ESTRO 2025 - Abstract Book

S3956

Radiobiology - Normal tissue radiobiology

ESTRO 2025

4258

Digital Poster Ultra-hypofractionated for whole breast/chest wall adjuvant radiotherapy, acute toxicity, risk of late toxicity and tumor control probability. Cheikh TAYEB, Hamza ALLAM, Zine Eddine BOURAOUI, Sofiane MELLOUK Radiation Oncology, Central Hospital Of Army, Algiers, Algeria Purpose/Objective: Based on the principle of low radio α/β of breast cancer, the aim of our work is to evaluate a series of 12 patients with invasive breast cancer treated from 1 April 2024, with an ultrafractionated radiotherapy protocol (Fast Forward) in terms of acute toxicity, the estimation of the late toxicity risk and the probability of local control (for 2 unfavorable cases in terms of dosimetry) were evaluated to help predict the effectiveness and safety of treatments. Material/Methods: The Median patient age was 51 years (range 35-74 years), 67% right tumors, 33% left tumors. The molecular subtypes, the Luminal A profile was found in 50% of tumors, while 25% of tumors have a Luminal B profile, 02 cases have a Luminal/HER2 profile, and one patient has a triple negative tumor. In 58% of cases, the tumor was classified as pT2, and 42% of cases as pT1, with an average tumor size of 25mm (5-45mm). 50% of patients received adjuvant chemotherapy, 25% neoadjuvant chemotherapy and 25% just hormonal therapy; mastectomy was performed in 75% of patien.All patients were treated with 3-dimensional Field In Field conformal radiotherapy technique (3- D FIF ), using a linear accelerator with photon beams of 6 to 18 MV of energy, The dose delivered is 26 Gy in 5 fractions on the whole breast/chest wall, +/- 12.5 Gy in 5 fractions on the tumor bed. Results: In terms of acute toxicity, upon evaluation at the end of treatment and at one month and 3 months post-radiotherapy, no toxicity was noted in 07 patients (58.3%), 04 patients (33.3%) presented with grade 1 radiodermatitis, and one patient (8.3%) presented with grade 2 radiodermatitis, exudative epithelitic type limited to the fold.Using the linear-quadratic formula and Poisson statistics of cell-kill, an α/β ratio of 2.7 Gy was assumed for breast tumor. However, for OAR, an α/β ratio of 3 was used for calculations. The results are shown the following table:

NTCP for Skin fibrosis

NTCP for radiation pneumonitis

EUD (cGy )

Patien t

TCP

NTCP for Pericarditis heart

Heart: 57 Lung: 836.1 Skin: 111.7 Heart: 55.4 Lung: 1342 Skin: 1313.4

1

96.5

0.09

0.13

0.15

2

95.3

0.08

0.20

0.17

Conclusion: The ultra-fractionated treatment in our series is associated with a low rate of acute skin toxicity in low-risk breast cancer. The probability of local control is excellent, the homogeneous dose to critical organs as well as the probability of late toxicities are acceptable.

Keywords: low radio α/β , TCP, NTCP, and EUD

References: 1/Ultra-hypofractionated one-week locoregional radiotherapy for patients with early breast cancer: Acute toxicity results Ivica Ratosa, Angel Montero, Raquel Ciervide c, Beatriz Alvarez c, Mariola García-Aranda c, Jeannette Valero c, Xin Chen-Zhao c, Mercedes Lopez c, Daniel Zucca e, Ovidio Hernando c, Emilio Sánchez c, Miguel Angel de la Casa e, Rosa Alonso c, Pedro Fernandez-Leton e, Carmen Rubio c