Abstract P4-16-10: Positive sentinel lymph nodes (SLNs) without axillary dissection in breast cancer: the tangent fields of irradiation may not allow optimal coverage and dose distribution in level I and II of the axilla

Abstract

Abstract Purpose: The recent Z0011 trial demonstrated equivalent survival in patients (pts) with breast cancer (BC) and 1 to 2 positive SLNs who were randomly assigned to SLN biopsy (SLNB) alone or followed by axillary lymph node dissection (ALND). More importantly, regional recurrence with SLNB alone was less than 1%, despite the fact that an estimated 27% of patients had additional metastases in the undissected axillary nodes. Currently, many teams do not recommend anymore ALND when the pts receive systemic therapy and whole breast irradiation (WBI). However, the optimal design of radiation fields for patients with positive SLNs who do not undergo ALND is uncertain. This prospective study was designed to define the dose distribution and coverage of level I and II of the axilla using only tangent fields after conservative surgery (CS) or total mastectomy (TM). Methods and Materials: Thirty four pts were included in this analysis. 5 (14.7%) had TM and 29 (85.3%) had CS. Median age was 54 (30–90) years. All pts had 3D conformal RT. The level I/II/III axillary volumes were contoured using the RTOG contouring atlas. The total dose delivered was 50Gy in 25 fractions (n = 11) or the same dose (D) followed by a boost of 10 to 16Gy (n = 23). Pts were analyzed according to the total dose delivered in these 2 groups: group 1 (50Gy; n=11), group 2 (60 to 66Gy; n=23). A subgroup analysis was also performed in the group 2 regarding the initial tumor site and delivered dose: 66Gy to the upper quadrant (n = 14 group 2a) vs the lower quadrant (n = 4; group 2b) vs 60Gy to the upper quadrant (n = 5, group 2c). All dose-volume-histograms were analyzed. Mean, median values derived from level I and level II volumes were compared using t-test. Level of significance was set at p-value = 0.05. Results: In the whole population, the median D delivered to level I and II was 16.2 and 1.7 Gy, respectively. The mean D at these levels were 21.2 Gy (rang: 1.0–48.1) and 5.0 Gy (0.1–40.9), respectively. The volume of 95% and 50%–isodose coverage were 0 cm3 and 17.2 cm3 for level I and 0 cm3 for level II. The mean values for level I and II volumes were 1.4 cm3 and 21.9 cm3, respectively. According to the total D delivered (with or without boost), no difference was found between group 1 and group 2 in terms mean, median, and minimal D delivered to axilla levels (p = 0.5 and 0.9). Conversely, the difference was statistically significant for maximal D (p = 0.01). Furthermore, there was no difference according to tumor site and total dose between group 2a and 2b and group 2c (p = 0.07 and 0.7). In addition, no difference was observed between irradiation of whole breast or chest wall at 50Gy (p = 0.3 and 0.7). Conclusion: In patients undergoing conservative surgery or post-mastectomy radiotherapy, tangent fields provide a limited coverage of level I and II of the axilla as defined by the RTOG contouring atlas. In addition, these regions were mainly underdosed with au total dose < 30Gy even for pts who received 66Gy at the upper quadrant. These data should be considered when only tangent fields are planed to target the axilla in patients with metastases in SLNB positive without axillary dissection. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-16-10.