ESTRO 2024 - Abstract Book

S5337

Radiobiology - Tumour biology

ESTRO 2024

The purpose of this work was to compare, for the SQ20B head and neck squamous cell carcinoma cell line, irradiated by helium ions in mixed field conditions, surviving curves predicted using the NanOx model and the GATE Monte Carlo simulation platform with experimental data.

Material/Methods:

An SOBP was formed by modulating the energy of the 67.4 ±0.3 MeV helium beam produced at the ARRONAX accelerator using an aluminium range-modulating wheel composed of eight sectors of different thicknesses. SQ20B cells were irradiated in three positions of this SOBP: the distal edge, the plateau, and the proximal edge with doses ranging from 0 to 4 Gy to determine cell survival curves.

The beamline used experimentally was accurately simulated in GATE. In order to verify experimentally the characteristics of the SOBP, a stack of six radio-chromic films (HDV2 - 109 µm thick) was irradiated and analysed.

To predict the biological response of the irradiated cells, a new actor: the Biodose Actor, recently developed in the GATE platform, has been tested. The Biodose Actor was used to predict the biological dose as well as the surviving fraction of the irradiated cells based on a dedicated database where alpha and beta values were precalculated using the NanOx model for monoenergetic ions.The surviving fractions of the SQ20B cells irradiated by helium ions were compared to the values resulting from the simulation.

Results:

The grey level of profiles of the six irradiated radio-chromic films is shown in Figure 1. While the simulation shows a maximal dose heterogeneity of 12% between the first five films, the darkness level measured on the radio-chromic films was found to vary within 19%. This variation follows a monotonous decrease in grey level as we move distally and may be attributed to saturation related to high LET. A steep decrease in darkness level is visible on the sixth film with a grey level reaching 35% of the darkness of the first film. Interestingly, in the GATE simulation, a sudden drop in dose corresponding to the distal end of the SOBP is also visible for the sixth film as it receives 14% of the dose of the first film (Figure 1 bottom right).