Examination of immunohistochemical of the effects of flattened and unflattened radiotherapy beams in nude mice breast cancer xenografts.

Purpose: The aim of this study was to investigate the radiobiological effects underlying the inhibition of breast cancer (BCa) following radiotherapy in nude mice models, and to evaluate the impact of changes in immunohistochemical parameters induced by FF and FFF beams.

Materials and methods: The study included thirty-six adult nude mouse models, which were randomly assigned to five groups: control (G1), breast cancer (BCa) (G2), FF-400 MU/min (G3), FFF-1100 MU/min (G4), and FFF-1800 MU/min (G5). The control group received neither radiation nor treatment, while the BCa group had a cancer model without radiation. The BCa models were subjected to a single dose of 20 Gy of radiotherapy at varying dose rates. Twenty days after the implantation of the MCF-7 cancer cell line, the nude mice were irradiated and sacrificed 48 h later for ER, PR, HER-2, Ki-67, CD-133, Caspase-3, APAF-1, NOS-2 and NOS-3 IHC analysis.

Results: A statistically significant decrease in IHC staining values for ER, Ki-67 and NOS-2 was observed in the FF-400 MU/min, FFF-1100 MU/min and FFF-1800 MU/min groups due to radiotherapy compared to the BCa group. The FFF beams demonstrated superior efficacy in the treatment of BCa. The significant differences in Caspase-3 and APAF-1 levels were found between BCa and control groups, while CD-133, NOS-3, HER-2, and PR staining showed no differences between groups.

Conclusions: It was concluded that FFF beam was more effective than FF beam for BCa, especially on ER, Ki-67 and NOS-2 IHC parameters.