ESTRO 2022 - Abstract Book

S717

Abstract book

ESTRO 2022

G. Garcia 1 , J. Fernandez 1 , M. Dzhugashvili 2 , K. Matskov 1 , A. Seradilla 1 , A. Seral 1 , P. Poortmans 3 , E. Lopez 1

1 GenesisCare, Radiation Oncology, Madrid, Spain; 2 GenesisCare, Radiation Oncology, Madrid , Spain; 3 Iridium Netwerk & University of Antwerp, Radiation Oncology, Antwerp, Belgium Purpose or Objective Several large randomized controlled trials have established superiority of moderate hypofractionation in maintaining cosmesis and limiting late effects without compromising locoregional control in breast cancer (BC), making moderate hypofractionation standard of care for breast cancer. The FAST Forward (FF) is a multicenter, phase 3, non-inferiority trial, randomising patients with pT1–3pN0–1M0 BC after breast-conserving surgery (BCS) or mastectomy to either 40 Gy in 15 fractions over 3 weeks, and 27 Gy or 26 Gy in five fractions over 1 week to the whole breast or chest wall. With a median follow-up of 71 · 5 months, the 26 Gy arm is demonstrated to being non-inferior to the standard of 40 Gy in 15 fractions over 3 weeks. A boost to the primary tumour bed was given to 24.3% of the patients. The EORTC boost versus no boost trial showed a benefit for the local relapse (LR) risk, with the largest absolute benefit in young patients. We considered that high-risk patients could benefit from a simultaneous integrated boost (SIB) integrated in a 5 days treatment. Materials and Methods Between March and October 2020, 246 consecutive early BC patients were treated with a schedule of 5 fractions over one week to a total dose of 26 Gy. High-risk patients (n=147, 58,9%) received a SIB of 4 Gy, up to a total dose of 29Gy. Mean age was 61.8±11.3 years. IMRT/VMAT was used in 96.7%; 28.5% received primary or adjuvant chemotherapy and 84.6% adjuvant endocrine therapy. We evaluated the dose distribution to the target volume and the organs at risk, also breast edema and erythema (RTOG criteria) with a median follow up to 6 months. Results Mean PTVbreast and PTVBoost volumes were 857.0±427.1cm3 and 60.2±36.2cm3. Mean PTVbreast and PTVBoost V95, V105 and V107 were 96.0%, 8.8%, 4.0% and 98.8%, 1.0% and 0.05%, respectively. Mean Dmean, V1.5 and V7 of heart were 129.2cGy, 21.7% and 1.25% and for anterior left descending artery Dmean was 349.4cGy and V8 was 5.82% in left breast. At the end of treatment, erythema score was G0 for 55.7%, G1 for 42.3% and G2 for 0,8%, respectively. Oedema G1 was present in 14,25% and <1% G2. At 6 months, 94.7%, 2,8% and 0% had erythema G0, G1 and G2, respectively; oedema G1 was seen in 11.4% and G2 in 2.4% of patients. There was no statistically significant difference on side effects between PTVbreast and PTVBoost volumes. Slightly more SIB patients experienced oedema G1-G2 at the end of treatment (17.4% vs. 12.2% without boost), and at 6 months (16.8% vs. 8.8%), without statistical significance (p=0.302 and p=0.096, respectively). Conclusion Ultra-hypofractionation combined with a SIB up to 29Gy to the primary tumour bed in high-risk is a clinically feasible novel technique with very low added side effects at 6 months. We continue including and following patients and initiated discussions about a prospective randomized phase III study. A. Bakker 1 , C.P. Tello Valverde 1 , G. van Tienhoven 1 , M.W. Kolff 1 , H.P. Kok 1 , B.J. Slotman 1 , I.R. Konings 2 , A.L. Oei 3 , H.S. Oldenburg 4 , E.J. Rutgers 4 , C.R. Rasch 5 , H.D. van den Bongard 1 , H. Crezee 1 1 Amsterdam UMC, Department of Radiation Oncology, Cancer Center Amsterdam, Amsterdam, The Netherlands; 2 Amsterdam UMC, Department of Medical Oncology, Cancer Center Amsterdam, Amsterdam, The Netherlands; 3 Amsterdam UMC, Laboratory for Experimental Oncology and Radiobiology, Center for Experimental and Molecular Medicine, Cancer Center Amsterdam, Amsterdam, The Netherlands; 4 Netherlands Cancer Institute, Department of Surgical Oncology, Amsterdam, The Netherlands; 5 LUMC, Department of Radiation Oncology, Leiden, The Netherlands Purpose or Objective Operable patients with locoregional (LR) recurrent breast cancer at high risk for re-recurrence are treated with postoperative re-irradiation combined with hyperthermia (HT), i.e. heating the target area to 40-43 °C for one hour, in the Netherlands. Early 2015, national consensus was reached using a new standard RT dose fractionation schedule of 23x2Gy, replacing the 8x4Gy RT schedule used in our center. We investigated the impact of both postoperative re-irradiation schedules combined with HT on LR control and late toxicity in patients with LR recurrent breast cancer treated at our center. Materials and Methods In this retrospective study, 112 women with resected LR recurrent breast cancer treated in 2010-2017 with postoperative re-irradiation combined with 4-5 weekly HT sessions were included. RT treatment consisted of 8x4Gy (n=34, twice a week) until 2014, or 23x2Gy (n=78, 5 times a week) after 2014. Due to frailty or long travel distance 5 patients received 8x4Gy after 2014. Re-irradiation was delivered using 3 consecutive different RT planning techniques. From 2010 to mid-2014 the lateral chest wall and/or regional lymph nodes areas were irradiated using two opposing AP-PA fields and the anterior chest wall with electrons, the breast was treated with two tangential fields. From mid-2014 IMRT was applied using 5-7 beam angles, and from early 2016 onward VMAT using two (counter)clockwise partial arcs. Actuarial LR control and grade 2-5 late toxicity incidence (>3 months after the first re-irradiation fraction) were analyzed. Toxicity was defined according to CTC-AE v5.0. Patients had multiple late toxicities. The cause of late toxicity might be current or previous treatments or an cumulative effect. Backward multivariable Cox regression was performed. Results Twenty-four patients (21.4%) developed an in-field recurrence. Median FU was 43 months (range 1-107 months). Three- year LR control was 89.4% vs. 68.7% in the 23x2Gy and 8x4Gy group, respectively ( p =0.01), LR control tended to be better for the 23x2Gy group after long FU ( p =0.094; Fig 1A). In multivariate analysis, distant metastasis (HR 17.6; 95%CI 5.2-60.2), MO-0798 Re-irradiation and hyperthermia for locoregional recurrent breast cancer: Outcome of 23x2Gy vs 8x4Gy