An Overview Of Alignment Issues For In Vivo Image Guided Protontherapy

Protontherapy is based on physical properties of ion beams which allow the delivery of high radiation doses at very precise location in the body of the patient. The treatment planning aims at maximizing the delivery in the target volume while avoiding any organs at risk. The treatment is generally planned prior the treatment, and the patient is aligned in the treatment room on the basis of fiducial markers. However, the alignment of the patient may suffer from lack of precision and moreover, the body of the patient may vary between the time of imaging for planning and the time of treatment in the protontherapy room. More precise protontherapy and adaptive treatment which can track modifications of the body and the treatment of mobile tumors require the design of in vivo imaging systems to be deployed in the treatment room. The goal of this paper is to overview the present and future development of in-vivo image guided protontherapy and to give some image processing related challenges. The technique mostly used today is to take 2 orthogonal X-ray views of the patient. It requires an efficient 2D-3D coregistration procedure but is quite easy to deploy. Cone Beam CT is a next step which allows the capture of an in-vivo 3-D view on which the 3-D planning can be registered. The ultimate goal is to develop 4-D imaging techniques suited for the treatment of mobile tumors, for the cases of lung cancer. The development of new detectors will allow to validate the treatment by an "a posteriori" validation of the dose delivery in the body.