An experimental setup for proton irradiation of a murine leg model for radiobiological studies

Abstract

Background

The purpose of this study was to introduce an experimental radiobiological setup used for in vivo irradiation of a mouse leg target in multiple positions along a proton beam path to investigate normal tissue- and tumor models with varying linear energy transfer (LET). We describe the dosimetric characterizations and an acute- and late-effect assay for normal tissue damage.

Methods

The experimental setup consists of a water phantom that allows the right hind leg of three to five mice to be irradiated at the same time. Absolute dosimetry using a thimble (Semiflex) and a plane parallel (Advanced Markus) ionization chamber and Monte Carlo simulations using Geant4 and SHIELD-HIT12A were applied for dosimetric validation of positioning along the spread-out Bragg peak (SOBP) and at the distal edge and dose fall-off. The mice were irradiated in the center of the SOBP delivered by a pencil beam scanning system. The SOBP was 2.8 cm wide, centered at 6.9 cm depth, with planned physical single doses from 22 to 46 Gy. The biological endpoint was acute skin damage and radiation-induced late damage (RILD) assessed in the mouse leg.

Results

The dose–response curves illustrate the percentage of mice exhibiting acute skin damage, and at a later point, RILD as a function of physical doses (Gy). Each dose–response curve represents a specific severity score of each assay, demonstrating a higher ED50 (50% responders) as the score increases. Moreover, the results reveal the reversible nature of acute skin damage as a function of time and the irreversible nature of RILD as time progresses.

Conclusions

We want to encourage researchers to report all experimental details of their radiobiological setups, including experimental protocols and model descriptions, to facilitate transparency and reproducibility. Based on this study, more experiments are being performed to explore all possibilities this radiobiological experimental setup permits.

Keywords:

• Radiobiology
• experimental setup
• dosimetry
• in vivo
• acute skin damage
• radiation-induced late damage (RILD)
• linear energy transfer (LET)

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The biological raw data is available on request.

[email protected]

The Monte Carlo Simulations are available on:

https://github.com/APTG/2022_DCPT_MICE

A CAD-file outlining the water phantom dimension in detail is provided.

Acknowledgements

The authors thank Dorthe Grand, Maria Bech, and Marianne Kristiansen for their excellent help in animal care and handling.

Additional information

Funding

Supported by the Novo Nordisk Foundation (grant no. NNF195A0059372), DCCC Radiotherapy - The Danish National Research Center for Radiotherapy, Danish Cancer Society (grant no. R167-A10976), INSPIRE (European Union’s Horizon 2020 research and innovation program under grant agreement no 730983), A.P. Moller Foundation, and Helga and Peter Korning Foundation.