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Tumor Volume Increase after Stereotactic Radiosurgery for Vestibular Schwannoma: Expected Radiographic Finding or Exception?
I. J. Radiation Oncology d Biology d Physics
S280
2169
Volume 78, Number 3, Supplement, 2010
Tumor Volume Increase after Stereotactic Radiosurgery for Vestibular Schwannoma: Expected Radiographic Finding or Exception?
A. Carai, S. Green, B. Delman, S. R. Blacksburg, K. Maloney-Lutz, Y. Lo, R. Sheu, I. Germano Mount Sinai Medical Center, New York, NY Purpose/Objective(s): Stereotactic radiosurgery (SRS) has emerged as a valuable alternative to microsurgery in the treatment of vestibular schwannomas (VS). Tumor control rates have been reported between 74% and 99% at 12 months. Despite these encouraging results, transient VS tumor enlargement after SRS has been reported in different series, with an incidence varying from 3% to 74% and an onset varying from 3 to 12 months. The aim of the present study is to determine the tumor volume changes 3, 6, and 12 months after SRS for VS. Materials/Methods: In this retrospective study, we reviewed the MRIs of 25 VS tumors in 24 patients treated with single fraction Novalis SRS at our Institution at baseline and at 3, 6, and 12 months after SRS. The most common regimen consisted of 1250 cGy prescribed to the 85% isodose line. Tumor volumes were calculated independently by a neurosurgeon and a neuroradiologist on axial and coronal MRI sections on T1W contrast-enhanced images. Correlation with clinical symptoms at the same time points was performed. Paired Student’s t-test and one-way ANOVA were used for statistical analysis. Results: Mean tumor volume before SRS was 10.75 + 15.5 cc3 (range, 1.08-60.24 cc3). A significant increase in volume was seen 3 and 6 months after SRS, 39% and 72%, respectively (p \ 0.05). Volumes returned toward baseline values at 12 months. At 3 months, 16/22 (73%) VS tumors showed an increase in volume .10% (range, 14-144%) and 16/18 (89%) at 6 months (range, 19-185%). Increased heterogeneity in contrast enhancement with a ‘‘soap-bubble’’ appearance was seen in the majority of cases. Increase in tumor volume, however, did not correlate with changes in neurological symptoms. Conclusions: Our study demonstrates that transient volume enlargement 3-6 months after SRS for VS should be considered part of the normal response to SRS treatment and should not be mistaken for treatment failure. There are no neurological symptoms that correlate with this radiographic feature and volumes return toward baseline values at 12 months. Therefore, when assessing MRIs 3-6 months after SRS, caution should be applied when prescribing potentially unnecessary treatment. Author Disclosure: A. Carai, None; S. Green, None; B. Delman, None; S.R. Blacksburg, None; K. Maloney-Lutz, None; Y. Lo, None; R. Sheu, None; I. Germano, None.
2170
Cone-Beam CT 6 Degree-of-Freedom Image-Guidance for Intracranial Frameless Stereotactic RadioSurgery using 6D Robotic Couch
Z. Chang1, Z. Wang1, J. Ma2,1, Q. Wu1, J. Kirkpatrick1, F. Yin1 1
Duke University, Durham, NC, 2Fudan University Cancer Hospital, Shanghai, China
Purpose/Objective(s): Cone-beam CT (CBCT) 6 degree-of-freedom (6D) image guidance has been successfully demonstrated with hypofractionated spinal stereotactic radiotherapy. In this work, this technique is further developed to investigate localization accuracy for image-guided intracranial frameless stereotactic radiosurgery with a large patient volume based on our previous study. Materials/Methods: Phantom and patient studies were performed on a Novalis Tx system, equipped with a BrainLAB 6D robotic couch and Varian CBCT imaging system. In the phantom studies, CBCT was performed on a head phantom and then registered with planning CT, enabling 6D fusion. Matching results were used to test the accuracy of CBCT 6D fusion for correcting translational and rotational setup errors. For patient studies, 50 intracranial SRS cases were randomly selected. Patients were initially positioned with the BrainLAB frameless mask system with target-positioning-overlays (TAPO). Patients were then scanned with CBCT to refine the setup. The position of each patient was adjusted or verified based on CBCT 3D and 6D image fusion. Setup displacements between TAPO, CBCT 3D and 6D image fusion were quantitatively analyzed with the paired Student’s t-test. Statistical significance was defined as p \ 0.05. Results: Phantom experiments showed root-mean-square (RMS) discrepancies of 0.6 mm translationally and 0.5o rotationally between CBCT 6D fusion and the known displacements. In the retrospective patient studies, the RMS of the differences between the initial setup with TAPO and CBCT 6D image fusion was greater than 1.5 mm in all the three translational directions. The corresponding rotational discrepancy in RMS was 1.5 . If positioning was corrected using standard CBCT 3D fusion, the residual translational and rotational discrepancies in RMS were 0.9 mm and 1.2o, as compared with CBCT 6D fusion. More specifically, the translational differences in RMS were 0.5 mm along anterior-posterior direction, 0.5 mm along longitudinal direction, and 0.6 mm along lateral direction; the rotational differences in RMS were 0.58 in pitch, 0.97 in roll, and 0.29 in yaw. The difference in the lateral direction was, however, found to be statistically significant (p = 0.033). It implies that uncorrected rotational discrepancies may introduce translational errors. CBCT 6D image fusion was used to evaluate the setups of all 50 patients. CBCT guided 6D correction was applied to 12 of the 50 cases using the robotic couch. After the 6D correction, both translational and rotational discrepancies were effectively minimized. Conclusions: CBCT 6D image fusion provides an explicit method of verify patient positioning, and, when combined with a 6D couch, minimizes both translational and rotational setup errors. Author Disclosure: Z. Chang, None; Z. Wang, None; J. Ma, None; Q. Wu, None; J. Kirkpatrick, None; F. Yin, None.
2171
Stereotactic Body Radiotherapy (SBRT) in Patients Previously Treated with External Beam Radiation Therapy
A. Ghafoori, K. Allen, J. Nelson, R. Clough, F. Yin, Z. Wang, Z. Chang, C. Kelsey, J. Kirkpatrick Duke University Medical Center, Durham, NC Purpose/Objective(s): Stereotactic body radiotherapy (SBRT) is increasingly used for the definitive treatment of primary malignancies or for palliation of metastases. We wished to determine the efficacy of SBRT in the treatment of patients who had received prior external beam radiation therapy (EBRT) to the treated site.
S280
2169
Volume 78, Number 3, Supplement, 2010
Tumor Volume Increase after Stereotactic Radiosurgery for Vestibular Schwannoma: Expected Radiographic Finding or Exception?
A. Carai, S. Green, B. Delman, S. R. Blacksburg, K. Maloney-Lutz, Y. Lo, R. Sheu, I. Germano Mount Sinai Medical Center, New York, NY Purpose/Objective(s): Stereotactic radiosurgery (SRS) has emerged as a valuable alternative to microsurgery in the treatment of vestibular schwannomas (VS). Tumor control rates have been reported between 74% and 99% at 12 months. Despite these encouraging results, transient VS tumor enlargement after SRS has been reported in different series, with an incidence varying from 3% to 74% and an onset varying from 3 to 12 months. The aim of the present study is to determine the tumor volume changes 3, 6, and 12 months after SRS for VS. Materials/Methods: In this retrospective study, we reviewed the MRIs of 25 VS tumors in 24 patients treated with single fraction Novalis SRS at our Institution at baseline and at 3, 6, and 12 months after SRS. The most common regimen consisted of 1250 cGy prescribed to the 85% isodose line. Tumor volumes were calculated independently by a neurosurgeon and a neuroradiologist on axial and coronal MRI sections on T1W contrast-enhanced images. Correlation with clinical symptoms at the same time points was performed. Paired Student’s t-test and one-way ANOVA were used for statistical analysis. Results: Mean tumor volume before SRS was 10.75 + 15.5 cc3 (range, 1.08-60.24 cc3). A significant increase in volume was seen 3 and 6 months after SRS, 39% and 72%, respectively (p \ 0.05). Volumes returned toward baseline values at 12 months. At 3 months, 16/22 (73%) VS tumors showed an increase in volume .10% (range, 14-144%) and 16/18 (89%) at 6 months (range, 19-185%). Increased heterogeneity in contrast enhancement with a ‘‘soap-bubble’’ appearance was seen in the majority of cases. Increase in tumor volume, however, did not correlate with changes in neurological symptoms. Conclusions: Our study demonstrates that transient volume enlargement 3-6 months after SRS for VS should be considered part of the normal response to SRS treatment and should not be mistaken for treatment failure. There are no neurological symptoms that correlate with this radiographic feature and volumes return toward baseline values at 12 months. Therefore, when assessing MRIs 3-6 months after SRS, caution should be applied when prescribing potentially unnecessary treatment. Author Disclosure: A. Carai, None; S. Green, None; B. Delman, None; S.R. Blacksburg, None; K. Maloney-Lutz, None; Y. Lo, None; R. Sheu, None; I. Germano, None.
2170
Cone-Beam CT 6 Degree-of-Freedom Image-Guidance for Intracranial Frameless Stereotactic RadioSurgery using 6D Robotic Couch
Z. Chang1, Z. Wang1, J. Ma2,1, Q. Wu1, J. Kirkpatrick1, F. Yin1 1
Duke University, Durham, NC, 2Fudan University Cancer Hospital, Shanghai, China
Purpose/Objective(s): Cone-beam CT (CBCT) 6 degree-of-freedom (6D) image guidance has been successfully demonstrated with hypofractionated spinal stereotactic radiotherapy. In this work, this technique is further developed to investigate localization accuracy for image-guided intracranial frameless stereotactic radiosurgery with a large patient volume based on our previous study. Materials/Methods: Phantom and patient studies were performed on a Novalis Tx system, equipped with a BrainLAB 6D robotic couch and Varian CBCT imaging system. In the phantom studies, CBCT was performed on a head phantom and then registered with planning CT, enabling 6D fusion. Matching results were used to test the accuracy of CBCT 6D fusion for correcting translational and rotational setup errors. For patient studies, 50 intracranial SRS cases were randomly selected. Patients were initially positioned with the BrainLAB frameless mask system with target-positioning-overlays (TAPO). Patients were then scanned with CBCT to refine the setup. The position of each patient was adjusted or verified based on CBCT 3D and 6D image fusion. Setup displacements between TAPO, CBCT 3D and 6D image fusion were quantitatively analyzed with the paired Student’s t-test. Statistical significance was defined as p \ 0.05. Results: Phantom experiments showed root-mean-square (RMS) discrepancies of 0.6 mm translationally and 0.5o rotationally between CBCT 6D fusion and the known displacements. In the retrospective patient studies, the RMS of the differences between the initial setup with TAPO and CBCT 6D image fusion was greater than 1.5 mm in all the three translational directions. The corresponding rotational discrepancy in RMS was 1.5 . If positioning was corrected using standard CBCT 3D fusion, the residual translational and rotational discrepancies in RMS were 0.9 mm and 1.2o, as compared with CBCT 6D fusion. More specifically, the translational differences in RMS were 0.5 mm along anterior-posterior direction, 0.5 mm along longitudinal direction, and 0.6 mm along lateral direction; the rotational differences in RMS were 0.58 in pitch, 0.97 in roll, and 0.29 in yaw. The difference in the lateral direction was, however, found to be statistically significant (p = 0.033). It implies that uncorrected rotational discrepancies may introduce translational errors. CBCT 6D image fusion was used to evaluate the setups of all 50 patients. CBCT guided 6D correction was applied to 12 of the 50 cases using the robotic couch. After the 6D correction, both translational and rotational discrepancies were effectively minimized. Conclusions: CBCT 6D image fusion provides an explicit method of verify patient positioning, and, when combined with a 6D couch, minimizes both translational and rotational setup errors. Author Disclosure: Z. Chang, None; Z. Wang, None; J. Ma, None; Q. Wu, None; J. Kirkpatrick, None; F. Yin, None.
2171
Stereotactic Body Radiotherapy (SBRT) in Patients Previously Treated with External Beam Radiation Therapy
A. Ghafoori, K. Allen, J. Nelson, R. Clough, F. Yin, Z. Wang, Z. Chang, C. Kelsey, J. Kirkpatrick Duke University Medical Center, Durham, NC Purpose/Objective(s): Stereotactic body radiotherapy (SBRT) is increasingly used for the definitive treatment of primary malignancies or for palliation of metastases. We wished to determine the efficacy of SBRT in the treatment of patients who had received prior external beam radiation therapy (EBRT) to the treated site.