Cosmetic outcome in patients receiving an interstitial implant as part of breast-conservation therapy

PURPOSE: To study factors related to breast cosmetic outcome in patients tr eated with an interstitial implant as part of breast-conservation therapy. MATERIALS AND METHODS: One hundred fifty-six patients with stage I or II br east carcinoma who received 50 Gy of external-beam irradiation followed by a 20-Gy interstitial boost were examined. The dose homogeneity index (DHI) was calculated for each evaluable implant and was examined in light of othe r patient-, treatment-, and tumor-related variables previously demonstrated to affect cosmesis. RESULTS: Of the variables examined, both the DHI (P =.021) and the total ex cision volume (P =.019) were significantly related to cosmetic outcome (exc ellent vs less than excellent) in a univariate model. In the multivariate a nalysis, only the total excision volume remained significant (P =.032). The mean total excision volume +/- SD in patients with excellent cosmetic outc ome (81.8 cm(3) +/- 84.0) was significantly less than that in patients with less than excellent cosmetic outcome (120 cm(3) +/- 84). The probability o f excellent cosmetic outcome linearly increased with an increase in DHI. Th e mean DHI was 0.74 +/- 0.12 for the cases with excellent cosmetic outcome and 0.68 +/- 0.10 for those with less than excellent cosmetic outcome. CONCLUSION: To achieve optimal cosmesis, DHI should be maximized. The volum e of tissue removed, however, remains the most significant determinant.