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Breast Cancer Regional Radiation Fields for Supraclavicular (SC) and Axillary (AX) Lymph Nodes Treatment: Is a Posterior Axillary Boost Field Technique Optimal?
I. J. Radiation Oncology d Biology d Physics
S192
Volume 72, Number 1, Supplement, 2008
toxicity. Although first clinically applied in breast radiotherapy, our ATTA program of fibrosis evaluation will also be valuable for evaluating tissue toxicity in other treatment sites. Author Disclosure: J. Zhou, None; G.J. Kutcher, None; S.A. Woodhouse, None; P.B. Schiff, None; L. Ballas, None; W. Vance, None; P. Zhang, None; Z. Lu, None; E. Pile-Spellman, None; T. Liu, None.
2052
Breast Cancer Regional Radiation Fields for Supraclavicular (SC) and Axillary (AX) Lymph Nodes Treatment: Is a Posterior Axillary Boost Field Technique Optimal?
X. Wang, T. Yu, M. Salehpour, S. Zhang, T. Liang, T. Buchholz M.D. Anderson Cancer Center, Houston, TX Purpose/Objective(s): To assess whether the historical standard technique of using an oblique anterior SC and AX field (SCV) with a traditional posterior AX boost field (PAB) is an optimal method to target SC and AX nodes compared with two alternative techniques: (1) SCV with an anterior AX boost field (AAB) and (2) intensity modulated radiotherapy (IMRT) utilizing 3 fixed fields. Materials/Methods: Computed tomography (CT) simulation data from 10 patients treated with postmastectomy radiation that included a SCV field were selected for the study. The SC nodes and AX level I-III nodes within SCV field were contoured and defined as the treatment target. A half-beam block was used in all fields to prevent divergence into the fields used to treat the chest wall. The treatment plans were normalized such that 99% of the target volume was covered by 90% of prescription dose. A two-tailed pairwise Wilcoxon signed rank test was used to compare dosimetry outcomes. Results: The mean maximum depth of the treatment target was 5.7 cm (range, 4.7-7.1 cm). For PAB and AAB techniques, the volume of hot spots receiving 105% (V105) of prescribed dose significantly correlated with the maximum depth of the target (linear regression analysis). The average of V105 for IMRT was 4.1 cc (range, 1.9-7.1 cc), significantly less than AAB technique (p = 0.002, average, 55.9 cc; range, 6.0-140.6 cc), which was significantly less than PAB technique (p = 0.04, average, 70.0 cc; range, 5.5-193.8 cc). The low dose volumes, such as V80 and V30, were significantly less with IMRT than AAB (both p = 0.002), which were significantly less than PAB (p = 0.002 and p = 0.004, respectively). For a prescribed dose of 50 Gy, the mean dose of the irradiated lung and V20Gy (% of volume of irradiated lung to receive .=20 Gy dose) was significantly less in IMRT compared to AAB (both p = 0.002), which was significantly less than PAB (p = 0.002 and p = 0.03, respectively). The maximum cord dose for IMRT was higher than the other two techniques but the average maximum dose to the cord with IMRT was only 7.1 Gy (range, 3.7-10.1 Gy). The conformality of the target volume coverage with IMRT was significantly greater than AAB, which is significantly better compared to PAB. More monitor units were required to deliver the IMRT plan (average, 377 MU; range, 313440 MU) than the PAB plan (average, 255 MU; range, 232-287 MU) or the AAB (average, 245 MU; range, 224-265 MU). Conclusions: An IMRT technique minimizes dose inhomogeneity and improves conformality resulting in less lung dose compared to PAB technique. A CT-planned AAB is also a significantly superior technique compared to PAB. We conclude CT-treatment planning with dose optimization around delineated target volumes should become standard for radiation treatments of SC and AX lymph nodes. Author Disclosure: X. Wang, None; T. Yu, None; M. Salehpour, None; S. Zhang, None; T. Liang, None; T. Buchholz, None.
2053
The Dynamic Tumor Bed: Volumetric Changes in the Lumpectomy Cavity during Breast Conserving Therapy
B. Prendergast1, D. J. Indelicato1, S. R. Grobmyer1, A. I. Saito2, F. Snead1, C. G. Morris1, E. M. Copeland1, N. P. Mendenhall1 1
University of Florida, Gainesville, FL, 2Juntendo University, Tokyo, Japan
Purpose/Objective(s): In breast conserving therapy, adding a radiation boost to the tumor bed following whole breast radiation decreases the risk of a local recurrence. However, dynamic post-lumpectomy changes in breast tissue associated with surgery and radiation often challenge the accurate definition of this high-risk region. The objective of this analysis was to characterize the magnitude of volume change in the postoperative tumor bed before and during radiotherapy and identify factors associated with large volumetric change. Materials/Methods: Thirty-six patients with early-stage or pre-invasive breast cancer underwent breast conserving therapy at our institution between June 2006 and October 2007. Thirty patients received irradiation to the entire breast to a total dose of 45-50.4 Gy at 1.8 Gy per daily fraction. Six patients were treated with partial breast irradiation to a dose of 38.5 Gy in 10 fractions. The CT scans of the breast were obtained shortly after surgery, before the start of radiotherapy for treatment planning, and, if applicable, before the tumor bed boost. The postoperative changes, seroma, and surgical clips were used to define the tumor bed through consensus agreement of three observers (BP, DI, JL). Multiple variables were examined for correlation with volumetric change. Results: Between the first and last scan obtained (median time, 7.2 weeks), the tumor bed volume decreased at least 20% in 86% of patients (n = 31) and at least 50% in 64% of patients (n = 23). From postoperative scan to planning scan (median time, 3 weeks), the tumor bed volume decreased by an average of 49.9%, or approximately 2.1% per postoperative day. This period of rapid change presumably reflects postoperative tissue remodeling. From planning scan to boost scan (median interval, 7 weeks), which is a complex period when the breast tissue is affected by both postoperative healing and radiotherapy, tumor bed volume decreased by an average of 44.6% at an average rate of 0.95% per postoperative day. No single factor was significantly associated with a change in tumor bed volume greater than 20%. Conclusions: The average postlumpectomy tumor bed undergoes dramatic volumetric changes following surgery, and these changes continue through radiotherapy. The rate of change is inversely proportional to the duration from surgery. However, no identifiable characteristics were found to predict large alterations of the tumor bed volume. Significant volumetric change may impact a radiation oncologist’s ability to accurately target the tumor bed for a 3D conformal radiation boost; however, the dosimetric implications and ultimate clinical significance of the dynamic tumor bed need to be explored further. Author Disclosure: B. Prendergast, None; D.J. Indelicato, None; S.R. Grobmyer, None; A.I. Saito, None; F. Snead, None; C.G. Morris, None; E.M. Copeland, None; N.P. Mendenhall, None.
S192
Volume 72, Number 1, Supplement, 2008
toxicity. Although first clinically applied in breast radiotherapy, our ATTA program of fibrosis evaluation will also be valuable for evaluating tissue toxicity in other treatment sites. Author Disclosure: J. Zhou, None; G.J. Kutcher, None; S.A. Woodhouse, None; P.B. Schiff, None; L. Ballas, None; W. Vance, None; P. Zhang, None; Z. Lu, None; E. Pile-Spellman, None; T. Liu, None.
2052
Breast Cancer Regional Radiation Fields for Supraclavicular (SC) and Axillary (AX) Lymph Nodes Treatment: Is a Posterior Axillary Boost Field Technique Optimal?
X. Wang, T. Yu, M. Salehpour, S. Zhang, T. Liang, T. Buchholz M.D. Anderson Cancer Center, Houston, TX Purpose/Objective(s): To assess whether the historical standard technique of using an oblique anterior SC and AX field (SCV) with a traditional posterior AX boost field (PAB) is an optimal method to target SC and AX nodes compared with two alternative techniques: (1) SCV with an anterior AX boost field (AAB) and (2) intensity modulated radiotherapy (IMRT) utilizing 3 fixed fields. Materials/Methods: Computed tomography (CT) simulation data from 10 patients treated with postmastectomy radiation that included a SCV field were selected for the study. The SC nodes and AX level I-III nodes within SCV field were contoured and defined as the treatment target. A half-beam block was used in all fields to prevent divergence into the fields used to treat the chest wall. The treatment plans were normalized such that 99% of the target volume was covered by 90% of prescription dose. A two-tailed pairwise Wilcoxon signed rank test was used to compare dosimetry outcomes. Results: The mean maximum depth of the treatment target was 5.7 cm (range, 4.7-7.1 cm). For PAB and AAB techniques, the volume of hot spots receiving 105% (V105) of prescribed dose significantly correlated with the maximum depth of the target (linear regression analysis). The average of V105 for IMRT was 4.1 cc (range, 1.9-7.1 cc), significantly less than AAB technique (p = 0.002, average, 55.9 cc; range, 6.0-140.6 cc), which was significantly less than PAB technique (p = 0.04, average, 70.0 cc; range, 5.5-193.8 cc). The low dose volumes, such as V80 and V30, were significantly less with IMRT than AAB (both p = 0.002), which were significantly less than PAB (p = 0.002 and p = 0.004, respectively). For a prescribed dose of 50 Gy, the mean dose of the irradiated lung and V20Gy (% of volume of irradiated lung to receive .=20 Gy dose) was significantly less in IMRT compared to AAB (both p = 0.002), which was significantly less than PAB (p = 0.002 and p = 0.03, respectively). The maximum cord dose for IMRT was higher than the other two techniques but the average maximum dose to the cord with IMRT was only 7.1 Gy (range, 3.7-10.1 Gy). The conformality of the target volume coverage with IMRT was significantly greater than AAB, which is significantly better compared to PAB. More monitor units were required to deliver the IMRT plan (average, 377 MU; range, 313440 MU) than the PAB plan (average, 255 MU; range, 232-287 MU) or the AAB (average, 245 MU; range, 224-265 MU). Conclusions: An IMRT technique minimizes dose inhomogeneity and improves conformality resulting in less lung dose compared to PAB technique. A CT-planned AAB is also a significantly superior technique compared to PAB. We conclude CT-treatment planning with dose optimization around delineated target volumes should become standard for radiation treatments of SC and AX lymph nodes. Author Disclosure: X. Wang, None; T. Yu, None; M. Salehpour, None; S. Zhang, None; T. Liang, None; T. Buchholz, None.
2053
The Dynamic Tumor Bed: Volumetric Changes in the Lumpectomy Cavity during Breast Conserving Therapy
B. Prendergast1, D. J. Indelicato1, S. R. Grobmyer1, A. I. Saito2, F. Snead1, C. G. Morris1, E. M. Copeland1, N. P. Mendenhall1 1
University of Florida, Gainesville, FL, 2Juntendo University, Tokyo, Japan
Purpose/Objective(s): In breast conserving therapy, adding a radiation boost to the tumor bed following whole breast radiation decreases the risk of a local recurrence. However, dynamic post-lumpectomy changes in breast tissue associated with surgery and radiation often challenge the accurate definition of this high-risk region. The objective of this analysis was to characterize the magnitude of volume change in the postoperative tumor bed before and during radiotherapy and identify factors associated with large volumetric change. Materials/Methods: Thirty-six patients with early-stage or pre-invasive breast cancer underwent breast conserving therapy at our institution between June 2006 and October 2007. Thirty patients received irradiation to the entire breast to a total dose of 45-50.4 Gy at 1.8 Gy per daily fraction. Six patients were treated with partial breast irradiation to a dose of 38.5 Gy in 10 fractions. The CT scans of the breast were obtained shortly after surgery, before the start of radiotherapy for treatment planning, and, if applicable, before the tumor bed boost. The postoperative changes, seroma, and surgical clips were used to define the tumor bed through consensus agreement of three observers (BP, DI, JL). Multiple variables were examined for correlation with volumetric change. Results: Between the first and last scan obtained (median time, 7.2 weeks), the tumor bed volume decreased at least 20% in 86% of patients (n = 31) and at least 50% in 64% of patients (n = 23). From postoperative scan to planning scan (median time, 3 weeks), the tumor bed volume decreased by an average of 49.9%, or approximately 2.1% per postoperative day. This period of rapid change presumably reflects postoperative tissue remodeling. From planning scan to boost scan (median interval, 7 weeks), which is a complex period when the breast tissue is affected by both postoperative healing and radiotherapy, tumor bed volume decreased by an average of 44.6% at an average rate of 0.95% per postoperative day. No single factor was significantly associated with a change in tumor bed volume greater than 20%. Conclusions: The average postlumpectomy tumor bed undergoes dramatic volumetric changes following surgery, and these changes continue through radiotherapy. The rate of change is inversely proportional to the duration from surgery. However, no identifiable characteristics were found to predict large alterations of the tumor bed volume. Significant volumetric change may impact a radiation oncologist’s ability to accurately target the tumor bed for a 3D conformal radiation boost; however, the dosimetric implications and ultimate clinical significance of the dynamic tumor bed need to be explored further. Author Disclosure: B. Prendergast, None; D.J. Indelicato, None; S.R. Grobmyer, None; A.I. Saito, None; F. Snead, None; C.G. Morris, None; E.M. Copeland, None; N.P. Mendenhall, None.