ESTRO 2024 - Abstract Book

S5424

Radiobiology - Tumour biology

ESTRO 2024

mainly to improve selectivity to tumour cells and physico-chemical stability of GNPs. Due to this diversity in GNP but also in the cell lines included in this study, results should be regarded with care.

α and β constants were obtained by fitting the Linear-Quadratic model to the experimental data using MATLAB R2023a. The difference between RT+GNP and RT for each constant: Δα and Δβ , were calculated. For each cell line, the derived models were used to estimate: SER (Sensitizer Enhancement Ratio, i.e., the ratio between the Mean Inactivation Dose for RT and RT+GNP); DEF (Dose Enhancement Factor for 2 and 10 Gy, i.e, the ratio between the selected dose of RT and the dose of RT+GNP that causes the same survival fraction); RER (Radiation Enhancement Ratio for 2 and 10 Gy, i.e., the ratio between the survival fraction obtained without and with GNP for the dose x Gy); and the DMR (Dose Modification Ratio for the survival levels 90%, 50% and 10%, i.e., the ratio of the dose of RT to the dose of RT+GNP producing x% survival).

Results:

The median Δα was 0.13 (IQR 0.05,0.21) and median Δβ was -0.002 (IQR -0.014,0.008), indicating that in general an increase in α and, for about half the cases, a reduction in β with RT+GNP compared to RT was obtained. For instance, the median α for RT and RT+GNP for the HeLa cell line was 0.16±0.09 Gy -1 and 0.40±0.16 Gy -1 and the median β was 0.035±0.024 Gy -2 and 0.015±0.021 Gy -2 , respectively; for MDA-MB-231, α was 0.07±0.11 Gy -1 and 0.14±0.17 Gy -1 and β was 0.057±0.040 Gy -2 and 0.084±0.041 Gy -2 , respectively; and for PC-3, α was 0.23±0.15 Gy -1 and 0.35±0.23 Gy -1 and β was 0.076±0.021 Gy -2 and 0.060±0.027 Gy -2 , respectively. The figure compares the results for some of the quantification methods evaluated showing the variability between the different measures. The median value for SER was 1.32 (IQR 1.17,1.48), for DEF2Gy was 1.53 (IQR 1.27,1.92), for RER2Gy was 1.31 (IQR 1.14,1.52) and for DMR50% was 1.50 (1.22,1.75). A strong correlation (r-pearson > 0.80) was found between DEF2Gy and DMR90%; RER2Gy and Δα /DMR50%/SER; DMR50% and SER/DEF2; and DEF10Gy and DMR10%/RER10Gy.

Conclusion:

The assessment of the features that maximize the outcome of RT concomitant with GNP is difficult due to a lack of standardization of the methods quantifying the benefits of the treatment being tested. Due to the wide applicability