ESTRO 2020 Abstract Book

S151 ESTRO 2020

Higher thermal dose during HT improved complete response, duration of local control and overall survival of patients with recurrent breast cancer treated with re- RT+HT. Higher maximum skin temperature increased incidence of thermal toxicity. PD-0294 Hypothyroidism in IMRT-VMAT breast cancer supraclavicular radiotherapy : a retrospective study G. Lazzari 1 , A. Terlizzi 2 , M.G. Leo 2 , G. Silvano 1 1 Azienda Ospedaliera SS. Annunziata Presidio Osped, Radiology, Taranto, Italy ; 2 Azienda Ospedaliera SS. Annunziata Presidio Osped, Department of Fisica Sanitaria, Taranto, Italy Purpose or Objective to estimate the incidence of hypothyroidism (HTy) and to evaluate the predictors affecting its development after IMRT-VMAT among breast cancer (BC) patients (pts) receiving supraclavicular (SC) radiation therapy (RT). Material and Methods Between May 2013 to May 2019, consecutive 50 BC pts undergoing adjuvant RT on breast/chest wall and supraclavicular (SC) nodes with IMRT-VMAT-SIB modalities 50 Gy/2Gy/fr and 48 Gy/1.92 Gy/fr and baseline normal thyroid function tests (TFTs), were retrospectively analyzed. Patients assuming antipsychotic were excluded. The thyroid gland had been already contoured for each pts at the planning time giving a constraint of V30 <50%. Each patient's dose volume histogram (DVH), whole thyroid volume (TYV) , the SC PTV volume, the volume percentages of the thyroid receiving 30 Gy (V30), the D mean (average dose in whole volume of gland) and the ratio between the whole thyroid volume and the SC -PTV (thyroid irradiated ratio or TYR) were then estimated. Free triiodothyronine (FT3), free thyroxin (FT4), and thyrotropin (TSH) , TG (thyroglobulin), and thyroid antibodies (anti-TG, antimicrosomal, and antiperoxidase) were monitored before and performed every six months after RT completion. The risk of HT according to dosimetry and other clinic factors were also performed. Univariate with χ 2 , t-test and Pearson covariance for multivariate analyses adjusted per age were used for statistical analysis to exclude the bias of advanced age . A p <0.05 was considered statistically significant. Results The median follow-up was 36 (6 -72) months. The median age was 54 years (32-80). Of 50 patients, 16 pts (32%) were diagnosed with HT. The median time to the onset of HT was 18 months (4-30). The mean SC PTV value was 108 cc ( 41-145cc) , the mean thyroid volume of was 15.6 cc (11.5- 38 cc) and D mean of thyroid gland was 22.5 Gy (18-35 Gy). The mean V30 Gy was 38 % ( 28- 45 %). In univariate analysis age > 70 yrs , D mean > 20 Gy , the TYV < 18 cc , the SC-PTV > 85 cc, the V30 Gy > 40 % and the TYR > 0.2 were significant associated prognosticators for HTy The D mean > 20 Gy (p < 0.001, odds ratio (OR) 20 [95%CI 18-30]) and the TIR > 0.2, (p < 0.001, OR15 [95%CI 10-25]) , age > 70 yrs (p < 0.005, OR 6.07 [CI 2.36–15.59]) were significant prognosticators of HT in multivariate analysis. No statistical correlation was found for chemotherapy (p = 0.35, OR 0.61 [95%CI 0.2-30.8]), TYV (p = 0.15, OR 0.53 [95%CI 0.2-1.2]), SC PTV (p = 0.18, OR 0.54 [95%CI 0.7- 1.8]), and V30 Gy > 40 % (p = 0.11 , OR 0.52 [95%CI 0.23- 1.19]). Conclusion With the limits of a retrospective analysis, despite the gland V30 < 50%, the risk of hypothyroidism in BC pts after SC-IMRT -VMAT seems t depend on several factors as the D mean > 20 Gy and a TYR > 0.2. Dosimetric efforts

should be done to minimized the risk of HTy mainly in younger patients.

PD-0295 FAST approach in early breast cancer irradiation: toxicity and outcome in a 3DCRT vs IMRT comparison M.A. Zerella 1,2 , S. Arculeo 1,2 , S. Dicuonzo 1 , V. Dell'Acqua 1 , M.A. Gerardi 1 , A. Morra 1 , L. Bergamaschi 1,2 , S. Frassoni 3 , V. Bagnardi 3 , C. Fodor 1 , F. Cattani 4 , V. Galimberti 5 , P. Veronesi 5 , R. Orecchia 6 , M.C. Leonardi 1 , B.A. Jereczek- Fossa 1,2 1 IEO European Institute of Oncology- IRCCS, Division of Radiation Oncology, Milan, Italy ; 2 University of Milan, Department of Oncology and Hemato-oncology, Milan, Italy ; 3 University of Milan-Bicocca, Department of Statistics and Quantitative Methods, Milan, Italy ; 4 IEO European Institute of Oncology- IRCCS, Unit of Medical Physics, Milan, Italy ; 5 IEO European Institute of Oncology- IRCCS, Division of Breast Surgery, Milan, Italy ; 6 IEO European Institute of Oncology- IRCCS, Scientific Direction, Milan, Italy Purpose or Objective To evaluate early and late reactions, local control and survival of elderly breast cancer (BC) patients (pts) treated with adjuvant once-weekly hypofractionated radiotherapy (RT), either with Intensity-modulated radiotherapy (IMRT) or 3D conformal radiotherapy (3DCRT). Material and Methods From 7/2011 to 7/2018, 271 BC pts were given received 5.7 Gy once a week for 5 weeks to the whole breast, without boost to the tumor bed, after breast conserving surgery. Data were extracted from a dedicated databank for research projects called “Adjuvant radiation treatments with intensity-modulated radiotherapy and/or hypofractionated schedules for breast cancer” which was notified to the IEO Ethical Committee. Pts were eligible if affected by T1-T3 invasive BC, with no or limited axillary involvement. The scheme was offered to elderly women (age threshold of 65 years) and to those with commuting difficulties or disabling diseases. Results Median age was 76 (45.5-86.4) years. Median follow-up was 2.92 (0.10-7.01) years. Most of BC were T1 (77%), while the remaining were T2 (22%), T3 (0.4%). Axillary status was negative in 68.3%, minimally involved in 14.4% (pN1) and not assessed in 17.3% of the cases (Nx). Most of the women received adjuvant hormonal therapy (84.1%), while 10.7% received chemotherapy +/- hormonal therapy. The schedule was delivered either with 3DCRT (n=133) or with IMRT (n=138). No statistically significant difference was observed between the two techniques in terms of toxicity and efficacy. Maximum acute toxicity at the end of RT for 271 pts was as follows: grade (G) 1, 2 and 3 erythema in 63.5%, 7% and 0.4% of pts, respectively. G2 edema was detected in 10% of pts. Desquamation occurred in 4.4% as G1 and 1.5% as G2 of cases. At median 18.1 (6.0-55.2) months follow up, LENT-SOMA assessment was available for 141 pts. Fibrosis (G1, G2 and G3 in 47.5%, 10.6% and 1.4%, respectively) and skin changes (G1 and G2 hyper- or hypo-pigmentation in 29.8% and 2.1%, respectively, G1 and G2 telangiectasia in 3.5% of pts) were observed. A minority complained pain of G1 (19.1%) and G2 (1.4%) intensity. At 2.92 years, overall survival was 97.8% (94.5-99.1) ( Table 1 ) and disease-free survival was 96.3% (92.2-98.3) ( Table 2 ). There was a total of 5 (1.9%) isolated locoregional recurrences: 4 involved the breast and 1 the axillary lymph nodes. Predictive factors for toxicity were breast volume