Peter du Plessis1*, Elsie Seane2, Xanthene Miles1, Shankari Nair1, Jacobus Slabbert1 and Charlot Vandevoorde1
1Department of Nuclear Medicine, Division of Radiation Biophysics, iThemba LABS (Laboratory for Accelerator Based Sciences), South Africa
2Department of Medical Imaging and Therapeutic Sciences, Cape Peninsula University of Technology, South Africa
Background: Worldwide, proton therapy is increasingly used as a radiation treatment alternative to photon therapy for breast cancer, primarily to decrease the risk for radiation-induced cardiovascular toxicity. However, uncertainties remain on the use of a constant Relative Biological Effectiveness (RBE) of 1.1 in clinical proton therapy. The beam at the position of the entrance plateau was used as the reference radiation in this study to signpost variation in RBEEP.
Objectives: This in vitro study aimed to determine the radiosensitivity of both cancerous and noncancerous breast cells to clinical proton irradiation. The variation in RBE at different depths along the proton Spread-Out Bragg Peak will be investigated.
Methods: Malignant (MCF-7) and non-Malignant (MCF-10A) breast cells were irradiated with doses ranging from 0.5 Gy to 4 Gy at 6 positions: the entrance plateau, 3 points on the Bragg peak (Proximal-, Middle- and Distal-SOBP), the 80% Dmax, and 40% Dmax. A Cytokinesis-Block Micronucleus (CBMN) assay was performed to determine cytogenetic damage using fluorescent
Results: A gradual increase was observed in α parameters with depth for both cell lines. Variations in the RBEEP between 0.99 to 1.99 for the cancerous cells and 0.92 to 1.60 for the non-cancerous breast cells, were observed. In fractionated proton therapy, the MCF-10A cells had a reduced repair in radiation-induced DNA damage between fractions compared to the cancerous MCF-7 cell line.
Conclusion: The RBEEP results showed a clear increase in RBEEP along the proton SOBP. This information could be used by the computational modeling community to further develop biologically motivated treatment planning for proton therapy. In addition, this study reveals a higher radiosensitivity for the non-cancerous breast cells.
Breast cancer; Proton therapy; Cytokinesis-block micronucleus assay; MCF-7 cells; MCF-10A cells; Radiobiology; RBE; Hypofractionation
du Plessis P, Seane E, Miles X, Nair S, Slabbert J, Vandevoorde C. Variations in Radiosensitivity of Breast Cancer and Normal Breast Cell Lines Using a 200 MeV Clinical Proton Beam. Clin Oncol. 2022;7:1943..