ESTRO 36 Abstract Book

S624 ESTRO 36 2017 _______________________________________________________________________________________________

1 Azienda Ospedaliera SS. Annunziata Presidio Osped, Radiology, Taranto, Italy Purpose or Objective Breast radiotherapy is associated with a minimal emetogenic risk in MASCC/ESMO guidelines. Although the emetogenic potential risk is estimated < 30%, VMAT adjuvant radiotherapy may induce an unexpected acute toxicity defined radiation induced nausea and vomiting (RINV) as we observed in our experience. Aim of our report is to find a correlation between dosimetrical factors and RINV occurrence in our patients (pts). Material and Methods In our institutionfrom January 2013 to May 2016 106 breast cancer pts were treated with adjuvant radiotherapy (RT) in VMAT modality. Al pts had surgery ( conservative or radical). Mean age was 54 years. Neoadjuvant or adjuvant chemotherapy was given in 6 pts and 68 pts respectively (62 pts had high risk emetogenic agents combination, 12 pts had CMF). Left side breasts were treated with in 95 pts, right breast RT occurred in 11 pts. CT planning included all the chest from C6 to D12-L3 vertebrae. PTV consisted of residual breast or chest wall and nodal sites. According ICRU 83 , the prescribed dose was 50 Gy total dose (2 Gy/25) to breast-chest wall and internal mammary chain (10 pts). Supraclavicular nodes (36 pts) were treated simultaneously , 1.92 Gy/25 fractions to 48 Gy total dose. VMAT was planned on treatment planning system Oncentra Masterplan® (collapsed cone algorithm) or Monaco® (Monte Carlo photon algorithm) and consisted of dual arc plan (170°/340° for left breast; 190°/20° for right breast) and 6 MV photons beams. In all the pts we retrospectively contoured on CT planning a volume containing the anatomical structures of emetic vagal-simpatical afferental pathways as the celiac plexus and gastroesophageal junction (GEJCPs). This area was identified as an organ at risk (OAR) for which the total volume, Dmax, Dmean and D1cc were calculated. Univariate analysis with χ 2 , t-test and Pearson covariance were used for statistical analysis. Results On 106 pts, 68 (64%) patients complained acute RINV according CTCAE v.3 criteria G1 nausea in 46 pts (43%), G2 nausea in 13 pts (12%), G1 vomiting in 8 pts (7 %) were recorded. Symptoms occurred at 34 Gy delivered dose (mean 30 Gy, range 20-34). In right side irradiated breasts RINV occurred in 3 pts (27%), in left side RT in 65 pts (60%). RINV was related to a Dmax >10 Gy on GEJCPs (p < 0.005). G1 vomiting and G2 nausea were related to a Dmax > 17 Gy (p < 0.005) and to a Dmax > 15 Gy (p < 0.005) respectively. Radiation breast side, age, systemic therapy, nodal radiation and PTVs volume values were not statistically significant for RINV. Conclusion RINV in breast radiation is not a common acute side effect. VMAT in breast radiation is responsible for a low dose bath to nearest structures as the GEJCPs and this may explain RINV in our cases. A useful constraint as Dmax < 10 Gy on GEJCPs like a serial structure may be considered in VMAT breast planning to avoid RINV. EP-1159 Hypofractionated adjuvant radiotherapy and concomitant trastuzumab for breast cancer: 5-year results M. Pasetti 1 , A. Fodor 1 , C. Sini 2 , F. Zerbetto 1 , P. Mangili 2 , P. Signorotto 2 , I. Dell'Oca 1 , C. Gumina 1 , M. Azizi 1 , A.M. Deli 1 , P. Passoni 1 , N. Slim 1 , C.L. Deantoni 1 , B. Noris Chiorda 1 , S. Foti 1 , A. Chiara 1 , G. Rossi 1 , C. Fiorino 2 , A. Bolognesi 1 , N.G. Di Muzio 1 1 San Raffaele Scientific Institute, Department of Radiotherapy, Milano, Italy 2 San Raffaele Scientific Institute, Medical Physics, Milano, Italy

occurring during 90 days from the start of HWBI, overall survival (OS), disease-free survival (DFS), ipsilateral- breast relapse-free survival (IB-RFS), and the proportion of breast cosmetic change. Early AEs and late ARs were evaluated using CTCAE ver3.0. Survival time was estimated by the Kaplan-Meier methods. Results Between 2010 and 2012, 312 women were registered. 306 patients received HWBI and 66 patients received HWBI with BI, but six chose CWBI prior to the start of irradiation. 301 patients (96.5%; 95%CI: 93.8-98.2) were treated within the recommended period. Evaluation of early AEs found that 38 patients (12.4%) had grade 2, including 25 patients (8.2%) with radiation dermatitis, and no patients had grade 3/4. On 306 patients receiving HWBI, 3-years OS, DFS and IB-RFS were 99.7% (95%CI: 97.7-100), 95.7% (95%CI: 92.7-97.5) and 99.0% (95%CI: 97.0-99.7). Among 303 (97%) patients, evaluation of late ARs found that 13 patients (4.3%; 90%CI: 2.6-6.7) had grade 2/3, including one of grade 3 pneumonitis. None had grade 4 or treatment-related death. Conclusion Short-course HWBI is considered as one of the standard treatments for Japanese women with margin-negative invasive breast cancer after BCS. Further follow-up is continued and cosmetic outcome will be analyzed. EP-1157 Serial changes of post-lumpectomy seroma during MRI-guided partial breast irradiation S.H. Jeon 1 , K.H. Shin 1 , S.Y. Park 1 , J.M. Park 1 1 Seoul National University Hospital, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective After breast conserving surgery, the volume of post- lumpectomy seroma changes by time. We analyzed serial changes of seroma volume (SV) using magnetic resonance image (MRI) to investigate the possible benefit of adaptive radiation therapy during partial breast irradiation (PBI). Material and Methods From October 2015 to July 2016, 37 patients were prospectively included in the study. A total dose of 38.5 Gy in 3.85 Gy fractions once daily was prescribed to the planning target volume (PTV). The PTV was defined as unequal margins of 1-1.5cm added according to the directional safety margin status of each seroma. Treatment was done using MRI-guided radiation therapy (ViewRay system). During the 10 fractions of treatment, MRI scans were acquired at the time of simulation, 1st, 6th and 10th fractions. Results The average time intervals of surgery-simulation, simulation-1st, 1st-6th, and 6th-10th fractions were 23.1, 8.5, 7.2, and 5.9 days, respectively. SV was smaller during treatment than at simulation in 34 patients. Mean SV decreased from 100% at simulation to 65%, 55%, and 47% at each MRI scan. Age, body mass index, tumor size, seroma location, SV and delivery of radiotherapy did not showed association with SV change (p>0.05, student’s t- test). In 34 patients with decreased SV, mean PTVs were 84.7 cm 3 and 56.9 cm 3 at simulation and 6th fraction, respectively, and their difference was proportional to SV at simulation (r=0.832, p<0.001, pearson’s correlation test). Conclusion During PBI, rate of SV change is associated with time elapsed from surgery. Frequent monitoring of seroma change with MRI seems helpful for all patients receiving PBI. EP-1158 Vmat radiation induced nausea/vomiting in adjuvant breast cancer radiotherapy: dosimetrical issues. G. Lazzari 1 , A. Terlizzi 1 , B. Turi 1 , M.G. Leo 1 , D. Becci 1 , G. Silvano 1

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