Postmastectomy radiotherapy of the chest wall. Comparison of electron-rotation technique and common tangential photon fields.

BACKGROUND AND PURPOSE: Different radiotherapy techniques are being used for postmastectomy irradiation. A retrospective analysis of patterns of locoregional failure (LRF) after modified radical mastectomy and axillary lymph node dissection followed by locoregional radiotherapy with or without systemic treatment was performed. Main emphasis was focused on the comparison of two postmastectomy radiotherapy techniques.

PATIENTS AND METHODS: 287 evaluable patients with locally advanced disease and/or adverse pathologic features (pT3 17% of patients, pT4 35%, multicentricity 25%, pN more than three positive nodes and/or pN1biii 70%, "close margins" 29%, infiltration of pectoral fascia 20%) with or without adjuvant chemo-hormonal treatment were included between 1989 and 2000. Median age was 61 years (range 24-88 years). All patients had modified radical mastectomy and axillary lymphonodectomy level I-II(III) for primary breast cancer. Median total dose of conventionally fractionated radiotherapy to the chest wall was 50 Gy (range 46-56 Gy). A local boost to the tumor bed of 10 Gy was applied in 72 patients. 80% of the patients received supraclavicular and 60% ipsilateral internal mammary lymph node irradiation of 50 Gy. 19% of the patients received adjuvant chemo-hormonal therapy, 38% hormonal therapy, and 27% chemotherapy. The median follow-up of patients at risk was 43 months (average 54 months).

RESULTS: The 5-year locoregional tumor control (LRC), LRC first event, disease-free, and overall survival were 85%, 91%, 61%, and 70% (Kaplan-Meier analysis), respectively. Cox regression analysis showed that stage III (relative risk [RR] 1.7), more than three involved axillary lymph nodes (RR 5.1), and infiltration of the pectoral fascia (RR 3.2) increased the risk of locoregional failure, while positive estrogen receptor status (RR 0.3) was associated with a reduced risk. No statistically significant differences in LRC were observed for patients treated either with the electron-rotation technique (LRC 92%) or with the photon-based technique (LRC 89%; p = 0.9). A subgroup analysis of tumors resected with "close margins" showed a higher LRF rate of 25% after electronbeam-rotation irradiation (n = 180) compared to an LRF of 13% with tangential opposed 6-MV photon fields (n = 107; p < 0.05). Large primary tumors of > or = 5 cm developed LRF in 29% of patients treated with electron-beam-rotation irradiation and in 17% of patients with photon-based irradiation (p = 0.1).

CONCLUSION: In locally advanced breast cancer, the LRC after postmastectomy irradiation with both techniques is comparable with published data from randomized studies. The tangential opposed photon field technique seems to be beneficial after marginal resection (histopathologic "close margins") of the primary tumor.