Radiotherapy for age-related macular degeneration: no more pilot studies please

Goverdhan, Srini; Gibbs, Frederic A.; Lotery, Andrew

doi:10.1038/sj.eye.6701744

Cited by 4 publications

(2 citation statements)

References 48 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[12][13][14][15][16][17][18] An analysis of patients treated with proton therapy was conducted in which the authors deemed this treatment option unacceptable due to the high risk of radiation retinopathy. 12 Another study using GKS included ten patients with CNV treated via a single-fraction 10 Gy dose to the macula.…”

Section: Introductionmentioning

confidence: 99%

Dosimetry characterization of a multibeam radiotherapy treatment for age‐related macular degeneration

Lee

Chell²,

Gertner³

et al. 2008

Medical Physics

View full text Add to dashboard Cite

Age-related macular degeneration (ARMD) is a major health problem worldwide. Advanced ARMD, which ultimately leads to profound vision loss, has dry and wet forms, which account for 20% and 80% of cases involving severe vision loss, respectively. A new device and approach for radiation treatment of ARMD has been recently developed by Oraya Therapeutics, Inc. (Newark, CA). The goal of the present study is to provide a initial dosimetry characterization of the proposed radiotherapy treatment via Monte Carlo radiation transport simulation. A 3D eye model including cornea, anterior chamber, lens, orbit, fat, sclera, choroid, retina, vitreous, macula, and optic nerve was carefully designed. The eye model was imported into the MCNPX2.5 Monte Carlo code and radiation transport simulations were undertaken to obtain absorbed doses and dose volume histograms (DVH) to targeted and nontargeted structures within the eye. Three different studies were undertaken to investigate (1) available beam angles that maximized the dose to the macula target tissue, simultaneously minimizing dose to normal tissues, (2) the energy dependency of the DVH for different x-ray energies (80, 100, and 120 kVp), and (3) the optimal focal spot size among options of 0.0, 0.4, 1.0, and 5.5 mm. All results were scaled to give 8 Gy to the macula volume, which is the current treatment requirement. Eight beam treatment angles are currently under investigation. In all eight beam angles, the source-to-target distance is 13 cm, and the polar angle of entry is 300 from the geometric axis of the eye. The azimuthal angle changes in eight increments of 45 degrees in a clockwise fashion, such that an azimuthal angle of 0 degreee corresponds to the 12 o'clock position when viewing the treated eye. Based on considerations of nontarget tissue avoidance, as well as facial-anatomical restrictions on beam delivery, treatment azimuthal angles between 135 degrees and 225 degrees would be available for this treatment system (i.e., directly upward and entering the eye from below). At beam directions approaching 225 degrees and higher, some dose contribution to the optic nerve would result under the assumption that the optic nerve is tilted cranially above the geometric axis in a given patient, a feature not typically seen in past studies. A total treatment dose of 24 Gy would be delivered in three 8 Gy treatments at these selected azimuthal angles. Dose coefficients, defined as the macula radiation absorbed dose per unit air kerma in units of Gy/Gy, were 16% higher for 120 kVp x-ray beams in comparison to those at 80 kVp, thus requiring only 86% of the integrated tube current (mAs) for equivalent dose delivery. When 0.0, 0.4, and 1.0 mm focal spot sizes were used, the dose profiles in the macula are very similar and relatively uniform, whereas a 5.5 mm focal spot size produced a more nonuniform dose profile. The results of this study dem onstrate the therapeutic promise of this device and provide important information for further design and clinical implementation for radio...

show abstract

Section: Introductionmentioning

confidence: 99%

Dosimetry characterization of a multibeam radiotherapy treatment for age‐related macular degeneration

Lee

Chell²,

Gertner³

et al. 2008

Medical Physics

View full text Add to dashboard Cite

show abstract

“…8 These treatments include both intraocular, epiretinal delivery of beta radiation 9,10 and external radiations including proton therapy, Gamma Knife radiosurgery ͑GKS͒, and high-energy external beam radiotherapy. [11][12][13][14][15][16][17] Research for a treatment option involving kilovoltage stereotactic radiosurgery is currently under development that addresses many of the inherent limitations of other systems used in the past to treat AMD. 18 The goal of the radiotherapy treatment is to destroy the leaky vasculature while minimizing radiation injury to surrounding tissues.…”

Section: Introductionmentioning

confidence: 99%

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

Hanlon

Lee

Chell³

et al. 2009

Med. Phys.

View full text Add to dashboard Cite

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.

show abstract