The rarity of tumour cells in the circulation of cancer patients has required various enrichment techniques in order to facilitate their counting and investigation. The circulating tumour cells (or CTCs) can be enriched based on size, marker expression or other physical properties, helping to remove the overwhelming background of normal blood cells. This however, risks missing CTCs which do not meet the pre-determined criteria and permanently losing atypical or damaged CTCs, which may have prognostic significance. To overcome this problem, we are using a high-throughput microscope-based examination of CTCs in the blood of non-small cell lung cancer (NSCLC) patients undergoing curative-intent radical radiotherapy at the Peter MacCallum Cancer Centre. By immediate fixation of blood samples, minimal processing and attaching the whole population of blood cells as a monolayer over several microscope slides, we are able to use a digitising fluorescence microscope to image all cells within the blood based on their marker expression. Multi-channel image analysis is able to automatically find rare candidate CTCs from among the millions of blood cells, and these parameters can be changed later to re-analyse images to find novel expression patterns. The choice of markers is flexible enough to find non-classical CTCs even where patient’s tumour phenotypes differ, and to enable additional markers to be added for immunophenotyping, for example PDL1. Thus, clustered tumour cells, CTCs caught inside microemboli, those of smaller size and those with non-canonical marker expression are all captured in an unbiased way, which can be re-analysed in a permanent record of a patient’s blood cell population as our understanding of tumour metastasis evolves. The kinetics of CTC mobilisation during radiotherapy (Martin, 2017) will ultimately be correlated with patient outcomes and radiological imaging data to determine its prognostic significance.