[Acute toxicity of breast cancer irradiation with modulated intensity by tomotherapy®]. / Toxicité aiguë de la tomothérapie des cancers mammaires.

PURPOSE: Helical radiation intensity modulated by tomotherapy improves dose distribution to complex and large volumes. The aim of the study was to assess acute toxicity of this technique during breast cancer irradiation after conserving surgery or mastectomy. PATIENTS AND METHODS: Cutaneous toxicities, lung and oesophageal side effects, and breast lymphedema were retrospectively collected according to the Common Terminology Criteria for Adverse Events Version 4.0 (CTCAE v4.0) in 292 patients treated for a breast cancer by tomotherapy between May 2010 and December 2014. After conservative surgery, the dose administered to breast volume and the tumour bed was respectively 52.2Gy and 63.8Gy in 29 fractions. After mastectomy, the dose was 50Gy in 25 fractions. Univariate and multivariate analyses were performed to highlight risk factors for dermatitis and breast oedema. RESULTS: The rate of dermatitis grade 2 and 3 were 22.9% and 1.7% respectively. In univariate analysis, factors associated with acute radiation dermatitis were breast volume (P=0.002), body mass index (BMI) (P<0.0001), the use of chest compression mask (net) (P=0.005) and the localization of the irradiation (P <0.0001). In multivariate analysis, BMI greater than 25kg/m2 (odds ratio [OR]: 3.61, 95% confidence interval [CI]: [1.93-6.74], P<0.0001), the use of a chest mask (OR 2.01, 95% CI [1.06-3.79] P=0.0328) and irradiation after conservative treatment increase the risk of acute radiation dermatitis (mastectomy: OR 0.64, 95% CI [0.04-0.43]; mastectomy with immediate reconstruction with prosthesis: OR 0.13 95% CI [0.10-0.38] P=0.0003). The incidence of breast oedema grade 2 or above was 19.5%, in univariate analysis, there was a correlation with BMI (P=0.003) and smoking (P=0.009). In multivariate analysis, smoking and BMI greater than 25kg/m2 increased the risk of breast oedema (OR 2.47, respectively [95% CI 1.22-5.01] P=0.012 and OR 2.37 [95% CI 1.22-4.59] P=0.01). The rate of radiation pneumonitis of grade 2 or above was 1.4%. Among the patients, 19.9% had esophagitis grade 1 or 2. CONCLUSION: The helical irradiation intensity modulation tomotherapy is a well-tolerated treatment for breast cancer that reduces the high radiation doses to organs at risk.