The influence of the boost technique on local control in breast conserving treatment in the EORTC ‘boost versus no boost’ randomised trial

Abstract Background and purpose The EORTC Trial 22881/10882 investigating the role of a boost dose in breast conserving therapy demonstrated a significantly better local control rate with the higher radiotherapy dose, especially in women younger than 50 years of age. This paper investigates the potential impact of the different boost techniques on local control and on fibrosis after breast conserving therapy. Patients and methods From 1989 to 1996, 2661 patients were randomised to receive a boost dose of 16 Gy to the primary tumour bed after microscopically complete tumorectomy and 50 Gy whole breast irradiation. The choice of the boost technique was left to the treating investigator. Treatment data were prospectively recorded as well as the clinical outcome in terms of local control and fibrosis. Sixty-three percent of the patients received a boost dose with fast electrons, 28% with photon beams and 9% with interstitial brachytherapy. Results At 5 years, local recurrences were seen in 74 of the 1635 patients who received an electron boost (4.8%, CI 3.6–5.9%), in 28 of the 753 patients who received a photon boost (4.0%, CI 3.4–5.5%) and in 6 of the 225 patients after an interstitial boost (2.5%, CI 0.3–4.6%). The grade of fibrosis in the whole breast as well as at the primary tumour bed, as scored by the treating radiation oncologist, was similar in the three groups. Conclusions Although the three groups are of a rather unequal size, the results of the interstitial boost seem similar in terms of fibrosis and at least as good in terms of local control, despite a lower treatment volume and a longer overall treatment time.