The majority of children with retinoblastoma manifest at the stage when the tumor is confined to the eye. About 90–95% of children in developed countries are present with intraocular retinoblastoma while 60–70% present at this stage in the developing world. Diagnosis of retinoblastoma at this stage and appropriate management are crucial to reduce mortality, save the eye and possibly save the remaining vision.
Cryotherapy is performed for small equatorial and peripheral retinal tumors measuring up to 4mm in basal diameter and 2mm in thickness. Triple freeze thaw cryotherapy is applied at 4–6week intervals until complete tumor regression. Cryotherapy produces a scar much larger than the tumor. Complications of cryotherapy include transient serous retinal detachment, retinal tear and rhegmatogenous retinal detachment. Cryotherapy administered 2–3h prior to chemotherapy can increase the delivery of chemotherapeutic agents across the blood retinal barrier and thus has a synergistic effect.
Laser photocoagulation is used for small posterior tumors 4mm in basal diameter and 2mm in thickness. The treatment is directed to delimit the tumor and coagulate the blood supply to the tumor by surrounding it with two rows of overlapping laser burns. Complications include transient serous retinal detachment, retinal vascular occlusion, retinal hole, retinal traction, and preretinal fibrosis. It is less often employed now with the advent of thermotherapy. In fact, laser photocoagulation is contraindicated while the patient is on an active chemoreduction protocol.
In thermotherapy, focused heat generated by infrared Otamixaban is applied to tissues at subphotocoagulation levels to induce tumor necrosis. The goal is to achieve a slow and sustained temperature range of 40 to 60°C within the tumor, thus sparing damage to the retinal vessels. The standard treatment for transpupillary thermotherapy involves using infrared radiation from a semiconductor diode laser delivered with a 1300-micron large spot indirect ophthalmoscope delivery system. Alternatively transpupillary delivery can be performed through an operating microscope or via a transscleral route with a diopexy probe. Thermotherapy provides satisfactory control for small tumors – 4mm in basal diameter and 2mm in thickness. Complete tumor regression can be achieved in over 85% of tumors using 3–4 sessions of thermotherapy. The common complications are focal iris atrophy, focal paraxial lens opacity, retinal traction and serous retinal detachment.
Plaque brachytherapy involves the placement of a radioactive implant on the sclera corresponding to the base of the tumor to trans-scleral irradiation of the tumor. Commonly used radioactive materials include Ruthenium 106 and Iodine 125. The advantages of plaque brachytherapy are focal delivery of radiation with minimal damage to the surrounding normal structures, minimal periorbital tissue damage, absence of cosmetic abnormality because of retarded bone growth in the field of irradiation as it occurs with external beam radiotherapy, reduced risk of second malignant neoplasm and shorter duration of treatment. Plaque brachytherapy requires precise tumor localization and measurement of its basal dimensions. The tumor thickness is measured by ultrasonography. The data are used for dosimetry on a three-dimensional computerized tumor modeling system. The plaque design is chosen depending on the basal tumor dimensions, its location, and configuration. The dose to the tumor apex ranges from 4000 to 5000cGy. The plaque is sutured to the sclera after confirming tumor centration and is left in situ for the duration of exposure, generally ranging from 36 to 72h. The common complications are radiation papillopathy and radiation retinopathy.
External beam radiotherapy
External beam radiotherapy was the preferred form of management of moderately advanced retinoblastoma in the late 1900s. Presently it is indicated in eyes where primary chemotherapy and local therapy had failed, or rarely when chemotherapy is contraindicated.