Breast Cancer

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TU_12_3433 - Comparative Outcome Analysis of Two Dose Schedules for Post-Mastectomy Radiation Therapy

Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3

Comparative Outcome Analysis of Two Dose Schedules for Post-Mastectomy Radiation Therapy
R. T. Nguyen1, C. R. Hauck2, J. T. Dilworth3, H. Ye4, K. Marvin5, G. S. Gustafson6, P. Y. Chen4, and M. S. Jawad4,5; 1Oakland University William Beaumont School of Medicine, Rochester, MI, 2Department of Radiation Oncology, Beaumont Health, Royal Oak, MI, 3Dept. of Radiation Oncology, Beaumont Health, Royal Oak, MI, 4Beaumont Health (Department of Radiation Oncology), Royal Oak, MI, 5Beaumont Health System, Royal Oak, MI, 6Beaumont Health System, Sterling Heights, MI

Purpose/Objective(s): Prior to 2015, patients at our institution who received radiation therapy following mastectomy with reconstruction were treated to 54Gy to the chest wall without boost (PMRT-noB) or 50-50.4Gy to the chest wall followed by a 10Gy scar boost (PMRT-B) at the discretion of the treating physician. The purpose of this study was to investigate clinical outcomes using these two treatment regimens.

Materials/Methods: We performed a matched-pair analysis to compare patients s/p mastectomy with reconstruction treated with PMRT-noB or PMRT-B at a single institution from 1996-2015. 116 patients (58 pairs) were matched by age (+/- 3y), T-stage, N-stage, chemotherapy (y/n), and ER status. Clinical outcomes were analyzed using t-tests for continuous variables, χ2 for categorical variables, and Kaplan-Meier estimates. P-values <0.05 were significant.

Results: Median follow-up for all patients was 6.1y (1.6-14.3y); 7.6y and 4.8y for PMRT-noB and PMRT-B, respectively (p=0.16). Median age at diagnosis was 47y (28-68y). 64% of patients underwent modified radical mastectomy, 34% simple mastectomy, and 2% total mastectomy. 89% of patients had immediate tissue expander reconstruction in a 2-stage process; others were immediate permanent implant, TRAM flap, or latissimus dorsi flap. Median tumor size was 3.2cm (0-18.5cm); 2cm v 2.5cm for PMRT-noB v PMRT-B (p=0.98). There were no statistical differences in menopausal status, histology, margin status, or tumor grade. 41% had neoadjuvant chemo, 57% had adjuvant chemo, and 85% received anti-hormone therapy. More patients in the PMRT-noB group received Herceptin, 29% v 14% (p=0.04). Clinical outcomes were excellent at 5 years and seen in Table 1. There were no differences in LC, LRC, CLBF, DM, DFS, or OS between the groups. Implant loss was 14% in both the PMRT-noB and PMRT-B groups (p=1). Tissue expander loss was higher in the PMRT-B group, 20% v 8%, trending to significance (p=0.07). Infection rates were similar, 14% v 17% in the PMRT-noB v PMRT-B groups (p=0.09). 16% of patients receiving PMRT-noB required surgery due to post-RT toxicity v 12% PMRT-B (p=0.56).

Conclusion: No differences were seen in clinical outcomes comparing 54Gy to chest wall v 50-50.4Gy followed by a 10Gy scar boost. Rates of implant/expander loss and infection were similar. Additional analysis of acute and chronic post-RT skin and chest wall toxicities is underway. These data support the use of a lower chest wall dose, which is expected to decrease integral dose to the chest wall, heart, and lungs, while achieving the same clinical outcomes. Table 1: Clinical Outcomes at 5 years
Outcome All patients (n=116) PMRT-noB (n=58) PMRT-B (n=58) p-value
Local Control (LC) 98% 100% 96.5% 0.135
Locoregional Control (LRC) 98% 100% 96.5% 0.152
Contralateral Breast Failure (CLBF) 0% 0% 0% 0.527
Distant Metastasis (DM) 12% 9% 14% 0.325
Disease Free Survival (DFS) 87% 91% 86% 0.428
Overall Survival (OS) 99% 100% 98% 0.632

Author Disclosure: R.T. Nguyen: None. C.R. Hauck: None. J.T. Dilworth: None. H. Ye: None. K. Marvin: None. G.S. Gustafson: None. P.Y. Chen: Stock; Greater Michigan Gamma Knife (GMGK).

Reginald Nguyen, BS

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