A patient sitting in an adjustable chair in preparation for treatment of the eye.

• ocular melanomas
• angiomas
• hemangiomas
• metastatic lesions contained within the eye

Tumors located in the very back of the eye and under orbital muscles are very difficult to treat with plaque therapy because it is not possible to suture the plaque over the tumor without causing significant damage to the muscles or nerves. Proton Ocular Radiotherapy does not require covering the tumor with a solid plaque and therefore its application is much less flexible.

The success of Proton Ocular Radiotherapy (PORT) treatments is very impressive with approximately 3,500 patients treated with a 5-year local control of 98% and 95% for small/medium and large ocular melanomas, respectively. The overall 5-year metastases-free survival is 80% with a better outcome for smaller lesions (95%) and a worst outcome (60%) for larger lesions. Improvement of vision depends on the original condition of the eye, tumor size and location and whether there is retinal detachment.

Planning & Treatment Process (PORT)

Most proton ocular radiotherapy patients are referred in collaboration with the Massachusetts Eye and Ear Infirmary (MEEI). Pre-treatment assessments involve a series of ophthalmologic studies including but not limited to fluorescein angiography and ultrasound imaging. In the angiography study an ophthalmologist injects a dye (fluorescein) into the veins of the arm. As the dye travels through the vessels of the eye a camera equipped with special filters is used to photograph the back of the eye. In the ultrasound imaging study mild anesthetic eye drops are used so that a probe coated with a sterile gel can be pressed against the eye. Sound waves are generated from the probe and reflected from the eye. The reflected signal is then fed to a computer, which generates images of the internal topography of the eye.

	A: A wide-angle photograph of the eye showing a tumor at the left of the image. The light colored circle located on the right side of the image is the optic nerve with a diameter around 2-3mm.
	B: Fluorescein angiography images combined to create a composite view of the back of the eye. The optic nerve is the circular structure at the top left of the image where much of the vasculature originates. The tumor is located at the bottom right of the image.
	C: An ultrasound image showing a cross-sectional view of a choroids melanoma measuring approximately 8x12mm.

The mask and bite mold minimize motion of the head ensuring that the treatment margins are reduced as much as possible.

Once accepted for proton ocular radiotherapy, patients are scheduled at Massachusetts Eye & Ear Institute (MEEI) for a surgical procedure that involves suturing tiny tantalum clips on the surface of the eye. During the surgery the ophthalmologist illuminates the front of the eye. Because the tumor is less opaque then the eye it creates a shadow on the outer surface of the eye. Four clips are sutured along the periphery of the tumor. Measurements describing the location of the clips with respect to various reference points are obtained by the MEEI ophthalmologist and recorded by a dosimetrist or physicists from the Francis H. Burr Proton Therapy Center. Depending on the diagnosis and location of the tumor some patients may not require surgical implantation of the tantalum markers.

A few days following the surgery patients are seen by a radiation oncologist at Massachusetts General Hospital Cancer Center. A customized mask and bite mold are then fabricated in preparation for the proton radiation planning process. The purpose of the mask and bite mold is to ensure that patients remain as still as possible during the treatment enabling the protons to be targeted to an area that has very little motion, thereby minimizing the need to treat a larger area which encompasses both the planned target and its motion.

Proton ocular radiotherapy patients who have had the tantalum implants undergo a treatment-planning simulation. The simulation involves sitting in the treatment chair and staring at a blinking red light that is fixed in space. Orthogonal (at right angles) x-rays are obtained for three fixation positions. The x-ray images show the tantalum clips very well.

	A: An x-ray image of an eye with tantalum clips. The image is taken from the front of the eye. Three of the clips look flat because they are at the side edge of the eye. Each tic-marks represent 1 mm.
	B: An x-ray image of the same eye as above with tantalum clips. The image is taken from the side of the eye with the eye unmoved from the first image (A). Three of the clips look flat because they are at the side edge of the eye. Using a 3D eye model and the coordinates of the clips obtained from a few pairs of x-ray images ensures that they eye is tracking reliably.

The planning process involves combining information from the x-ray, ultrasound and angiography images to model the tumor and its location on the eye. The radiation oncologist in collaboration with the ophthalmologist, the dosimetrists, physicists and ophthalmologic technician outlines the tumor and determine the optimal direction for the proton treatment. The radiation oncologist then defines the dose to be delivered.

Once a plan is finalized and approved by the radiation oncologist and the ophthalmologist special hardware is fabricated for each treatment direction to be used. A thorough quality assurance process ensures that every device being made adheres to the intended specifications. Before devices are used for treatment, measurements ensure that the computer plan is properly modeled.

The whole pre-planning process from surgery, immobilization to the first treatment typically takes a few days to a week.

Proton ocular radiotherapy treatment sessions usually last between 10 and 15 minutes. As the treatment session starts the patient is greeted by radiation therapists. Mild anesthetic eye drops are inserted into the eye. The therapists assist the patients into the treatment chair and into their mask and bite mold, which is attached to the treatment apparatus. The patient is positioned in the treatment position. Eyelid retractors are used to minimize their irradiation as much as possible. With the retractors in place the patient is asked to stare at a fixed blinking red light. X-ray images are acquired and adjustments are made to correct any misalignment. With the patient in the treatment position the therapists request for radiation from the delivery system. Radiation is delivered to one of three treatment rooms sequentially therefore small delays are possible from the time radiation is requested to the time it is ready to be delivered. Only when the delivery system is ready to deliver radiation will the therapists take a final confirming x-ray and leave the treatment room. Final radiation parameters are confirmed and the radiation is delivered while the therapists monitor the patient’s eye position via closed circuit video cameras.

Physicians and nurses regularly examine patients throughout the proton ocular radiotherapy treatment course to monitor progress and address any concerns patient may have. Follow-up instructions are provided to monitor patient progress following the treatment course.