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EP-1664: Should organs at risk respiratory induced motion be considered during tumor tracking in radiotherapy?
ESTRO 33, 2014 dose difference map together with the gamma results showing the average value and the standard deviation of the 3 experimental determinations.
The usual gamma criteria of 95% of analysed points having a gamma 3%/3mm<1 has to be increased to 5%/3mm to include film dosimetry uncertainties in dose. According to the latter criteria, movements with amplitude of 7 mm or less do not significantly modify the dosimetry. Gating duty cycles of 40% yield also acceptable results for a 2 cm amplitude, which accounts for a 7-8 mm residual movement. The standard deviations increased when increasing the residual movement due to the interplay effect. Although some authors demonstrate that deleterious effects average out in long treatments with several fractions, we strongly recommend to minimize the movement to correctly treat patients in every single fraction.
S231 Figure 1: AlignRT breast surface registration, ROI covering whole of treated breast.
Results: During treatment delivery the mean ± 2SD of the intra-fraction motion was -0.2 ± 4.0, 0.7 ± 4.2 and 0.8 ± 3.8 mm in the AP, SI and LR directions indicating there is no clinically significant systematic drift as might be expected if patients relax on an inclined board. 95% of all rotations were within 2.1° (2SD of the distribution). The observed patient shift tends to increase in magnitude as the time interval between surface capture increases (Table 1). Table 1: Translational shifts of the breast surface in the AP, SI and LR directions (with applied couch shifts removed). Mean values and 2SD are shown. Note positive values correspond to anterior, superior and left shifts for a HFS breast patient.
Conclusions: To safely perform daily accurate dynamic treatments, movements have to be restricted to 7 mm amplitude. Otherwise, a gating strategy must be applied. This work funded by grants FIS PI12-00521 and JP Barcelona AECC 2012 EP-1663 The use of a 3D surface based imaging system to assess intra-fraction motion for breast cancer patients S. Wright1, Y.G.J. Lau1, M. Naisbit1, A. Needham1, R.E.R. Artschan1, J.R. Sykes1 1 Leeds Teaching Hospitals NHS Trust, Medical Physics and Engineering, Leeds, United Kingdom Purpose/Objective: For the IMPORT High trial (CRUK/06/003) a treatment margin of 5 mm around the tumour bed CTV necessitates image guidance for accurate localisation. At our institute IMPORT High patients have CBCT as standard. Conformal breast techniques such as IMPORT High warrant the consideration of breast intra-fraction motion. This study investigates the magnitude of intra-fraction motion using an optical surface based imaging system. Materials and Methods: Nine patients were included in this study. For each patient, three gated surface images were captured using a three camera (pod) AlignRT system (VisionRT, UK) enabling a full lateral wraparound field of view. Surfaces were captured at end exhale: the first, immediately after patient set-up on a Posiboard (Sinmed, Netherlands) with ipsilateral arm raised (reference surface); the second, immediately after CBCT acquisition and any subsequent re-positioning; and the third, following beam delivery. A registration region of interest covering the treated breast was created on the reference surface (Figure 1). The post CBCT and post treatment surface images were registered with the reference (six degrees of freedom). Registration results were corrected for any couch shifts applied to assess the magnitude of intra-fraction motion from set-up to post imaging and from set-up to post treatment delivery.
Conclusions: The intra-fraction motion observed for some breast cancer patients is of a comparable magnitude to the tumour bed CTV to PTV margin. It is worth noting that, as a dual registration technique is utilised and the CBCT correction made prior to treatment is a compromise between the chest wall position and tumour bed coverage, initial alignment to the tumour bed can only be guaranteed to within 5mm. Effective immobilisation for breast patients is increasingly critical with the introduction of conformal treatment techniques such as IMPORT High. This study demonstrates changes in patient position will be increasingly apparent if the patient remains on the bed for longer; efforts should be made to optimise the time required to perform imaging registration techniques for example by considering automatic as opposed to manual matching techniques. EP-1664 Should organs at risk respiratory induced motion be considered during tumor tracking in radiotherapy? M. Gilles1, N. Boussion1, O. Pradier2, D. Visvikis1, H. Fayad3 1 INSERM UMR 1101, LaTIM, Brest, France 2 CHU Morvan, Radiotherapy, Brest, France 3 INSERM UMR 1101 - LaTIM, UBO, Brest, France Purpose/Objective: The objective of this study is to evaluate the necessity to account for the organs at risk (OARs) respiratory induce motion in conformal radiotherapy in addition to tumor displacement. Materials and Methods: For 18 patients with lung cancer, all radiotherapy treatment planning were generated using three different CT volumes: the two extreme respiratory phases corresponding to the full inspiration (planning 1) and the full expiration (planning 3) as well as a manually deformed phase (full inspiration with the full expiration tumor location, planning 2) simulating the idea of taking into account tumor motion without handling OARs motion. Planning was initially done on the full inspiration CT then transferred to planning 2 and planning 3. The dose coverage of the different planning schemes and the dose delivered to the OARs were compared using conformational indexes and generalized equivalent uniform dose. Results: This study indicates no correlation between the tumor displacement and the planning quality nor with the dose received by the
S232
ESTRO 33, 2014
OARs. Planning schemes differ while considering tumor and OARs motion in comparison to those considering only tumor variations. 83% of planning 3 are worse than planning 2 for both Healthy Tissue Conformity Index and Healthy Tissue Overdosage Factor indexes. Mean doses to the OARs when accounting for all the anatomic changes are always superior than considering only the tumor displacement: we noticed a mean difference between these two planning scenarios of 1±1.37 Gy for the heart with a maximum of 3.8 Gy and 1.4±1.42 Gy for the ill lung with a maximum of 4.8 Gy as reported in Figure 1.
Conclusions: OARs deformations due to breathing motion are better to be included in the treatment planning rather than just tracking the tumor. This allows an OARs dose reduction and/or a tumor dose escalation. As regard to the diversity of patient cases, a generic study would not be feasible and patient specific respiratory motion characteristics should be identified before proceeding to the radiotherapy planning and delivery. EP-1665 2D/3D registration for pre-treatment lung tumor motion analysis using CBCT for intra-fractional tracking H. Furtado1, E. Steiner2, M. Stock2, D. Georg2, W. Birkfellner1 1 Medical University of Vienna/AKH Vienna, Center for Medical Physics and Biomedical Engineering & Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria 2 Medical University of Vienna/AKH Vienna, Department of Radiation Oncology & Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria Purpose/Objective: Intra-fractional tumor motion during radiotherapy is typically dealt with by enlarging the PTV to guarantee full tumor volume irradiation. Real-time 2D/3D registration with on-board kilo-voltage (kV) images is used successfully for tumor motion tracking and can lead to a reduced PTV. The success of this technique is highly dependent on X-ray histogram content, adjusted by changing brightness and contrast. To apply the technique from the beginning of treatment, adjustments have to be determined beforehand. In this work, we performed tumor motion tracking in CBCT projection images and pre-determined settings to automatically adjust intensities of intra-fractional kV X-rays for subsequent applications during treatment. Materials and Methods: For the study we used data from five patients suffering from NSCLC undergoing regular SBRT treatment at our center. Initially we performed 2D/3D registration in 5 degrees-of-freedom (DOF) using the planning CT for DRR generation comparing with sequences of approximately 650 X-ray images acquired previous to treatment for CBCT reconstruction. The contrast was automatically maximized in the PTV region. The motion signal was compared to a manually annotated ground truth. Manual adjustments were made until tracking was successful for as many projections as possible. Then, 5DOF intra-fractional motion tracking by 2D/3D registration was performed for a fixed gantry angle using the settings obtained in the previous step and compared with tracking using manual adjustments. We computed the root-mean-square (RMS) of the difference between the tracking signals obtained for automatic and manual approaches and the correlation between both signals. Results: Figure 1a shows a plot of the extracted tumor motion in the CBCT projections in CC direction (red) and, the annotated motion (dashed) for one patient. Tracking is successful for most projections except at angles where tumor visibility is obstructed, typically close to lateral projections. Fig. 1b shows the tracking result and Fig. 1c the error, between manual and automated approaches for one of the treatment angles. Table 1 summarizes the results for the fixed gantry angle motion tracking during treatment. The difference between both approaches is very small with an RMS error in translation smaller than 1 mm and excellent correlation in most cases (see Table).
Conclusions: We evaluated tumor motion extraction on CBCT projection images using 2D/3D registration and used the obtained intensity settings for adjustment of X-ray intensities for intra-fractional registration. Our results show that the automatic adjustment leads to motion extraction which is as accurate as with manual adjustment. This enables tumor tracking for fixed gantry angles as soon as treatment starts. Motion could not be extracted in an optimal manner for all projections but paired registration with mega-voltage treatment beam images might improve the results. This technique could also be applied for motion tracking during VMAT treatments. EP-1666 Evaluation of methods for proton treatment planning in lung cancer patients M. Sutto1, D. Ravanelli2, F. Fellin2, M.L. Belli3, G.M. Cattaneo3, E. Scalco4, G. Rizzo4, M. Schwarz2 1 Università degli studi di Trento, Physics, Trento, Italy 2 ATREP, Medical Physics, Trento, Italy 3 Ospedale San Raffaele, Medical Physics, Milano, Italy 4 CNR, Istituto di Bioimmagini e Fisiologia Molecolare, Milano, Italy Purpose/Objective: Identify the best anatomy representation(s) of lung cancer patients with respect to the aim of producing proton therapy plans as robust as photon plans in presence of intra-fraction respiratory motion. Materials and Methods: 64DCT studies with 6 breathing phases each were used. Initially,2-fields IMPT plans were optimized for 2 of these studies (1-2, Table1) on 5 artificial anatomies: average, MIP, mid-exhale phase (X), X +ITV filled with MIP (X-ITVMIP), average + ITV filled with MIP(Avg-ITVMIP). The nominal dose distributions met the objectives on the ITV: Dprescription=70Gy, V95%>98%,V98%>95%,V107%<2%,and on the lung parenchyma: Davg< 15 Gy, V20< 25%. The nominal plans were recalculated on each phase, deformed on a reference phase and accumulated into the actual delivered 4D dose distributions. Accumulated doses were evaluated in terms of GTV coverage and OARs sparing. The 2 planning anatomies performing the best were selected for further IMPT plans on the remaining 4 patient dataset studies (3-6, Table 1). In 2 studies Rapid-Arc plans were optimized on X, average and MIP anatomies with the same objectives except V98%>95%.
The usual gamma criteria of 95% of analysed points having a gamma 3%/3mm<1 has to be increased to 5%/3mm to include film dosimetry uncertainties in dose. According to the latter criteria, movements with amplitude of 7 mm or less do not significantly modify the dosimetry. Gating duty cycles of 40% yield also acceptable results for a 2 cm amplitude, which accounts for a 7-8 mm residual movement. The standard deviations increased when increasing the residual movement due to the interplay effect. Although some authors demonstrate that deleterious effects average out in long treatments with several fractions, we strongly recommend to minimize the movement to correctly treat patients in every single fraction.
S231 Figure 1: AlignRT breast surface registration, ROI covering whole of treated breast.
Results: During treatment delivery the mean ± 2SD of the intra-fraction motion was -0.2 ± 4.0, 0.7 ± 4.2 and 0.8 ± 3.8 mm in the AP, SI and LR directions indicating there is no clinically significant systematic drift as might be expected if patients relax on an inclined board. 95% of all rotations were within 2.1° (2SD of the distribution). The observed patient shift tends to increase in magnitude as the time interval between surface capture increases (Table 1). Table 1: Translational shifts of the breast surface in the AP, SI and LR directions (with applied couch shifts removed). Mean values and 2SD are shown. Note positive values correspond to anterior, superior and left shifts for a HFS breast patient.
Conclusions: To safely perform daily accurate dynamic treatments, movements have to be restricted to 7 mm amplitude. Otherwise, a gating strategy must be applied. This work funded by grants FIS PI12-00521 and JP Barcelona AECC 2012 EP-1663 The use of a 3D surface based imaging system to assess intra-fraction motion for breast cancer patients S. Wright1, Y.G.J. Lau1, M. Naisbit1, A. Needham1, R.E.R. Artschan1, J.R. Sykes1 1 Leeds Teaching Hospitals NHS Trust, Medical Physics and Engineering, Leeds, United Kingdom Purpose/Objective: For the IMPORT High trial (CRUK/06/003) a treatment margin of 5 mm around the tumour bed CTV necessitates image guidance for accurate localisation. At our institute IMPORT High patients have CBCT as standard. Conformal breast techniques such as IMPORT High warrant the consideration of breast intra-fraction motion. This study investigates the magnitude of intra-fraction motion using an optical surface based imaging system. Materials and Methods: Nine patients were included in this study. For each patient, three gated surface images were captured using a three camera (pod) AlignRT system (VisionRT, UK) enabling a full lateral wraparound field of view. Surfaces were captured at end exhale: the first, immediately after patient set-up on a Posiboard (Sinmed, Netherlands) with ipsilateral arm raised (reference surface); the second, immediately after CBCT acquisition and any subsequent re-positioning; and the third, following beam delivery. A registration region of interest covering the treated breast was created on the reference surface (Figure 1). The post CBCT and post treatment surface images were registered with the reference (six degrees of freedom). Registration results were corrected for any couch shifts applied to assess the magnitude of intra-fraction motion from set-up to post imaging and from set-up to post treatment delivery.
Conclusions: The intra-fraction motion observed for some breast cancer patients is of a comparable magnitude to the tumour bed CTV to PTV margin. It is worth noting that, as a dual registration technique is utilised and the CBCT correction made prior to treatment is a compromise between the chest wall position and tumour bed coverage, initial alignment to the tumour bed can only be guaranteed to within 5mm. Effective immobilisation for breast patients is increasingly critical with the introduction of conformal treatment techniques such as IMPORT High. This study demonstrates changes in patient position will be increasingly apparent if the patient remains on the bed for longer; efforts should be made to optimise the time required to perform imaging registration techniques for example by considering automatic as opposed to manual matching techniques. EP-1664 Should organs at risk respiratory induced motion be considered during tumor tracking in radiotherapy? M. Gilles1, N. Boussion1, O. Pradier2, D. Visvikis1, H. Fayad3 1 INSERM UMR 1101, LaTIM, Brest, France 2 CHU Morvan, Radiotherapy, Brest, France 3 INSERM UMR 1101 - LaTIM, UBO, Brest, France Purpose/Objective: The objective of this study is to evaluate the necessity to account for the organs at risk (OARs) respiratory induce motion in conformal radiotherapy in addition to tumor displacement. Materials and Methods: For 18 patients with lung cancer, all radiotherapy treatment planning were generated using three different CT volumes: the two extreme respiratory phases corresponding to the full inspiration (planning 1) and the full expiration (planning 3) as well as a manually deformed phase (full inspiration with the full expiration tumor location, planning 2) simulating the idea of taking into account tumor motion without handling OARs motion. Planning was initially done on the full inspiration CT then transferred to planning 2 and planning 3. The dose coverage of the different planning schemes and the dose delivered to the OARs were compared using conformational indexes and generalized equivalent uniform dose. Results: This study indicates no correlation between the tumor displacement and the planning quality nor with the dose received by the
S232
ESTRO 33, 2014
OARs. Planning schemes differ while considering tumor and OARs motion in comparison to those considering only tumor variations. 83% of planning 3 are worse than planning 2 for both Healthy Tissue Conformity Index and Healthy Tissue Overdosage Factor indexes. Mean doses to the OARs when accounting for all the anatomic changes are always superior than considering only the tumor displacement: we noticed a mean difference between these two planning scenarios of 1±1.37 Gy for the heart with a maximum of 3.8 Gy and 1.4±1.42 Gy for the ill lung with a maximum of 4.8 Gy as reported in Figure 1.
Conclusions: OARs deformations due to breathing motion are better to be included in the treatment planning rather than just tracking the tumor. This allows an OARs dose reduction and/or a tumor dose escalation. As regard to the diversity of patient cases, a generic study would not be feasible and patient specific respiratory motion characteristics should be identified before proceeding to the radiotherapy planning and delivery. EP-1665 2D/3D registration for pre-treatment lung tumor motion analysis using CBCT for intra-fractional tracking H. Furtado1, E. Steiner2, M. Stock2, D. Georg2, W. Birkfellner1 1 Medical University of Vienna/AKH Vienna, Center for Medical Physics and Biomedical Engineering & Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria 2 Medical University of Vienna/AKH Vienna, Department of Radiation Oncology & Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria Purpose/Objective: Intra-fractional tumor motion during radiotherapy is typically dealt with by enlarging the PTV to guarantee full tumor volume irradiation. Real-time 2D/3D registration with on-board kilo-voltage (kV) images is used successfully for tumor motion tracking and can lead to a reduced PTV. The success of this technique is highly dependent on X-ray histogram content, adjusted by changing brightness and contrast. To apply the technique from the beginning of treatment, adjustments have to be determined beforehand. In this work, we performed tumor motion tracking in CBCT projection images and pre-determined settings to automatically adjust intensities of intra-fractional kV X-rays for subsequent applications during treatment. Materials and Methods: For the study we used data from five patients suffering from NSCLC undergoing regular SBRT treatment at our center. Initially we performed 2D/3D registration in 5 degrees-of-freedom (DOF) using the planning CT for DRR generation comparing with sequences of approximately 650 X-ray images acquired previous to treatment for CBCT reconstruction. The contrast was automatically maximized in the PTV region. The motion signal was compared to a manually annotated ground truth. Manual adjustments were made until tracking was successful for as many projections as possible. Then, 5DOF intra-fractional motion tracking by 2D/3D registration was performed for a fixed gantry angle using the settings obtained in the previous step and compared with tracking using manual adjustments. We computed the root-mean-square (RMS) of the difference between the tracking signals obtained for automatic and manual approaches and the correlation between both signals. Results: Figure 1a shows a plot of the extracted tumor motion in the CBCT projections in CC direction (red) and, the annotated motion (dashed) for one patient. Tracking is successful for most projections except at angles where tumor visibility is obstructed, typically close to lateral projections. Fig. 1b shows the tracking result and Fig. 1c the error, between manual and automated approaches for one of the treatment angles. Table 1 summarizes the results for the fixed gantry angle motion tracking during treatment. The difference between both approaches is very small with an RMS error in translation smaller than 1 mm and excellent correlation in most cases (see Table).
Conclusions: We evaluated tumor motion extraction on CBCT projection images using 2D/3D registration and used the obtained intensity settings for adjustment of X-ray intensities for intra-fractional registration. Our results show that the automatic adjustment leads to motion extraction which is as accurate as with manual adjustment. This enables tumor tracking for fixed gantry angles as soon as treatment starts. Motion could not be extracted in an optimal manner for all projections but paired registration with mega-voltage treatment beam images might improve the results. This technique could also be applied for motion tracking during VMAT treatments. EP-1666 Evaluation of methods for proton treatment planning in lung cancer patients M. Sutto1, D. Ravanelli2, F. Fellin2, M.L. Belli3, G.M. Cattaneo3, E. Scalco4, G. Rizzo4, M. Schwarz2 1 Università degli studi di Trento, Physics, Trento, Italy 2 ATREP, Medical Physics, Trento, Italy 3 Ospedale San Raffaele, Medical Physics, Milano, Italy 4 CNR, Istituto di Bioimmagini e Fisiologia Molecolare, Milano, Italy Purpose/Objective: Identify the best anatomy representation(s) of lung cancer patients with respect to the aim of producing proton therapy plans as robust as photon plans in presence of intra-fraction respiratory motion. Materials and Methods: 64DCT studies with 6 breathing phases each were used. Initially,2-fields IMPT plans were optimized for 2 of these studies (1-2, Table1) on 5 artificial anatomies: average, MIP, mid-exhale phase (X), X +ITV filled with MIP (X-ITVMIP), average + ITV filled with MIP(Avg-ITVMIP). The nominal dose distributions met the objectives on the ITV: Dprescription=70Gy, V95%>98%,V98%>95%,V107%<2%,and on the lung parenchyma: Davg< 15 Gy, V20< 25%. The nominal plans were recalculated on each phase, deformed on a reference phase and accumulated into the actual delivered 4D dose distributions. Accumulated doses were evaluated in terms of GTV coverage and OARs sparing. The 2 planning anatomies performing the best were selected for further IMPT plans on the remaining 4 patient dataset studies (3-6, Table 1). In 2 studies Rapid-Arc plans were optimized on X, average and MIP anatomies with the same objectives except V98%>95%.