Kilovoltage stereotactic radiosurgery for age-related macular degeneration: Assessment of optic nerve dose and patient effective dose

Abstract

Age-related macular degeneration (AMD) is a leading cause for vision loss for people over the age of 65 in the United States and a major health problem worldwide. Research for new treatments of the wet form of the disease using kilovoltage stereotactic radiosurgery is currently underway at Oraya Therapeutics, Inc. In the present study, the authors extend their previous computational stylized model of a single treated eye [Med. Phys. 35, 5151-5160 (2008)] to include full NURBS-based reference head phantoms of the adult male and female using anatomical data from ICRP Publication 89. The treatment was subsequently modeled in MCNPX 2.5 using a 1 x 1 x 1 mm3 voxelized version of the NURBS models. These models incorporated several organs of interest including the brain, thyroid, salivary glands, cranium, mandible, and cervical vertebrae. A higher resolution eye section at 0.5 x 0.5 x 0.5 mm3 voxel resolution was extracted from the head phantoms to model smaller eye structures including the macula target, cornea, lens, vitreous humor, sclera/retina layer, and optic nerve. Due to lack of literature data on optic nerve pathways, a CT imaging study was undertaken to quantify the anatomical position of the optic nerve. The average absorbed doses to the organs of interest were below generally accepted thresholds for radiation safety. The estimated effective dose was 0.28 mSv which is comparable to diagnostic procedures such as a head radiograph and a factor of 10 lower than a head CT scan.

Three-Year Follow-Up of a Pilot Study of Ranibizumab Combined With Proton Beam Irradiation as Treatment for Exudative Age-Related Macular Degeneration

“…20 Recently, a commercial company, Oraya Therapeutics, Inc (Newark, CA), has introduced the IRay system, a stereotactic system for delivering radiotherapy for eAMD. 21,22 The results of a Phase 1 study show no safety concerns after 12 months at a dose of 24 Gy with stabilization of vision in 96% of eyes with 52% of eyes requiring no additional anti-VEGF therapy (Kaiser et al, abstract presented at Retina Congress, 2010). This system uses a 100-kV x-ray source, which has a depth of maximum dose at the surface and 52% dose at 25 mm, at the depth of macula.…”

“…Given this target treatment size, 50% of the retina will receive 0.47 Gy and 50% of the ciliary body will receive 0.64 Gy. 22 In addition, the mean dose to the lens, optic disk, and nerve would be 0.124, 0.612, and 0.2 Gy, respectively. 22 A comparable-size single-beam proton beam treatment (PBT) was used to treat Subject 3 in our study.…”

Safety Testing of Epimacular Brachytherapy With Microperimetry and Indocyanine Green Angiography

“…The result of this study is nonetheless as expected, in that radiation and PDT produce a therapeutic effect in very different ways, and the dose delivered is much lower than the anticipated threshold for choroidal damage (Table 4). 2,[19][20][21][22][23] It should be noted that retinal damage from radiotherapy may not manifest in the first year after the treatment, and the protocol has been designed for assessments up to 3 years of follow-up. Although ICG angiography may be able to detect extensive damage to the larger choroidal vessels, it may be less sensitive in detecting subtle perfusion defects in the choriocapillaris.…”

Brachytherapy in Neovascular AMD

“…An active suction apparatus along with infrared markers tracks the eye in the X, Y, and Z planes or rotational angles. The device delivers the full dose to the plane of the macula (which is situated 150 mm from the robotically positioned and tracked X-ray tube aperture) within a 4-mm-diameter spot size [72][73][74][75]. Fig.…”