ESTRO 36 Abstract Book

S346 ESTRO 36 _______________________________________________________________________________________________

Associate Professor- Department of Oncology and Hemato-oncology- Director Radiation Oncology 1 and Prostate Cancer Program, Milan, Italy Purpose or Objective To evaluate the impact of trastuzumab on acute skin toxicity in breast cancer patients treated with hypofractionated radiotherapy to the whole breast and chemotherapy with anthracycline and taxane. Material and Methods From April 2009 to April 2016, we enrolled 632 patients who underwent breast conservative surgery followed by adjuvant hypofractionated whole breast irradiation. Patients received 42.4 Gy in 16 daily fractions, 2.65 Gy per fraction. The boost to the tumor bed was administered only in grade 3 patients and in patients with close or positive margins (< 1mm). Acute and late toxicity was prospectively assessed during and after radiotherapy according to RTOG scale. Multivariable logistic regression models were applied to evaluate the impact of trastuzumab on the occurrence of acute skin toxicity In all patients enrolled,the mean age was 74 (range 46-91 yrs). Regression adjusted models showed that chemotherapy (OR= 2.0, p=0.03) and boost administration (OR=2.2, p<0.01) had a significant impact on acute skin toxicity (Figure 1). (>=G2). Results

Conclusion The results of our study demonstrated that chemotherapy impact on acute toxicity in patients undergoing hypofractionated whole breast irradiation, probably due to the recall phenomena. Trastuzumab seems to be a protective factor on acute skin toxicity. PO-0663 Early toxicity of 150 patients treated with hypofractionated breast SIB-RT using advanced techniques F. Lakosi 1 , C. Pirson 2 , P.V. Nguyen 2 , P. Berkovic 2 , S. Ben- Mustapha 2 , F. Princen 2 , S. Cucchiaro 2 , A. Gulyban 2 , V. Baart 2 , P. Coucke 2 1 Kaposvar University, Radiotherapy, Kaposvar, Hungary 2 CHU de Liège, Radiotherapy, Liège, Belgium Purpose or Objective To report physician-and patient reported early toxicity of hypofractionated breast simultaneous integrated boost (SIB) approach with Field-in-Field (breast±nodes) and Volumetric Modulated Arc Therapy (boost) (FiF+VMAT) after breast-conserving surgery. Material and Methods Between November 2013 and July 2016, 150 breast cancer patients with 154 lesions (T1-2, N0-1, M0) were treated with adjuvant radiotherapy using VMAT breast SIB technique. For whole breast irradiation two tangential field-in-field beams were used, while for SIB a full/half arc VMAT between the two tangents were applied. Doses to whole breast and tumor bed were 40.05/45.57 Gy and 48/55.86 Gy respectively, delivered in 15/21 fractions depending whether elective nodal irradiation (n=41) was required. Acute toxicities were scored using the Common Toxicity Criteria for Adverse Events (CTCAEvs4). Desquamation was scored as: 0- none; 1- dry and 2- moist. Toxicity was also evaluated with BCTOS and Treatment related symptoms questionnaires. For analysis radiotherapy-related cosmetic and breast specific pain items were selected. Data were recorded baseline, during, 6 weeks and 1 year after treatment. Results The median follow-up was 20 months (range:3-36) and 105 patients remained evaluable at 1 year. The maximum acute toxicities (%) during treatment were the followings: (G0/G1/G2/≥G3): Dermatitis: 8/79/13/-, Desquamation: 69/27/4/-, Pruritus 49/47/4/-, Oedema: 34/59/7/- and Pain: 45/48/7/-, Oesophagitis: 83/16/1-. There were no Grade 3 physician reported acute toxicities. A remarkable incline in Treatment related symptom scores was observed during SIB, which improved thereafter in almost all items, but remained superior to baseline status at 1 year follow up (Figure). The evolution of BCTOS scores showed the same pattern (Table).

One hundred and sixty-three patients received chemotherapy. Fifty one of them (30.7%) underwent also trastuzumab therapy. In this group, we found that G1 and G2/G3 acute skin toxicity were 50.4% and 33.9% in patients received only chemotherapy and 64.7% and 21.6% in patients who receive it associated with trastuzumab, respectively. Multivariate analysis showed that patients receiving trastuzumab had decreased risk of acute skin toxicity >=G2 (OR=0.04, p=0.03) (Figure 2).