ESTRO 36 Abstract Book

S162 ESTRO 36 2017 _______________________________________________________________________________________________

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.

Acknowledgement: BVO was supported by The Danish Cancer Society and CIRRO OC-0316 Single dose external beam preoperative radiotherapy in breast cancer: experience and guidelines K.R. Charaghvandi 1 , S. Yoo 2 , B. Van Asselen 1 , M.D. Den Hartogh 1 , H.J.G.D. Van den Bongard 1 , J.K. Horton 2 1 University Medical Center Utrrecht, Radiation Oncology Department, Utrecht, The Netherlands 2 Duke Cancer Center, Department of Radiation Oncology, Durham, USA Purpose or Objective In patients treated with breast-conserving surgery, suboptimal cosmetic results have been reported following post-operative 3D-conformal accelerated partial breast irradiation (APBI) [1]. The delivery of radiation (RT) preoperatively to the intact tumor enables better target visualization and reduction in treatment volumes, and thus, the potential for less normal tissue toxicity [2]. We compiled our clinical experience and dosimetric data to develop practical guidelines for this new treatment approach. Material and Methods Dosimetry and toxicity data were pooled from 2 preoperative single dose APBI cohorts and 1 planning-study [table 1]. In an American dose escalation trial, patients ≥55 years, with non-lobular cT1N0Mx or DCIS received a single dose of 15, 18 or 21Gy (1.5cm CTV margin) using IMRT in the prone position (n=32) followed by lumpectomy within 10 days [fig 1A]. In the Netherlands, the feasibility of VMAT-based supine APBI (20 Gy to tumor, 15Gy to 20mm clinical target volume(CTV)) was evaluated initially in a planning study (n=20) and is currently ongoing in women ≥50 years with cT1-2(max. 3 cm)N0Mx non-lobular carcinoma (n=10) [fig. 1]. In this trial, lumpectomy is planned 6 months after RT. Acute toxicity was scored according to CTCAE version 4.03. Single dose APBI constraints were derived from pooled OAR estimates. The limit for optimal OAR dosimetry was set at the 75 th percentile, whereas the 90 th percentile represented non- optimal but acceptable dosimetry. Replanning of the US cohort was performed to check the adherence of these constraints for uniform single dose 21Gy APBI with a 20mm CTV margin (n=32). Results In the dose escalation cohort (n=32), grade 1 local radiation dermatitis, fibrosis and fatigue developed in 39%, 23% and 6% of the cases within 90 days after RT. At a median follow-up of 57 days in the 15/20Gy simultaneous boost cohort (n=10) grade 1 fatigue and local fibrosis was encountered in 90% and 80% of patients, without any radiation dermatitis. In both cohorts no acute ≥grade 3 toxicity developed. Based on pooled OAR estimates, optimal dosimetry was defined as a maximum value of 0.7Gy for the mean heart dose, 1.5Gy Dmax for contralateral breast, 1.3Gy for mean ipsilateral lung dose, and 12.3Gy as D20cc dose to chest wall [table 1]. All replanning plans adhered to these constraints. At least acceptable mean ipsilateral breast dose (max. 5.5Gy) was achieved in 97% of cases. Optimal skin dosimetry was set at Dmax ≤100% prescription dose, D1cc ≤13.2Gy and D10cc ≤10.0Gy.