- Email: [email protected]
Intrafraction Verification using Beam Level kV Images for Gated RapidArc
I. J. Radiation Oncology d Biology d Physics
S152
Volume 81, Number 2, Supplement, 2011
respectively with or without vacuum cushions, 23 patients treated for Hodgkin’s disease with 9-point TM, 13 and 16 patients treated for pulmonary located tumors, respectively with 9-point TM or arm support, and 40 patients treated for brain tumors with 5-point TM. Systematic and random shifts were calculated for the automatic and total deviations on a patient and a population basis. A t test was used to determine if the registration results obtained after the manual refinements performed by the radiation therapists was statistically different from the automatic registration. Furthermore, residual deviations and additional PTV margin were calculated if manual corrections were not applied. Five imaging protocols were investigated: every other day, one day out of 3, the first 3 days followed by once per week, the first five fractions and on an alternate week basis. Residual deviations obtained by comparing these protocols with daily imaging and the resulting additional PTV margin were then calculated. Results: Statistically significant differences between automatic and manual deviations are shown for 50 to 80% of the patients, depending on the tumor site. The additional margin that should be applied to PTV if manual corrections were not applied range from 2.5 mm for the brain tumors to 8 mm for pulmonary tumors treated with an arm support. The ‘‘every other day’’ and ‘‘one day out of 3’’ give similar results and are the most accurate imaging protocols, involving additional margins to the PTV of 3 mm for head and neck and brain tumors, 5 mm for the pulmonary tumors treated with a 9-point TM and 8 mm for all the other tumor sites. Conclusions: Applying no manual corrections after automatic registration or no MVCT daily imaging implies a significant increase in the PTV margins. The magnitude of this increase depends on the contentions used and treated tumor site. Author Disclosure: P. Meyer: None. S. Chami: None. E. Enderlin: None. C. Niederst: None. D. Jarnet: None. R. Guerra: None. D. Karamanoukian: None. G. Noel: None.
306
Assessing the Frequency, Magnitude, and Clinical Predictors of Tumor Misalignment when Skeletal Alignment is used Alone for Radiation Treatment Setup in Lung Cancer Patients
D. P. Kulkarni, H. Chung, P. A. Balter, L. E. Court, L. Dong, R. Komaki, J. Y. Chang, S. H. Lin MD Anderson Cancer Center, Houston, TX Purpose/Objective(s): While daily treatment positioning utilizing skeletal alignment may be adequate for a majority of patients being treated with radiation therapy, the frequency and the clinical predictors of inadequate tumor targeting using skeletal alignment alone for lung cancer patients are not well known. Utilizing data from daily cone beam CT (CBCT) in lung cancer patients treated with 4 fraction stereotactic body radiation therapy (SBRT), our goal for this study was to examine the magnitude of the body positioning shifts from skeletal landmarks that are necessary for tumor alignment and determine whether there are any associated clinical predictors of this shift. Materials/Methods: One hundred eighty consecutive SBRT patients treated at MD Anderson Cancer Center from 4/2008-11/ 2010 to a dose of 50 Gy at 12.5 Gy daily fractions were included. We used daily CBCT and 4D-CT to evaluate the treatment positioning using boney and soft tissue alignment. The difference was recorded as a shift in mm along the Antero-Posterior (AP), Supero-Inferior (SI) and Left-Right (LR) axes. 3 dimensional (3D) vector shifts were calculated using these numbers. Wilcoxon Rank Sum was used to test for clinical predictors of shifts using information such as tumor location, size, stage, histology, as well patient parameters like age, gender, KPS and BMI. Intraclass Correlation Coefficients (ICC) were calculated to determine the correlation between daily shifts according to magnitude of the shifts. Results: Average differences in boney registration and soft tissue (tumor) registration along AP, SI, and LR axes (mean ± SD) were 2.2 ± 2.6 mm, 2.1 ± 2.3 mm, and 1.2 ± 1.6 mm, respectively. For the 3D shift, this value was 4.0 ± 3.4 mm. Out of 180 3D shifts, 131 (72.7%) were #5 mm, 36 (20%) were from 5.1-10 mm and 13 (7.2%) were .10 mm. There was strong correlation of the shifts in the AP direction related to the shift magnitude. For shifts .10 mm, 5-10 mm and\5 mm the single measures ICC was found to be 0.859, 0.686, and 0.485, respectively. We identify no significant clinical predictors for the shifts made. Conclusions: The difference in soft tissue (tumor) alignment compared with boney alignment was .5 mm for more than a quarter of the patient-fractions. In some of these patients (7%), .1 cm shifts were necessary. Along the AP direction, larger shifts were highly correlated, suggesting a systematic error in the daily treatment positioning that is independent of any tumor or patient factors. This finding indicates that skeletal landmarks alone are not adequate as a clinical surrogate for tumor positioning in a significant proportion of patients, suggesting the need to increase utilization of cone beam CT for daily patient setup in lung cancer patients undergoing radiation therapy. Author Disclosure: D.P. Kulkarni: None. H. Chung: None. P.A. Balter: None. L.E. Court: None. L. Dong: None. R. Komaki: None. J.Y. Chang: None. S.H. Lin: None.
307
Intrafraction Verification using Beam Level kV Images for Gated RapidArc
R. Li, E. Mok, D. Chang, A. Koong, M. E. Daly, L. Xing Stanford University, Stanford, CA Purpose/Objective(s): To verify gated RapidArc treatment using kV images acquired during dose delivery. Materials/Methods: Three patients (one liver case and two pancreas cases) were treated using the gated RapidArc technique on a Varian TrueBeam STx Linac. Three to five gold fiducial markers were implanted inside or near the target before treatment simulation. These fiducial markers were contoured in the planning CT by the physician and a 2-mm margin was added to the fiducial contours to create a field aperture for treatment setup and verification purposes. An RPM block was placed on the patients’ abdominal surface and the gating signal was generated from the RPM system which controls the MV beam. During the gated RapidArc treatment, we acquired kV images immediately before MV beam-on at every breathing cycle, using the on-board imaging system. Depending on the specific breathing patterns, the total number of kV images ranged from 13 to 36 for one arc. After the kV images acquisition, we automatically detected one of the fiducial markers. A nonparametric Bayesian 3D real-time tracking algorithm was then used to estimate the 3D marker positions in the patient coordinate system. The percentage of time when the fiducial marker was inside its aperture (with the 2-mm margin added) as well as its distance to the edge of the aperture when outside were calculated to verify the geometric accuracy of gated treatment.
Proceedings of the 53rd Annual ASTRO Meeting Results: For the liver patient, the fiducial marker was within the aperture 100% of the time. For the first pancreas patient with kV imaging data, 95% of the time, the fiducial marker was within 2.2 mm of the aperture. The average and maximum distance to the aperture was 1.7 and 2.3 mm. For the second pancreas patient, 95% of the time, the fiducial marker was within 1.9 mm of the aperture. The average and maximum distance was 0.6 and 2.3 mm. Conclusions: To our knowledge, this is the first report of direct intrafraction real-time verification of implanted fiducials for respiratory gated RapidArc SBRT. It was found that a margin of around 4 mm is able to account for 95% of the intrafraction uncertainty in RPM-based RapidArc gating. In addition, narrowing the gating window can reduce the variability of positioning. For some patients and in some fractions, the fiducial deviated significantly from the fiducial aperture by more than 2 mm at the beginning of the MV beam on, indicating further investigation in need to ensure that the ITV is within the treatment field. This also emphasizes the need for gating techniques with beam-on/off controlled directly by the actual position of the tumor target instead of external surrogates such as RPM. Author Disclosure: R. Li: None. E. Mok: None. D. Chang: None. A. Koong: None. M.E. Daly: None. L. Xing: None.
308
Toward Intra-fraction Tumor Motion Tracking Using On-board Imaging and Dynamic Couch Compensation 1
D. Shah , K. Malinowski2, T. J. McAvoy3, W. D. D’Souza4 University of Maryland, Baltimore, Baltimore, MD, 2University of Maryland, College Park, College Park, MD, 3University of Maryland, College Park, Baltimore, MD, 4University of Maryland School of Medicine, Baltimore, MD 1
Purpose/Objective(s): To investigate the accuracy of real-time tumor tracking using external surrogates and a dynamic couchbased compensation system using on-board fluoroscopic kV imaging. Materials/Methods: We have developed an integrated intra-fraction tumor tracking and dynamic couch compensation system. The system tracks patient breathing motion by monitoring the position of optical sensors, placed on the patient. These optical sensors coupled with periodic on-board fluoroscopic imaging can be used to derive the relation to infer the position of the tumor using the position of the optical sensors. The inferred tumor motion is compensated for by feedback control using a dynamic couch-based motion correction system. To investigate the accuracy in real-time, a 4-D phantom simulated a time-varying 3D breathing motion with and optical sensor attached to it (Phantom1) and a separate 4D phantom (Phantom2) simulated tumor motion with a radio-opaque fiducial marker, tracking target, attached to it. Both phantoms, placed on the couch, were programmed to simulate 20 actual tumor trajectories. The inferential prediction of the target position using the optical sensor position was established a priori by partial-least-squares regression between known target and the sensor positions. By tracking the position of the optical sensor on Phantom1 using an infra-red camera, the position of fiducial marker on Phantom2 was inferred and compensated in real-time with dynamic couch control. The accuracy and latency of dynamic couch based motion compensation was determined by imaging the position of the fiducial before and after couch control using on-board kV fluoroscopy. Net fiducial displacements were derived by analyzing fluoroscopy image frames. Results: The average latency of the system was 116.7 ms. This latency comprises the camera latency, online calculation of tumor position, control system and couch dynamics. The SD of the fiducial displacement without motion compensation ranged from 0.6 mm to 4.5 mm and the peak-to-peak displacements ranged from 3.6 mm to 20.3 mm. The net fiducial displacement after compensation decreased significantly with the SD ranging from 0.1 mm to 0.6 mm and the peak-to-peak displacement ranging from 0.9 mm to 4.2 mm. The fraction of fiducial displacements \3 mm was increased from 49% without compensation to 95% after couch-based compensation. Conclusions: A first-of-its kind real-time dynamic couch based target tracking system, integrated with conventional linear accelerator, is able to accurately localize target using surrogates and reduce target motion to within 3 mm during radiation therapy. Author Disclosure: D. Shah: B. Research Grant; NIH Grant. K. Malinowski: B. Research Grant; NIH Grant. T.J. McAvoy: B. Research Grant; NIH Grant. W.D. D’Souza: B. Research Grant; NIH Grant.
309
Spatial Correlation of Proton Beam-Induced Dose and Positron Emission Activity in Polymer Gels
O. Lopatiuk-Tirpak1, Z. Su2, Z. Li2, W. Hsi3, S. Meeks1, O. Zeidan4 1 3
MD Anderson Cancer Center Orlando, Orlando, FL, 2University of Florida Proton Therapy Institute, Jacksonville, FL, ProCure TDS, Bloomington, IN, 4Procure Proton Therapy Center, Oklahoma City, OK
Purpose/Objective(s): In-vivo PET/CT verification of proton beam deliveries is based on the treatment-induced generation of positron-emitting isotopes in the irradiated tissues. BANG3-Pro2 polymer gel dosimeters have similar composition to that of human muscle and thus are well-suited for phantom PET/CT verification studies. The purpose of this study is to explore the use of these phantoms for direct spatial correlation of delivered dose and the corresponding positron emission distributions in three dimensions. This is of particular importance in the experimental investigations of the PET signature of delivery uncertainties that includes target motion, setup uncertainties, and effect of tissue heterogeneities. Materials/Methods: BANG3-Pro2 dosimeters were irradiated with a pristine beam (16 cm range in water) and an SOBP distribution (16 cm range in water, 6 cm modulation), the latter with and without phantom motion. The motion trace was a sinusoidal perpendicular to the beam direction, with 2-cm amplitude and the frequency of 0.25 Hz. Each of the three dosimeters was imaged in a nearby PET/CT unit within 3 minutes of irradiation. The time between beam-off and the start of the PET scanning was reduced by acquiring the CT set prior to proton beam irradiation. The profile of PET activity along the central axis of the beam was validated against the results of an analytical model. The dose was read out using an established optical CT procedure. The effects of target motion on activity and dose distributions were evaluated by modified volumetric gamma analysis against the treatment plan. Results: Time dependence of PET activity decay revealed that the majority of measured activity was due to the decay of 15O and 11 C. The results of PET imaging for the stationary deliveries were found to agree well with the analytical predictions. Lateral profiles of dose and PET activity exhibited good correlation throughout the beam range, which allowed employing a modified
S153
S152
Volume 81, Number 2, Supplement, 2011
respectively with or without vacuum cushions, 23 patients treated for Hodgkin’s disease with 9-point TM, 13 and 16 patients treated for pulmonary located tumors, respectively with 9-point TM or arm support, and 40 patients treated for brain tumors with 5-point TM. Systematic and random shifts were calculated for the automatic and total deviations on a patient and a population basis. A t test was used to determine if the registration results obtained after the manual refinements performed by the radiation therapists was statistically different from the automatic registration. Furthermore, residual deviations and additional PTV margin were calculated if manual corrections were not applied. Five imaging protocols were investigated: every other day, one day out of 3, the first 3 days followed by once per week, the first five fractions and on an alternate week basis. Residual deviations obtained by comparing these protocols with daily imaging and the resulting additional PTV margin were then calculated. Results: Statistically significant differences between automatic and manual deviations are shown for 50 to 80% of the patients, depending on the tumor site. The additional margin that should be applied to PTV if manual corrections were not applied range from 2.5 mm for the brain tumors to 8 mm for pulmonary tumors treated with an arm support. The ‘‘every other day’’ and ‘‘one day out of 3’’ give similar results and are the most accurate imaging protocols, involving additional margins to the PTV of 3 mm for head and neck and brain tumors, 5 mm for the pulmonary tumors treated with a 9-point TM and 8 mm for all the other tumor sites. Conclusions: Applying no manual corrections after automatic registration or no MVCT daily imaging implies a significant increase in the PTV margins. The magnitude of this increase depends on the contentions used and treated tumor site. Author Disclosure: P. Meyer: None. S. Chami: None. E. Enderlin: None. C. Niederst: None. D. Jarnet: None. R. Guerra: None. D. Karamanoukian: None. G. Noel: None.
306
Assessing the Frequency, Magnitude, and Clinical Predictors of Tumor Misalignment when Skeletal Alignment is used Alone for Radiation Treatment Setup in Lung Cancer Patients
D. P. Kulkarni, H. Chung, P. A. Balter, L. E. Court, L. Dong, R. Komaki, J. Y. Chang, S. H. Lin MD Anderson Cancer Center, Houston, TX Purpose/Objective(s): While daily treatment positioning utilizing skeletal alignment may be adequate for a majority of patients being treated with radiation therapy, the frequency and the clinical predictors of inadequate tumor targeting using skeletal alignment alone for lung cancer patients are not well known. Utilizing data from daily cone beam CT (CBCT) in lung cancer patients treated with 4 fraction stereotactic body radiation therapy (SBRT), our goal for this study was to examine the magnitude of the body positioning shifts from skeletal landmarks that are necessary for tumor alignment and determine whether there are any associated clinical predictors of this shift. Materials/Methods: One hundred eighty consecutive SBRT patients treated at MD Anderson Cancer Center from 4/2008-11/ 2010 to a dose of 50 Gy at 12.5 Gy daily fractions were included. We used daily CBCT and 4D-CT to evaluate the treatment positioning using boney and soft tissue alignment. The difference was recorded as a shift in mm along the Antero-Posterior (AP), Supero-Inferior (SI) and Left-Right (LR) axes. 3 dimensional (3D) vector shifts were calculated using these numbers. Wilcoxon Rank Sum was used to test for clinical predictors of shifts using information such as tumor location, size, stage, histology, as well patient parameters like age, gender, KPS and BMI. Intraclass Correlation Coefficients (ICC) were calculated to determine the correlation between daily shifts according to magnitude of the shifts. Results: Average differences in boney registration and soft tissue (tumor) registration along AP, SI, and LR axes (mean ± SD) were 2.2 ± 2.6 mm, 2.1 ± 2.3 mm, and 1.2 ± 1.6 mm, respectively. For the 3D shift, this value was 4.0 ± 3.4 mm. Out of 180 3D shifts, 131 (72.7%) were #5 mm, 36 (20%) were from 5.1-10 mm and 13 (7.2%) were .10 mm. There was strong correlation of the shifts in the AP direction related to the shift magnitude. For shifts .10 mm, 5-10 mm and\5 mm the single measures ICC was found to be 0.859, 0.686, and 0.485, respectively. We identify no significant clinical predictors for the shifts made. Conclusions: The difference in soft tissue (tumor) alignment compared with boney alignment was .5 mm for more than a quarter of the patient-fractions. In some of these patients (7%), .1 cm shifts were necessary. Along the AP direction, larger shifts were highly correlated, suggesting a systematic error in the daily treatment positioning that is independent of any tumor or patient factors. This finding indicates that skeletal landmarks alone are not adequate as a clinical surrogate for tumor positioning in a significant proportion of patients, suggesting the need to increase utilization of cone beam CT for daily patient setup in lung cancer patients undergoing radiation therapy. Author Disclosure: D.P. Kulkarni: None. H. Chung: None. P.A. Balter: None. L.E. Court: None. L. Dong: None. R. Komaki: None. J.Y. Chang: None. S.H. Lin: None.
307
Intrafraction Verification using Beam Level kV Images for Gated RapidArc
R. Li, E. Mok, D. Chang, A. Koong, M. E. Daly, L. Xing Stanford University, Stanford, CA Purpose/Objective(s): To verify gated RapidArc treatment using kV images acquired during dose delivery. Materials/Methods: Three patients (one liver case and two pancreas cases) were treated using the gated RapidArc technique on a Varian TrueBeam STx Linac. Three to five gold fiducial markers were implanted inside or near the target before treatment simulation. These fiducial markers were contoured in the planning CT by the physician and a 2-mm margin was added to the fiducial contours to create a field aperture for treatment setup and verification purposes. An RPM block was placed on the patients’ abdominal surface and the gating signal was generated from the RPM system which controls the MV beam. During the gated RapidArc treatment, we acquired kV images immediately before MV beam-on at every breathing cycle, using the on-board imaging system. Depending on the specific breathing patterns, the total number of kV images ranged from 13 to 36 for one arc. After the kV images acquisition, we automatically detected one of the fiducial markers. A nonparametric Bayesian 3D real-time tracking algorithm was then used to estimate the 3D marker positions in the patient coordinate system. The percentage of time when the fiducial marker was inside its aperture (with the 2-mm margin added) as well as its distance to the edge of the aperture when outside were calculated to verify the geometric accuracy of gated treatment.
Proceedings of the 53rd Annual ASTRO Meeting Results: For the liver patient, the fiducial marker was within the aperture 100% of the time. For the first pancreas patient with kV imaging data, 95% of the time, the fiducial marker was within 2.2 mm of the aperture. The average and maximum distance to the aperture was 1.7 and 2.3 mm. For the second pancreas patient, 95% of the time, the fiducial marker was within 1.9 mm of the aperture. The average and maximum distance was 0.6 and 2.3 mm. Conclusions: To our knowledge, this is the first report of direct intrafraction real-time verification of implanted fiducials for respiratory gated RapidArc SBRT. It was found that a margin of around 4 mm is able to account for 95% of the intrafraction uncertainty in RPM-based RapidArc gating. In addition, narrowing the gating window can reduce the variability of positioning. For some patients and in some fractions, the fiducial deviated significantly from the fiducial aperture by more than 2 mm at the beginning of the MV beam on, indicating further investigation in need to ensure that the ITV is within the treatment field. This also emphasizes the need for gating techniques with beam-on/off controlled directly by the actual position of the tumor target instead of external surrogates such as RPM. Author Disclosure: R. Li: None. E. Mok: None. D. Chang: None. A. Koong: None. M.E. Daly: None. L. Xing: None.
308
Toward Intra-fraction Tumor Motion Tracking Using On-board Imaging and Dynamic Couch Compensation 1
D. Shah , K. Malinowski2, T. J. McAvoy3, W. D. D’Souza4 University of Maryland, Baltimore, Baltimore, MD, 2University of Maryland, College Park, College Park, MD, 3University of Maryland, College Park, Baltimore, MD, 4University of Maryland School of Medicine, Baltimore, MD 1
Purpose/Objective(s): To investigate the accuracy of real-time tumor tracking using external surrogates and a dynamic couchbased compensation system using on-board fluoroscopic kV imaging. Materials/Methods: We have developed an integrated intra-fraction tumor tracking and dynamic couch compensation system. The system tracks patient breathing motion by monitoring the position of optical sensors, placed on the patient. These optical sensors coupled with periodic on-board fluoroscopic imaging can be used to derive the relation to infer the position of the tumor using the position of the optical sensors. The inferred tumor motion is compensated for by feedback control using a dynamic couch-based motion correction system. To investigate the accuracy in real-time, a 4-D phantom simulated a time-varying 3D breathing motion with and optical sensor attached to it (Phantom1) and a separate 4D phantom (Phantom2) simulated tumor motion with a radio-opaque fiducial marker, tracking target, attached to it. Both phantoms, placed on the couch, were programmed to simulate 20 actual tumor trajectories. The inferential prediction of the target position using the optical sensor position was established a priori by partial-least-squares regression between known target and the sensor positions. By tracking the position of the optical sensor on Phantom1 using an infra-red camera, the position of fiducial marker on Phantom2 was inferred and compensated in real-time with dynamic couch control. The accuracy and latency of dynamic couch based motion compensation was determined by imaging the position of the fiducial before and after couch control using on-board kV fluoroscopy. Net fiducial displacements were derived by analyzing fluoroscopy image frames. Results: The average latency of the system was 116.7 ms. This latency comprises the camera latency, online calculation of tumor position, control system and couch dynamics. The SD of the fiducial displacement without motion compensation ranged from 0.6 mm to 4.5 mm and the peak-to-peak displacements ranged from 3.6 mm to 20.3 mm. The net fiducial displacement after compensation decreased significantly with the SD ranging from 0.1 mm to 0.6 mm and the peak-to-peak displacement ranging from 0.9 mm to 4.2 mm. The fraction of fiducial displacements \3 mm was increased from 49% without compensation to 95% after couch-based compensation. Conclusions: A first-of-its kind real-time dynamic couch based target tracking system, integrated with conventional linear accelerator, is able to accurately localize target using surrogates and reduce target motion to within 3 mm during radiation therapy. Author Disclosure: D. Shah: B. Research Grant; NIH Grant. K. Malinowski: B. Research Grant; NIH Grant. T.J. McAvoy: B. Research Grant; NIH Grant. W.D. D’Souza: B. Research Grant; NIH Grant.
309
Spatial Correlation of Proton Beam-Induced Dose and Positron Emission Activity in Polymer Gels
O. Lopatiuk-Tirpak1, Z. Su2, Z. Li2, W. Hsi3, S. Meeks1, O. Zeidan4 1 3
MD Anderson Cancer Center Orlando, Orlando, FL, 2University of Florida Proton Therapy Institute, Jacksonville, FL, ProCure TDS, Bloomington, IN, 4Procure Proton Therapy Center, Oklahoma City, OK
Purpose/Objective(s): In-vivo PET/CT verification of proton beam deliveries is based on the treatment-induced generation of positron-emitting isotopes in the irradiated tissues. BANG3-Pro2 polymer gel dosimeters have similar composition to that of human muscle and thus are well-suited for phantom PET/CT verification studies. The purpose of this study is to explore the use of these phantoms for direct spatial correlation of delivered dose and the corresponding positron emission distributions in three dimensions. This is of particular importance in the experimental investigations of the PET signature of delivery uncertainties that includes target motion, setup uncertainties, and effect of tissue heterogeneities. Materials/Methods: BANG3-Pro2 dosimeters were irradiated with a pristine beam (16 cm range in water) and an SOBP distribution (16 cm range in water, 6 cm modulation), the latter with and without phantom motion. The motion trace was a sinusoidal perpendicular to the beam direction, with 2-cm amplitude and the frequency of 0.25 Hz. Each of the three dosimeters was imaged in a nearby PET/CT unit within 3 minutes of irradiation. The time between beam-off and the start of the PET scanning was reduced by acquiring the CT set prior to proton beam irradiation. The profile of PET activity along the central axis of the beam was validated against the results of an analytical model. The dose was read out using an established optical CT procedure. The effects of target motion on activity and dose distributions were evaluated by modified volumetric gamma analysis against the treatment plan. Results: Time dependence of PET activity decay revealed that the majority of measured activity was due to the decay of 15O and 11 C. The results of PET imaging for the stationary deliveries were found to agree well with the analytical predictions. Lateral profiles of dose and PET activity exhibited good correlation throughout the beam range, which allowed employing a modified
S153