ESTRO 2021 Abstract Book

S247

ESTRO 2021

(biopsy versus surgery) and MGMT status. An online prospective quality control (QC) of volumes and dose was performed in the experimental arm. The main objective was overall survival, estimated by the Kaplan-Meier method in each randomization arm and compared by the Logrank test, as well as by the Cox model adjusted on the stratification factors and on the already known prognostic factors. Results There was no significant difference between the 2 groups regarding characteristics: gender; age median age, weight, PS, 46% were MGMT unmethylated, 85% were surgically resected. Initial tumors were more frequently <30mm diameter in arm A (36% vs 27%) (p=0.0316). General, neurological and hematological secondary effects were comparable between the 2 arms, except more frequent grade 1-2 cephalalgia in arm A(59.1% vs 42.9%,p= 0.0075) and more frequent grade 1-2 neurological deficit in Arm B ( 45.7% vs 35.4%,p=0.0043). After a median follow-up of 43.7 Months (95% IC [35.8; 45.8]), no statistical difference between arms were observed for OS (HR=0.90 [0.64;1.27], p=0.5526)) and PFS (HR=1.09 [0.80;1.48], p = 0.6027). Overall survival (OS) and Progression Free Survival ( PFS) were comparable between arm A and B, respectively OS 22.6 months versus 22.2 months (p=0.55) and PFS 8.6 vs 7.8 months (p=0.6) Conclusion In this dose-painting trial, i.e. delivery of heterogeneous dose guided by metabolic imaging, dose increase was well tolerated. Overall survival was not improved. This study yields a large amount of longitudinal multimodal MR imaging data including planning CT, radiotherapy dosimetry, MR spectroscopic, diffusion and perfusion imaging to participate in the efforts in deciphering the pathways of pseudoprogression and radioresistance of glioblastoma. Trial registration : NCT01507506 [1] : Laprie et al, BMC Cancer 2019 Feb 21;19(1):167. Thomsen 7 , E. Yates 7 , M. Berg 8 , E. Lorenzen 9 , I. Jensen 10 , M. Josipovic 11 , M. Jensen 12 , J. Overgaard 1 1 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark; 2 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 3 Lillebaelt Hospital, Department of Oncology, Vejle, Denmark; 4 Odense University Hospital, Department of Oncology, Odense, Denmark; 5 Aalborg University Hospital, Department of Oncology, Aalborg, Denmark; 6 Rigshospitalet, Department of Oncology, Copenhagen, Denmark; 7 Aarhus University Hospital, Department of Physics, Aarhus, Denmark; 8 Lillebaelt Hospital, Department of Physics, Vejle, Denmark; 9 Odense University Hospital, Department of Physics, Odense, Denmark; 10 Aalborg University Hospital, Department of Physics, Aalborg, Denmark; 11 Rigshospitalet, Department of Physics, Copenhagen, Denmark; 12 Rigshospitalet, Danish Breast Cancer Group, Copenhagen, Denmark Purpose or Objective Based on low risk of local recurrence in selected elderly breast cancer patients, the Danish Breast Cancer Group (DBCG) initiated the randomized DBCG Partial Breast Irradiation (PBI) trial (ClinicalTrials.gov identifier: NCT00892814 ). The radiotherapy was similar to the external beam 40 Gy/15 fr, 2.67 Gy/fr used in the UK IMPORT Low trial. The hypothesis was that PBI did not increase the risk of grade 2-3 breast induration compared with whole breast irradiation (WBI). Materials and Methods 880 patients ≥60 years old and operated with breast conservation for relatively low-risk breast cancer (non- lobular unifocal pT1N0, ER+, HER2-, grade 1-2, margin ≥2mm) were enrolled during 2009-16 and randomized WBI vs. PBI. The primary endpoint was grade 2-3 induration, and secondary endpoints were the pattern of recurrence and a number of radiation-associated morbidities. Results 866 patients (434 WBI, 432 PBI) were eligible from five centers. Median age was 66 years. Median follow up was 6.7 years. The 3-yr rate of induration was 9.9% (95% CI 7.2, 13.2) (WBI) and 5.4% (3.4, 7.9) (PBI), risk difference 4.5% (95% CI -8.3, -0.8), p=0.017. Irradiated volume was significantly associated with breast induration with a 3-year incidence in large-breasted women of 13% (WBI) and 6% (PBI) versus 6% (WBI) and 5% (PBI) in small-breasted women. Endocrine therapy did not influence the risk of induration. All radiation- associated morbidities (including dyspigmentation, telangiectasia, pain, oedema, scar appearance, sensibility changes, cosmetic outcome, patient satisfaction) were similar or significantly better for the PBI group. As first event, 15 patients (1.7%) had a loco-regional recurrence (4 WBI, 11 PBI), HR 2.35 (95% CI 0.72, 7.62), p=0.16, and 13 of these were local. Five were considered new primaries (1 WBI and 4 PBI) and treated accordingly, the rest were considered true local recurrences (3 WBI and 5 PBI). Contralateral breast cancer was detected in 18 patients (2.1%) (17 invasive, 1 DCIS), equally distributed in the treatment groups. Distant recurrence as first event was detected in 3 patients (1 WBI, 2 PBI), and simultaneous with loco-regional failures in 3 patients (2 WBI and 1 PBI). Non-breast second cancer was diagnosed in 62 patients (7.2%), no difference between the groups. In total, 70 patients (8.1%) had died, 5 from breast cancer and 65 from other causes (including 33 from second cancers). Among the 32 patients who died without cancer, two patients died from cardiac disease (both WBI left-sided). The 9-year overall survival was 89.3% (WBI) versus 86.5% (PBI), risk difference 2.8% (-9.1, 3.5), p=0.37. Conclusion Moderately hypofractionated external-beam PBI for relatively low-risk breast cancer patients did not result in more induration compared to WBI. Irradiated volume was a risk factor for developing induration. Few loco- regional recurrences were detected and not related to PBI. Updated results with longer follow-up will be provided. OC-0334 Partial vs whole-breast irradiation for breast cancer patients in the randomized DBCG PBI trial B. Offersen 1 , J. Alsner 1 , H.M. Nielsen 2 , E.H. Jacobsen 3 , M.H. Nielsen 4 , L. Stenbygaard 5 , A.N. Pedersen 6 , M.S.

OC-0335 Final results of TROG 13.01 SAFRON II: Single vs multi-fraction SABR for pulmonary