Abstract Book

S703

ESTRO 37

EP-1278 Postoperative radiotherapy on the breast and influence on acute haematological toxicity A. Zamagni 1 , G. Macchia 2 , M. Boccardi 2 , S. Cammelli 1 , M. Ferro 2 , S. Cilla 3 , I. Ammendolia 1 , G. Tolento 1 , F. Bertini 1 , E. Galofaro 1 , S. Ciabatti 1 , V. Dionisi 1 , M. Ferioli 1 , G. Siepe 1 , A. Cortesi 1,4 , D. Smaniotto 5 , F. Deodato 2 , G.P. Frezza 6 , A.G. Morganti 1 1 Department of Experimental- Diagnostic and Specialty Medicine - DIMES, Radiation Oncology Center, Bologna, Italy 2 Radiotherapy Unit, Fondazione di Ricerca e Cura “Giovanni Paolo II”, Campobasso, Italy 3 Medical Physics Unit, Fondazione di Ricerca e Cura “Giovanni Paolo II”, Campobasso, Italy 4 Radiotherapy Department, Istituto Scientifico Romagnolo per lo Studio e la Cura dei Tumori IRST, IRCCS, Italy 5 Department of Radiotherapy, Policlinico Universitario «A. Gemelli» Università Cattolica del Sacro Cuore, Roma, Italy 6 Radiation Oncology Unit, Bellaria Hospital, Bologna, Italy Purpose or Objective Purpose/Objective. To evaluate haematological toxicity in two cohorts of breast cancer patients (pts) treated with standard 3D postoperative radiotherapy (control group: CG) or accelerated intensity-modulated postoperative radiotherapy (clinical trial MARA-1). Material and Methods Material/ methods. Prescribed dose to the breast was 50.4 Gy with sequential 10 Gy electron boost on tumor bed in the CG (n= 130) and 40 Gy with concomitant 4 Gy boost in MARA-1 (n=317). Overall treatment time was of 32 daily fractions for CG and 16 fractions for MARA-1. In CG cohort 85/130 pts (65%) had received adjuvant chemotherapy before radiotherapy, compared to 104/317 (33%) pts in MARA-1 cohort. Complete blood count was performed weekly. Results Results. Haematological toxicity was observed in 49/130 (37.7%) pts in CG and in 75/317 (23.7%) pts in MARA-1, respectively (p: 0.0026). As expected, myelotoxicity was more frequent (p: 0.00001) in pts pre-treated with chemotherapy (73/189: 38.6%) compared to pts not receiving chemotherapy (51/258: 19.8%). However, haematological toxicity was clinically irrelevant. No myelotoxicity grade > 3 was observed. Grade 2 or 3 toxicity was observed only in 4.6% pts in CG (6/130: 4 leukopenia grade 2, one anemia grade 2, one neutropenia grade 3) vs none in MARA-1. Five out of these 6 pts had received chemotherapy. Anemia or neutropenia grade 2 or 3 occurred in less than 2% of CG pts (2/130). No thrombocytopenia grade > 1 was recorded. Conclusion Conclusion. Haematological toxicity in breast cancer pts treated with postoperative radiotherapy (3D standard technique or accelerated IMRT) depends on radiotherapy protocol and previous adjuvant chemotherapy treatment. However, myelotoxicity induced by radiotherapy in these pts is mild and does not require regular monitoring during treatment. EP-1279 Molecular factors on local control in breast hypofractionated radiotherapy : a control group study G. Lazzari 1 , A. Terlizzi 2 , M.G. Leo 2 , A. Nikolaou 1 , G. Silvano 1 1 Azienda Ospedaliera SS. Annunziata Presidio Osped, Radiology, Taranto, Italy 2 Azienda Ospedaliera SS. Annunziata Presidio Osped, Physic, Taranto, Italy Purpose or Objective To assess whether tumor grade and molecular prognostic factors have influenced local control in hypofractionated

post-mastectomy radiotherapy (PMRT). The pathological stage distributions as following, 11 cases were pT0, 90 were pT1, 104 were pT2, 9 were pT3 and 8 were pT4; 58 cases were pN0, 62 were pN1, 48 were pN2, 54 were pN3. Results With a median follow-up time of 62 months, the 5-year cumulative locoregional failure (LRF) rate and distant metastasis (DM) rate were 12% and 21%. The 5 year overall survival and 5-year disease free survival were 82% and 75% in the whole group. Univariate and multivariate demonstrated that histological grade, pathological N stage were independent prognostic factors associated with LRF. We deeply scored grade and pathological N stage, and then categorized patients into 3 risk groups depend on the scoring, the 5y- LRF rates were 4%, 15% and 36% in low, moderate and high risk group, respectively. In low risk group, radiotherapy did not decrease LRF rate (3.2% in PMRT group, 4.5% in no PMRT group, p=0.897), while in moderate and high risk group, PMRT significantly decreased LRF rate (21.9% in PMRT group vs. 46.7% in no PMRT group, p=0.01). Conclusion Histological grade and pathological N stage were important prognostic factors associated with LRF in breast cancer staged in cT1-2N0-1, who were managed with NAC and mastectomy, and PMRT significantly decreased LRF in moderate and high risk subgroups. EP-1277 Comparison of RIR and DIR through the respiratory phases of 4DCT for radiotherapy after BCS A. Zhang 1 , J. Li 1 1 Shandong Cancer Hospital affiliated to Shandong University, Department of Radiation Oncology, Jinan, China Purpose or Objective To compare the geometric differences in gross tumor volume (GTV) and surgical clips propagated by rigid image registration (RIR) and deformable image registration (DIR) using a four-dimensional computed tomography (4DCT) image data set for patients treated with boost irradiation or accelerated partial breast irradiation after breast-conserving surgery (BCS). Material and Methods The 4DCT data sets of 44 patients who had undergone BCS were acquired. GTV and selected clips were manually delineated on end-inhalation phase (CT 0 ) and end- exhalation phase (CT 50 ) images of 4DCT data sets. Subsequently, the GTV and selected clips from CT 0 images were transformed and propagated to CT 50 images using RIR and DIR, respectively. The geometric differences in GTV and surgical clips from DIR were compared with those of RIR. Results The mean Dice similarity coefficient (DSC) index was 0.860 ± 0.042 for RIR and 0.870 ± 0.040 for DIR for GTV (P = 0.000). The three-dimensional distance to the center of mass (COM) of the GTV from RIR was longer than that from DIR (1.22 mm and 1.10 mm, respectively, P = 0.000). Moreover, in the anterior-posterior direction, displacements from RIR were significantly greater than those from DIR for both GTV (0.70 mm and 0.50 mm, respectively) and selected clips (upper clip, 0.45 mm vs 0.20 mm; inner clip, 0.55 mm vs 0.30 mm; outer clip, 0.40 mm vs 0.20 mm; lower clip, 0.50 mm vs 0.25 mm) (P = 0.000). However, in the left-right and superior-inferior directions, there were no significant displacement differences between RIR and DIR for GTV and the selected clips (all P > 0.050). Conclusion DIR can improve the overlap for GTV registration from CT 0 to CT 50 images from 4DCT scanning. Furthermore, DIR is superior to RIR in reflecting the displacement of GTV and selected clips in the anterior-posterior direction induced by respiratory movement.