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Are Post-RT Cardiac Perfusion Defects Due to Cardiac Toxicity, or are they Artifacts from Attenuation Changes in Surrounding Soft Tissues?
I. J. Radiation Oncology d Biology d Physics
S518
2780
Volume 72, Number 1, Supplement, 2008
Errors and Uncertainties in Accelerated Partial Breast Irradiation (APBI) with Balloon Brachytherapy: Are Current Target Coverage Goals Adequate?
S. Stojadinovic, L. W. Cuttino, I. J. Barani, D. Todor, D. W. Arthur Virginia Commonwealth University, Richmond, VA Purpose/Objective(s): The objective of this study was to evaluate systematic and random errors in the imaging, planning, and delivery of APBI treatments using single-lumen balloon brachytherapy. The impact of these errors on the actual delivered dose was studied. Materials/Methods: After simulation, balloon brachytherapy plans are created through the delineation of applicator position and planning structures, dwell position placement, and dose optimization. The balloon contour is assumed to be accurate, and the locations of the catheter and source are assumed to be constant throughout treatment. A retrospective analysis of 15 patients treated with the MammoSite was performed simulating for each fraction the effect of allowed source position uncertainty and applicator tip identification. Phantom measurements were used to quantify the importance of respiratory motion on the accuracy of balloon delineation using computed tomography (CT) and cone-beam CT (CBCT) imaging. Four experienced users contoured the applicator and planning structures to estimate the intra-observer variability. In the final stage of the analysis, all uncertainties were simulated on each of the ten different fractions and a sum plan was created, allowing a realistic estimate of the actual dose delivered. Results: Respiratory motion resulted in an underestimation of the balloon volume of up to 8% and 18% for CT and CBCT, respectively. The coverage was assessed based on the volume of the target receiving 95% of the prescribed dose (V95). On average, the allowed daily ± 1.0 mm source position uncertainty combined with up to a 3mm error in positioning the applicator tip degraded the coverage from 96.2% to 89.0% over the course of 10 fractions. Additionally, when the effect of respiratory motion on delineating the balloon surface was included, coverage further decreased to 88%. Conclusions: Current treatment protocols require that at least 90% of the target volume receive at least 90% of the prescribed dose. These findings suggest that significantly higher dosimetric coverage goals may be necessary to compensate for the identified errors inherent in balloon brachytherapy dose delivery. This will insure that the expected degradation of the actual dose delivered from the planned dose, as a consequence of random and systematic uncertainties, does not fall below an acceptable threshold. Author Disclosure: S. Stojadinovic, None; L.W. Cuttino, Hologic, D. Speakers Bureau/Honoraria; I.J. Barani, None; D. Todor, None; D.W. Arthur, SenoRx, F. Consultant/Advisory Board.
2781
Evaluation of Hypofractionated Simultaneous Integrated Breast Boost using Tomotherapy-based Topotherapy
A. F. McIntosh, K. Sheng, P. Read University of Virginia Hospital, Charlottesville, VA Purpose/Objective(s): Previous dosimetric studies have shown that intensity modulated coplanar breast irradiation can be delivered effectively using Helical Tomotherapy with fixed gantry angles, known as Topotherapy. Delivery of a simultaneous integrated boost to the breast has been proposed as an approach to shorten patient treatment time without compromising cosmetic outcomes. We evaluated the dosimetric feasibility of Topotherapy for simultaneous integrated boost (SIB) to the breast using standard fractionation and hypofractionation with regard to target coverage, uniformity, homogeneity and dose to sensitive structures, including skin. Materials/Methods: Eight patients with left sided breast cancer treated at our institution with conventional tangent breast fields and an electron boost to the lumpectomy cavity were contoured using Tomotherapy planning. The boost PTV was contoured as the lumpectomy cavity and clips with a 1.5 cm margin, and the breast PTV included the entire breast covered by tangent fields minus 5 mm of skin and the boost PTV. Three plans were generated for each patient to compare conventional sequential treatment of 50 Gy to the whole breast plus a 10 Gy electron boost in 30 fractions (SEQ), to standard fractionation Topotherapy with 50 Gy to the breast and 60 Gy to the PTV in 25 fractions (SIB50/60), and hypofractionated Topotherapy with 42.4 Gy to the breast and 51.2 Gy to the PTV in 16 fractions (SIB42/51). Results: Boost PTV and whole breast PTV conformality were improved for both Topotherapy SIB plans over the SEQ plans. PTV uniformity was equivalent for all plans, but whole breast coverage was better when using Topotherapy planning. Target coverage was equivalent for all methods with 95% of the prescribed dose covering 99.9% ± 0.1 of PTV boost for both SIB plans, and 98.0% ± 2.0 for the SEQ plans. Volume of skin receiving greater than 50 Gy was highest for SIB50/60 plan (49%) compared to the SIB42/ 51 and SEQ plans (9% and 13%, respectively). The left lung V20 and heart V10 were clinically equivalent - 10.4/2.4 Gy, 8.8/3.6 Gy, and 3.6/3.7 Gy for SEQ, SIB50/60, and SIB42/52, respectively. Conclusions: Topotherapy treatment delivery using simultaneous integrated boost provides dosimetrically equivalent target coverage and uniformity with improved conformality when compared to conventional treatment. This method of treatment delivery may facilitate shorter patient treatment times without increasing dose to sensitive structures. Author Disclosure: A.F. McIntosh, None; K. Sheng, None; P. Read, None.
2782
Are Post-RT Cardiac Perfusion Defects Due to Cardiac Toxicity, or are they Artifacts from Attenuation Changes in Surrounding Soft Tissues?
J. Roper, A. Manzoor, J. Bowsher, F. Yin, S. Zhou, T. Wong, S. Borges-Neto, J. Hubbs, S. Demirci, L. Marks Duke University, Durham, NC Purpose/Objective(s): Following RT for left-sided breast cancer, perfusion defects (i.e., cold regions) are often noted on SPECT images. Almost all new defects are in the cardiac apex. Since SPECT is not absolutely quantitative, defects are detected by comparing regional intensities on pre-RT and post-RT images. Further, as SPECT images are not corrected for attenuation, and since
Proceedings of the 50th Annual ASTRO Meeting RT may increase soft tissue density, apparent defects may be, at least partially, attributable to changes in attenuation of surrounding soft tissue. We herein perform a series of computer-based simulations to assess this possibility. Materials/Methods: The perfusion tracer 99mTc-Sestamibi was simulated in a female NCAT phantom. Two tangential breast fields were considered: the deep border of one excluded the heart while a second included 2.5 cm of anterior heart. Within RT fields, tissue densities were increased in increments of 10% up to 50%. Noise-free images were simulated for a cardiac SPECT protocol 180o circular orbit, 60 views, parallel hole collimation - by modeling photon detection efficiency, distance-dependent spatial resolution, and non-uniform attenuation. Images were reconstructed without attenuation correction by OSEM (10 subsets, 20 iterations) onto a grid with 0.36 cm wide voxels. For varying degrees of change in soft tissue density, apparent reductions within the apex were noted, and compared with effects elsewhere. Simulations were repeated with the left (222 ml) breast removed to model mastectomy. Results: As tissue density is increased by 10, 20, 30, 40, and 50%, corresponding reductions in apparent apical perfusion, for the different scenarios, are, respectively: intact breast, 2.5 cm heart in field: 13, 24, 34, 42, 50%; intact breast, heart sparing: 8, 15, 22, 28, 34%; mastectomy, 2.5 cm heart in field: 10, 19, 26, 34, 40%; mastectomy, heart sparing: 5, 9, 14, 18, 21%. Changes in cardiac perfusion were not uniform; the apex was affected more than other areas. Conclusions: RT-induced increases in soft-tissue attenuation can cause apparent changes in apical perfusion that might account for some of the defects seen clinically. However, the simulations also suggest that apparent defects should be seen even if the heart is excluded from the RT beam. Since perfusion defects are rarely seen in patients with no heart in the field, the possible changes in soft tissue attenuation/density are likely not the primary cause of perfusion defects seen clinically. Additional work is needed to understand the degree and impact of RT-induced soft tissue changes. Author Disclosure: J. Roper, None; A. Manzoor, None; J. Bowsher, None; F. Yin, None; S. Zhou, None; T. Wong, None; S. Borges-Neto, None; J. Hubbs, None; S. Demirci, None; L. Marks, Varian, B. Research Grant.
2783
Feasibility of AC Electromagnetic Localization for External Beam Partial Breast Irradiation
S. M. Eulau1, A. Morris1, P. Hallam1, M. Afghan1, J. Ye1, T. Zeller2, T. Mate1 1
Swedish Medical Center, Seattle, WA, 2Calypso Medical, Seattle, WA
Purpose/Objective(s): Partial breast irradiation (PBI) is being evaluated as an alternative to whole breast irradiation for selected patients. A challenge for EB PBI is ensuring that the beam is continuously ‘‘on target’’ due to variations in daily patient setup and motion during treatment. The current NSABP trial requires the GTV to be expanded by 15 mm (CTV), then the CTV to b expanded by 10 mm to account for setup error (5 mm) and patient movement/breathing (5 mm). A system that continuously tracks the prostate during EB has been developed (Calypso 4D Localization System, Seattle, WA) and uses non-ionizing AC magnetics to locate implanted transponders in real-time. The feasibility of using this system during EB PBI was investigated. Materials/Methods: The study included patients treated with EB PBI on an IRB approved protocol. Six patients first underwent ultrasonically guided percutaneous insertion of three transponders into peri-lumpectomy tissue. In 4 patients whom follow-up MR imaging was indicated, two interstitial catheters were placed, into which the transponders and gold markers (GM) were afterloaded, then removed post PBI. Patients in custom made immobilization devices were setup using a traditional laser alignment process, and then a GM determination of isocenter offset was made. While the GM shift was being processed, Calypso localization was performed. Next, the calculated GM isocenter shift was performed and the Calypso shift recorded for comparison. During PBI delivery, continuous tracking with Calypso was performed. Results: Percutaneous insertion of the transponders or catheters generally took less than 30 minutes and was well tolerated through PBI. Transponders/GMs remained stable in catheters. To date there have 45 fractions setup with both GM and transponder localization. Following laser alignment, GM detected an average residual isocenter offset of 8 mm. Average isocenter shifts by GM and Calypso differed by 1.5 mm in patients. Procedural QA testing in rigid phantom yielded shift differences less than 1 mm. Continuous tracking by Calypso detected average patient movement of 1.9 mm (range, 0.5 mm - 7.1 mm). Conclusions: The potential of this ac magnetic technology to localize and continuously tract the breast during PBI appears feasible. It provides a very efficient means to readily correct initial setup error, even after couch kicks, and then manage intrafractional motion, with gating or intermittent table re-positioning when movement goes beyond a user specified limit. This potentially enables the use of tighter margins on an individualized basis while having the advantage of no added radiation. Expanded results will be presented. Author Disclosure: S.M. Eulau, Calypso Medical, F. Consultant/Advisory Board; A. Morris, None; P. Hallam, None; M. Afghan, None; J. Ye, None; T. Zeller, Calypso Medical, A. Employment; T. Mate, Calypso Medical, E. Ownership Interest.
2784
Electronic Compensation vs. Regular 3 Field for Left Sided Breast with Positive SCV and IFV Nodes
P. Metuge, L. Kumaraswamy, S. Fernando, L. Hales, T. Stanley, M. Podgorsak Roswell Park Cancer Institute, Buffalo, NY Purpose/Objective(s): Studies have shown that electronic compensation technique (EC) improves dose homogeneity as compared to IMRT or standard 3-D tangent techniques for left sided whole breast irradiation. The purpose of our study is to compare the EC technique with a mono-isocentric 3 field technique for ten left sided breast cancer patients who also have positive supraclavicular (SCV) and infraclavicular (IFV) nodes. Materials/Methods: Ten patients with left sided breast cancer treated within a span of 6 months were selected for planning. The EC technique comprised of electronically compensated medial and lateral fields to treat the whole left breast in addition to an electronically compensated supraclavicular field to treat the SCV and IFV nodes. The whole left breast, heart, lungs, SCV, and IFV nodes were contoured. During planning, special attention was given to hot spots and dose coverage to SCV and IFV nodes. Isodose distributions and DVHs for contoured structures were compared between plans. The homogeneity of dose delivered to the left breast was measured as HI = ratio of planned treatment volume between D95 and D105 to the total volume of the contoured breast.
S519
S518
2780
Volume 72, Number 1, Supplement, 2008
Errors and Uncertainties in Accelerated Partial Breast Irradiation (APBI) with Balloon Brachytherapy: Are Current Target Coverage Goals Adequate?
S. Stojadinovic, L. W. Cuttino, I. J. Barani, D. Todor, D. W. Arthur Virginia Commonwealth University, Richmond, VA Purpose/Objective(s): The objective of this study was to evaluate systematic and random errors in the imaging, planning, and delivery of APBI treatments using single-lumen balloon brachytherapy. The impact of these errors on the actual delivered dose was studied. Materials/Methods: After simulation, balloon brachytherapy plans are created through the delineation of applicator position and planning structures, dwell position placement, and dose optimization. The balloon contour is assumed to be accurate, and the locations of the catheter and source are assumed to be constant throughout treatment. A retrospective analysis of 15 patients treated with the MammoSite was performed simulating for each fraction the effect of allowed source position uncertainty and applicator tip identification. Phantom measurements were used to quantify the importance of respiratory motion on the accuracy of balloon delineation using computed tomography (CT) and cone-beam CT (CBCT) imaging. Four experienced users contoured the applicator and planning structures to estimate the intra-observer variability. In the final stage of the analysis, all uncertainties were simulated on each of the ten different fractions and a sum plan was created, allowing a realistic estimate of the actual dose delivered. Results: Respiratory motion resulted in an underestimation of the balloon volume of up to 8% and 18% for CT and CBCT, respectively. The coverage was assessed based on the volume of the target receiving 95% of the prescribed dose (V95). On average, the allowed daily ± 1.0 mm source position uncertainty combined with up to a 3mm error in positioning the applicator tip degraded the coverage from 96.2% to 89.0% over the course of 10 fractions. Additionally, when the effect of respiratory motion on delineating the balloon surface was included, coverage further decreased to 88%. Conclusions: Current treatment protocols require that at least 90% of the target volume receive at least 90% of the prescribed dose. These findings suggest that significantly higher dosimetric coverage goals may be necessary to compensate for the identified errors inherent in balloon brachytherapy dose delivery. This will insure that the expected degradation of the actual dose delivered from the planned dose, as a consequence of random and systematic uncertainties, does not fall below an acceptable threshold. Author Disclosure: S. Stojadinovic, None; L.W. Cuttino, Hologic, D. Speakers Bureau/Honoraria; I.J. Barani, None; D. Todor, None; D.W. Arthur, SenoRx, F. Consultant/Advisory Board.
2781
Evaluation of Hypofractionated Simultaneous Integrated Breast Boost using Tomotherapy-based Topotherapy
A. F. McIntosh, K. Sheng, P. Read University of Virginia Hospital, Charlottesville, VA Purpose/Objective(s): Previous dosimetric studies have shown that intensity modulated coplanar breast irradiation can be delivered effectively using Helical Tomotherapy with fixed gantry angles, known as Topotherapy. Delivery of a simultaneous integrated boost to the breast has been proposed as an approach to shorten patient treatment time without compromising cosmetic outcomes. We evaluated the dosimetric feasibility of Topotherapy for simultaneous integrated boost (SIB) to the breast using standard fractionation and hypofractionation with regard to target coverage, uniformity, homogeneity and dose to sensitive structures, including skin. Materials/Methods: Eight patients with left sided breast cancer treated at our institution with conventional tangent breast fields and an electron boost to the lumpectomy cavity were contoured using Tomotherapy planning. The boost PTV was contoured as the lumpectomy cavity and clips with a 1.5 cm margin, and the breast PTV included the entire breast covered by tangent fields minus 5 mm of skin and the boost PTV. Three plans were generated for each patient to compare conventional sequential treatment of 50 Gy to the whole breast plus a 10 Gy electron boost in 30 fractions (SEQ), to standard fractionation Topotherapy with 50 Gy to the breast and 60 Gy to the PTV in 25 fractions (SIB50/60), and hypofractionated Topotherapy with 42.4 Gy to the breast and 51.2 Gy to the PTV in 16 fractions (SIB42/51). Results: Boost PTV and whole breast PTV conformality were improved for both Topotherapy SIB plans over the SEQ plans. PTV uniformity was equivalent for all plans, but whole breast coverage was better when using Topotherapy planning. Target coverage was equivalent for all methods with 95% of the prescribed dose covering 99.9% ± 0.1 of PTV boost for both SIB plans, and 98.0% ± 2.0 for the SEQ plans. Volume of skin receiving greater than 50 Gy was highest for SIB50/60 plan (49%) compared to the SIB42/ 51 and SEQ plans (9% and 13%, respectively). The left lung V20 and heart V10 were clinically equivalent - 10.4/2.4 Gy, 8.8/3.6 Gy, and 3.6/3.7 Gy for SEQ, SIB50/60, and SIB42/52, respectively. Conclusions: Topotherapy treatment delivery using simultaneous integrated boost provides dosimetrically equivalent target coverage and uniformity with improved conformality when compared to conventional treatment. This method of treatment delivery may facilitate shorter patient treatment times without increasing dose to sensitive structures. Author Disclosure: A.F. McIntosh, None; K. Sheng, None; P. Read, None.
2782
Are Post-RT Cardiac Perfusion Defects Due to Cardiac Toxicity, or are they Artifacts from Attenuation Changes in Surrounding Soft Tissues?
J. Roper, A. Manzoor, J. Bowsher, F. Yin, S. Zhou, T. Wong, S. Borges-Neto, J. Hubbs, S. Demirci, L. Marks Duke University, Durham, NC Purpose/Objective(s): Following RT for left-sided breast cancer, perfusion defects (i.e., cold regions) are often noted on SPECT images. Almost all new defects are in the cardiac apex. Since SPECT is not absolutely quantitative, defects are detected by comparing regional intensities on pre-RT and post-RT images. Further, as SPECT images are not corrected for attenuation, and since
Proceedings of the 50th Annual ASTRO Meeting RT may increase soft tissue density, apparent defects may be, at least partially, attributable to changes in attenuation of surrounding soft tissue. We herein perform a series of computer-based simulations to assess this possibility. Materials/Methods: The perfusion tracer 99mTc-Sestamibi was simulated in a female NCAT phantom. Two tangential breast fields were considered: the deep border of one excluded the heart while a second included 2.5 cm of anterior heart. Within RT fields, tissue densities were increased in increments of 10% up to 50%. Noise-free images were simulated for a cardiac SPECT protocol 180o circular orbit, 60 views, parallel hole collimation - by modeling photon detection efficiency, distance-dependent spatial resolution, and non-uniform attenuation. Images were reconstructed without attenuation correction by OSEM (10 subsets, 20 iterations) onto a grid with 0.36 cm wide voxels. For varying degrees of change in soft tissue density, apparent reductions within the apex were noted, and compared with effects elsewhere. Simulations were repeated with the left (222 ml) breast removed to model mastectomy. Results: As tissue density is increased by 10, 20, 30, 40, and 50%, corresponding reductions in apparent apical perfusion, for the different scenarios, are, respectively: intact breast, 2.5 cm heart in field: 13, 24, 34, 42, 50%; intact breast, heart sparing: 8, 15, 22, 28, 34%; mastectomy, 2.5 cm heart in field: 10, 19, 26, 34, 40%; mastectomy, heart sparing: 5, 9, 14, 18, 21%. Changes in cardiac perfusion were not uniform; the apex was affected more than other areas. Conclusions: RT-induced increases in soft-tissue attenuation can cause apparent changes in apical perfusion that might account for some of the defects seen clinically. However, the simulations also suggest that apparent defects should be seen even if the heart is excluded from the RT beam. Since perfusion defects are rarely seen in patients with no heart in the field, the possible changes in soft tissue attenuation/density are likely not the primary cause of perfusion defects seen clinically. Additional work is needed to understand the degree and impact of RT-induced soft tissue changes. Author Disclosure: J. Roper, None; A. Manzoor, None; J. Bowsher, None; F. Yin, None; S. Zhou, None; T. Wong, None; S. Borges-Neto, None; J. Hubbs, None; S. Demirci, None; L. Marks, Varian, B. Research Grant.
2783
Feasibility of AC Electromagnetic Localization for External Beam Partial Breast Irradiation
S. M. Eulau1, A. Morris1, P. Hallam1, M. Afghan1, J. Ye1, T. Zeller2, T. Mate1 1
Swedish Medical Center, Seattle, WA, 2Calypso Medical, Seattle, WA
Purpose/Objective(s): Partial breast irradiation (PBI) is being evaluated as an alternative to whole breast irradiation for selected patients. A challenge for EB PBI is ensuring that the beam is continuously ‘‘on target’’ due to variations in daily patient setup and motion during treatment. The current NSABP trial requires the GTV to be expanded by 15 mm (CTV), then the CTV to b expanded by 10 mm to account for setup error (5 mm) and patient movement/breathing (5 mm). A system that continuously tracks the prostate during EB has been developed (Calypso 4D Localization System, Seattle, WA) and uses non-ionizing AC magnetics to locate implanted transponders in real-time. The feasibility of using this system during EB PBI was investigated. Materials/Methods: The study included patients treated with EB PBI on an IRB approved protocol. Six patients first underwent ultrasonically guided percutaneous insertion of three transponders into peri-lumpectomy tissue. In 4 patients whom follow-up MR imaging was indicated, two interstitial catheters were placed, into which the transponders and gold markers (GM) were afterloaded, then removed post PBI. Patients in custom made immobilization devices were setup using a traditional laser alignment process, and then a GM determination of isocenter offset was made. While the GM shift was being processed, Calypso localization was performed. Next, the calculated GM isocenter shift was performed and the Calypso shift recorded for comparison. During PBI delivery, continuous tracking with Calypso was performed. Results: Percutaneous insertion of the transponders or catheters generally took less than 30 minutes and was well tolerated through PBI. Transponders/GMs remained stable in catheters. To date there have 45 fractions setup with both GM and transponder localization. Following laser alignment, GM detected an average residual isocenter offset of 8 mm. Average isocenter shifts by GM and Calypso differed by 1.5 mm in patients. Procedural QA testing in rigid phantom yielded shift differences less than 1 mm. Continuous tracking by Calypso detected average patient movement of 1.9 mm (range, 0.5 mm - 7.1 mm). Conclusions: The potential of this ac magnetic technology to localize and continuously tract the breast during PBI appears feasible. It provides a very efficient means to readily correct initial setup error, even after couch kicks, and then manage intrafractional motion, with gating or intermittent table re-positioning when movement goes beyond a user specified limit. This potentially enables the use of tighter margins on an individualized basis while having the advantage of no added radiation. Expanded results will be presented. Author Disclosure: S.M. Eulau, Calypso Medical, F. Consultant/Advisory Board; A. Morris, None; P. Hallam, None; M. Afghan, None; J. Ye, None; T. Zeller, Calypso Medical, A. Employment; T. Mate, Calypso Medical, E. Ownership Interest.
2784
Electronic Compensation vs. Regular 3 Field for Left Sided Breast with Positive SCV and IFV Nodes
P. Metuge, L. Kumaraswamy, S. Fernando, L. Hales, T. Stanley, M. Podgorsak Roswell Park Cancer Institute, Buffalo, NY Purpose/Objective(s): Studies have shown that electronic compensation technique (EC) improves dose homogeneity as compared to IMRT or standard 3-D tangent techniques for left sided whole breast irradiation. The purpose of our study is to compare the EC technique with a mono-isocentric 3 field technique for ten left sided breast cancer patients who also have positive supraclavicular (SCV) and infraclavicular (IFV) nodes. Materials/Methods: Ten patients with left sided breast cancer treated within a span of 6 months were selected for planning. The EC technique comprised of electronically compensated medial and lateral fields to treat the whole left breast in addition to an electronically compensated supraclavicular field to treat the SCV and IFV nodes. The whole left breast, heart, lungs, SCV, and IFV nodes were contoured. During planning, special attention was given to hot spots and dose coverage to SCV and IFV nodes. Isodose distributions and DVHs for contoured structures were compared between plans. The homogeneity of dose delivered to the left breast was measured as HI = ratio of planned treatment volume between D95 and D105 to the total volume of the contoured breast.
S519