Malnutrition and weight loss are prevalent in non-small cell lung cancer (NSCLC) patients receiving radiotherapy and are associated with poorer patient and clinical outcomes. The identification of factors present at the onset of radiotherapy treatment that predict patients at risk of clinically significant weight loss (>5%) is vital in order to direct resources towards early intervention in patients at high nutritional risk prior to the onset of malnutrition. In a series of studies, the clinical, treatment, and radiotherapy dosimetric factors predictive of clinically significant weight loss (>5%) have been identified. The development and validation of preliminary models to screen NSCLC patients at high nutritional risk from radiotherapy treatment will be presented.