The aim of this study was to set up the appropriate geometry to perform a high-precision irradiation, based on tumor activity (TA). The elaboration of a new treatment protocol based on TA required a specific geometry in order to use this type of irradiation. Using a treatment planning system TPS and two head and neck phantoms specially created, we have performed TPS characterization according to different treatment plans. Two models were created and used: a simplistic and an anatomical model. Our results showed that high-precision radiotherapy in limited zones is possible with intensity modulated radiation therapy (IMRT) when several conditions such as location, number of organs at risk (OAR's), distance between planning target volume (PTV) and OAR, presence, volume and location of the TA, number of fields are met. In order to use this irradiation method adapted to the TA, a precise geometry will be necessary. However such high total and fractionated doses should be carefully evaluated before being prescribed clinically.