Eye tracking based navigation for proton beam therapy

Abstract

Cancers of the eye, so-called ocular tumors, are a severe disease that may lead to blindness or even death if left untreated. A possibility to remove the tumor from the body of the patient is a so-called enucleation surgery, the removal of the eye. However, it is a drastic action and oncologists usually try to avoid it. Another treatment option is the therapy with protons. The actual proton therapy to treat ocular tumors is very successful and non-invasive. However, the navigation method that is applied for this kind of therapy requires a pre-treatment surgery, where radio-opaque clips are sutured onto the affected eyeball. These clips are used during the actual treatment to align the diseased eye with two orthogonal X-ray units. Hence, the overall treatment is invasive. The work at hand presents an alternative, completely non-invasive navigation method based on eye tracking technology. We present a new treatment scheme with a first eye tracking prototype integrated into the treatment facility at Paul Scherrer Institute (PSI). This system together with a patient specific eye model enables the medical physicist to align the patient’s eye such that the tumor gets accurately treated by the proton beam. Further, we present a second, improved eye tracking system. This time, we propose a stereo eye tracker, which only uses one physical camera to save physical space. We combine a stereo eye tracking algorithm with a clever arrangement of two planar mirrors and a single camera to get high accuracy, precision, and a compact design altogether. Finally, we present a method to quantitatively evaluate the proposed navigation system. Verifying the accuracy of the location estimate of a volunteer’s eye center is not easily possible. This is because the eye center is an intangible point, that does not correspond to an anatomical structure. Our evaluation method is based on an eye phantom on microstages and a corresponding kinematic model. Our research and development may lead to an ocular tumor treatment which will be safer, more cost-effective, and more accessible to patients suffering from this serious disease.