Role of portal imaging in clinical radiotherapy: Florence experience.

A portal imaging device developed at the Netherlands' Cancer Institute (NKI) in Amsterdam was provided to the Radiotherapy Section of the University of Florence as a partner of a cooperative study on quality assurance (QUIRT) granted by the EC (AIM Project). The device was used for portal imaging in 30 patients treated for tumors of different sites (5 rectum, 6 prostate, 5 Hodgkin's lymphomas, 5 head and neck tumors, 9 other sites). Portal images were obtained three times per week over the whole treatment period. An off-line quantitative analysis of discrepancies with respect to the simulation image was performed for the 5 rectum cases; a similar analysis was also done on the portal images of 4 rectal cases treated at the NKI in Amsterdam. The analysis proved capable of demonstrating the existence of some systematic errors in both centres and the different level of global accuracy between them. The on-line use of the device was also able to demonstrate some major errors of patient setup during the first session, which were immediately corrected.