Automated lattice radiation therapy treatment planning personalised to tumour size and shape
Mathieu Gaudreault, Kelvin K. Yu, David Chang, Tomas Kron, Nicholas Hardcastle, Sarat Chander, Adam Yeo, Physica Medica, Volume 125, 2024, 104490, ISSN 1120-1797,
https://doi.org/10.1016/j.ejmp.2024.104490
What inspired this study?
This study addresses the personalisation of the lattice radiation therapy (LRT) technique for easy implementation in a conventional radiotherapy linear accelerator. This technique involves irradiation of several boost regions in the tumour, in opposition with traditional uniform target coverage. It is usually prescribed to palliative patients with large tumours with cytoreduction (reduction in tumour volume) intent. When this treatment is needed, patients are generally in pain and time is an issue. However, preparing an LRT treatment plan manually takes a lot of time as each boost region must be contoured and managed individually during dose optimisation. Motivated by a former study of our research group automating the technique (10.1016/j.ejmp.2024.104490), we hypothesised that the overall technique could be personalised to the tumour volume to quickly generate treatment plans so that LRT could become an attractive option for clinical routine.
What were the key challenges in this research?
The underlying physiological mechanisms of the LRT technique are unknown. However, it is believed that irradiation triggers an immune response resulting in tumour cytoreduction. Therefore, a significant fraction of the tumour volume must be spared from high-dose regions for the immune response to occur.
However, parameters in terms of vertex size and centre-to centre distance leading to the optimal response are yet unknown in the literature. Consequently, the automation could not have been driven by gold standards based on clinical evidence.
What are the key takeaways from this study?
As we were missing clinical guidance, we explored the parameter space by varying the size and spacing of boost regions. We further devised a score based on the resulting dosimetry to judge the resulting plan quality. Plans with dosimetry clinically satisfactory were achieved with a size of 1.5 cm of diameter and 2.5 – 5 cm of centre-to-centre distance. Furthermore, a follow-up study from our research group demonstrated that satisfactory dosimetry could be achieved with a few boost regions (< 15), which might allow manual planning in centres with low scripting ability.
How does this research impact the future?
Personalising the LRT technique allowed the design of clinical trials aiming to drive the determination of parameters leading to optimal response. Cytoreduction is currently observed in around 50% of patients prescribed LRT. We hope that this number can be improved with a better understanding of the mechanisms driving the immune response, which might be correlated with the parameters used in the LRT technique.
On behalf of the lattice radiation therapy research group,Dr Mathieu Gaudreault, Senior Researcher,Peter MacCallum Cancer Centre, Melbourne, Australia
