ESTRO 36 Abstract Book

S163 ESTRO 36 _______________________________________________________________________________________________

5 Beatson West of Scotland Cancer Centre, Oncology Department, Glasgow, United Kingdom 6 Royal Stoke Hospital, Oncology Department, Stoke-on- Trent, United Kingdom 7 Aukland Hospital, Physics Department, Aukland, New Zealand 8 Nuffield Health Cheltenham Hospital, Department of Surgery, Cheltenham, United Kingdom 9 Norfolk and Norwich University Hopsitals NHS Foundation Trust, Oncology Department, Norwich, United Kingdom 11 Kings College London, Oncology Department, London, United Kingdom 12 Clatterbridge Cancer Centre, Oncology Department, Bebington, United Kingdom 13 Mount Vernon Cancer Centre, Radiotherapy Department, Northwood, United Kingdom 14 Royal Cornwall Hospital, Oncology Department, Truro, United Kingdom 15 Independent Cancer Patient Voice, London, United Kingdom 16 Institute of Cancer Research, Academic Department of Radiotherapy, London, United Kingdom Background: Local cancer relapse rates after breast conservation surgery followed by radiotherapy have fallen sharply in many countries with risk influenced by patient age and clinico-pathological factors. In women at lower than average risk of local relapse, partial breast radiotherapy restricted to the vicinity of the original tumour is hypothesised to improve the balance of beneficial versus adverse effects compared with whole breast radiotherapy. Methods: The IMPORT LOW trial (ISRCTN12852634) recruited women aged ≥50 years after breast conserving surgery for invasive ductal adenocarcinoma pT≤3cm, pN0- 3, G1-3 and ≥2mm resection margins. Using 15 daily treatments, patients were randomly allocated (1:1:1) to 40 Gy whole breast radiotherapy (control), 36 Gy whole breast plus 40 Gy to partial breast (reduced dose) or 40 Gy partial breast only (partial breast). Primary endpoint was ipsilateral local relapse rate (80% power to exclude a +2.5% non-inferiority margin at 5 years for each test group). Findings: Between May 2007 and October 2010, 2018 women were recruited (control n=675, reduced dose: n=674, partial breast: n=669). With a 72.2 month median follow-up (IQR 61.7-83.2), 5-year local relapse rates were 1.1% (95%CI 0.5-2.3), 0.2% (0.02-1.2) and 0.5% (0.2-1.4) in control, reduced dose and partial breast groups. Absolute differences in local relapse rate compared with the control group were -0.73% (-0.99, 0.22) for the reduced dose and -0.38% (-0.84, 0.90) for the partial breast groups, demonstrating non-inferiority for both test groups. Photographs, patients and clinicians reported similar or lower levels of adverse effects after reduced dose or partial breast radiotherapy compared with whole breast radiotherapy (see Table 1).

produced equivalent or milder late normal tissue side effects. This simple radiotherapy technique is implementable in radiotherapy centres worldwide. Funding: Cancer Research UK (CRUK/06/003). SP-0315 Partial breast radiotherapy after breast conservation for breast cancer: early results from the randomised DBCG PBI trial B. Offersen 1 , H.M. Nielsen 1 , M.S. Thomsen 2 , E.H. Jacobsen 3 , M.H. Nielsen 4 , L. Stenbygaard 5 , A.N. Pedersen 6 , M. Krause 7 , M.B. Jensen 8 , J. Overgaard 9 1 Aarhus University Hospital, Dept Oncology, Aarhus C, Denmark 2 Aarhus University Hospital, Dept Physics, Aarhus C, Denmark 3 Lillebaelt Hospital, Dept Oncology, Vejle, Denmark 4 Odense University Hospital, Dept Oncology, Odense, Denmark 5 Aalborg University Hospital, Dept Oncology, Aalborg, Denmark 6 Copenhagen University Hospital- Rigshospitalet, Dept Oncology, Copenhagen, Denmark 7 University Clinic Carl Gustav Carus- Technical University Dresden, Clinic for Radiotherapy and Oncology, Dresden, Germany 8 Copenhagen University Hospital- Rigshospitalet, DBCG, Copenhagen, Denmark 9 Aarhus University Hospital, Dept Expt. Clin. Oncology, Aarhus C, Denmark Objective The risk of local recurrence after adjuvant radiation therapy (RT) of early breast cancer (BC) is now so low that ESTRO and ASTRO have suggested guidelines to select patients who may be safely treated with partial breast (PBI) and not whole breast irradiation (WBI). In the Danish Breast Cancer Group (DBCG) the randomized DBCG PBI trial was initiated to safely introduce PBI as standard in DK. Material/Methods Patients ≥60 years operated with breast conservation for early non-lobular breast cancer (BC) pT1 pN0, ER+, grade 1 or 2, HER2-, margin ≥2mm were enrolled and randomized to PBI vs WBI, all cases based on 40Gy/15 fr. Strata were institution and endocrine therapy. The primary endpoint was breast induration 3 years after RT, secondary endpoints were other morbidities, genetic risk profile for RT-induced fibrosis and recurrences. ClinicalTrial NCT00892814. Results In 6 RT departments in DK and D 882 pts were enrolled in 2009-16. At analysis 353 pts (40%) had ≥ 3 years follow up. At 3 years grade 2-3 induration was detected in 6.4% in the PBI arm and in 7.7% in the WBI arm (HR 0.76, 95% CI, 0.39-1.47). At 3 years, comparing the PBI with the WBI arm there were no differences in dyspigmentation (8.1% vs 11.0%), telangiectasia grade 2-3 (5.3% vs 8.9%), edema grade 2-3 (0.6% vs 0.6%), scar grade 2-3 (21.5% vs 17.1%), and global cosmetic outcome (excellent/good) was 84.3% vs 83.9%, respectively. At 3 years patients treated with PBI or WBI reported excellent/good satisfaction with the treated breast in 92.5% vs 91.2% of cases, and 83.2% vs 81.8% when reporting satisfaction with the treated breast compared with the non-treated breast. In the PBI / WBI arm local recurrence was reported in 1 pt/ 2 pts, regional recurrences 0 pt / 0 pt, distant failure 1 pt / 2 pts, new contralateral BC / DCIS 2 pts / 2 pts and other malignancy 8 pts / 16 pts. One patient had died from BC, 7 from other malignancy, 7 from non-cancer causes. Updated results will be provided at ESTRO 36. Conclusion Using 40/15 fr for PBI in selected early node- negative BC patients results in few late RT induced morbidities with no difference compared with WBI. These results are in harmony with results from the large UK IMPORT LOW trial using the same RT technique. Thus 40 Gy/15 fr external beam PBI is now DBCG standard for breast RT in patients fulfilling the inclusion criteria for the DBCG PBI trial.

Interpretation: At 5 years, partial breast and reduced dose radiotherapy showed local relapse rates non-inferior to that observed following whole breast radiotherapy and