Patterns of locoregional failure in women with early-stage breast cancer treated by whole breast irradiation in the lateral isocentric decubitus position: Large-scale single-centre experience

Purpose: The purpose of this study was to evaluate locoregional control and describe the patterns of failure in patients with breast cancer receiving whole breast radiotherapy in the isocentric lateral decubitus position technique.

Patients and methods: In a series of 832 consecutive female patients with early-stage breast cancer including invasive and in situ tumours treated by breast-conserving surgery followed by three-dimensional conformal whole breast irradiation in the isocentric lateral decubitus position between 2005 and 2010, all patients who experienced locoregional recurrence were studied. Five-year recurrence-free and overall survival rates were calculated. Regional recurrence mapping patterns were also determined.

Results: The median age of this series of 832 women was 61.5 years (range: 29-90 years). Various types of fractionation were used: 50Gy in 25 fractions (17.9%), 66Gy in 33 fractions (50Gy in 25 fractions to breast followed by sequential boost to tumour bed to a total dose 66Gy in 33 fractions.) (46.5%), 40Gy in 15 fractions or 41.6Gy in 13 fractions (26.1%) and 30Gy in 5 fractions (9.5%). With a median follow-up of 6.4 years, only 36 patients experienced locoregional recurrence and no association with the fractionation regimen was identified (P=0.2). In this population of 36 patients, 28 (3.3%) had "in-breast" local recurrences (77.8%), two had local recurrences and regional lymph node recurrence (5.6%), and six had regional lymph node recurrence only (in non-irradiated areas; 16.6%). The median time to recurrence was 50 months. Complete mapping of patterns of recurrences was performed and, in most cases, local recurrences were situated adjacent to the primary tumour bed. Cases of local recurrences presented a significantly lower distant metastasis rate (P<0.001) and had a significantly longer overall survival compared to patients with regional lymph node recurrence (P<0.001). However, multivariate Cox regression analysis showed that the site of recurrence had no significant impact on overall survival (P=0.14).

Conclusion: The results of this study indicate a low local recurrence rate. Further careful follow-up and recording of recurrences is needed to improve the understanding of patterns of recurrence.