Molecular verification of stereotactic radiotherapy in rats using ATMpS1981 immunofluorescence

Stereotactic radiation therapy and radiosurgery (STS) might be useful for focused treatment in orthotopic tumor models or to evaluate normal tissues. Spatial accuracy of dose-delivery is crucial and needs to be proven. This study intended to show on a molecular level precision of STS using the radiation activated molecule phospho-serine 1981-ATM (ATMpS1981).

Wistar rats underwent MRI fused with CT for treatment with a NOVALIStrade mark (BrainLab) STS device. Rats (body weight = 350 g, respectively) were irradiated with 2 Gy to selected areas of the brain, the lung, the liver, and the pancreas. Animals were sacrificed 1h after STS and organs were explanted for pathohistological workup. Coronal HE-stained sections of treated organs were matched with coronal MRI and CT reconstructions and isodose distributions of STS. Immunofluorescence signal expression in the nuclei after incubation with anti-ATMpS1981 antibody was compared to the target volume of STS.

Three consecutive animals were treated with STS using 2 Gy single dose which resulted in no apparent changes on HE staining but obvious immunofluorescence signals in irradiated regions. In concordance with isodose distributions these signals had a maximum intensity within the 90% isodose and gradually decreased to a background level with very low nuclear immunofluorescence signals for ATMpS1981. These results were consistent throughout all of the four investigated organs (brain, lung, liver, pancreas) and could be repeated in all of the investigated animals.

ATMpS1981 immunofluorescence confirms accuracy of STS allowing for partial organ irradiation in small animals. It can be used for quality assurance in STS treatment of normal tissue or orthotopic tumor models.