DNA Damage Responses following Exposure to Modulated Radiation Fields

Abstract

During the delivery of advanced radiotherapy treatment techniques modulated beams are utilised to increase dose conformity across the target volume. Recent investigations have highlighted differential cellular responses to modulated radiation fields particularly in areas outside the primary treatment field that cannot be accounted for by scattered dose alone. In the present study, we determined the DNA damage response within the normal human fibroblast AG0-1522B and the prostate cancer cell line DU-145 utilising the DNA damage assay. Cells plated in slide flasks were exposed to 1 Gy uniform or modulated radiation fields. Modulated fields were delivered by shielding 25%, 50% or 75% of the flask during irradiation. The average number of 53BP1 or γH2AX foci was measured in 2 mm intervals across the slide area. Following 30 minutes after modulated radiation field exposure an increase in the average number of foci out-of-field was observed when compared to non-irradiated controls. In-field, a non-uniform response was observed with a significant decrease in the average number of foci compared to uniformly irradiated cells. Following 24 hrs after exposure there is evidence for two populations of responding cells to bystander signals in-and out-of-field. There was no significant difference in DNA damage response between 25%, 50% or 75% modulated fields. The response was dependent on cellular secreted intercellular signalling as physical inhibition of intercellular communication abrogated the observed response. Elevated residual DNA damage observed within out-of-field regions decreased following addition of an inducible nitric oxide synthase inhibitor (Aminoguanidine). These data show, for the first time, differential DNA damage responses in-and out-of-field following modulated radiation field delivery. This study provides further evidence for a role of intercellular communication in mediating cellular radiobiological response to modulated radiation fields and may inform the refinement of existing radiobiological models for the optimization of advanced radiotherapy treatment plans.

Is There More to Radiotherapy than Hitting the Target?

“…We have shown that a radiation field with many high dose gradients may have an advantage over a uniform field [2], because it is more lethal to cancer cells than to normal cells. We attribute this effect predominantly to the production, diffusion and response to radiation induced bystander signals, which is consistent with previous reports of up to 60% of cell death following irradiation being attributed to bystander effects [3,4].…”

Is There More to Radiotherapy than Hitting the Target?

“…We have shown that a radiation field with many high dose gradients may have an advantage over a uniform field [2], because it is more lethal to cancer cells than to normal cells. We attribute this effect predominantly to the production, diffusion and response to radiation induced bystander signals, which is consistent with previous reports of up to 60% of cell death following irradiation being attributed to bystander effects [3,4].The use of a radiation field that delivers a non-uniform dose with high dose gradients is not new. Spatially fractionated radiotherapy or grid therapy, delivers radiation through a collimating grid block or by using the multileaf collimator of a linear accelerator.…”

Radiation induced bystander effect and DNA damage

“…DNA damage responses following exposure to modulated radiation fields was evaluated. [50] A fibroblast cell line AG-1522B and prostate cancer cell line DU-145 was shielded 25, 50 and 75% from a dose of 1Gy to measure 53BP1 and γ-H 2 AX foci at 2mm intervals. The study reported an observation of out-of-field foci compared to the controls.…”