ESTRO 2023 - Abstract Book

S99

Saturday 13 May

ESTRO 2023

final pathological margins were < 1mm and re-excision surgery was not performed. Patients were assessed for surgical complications, cosmetic outcome, and local recurrence on post-operative days 7, 14, and then at 3, 6, and 12 months for the first year and then annually for 10 years. Results 25 patients were recruited with a median age of 67, and a median follow-up of 3.5 years. Treatment was successfully completed as per protocol in all patients. Following initial BCS, 6 patients were found to have close or positive margins. 5 patients underwent surgical margin revision, one of which underwent a second completion mastectomy for persistent close margins. Another patient with margins <1mm received adjuvant breast RT without revision surgery. Only one patient had a positive sentinel lymph node, and received adjuvant locoregional RT. None of the patients had surgical complications, including wound infections or healing delays, and all had grade 0-1 skin toxicity at day 7 and 14 post-op. There were no local, regional or metastatic recurrences. The cosmetic outcome was assessed in 21 out of 25 patients: 95% of assessed patients had an excellent or good cosmetic outcome, while it was fair in one patient. Conclusion Pre-operative PBI is a safe and feasible treatment for elderly patients with low-risk early-breast cancer, providing excellent local control and cosmetic outcomes with minimal acute adverse effects. Randomized controlled trials are needed to compare pre-operative to adjuvant PBI in this patient population. MO-0137 MC1635: final results of a randomized phase III trial of hypofractionated radiotherapy for breast CA C. Vargas 1 , K. Corbin 2 , T. DeWees 3 , L. McGee 4 , R. Mutter 2 , L. Vallow 5 , D. Shumway 2 , T. Vern-Gross 4 , M. Halyard 4 , S. Keole 4 , S. Park 2 , W. William 4 , M. sarah 6 , M. Golafshar 7 , B. Laughlin 4 , C. Thorpe 4 , B. Pockaj 8 1 Mayo Clinic, Radiation Oncology, Scottsdale, USA; 2 Mayo, RO, RST, USA; 3 Mayo, Stats, Scottsdale, USA; 4 Mayo, RO, Scottsdale, USA; 5 Mayo, RO, Jacksonville, USA; 6 Mayo, Surgery, Jacksonville, USA; 7 Mayo, Stats, scottsdale, USA; 8 Mayo, Surgery, Scottsdale, USA Purpose or Objective Hypofractionated radiation therapy (RT) for localized breast cancer improves patient convenience and reduces treatment cost. Here, we report the results of MC1635 randomized trial. Materials and Methods Between 04/04/2018 and 02/11/2020, localized breast cancer patients (T1-T3, N0-N1, M0) after breast conserving surgery (BCS) were enrolled. Patients were randomized to receive whole breast RT with moderate hypofractionation to 40 Gy in 15 fractions (Arm A) or extreme hypofractionation to 25 Gy in 5 fractions (Arm B). An optional concurrent integrated boost to 48 Gy on Arm A or 30 Gy on Arm B was allowed. All patients were treated daily (Monday-Friday). Analysis of early toxicity (CTCAE V5.0) (<3 months), late toxicity (>3months) quality of life (QOL), cosmesis, PRO-CTCAE, and our final end point (1) grade 3 or higher late adverse event, 2) deterioration of cosmesis from excellent/good to fair/poor or from fair to poor. QOL was assessed via PROMIS, overall Linear Analogue Self-Assessment (LASA), and The Breast Cancer Treatment Outcome Scale (BCTOS). Deterioration of cosmesis was defined as change from excellent/good to fair/poor or from fair to poor according to the Harvard Cosmesis Scale. Results One hundred seven patients were randomized to either Arm A (n=54) or Arm B (n=53). Median follow-up was 36 months. Patient characteristics included: IDC 55%, ILC 20%, mixed 7%, DCIS 16%, other 3%; grade 1 or 2 72%, grade 3 28%; triple negative 9%, ER/PR+ 84%, and Her2+ 7%. Treatment characteristics included: SLNB 68%, ALND 32%; spot scanned protons 50%, 3D x-rays 50%; and an integrated boost 21%. No significant differences in any characteristics were noted between the two arms. For our final end point no patient present with a grade 3 or higher toxicity and no deterioration in cosmesis were seen (p=0.89). Grade 2 toxicities were seen in 7.4% of Arm A and 7.5% of Arm B. This primarily consisted of radiation dermatitis (6 patients) with 1 patient with fibrosis and 1 patient with lymphedema. The average Harvard Cosmesis score was similar between arms at all timepoints. QOL was similar between arms, as well. Patient-reported radiation skin burns of ‘moderate to severe’ as assessed by PRO-CTCAE were more commonly reported in Arm A (58.7%) vs Arm B (27.9%) (odds ratio 3.7, CI 1.5-8.9; p=0.004). Patient satisfaction was very high with more than 98% of patients in both arms saying that they would do RT again. No cancer recurrences or deaths have been seen in either arm. Conclusion Extreme hypofractionation using 25 Gy in 5 fractions is non inferior to moderate hypofractionation in terms of toxicity and cosmesis. Our final results in addition to the results from Fast Forward stablish extreme hypofractionation over 5 days as the most appropriate treatment schedule after BCS. Our schedule of 25 Gy may have some additional advantages over other extreme hypofractionations doses given its superiority in patient reported toxicity over moderate hypofractionation. MO-0138 Nationwide RT trends & variation in locoregional M0 breast cancer treatment in NL – 2008 until 2019 J. Evers 1,2 , M. Van der Sangen 3 , M. Van Maaren 2,1 , M. Bloemers 4 , D. Van den Bongard 5 , L. Strobbe 6 , J. Maduro 7 , M. Aarts 1 , H. Struikmans 8 , S. Siesling 1,2 1 Netherlands Comprehensive Cancer Organisation, Department of Research and Development, Utrecht, The Netherlands; 2 University of Twente, Department of Health Technology and Services Research, Enschede, The Netherlands; 3 Catharina Hospital, Department of Radiation Oncology, Eindhoven, The Netherlands; 4 The Netherlands Cancer Institute, Department of Radiation Oncology, Amsterdam, The Netherlands; 5 Amsterdam University Medical Center, Department of Radiation Oncology, Amsterdam, The Netherlands; 6 Canisius Wilhelmina Hospital, Department of Surgical Oncology, Nijmegen, The Netherlands; 7 University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands; 8 Leiden University Medical Center, Department of Radiation Oncology, Leiden, The Netherlands Purpose or Objective Describing nationwide trends and variation in radiotherapy (RT) use in the context of locoregional non-metastatic (M0) breast cancer treatment in the Netherlands from 2008 until 2019. Materials and Methods Women diagnosed with M0 breast cancer in 2008-2019 were selected from the population-based Netherlands Cancer Registry. Primary treatment was presented over time. Non-specified RT use was available in all study years. RT details were available from 2011. Use of whole breast irradiation (WBI) with boost/WBI without boost/partial breast irradiation