Accelerated partial-breast irradiation with interstitial implants: the clinical relevance of the calculation of skin doses.

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.