- Email: [email protected]
Feasibility of Gating Using a Magnetic-Resonance Image Guided Radiation Therapy (MR-IGRT) System
Volume 90 Number 1S Supplement 2014 motion X Z 6.3 (range: 5.9-7.1) mm, Y Z 10.4 (9.6-11.2) mm, and Z Z 7.1 (6.6-7.7) mm. Root Mean Square (RMS) error between TT-tracked tumor motion and RPM was <0.9mm in all directions. Tumor B (4cm3): TT could not track the position of the tumor at all angles as half-fan CBCT captured the tumor in only half of the images and high density and central airway structures obscured the target. Therefore, analysis was only performed for 100 (300-40 ) kV-source rotation. 4DCT motion was X Z 1.8, Y Z 7.5 and Z Z 8.6 mm. 100 TT on clinical kV projection series showed mean motion X Z 3.7 (2.5-5.8) mm, Y Z 7.3 (5.3-9.2) mm, and Z Z 7.8 (5.5-10.6) mm. RMS error between TT and RPM was <1.1mm. Benchmarking tumor A: 360 TT showed mean motion X Z 3.5, Y Z 11.6 and Z Z 5.2 mm with standard deviation (SD) <0.7mm. Correlation coefficients of TT-tracked tumor motion with center of mass displacement on 4DCT were 0.64, 0.95 and 0.84 (X, Y, Z). For tumor B: 2 sets of TT over 100 (300-40 /120-220 ) showed mean motion X Z 1.9, Y Z 7.7 and Z Z 8.4mm (SD<0.8mm) and correlation coefficients of 0.63, 0.94 and 0.91 (X, Y, Z). Conclusions: TT software can track small lung tumors when they are visible in kV projections. Tumor motion during CBCT can vary from the planning 4DCT. TT and RPM motion were closely associated. Benchmarking TT against known tumor displacements showed good agreement. Author Disclosure: J.R. van Sornsen de Koste: I. Travel Expenses; has received travel support of Varian Medical Systems. M. Dahele: I. Travel Expenses; has received travel support/honoraria from Varian Medical Systems and travel support from Brainlab. S. Senan: I. Travel Expenses; has received travel support and honoraria from Varian Medical Systems. B. Slotman: I. Travel Expenses; has received travel support/honoraria from Varian Medical Systems. W. Verbakel: I. Travel Expenses; has received travel/honoraria support from Varian Medical Systems.
3609 Feasibility of X-Ray Acoustic Computed Tomography as a Tool for Noninvasive Volumetric In Vivo Dosimetry S. Hickling,1 M. Hobson,2 and I. El Naqa2; 1McGill University, Montreal, QC, Canada, 2McGill University Health Centre, Montreal, QC, Canada Purpose/Objective(s): We propose that the novel modality of x-ray acoustic computed tomography (XACT) has the potential to be an effective tool for non-invasive in vivo dosimetry during external beam radiation therapy. XACT is based on the principle that acoustic waves proportional to the dose deposited are created following each radiation pulse. After detecting these acoustic waves with an ultrasound transducer array, an image of the dose distribution can be reconstructed. This work tests the feasibility of using XACT as a real-time dosimeter by performing realistic simulations to determine the expected amplitude and frequency of the induced acoustic waves for a typical clinical prostate case. The dose distribution is then reconstructed and compared to the treatment plan. Materials/Methods: Commercially available treatment planning software was used to obtain the dose distribution for a clinical prostate patient treated using a four-field box technique with 18 MV photon beams. A 2D map of the initial acoustic pressure distribution for a slice in the middle of the target was calculated for each LINAC pulse using the dose and CT data. An open source toolkit for the simulation of acoustic wave fields was then used to generate the expected time-varying signal at 360 transducer locations spaced equally around the patient. The transducers were assumed to be ideal and able to detect all wave frequencies up to a maximum simulated frequency of 1.6 MHz. Acoustic wave attenuation was not accounted for. A time reversal reconstruction algorithm was then used to obtain an XACT image of the dose for each LINAC pulse, after which a composite dose distribution for the entire fraction was derived. Results: The detected acoustic waves had a differential pressure amplitude on the order of 1 Pa to 10 Pa, with the main frequency component of the signal falling below 1 MHz. The reconstructed dose distribution closely resembled the plan, with 89% of pixels passing a 3% / 3 mm 2D gamma test. The largest dose discrepancies occurred at the interfaces of anatomical structures, such as the femur, pelvic bone, and seminal vesicles. This could be caused by the lack of frequency information above 1.6 MHz and the finite number of transducer positions.
Poster Viewing Abstracts S843 Conclusions: The simulated amplitude and frequency of the induced acoustic waves for a typical clinical prostate case indicate that they should be detectable with commercial ultrasound transducers. Further investigation of detector geometry, reconstruction algorithms and image post-processing could improve the agreement of the reconstructed and original dose distributions. An experimental validation of these simulations is ongoing. We conclude that XACT is a promising technique for volumetric non-invasive in vivo dosimetry and merits further research. Author Disclosure: S. Hickling: None. M. Hobson: None. I. El Naqa: None.
3610 Quantification of PTV Margin When Using a Robotic Radiosurgery System to Treat Lung Tumors With Spine Tracking J.A. James, B. Lynch, C. Swanson, B. Wang, and N.E. Dunlap; University of Louisville, Louisville, KY Purpose/Objective(s): The use of fiducial markers or direct tumor visualization allows for tumor tracking and ultimately smaller PTV margins when treating lung tumors, yet many patients are either not amenable to fiducial marker placement or tumors are unable to be visualized on orthogonal x-rays. Spine tracking is an alternative method for localizing the tumor but is limited by the assumption that the location of the lung tumor relative to the spine is constant. The purpose of this study is to quantify the additional PTV margin needed when using spine tracking to ensure the ITV receives the prescription dose during treatment. Materials/Methods: Daily CBCTs, registered based on tumor position, from 63 patients treated with lung SBRT were collected and analyzed. Rigid registrations were re-performed so that the position of the spine on the CBCT was aligned to its position on the planning CT. Shifts from the treatment position to the new position were recorded, and per patient mean shifts and standard deviations were calculated as well as group systematic and random standard deviations. This data was used with van Herk’s margin recipe to determine the additional margin required to adequately treat the patient population if spine tracking were used instead of direct daily tumor imaging. A retrospective dosimetric analysis was also performed on 6 lung patients previously treated on CyberKnife using spine tracking to determine the potential decrease in target coverage due to insufficient margin on the ITV. This analysis was performed by shifting the PTV volume relative to the CyberKnife treatment geometry to simulate a setup error due to tracking the spine as opposed to the tumor. Results: The additional margin calculated by van Herk’s margin recipe to adequately cover the ITV with the 95% isodose surface for 90% of the entire patient population in the vertical, longitudinal, and lateral directions are 6.4, 6.0 and 4.5 mm, respectively. The retrospective analysis showed a decrease in PTV coverage from 95.6% to 93.1% and an increase in new conformity index (nCI) by 2.7% when using the average shift data to simulate setup error. When using the maximum shift data to simulate the worst possible outcome, the PTV coverage decreased to 73.4% and the nCI increased by 26.8%. Conclusions: Standard margins of 5 mm on the ITV for treating lung SBRT patients is insufficient and may result in geographic misses of the tumor when using spine tracking to locate the position of tumor in the lung. Therefore, we recommend the addition of 5 mm margins in all directions for a total of 10 mm to take into account the change in position of the tumor relative to the spine from the time of simulation to treatment. Author Disclosure: J.A. James: A. Employee; clinical staff at the University of Louisville. B. Lynch: A. Employee; clinical staff for the Oncology Services of North Alabama. C. Swanson: A. Employee; clinical staff for Baptist Health. B. Wang: A. Employee; Faculty at the University of Louisville. N.E. Dunlap: A. Employee; Faculty at the University of Louisville.
3611 Feasibility of Gating Using a Magnetic-Resonance Image Guided Radiation Therapy (MR-IGRT) System R. Kashani,1 K. Tanderup,1 J.R. Victoria,2 L. Santanam,1 H. Wooten,1 O.L. Green,1 J.F. Dempsey,2 and S. Mutic1; 1Washington University School of Medicine, St. Louis, MO, 2ViewRay, Cleveland, OH
S844
International Journal of Radiation Oncology Biology Physics
Purpose/Objective(s): Current gating methodologies rely mainly on external or internal markers as surrogates for tumor volume location. A newly developed MR-IGRT system with a 0.35T MR scanner and three 60 Co heads has the capability to acquire real-time planar MR images during treatment delivery. The purpose of this study was to evaluate the feasibility of gating based on real-time MRI. Materials/Methods: An MR-IGRT system equipped with non-radioactive sources was used to simulate gated treatment delivery to the kidney during voluntary breath-holds at inhale on a volunteer recruited under an IRB-approved protocol. The 0.35T on-board MR is capable of capturing high resolution volumetric images, as well as real-time planar cine images during treatment delivery. One or Three sagittal planes can be acquired at rates of 4 or 2 frames per second (fps) respectively. The gating target (tumor or normal anatomy) and the gating boundary are defined on volumetric MRI. Once the gated delivery is initiated, a preview scan is acquired in a specified plane. The target contour is automatically projected and deformed from the reference plane to each of the frames acquired during preview, and the best matching frame is selected and deformably mapped to each frame acquired subsequently during delivery. If the target structure moves out of the boundary, the beam is turned off. In this study, we selected the left kidney as the gating target, and evaluated the feasibility of gating with 3 and 5 mm isotropic gating margins at voluntary inhale breath-hold. The deformed target contour was evaluated visually on each frame during delivery, and the beam-on duty cycle was determined, not including the impact of multileaf collimator and gantry motion on delivery time. In addition, an MR marker was placed on the skin, and its position was tracked to determine the degree of correlation between the external and internal anatomy. Results: Simulated treatment delivery was completed with both 3 and 5 mm margins for the kidney at voluntary end-inhale breath-hold with a duty cycle of 72% and 56% respectively. The system’s ability to track the soft tissue contour on each frame was deemed acceptable. The position of the external marker was evaluated in each frame and found to be sufficiently accurate for a 5 mm margin, but not sufficient for a 3 mm margin. The surrogate accuracy was evaluated in a single session and not from simulation to delivery. The correlation between the external marker and the internal target also showed a drift in the baseline over the time of the treatment. Conclusions: The MR-IGRT system is capable of tracking the kidney in real-time sagittal MR images acquired at 4 fps. MR-IGRT gating showed an advantage over skin marker surrogate, allowing for a more precise assessment of tumor location and potential treatment margin reduction. Author Disclosure: R. Kashani: I. Travel Expenses; ViewRay. K. Tanderup: I. Travel Expenses; ViewRay. J.R. Victoria: A. Employee; ViewRay. N. Stock Options; ViewRay. L. Santanam: None. H. Wooten: I. Travel Expenses; ViewRay. O.L. Green: I. Travel Expenses; ViewRay. J.F. Dempsey: A. Employee; ViewRay. M. Stock; ViewRay. N. Stock Options; ViewRay. S. Leadership; ViewRay. S. Mutic: F. Honoraria; Varian Medical Systems, ViewRay. I. Travel Expenses; Varian Medical Systems, ViewRay. K. Advisory Board; ViewRay. M. Stock; Radialogica LLC. O. Partnership; Treat Safely. P. Royalty; Modus Medical. Q. Patent/ License Fee/Copyright; Varian Medical Systems. S. Leadership; Radialogica LLC.
5251 F-33400 Talence, Talence, France, 3Univ. Bordeaux, F-33000 Bordeaux, France, Bordeaux, France
3612 Geometrical Analysis of Organ Motion for Preoperative Helical Tomotherapy of Retroperitoneal Liposarcomas M. Antoine,1 P. Sargos,1 O. Saut,2 C. Pouypoudat,1 M. Desjardin,1 H. Loizeau,1 P. Ternisien,2 R. Yildizoglu,2 B. Henriques De Figueiredo,1 J. Caron,1 and G. Kantor1,3; 1Department of Radiotherapy, Institut Bergonie´, Comprehensive Cancer Centre, F-33000 Bordeaux, France, Bordeaux, France, 2Institut de Mathe´matiques de Bordeaux UMR CNRS Scientific Abstract 3612; Table
3613 Performance Improvement of MLC Tracking Investigated With an Experimentally Validated Tracking Simulator P.R. Poulsen,1 T. Ravkilde,1 J. Toftegaard,1 R. O’Brien,2 and P.J. Keall2; 1 Aarhus University Hospital, Aarhus C, Denmark, 2The University of Sydney, Sydney, Australia Purpose/Objective(s): Multi-leaf collimator (MLC) tracking is a promising method for intrafraction tumor motion management by real-time adaptation of the MLC aperture to the moving target. However, inadequate MLC adaption during tracking causes residual dosimetric errors. In this study, we first validate an MLC tracking simulator against experiments and
Results for CTV and CK barycenter preferential motion for each operator
Operator 1 (op1) delineation mean preferential motion (in mm)
CTV CK
Purpose/Objective(s): To analyze the barycenter motions of the Clinical Target Volume (CTV) and of the contralateral kidney (CK), the main organ at risk (OAR) when applying preoperative radiation therapy for retroperitoneal liposarcomas. This evaluation allows to estimate the organ motion component of Planning Target Volume (PTV) and CK Planning at Risk Volume (CK-PRV). Materials/Methods: A series of 11 consecutive patients were identified from a national phase II multicentric study. CTV and CK were retrospectively delineated on MV/CT images .Two of the five weekly MV/CT scans obtained after set-up adjustment were used for delineation. To estimate inter-operator variability, delineation was performed separately by two different radiation oncologists. Dice Similarity Coefficient (DSC) was calculated as follows: DSC Z 1- (2(CTVop1 X CTVop2)/(CTVop1 W CTVop2)), the ideal value being 0. CTV and CK volumes and volume variations were measured for each operator. Organs motion was defined as the distance variation between the reference barycenter (defined on the planning scan) and the new barycenter (defined on MVCT). Preferential motion directions were also identified. Results: Mean DSC was 0.11 0.04 for CTV and 0.11 0.02 for CK. Table 1 shows the results for barycenter preferential motion of CTV and CK calculated on 77 scans. Mean CTV volume were 4134 2476cc and 4038 2401cc for op1 and op2, respectively, with a mean volume increase of 4.2 5.0% and 6.4 14.0%. CTV motion was less than 10mm in 97% (op1) and 95% (op2) of the cases for the craniocaudal axis, less than 7mm in 86% (op1) and 93% (op2) of the cases for the anteroposterior axis, and less than 5 mm in 96% (op1) and 87% (op2) of the cases for the lateral axes. For CK the mean motion volume was 394 75 and 353 74cc for op1 and op2, respectively, with a mean volume increase of 3.9 4% and -0.1 3%. CK motion was less than 7 mm in 87% (op1) and 98% (op2) of the cases for the craniocaudal axis, less than 5mm in 84% (op1) and 95% (op2) of the cases for the anteroposterior axis, and 5mm in 100% (op1) and 98% (op2) of the cases for the lateral axes. Conclusions: Despite difficulties in delineating structures on MV/CT images this study shows that after set-up adjustment, motions variations of CTV and CK are larger in craniocaudal directions. The results on the estimation of the organ motion component of the PTV encourage the use of anisotropic margins of not less than 10mm in craniocaudal, and 7 mm in other axes. For CK-PRV the use of anisotropic margins of not less than 7 mm in craneoscodal axis and 5mm in other axes appears relevant. Author Disclosure: M. Antoine: None. P. Sargos: None. O. Saut: None. C. Pouypoudat: None. M. Desjardin: None. H. Loizeau: None. P. Ternisien: None. R. Yildizoglu: None. B. Henriques De Figueiredo: None. J. Caron: None. G. Kantor: None.
craniocaudal axis
Anteroposterior axis
Lateral axis
6.0.5.9 5.7 3.1
1.96.4 1.52.8
-4.16.5 -1.62.9
Operator 2 (op2) delineation mean preferential motion (in mm) craniocaudal axis
Anteroposterior axis
Lateral axis
3.71.1 3.62.0
0.23.5 0.51.5
0.82.7 0.42.0
3609 Feasibility of X-Ray Acoustic Computed Tomography as a Tool for Noninvasive Volumetric In Vivo Dosimetry S. Hickling,1 M. Hobson,2 and I. El Naqa2; 1McGill University, Montreal, QC, Canada, 2McGill University Health Centre, Montreal, QC, Canada Purpose/Objective(s): We propose that the novel modality of x-ray acoustic computed tomography (XACT) has the potential to be an effective tool for non-invasive in vivo dosimetry during external beam radiation therapy. XACT is based on the principle that acoustic waves proportional to the dose deposited are created following each radiation pulse. After detecting these acoustic waves with an ultrasound transducer array, an image of the dose distribution can be reconstructed. This work tests the feasibility of using XACT as a real-time dosimeter by performing realistic simulations to determine the expected amplitude and frequency of the induced acoustic waves for a typical clinical prostate case. The dose distribution is then reconstructed and compared to the treatment plan. Materials/Methods: Commercially available treatment planning software was used to obtain the dose distribution for a clinical prostate patient treated using a four-field box technique with 18 MV photon beams. A 2D map of the initial acoustic pressure distribution for a slice in the middle of the target was calculated for each LINAC pulse using the dose and CT data. An open source toolkit for the simulation of acoustic wave fields was then used to generate the expected time-varying signal at 360 transducer locations spaced equally around the patient. The transducers were assumed to be ideal and able to detect all wave frequencies up to a maximum simulated frequency of 1.6 MHz. Acoustic wave attenuation was not accounted for. A time reversal reconstruction algorithm was then used to obtain an XACT image of the dose for each LINAC pulse, after which a composite dose distribution for the entire fraction was derived. Results: The detected acoustic waves had a differential pressure amplitude on the order of 1 Pa to 10 Pa, with the main frequency component of the signal falling below 1 MHz. The reconstructed dose distribution closely resembled the plan, with 89% of pixels passing a 3% / 3 mm 2D gamma test. The largest dose discrepancies occurred at the interfaces of anatomical structures, such as the femur, pelvic bone, and seminal vesicles. This could be caused by the lack of frequency information above 1.6 MHz and the finite number of transducer positions.
Poster Viewing Abstracts S843 Conclusions: The simulated amplitude and frequency of the induced acoustic waves for a typical clinical prostate case indicate that they should be detectable with commercial ultrasound transducers. Further investigation of detector geometry, reconstruction algorithms and image post-processing could improve the agreement of the reconstructed and original dose distributions. An experimental validation of these simulations is ongoing. We conclude that XACT is a promising technique for volumetric non-invasive in vivo dosimetry and merits further research. Author Disclosure: S. Hickling: None. M. Hobson: None. I. El Naqa: None.
3610 Quantification of PTV Margin When Using a Robotic Radiosurgery System to Treat Lung Tumors With Spine Tracking J.A. James, B. Lynch, C. Swanson, B. Wang, and N.E. Dunlap; University of Louisville, Louisville, KY Purpose/Objective(s): The use of fiducial markers or direct tumor visualization allows for tumor tracking and ultimately smaller PTV margins when treating lung tumors, yet many patients are either not amenable to fiducial marker placement or tumors are unable to be visualized on orthogonal x-rays. Spine tracking is an alternative method for localizing the tumor but is limited by the assumption that the location of the lung tumor relative to the spine is constant. The purpose of this study is to quantify the additional PTV margin needed when using spine tracking to ensure the ITV receives the prescription dose during treatment. Materials/Methods: Daily CBCTs, registered based on tumor position, from 63 patients treated with lung SBRT were collected and analyzed. Rigid registrations were re-performed so that the position of the spine on the CBCT was aligned to its position on the planning CT. Shifts from the treatment position to the new position were recorded, and per patient mean shifts and standard deviations were calculated as well as group systematic and random standard deviations. This data was used with van Herk’s margin recipe to determine the additional margin required to adequately treat the patient population if spine tracking were used instead of direct daily tumor imaging. A retrospective dosimetric analysis was also performed on 6 lung patients previously treated on CyberKnife using spine tracking to determine the potential decrease in target coverage due to insufficient margin on the ITV. This analysis was performed by shifting the PTV volume relative to the CyberKnife treatment geometry to simulate a setup error due to tracking the spine as opposed to the tumor. Results: The additional margin calculated by van Herk’s margin recipe to adequately cover the ITV with the 95% isodose surface for 90% of the entire patient population in the vertical, longitudinal, and lateral directions are 6.4, 6.0 and 4.5 mm, respectively. The retrospective analysis showed a decrease in PTV coverage from 95.6% to 93.1% and an increase in new conformity index (nCI) by 2.7% when using the average shift data to simulate setup error. When using the maximum shift data to simulate the worst possible outcome, the PTV coverage decreased to 73.4% and the nCI increased by 26.8%. Conclusions: Standard margins of 5 mm on the ITV for treating lung SBRT patients is insufficient and may result in geographic misses of the tumor when using spine tracking to locate the position of tumor in the lung. Therefore, we recommend the addition of 5 mm margins in all directions for a total of 10 mm to take into account the change in position of the tumor relative to the spine from the time of simulation to treatment. Author Disclosure: J.A. James: A. Employee; clinical staff at the University of Louisville. B. Lynch: A. Employee; clinical staff for the Oncology Services of North Alabama. C. Swanson: A. Employee; clinical staff for Baptist Health. B. Wang: A. Employee; Faculty at the University of Louisville. N.E. Dunlap: A. Employee; Faculty at the University of Louisville.
3611 Feasibility of Gating Using a Magnetic-Resonance Image Guided Radiation Therapy (MR-IGRT) System R. Kashani,1 K. Tanderup,1 J.R. Victoria,2 L. Santanam,1 H. Wooten,1 O.L. Green,1 J.F. Dempsey,2 and S. Mutic1; 1Washington University School of Medicine, St. Louis, MO, 2ViewRay, Cleveland, OH
S844
International Journal of Radiation Oncology Biology Physics
Purpose/Objective(s): Current gating methodologies rely mainly on external or internal markers as surrogates for tumor volume location. A newly developed MR-IGRT system with a 0.35T MR scanner and three 60 Co heads has the capability to acquire real-time planar MR images during treatment delivery. The purpose of this study was to evaluate the feasibility of gating based on real-time MRI. Materials/Methods: An MR-IGRT system equipped with non-radioactive sources was used to simulate gated treatment delivery to the kidney during voluntary breath-holds at inhale on a volunteer recruited under an IRB-approved protocol. The 0.35T on-board MR is capable of capturing high resolution volumetric images, as well as real-time planar cine images during treatment delivery. One or Three sagittal planes can be acquired at rates of 4 or 2 frames per second (fps) respectively. The gating target (tumor or normal anatomy) and the gating boundary are defined on volumetric MRI. Once the gated delivery is initiated, a preview scan is acquired in a specified plane. The target contour is automatically projected and deformed from the reference plane to each of the frames acquired during preview, and the best matching frame is selected and deformably mapped to each frame acquired subsequently during delivery. If the target structure moves out of the boundary, the beam is turned off. In this study, we selected the left kidney as the gating target, and evaluated the feasibility of gating with 3 and 5 mm isotropic gating margins at voluntary inhale breath-hold. The deformed target contour was evaluated visually on each frame during delivery, and the beam-on duty cycle was determined, not including the impact of multileaf collimator and gantry motion on delivery time. In addition, an MR marker was placed on the skin, and its position was tracked to determine the degree of correlation between the external and internal anatomy. Results: Simulated treatment delivery was completed with both 3 and 5 mm margins for the kidney at voluntary end-inhale breath-hold with a duty cycle of 72% and 56% respectively. The system’s ability to track the soft tissue contour on each frame was deemed acceptable. The position of the external marker was evaluated in each frame and found to be sufficiently accurate for a 5 mm margin, but not sufficient for a 3 mm margin. The surrogate accuracy was evaluated in a single session and not from simulation to delivery. The correlation between the external marker and the internal target also showed a drift in the baseline over the time of the treatment. Conclusions: The MR-IGRT system is capable of tracking the kidney in real-time sagittal MR images acquired at 4 fps. MR-IGRT gating showed an advantage over skin marker surrogate, allowing for a more precise assessment of tumor location and potential treatment margin reduction. Author Disclosure: R. Kashani: I. Travel Expenses; ViewRay. K. Tanderup: I. Travel Expenses; ViewRay. J.R. Victoria: A. Employee; ViewRay. N. Stock Options; ViewRay. L. Santanam: None. H. Wooten: I. Travel Expenses; ViewRay. O.L. Green: I. Travel Expenses; ViewRay. J.F. Dempsey: A. Employee; ViewRay. M. Stock; ViewRay. N. Stock Options; ViewRay. S. Leadership; ViewRay. S. Mutic: F. Honoraria; Varian Medical Systems, ViewRay. I. Travel Expenses; Varian Medical Systems, ViewRay. K. Advisory Board; ViewRay. M. Stock; Radialogica LLC. O. Partnership; Treat Safely. P. Royalty; Modus Medical. Q. Patent/ License Fee/Copyright; Varian Medical Systems. S. Leadership; Radialogica LLC.
5251 F-33400 Talence, Talence, France, 3Univ. Bordeaux, F-33000 Bordeaux, France, Bordeaux, France
3612 Geometrical Analysis of Organ Motion for Preoperative Helical Tomotherapy of Retroperitoneal Liposarcomas M. Antoine,1 P. Sargos,1 O. Saut,2 C. Pouypoudat,1 M. Desjardin,1 H. Loizeau,1 P. Ternisien,2 R. Yildizoglu,2 B. Henriques De Figueiredo,1 J. Caron,1 and G. Kantor1,3; 1Department of Radiotherapy, Institut Bergonie´, Comprehensive Cancer Centre, F-33000 Bordeaux, France, Bordeaux, France, 2Institut de Mathe´matiques de Bordeaux UMR CNRS Scientific Abstract 3612; Table
3613 Performance Improvement of MLC Tracking Investigated With an Experimentally Validated Tracking Simulator P.R. Poulsen,1 T. Ravkilde,1 J. Toftegaard,1 R. O’Brien,2 and P.J. Keall2; 1 Aarhus University Hospital, Aarhus C, Denmark, 2The University of Sydney, Sydney, Australia Purpose/Objective(s): Multi-leaf collimator (MLC) tracking is a promising method for intrafraction tumor motion management by real-time adaptation of the MLC aperture to the moving target. However, inadequate MLC adaption during tracking causes residual dosimetric errors. In this study, we first validate an MLC tracking simulator against experiments and
Results for CTV and CK barycenter preferential motion for each operator
Operator 1 (op1) delineation mean preferential motion (in mm)
CTV CK
Purpose/Objective(s): To analyze the barycenter motions of the Clinical Target Volume (CTV) and of the contralateral kidney (CK), the main organ at risk (OAR) when applying preoperative radiation therapy for retroperitoneal liposarcomas. This evaluation allows to estimate the organ motion component of Planning Target Volume (PTV) and CK Planning at Risk Volume (CK-PRV). Materials/Methods: A series of 11 consecutive patients were identified from a national phase II multicentric study. CTV and CK were retrospectively delineated on MV/CT images .Two of the five weekly MV/CT scans obtained after set-up adjustment were used for delineation. To estimate inter-operator variability, delineation was performed separately by two different radiation oncologists. Dice Similarity Coefficient (DSC) was calculated as follows: DSC Z 1- (2(CTVop1 X CTVop2)/(CTVop1 W CTVop2)), the ideal value being 0. CTV and CK volumes and volume variations were measured for each operator. Organs motion was defined as the distance variation between the reference barycenter (defined on the planning scan) and the new barycenter (defined on MVCT). Preferential motion directions were also identified. Results: Mean DSC was 0.11 0.04 for CTV and 0.11 0.02 for CK. Table 1 shows the results for barycenter preferential motion of CTV and CK calculated on 77 scans. Mean CTV volume were 4134 2476cc and 4038 2401cc for op1 and op2, respectively, with a mean volume increase of 4.2 5.0% and 6.4 14.0%. CTV motion was less than 10mm in 97% (op1) and 95% (op2) of the cases for the craniocaudal axis, less than 7mm in 86% (op1) and 93% (op2) of the cases for the anteroposterior axis, and less than 5 mm in 96% (op1) and 87% (op2) of the cases for the lateral axes. For CK the mean motion volume was 394 75 and 353 74cc for op1 and op2, respectively, with a mean volume increase of 3.9 4% and -0.1 3%. CK motion was less than 7 mm in 87% (op1) and 98% (op2) of the cases for the craniocaudal axis, less than 5mm in 84% (op1) and 95% (op2) of the cases for the anteroposterior axis, and 5mm in 100% (op1) and 98% (op2) of the cases for the lateral axes. Conclusions: Despite difficulties in delineating structures on MV/CT images this study shows that after set-up adjustment, motions variations of CTV and CK are larger in craniocaudal directions. The results on the estimation of the organ motion component of the PTV encourage the use of anisotropic margins of not less than 10mm in craniocaudal, and 7 mm in other axes. For CK-PRV the use of anisotropic margins of not less than 7 mm in craneoscodal axis and 5mm in other axes appears relevant. Author Disclosure: M. Antoine: None. P. Sargos: None. O. Saut: None. C. Pouypoudat: None. M. Desjardin: None. H. Loizeau: None. P. Ternisien: None. R. Yildizoglu: None. B. Henriques De Figueiredo: None. J. Caron: None. G. Kantor: None.
craniocaudal axis
Anteroposterior axis
Lateral axis
6.0.5.9 5.7 3.1
1.96.4 1.52.8
-4.16.5 -1.62.9
Operator 2 (op2) delineation mean preferential motion (in mm) craniocaudal axis
Anteroposterior axis
Lateral axis
3.71.1 3.62.0
0.23.5 0.51.5
0.82.7 0.42.0