ESTRO 2024 - Abstract Book

S531

Clinical - Breast

ESTRO 2024

tumor bed (PTV2) and doses of the organs at risk (OARs) were evaluated. The LQ model was used to convert doses of OARs in HFI group using α/β = 3Gy (EQD2 3 ) for comparison.

Results:

Between Feb 21, 2019 and Feb 14, 2022, 801 patients were enrolled at 8 centers with 401 and 400 in CFI and HFI group, respectively. There were 182 patients received BCS and 387 patients were with more than three positive lymph nodes. In the CFI group, the D90 and V45 of PTV1 reached the prescribed dose in 70.6% and 96.0% of the patients, respectively. In the HFI group, the D90 and V36 of PTV1 reached the prescribed dose in 87.8% and 95.5% of the patients, respectively. When the tumor bed was irradiated, the D90 of PTV2 reached the prescribed dose in 95.6% in the CFI group and 100% in the HFI group, respectively. The mean D90 of PTV1 and PTV2 were 50.09±0.65Gy and 60.63±0.91Gy in CFI group while 40.11±0.56Gy and 50.79±2.03Gy in HFI group. For OARs constraints, protocol compliance was all above 95% (heart: 95.3%; ipsilateral lung: 95.5%; contralateral lung: 97.1%; humeral head: 98.2% and spinal cord: 100%) with no significant difference between CFI and HFI groups. For patients with left-sided breast cancer, the Dmean of the heart was 5.10±1.75Gy vs. 4.59±1.86Gy (EQD2 3 ) in CFI and HFI groups (p=0.51), respectively. No significant differences in Dmean of the heart (1.45±0.71Gy vs. 1.33±0.77Gy (EQD2 3 ), p=0.40) was found either between two groups in right-sided patients. The differences were significant in the Dmean of the ipsilateral lung (13.37±1.99Gy vs. 11.17±3.50Gy (EQD2 3 ), p ＜ 0.01), contralateral lung (0.88±0.73Gy vs. 0.74±0.61Gy (EQD2 3 ), p ＜ 0.01) and the ipsilateral humeral head (15.27±7.62Gy vs. 13.05±6.19Gy (EQD2 3 ), p ＜ 0.01) and the Dmax of spinal cord (21.40±8.82Gy vs. 19.47±7.99Gy (EQD2 3 ), p=0.05) between CFI and HFI groups.

Conclusion:

A high degree of compliance with protocol dose constraints was found for treatment plans in the HARVEST trial and doses to the most of OARs decreased in HFI group.

Keywords: hypofractionated irradiation, breast cancer

1064

Mini-Oral

Cumulative Incidence of Major Adverse Cardiac Events in Breast Cancer Patients after Radiotherapy

Tae Hyun Kim 1,2 , Ji Hyun Chang 1,2 , Kyung Hwan Shin 1,2,3 , Bum-Sup Jang 1,2

1 Seoul National University College of Medicine, Department of Radiation Oncology, Seoul, Korea, Republic of. 2 Seoul National University Hospital, Department of Radiation Oncology, Seoul, Korea, Republic of. 3 3Institute of Radiation Medicine, Institute of Radiation Medicine, Seoul, Korea, Republic of