Accuracy of ultrasound in localization of breast boost field.

Abstract

To prospectively compare diagnostic ultrasound to the 'gold standard' of surgical clips for localization of the lumpectomy site for electron boost irradiation. Consecutive breast cancer patients referred following lumpectomy underwent diagnostic ultrasound in radiation treatment position 21-100 days post-surgery. All patients had 3-6 surgical clips defining the excision cavity. The site was marked on the skin and depth was measured. Target depth was the deepest aspect of the cavity plus a 1 cm deep margin. Treatment fields were prescribed with a 2 cm margin on the cavity, and electron energy was chosen to cover the target depth. Surgical clip position was assessed on orthogonal simulator films. Localizations were performed in 54 breasts (52 women). The mean interval post-surgery was 53 (SD 17) days. Overall, 35/54 (65%) of localizations were adequate, 15/54 (28%) were marginal and 4/54 (7%) were inadequate. Regression showed that lower patient weight (r=-0.37, P=0.006) predicted adequacy of localization, with better accuracy in lighter women. The accuracy rate for ultrasound exceeds the 20-50% reported for clinical localization. Diagnostic ultrasound may be used to improve the accuracy when surgical clips are not present.