Relative peripheral dose at IMRT- A comparison between Siemens Oncor and Artiste

摘要

The aim of this work was to investigate how the relative peripheral dose (RPD) outside the primary treatment field changes in IMRT in connection with the use of either the 82-leaf MLC or the 160-leaf MLC from Siemens. 9-beam plans based on the CT data set of an acrylic phantom for 6MV photon energy were calculated for the Oncor and Artiste linacs in such a way as to get nearly identical DVHs for the artificial PTV- and OARs. Horizontal and vertical dose profiles inside the phantom were measured using thermoluminescent detectors TLD700 (rods). The measured dose values were normalized to lOGy median dose in the PTV. With increasing distance from the isocentre the RPD follows a slightly exponential decrease. On average, values for the 160MLC are 15% lower than those of the 82MLC up to a distance of 23.5cm from isocentre. This is attributed to the 2cm thicker MLC material which absorbes headscatter. Based on these observations it can be stated that the Artiste with the new MLC produces less peripheral dose and offers an improved treatment of patients with IMRT.