Thermal boost combined with interstitial brachytherapy in breast conserving therapy - Assessment of early toxicity.

BACKGROUND: Hyperthermia (HT) causes a direct damage to cancerous cells and/or sensitize them to radiotherapy with usually minimal injury to normal tissues. Adjuvant HT is probably one of the most effective radiation sensitizers known and works best when delivered simultaneously with radiation. In breast conserving therapy, irradiation has to minimize the risk of local relapse within the treated breast, especially in an area of a tumor bed. Brachytherapy boost reduces 5-year local recurrence rate to mean 5,5%, so there still some place for further improvement. The investigated therapeutic option is an adjuvant single session of local HT (thermal boost) preceding standard CT-based multicatheter interstitial HDR brachytherapy boost in order to increase the probability of local cure. AIM: To report the short-term results in regard to early toxicity of high-dose-rate (HDR) brachytherapy (BT) boost with or without interstitial microwave hyperthermia (MV HT) for early breast cancer patients treated with breast conserving therapy (BCT).
MATERIALS AND METHODS: Between February 2006 and December 2007, 57 stage IA-IIIA breast cancer patients received a 10 Gy HDR BT boost after conservative surgery and 42.5-50 Gy whole breast irradiation (WBI) ± adjuvant chemotherapy. 32 patients (56.1%) were treated with additional pre-BT single session of interstitial MW HT to a tumor bed (multi-catheter technique). Reference temperature was 43 °C and therapeutic time (TT) was 1 h. Incidence, severity and duration of radiodermatitis, skin oedema and skin erythema in groups with (I) or without HT (II) were assessed, significant p-value ≤ 0.05.
RESULTS: Median follow-up was 40 months. Local control was 100% and distant metastasis free survival was 91.1%. HT sessions (median): reference temperature 42.2 °C, therapeutic time (TT) 61.4 min, total thermal dose 42 min and a gap between HT and BT 30 min. Radiodermatitis grades I and II occurred in 24 and 6 patients, respectively, differences between groups I and II were not significant. Skin oedema and erythema occurred in 48 (85.7%) and 36 (64.3%) cases, respectively, and were equally distributed between the groups. The incidence and duration of skin oedema differed between the subgroups treated with different fractionation protocols of WBI, p = 0.006. Skin oedema was present up to 12 months. No difference in pattern of oedema regression between groups I and II was observed, p = 0.933.
CONCLUSION: Additional thermal boost preceding standard HDR BT boost has a potential of further improvement in breast cancer local control in BCT. Pre-BT hyperthermia did not increase early toxicity in patients treated with BCT and was well tolerated. All side effects of combined treatment were transient and were present for up to 12 months. The increase in incidence of skin oedema was related to hypofractionated protocols of WBI. The study has to be randomized and continued on a larger group of breast cancer patients to verify the potential of local control improvement and to assess the profile of late toxicity.