ESTRO 2024 - Abstract Book

S3447

Physics - Dose calculation algorithms

ESTRO 2024

82.2 ± 9.5

559.8

±

H3

97.6 + 2.5

259 .5 ± 48.7 265.6 ± 48.5

255.8 ± 49.9 262.7 ± 50.5

561.6 ± 103.7

103.2

Table 1: Different metrics for volume and dose assessment by lymphocytes in the 3 models (H1, H2 and H3) after irradiation, averaged over the whole cohort. V >0Gy (fraction of lymphocyte having received a non-null dose), V >0.125Gy (fraction of lymphocytes having received a dose greater or equal to 0.125Gy), the average, median and 98-th percentile dose. The last 3 metrics are calculated on all lymphocytes (irradiated or not) and on irradiated lymphocytes only (V >0Gy ).

Conclusion:

In this work, a new in-silico model, efficient in terms of calculation time and closer to biological reality, was proposed, highlighting the major role of out-of-field doses and recirculation for the correct calculation of the dose received by lymphocytes during brain irradiation. Despite the high level of radiosensitivity of lymphocytes [8], our results (regardless of the H1, H2 or H3 model used) hardly explain the 40% sRIL rates observed clinically in patients with brain tumours treated with radiochemotherapy. These results call into question the relative contribution of the direct cytotoxic effect of irradiation on lymphocytes to the induction of RIL, and several other immunosuppressive effects will certainly have to be taken into account in order to potentiate treatments [9]–[11] (Fig. 2).

This work has benefited from the grant ANR-21-RHU5-0005 within the FRANCE2030 investment plan.

Keywords: lymphopenia, brain, Monte Carlo