P35. On the use of an on-line amorphous silicon detector for patient’s positioning in total body irradiation

Abstract

Introduction In 1994, to improve the quality of total body irradiation (TBI) treatments and reduce treatment times, we developed a dedicated chair to treat patients in a seating position [1] . In 2015, we have replaced films with an on-line amorphous silicon detector in order to be even faster and precise. Materials/Methods The verification of the correct position of lung block shields, typically used to reduce lung doses, was initially made using silver halide films and later on using digital film (KODAK ACR-2000i). Time between one image acquisition and film development was of the order of 3-4 min. At our last linac replacement, we recovered a Varian Medical Systems electronic portal imaging device (EPID) to try to use it as replacement of films for on-line imaging TBI. The EPID is mounted against the wall of the treatment bunker via a dedicated mobile support. Its displacement in and out of the field is made remotely at the linac console. Image acquisition needs only 1 monitor unit. This system is coupled and controlled by the linac via a switch allowing it to be used in place of the MV EPID, though using a separate dedicated imaging station. Images are reviewed on the fly by the doctor and later exported on the R&V system in the patient’s image folder. Results With this new imaging system, the visualization of the correct lung block position is more rapid and of better quality than with the previous systems. This rapidity allows: to more easily re-acquire images for optimal lung shielding, to monitor the patients during as well as at the end of the treatment. Treatment session time is reduced by 5–10 min or more, depending on the number of images acquired. These control images are also available in the digital folder of the patient for revision during board meetings. Conclusions This system allows for a better positioning of lung blocks before treatment and mostly reduces treatments times, with a better comfort of the patient. Next step should be to improve the EPID radiation hardness to implement cine mode image acquisition. Such a system could also be used to monitor other TBI treatment configurations.