- Email: [email protected]
Maximum Intensity Projection (MIP) and Average Intensity Projection (AIP) in Image Guided Stereotactic Body Radiation Therapy (SBRT) for Lung Cancer
S718
International Journal of Radiation Oncology Biology Physics
3331
head rests and thermoplastic masks are the conventional method of immobilization. Although the intrafraction image guidance system corrects for patient movement prior to delivery of the beam, patient movement after imaging can be a source of errors during beam delivery and cause inefficiency which lengthens treatment for individual patients. We conducted a study using customized head cushions (HC), in addition to the standard immobilization for patients receiving intracranial SRS to determine if this would help reduce patient movement. Materials/Methods: CK correction logs of 86 consecutive patients treated with 245 fractions of frameless SRT for intracranial lesions between Sept 2010 and Oct 2011 were extracted using TFDL software. Data regarding intrafraction imaging, translation and rotation corrections, couch shifts and e-stops were extracted from the logs using customized in house program and analysed using statistical software. The nonparametric Mann-Whitney U test was used to detect differences in the medians. Results: Twenty-seven patients (102 fractions) had SRT using the HC and 59 patients (143 fractions) were treated without it. Addition of the HC reduced the median number of couch shifts required per fraction from 10 to 7 (p Z 0.00042). The reduction persisted even if the initial setup shifts (4 to 2; p Z 0.0043) and the shifts prior to path changes were eliminated (1 to 0; p Z 0.037). Use of the HC reduced translation along the long axis of the couch (Std dev Y: 0.18 to 0.13mm; p Z 0.000013); there was trend to reduction in translations in the other 2 directions but this did not reach statistical significance. The median no. of imaging X-rays/fraction was reduced from 144 to 139 (p Z 0.031). The mean no. of e-stops were also reduced from 0.98 to 0.66 but this difference did not reach significance (p Z 0.27). Conclusion: A customized inexpensive HC has become the standard of care in our department as it reduced intrafraction patient motion and imaging frequency, improving overall treatment efficiency. Further research to determine a margin recipe for these treatments from this data is underway. This could have implications for cranial immobilization in other radiation delivery systems which do not have intrafraction image guidance. Author Disclosure: A. Haridass: None. E. Vandervoort: None. J. Szanto: None. J. Sinclair: None. J. Gratton: None. K. Malone: None. S. Malone: None.
Maximum Intensity Projection (MIP) and Average Intensity Projection (AIP) in Image Guided Stereotactic Body Radiation Therapy (SBRT) for Lung Cancer K. Shirai,1 K. Nishiyama,1 T. Katsuda,2 Y. Ueda,1 M. Miyazaki,1 K. Tsujii,1 and S. Ueyama1; 1Osaka Medical Center for Cancer and Cardiovascular Diseases, 1-3-3, Nakamichi, Higashinari-ku, Osaka, Japan, 2National Cerebral and Cardiovascular Center, 5-7-1, Fujishirodai, Suita-City, Osaka, Japan Purpose/Objective(s): In SBRT for stage I non-small cell lung cancer (NSCLC), MIP or AIP computed tomography (CT) images composed from respiratory-correlated 4-dimensional CT (4DCT) are used as reference to register with cone-beam CT (CBCT) images. The purpose of this study is to compare registration variations between MIP-CBCT and AIP-CBCT. Materials/Methods: Simulation CT and 4DCT images of a dynamic target ball phantom was acquired when it was at the motion center and moving along the superior-inferior (SI) direction in 3 patterns. The motion profile was the cosine-fourth-power waveform simulating respiratory tumor motion in which expiratory phases were longer than inspiratory phases. The motion patterns were a cycle time of 4 seconds with amplitudes of 10, 15, 20 mm. The 4DCT was sorted into 10 bins from which MIP and AIP were generated. CBCT images of the phantom were acquired in the same manner as Simulation CT and 4DCT. CBCT image of the stationary phantom was registered with CT image of the stationary phantom. The resultant couch position was the baseline. CBCT images of the moving phantom were registered with MIP and AIP of the corresponding amplitudes. The couch shift from baseline at each registration was defined as the registration error. The method used for the registration was the mutual information. In 4 sessions of 17 patients with stage I NSCLC (68 sessions in total), MIP and AIP generated from respiratory-correlated 4DCT were registered with free-breathing CBCT images. The couch shift along the SI direction at the registration was measured. Results: The Table shows registration errors along SI direction by MIP and AIP registration. Negative values indicate that the couch shifts inferiorly. The AIP registration errors were minor. The couch positions at MIP registration were inferior to AIP registration in all amplitude. MIP registration errors increased with amplitude and were more than 1.0 mm greater than the AIP registration errors. In patient study, the average couch position at MIP registration was 0.6 mm (standard deviation: 1.0 mm) inferior to the AIP registration. The shift was more than 1.0 mm in 23 of 68 sessions (33%) and 3.5 mm at a maximum. Poster Viewing Abstract 3331; Table MIP and AIP registration
Comparison of registration error by
Amplitude (mm)
MIP
AIP
10 15 20
-1.2 -1.6 -1.7
-0.1 0.2 0.4
Registration error (mm)
Conclusion: In the phantom study, the couch position at AIP registration was close to the baseline. In both phantom and patient study, the couch position at MIP registration was inferior to AIP registration. AIP registration is more appropriate to Image Guided SBRT for NSCLC. Author Disclosure: K. Shirai: None. K. Nishiyama: None. T. Katsuda: None. Y. Ueda: None. M. Miyazaki: None. K. Tsujii: None. S. Ueyama: None.
3332 Customized Head Cushions Reduce Patient Movement During Intracranial Radiosurgery A. Haridass, E. Vandervoort, J. Szanto, J. Sinclair, J. Gratton, K. Malone, and S. Malone; The Ottawa Hospital Cancer Centre (TOHCC), Ottawa, ON, Canada Purpose/Objective(s): Patient movement during the delivery of frameless Stereotactic Radiation therapy (SRT) can be a source for errors. Silverman
3333 Is the Prostatic Bed a Rigid Structure? Evaluation Using Real-time Electromagnetic Tracking M. Zhu,1 W. Hou,2 H. Gay,1 J. Ge,1 J.M. Michalski,1 and P.J. Parikh1; 1 Washington University School of Medicine, St. Louis, MO, 2St. Louis University School of Medicine, St. Louis, MO Purpose/Objective(s): Fiducials have been routinely utilized for prostate cancer patients undergoing external beam radiation therapy. For postprostatectomy patients, the target shape, fiducial placement and dose coverage are more variable than intact prostate radiation therapy. To date, there have been no reports on the fiducial geometry and target deformation for post-prostatectomy patients. In this study, we assess deformation of the prostate and prostatic bed using the real-time tracked fiducial geometry as a surrogate. Materials/Methods: Records from 40 patients (25 post-prostatectomy and 15 with intact prostates) treated with intensity modulated radiation therapy using real-time electromagnetic transponder tracking, 5mm clinical-targetvolume to planning-target-volume expansion margin and 3 mm tracking tolerances were analyzed. The relative position of the fiducials to the rectum, bladder and vesicourethral anastomosis (VUA) was recorded from the simulation computed tomography (CT) images. The inter-transponderdistance variations were calculated for all patients and were used as a surrogate to determine fiducial deformation. Cutoff values were selected to determine whether the transponders implanted in the prostatic bed have a rigid geometry. Results: Intra-fractional inter-transponder-distance variations were small (all less than 0.24 cm) for all 40 patients and therefore were not considered in the analysis. For the 15 patients with intact prostates, the ranges of interfractional inter-transponder-distance variations were all smaller than 0.47 cm (Mean Z 0.22 cm, STD Z 0.09 cm, Range: 0.058 cm e 0.47 cm) and 20% (Mean Z 8.0%, STD Z 3.5%, Range: 2.1% e 20.0%) of the original
International Journal of Radiation Oncology Biology Physics
3331
head rests and thermoplastic masks are the conventional method of immobilization. Although the intrafraction image guidance system corrects for patient movement prior to delivery of the beam, patient movement after imaging can be a source of errors during beam delivery and cause inefficiency which lengthens treatment for individual patients. We conducted a study using customized head cushions (HC), in addition to the standard immobilization for patients receiving intracranial SRS to determine if this would help reduce patient movement. Materials/Methods: CK correction logs of 86 consecutive patients treated with 245 fractions of frameless SRT for intracranial lesions between Sept 2010 and Oct 2011 were extracted using TFDL software. Data regarding intrafraction imaging, translation and rotation corrections, couch shifts and e-stops were extracted from the logs using customized in house program and analysed using statistical software. The nonparametric Mann-Whitney U test was used to detect differences in the medians. Results: Twenty-seven patients (102 fractions) had SRT using the HC and 59 patients (143 fractions) were treated without it. Addition of the HC reduced the median number of couch shifts required per fraction from 10 to 7 (p Z 0.00042). The reduction persisted even if the initial setup shifts (4 to 2; p Z 0.0043) and the shifts prior to path changes were eliminated (1 to 0; p Z 0.037). Use of the HC reduced translation along the long axis of the couch (Std dev Y: 0.18 to 0.13mm; p Z 0.000013); there was trend to reduction in translations in the other 2 directions but this did not reach statistical significance. The median no. of imaging X-rays/fraction was reduced from 144 to 139 (p Z 0.031). The mean no. of e-stops were also reduced from 0.98 to 0.66 but this difference did not reach significance (p Z 0.27). Conclusion: A customized inexpensive HC has become the standard of care in our department as it reduced intrafraction patient motion and imaging frequency, improving overall treatment efficiency. Further research to determine a margin recipe for these treatments from this data is underway. This could have implications for cranial immobilization in other radiation delivery systems which do not have intrafraction image guidance. Author Disclosure: A. Haridass: None. E. Vandervoort: None. J. Szanto: None. J. Sinclair: None. J. Gratton: None. K. Malone: None. S. Malone: None.
Maximum Intensity Projection (MIP) and Average Intensity Projection (AIP) in Image Guided Stereotactic Body Radiation Therapy (SBRT) for Lung Cancer K. Shirai,1 K. Nishiyama,1 T. Katsuda,2 Y. Ueda,1 M. Miyazaki,1 K. Tsujii,1 and S. Ueyama1; 1Osaka Medical Center for Cancer and Cardiovascular Diseases, 1-3-3, Nakamichi, Higashinari-ku, Osaka, Japan, 2National Cerebral and Cardiovascular Center, 5-7-1, Fujishirodai, Suita-City, Osaka, Japan Purpose/Objective(s): In SBRT for stage I non-small cell lung cancer (NSCLC), MIP or AIP computed tomography (CT) images composed from respiratory-correlated 4-dimensional CT (4DCT) are used as reference to register with cone-beam CT (CBCT) images. The purpose of this study is to compare registration variations between MIP-CBCT and AIP-CBCT. Materials/Methods: Simulation CT and 4DCT images of a dynamic target ball phantom was acquired when it was at the motion center and moving along the superior-inferior (SI) direction in 3 patterns. The motion profile was the cosine-fourth-power waveform simulating respiratory tumor motion in which expiratory phases were longer than inspiratory phases. The motion patterns were a cycle time of 4 seconds with amplitudes of 10, 15, 20 mm. The 4DCT was sorted into 10 bins from which MIP and AIP were generated. CBCT images of the phantom were acquired in the same manner as Simulation CT and 4DCT. CBCT image of the stationary phantom was registered with CT image of the stationary phantom. The resultant couch position was the baseline. CBCT images of the moving phantom were registered with MIP and AIP of the corresponding amplitudes. The couch shift from baseline at each registration was defined as the registration error. The method used for the registration was the mutual information. In 4 sessions of 17 patients with stage I NSCLC (68 sessions in total), MIP and AIP generated from respiratory-correlated 4DCT were registered with free-breathing CBCT images. The couch shift along the SI direction at the registration was measured. Results: The Table shows registration errors along SI direction by MIP and AIP registration. Negative values indicate that the couch shifts inferiorly. The AIP registration errors were minor. The couch positions at MIP registration were inferior to AIP registration in all amplitude. MIP registration errors increased with amplitude and were more than 1.0 mm greater than the AIP registration errors. In patient study, the average couch position at MIP registration was 0.6 mm (standard deviation: 1.0 mm) inferior to the AIP registration. The shift was more than 1.0 mm in 23 of 68 sessions (33%) and 3.5 mm at a maximum. Poster Viewing Abstract 3331; Table MIP and AIP registration
Comparison of registration error by
Amplitude (mm)
MIP
AIP
10 15 20
-1.2 -1.6 -1.7
-0.1 0.2 0.4
Registration error (mm)
Conclusion: In the phantom study, the couch position at AIP registration was close to the baseline. In both phantom and patient study, the couch position at MIP registration was inferior to AIP registration. AIP registration is more appropriate to Image Guided SBRT for NSCLC. Author Disclosure: K. Shirai: None. K. Nishiyama: None. T. Katsuda: None. Y. Ueda: None. M. Miyazaki: None. K. Tsujii: None. S. Ueyama: None.
3332 Customized Head Cushions Reduce Patient Movement During Intracranial Radiosurgery A. Haridass, E. Vandervoort, J. Szanto, J. Sinclair, J. Gratton, K. Malone, and S. Malone; The Ottawa Hospital Cancer Centre (TOHCC), Ottawa, ON, Canada Purpose/Objective(s): Patient movement during the delivery of frameless Stereotactic Radiation therapy (SRT) can be a source for errors. Silverman
3333 Is the Prostatic Bed a Rigid Structure? Evaluation Using Real-time Electromagnetic Tracking M. Zhu,1 W. Hou,2 H. Gay,1 J. Ge,1 J.M. Michalski,1 and P.J. Parikh1; 1 Washington University School of Medicine, St. Louis, MO, 2St. Louis University School of Medicine, St. Louis, MO Purpose/Objective(s): Fiducials have been routinely utilized for prostate cancer patients undergoing external beam radiation therapy. For postprostatectomy patients, the target shape, fiducial placement and dose coverage are more variable than intact prostate radiation therapy. To date, there have been no reports on the fiducial geometry and target deformation for post-prostatectomy patients. In this study, we assess deformation of the prostate and prostatic bed using the real-time tracked fiducial geometry as a surrogate. Materials/Methods: Records from 40 patients (25 post-prostatectomy and 15 with intact prostates) treated with intensity modulated radiation therapy using real-time electromagnetic transponder tracking, 5mm clinical-targetvolume to planning-target-volume expansion margin and 3 mm tracking tolerances were analyzed. The relative position of the fiducials to the rectum, bladder and vesicourethral anastomosis (VUA) was recorded from the simulation computed tomography (CT) images. The inter-transponderdistance variations were calculated for all patients and were used as a surrogate to determine fiducial deformation. Cutoff values were selected to determine whether the transponders implanted in the prostatic bed have a rigid geometry. Results: Intra-fractional inter-transponder-distance variations were small (all less than 0.24 cm) for all 40 patients and therefore were not considered in the analysis. For the 15 patients with intact prostates, the ranges of interfractional inter-transponder-distance variations were all smaller than 0.47 cm (Mean Z 0.22 cm, STD Z 0.09 cm, Range: 0.058 cm e 0.47 cm) and 20% (Mean Z 8.0%, STD Z 3.5%, Range: 2.1% e 20.0%) of the original