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The Uncertainties in Target Localization for Prostate and Prostate-bed Radiotherapy with Calypso 4D
I. J. Radiation Oncology d Biology d Physics
S594
Volume 75, Number 3, Supplement, 2009
Synergy cone beam CT. As this is a gantry-mounted system, accuracy may be dependent on the linac on which it is mounted. The purpose of this study is to evaluate the localization accuracy of this radioactive tracking system mounted on a Varian Trilogy linac. Materials/Methods: A 100 uCi Ba133 radioactive marker was located inside a tissue equivalent pelvic phantom in the approximate location of the prostate. The phantom was scanned in a wide bore treatment planning CT. The radioactive fiducial was identified in the CT image and its position relative to the target isocenter was recorded. The tracking system was installed on a Varian Trilogy linac and the tracker coordinate system was aligned with the treatment room fixed coordinate system by measuring known locations in an alignment phantom in both coordinate systems. The pelvic phantom containing the radioactive fiducial was placed on the treatment couch and positioned approximately at isocenter using lasers. The required positioning correction was then measured using the radioactive tracking system and using the cone beam CT imaging and the corrections recommended by the two systems were compared. Results: The overall mean error between the 3-dimensional corrections recommended by the tracking system and by the cone beam CT was smaller than 1.5mm. This error includes the tracking system error, fiducial identification in CT planning error, cone beam CT 3D matching errors, and the Varian position correction round-off error. Conclusions: The radioactive tracking system is accurate and objective and is appropriate for patient positioning in the Varian Trilogy environment. Author Disclosure: D. Alezra, Navotek Medical Ltd., C. Other Research Support; T. Shchory, Navotek Medical Ltd., A. Employment; I. Lifshitz, Navotek Medical Ltd., A. Employment; R. Pfeffer, Navotek Medical Ltd., F. Consultant/Advisory Board.
2920
The Uncertainties in Target Localization for Prostate and Prostate-bed Radiotherapy with Calypso 4D
K. Wang, X. Wu, E. Bossart, J. A. Both, R. Stoyanova, A. Pollack Department of Radiation Oncology, Miller School of Medicine, University of Miami, Miami, FL Purpose/Objective(s): The Calypso 4D system allows real-time localization of the prostate during radiotherapy. The inter- and intra-fraction target motion have been studied and reported. The results indicate the apparent advantages of the use of real-time tracking system for definitive prostate treatment. We describe here the extension of this system to prostate bed radiotherapy, post prostatectomy. The tracking accuracy is heavily relying on the integrity of the rigid body condition of the transponder array. We evaluated two groups of patients treated for intact prostate and prostate bed. The integrity of the rigid-body was examined by analyzing the inter-transponder variation and its implication on tracking accuracy discussed. Materials/Methods: All patients were implanted with three Calypso transponders. For intact prostate, efforts were made to place the three transponders with equidistance (1 cm as recommended by the manufacturer) to the midpoint of the prostate, typically one at the right base (R), one at the left base (L) and one at the apex (A). For prostate bed, two transponders are placed between the bladder and rectal wall, one on the right side (R) and one on the left side (L), behind the trigone. The third transponder is placed on the right side of the anastomosis site (A). For each treatment fraction, the Calypso system provides 6 degrees of alignment parameters and reports the three lengths of the transponders triangulation (a=RL, b=AR, c=AL). The integrity of the transponder triangulation is determined by the consistency of these three lengths and the three angles, a, b and g which can be easily determined by the Cosine Law. The variation of these six parameters as well as the areas of the triangles were obtained for each treatment fraction and compared with the initial values determined by the simulation CT. Results: Different degrees of incoherent movement of the transponders are observed in both groups of patients. The average variation of the triangular lengths in the intact prostate patients is 1.1±1.0 (maximum 4.8) mm, and 1.7±1.3 (maximum 6.4) mm in the prostate bed patients. The average angular variation is 3.1±2.6 (maximum 13.6) degree in the intact prostate patients and 4.6±3.3 (maximum 15.5) degree in the prostate bed patients. A greater degree of randomness of the variation was observed in the prostate bed group. Conclusions: Local deformation of Calypso transponder triangulations is inevitable. These deformations add uncertainties to the reported setup parameters. The effect on translation tracking accuracy is in the order of 1.0 mm for intact prostate and 2.0 mm for prostate bed. The effects on angular tracking is however quite significant in both groups and may render the angular tracking parameters unreliable. Author Disclosure: K. Wang, None; X. Wu, None; E. Bossart, None; J.A. Both, None; R. Stoyanova, None; A. Pollack, None.
2921
Evaluation of Rotational and Translational Setup Variations for Brain Tumor Patients with Mask Immobilization System
C. Han, E. H. Radany, T. E. Schultheiss, J. Y. C. Wong City of Hope National Medical Center, Duarte, CA Purpose/Objective(s): Brain tumor patients undergoing fractionated external beam radiotherapy are commonly immobilized with a thermoplastic mask system. Previous studies on setup errors for mask systems primarily focused on translational errors. However, rotational setup errors could have significant effect on the overall setup accuracy. For example, given a skull dimension of 10 cm to 20 cm, a 1 rotation leads to a maximum deviation of 1.7 mm to 3.5 mm over the skull length. In this study, both translational and rotational setup variations are evaluated for brain tumor patients undergoing external beam radiotherapy, using daily helical tomotherapy megavoltage computed tomography (MVCT) scans. Materials/Methods: 15 brain tumor patients who finished fractionated helical tomotherapy treatment were retrospectively selected. The number fractions ranged from 24 to 34. For each fraction, the patient was first set up based on laser alignment to the marks on the mask, and an MVCT scan was performed over the brain volume. The MVCT images were first registered with planning CT images using six degrees of freedom with three translations and three rotations, then they were registered using three translations and roll only, which were used in actual treatments. Results: With three translations and three rotations used in the registration process, the overall standard deviations (SD) for translations were 2.6 mm (range: 0.78 - 2.32 mm), 2.5 mm (range: 1.11 - 2.65 mm), and 2.0 mm (range: 0.52 to 6.65 mm) in the right-left
S594
Volume 75, Number 3, Supplement, 2009
Synergy cone beam CT. As this is a gantry-mounted system, accuracy may be dependent on the linac on which it is mounted. The purpose of this study is to evaluate the localization accuracy of this radioactive tracking system mounted on a Varian Trilogy linac. Materials/Methods: A 100 uCi Ba133 radioactive marker was located inside a tissue equivalent pelvic phantom in the approximate location of the prostate. The phantom was scanned in a wide bore treatment planning CT. The radioactive fiducial was identified in the CT image and its position relative to the target isocenter was recorded. The tracking system was installed on a Varian Trilogy linac and the tracker coordinate system was aligned with the treatment room fixed coordinate system by measuring known locations in an alignment phantom in both coordinate systems. The pelvic phantom containing the radioactive fiducial was placed on the treatment couch and positioned approximately at isocenter using lasers. The required positioning correction was then measured using the radioactive tracking system and using the cone beam CT imaging and the corrections recommended by the two systems were compared. Results: The overall mean error between the 3-dimensional corrections recommended by the tracking system and by the cone beam CT was smaller than 1.5mm. This error includes the tracking system error, fiducial identification in CT planning error, cone beam CT 3D matching errors, and the Varian position correction round-off error. Conclusions: The radioactive tracking system is accurate and objective and is appropriate for patient positioning in the Varian Trilogy environment. Author Disclosure: D. Alezra, Navotek Medical Ltd., C. Other Research Support; T. Shchory, Navotek Medical Ltd., A. Employment; I. Lifshitz, Navotek Medical Ltd., A. Employment; R. Pfeffer, Navotek Medical Ltd., F. Consultant/Advisory Board.
2920
The Uncertainties in Target Localization for Prostate and Prostate-bed Radiotherapy with Calypso 4D
K. Wang, X. Wu, E. Bossart, J. A. Both, R. Stoyanova, A. Pollack Department of Radiation Oncology, Miller School of Medicine, University of Miami, Miami, FL Purpose/Objective(s): The Calypso 4D system allows real-time localization of the prostate during radiotherapy. The inter- and intra-fraction target motion have been studied and reported. The results indicate the apparent advantages of the use of real-time tracking system for definitive prostate treatment. We describe here the extension of this system to prostate bed radiotherapy, post prostatectomy. The tracking accuracy is heavily relying on the integrity of the rigid body condition of the transponder array. We evaluated two groups of patients treated for intact prostate and prostate bed. The integrity of the rigid-body was examined by analyzing the inter-transponder variation and its implication on tracking accuracy discussed. Materials/Methods: All patients were implanted with three Calypso transponders. For intact prostate, efforts were made to place the three transponders with equidistance (1 cm as recommended by the manufacturer) to the midpoint of the prostate, typically one at the right base (R), one at the left base (L) and one at the apex (A). For prostate bed, two transponders are placed between the bladder and rectal wall, one on the right side (R) and one on the left side (L), behind the trigone. The third transponder is placed on the right side of the anastomosis site (A). For each treatment fraction, the Calypso system provides 6 degrees of alignment parameters and reports the three lengths of the transponders triangulation (a=RL, b=AR, c=AL). The integrity of the transponder triangulation is determined by the consistency of these three lengths and the three angles, a, b and g which can be easily determined by the Cosine Law. The variation of these six parameters as well as the areas of the triangles were obtained for each treatment fraction and compared with the initial values determined by the simulation CT. Results: Different degrees of incoherent movement of the transponders are observed in both groups of patients. The average variation of the triangular lengths in the intact prostate patients is 1.1±1.0 (maximum 4.8) mm, and 1.7±1.3 (maximum 6.4) mm in the prostate bed patients. The average angular variation is 3.1±2.6 (maximum 13.6) degree in the intact prostate patients and 4.6±3.3 (maximum 15.5) degree in the prostate bed patients. A greater degree of randomness of the variation was observed in the prostate bed group. Conclusions: Local deformation of Calypso transponder triangulations is inevitable. These deformations add uncertainties to the reported setup parameters. The effect on translation tracking accuracy is in the order of 1.0 mm for intact prostate and 2.0 mm for prostate bed. The effects on angular tracking is however quite significant in both groups and may render the angular tracking parameters unreliable. Author Disclosure: K. Wang, None; X. Wu, None; E. Bossart, None; J.A. Both, None; R. Stoyanova, None; A. Pollack, None.
2921
Evaluation of Rotational and Translational Setup Variations for Brain Tumor Patients with Mask Immobilization System
C. Han, E. H. Radany, T. E. Schultheiss, J. Y. C. Wong City of Hope National Medical Center, Duarte, CA Purpose/Objective(s): Brain tumor patients undergoing fractionated external beam radiotherapy are commonly immobilized with a thermoplastic mask system. Previous studies on setup errors for mask systems primarily focused on translational errors. However, rotational setup errors could have significant effect on the overall setup accuracy. For example, given a skull dimension of 10 cm to 20 cm, a 1 rotation leads to a maximum deviation of 1.7 mm to 3.5 mm over the skull length. In this study, both translational and rotational setup variations are evaluated for brain tumor patients undergoing external beam radiotherapy, using daily helical tomotherapy megavoltage computed tomography (MVCT) scans. Materials/Methods: 15 brain tumor patients who finished fractionated helical tomotherapy treatment were retrospectively selected. The number fractions ranged from 24 to 34. For each fraction, the patient was first set up based on laser alignment to the marks on the mask, and an MVCT scan was performed over the brain volume. The MVCT images were first registered with planning CT images using six degrees of freedom with three translations and three rotations, then they were registered using three translations and roll only, which were used in actual treatments. Results: With three translations and three rotations used in the registration process, the overall standard deviations (SD) for translations were 2.6 mm (range: 0.78 - 2.32 mm), 2.5 mm (range: 1.11 - 2.65 mm), and 2.0 mm (range: 0.52 to 6.65 mm) in the right-left