ESTRO 2020 Abstract Book

S525 ESTRO 2020

(V30 Gy, V5 Gy), heart (V5 Gy), ipsilateral/contralateral lung (V5 Gy), skin strip (V20 Gy, V10 Gy, V3 Gy). Student’s T-test was performed to identify differences between means in 3D-CRT and MRgRT plans. Results 198 patients receiving APBI with 3D-CRT (98 patients, 49.5%) and MRgRT (100 patients, 50.5%) were included. PTV cavity volume was larger with 3D-CRT (mean: 188 cc) compared to MRgRT plans (mean: 98 cc) (p<0.001), inversely correlated with PTV Dmax (mean: 41.9 Gy and 43.3 Gy, p<0.001). Both modalities demonstrated adequate coverage of PTV V95% Rx (mean: 98.2% and 97.4%, p=0.38) and V90% Rx (mean: 99.9% and 99.87%, p=0.39). The percent of ipsilateral breast receiving high dose radiation, 30 Gy, was significantly higher amongst patients receiving 3D-CRT (mean: 32.4% and 19.0%, p<0.001). However, the percent of ipsilateral lung receiving 5 Gy was lower in 3D-CRT patients (mean 27.1% and 32.4%, p=0.01). Additionally, patients undergoing MRgRT had significantly lower volume of skin receiving 20 Gy (mean: 613.9cc and 337.3 cc, p<0.001) and 10 Gy (mean: 994.7cc and 774.7cc, p<0.001), but not 3 Gy (mean: 2576cc and 2301.6cc, p=0.09). There was no significant difference between 3D-CRT and MRgRT plan dosimetrics for: PTV Dmin (mean: 34.1 Gy and 33.8 Gy, p=0.61), percent ipsilateral breast receiving 5 Gy (mean: 63.1% and 60.5%, p=0.18), heart receiving 5 Gy (mean: 3.1% and 2.4%, p=0.42), and contralateral lung receiving 5 Gy (mean: 0.27% and 0.13%, p=0.35). Conclusion For APBI with either 3D-CRT or MRgRT, acceptable PTV coverage was demonstrated with both modalities. MRgRT had greater high-dose sparing of the ipsilateral breast and skin attributable to smaller volumetric expansions from minimizing setup uncertainty, which may result in improved cosmetic outcomes and decreased acute/long term toxicities. PO-0985 Hypofractionated radiotherapy with SIB in advanced incurable breast cancer-HYPORT B study R. Santosham 1 , S. Chatterjee 1 , S. Chakraborty 1 , A. Mahata 1 , S. Mandal 1 , A. Das 1 , A. Kumari 1 , S. Ray 2 , R. Ahmed 3 1 Tata Medical Center, Radiation oncology, Kolkata, India ; 2 Tata Medical Center, Nuclear Medicine, Kolkata, India ; 3 Tata Medical Center, Surgical oncology, Kolkata, India Purpose or Objective To report the early clinical outcome and acute toxicity data of a single arm prospective study evaluating a 5 day hypofractionated external beam radiotherapy schedule with simultaneous integrated boost (SIB) in patients with advanced incurable breast cancer. Material and Methods Patients with locoregionally advanced incurable or metastatic breast cancer requiring palliation of local symptoms were enrolled in this study. Hypofractionated radiotherapy was delivered to a dose of 26Gy in 5 fractions over 1 week to the whole breast and ipsilateral supraclavicular fossa along with 6Gy SIB to the metabolically active tumor. Axillary nodes were irradiated only if involved. Regional PET CT was done before and 3 months after completion of radiotherapy. Acute toxicity was assessed using CTCAE version 4.03 toxicity grading criteria. Clinical response was assessed at 2 weeks and 3 months after completion of radiotherapy. Radiological response was assessed using the PERCIST 1.0 criteria. Results Nineteen out of thirty patients have been enrolled in this study between April 2018 to August 2019. One patient expired prior to the third month evaluation. Hence, we present our analysis on the remaining 18 patients. At presentation, 2 patients had breast related pain score above 5, 3 patients had bleeding from the tumour site and 5 patients had a fungating mass. 4 (22.2%) patients had Gr

II skin toxicity at 2 weeks after completion of radiotherapy,. At 3 months, none of the patients had acute toxicity or breast related pain, only one patient had persistent tumour bleed and one patient had a residual fungating tumour. Clinical examination done at 3 months showed that 10 (55.5%) patients had partial response (PR), 6 (33.3%) patients had complete response (CR) and 2 (11.1%) patients had clinical progression. Radiological response assessment revealed that 10 (55.5%) patients had partial metabolic response(PMR), 4 (22.2%) patients had complete metabolic response(CMR), 1 (5.5%) patient had stable metabolic disease(SMD) and 3 (16.6%) patients had progressive metabolic disease. Of the three patients who had progressed, 1 patient progressed in the internal mammary nodal region. Conclusion Hypofractionated radiotherapy using this 1 week schedule showed acceptable toxicity, satisfactory local control and excellent palliation in patients with advanced incurable breast cancer. PO-0986 Concurrent Chemoradiation for Inoperable Locally Advanced Breast Cancer after Primary Chemotherapy B. Castro 1 , I. Rodrigues 1 , I. Azevedo 1 , J. Savva-Bordalo 2 , D. Moreira 1 , H. Pereira 1 1 Instituto Português de Oncologia do Porto, Serviço de Radioterapia Externa, Porto, Portugal ; 2 Instituto Português de Oncologia do Porto, Serviço de Oncologia Médica, Porto, Portugal Purpose or Objective Locally Advanced Breast Cancer (LABC) entitles a heterogeneous group of tumors with poor prognosis for whom initial systemic treatment is proposed to downsize the tumor. Concurrent chemoradiation (CCCR) schemes, based on the radiosensitizing properties of anti-neoplasm drugs, are largely used as a radical option for inoperable tumors, such as those of the head and neck and digestive tract, with increased rates of local control. The use of CCCR in the LABC has been hypothesized for both palliation and locoregional control. The primary objective of this study was to evaluate the efficacy of CCCR through response rates and survival analysis; the secondary objective was to report the associated toxicity. Material and Methods Data from patients with LABC (stage III/IV) submitted to CCCR in a cancer center between January 2009 and December 2018 were retrospectively reviewed. Descriptive analysis was used to characterize population and clinical-pathological variables. Progression-free survival (PFS) and overall survival (OS) were estimated by Kaplan-Meier method. The response and toxicity (CTCAE 5.0) rates were also evaluated. Results Twenty-eight female patients were included, with median age at diagnosis of 52 years (32-79) and PS ≤2. The majority of patients (N=25, 89%) were treated for ductal carcinoma, mostly grade 3 (N=17, 61%), 8 (29%) Her2 positive and 9 (32%) triple-negative tumors. The majority presented at stage IV (N=15, 54%). All patients were submitted to CCCR due to inoperable disease after primary chemotherapy. Weekly taxotere 25- 35mg/m 2 was used as radiosensitizer (3 to 8 cycles). Radiotherapy was prescribed to 50Gy in 25 daily fractions in a median overall treatment time of 34 days (33-62). In the majority of patients (N=23, 32%), regional nodes were irradiated in addition to the breast. Regarding toxicity, were reported 19 (68%) cases of radiodermatitis, 4 of which were grade 3; 7 (25%) cases of mucositis grade ≤2; and 3 (11%) cases of hematological toxicity grade 3. One patient did not complete CCCR because of non-related death. The majority of patients (N=18, 64%) achieved partial response, 3 (11%) had complete clinical response and 2