Electron arc irradiation of the postmastectomy chest wall with CT treatment planning: 20-year experience

Purpose: Since 1980, electron arc irradiation of the postmastectomy chest w all has been the preferred radiotherapy technique at the University of Utah for patients with advanced breast cancer. We report the results of this te chnique in 156 consecutive Stage IIA-IIIB patients treated from 1980 to 199 8. Methods: CT treatment planning was used in all patients to identify chest w all thickness and internal mammary lymph node depth. Computerized dosimetry was used to deliver total doses of 50 Gy in 5-1/2 weeks to the chest wall and the internal mammary lymph nodes with electron are therapy. Patients we re assessed for local, regional, and distant control of disease and for sur vival. Univariate and multivariate proportional hazards were modeled using a hierarchical nonproportional semiparametric model testing the following p rognostic factors: age, stage, tumor size, number of positive lymph nodes, estrogen receptor status, and dose. End points evaluated included disease-f ree survival, cause-specific survival, and overall survival. Results: Eighty-one percent of patients were at high risk for local-regiona l failure because of > T2 primary tumor or >3 positive axillary lymph nodes . The median number of positive lymph nodes was 5, and the median tumor siz e was 3.5 cm. Actuarial 10-year local-regional control and overall survival were 95% and 52%, respectively. In multivariate analysis, the only factor prognostic for disease-free survival, cause-specific survival, and overall survival was the number of positive lymph nodes (p < 0.001). The 10-year ra tes of local-regional control for patients with 0, 1-3, 4-9, and greater th an or equal to 10 involved lymph nodes were 100%, 98%, 93%, and 89%, respec tively. The only rates of acute and chronic radiotherapy toxicity greater t han or equal to2 by RTOG/EORTC criteria were skin related and observed in 4 4% and 10% for acute and late reactions, respectively. Conclusion: These data demonstrate excellent local-regional control rates w ith electron arc therapy of the postmastectomy chest wall in patients with advanced breast cancer. Our 20-year experience with electron are radiothera py has demonstrated the safety and efficacy of this technique. The advantag e of this technique is that the internal mammary lymph node chain can be ea sily encompassed while the dose to heart and lung is minimized; it also obv iates match lines in areas of high risk. (C) 2001 Elsevier Science Inc.