ESTRO 36 Abstract Book

S615 ESTRO 36 2017 _______________________________________________________________________________________________

myeloablative chemotherapy prior to stem cell transplant. Here we report our initial clinical experience regarding patient setup error and its dosimetric consequences. Material and Methods 7 patients with advanced hematological malignancies were treated according to our institutional phase I clinical trial designed to evaluate the feasibility of IMTMI in addition to preconditioning chemotherapy regimen. Patients were immobilized using a customized whole body mold. The bones are contoured and a 3 mm margin is added to obtain PTV. Three separate treatment plans, for the head and neck, chest, and pelvic were generated. Plans were optimized for 95% PTV coverage with the 95% of prescription dose. Positioning and alignment of all three isocenters were confirmed prior to each treatment with megavoltage orthogonal port films. Residual setup errors of each patient and each fraction were retrospectively analyzed by co-registering port films and digitally reconstructed radiographs. Dosimetric consequences of setup errors were evaluated by shifting the isocenters based on the determined setup errors. We applied previously determined actual isocenter shifts for each session and recalculated dose distributions to determine delivered dose distributions. Simulated dose distributions were then compared with the planned dose distributions. Results Setup errors were less than 5 mm, more specifically, they were, on average, 3.1±0.7 mm, 2.3±0.8 mm, 3.2±0.8 mm in vertical, longitudinal, and lateral directions, respectively. Maximum vectoral displacement was 4.6 mm. When the determined isocenter shifts were applied and the new dose distributions were calculated, the bone marrow volume that received the 95% of the prescription dose (V 95 ) was reduced from 99.4% (±0.7%) to 96.8% (±1.3%), on average. The mean lung dose and the mean PTV dose changed less than 5%. The change in the maximum dose ranged between 6% and 19%. Conclusion Linac-based IMTMI is clinically feasible affording significant OAR sparing in a combined chemo-RT treatment. Based on our clinical experience with the first 7 patients in this study, we found a 3 mm bone to PTV expansion was adequate to accurately target bone marrow in IM-TMI treatments. EP-1139 eliot- boost and conservative surgery followed by hypofractionated EBRT in breast cancer patients S. Takanen 1 , G. Gritti 1 , M. Källi 1 , L. Feltre 1 , F. Filippone 1 , E. Iannacone 1 , L. Maffioletti 1 , R. Muni 1 , P. Fabio 1 , E.M.P. Mauri 2 , M. Giovanelli 2 , L. Burgoa 2 , A. Paludetti 2 , C. Valerii 2 , F. Palamara 2 , M. Ferro 2 , P. Fenaroli 2 , S. Andreoli 3 , M. Fortunato 3 , L.F. Cazzaniga 1 1 Azienda Socio-Sanitaria Territoriale Papa Giovanni XXIII, Radiation Oncology, Bergamo, Italy 2 Azienda Socio-Sanitaria Territoriale Papa Giovanni XXIII, Breast Cancer Surgery, Bergamo, Italy 3 Azienda Socio-Sanitaria Territoriale Papa Giovanni XXIII, Medical Physics, Bergamo, Italy Purpose or Objective We report preliminary results from a clinical trial aimed to evaluate the incidence of in-breast tumour recurrence (IBR) and the acute and late toxicity in patients affected by early breast cancer (BC), undergoing conservative surgery and electron intraoperative radiation (ELIOT) boost, followed by hypofractionated external beam Electronic Poster: Clinical track: Breast

Patients inclusion criteria are: infiltrating carcinoma histology (T1-2, N0-1, M0), unifocality or multifocality (maximum distance between two lesions ≤ 2 cm), PS (ECOG) ≤ 2, age > 18, premenopausal status. ELIOT boost was delivered for all patients at the level of tumour bed by a dedicated linear accelerator NOVAC 7 HITESYS (NRT, Italy), using 9 MeV electron beam, a single dose of 12 Gy at 90%. EBRT was given at the whole breast in 13 daily fractions of 2.85 Gy. Fifteen patients underwent adjuvant chemotherapy and 74 patients underwent hormone therapy. IBR is any local relapse within the treated breast. Acute and late toxicity were assessed using RTOG toxicity scale. Results Forty-seven patients (56.6%) started EBRT boost in 28 days after ELIOT boost procedure. Current median follow up was 23 months and is too short to evidence any IBR. After ELIOT, 2 patients underwent mastectomy, after the identification of another breast metachronous nodule and BRCA1 mutation respectively. Four patients underwent conventional scheduled EBRT: 3 for the presence of unfavourable prognostic disease factors as discovered on the surgical specimen and 1 for severe post-surgical side effects. Most patients had slight local post-surgical oedema: 1 patient had necrosis of the scar area. After EBRT, slight skin erythema (G1) was evidenced in all patients. Considering late toxicity, slight scar fibrosis (G1) was assessed in most patients: 1 patient showed scar retraction and 1 dehiscence of surgical scar. Conclusion The advantages of the ELIOT-boost followed by hypofractionated EBRT in early BC are the reduction of treatment duration and skin toxicity with better cosmetic results, the delineation of tumour bed under direct visual and palpable evaluation, no adjuvant chemotherapy delay and the immediate inhibition of cells repopulation. With these preliminary results, it seems to be manageable with acceptable acute toxicity. A longer follow up is needed in order to show IBR and late effects rate. EP-1140 Dosimetric comparison between Helical Tomotherapy and IMRT for Bilateral Breast Cancer M.H. Wang 1 1 Shuang Ho Hospital, Department of Radiation Oncology, Taipei, Taiwan Purpose or Objective This study aimed to compare treatment between Tomotherapy and IMRT for bilateral breast cancer. Material and Methods We selected 10 patients of breast cancer who were performed partial mastectomy for study. All patient were early stage breast cancer pT1~T2. A total dose of 5040cGy was delivered for definitive breast irradiation of IMRT and Tomotherapy for each patient in treatment planning system. In this study, we analyzed comparable treatment of IMRT vs Tomotherapy for bilateral breast. Bilateral whole breast dose coverage, Conformity index, Homogeneity index and dose volume constraints of normal tissue (Right and Left lung, Heart) were analyzed. Results Tomotherapy was better than IMRT for significant improvements in reducing the volume of normal tissue. In volume of heart in V20 (Tomo:1.543% versus IMRT: 2.955%; p=0.023) and in lung volume achieving lower mean lung dose (MLD) (Rt lung mean dose: Tomo: 6.388 Gy versus IMRT: 8.828Gy; p = 0.017; Lt lung mean dose Tomo: 6.24 Gy versus IMRT: 7.71Gy; p = 0.013). The conformity indices (V 95% /V PTV ) of right and left breast were (1.08 +/- 0.01) & (1.07 +/- 0.02) in Tomo and (1.07 +/-0.02) & (1.08 +/- 0.01) in IMRT. For homogeneity indices, Tomo were (1.36

radiotherapy (EBRT). Material and Methods

From February 2012 to January 2016, 83 early BC patients underwent conservative surgery and ELIOT boost, followed by EBRT at Papa Giovanni XXIII Hospital in Bergamo (Italy).