X-ray imager for in vivo dosimetry in radiotherapy

Project partners: Dosisoft, Medasys, Institut Curie, AP-HP, CEA, CNRS, INSERM, INRIA, Telecom Paris

MINIARA(*) is a collaborative project in which several partners are working together to develop a 3rd generation oncological imaging workstation. The aim of these manufacturers (Dosisoft and Medasys), public research laboratories (INSERM, CNRS, INRIA, ENST and CEA) and doctors and physicians from Paris public hospitals (Pitié-Salpêtrière and Tenon) is to improve on the use of imaging techniques in cancer therapy so that it is easier to schedule, more accurately targeted and more rapid.
LIST manages the dosimetrics imaging subgroup working on the development of software tools to properly utilize the digital images acquired through EPID (Electronic Portal Imaging Device) X-ray imagers used in transit dosimetry. The stakes are high, as only EPID units can currently be used to check in vivo the dose actually given to a patient during therapy.
Two of LIST’s accelerators, Delphes and SAPHIR, were used in several characterization campaigns performed on an EPID unit with a fluorescent display and a CCD camera, both of which are sold by FIMEL. These measurements have been used to study the EPID’s response to different acquisition parameters: beam size, photon energy, integration time and dose rate. The EPID’s linear operating range and dose linearity have both been characterized.
The LNHB has also measured the reference dose with an ionization chamber. After the EPID images have been processed correctly, the dose profiles acquired by the EPID were compared with those acquired by the ionization chamber to check that the dose measured using the EPID equals the dose measured in water, the only radiotherapeutic reference.