Our goal was to determine the extent of the CTV-PTV margin. Accuracy of patient setup was checked with daily CBCT. Two radiation oncologists performed the image matching independently. The CTV-PTV margin was calculated with the van Herk formula. The treatment plans were created with the Varian Eclipse v11 planning system, and the treatments were carried out with a Varian TrueBeam accelerator by using RapidArc technique with two full arcs. Dose constraints on the target volume and organs at risk recommended by international bodies were applied. Conformity number (CN) for PTV, V45 and V50 for organs at risk were used to assess and compare the treatment plans of RapidArc and 3D-KRT (conformal radiotherapy) techniques. The average CTV-PTV margins with or without IGRT were 0.67 cm vs. 1.53 cm, 0.66 cm vs. 1.25 cm and 0.34 cm vs. 0.98 cm in vertical, longitudinal and lateral directions, respectively. In case of daily on-line CBCT verification 0.5 cm margin can be used
