- Email: [email protected]
Interfractional Change of Lumpectomy Cavity during Partial Breast Irradiation
I. J. Radiation Oncology d Biology d Physics
S142
Volume 75, Number 3, Supplement, 2009
Voxel Monte Carlo method (XVMC) in iPlan. Dose distribution was calculated using RPL and XVMC under the same monitor unit as in the plan prescribed 48 Gy at the isocenter using BPL. In addition, the plans were recalculated in two ways of dose prescription, 48 Gy at the isocenter and 48 Gy to 95% volume of the planning target volume (PTV). Thereafter, in both of the dose prescription methods, dose–volumetric data were compared with analyses of variance (ANOVA) among the three methods of heterogeneity correction. All pairwise comparisons were performed using Tukey’s test. Results: Mean values of the minimal dose and D95 for the PTV were 43.7 Gy and 45.7 Gy, respectively, when prescribed 48 Gy at the isocenter using BPL. Meanwhile, if the doses were recalculated with RPL and XVMC under the same monitor unit as in BPL, those values for RPL were 48.4 Gy and 49.4 Gy, and those values for XVMC were 39.7 Gy and 42.7 Gy, respectively. The marginal doses (minimal dose and D95) were significantly lower with XVMC than with BPL (p \ 0.001). In addition, when prescribed 48 Gy to 95% volume of the PTV, mean doses at the isocenter with BPL, RPL, and XVMC were 50.4 Gy, 49.3Gy, and 55.7 Gy, respectively. In this condition of the D95 prescription, the isocenter doses were significantly higher with XVMC than with BPL calculation (p \ 0.001). When prescribed 48 Gy at the isocenter using BPL, RPL, and XVMC, mean values of monitor units were 1540, 1477, and 1519, respectively. Meanwhile, under the D95 prescription using BPL, RPL, and XVMC, mean values of monitor units were 1619, 1517, and 1761, respectively. The difference in monitor units between BPL and XVMC was significantly higher when using the D95 prescription (p \ 0.001). Conclusions: Heterogeneity corrections can have significant impacts on dose distributions of SBRT for lung tumors. Careful attentions should be paid to differences in dose calculation results among different heterogeneity correction methods and the ways of dose prescription. Author Disclosure: M. Narabayashi, None; Y. Matsuo, None; T. Mizowaki, None; Y. Narita, None; S. Sato, None; M. Nakamura, None; K. Takayama, None; Y. Norihisa, None; K. Sakanaka, None; M. Hiraoka, None.
1040
A Model for Predicting Target Positions via Real-time Electromagnetic Internal Position Monitoring
R. L. Smith1, K. M. Lechleiter1, J. Newell2, J. D. Bradley1, D. A. Low1, P. J. Parikh1 1
Washington University Saint Louis, Saint Louis, MO, 2Calypso Medical, Seattle, WA
Purpose/Objective(s): Respiratory motion causes significant dosimetric error for targets within the lung/abdomen. Ideally, the target position would be known throughout the course of treatment. Fiducials are often used for the purpose of tracking lung tumors, however there are anatomic limitations of bronchoscopic fiducial placement. We investigated the utility of electromagnetic transponders (CalypsoÒ Medical Technologies, Seattle, WA) to predict the location of a tumor that may be up to 5 cm away, and compared that with an external bellows surrogate. Materials/Methods: Under IRB approved trials, nine electromagnetic transponders were bronchoscopically implanted into the lungs of three dogs, and two transponders were implanted into the lung of a human lung cancer patient. Data was recorded from three sessions of simultaneous electromagnetic tracking at 10 Hz with concurrent measurements of abdominal circumference with a bellows device for the canines, and 5 sessions recorded during treatment for the human patient with one additional session recording bellows with concurrent fiducial position measurement. Each session had .1300 points in the presence of free-breathing. A previously reported lung model (Low 2005) was modified in order to use the position/velocity of an internal transponder to predict motion of a target point within the lung. The model was calibrated by using the external signal (bellows) or the position of an internal surrogate transponder. For each case, the model was used to predict the motion of a second implanted target transponder whose position was recorded throughout the session. The mean 3D error, SD and maximum error for each prediction was recorded. Results: For the canine data, the range of motion was 20 mm. A bellows surrogate yielded a mean error of 0.72 mm (std: 0.67) and a maximum error of 4.78 mm. The internal fiducial model yielded a mean error of 0.37 mm (std: 0.32) and a maximum error of 2.87 mm with errors scaling linearly with distance between the fiducial surrogate and target. For the human data, the range of motion was 19mm. Using the bellows for model calibration yielded a mean error of 1.0 mm (std: 0.73) and a maximum error of 4.0 mm. The internal fiducial model yielded a mean error of 0.75 mm (std: 0.37) and a maximum error of 3.85 mm. Conclusions: Both external surrogate and an internal fiducial performed well for prediction of intrafraction motion for a given session, but the internal fiducial’s performance was twice as accurate. Internal fiducials provide \2 mm localization even when relatively distant from the target. Author Disclosure: R.L. Smith, Calypso Medical, B. Research Grant; K.M. Lechleiter, Calypso Medical, B. Research Grant; J. Newell, Calypso Medical, A. Employment; J.D. Bradley, None; D.A. Low, Philips, B. Research Grant; P.J. Parikh, Calypso Medical, B. Research Grant; Philips, B. Research Grant.
1041
Interfractional Change of Lumpectomy Cavity during Partial Breast Irradiation
E. E. Ahunbay, J. Robbins, A. Godley, J. White, X. A. Li Medical College of Wisconsin, Milwaukee, WI Purpose/Objective(s): Partial breast irradiation (PB) with conformal dose distributions relies on accurate localization of lumpectomy cavity. In this work, by analyzing the daily CT data acquired during CT-guided PBI, we quantify the interfractional variations in position, shape and volume of CTV (lumpectomy cavity plus a margin). Materials/Methods: The daily CT data for 12 breast cancer patients treated with PBI in either prone (9 patients) or supine (3 patients) with daily kV CT guidance using a CT-on-Rails and linac combo (CTVision, Siemens), were analyzed. The contours of lumpectomy cavity and CTV were obtained on each daily CT set using an auto-segmentation tool with deformable image registration (ABAS, CMS). In addition, the planning CT was deformably registered with daily CT using an in-house developed tool with symmetric Demons algorithm to obtain the registration matrix and to verify the contours generated by ABAS. All contours were also validated manually. The vector field information of the registration was utilized along with the surface normal vectors of CTV structures to calculate the surface displacement maps, which was used to determine the systematic (S) and random (s) displacement for all surface points. The overlaps between the planning CTV and daily CTV was measured by Dice coefficient for different image
Proceedings of the 51st Annual ASTRO Meeting registration methods used in the clinic, including alignment using the center of mass (COM), external breast contour, surgical clips (SC) and chest wall (CW). Results: The location, shape and volume of lumpectomy cavity, thus, the CTV, varied significantly during the course of treatment. The average overlap between planning and daily treatment CTVs was 0.64, when both CTVs were aligned based on their COM. The CTV and breast volumes showed large, patient dependent variation (maximum CTV volume change =30%); some patients’ volumes increased and some decreased throughout the treatment. CTV and breast volume varied similarly, CTV with a larger magnitude. Distance between anatomic landmarks and CTV varied throughout the course: chest wall -CTV (s = 4.1mm), tip of breast CTV (s = 4.1mm), and the clips - CTV (s = 3.8mm). Systematic and random displacements along surface normals were s # 3.6mm, and S # 0.9mm for 95% of CTV surface area if alignment for maximum overlap is used; however this increased to .4mm for both s and S when aligned to COM, and was larger for SC and CW alignments. Generic margin formula (2S + .7s) applied to surface points resulted in a margin of 5.7, 7, 9, and 9.3mm for the maximum-overlap, COM, SC and CW based alignments. Conclusions: Considerable displacement of chest wall and surgical clips relative to CTV indicates that best alignment is based on CTV matching. Large volume change and deformation necessitates PTV margins .5mm, unless more effective correction strategies (e.g., adaptive replanning) are employed. Author Disclosure: E.E. Ahunbay, None; J. Robbins, None; A. Godley, None; J. White, None; X.A. Li, None.
1042
Validation of an Automated Segmentation Method for Head and Neck Adaptive Radiotherapy using Conebeam Computed Tomography (CBCT)
L. Chau1, S. Allaire1,2, K. K. Brock1,3, V. Pekar4, J. N. Waldron1,3, S. L. Breen1,3 1 Radiation Medicine Program, Princess Margaret Hospital, Toronto, ON, Canada, 2Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada, 3Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, 4 Philips Research North America, Markham, ON, Canada
Purpose/Objective(s): An efficient and robust deformable registration method to propagate contours from the planning computed tomography (CT) to the daily online CBCT is needed to facilitate adaptive radiotherapy in clinical practice. The goal of this study is to quantitatively validate an automatic segmentation method based on 3D salient interest points on daily CBCT of the head and neck. Materials/Methods: Ten patients were identified who received radical intensity-modulated radiation therapy (IMRT) for head and neck cancer and presented with bulky neck nodes that were radiologically evident on CBCT. Ten observers (six radiation oncologists, three fellows and one specialized dosimetrist) volunteered for this study. For each patient, the observers manually delineated one nodal volume, the cervical spinal cord and one parotid on the planning CT images and on 3 CBCT images acquired in the first, middle and last week of radiotherapy. The observers evaluated the manually delineated structures on the planning CT and chose representative contours as consensus structures for each patient. These consensus structures were automatically propagated to each CBCT image. For each structure in each CBCT, a reference contour was created consisting of the sum of all observers’ contours. Finite element modeling was used to quantify the mean displacement of surface elements from the reference contour to every contoured structure. The average of the mean displacements across all observers was compared with the automatic segmentation for all patients using a Wilcoxon rank test for each structure in each image. Results: The auto-segmentation method took less than 2 minutes to propagate all consensus structures from the planning CT images to the 3 CBCT images. Qualitatively, all propagated nodal volumes and cords successfully followed the anatomic deformations as seen on the CBCT images; 5 out of 30 propagated parotids presented a small overlap into bone and/or beyond the patient outline. According to the Wilcoxon rank test for each CBCT, no statistically significant difference was observed between the autosegmented and manual contours the nodal volumes, parotid and cord(a = 0.05). Conclusions: The results from this study demonstrated that the 3D salient interest point based automated segmentation is a reliable and efficient method to propagate large series of contours from a planning CT image to subsequent CBCT images with anatomic deformations. The automatically propagated contours were consistent with the observers’ contours across all CBCT images. This provides a systematic framework to quantify the dosimetric effect of anatomic and geometric changes during a course of fractionated radiotherapy, to determine whether there is a need for replanning. Author Disclosure: L. Chau, Philips Healthcare, C. Other Research Support; S. Allaire, Philips Healthcare, C. Other Research Support; K.K. Brock, Philips Healthcare, Elekta Oncology Systems, RaySearch Laboratories, B. Research Grant; IMPAC Physics Advisory Board, F. Consultant/Advisory Board; V. Pekar, Philips Research North America, A. Employment; J.N. Waldron, None; S.L. Breen, Philips Healthcare, B. Research Grant.
1043
Tumor Nodule Location Predicts the Feasibility of Intraprostatic High-dose Irradiation in Men with Localized Prostate Cancer
N. Housri1, J. Ondos1, P. L. Choyke2, A. Barbara1, H. Ning1, D. Citrin1, A. K. Singh3, A. Kaushal1 Radiation Oncology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, 2Molecular Imaging Program, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 3Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, NY 1
Purpose/Objective(s): A number of randomized trials have reported improved outcomes for men with prostate cancer treated with radiation dose escalation. Dose escalation is limited by the possibility of toxicity to surrounding critical structures. We are evaluating the feasibility of dose escalation to MRI-identified intraprostatic cancer lesions (IPL) with standard doses to the surrounding prostate tissue in a Phase I trial with the aim of improving intraprostatic tumor control and prostate cancer specific survival. The parameters that make patients amenable to these high-dose simultaneous integrated boosts (SIB) are largely unknown. We sought to identify whether factors related to IPLs or those related to individual patients predict the feasibility of high-dose intraprostatic SIB.
S143
S142
Volume 75, Number 3, Supplement, 2009
Voxel Monte Carlo method (XVMC) in iPlan. Dose distribution was calculated using RPL and XVMC under the same monitor unit as in the plan prescribed 48 Gy at the isocenter using BPL. In addition, the plans were recalculated in two ways of dose prescription, 48 Gy at the isocenter and 48 Gy to 95% volume of the planning target volume (PTV). Thereafter, in both of the dose prescription methods, dose–volumetric data were compared with analyses of variance (ANOVA) among the three methods of heterogeneity correction. All pairwise comparisons were performed using Tukey’s test. Results: Mean values of the minimal dose and D95 for the PTV were 43.7 Gy and 45.7 Gy, respectively, when prescribed 48 Gy at the isocenter using BPL. Meanwhile, if the doses were recalculated with RPL and XVMC under the same monitor unit as in BPL, those values for RPL were 48.4 Gy and 49.4 Gy, and those values for XVMC were 39.7 Gy and 42.7 Gy, respectively. The marginal doses (minimal dose and D95) were significantly lower with XVMC than with BPL (p \ 0.001). In addition, when prescribed 48 Gy to 95% volume of the PTV, mean doses at the isocenter with BPL, RPL, and XVMC were 50.4 Gy, 49.3Gy, and 55.7 Gy, respectively. In this condition of the D95 prescription, the isocenter doses were significantly higher with XVMC than with BPL calculation (p \ 0.001). When prescribed 48 Gy at the isocenter using BPL, RPL, and XVMC, mean values of monitor units were 1540, 1477, and 1519, respectively. Meanwhile, under the D95 prescription using BPL, RPL, and XVMC, mean values of monitor units were 1619, 1517, and 1761, respectively. The difference in monitor units between BPL and XVMC was significantly higher when using the D95 prescription (p \ 0.001). Conclusions: Heterogeneity corrections can have significant impacts on dose distributions of SBRT for lung tumors. Careful attentions should be paid to differences in dose calculation results among different heterogeneity correction methods and the ways of dose prescription. Author Disclosure: M. Narabayashi, None; Y. Matsuo, None; T. Mizowaki, None; Y. Narita, None; S. Sato, None; M. Nakamura, None; K. Takayama, None; Y. Norihisa, None; K. Sakanaka, None; M. Hiraoka, None.
1040
A Model for Predicting Target Positions via Real-time Electromagnetic Internal Position Monitoring
R. L. Smith1, K. M. Lechleiter1, J. Newell2, J. D. Bradley1, D. A. Low1, P. J. Parikh1 1
Washington University Saint Louis, Saint Louis, MO, 2Calypso Medical, Seattle, WA
Purpose/Objective(s): Respiratory motion causes significant dosimetric error for targets within the lung/abdomen. Ideally, the target position would be known throughout the course of treatment. Fiducials are often used for the purpose of tracking lung tumors, however there are anatomic limitations of bronchoscopic fiducial placement. We investigated the utility of electromagnetic transponders (CalypsoÒ Medical Technologies, Seattle, WA) to predict the location of a tumor that may be up to 5 cm away, and compared that with an external bellows surrogate. Materials/Methods: Under IRB approved trials, nine electromagnetic transponders were bronchoscopically implanted into the lungs of three dogs, and two transponders were implanted into the lung of a human lung cancer patient. Data was recorded from three sessions of simultaneous electromagnetic tracking at 10 Hz with concurrent measurements of abdominal circumference with a bellows device for the canines, and 5 sessions recorded during treatment for the human patient with one additional session recording bellows with concurrent fiducial position measurement. Each session had .1300 points in the presence of free-breathing. A previously reported lung model (Low 2005) was modified in order to use the position/velocity of an internal transponder to predict motion of a target point within the lung. The model was calibrated by using the external signal (bellows) or the position of an internal surrogate transponder. For each case, the model was used to predict the motion of a second implanted target transponder whose position was recorded throughout the session. The mean 3D error, SD and maximum error for each prediction was recorded. Results: For the canine data, the range of motion was 20 mm. A bellows surrogate yielded a mean error of 0.72 mm (std: 0.67) and a maximum error of 4.78 mm. The internal fiducial model yielded a mean error of 0.37 mm (std: 0.32) and a maximum error of 2.87 mm with errors scaling linearly with distance between the fiducial surrogate and target. For the human data, the range of motion was 19mm. Using the bellows for model calibration yielded a mean error of 1.0 mm (std: 0.73) and a maximum error of 4.0 mm. The internal fiducial model yielded a mean error of 0.75 mm (std: 0.37) and a maximum error of 3.85 mm. Conclusions: Both external surrogate and an internal fiducial performed well for prediction of intrafraction motion for a given session, but the internal fiducial’s performance was twice as accurate. Internal fiducials provide \2 mm localization even when relatively distant from the target. Author Disclosure: R.L. Smith, Calypso Medical, B. Research Grant; K.M. Lechleiter, Calypso Medical, B. Research Grant; J. Newell, Calypso Medical, A. Employment; J.D. Bradley, None; D.A. Low, Philips, B. Research Grant; P.J. Parikh, Calypso Medical, B. Research Grant; Philips, B. Research Grant.
1041
Interfractional Change of Lumpectomy Cavity during Partial Breast Irradiation
E. E. Ahunbay, J. Robbins, A. Godley, J. White, X. A. Li Medical College of Wisconsin, Milwaukee, WI Purpose/Objective(s): Partial breast irradiation (PB) with conformal dose distributions relies on accurate localization of lumpectomy cavity. In this work, by analyzing the daily CT data acquired during CT-guided PBI, we quantify the interfractional variations in position, shape and volume of CTV (lumpectomy cavity plus a margin). Materials/Methods: The daily CT data for 12 breast cancer patients treated with PBI in either prone (9 patients) or supine (3 patients) with daily kV CT guidance using a CT-on-Rails and linac combo (CTVision, Siemens), were analyzed. The contours of lumpectomy cavity and CTV were obtained on each daily CT set using an auto-segmentation tool with deformable image registration (ABAS, CMS). In addition, the planning CT was deformably registered with daily CT using an in-house developed tool with symmetric Demons algorithm to obtain the registration matrix and to verify the contours generated by ABAS. All contours were also validated manually. The vector field information of the registration was utilized along with the surface normal vectors of CTV structures to calculate the surface displacement maps, which was used to determine the systematic (S) and random (s) displacement for all surface points. The overlaps between the planning CTV and daily CTV was measured by Dice coefficient for different image
Proceedings of the 51st Annual ASTRO Meeting registration methods used in the clinic, including alignment using the center of mass (COM), external breast contour, surgical clips (SC) and chest wall (CW). Results: The location, shape and volume of lumpectomy cavity, thus, the CTV, varied significantly during the course of treatment. The average overlap between planning and daily treatment CTVs was 0.64, when both CTVs were aligned based on their COM. The CTV and breast volumes showed large, patient dependent variation (maximum CTV volume change =30%); some patients’ volumes increased and some decreased throughout the treatment. CTV and breast volume varied similarly, CTV with a larger magnitude. Distance between anatomic landmarks and CTV varied throughout the course: chest wall -CTV (s = 4.1mm), tip of breast CTV (s = 4.1mm), and the clips - CTV (s = 3.8mm). Systematic and random displacements along surface normals were s # 3.6mm, and S # 0.9mm for 95% of CTV surface area if alignment for maximum overlap is used; however this increased to .4mm for both s and S when aligned to COM, and was larger for SC and CW alignments. Generic margin formula (2S + .7s) applied to surface points resulted in a margin of 5.7, 7, 9, and 9.3mm for the maximum-overlap, COM, SC and CW based alignments. Conclusions: Considerable displacement of chest wall and surgical clips relative to CTV indicates that best alignment is based on CTV matching. Large volume change and deformation necessitates PTV margins .5mm, unless more effective correction strategies (e.g., adaptive replanning) are employed. Author Disclosure: E.E. Ahunbay, None; J. Robbins, None; A. Godley, None; J. White, None; X.A. Li, None.
1042
Validation of an Automated Segmentation Method for Head and Neck Adaptive Radiotherapy using Conebeam Computed Tomography (CBCT)
L. Chau1, S. Allaire1,2, K. K. Brock1,3, V. Pekar4, J. N. Waldron1,3, S. L. Breen1,3 1 Radiation Medicine Program, Princess Margaret Hospital, Toronto, ON, Canada, 2Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada, 3Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, 4 Philips Research North America, Markham, ON, Canada
Purpose/Objective(s): An efficient and robust deformable registration method to propagate contours from the planning computed tomography (CT) to the daily online CBCT is needed to facilitate adaptive radiotherapy in clinical practice. The goal of this study is to quantitatively validate an automatic segmentation method based on 3D salient interest points on daily CBCT of the head and neck. Materials/Methods: Ten patients were identified who received radical intensity-modulated radiation therapy (IMRT) for head and neck cancer and presented with bulky neck nodes that were radiologically evident on CBCT. Ten observers (six radiation oncologists, three fellows and one specialized dosimetrist) volunteered for this study. For each patient, the observers manually delineated one nodal volume, the cervical spinal cord and one parotid on the planning CT images and on 3 CBCT images acquired in the first, middle and last week of radiotherapy. The observers evaluated the manually delineated structures on the planning CT and chose representative contours as consensus structures for each patient. These consensus structures were automatically propagated to each CBCT image. For each structure in each CBCT, a reference contour was created consisting of the sum of all observers’ contours. Finite element modeling was used to quantify the mean displacement of surface elements from the reference contour to every contoured structure. The average of the mean displacements across all observers was compared with the automatic segmentation for all patients using a Wilcoxon rank test for each structure in each image. Results: The auto-segmentation method took less than 2 minutes to propagate all consensus structures from the planning CT images to the 3 CBCT images. Qualitatively, all propagated nodal volumes and cords successfully followed the anatomic deformations as seen on the CBCT images; 5 out of 30 propagated parotids presented a small overlap into bone and/or beyond the patient outline. According to the Wilcoxon rank test for each CBCT, no statistically significant difference was observed between the autosegmented and manual contours the nodal volumes, parotid and cord(a = 0.05). Conclusions: The results from this study demonstrated that the 3D salient interest point based automated segmentation is a reliable and efficient method to propagate large series of contours from a planning CT image to subsequent CBCT images with anatomic deformations. The automatically propagated contours were consistent with the observers’ contours across all CBCT images. This provides a systematic framework to quantify the dosimetric effect of anatomic and geometric changes during a course of fractionated radiotherapy, to determine whether there is a need for replanning. Author Disclosure: L. Chau, Philips Healthcare, C. Other Research Support; S. Allaire, Philips Healthcare, C. Other Research Support; K.K. Brock, Philips Healthcare, Elekta Oncology Systems, RaySearch Laboratories, B. Research Grant; IMPAC Physics Advisory Board, F. Consultant/Advisory Board; V. Pekar, Philips Research North America, A. Employment; J.N. Waldron, None; S.L. Breen, Philips Healthcare, B. Research Grant.
1043
Tumor Nodule Location Predicts the Feasibility of Intraprostatic High-dose Irradiation in Men with Localized Prostate Cancer
N. Housri1, J. Ondos1, P. L. Choyke2, A. Barbara1, H. Ning1, D. Citrin1, A. K. Singh3, A. Kaushal1 Radiation Oncology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, 2Molecular Imaging Program, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 3Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, NY 1
Purpose/Objective(s): A number of randomized trials have reported improved outcomes for men with prostate cancer treated with radiation dose escalation. Dose escalation is limited by the possibility of toxicity to surrounding critical structures. We are evaluating the feasibility of dose escalation to MRI-identified intraprostatic cancer lesions (IPL) with standard doses to the surrounding prostate tissue in a Phase I trial with the aim of improving intraprostatic tumor control and prostate cancer specific survival. The parameters that make patients amenable to these high-dose simultaneous integrated boosts (SIB) are largely unknown. We sought to identify whether factors related to IPLs or those related to individual patients predict the feasibility of high-dose intraprostatic SIB.
S143