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Oxygen Depletion From Proton Spot Scanning: Could Delivery-Optimisation Meet the Conditions for FLASH?

B Rothwell1*, M Lowe2,1, N Kirkby1, M Merchant1, A Chadwick1, R Mackay2,1, K Kirkby1, (1) Division of Cancer Sciences, The University of Manchester, Manchester, UK (2) Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
The revival of FLASH radiotherapy has gained widespread interest in recent years, with promise of improved normal-tissue protection compared to conventional irradiation and no compromise on tumour growth restraint. The transient hypoxic state induced by depletion of oxygen at high dose rates provides a well-accepted explanation. Combining this apparent sparing effect with the often-superior dose conformality of proton spot-scanning treatments is an attractive area of research. However, there exists a lack of understanding of the oxygen depletion effects taking place during conventional spot scanning, where dose rates from spot delivery at particular locations within the patient could meet the criteria for the FLASH effect.

Methods:
Cellular automaton techniques have been combined with a model of clinical spot scanning, to solve the complex, multi-scale problem of oxygen diffusion and reaction in cells, and the spatially- and temporally-varied irradiation that results in their depletion of oxygen.

Results:
In silico results so far have demonstrated the relevance in timescales for both models. A significant decrease in oxygen levels, and therefore radiosensitivity, is able to be maintained for a substantial duration of the spot-scanning treatment for cells that are sufficiently far from a capillary. This effect is especially important for cells at shallower depths in a spot scanning treatment, where normal tissue is likely to reside.

Conclusion:
Proton spot scanning is particularly under-explored with regards to FLASH, with its spatial variation and timing considerations making it unique amongst other modalities. This model provides a tool to explore the optimisation of its delivery to utilise any possible sparing effect that may be observed from oxygen depletion. This will further tighten the link between FLASH research and its potential clinical implementation.

Download ePoster [PDF]

Keywords

Protons, Modeling, Hypoxia

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – Development (new technology and techniques)

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