[Use of multimodality imagery in radiotherapy].
The quality of treatment that one can realize today in conformal radiotherapy, can be reached only if one has access to 3D imaging allowing a precise determination of the volume of the organs at risk and of the GTV. For this reason, one has access to anatomical imaging, CT or MRI, and functional and metabolic imaging, PET or SPECT imaging. CT gives the electronic density of the tissues, which is essential to ensure a very precise calculation of dose distribution. Its insufficiency in the visualization of the tumor and some anatomical structures makes necessary the registration of these images with MRI of which distortions are sufficiently weak to be usable in radiotherapy. The registration will be usable only if images of each modality are realized with the patient in treatment position, except for brain, where only CT, on which is based the registration, must be done in treatment position. At least, if one wants to visualize the active parts of a tumor or to make the difference between fibrosis and tumor left or recurrence after radiotherapy or chemotherapy, it is necessary to use PET or SPECT. To define correctly the CTV using these images, one must realize the anatomical localization of the metabolic abnormalities, which they highlight with a registration based on CT or MRI. The difficulties to obtain the registration of these images led the manufacturer to propose mixed machines allowing to realize, at the same time, a CT imaging and a PET or a SPECT imaging with the patient in treatment position.
Boisserie
G
G
Service de radiothérapie, hôpital Pitié-Salpêtrière, 47-83, boulevard de l'hôpital 75013 Paris, France. gilbert.boisserie@psl.ap-hop-paris.fr
Hasboun
D
D
D003952:Diagnostic Imaging / Q000379:methods*; D006801:Humans; D008279:Magnetic Resonance Imaging; D009369:Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D020266:Radiotherapy, Conformal / Q000379:methods*; D014055:Tomography, Emission-Computed; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed