- Email: [email protected]
An Aperture-morphing Based Online Adaptive Scheme for Prostate Radiotherapy
I. J. Radiation Oncology d Biology d Physics
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Volume 72, Number 1, Supplement, 2008
Treatment Planning and Delivery of Volume Modulated Arc Therapy (VMAT)
D. Cao, M. K. N. Afghan, J. Ye, T. P. Wong, V. Mehta, D. M. Shepard Swedish Cancer Institute, Seattle, WA Purpose/Objective(s): Elekta and Varian have each developed linac control systems capable of delivering volumetric modulated arc therapy (VMAT), a rotational approach to IMRT delivered on conventional linear accelerators. In this study, we reported our clinical experience in both treatment planning and delivery of VMAT. Materials/Methods: Using an in-house arc sequencer, we can provide single-arc and multi-arc VMAT solutions for both the Elekta PreciseBeam InfinityÒ and Varian RapidArcÒ delivery systems. VMAT plans were generated for 10 patient cases with various treatment sites. An IMRT optimization was performed using direct machine parameter optimization (DMPO) in Pinnacle3 with multiple equispaced beams. A ‘‘deliverable fluence map’’ was then generated using the optimized aperture shapes and weights for each beam. The arc sequencer translated these maps into deliverable VMAT arc(s). The accuracy and efficiency of VMAT delivery was tested in our clinic using Elekta’s PreciseBeam InfinityÒ system. In particular, we studied the degree to which the efficiency are impacted by parameters such as the number of arcs and the allowable distance of MLC leaf motion per degree of gantry rotation. Results: On average, the arc sequencing procedure took less than 8 minutes. All VMAT plans provided highly uniform target doses with an average standard deviation in the PTV dose of 5.79 cGy/fraction. On average 98.1% of the PTV volume was covered by 95% of the prescribed dose. VMAT plans are also more MU efficient with an average 43% reduction comparing to fixed-field IMRT plans. Similar plan quality was observed for single-arc VMAT plans using Varian and Elekta MLCs. Improvement in plan quality was observed as the number of arcs increased from 1 to 3. The improvement was more pronounced for complex head-and-neck cases. The average delivery time for single-arc and 3-arc prostate cases were 3.2 and 4.5 minutes, respectively. For head-and-neck cases, these values increase to 5 and 5.6 minutes. For the prostate cases, the delivery time increased from 2.9 minutes to 3.9 minutes when the maximum leaf-motion per degree of gantry rotation was increased from 0.5 cm to 0.8 cm. In terms of accuracy, the measured ion chamber doses agreed within 3%. The film measurements also showed close agreement between the predicted and measured isodose curves. Conclusions: An arc sequencer has been developed that can perform VMAT inverse planning for both Elekta and Varian linacs. Results demonstrate that highly conformal plans can be created for both single-arc and multi-arc deliveries. Single arc delivery should be sufficient for most cases, but multiple arcs provide dosimetric advantages in the most complicated cases. The MLC leaf-motion constraints impact both plan quality and delivery efficiency and an appropriate balance needs to be determined for each case. Author Disclosure: D. Cao, Elekta, B. Research Grant; M.K.N. Afghan, Elekta, B. Research Grant; J. Ye, Elekta, B. Research Grant; T.P. Wong, Elekta, B. Research Grant; V. Mehta, Elekta, B. Research Grant; D.M. Shepard, Elekta, B. Research Grant.
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Experimental Validation for Real-time Motion Adapted Optimization (MAO) Guided Delivery
W. Lu, C. Mauer, M. Chen, K. Ruchala, J. Zhang, D. Lucas, Q. Chen, G. Olivera TomoTherapy Inc., Madison, WI Purpose/Objective(s): Real-time MAO-guided delivery is to model the radiation delivery with the real-time motion information as a negative feedback system. It optimizes the leaf sequence in real-time, right before the delivery of each projection. The purpose of this work is to test each module and the integrated system of MAO-guided delivery. Materials/Methods: We implemented and tested the real-time MAO-guided delivery with the current TomoTherapyÒ machine. TomoTherapySM treatment delivery consists of thousands of projections with projection time around 200-500 ms. The leaf latency plus transition of TomoTherapyÒ binary MLC takes less than 50 ms. Besides the existing TomoTherapyÒ hardware, a real-time camera system and a programmable motor-driven phantom are integrated into the system. The integrated system consists of several real-time software modules including ‘‘motion detection and prediction,’’ ‘‘motion-encoded dose accumulation,’’ and ‘‘leaf sequence optimization for the coming projection.’’ The latency of the integrated system is designed to be less than 200 ms to catch the fastest projection rate in TomoTherapyÒ system. We validated each hardware and software modules individually. We also tested different TomoTherapySM plans with various simulated and real respiration traces. We used film dosimetry to verify and validate the final results. Results: MAO-guided delivery runs smoothly in the integrated TomoTherapyÒ system. The MAO procedure takes less than 100 ms per projection. The whole system latency is less than 150ms. For both simulated motion and real respiration of 2cm amplitude, motion prediction error within this latency is less than 0.3 mm. For a typical TomoTherapySM treatment configuration, the real-time MAO-guided delivery doses matched with the planning dose within 3% and 3mm criteria for both tumor and OAR. No hot and cold spots are noticeable. Conclusions: We designed an integrated system to implement and test real-time MAO-guided delivery within current TomoTherapyÒ hardware. Experiments conceptually proved this technique. The integrated system will be further tested at different clinic sites. Author Disclosure: W. Lu, TomoTherapy Inc., A. Employment; C. Mauer, TomoTherapy Inc., A. Employment; M. Chen, TomoTherapy Inc., A. Employment; K. Ruchala, TomoTherapy Inc., A. Employment; J. Zhang, TomoTherapy Inc., A. Employment; D. Lucas, TomoTherapy Inc., A. Employment; Q. Chen, TomoTherapy Inc, A. Employment; G. Olivera, TomoTherapy Inc., A. Employment.
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An Aperture-morphing Based Online Adaptive Scheme for Prostate Radiotherapy
E. E. Ahunbay, G. Chen, C. Peng, C. Lawton, A. X. Li Medical College of Wisconsin, Milwaukee, WI Purpose/Objective(s): Interfraction organ deformations of the prostate and the surrounding anatomy can not be completely corrected by the current rigid translation, and a full-scope re-optimization based on the daily CT takes too long to be practical. We have
Proceedings of the 50th Annual ASTRO Meeting previously proposed an online adaptive correction scheme including 3 major steps: 1) rapid delineation of targets and OAR on the CT of the day, 2) segment aperture morphing (SAM) based on the change of target contour, and 3) segment weight optimization (SWO) for the new apertures. To prepare a clinical trial to test this novel scheme for prostate cancer, we study its benefits and specific issues for prostate radiotherapy. Materials/Methods: Daily CT images acquired for 10 prostate cancer patients, treated on a linac and CT-on-Rails combo (Siemens), were retrospectively evaluated for following specific issues for using the SAM/SWO scheme: (1) dosimetry benefits, (2) execution frequency, (3) time required, (4) work flow, and (5) possible prostate motion during the execution of SAM/SWO. To evaluate dosimetry benefits, dose distributions and DVHs generated for the SAM/SWO scheme based on the CT of the day were compared with those generated for the current standard of repositioning and for the full-scale re-optimization. Several parameters including the maximum overlap ratio (MOR) were used to quantify the prostate change and to indicate the need of SAM/ SWO. The published intrafraction prostate motion data were used to assess the impact of prostate motion during the execution of SAM/SWO. Results: For all cases studied, the SAM/SWO method leads to better target coverage and equivalent or better OAR sparing as compared with the repositioning. For example, prostate minimum dose and D90 increased by 47% and 11% (p \ 0.0004), and, in the mean time, the mean rectal and bladder doses decreased by 25% (p \ 0.0002) and 13% (p . 0.1). The larger the prostate deformation, the larger were the benefits. The target coverage and OAR sparing of the full-scale reoptimization were practically equivalent to those with the SAM/SWO method (p . 0.1 all parameters). The time required to complete the whole process was 6 (±2) minutes. Dosimetric simulations assuming the worse scenario of ‘‘full-rectum’’ for the prostate motion during correction period (6 min) indicated that a net benefit of .5% prostate EUD increase is still achieved by SAM/SWO for 85-90% of large deformation days (MOR \ 0.7) and for 50% of small deformation days. Conclusions: The proposed online adaptive method can be applied for interfraction correction for prostate RT with practically acceptable timeframe (6 min). It has clear dosimetric benefits over the current repositioning method. Based on the results for this study, a clinical trial to test the feasibility of the proposed scheme for prostate RT has been initiated. Author Disclosure: E.E. Ahunbay, None; G. Chen, None; C. Peng, None; C. Lawton, None; A.X. Li, None.
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Experimental Validation of a Beam Tracking System for the Treatment of Moving Targets with Scanned Ion Beams
A. Schmidt1, C. Bert1, N. Saito1, G. Iancu1, C. von Neubeck1, N. Chaudhri1, D. Schardt1, E. Rietzel1,2 1 Gesellschaft fuer Schwerionenforschung, Darmstadt, Germany, 2Siemens Healthcare, Erlangen, Germany Purpose/Objective(s): A beam tracking system was developed to allow irradiation of moving targets with scanned ion beams by 3D adaptation of pencil beam positions in quasi real time. Several experiments were conducted with ionization chambers and cell samples to validate the dosimetric performance of the beam tracking system. Materials/Methods: The tracking system provides fast adaptation of pencil beam positions laterally as well as longitudinally. The system utilizes the beam scanning magnets for lateral adaptation of beam positions and a dedicated energy modulation system consisting of two absorber wedges on linear motors to adapt the particle range. Several experiments were performed repeatedly to validate the overall system performance with various detector systems. For 3D-dosimetry, an array of pinpoint ionization chambers was used to measure absorbed doses. Cell samples were used to measure biologically effective doses in 3D (cell survival). Results from beam tracking with moving detector systems were compared to results of stationary reference irradiations. Results: For the absorbed dose within the target volume, the comparison between stationary and motion compensated irradiation yielded a dose difference of 0.3 ± 1.5%. For the biologically effective dose, a difference of 6 ± 9% was deduced from cell survival measurements. This is below the precision of the cell detector system for single measurements that shows a relative error of 11% introduced by biological variability of the cells. Conclusions: Experimental validation of the GSI beam tracking system for irradiation of moving targets with scanned ion beams has been performed successfully. Absorbed as well as biologically effective doses for motion compensated irradiations demonstrated conformal dose distributions that were comparable to those for reference measurements with stationary detector systems. Author Disclosure: A. Schmidt, None; C. Bert, None; N. Saito, None; G. Iancu, None; C. von Neubeck, None; N. Chaudhri, None; D. Schardt, None; E. Rietzel, Siemens Healthcare, A. Employment.
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Geometric Accuracy and Latency of an Integrated 4D IMRT Delivery System using Real-time Internal Position Monitoring and Dynamic MLC Tracking
A. Sawant1, R. L. Smith2, R. B. Venkat1, L. Santanam2, B. Cho1, P. Poulsen1, H. Cattell3, J. Newell4, P. Parikh2, P. Keall1 1 Stanford Cancer Center, Stanford, CA, 2Washington University School of Medicine, St. Louis, MO, 3Varian Medical Systems, Palo Alto, CA, 4Calypso Medical Systems, Seattle, WA
Purpose/Objective(s): The ideal radiation delivery to moving tumors has two requirements—complete spatial and temporal knowledge of the anatomy and, continuous adaptation of the radiation beam to account for these spatiotemporal changes. Toward this goal, we have developed and characterized the geometric accuracy and latency of an integrated radiation delivery system that combines two promising technologies—3D position monitoring without ionizing radiation using electromagnetically excitable fiducials implanted in or around (and, therefore, spatially correlated with) the tumor target and corresponding real-time adaptation of the beam aperture using a dynamic multileaf collimator (DMLC). Materials/Methods: In a multi-institutional academic and industrial collaboration, a research version of the Calypso position monitoring system was integrated with a real-time DMLC-based 4D IMRT delivery system using a Varian 120-leaf MLC. This system uses 3D position information provided by three electromagnetic transponders (at 25 Hz) and recalculates the position of each MLC leaf in real-time so as to interpolate the shape of the beam aperture(s) as a function of position and dose fraction. Two important determinants of overall system performance—latency (i.e., elapsed time between target motion and MLC response) and
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Volume 72, Number 1, Supplement, 2008
Treatment Planning and Delivery of Volume Modulated Arc Therapy (VMAT)
D. Cao, M. K. N. Afghan, J. Ye, T. P. Wong, V. Mehta, D. M. Shepard Swedish Cancer Institute, Seattle, WA Purpose/Objective(s): Elekta and Varian have each developed linac control systems capable of delivering volumetric modulated arc therapy (VMAT), a rotational approach to IMRT delivered on conventional linear accelerators. In this study, we reported our clinical experience in both treatment planning and delivery of VMAT. Materials/Methods: Using an in-house arc sequencer, we can provide single-arc and multi-arc VMAT solutions for both the Elekta PreciseBeam InfinityÒ and Varian RapidArcÒ delivery systems. VMAT plans were generated for 10 patient cases with various treatment sites. An IMRT optimization was performed using direct machine parameter optimization (DMPO) in Pinnacle3 with multiple equispaced beams. A ‘‘deliverable fluence map’’ was then generated using the optimized aperture shapes and weights for each beam. The arc sequencer translated these maps into deliverable VMAT arc(s). The accuracy and efficiency of VMAT delivery was tested in our clinic using Elekta’s PreciseBeam InfinityÒ system. In particular, we studied the degree to which the efficiency are impacted by parameters such as the number of arcs and the allowable distance of MLC leaf motion per degree of gantry rotation. Results: On average, the arc sequencing procedure took less than 8 minutes. All VMAT plans provided highly uniform target doses with an average standard deviation in the PTV dose of 5.79 cGy/fraction. On average 98.1% of the PTV volume was covered by 95% of the prescribed dose. VMAT plans are also more MU efficient with an average 43% reduction comparing to fixed-field IMRT plans. Similar plan quality was observed for single-arc VMAT plans using Varian and Elekta MLCs. Improvement in plan quality was observed as the number of arcs increased from 1 to 3. The improvement was more pronounced for complex head-and-neck cases. The average delivery time for single-arc and 3-arc prostate cases were 3.2 and 4.5 minutes, respectively. For head-and-neck cases, these values increase to 5 and 5.6 minutes. For the prostate cases, the delivery time increased from 2.9 minutes to 3.9 minutes when the maximum leaf-motion per degree of gantry rotation was increased from 0.5 cm to 0.8 cm. In terms of accuracy, the measured ion chamber doses agreed within 3%. The film measurements also showed close agreement between the predicted and measured isodose curves. Conclusions: An arc sequencer has been developed that can perform VMAT inverse planning for both Elekta and Varian linacs. Results demonstrate that highly conformal plans can be created for both single-arc and multi-arc deliveries. Single arc delivery should be sufficient for most cases, but multiple arcs provide dosimetric advantages in the most complicated cases. The MLC leaf-motion constraints impact both plan quality and delivery efficiency and an appropriate balance needs to be determined for each case. Author Disclosure: D. Cao, Elekta, B. Research Grant; M.K.N. Afghan, Elekta, B. Research Grant; J. Ye, Elekta, B. Research Grant; T.P. Wong, Elekta, B. Research Grant; V. Mehta, Elekta, B. Research Grant; D.M. Shepard, Elekta, B. Research Grant.
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Experimental Validation for Real-time Motion Adapted Optimization (MAO) Guided Delivery
W. Lu, C. Mauer, M. Chen, K. Ruchala, J. Zhang, D. Lucas, Q. Chen, G. Olivera TomoTherapy Inc., Madison, WI Purpose/Objective(s): Real-time MAO-guided delivery is to model the radiation delivery with the real-time motion information as a negative feedback system. It optimizes the leaf sequence in real-time, right before the delivery of each projection. The purpose of this work is to test each module and the integrated system of MAO-guided delivery. Materials/Methods: We implemented and tested the real-time MAO-guided delivery with the current TomoTherapyÒ machine. TomoTherapySM treatment delivery consists of thousands of projections with projection time around 200-500 ms. The leaf latency plus transition of TomoTherapyÒ binary MLC takes less than 50 ms. Besides the existing TomoTherapyÒ hardware, a real-time camera system and a programmable motor-driven phantom are integrated into the system. The integrated system consists of several real-time software modules including ‘‘motion detection and prediction,’’ ‘‘motion-encoded dose accumulation,’’ and ‘‘leaf sequence optimization for the coming projection.’’ The latency of the integrated system is designed to be less than 200 ms to catch the fastest projection rate in TomoTherapyÒ system. We validated each hardware and software modules individually. We also tested different TomoTherapySM plans with various simulated and real respiration traces. We used film dosimetry to verify and validate the final results. Results: MAO-guided delivery runs smoothly in the integrated TomoTherapyÒ system. The MAO procedure takes less than 100 ms per projection. The whole system latency is less than 150ms. For both simulated motion and real respiration of 2cm amplitude, motion prediction error within this latency is less than 0.3 mm. For a typical TomoTherapySM treatment configuration, the real-time MAO-guided delivery doses matched with the planning dose within 3% and 3mm criteria for both tumor and OAR. No hot and cold spots are noticeable. Conclusions: We designed an integrated system to implement and test real-time MAO-guided delivery within current TomoTherapyÒ hardware. Experiments conceptually proved this technique. The integrated system will be further tested at different clinic sites. Author Disclosure: W. Lu, TomoTherapy Inc., A. Employment; C. Mauer, TomoTherapy Inc., A. Employment; M. Chen, TomoTherapy Inc., A. Employment; K. Ruchala, TomoTherapy Inc., A. Employment; J. Zhang, TomoTherapy Inc., A. Employment; D. Lucas, TomoTherapy Inc., A. Employment; Q. Chen, TomoTherapy Inc, A. Employment; G. Olivera, TomoTherapy Inc., A. Employment.
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An Aperture-morphing Based Online Adaptive Scheme for Prostate Radiotherapy
E. E. Ahunbay, G. Chen, C. Peng, C. Lawton, A. X. Li Medical College of Wisconsin, Milwaukee, WI Purpose/Objective(s): Interfraction organ deformations of the prostate and the surrounding anatomy can not be completely corrected by the current rigid translation, and a full-scope re-optimization based on the daily CT takes too long to be practical. We have
Proceedings of the 50th Annual ASTRO Meeting previously proposed an online adaptive correction scheme including 3 major steps: 1) rapid delineation of targets and OAR on the CT of the day, 2) segment aperture morphing (SAM) based on the change of target contour, and 3) segment weight optimization (SWO) for the new apertures. To prepare a clinical trial to test this novel scheme for prostate cancer, we study its benefits and specific issues for prostate radiotherapy. Materials/Methods: Daily CT images acquired for 10 prostate cancer patients, treated on a linac and CT-on-Rails combo (Siemens), were retrospectively evaluated for following specific issues for using the SAM/SWO scheme: (1) dosimetry benefits, (2) execution frequency, (3) time required, (4) work flow, and (5) possible prostate motion during the execution of SAM/SWO. To evaluate dosimetry benefits, dose distributions and DVHs generated for the SAM/SWO scheme based on the CT of the day were compared with those generated for the current standard of repositioning and for the full-scale re-optimization. Several parameters including the maximum overlap ratio (MOR) were used to quantify the prostate change and to indicate the need of SAM/ SWO. The published intrafraction prostate motion data were used to assess the impact of prostate motion during the execution of SAM/SWO. Results: For all cases studied, the SAM/SWO method leads to better target coverage and equivalent or better OAR sparing as compared with the repositioning. For example, prostate minimum dose and D90 increased by 47% and 11% (p \ 0.0004), and, in the mean time, the mean rectal and bladder doses decreased by 25% (p \ 0.0002) and 13% (p . 0.1). The larger the prostate deformation, the larger were the benefits. The target coverage and OAR sparing of the full-scale reoptimization were practically equivalent to those with the SAM/SWO method (p . 0.1 all parameters). The time required to complete the whole process was 6 (±2) minutes. Dosimetric simulations assuming the worse scenario of ‘‘full-rectum’’ for the prostate motion during correction period (6 min) indicated that a net benefit of .5% prostate EUD increase is still achieved by SAM/SWO for 85-90% of large deformation days (MOR \ 0.7) and for 50% of small deformation days. Conclusions: The proposed online adaptive method can be applied for interfraction correction for prostate RT with practically acceptable timeframe (6 min). It has clear dosimetric benefits over the current repositioning method. Based on the results for this study, a clinical trial to test the feasibility of the proposed scheme for prostate RT has been initiated. Author Disclosure: E.E. Ahunbay, None; G. Chen, None; C. Peng, None; C. Lawton, None; A.X. Li, None.
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Experimental Validation of a Beam Tracking System for the Treatment of Moving Targets with Scanned Ion Beams
A. Schmidt1, C. Bert1, N. Saito1, G. Iancu1, C. von Neubeck1, N. Chaudhri1, D. Schardt1, E. Rietzel1,2 1 Gesellschaft fuer Schwerionenforschung, Darmstadt, Germany, 2Siemens Healthcare, Erlangen, Germany Purpose/Objective(s): A beam tracking system was developed to allow irradiation of moving targets with scanned ion beams by 3D adaptation of pencil beam positions in quasi real time. Several experiments were conducted with ionization chambers and cell samples to validate the dosimetric performance of the beam tracking system. Materials/Methods: The tracking system provides fast adaptation of pencil beam positions laterally as well as longitudinally. The system utilizes the beam scanning magnets for lateral adaptation of beam positions and a dedicated energy modulation system consisting of two absorber wedges on linear motors to adapt the particle range. Several experiments were performed repeatedly to validate the overall system performance with various detector systems. For 3D-dosimetry, an array of pinpoint ionization chambers was used to measure absorbed doses. Cell samples were used to measure biologically effective doses in 3D (cell survival). Results from beam tracking with moving detector systems were compared to results of stationary reference irradiations. Results: For the absorbed dose within the target volume, the comparison between stationary and motion compensated irradiation yielded a dose difference of 0.3 ± 1.5%. For the biologically effective dose, a difference of 6 ± 9% was deduced from cell survival measurements. This is below the precision of the cell detector system for single measurements that shows a relative error of 11% introduced by biological variability of the cells. Conclusions: Experimental validation of the GSI beam tracking system for irradiation of moving targets with scanned ion beams has been performed successfully. Absorbed as well as biologically effective doses for motion compensated irradiations demonstrated conformal dose distributions that were comparable to those for reference measurements with stationary detector systems. Author Disclosure: A. Schmidt, None; C. Bert, None; N. Saito, None; G. Iancu, None; C. von Neubeck, None; N. Chaudhri, None; D. Schardt, None; E. Rietzel, Siemens Healthcare, A. Employment.
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Geometric Accuracy and Latency of an Integrated 4D IMRT Delivery System using Real-time Internal Position Monitoring and Dynamic MLC Tracking
A. Sawant1, R. L. Smith2, R. B. Venkat1, L. Santanam2, B. Cho1, P. Poulsen1, H. Cattell3, J. Newell4, P. Parikh2, P. Keall1 1 Stanford Cancer Center, Stanford, CA, 2Washington University School of Medicine, St. Louis, MO, 3Varian Medical Systems, Palo Alto, CA, 4Calypso Medical Systems, Seattle, WA
Purpose/Objective(s): The ideal radiation delivery to moving tumors has two requirements—complete spatial and temporal knowledge of the anatomy and, continuous adaptation of the radiation beam to account for these spatiotemporal changes. Toward this goal, we have developed and characterized the geometric accuracy and latency of an integrated radiation delivery system that combines two promising technologies—3D position monitoring without ionizing radiation using electromagnetically excitable fiducials implanted in or around (and, therefore, spatially correlated with) the tumor target and corresponding real-time adaptation of the beam aperture using a dynamic multileaf collimator (DMLC). Materials/Methods: In a multi-institutional academic and industrial collaboration, a research version of the Calypso position monitoring system was integrated with a real-time DMLC-based 4D IMRT delivery system using a Varian 120-leaf MLC. This system uses 3D position information provided by three electromagnetic transponders (at 25 Hz) and recalculates the position of each MLC leaf in real-time so as to interpolate the shape of the beam aperture(s) as a function of position and dose fraction. Two important determinants of overall system performance—latency (i.e., elapsed time between target motion and MLC response) and
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