Another important criterion for theTCP is the tumour cell proliferation. In today’s radiotherapy planning it isalready taken into account in terms of biological effectiveness of a prescribeddose. An overall increased treatment time demands a higher overall dose tocompensate for the new tumour cells emerging during treatment (missingcitation). Experience in radiotherapy associates higher proliferation rateswith a worse therapy outcome. Higher radiation doses are required to controlrapidly proliferating tumours. Therefore varying proliferation rates within atumour volume are a motivating factor for dose painting on the basis ofproliferation biomarkers.Various PET tracers have been associated with tumour proliferation. Researchhad initially been centered on