AbstractID: 8105 Title: IMRT treatment at Trois-Rivières using Varian products Treatment of cancer has radically changed with the spread of Intensity Modulated Radiation Therapy (IMRT). Higher tumour doses could be given, over conventional radiation therapy, while substantially decreasing doses to normal tissues. The technologies available commercially together with the increased demand of treatment have made the number of clinics using this technology larger in the last few years. Our clinic is one of the two clinics in Quebec, Canada, which has started an IMRT treatment program this year. The first three patients treated were for nasopharynx, meningioma and oropharynx tumors. IMRT has spared substantial brain volume and parotid salivary glands. Patients have been CT-scanned with 3 mm slices (PQ 5000 CT-Sim, Marconi Medical Systems). Planning has been performed with the inverse planning module Helios of CadPlan 6.2.7 along with SomaVision 6.1 (Varian Medical Systems). Helios uses a sliding window technique. Dose modulation has been performed with the 80 leafs Millenium MLC incorporated to the head of the linear accelerator (Clinac 2100, Varian Medical Systems). A Mark II portal imager was used for patient positioning. Patient base QC is performed in order to verify the dose distributions and the MU calculations. Dose distributions of each independent field are measured with films and compared with the treatment planning software calculation, using RIT 113 film dosimetry system, version 3.13. MU calculations are verified by relative dose measurements performed with a pin-point ionisation chamber. Thermoluminescent dosimetry had also been used to validate the technique.