# Local Disease-Free Survival Rate (LSR) Application to Personalize Radiation Therapy Treatments in Breast Cancer Models

^{1}

^{2}

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^{†}

## Abstract

**:**

## 1. Introduction

_{d}) and clonogen numbers (K), together with the $\mathsf{\alpha}$/$\mathsf{\beta}$ ratio, our approach could be tested at a preclinical level, to confirm its application as a variant of the classical LQ and create a more personalized approach for radiotherapy planning.

## 2. Materials and Methods

#### 2.1. Cell Cultures and Radiation Treatments

#### 2.2. Clonogenic Survival Assay, Dose Response Curves, and Alfa and Beta Parameter Calculations

#### 2.3. Local Disease-Free Survival Rate (LSR) Model

#### 2.4. Statistical Analysis

**χ**

^{2}) test was applied, referring to the mean of the surviving fractions obtained in three experiments. When the tolerated error was set to 5% (α = 0.05) and the degrees of freedom were 4, referring to the table of the Chi-squared distribution, we obtained a value equal to 9.49, which is greater than our value of 1.00. Therefore, we concluded that we can accept the null hypothesis or that the data sets follow a Gaussian probability distribution, or more simply, they belong to the same statistical set. Moreover, in our analysis, we used the adjusted R

^{2}as the main goodness index of the non-linear regression curve (SF = e^(−αx−βx^2)) for the SF(D) data, with the known meaning that an R

^{2}close to 1 means that the data predict the value of the dependent variable in the sample, while if it is equal to 0 it means that they do not. The

**χ**

^{2}and the adjusted R

^{2}values for each cell line are shown in the Supplementary Materials, Table S2.

## 3. Results

#### 3.1. Radiobiological Characterization of Breast Cancer(BC) Cell Lines and Primary Cultures

^{+}/PR

^{+}/HER2

^{-}MCF7 cell line; the ER

^{-}/PR

^{-}/HER2

^{-}, metastatic, and radioresistant MDA-MB-231 cell line [20]; and the ER

^{-}/PR

^{-}/HER2

^{-}, non-tumorigenic MCF10A cell line, chosen as a healthy control [32]. In addition, to closely resemble a real pathological setting, two primary cultures were used: the TNBC ER

^{-}/PR

^{-}/HER2

^{-}BcPcEMT and the ER

^{+}/PR

^{+}HER2

^{-}BcPc7, previously isolated and characterized at the phenotypic and molecular levels by our research group. In particular, the BcPcEMT cells were characterized by a strong “epithelial to mesenchymal transition” (EMT) phenotype [25,26,33].

#### 3.2. Experimental LSR

_{d}, and the k values for each cell culture. We also compared these experimental data with those obtained with the standard treatment of BC, where a theoretical α/β ratio equal to 3 is usually considered. LSR graphs that were obtained with k values reported in the literature, i.e., k = 36 [23,31] (Figure 2A) and k = 14.5 (Figure 2B), as well as those with k values experimentally measured (Figure 2C), are reported below.

## 4. Discussion

- -
- dose per fraction to achieve controlled death of cancer cells;
- -
- the intrinsic radiosensitivity values $\alpha $ and $\beta $;
- -
- k, which represents tumor clonogens;
- -
- ${T}_{d}$ or the doubling time.

## 5. Conclusions

## Supplementary Materials

^{2}) and adjusted R

^{2}values obtained by statistical analysis.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Clonogenic survival curves of breast cancer (BC) cells exposed to different doses of therapeutic X-rays. The data shown represent the mean values plus errors from three independent experiments.

**Figure 2.**Local disease-free survival rate (LSR) curves with k = 36 (

**A**) and k = 14.5 (

**B**), as well as k values experimentally calculated (

**C**) on BC cells exposed to increasing doses of therapeutic X-rays. The data shown are represented with their own error in x and y.

BC Cells | α (Gy^{−1}) | β (Gy^{−2}) | α/β (Gy) |
---|---|---|---|

MCF7 | $0.285\text{}\pm \text{}$0.012 | $0.044\text{}\pm \text{}$0.003 | 6.47 ± 0.52 |

MCF10A | $0.236\text{}\pm \text{}$0.007 | $0.024\text{}\pm \text{}$0.002 | 9.83 ± 0.87 |

MDA-MB-231 | $0.110\text{}\pm $ 0.034 | $0.029\text{}\pm \text{}$0.010 | 3.79 ± 2.24 |

BcPc7 | $0.203\text{}\pm \text{}$0.022 | $0.029\text{}\pm \text{}$0.006 | 7.00 ± 1.63 |

BcPcEMT | $0.264\text{}\pm \text{}$0.008 | $0.030\text{}\pm \text{}$0.002 | 8.83 ± 0.64 |

**Table 2.**Dose values for fraction calculated to obtain an LSR(D) of 100% in the three conditions, analyzed with an experimental k (k exp), k = 36 and k = 14.5.

BC Cells | Dose (Gy) [k exp] | Dose (Gy) [k = 36] | Dose (Gy) [k = 14.5] |
---|---|---|---|

MCF7 | $1.5$ | $1.5$ | 1.5 |

MCF10A | $2.0$ | $2.0$ | 2.0 |

MDA-MB-231 | $2.0$ | $2.0$ | 1.8 |

BcPc7 | $2.9$ | $2.9$ | 2.8 |

BcPcEMT | $2.9$ | $2.8$ | 2.6 |

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**MDPI and ACS Style**

Savoca, G.; Calvaruso, M.; Minafra, L.; Bravatà, V.; Cammarata, F.P.; Iacoviello, G.; Abbate, B.; Evangelista, G.; Spada, M.; Forte, G.I.; Russo, G. Local Disease-Free Survival Rate (LSR) Application to Personalize Radiation Therapy Treatments in Breast Cancer Models. *J. Pers. Med.* **2020**, *10*, 177.
https://doi.org/10.3390/jpm10040177

**AMA Style**

Savoca G, Calvaruso M, Minafra L, Bravatà V, Cammarata FP, Iacoviello G, Abbate B, Evangelista G, Spada M, Forte GI, Russo G. Local Disease-Free Survival Rate (LSR) Application to Personalize Radiation Therapy Treatments in Breast Cancer Models. *Journal of Personalized Medicine*. 2020; 10(4):177.
https://doi.org/10.3390/jpm10040177

**Chicago/Turabian Style**

Savoca, Gaetano, Marco Calvaruso, Luigi Minafra, Valentina Bravatà, Francesco Paolo Cammarata, Giuseppina Iacoviello, Boris Abbate, Giovanna Evangelista, Massimiliano Spada, Giusi Irma Forte, and Giorgio Russo. 2020. "Local Disease-Free Survival Rate (LSR) Application to Personalize Radiation Therapy Treatments in Breast Cancer Models" *Journal of Personalized Medicine* 10, no. 4: 177.
https://doi.org/10.3390/jpm10040177