Purpose: Recent studies have demonstrated low regional recurrence rates in early-stage breast cancer omitting axillary lymph node dissection (ALND) in patients who have positive nodes in sentinel lymph node dissection (SLND). This finding has triggered an active discussion about the effect of radiotherapy within this approach. The purpose of this study was to analyze the dose distribution in the axilla in standard tangential radiotherapy (SRT) for breast cancer and the effects on normal tissue exposure when anatomic level I-III axillary lymph node areas are included in the tangential radiotherapy field configuration.
Patients and methods: We prospectively analyzed the dosimetric treatment plans from 51 consecutive women with early-stage breast cancer undergoing radiotherapy. We compared and analyzed the SRT and the defined radiotherapy (DRT) methods for each patient. The clinical target volume (CTV) of SRT included the breast tissue without specific contouring of lymph node areas, whereas the CTV of DRT included the level I-III lymph node areas.
Results: We evaluated the dose given in SRT covering the axillary lymph node areas of level I-III as contoured in DRT. The mean VD95% of the entire level I-III lymph node area in SRT was 50.28% (range, 37.31-63.24%), VD45 Gy was 70.1% (54.8-85.4%), and VD40 Gy was 83.5% (72.3-94.8%). A significant difference was observed between lung dose and heart toxicity in SRT vs. DRT. The V20 Gy and V30 Gy of the right and the left lung in DRT were significantly higher in DRT than in SRT (p<0.001). The mean heart dose in SRT was significantly lower (3.93 vs. 4.72 Gy, p=0.005).
Conclusion: We demonstrated a relevant dose exposure of the axilla in SRT that should substantially reduce local recurrences. Furthermore, we demonstrated a significant increase in lung and heart exposure when including the axillary lymph nodes regions in the tangential radiotherapy field set-up.