Session Item

Systemic (abscopal) effects of stereotactic ablative radiation therapy (SABR) are associated with activation of immunologic response triggered by irradiation. Clinical manifestation of this phenomenon is rare and need further evaluation.

In this study we determine dynamic of immune status before and at different time points after SABR.

In 38 patients with oligometastatic lesions in the lungs and/or liver SABR was performed as 4 fractions of 10-13.5Gy or 3 fractions of 15Gy-20Gy. A quantitative assessment and analysis of blood immunological parameters was conducted before SABR (point A), 3-4 weeks (point B) and 6-8 weeks (point C) after the end of SABR. Peripheral blood samples were analyzed by flow cytometry on a FACS Canto ™ II cytometer. We used Friedman test for multiple (χ2) and Nemenyi test for group comparisons. Depending on the radiation dose, we divided patients for two groups: total focal dose (TFD) ≤45 Gy (16 patients) and TFD> 45 Gy (22 patients). Also, we analyzed indicators of the immune status in groups with irradiation of one metastatic focus (25 patients) and group with irradiation of ≥2 metastatic foci (13 patients)

We detected statistically significant increase of T-lymphocytes (CD3+CD19-), χ2 = 13,9, p = 0,001, pairwise p(A, B) = 0,001; T-helpers (CD3+CD4+), χ2 = 8,6, p = 0,01, pairwise p(A, B) = 0,01; activated T-helpers (CD3+CD4+HLA-DR+), χ2 = 38,6; p = 0,001; pairwise p(A, B) = 0,001, p(A, C) = 0,001; and activated cytotoxic T lymphocytes (CD3+СD8+HLA-DR+), χ2 = 14,4; p = 0,001; pairwise p(A, B) = 0,002, p(A, C) = 0,01 and decrease of B-lymphocytes (CD3-CD19+), χ2 = 35,4; p < 0,001, pairwise p(A, B) = 0,001, p(A, C) = 0,002. Interesting. that we noted decline of T-regulatory lymphocytes that associated with immunosuppressive mechanisms (CD4+CD25brightCD127low) in point B compared with the values obtained  before radiotherapy χ2 = 7,1; p = 0,03 pairwise p (A, B) = 0,03].

Also 6-8 weeks after SABR, in comparison with values obtained 3-4 weeks after SABR, we detected statistically significant decrease of T-lymphocytes (pairwise p (B, C) = 0.03)

Immunologic effects of SABR characterized by activation of the T- effectors and T-helpers with moderate but significant decline in T-regularity cells. In dynamic, this changes expressed by a greater extent 3-4 weeks after SABR.