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Despite advancements in functional imaging, the resolution of modern techniques is still limited with respect to the tumour microenvironment. Radiotherapy strategies to counteract e.g., tumour hypoxia based on functional imaging therefore carry an inherent uncertainty that could compromise the outcome of the treatment. It was the aim of this study to investigate the impact of variations in the radiosensitivity of hypoxic tumours in small regions in comparison to the resolution of current imaging techniques on the probability of obtaining tumour control. A novel in silico model of three-dimensional tumour vasculature and oxygenation was used to model three tumours with different combinations of diffusion-limited, perfusion-limited and anaemic hypoxia. Specifically, cells in the transition region from a tumour core with diffusion-limited hypoxia to the well-oxygenated tumour rim were considered with respect to their differential radiosensitivity depending on the character of the hypoxia. The results showed that if the cells in the transition region were under perfusion-limited hypoxia, the tumour control probability was substantially lower in comparison to the case when the cells were anaemic (or under diffusion-limited hypoxia). This study therefore demonstrates the importance of differentiating between different forms of hypoxia on a scale currently unattainable to functional imaging techniques, lending support to the use and importance of radiobiological modelling of the cellular radiosensitivity and response at microscale., (© 2022. Springer Nature Switzerland AG.)

Background/aim: The aim of this study was to investigate radiation-induced tumour vascular damage and its impact thereof on the outcome of stereotactic body radiotherapy (SBRT)., Materials and Methods: Vessel densities in animal tumours before and after a single dose of 20 Gy were quantified and used as input for simulations of three-dimensional tumours with heterogeneous oxygenation. SBRT treatments of the modelled tumours in 1-8 fractions were simulated. The impact of vessel collapse on the outcome of SBRT was investigated by calculating tumour control probability (TCP) and the dose required to obtain a TCP of 50% (D 50 )., Results: A radiation-induced increase of acute hypoxia in tumours during SBRT treatment could be simulated based on the experimental data. The D 50 values for these tumours were higher than for the simulated tumours without vessel collapse., Conclusion: The vascular changes after high doses of radiation could compromise the outcome of SBRT by increasing tumour hypoxia., (Copyright© 2019, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Background/aim: This study investigated the impact of temporary vascular collapse on tumour control probability (TCP) in stereotactic body radiotherapy (SBRT), taking into account different radiosensitivities of chronically and acutely hypoxic cells., Materials and Methods: Three-dimensional tumours with heterogeneous oxygenation were simulated assuming different fractions of collapsed vessels at every treatment fraction. The modelled tumours contained a chronically hypoxic subvolume of 30-60% of the tumour diameter, and a hypoxic fraction ≤5 mm Hg of 30-50%. The rest of the tumours were well-oxygenated at the start of the simulated treatment., Results: For all simulated cases, the largest reduction in TCP from 97% to 2% was found in a tumour with a small chronically hypoxic core treated with 60 Gy in eight fractions and assuming a treatment-induced vascular collapse of 35% in the well-oxygenated region., Conclusion: The timing of SBRT fractions should be considered together with the tumour oxygenation to avoid loss of TCP in SBRT., (Copyright© 2019, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)