Background and Aims

We present the current status and outcomes of the joint radiobiological experiment performed at eight European proton therapy centers or research institutes. The study aims to spot the potential differences in the in vitro proton RBE values measured by different groups sharing a similar setup and identify its causes.

Methods

A phantom and a protocol for sample preparation and post-processing are shared among the participants to ensure minimal differences in the biological part of the experimental procedure. In this phantom, V79 cells grow on the polyester slides that can be inserted at different depths, which enables their simultaneous irradiation at multiple positions within the radiation field. The setup is irradiated with proton beams with two SOBP configurations (6 cm, 6 Gy, and 4 cm, 8 Gy), followed by the reference photon irradiation (LINAC or x-ray), and the biological effect is evaluated using a colony-forming assay.

Results

The study is still ongoing, and the spread of data for measured cell survival is yet to be evaluated. However, some non-obvious differences in the experimental procedures and setups are already revealed, e.g. post-processing timing or varying dose distributions in the beam plateau/fall-off regions.

Conclusions

As an outcome of the experiment, we plan to summarize the details of the experimental procedure for biological experiments with proton beams, differing between the centers across Europe. Accounting for these details would help to harmonize future studies in the field.

This work was supported by EU Horizon2020 grant 730983 (INSPIRE).