respiration as described in a 4D deformation vector field and 2) An Amsterdam shroud analysis of the breathing motion on actual patients during acquisition of 4D cone beam CT by analyzing the diaphragm position in projection images. The phase in the 4D CT model, scale and offset of the deformation is derived from the Amsterdam shroud data to accurately simulate irregular respiration. Differences in range were simulated by ray tracing the reference CT and deformed CT and shifting the location of the Bragg peaks according to their difference. As reference dose distribution the total dose without motion was blurred according to instantaneous motion model, i.e., without interplay and range effects. For SFUD and IMPT plans, the distribution of the dose difference between blurred dose and simulated dose was evaluated inside the PTV.
EP-1641 PTV margin calculation and time dependency monitoring of intrafraction isocenter movement in lung SBRT by ExacTrac S. Paul1, B. Sarkar1, T. Ganesh1, A. Munshi1, R. Kumar1, B.K. Mohanti1 1 Fortis Memorial Research Institute, Radiation Oncology, Gurgaon, India Purpose/Objective: Lung stereotactic body radiotherapy (SBRT) is the new emerging treatment modality of delivering high dose per fraction in early stage lung cancer. Because of high dose gradient set up accuracy is of utmost importance to avoid geographic miss and high normal tissue complication probability. Many research works have been done to manage organ motion in lung SBRT but intra fraction set up accuracy data is sparse. We monitored the time dependency of intra-fraction isocenter movement by intra-fraction translational error determination by ExacTrac in room kv imaging and subsequently calculated appropriate planning targetvolume (PTV) margin to incorporate this intrafraction isocenter movement. Materials and Methods: Five patients were planned for lung SBRT using bluebag and body fix. 4-D CT scan were taken and Internal target volume (ITV) generated on maximum intensity projection (MIP) image and 6 mm set up margin were given to produce PTV. Total 22 fractions were delivered for five patients and 265 pair of KV images were acquired by ExacTrac. Before starting of treatment and during treatment in 20 second interval ExacTrac translational shift data recorded for each fraction by automated bony matching of vertebrae. Statistical analysis of dependency of isocenter movement on time and no of fraction was done and PTV margin appropriate to incorporate these movement based on these shift data was calculated using van Herk's formula.
Conclusions: We developed a novel method to estimate the impact of interplay effecton spot scanning proton plans using realistic respiratory traces. Preliminary results indicate similar sensitivity of SFUD and IMPT to the interplay effect. Evaluation of repaint strategies and inclusion of more cases remain to be done.
Results: Mean and standard deviation (SD) of Rt-Lt (X), AnteroPosterior(Z) and Supero-Inferior(Y) shifts are calculated for each fraction of delivery. Each treatment session consists of 10-13 acceptable shift data determined by both the floor mounted X ray image matching of ExacTrac. The calculated margins by van Herk's formula in X, Y and Z direction is 31 mm, 37 mm, 45 mm respectively. Further the time dependency of the isocenter movement was plotted.This shows a typical sinusoidal variation for all cases with different periodicity. We could plot the mean±1.96SD for 4 cases. All the shifts in x, y and z direction can be correlated to a definite mathematical formulation, however X and Z direction shows a periodicity with sinusoidal variation. All patients in all directions show a reduction in the set up error with increasing number of fraction.
EP-1640 Can pre-treatment 4DCT-based motion margins estimates be trusted for proton radiotherapy? J. Seco1, O. Koybasi1, P. Mishra2, S. St James2, J.H. Lewis2 1 Massachusetts General Hospital, Radiation Oncology, Boston, USA 2 Brigham and Women Hospital, Radiation Oncology, Boston, USA
Conclusions: From our observation it is clear that isocenter movement increases with increasing treatment time and decreases with increasing fraction number . These intrafraction movement should also be considered along with radiobiological evidence during optimizing treatment delivery time and no of fraction and at least 5 mm PTV margin should be given to incorporate these intrafraction shifts.
Purpose/Objective: Radiotherapy motion margins are generated using pre-treatment 4DCT data. The purpose of this study is to assess ifpretreatment 4DCT is sufficient in proton therapy to provide accurate estimate of motion margins. A dosimetric assessment is performed comparing pre-treatment margins with daily-customized margins.
EP-1642 Control of respiratory motion by hypnosis intervention during radiotherapy of lung cancer Y. Xie1, R. Li1 1 Shenzhen Institutes of Advanced Technology, Institute of Biomedical and Health Engineering, Shenzhen, China
Results: Simulation of a typical 2 field plan took around 40 minutes on an 8 core processor.To assess the impact of interplay effect the SD (standard deviation) of the dose differences between reference and simulated dose distribution was calculated over the mean of the blurred dose.Our preliminary results demonstrate a dose inhomogeneity of around 10% for both in SFUD and IMPT inside the PTV.
Materials and Methods: Gold fiducial markers implanted in lung tumors of patients were used to track the tumor. A spherical tumor of diameter 20 mm isinserted into a realistic digital respiratory phantom, where the
Purpose/Objective: To effectively control respiratory motion during radiotherapy of lung cancer without any side effects.
S221
the new monitoring system was detected to be ≤ 1 mm and ≤ 1° with threshold values of three sensors in real-time.The threshold values of sensor pressures with 87% of detection accuracy were +4.1 kPa at superior side, -4.3 kPa and +4.9 kPa at left side, and -6.4 kPa and +5.5 kPa at right side, respectively. In addition, there was a statistical significant difference between the groups of the RSS values > 1 mm and ≤ 1 mm in the values of absolute pressures at left and right side of the sensor, and the mean values of absolute pressure of all sensors. The pressures in the RSS values ≤ 1 mm were smaller than those values > 1 mm (falling12.2 kPa vs. exceeding 12.4 kPa).
tumor motionis based on real patient lung tumor trajectories recorded over multiple days.Using 'Day 1' patient data, 100 ITVs were generated with 1 s interval betweenconsecutive scan start times. Each ITV was made up by the union of 10 tumor positions obtained from 6 s scan time. Two ITV volumes were chosen for treatment planning: ITVmean-σ and ITVmean+σ. The delivered dose was computed on i) 10phases forming the planning ITV ('10-phase' - simulating dose calculation basedon 4D-CT) and ii) 50 phantoms produced from 100 s of data from any other day with tumor positions sampled every 2 s('dynamic' - simulating the dose that would actually be delivered).
Conclusions: The dedicated real-time monitoring system using patient surface pressure can detect intra-fractional motion in intracranial treatment with high precision of 1 mm and 1°. Intra-fractional head motion could be reduced by using the pressure within 12 kPa given to the head.
Results: For similar breathing patterns between 'Day 1' and any other 'DayN(>1)', the 95% volume coverage (D95) for 'dynamic' case was 8.13% lower than the '10-phase' case for ITVmean+σ. For breathing patterns that were very different between 'Day 1' and any other 'Day N(>1)', this difference was as high as 24.5% for ITVmean-σ.
EP-1639 Fast evaluation of interplay effects in proton scanning therapy for mobile targets in free breathing patients A. Protik1, M. Van Herk1, J.J. Sonke1, Y. Szeto1 1 The Netherlands Cancer Institute, Radiation Oncology, Amsterdam, The Netherlands
Conclusions: Proton treatment planning based on pre-treatment 4DCT can lead to under-dosage of the tumor and over-dosage of the surrounding tissues, because of inadequate estimate of the range of motion of the tumor. This is due to the shift of the Bragg peak compared to photon therapy in which the tumor is surrounded by an electron bath.
Purpose/Objective: To compare Single Field Uniform Dose (SFUD) and Intensity ModulatedProton Therapy (IMPT) treatment plans for lung cancer patients in terms of dose inhomogeneity introduced by interplay and range effects under realistic respiration motion. Materials and Methods: We analyzed three patients with an isolated lung tumor with motion amplitudes of 2cm, 1.8cm and 1.7cm in craniocaudal direction. SFUD and IMPTplans with two beams were optimized with Pinnacle v 9.2 on the mid-position CT with IGTV density override. The 3D dose distributions were recreated from a single spot dose with inhouse software utilizing spot position and weight data from the pinnacle plan. Interplay effects occur due to the scanning beam delivery, respiration motion and breathing irregularities. To take these effects into account in the dose reconstruction process each single spot is synchronously deformed with previously developed instantaneous motion model.The model has two components: 1) a 4D CT motion model that tracks the anatomical changes due to the respiration as described in a 4D deformation vector field and 2) An Amsterdam shroud analysis of the breathing motion on actual patients during acquisition of 4D cone beam CT by analyzing the diaphragm position in projection images. The phase in the 4D CT model, scale and offset of the deformation is derived from the Amsterdam shroud data to accurately simulate irregular respiration. Differences in range were simulated by ray tracing the reference CT and deformed CT and shifting the location of the Bragg peaks according to their difference. As reference dose distribution the total dose without motion was blurred according to instantaneous motion model, i.e., without interplay and range effects. For SFUD and IMPT plans, the distribution of the dose difference between blurred dose and simulated dose was evaluated inside the PTV.
EP-1641 PTV margin calculation and time dependency monitoring of intrafraction isocenter movement in lung SBRT by ExacTrac S. Paul1, B. Sarkar1, T. Ganesh1, A. Munshi1, R. Kumar1, B.K. Mohanti1 1 Fortis Memorial Research Institute, Radiation Oncology, Gurgaon, India Purpose/Objective: Lung stereotactic body radiotherapy (SBRT) is the new emerging treatment modality of delivering high dose per fraction in early stage lung cancer. Because of high dose gradient set up accuracy is of utmost importance to avoid geographic miss and high normal tissue complication probability. Many research works have been done to manage organ motion in lung SBRT but intra fraction set up accuracy data is sparse. We monitored the time dependency of intra-fraction isocenter movement by intra-fraction translational error determination by ExacTrac in room kv imaging and subsequently calculated appropriate planning targetvolume (PTV) margin to incorporate this intrafraction isocenter movement. Materials and Methods: Five patients were planned for lung SBRT using bluebag and body fix. 4-D CT scan were taken and Internal target volume (ITV) generated on maximum intensity projection (MIP) image and 6 mm set up margin were given to produce PTV. Total 22 fractions were delivered for five patients and 265 pair of KV images were acquired by ExacTrac. Before starting of treatment and during treatment in 20 second interval ExacTrac translational shift data recorded for each fraction by automated bony matching of vertebrae. Statistical analysis of dependency of isocenter movement on time and no of fraction was done and PTV margin appropriate to incorporate these movement based on these shift data was calculated using van Herk's formula.
Conclusions: We developed a novel method to estimate the impact of interplay effecton spot scanning proton plans using realistic respiratory traces. Preliminary results indicate similar sensitivity of SFUD and IMPT to the interplay effect. Evaluation of repaint strategies and inclusion of more cases remain to be done.
Results: Mean and standard deviation (SD) of Rt-Lt (X), AnteroPosterior(Z) and Supero-Inferior(Y) shifts are calculated for each fraction of delivery. Each treatment session consists of 10-13 acceptable shift data determined by both the floor mounted X ray image matching of ExacTrac. The calculated margins by van Herk's formula in X, Y and Z direction is 31 mm, 37 mm, 45 mm respectively. Further the time dependency of the isocenter movement was plotted.This shows a typical sinusoidal variation for all cases with different periodicity. We could plot the mean±1.96SD for 4 cases. All the shifts in x, y and z direction can be correlated to a definite mathematical formulation, however X and Z direction shows a periodicity with sinusoidal variation. All patients in all directions show a reduction in the set up error with increasing number of fraction.
EP-1640 Can pre-treatment 4DCT-based motion margins estimates be trusted for proton radiotherapy? J. Seco1, O. Koybasi1, P. Mishra2, S. St James2, J.H. Lewis2 1 Massachusetts General Hospital, Radiation Oncology, Boston, USA 2 Brigham and Women Hospital, Radiation Oncology, Boston, USA
Conclusions: From our observation it is clear that isocenter movement increases with increasing treatment time and decreases with increasing fraction number . These intrafraction movement should also be considered along with radiobiological evidence during optimizing treatment delivery time and no of fraction and at least 5 mm PTV margin should be given to incorporate these intrafraction shifts.
Purpose/Objective: Radiotherapy motion margins are generated using pre-treatment 4DCT data. The purpose of this study is to assess ifpretreatment 4DCT is sufficient in proton therapy to provide accurate estimate of motion margins. A dosimetric assessment is performed comparing pre-treatment margins with daily-customized margins.
EP-1642 Control of respiratory motion by hypnosis intervention during radiotherapy of lung cancer Y. Xie1, R. Li1 1 Shenzhen Institutes of Advanced Technology, Institute of Biomedical and Health Engineering, Shenzhen, China
Results: Simulation of a typical 2 field plan took around 40 minutes on an 8 core processor.To assess the impact of interplay effect the SD (standard deviation) of the dose differences between reference and simulated dose distribution was calculated over the mean of the blurred dose.Our preliminary results demonstrate a dose inhomogeneity of around 10% for both in SFUD and IMPT inside the PTV.
Materials and Methods: Gold fiducial markers implanted in lung tumors of patients were used to track the tumor. A spherical tumor of diameter 20 mm isinserted into a realistic digital respiratory phantom, where the
Purpose/Objective: To effectively control respiratory motion during radiotherapy of lung cancer without any side effects.