Purpose: To describe relative skin dose estimations and their impact on cosmetic outcome in interstitial multicatheter accelerated partial-breast irradiation (APBI).
Patients and methods: Between April 2001 and January 2005, 105 consecutive patients with early breast cancer were recruited in Erlangen, Germany, for this substudy of the German-Austrian APBI phase II trial. 51% (54/105) received pulsed-dose-rate (PDR), and 49% (51/105) high-dose-rate (HDR) brachytherapy. Prescribed reference dose for HDR brachytherapy was 32 Gy in eight fractions of 4 Gy, twice daily. Prescribed reference dose in PDR brachytherapy was 49.8 Gy in 83 consecutive fractions of 0.6 Gy every hour. Total treatment time was 3-4 days. With a wire cross on the skin surface during the brachytherapy-planning procedure the minimal, mean and maximal relative skin doses (SD(min%), SD(max%), SD(mean%)) were recorded. Endpoint of this evaluation was the cosmetic outcome in relation to the relative skin doses.
Results: Median follow-up time was 38 months (range, 19-65 months). Cosmetic results for all patients were excellent in 57% (60/105), good in 36% (38/105), and fair in 7% (7/105). The SD(min%) (27.0% vs. 31.7%; p = 0.032), SD(mean%) (34.2% vs. 38.1%; p = 0.008), and SD(max%) (38.2% vs. 46.4%; p = 0.003) were significantly lower for patients with excellent cosmetic outcome compared to patients with a suboptimal outcome. SD(mean%) (37.6% vs. 34.2%; p = 0.026) and SD(max%) (45.4% vs. 38.2%; p = 0.008) were significantly higher for patients with good cosmetic outcome compared with the patients with excellent results.
Conclusion: The appraisal of skin doses has been shown to be relevant to the achievement of excellent cosmetic outcome. Further investigations are necessary, especially on the basis of CT-based brachytherapy planning, to further improve the treatment results of multicatheter APBI.