Eye Plaque Research Articles

Keeping an eye on the ring: COMS plaque loading optimization for improved dose conformity and homogeneity.

PurposeTo improve tumor dose conformity and homogeneity for COMS plaque brachytherapy by investigating the dosimetric effects of varying component source ring radionuclides and source strengths.Material and methodsThe MCNP5 Monte Carlo (MC) radiation transport code was used to simulate plaque heterogeneity-corrected dose distributions for individually-activated source rings of 14, 16 and 18 mm diameter COMS plaques, populated with 103Pd, 125I and 131Cs sources. Ellipsoidal tumors were contoured for each plaque size and MATLAB programming was developed to generate tumor dose distributions for all possible ring weighting and radionuclide permutations for a given plaque size and source strength resolution, assuming a 75 Gy apical prescription dose. These dose distributions were analyzed for conformity and homogeneity and compared to reference dose distributions from uniformly-loaded 125I plaques. The most conformal and homogeneous dose distributions were reproduced within a reference eye environment to assess organ-at-risk (OAR) doses in the Pinnacle3 treatment planning system (TPS). The gamma-index analysis method was used to quantitatively compare MC and TPS-generated dose distributions.ResultsConcentrating > 97% of the total source strength in a single or pair of central 103Pd seeds produced the most conformal dose distributions, with tumor basal doses a factor of 2-3 higher and OAR doses a factor of 2-3 lower than those of corresponding uniformly-loaded 125I plaques. Concentrating 82-86% of the total source strength in peripherally-loaded 131Cs seeds produced the most homogeneous dose distributions, with tumor basal doses 17-25% lower and OAR doses typically 20% higher than those of corresponding uniformly-loaded 125I plaques. Gamma-index analysis found > 99% agreement between MC and TPS dose distributions.ConclusionsA method was developed to select intra-plaque ring radionuclide compositions and source strengths to deliver more conformal and homogeneous tumor dose distributions than uniformly-loaded 125I plaques. This method may support coordinated investigations of an appropriate clinical target for eye plaque brachytherapy.

A Five-Year Study of Slotted Eye Plaque Radiation Therapy for Choroidal Melanoma: Near, Touching, or Surrounding the Optic Nerve

To evaluate slotted eye plaque radiation therapy for choroidal melanomas near the optic disc. A clinical case series. Twenty-four consecutive patients with uveal melanomas that were near, touching, or surrounding the optic disc. Slotted eye plaque radiation therapy. Recorded characteristics were related to patient, clinical, and ophthalmic imaging. Data included change in visual acuity, tumor size, recurrence, eye retention, and metastasis. From 2005 to 2010, 24 consecutive patients were treated with custom-sized plaques with 8-mm-wide, variable-depth slots. Radiation doses ranged from 69.3 to 163.8 Gy (mean, 85.0 Gy) based on delivering a minimum tumor dose of 85 Gy. All treatments were continuously delivered over 5 to 7 days. Mean patient age at presentation was 57 years. Tumors were within 1.5 mm of the optic nerve (n = 3, 13%), juxtapapillary (n = 6, 25%), touching ≥180 degrees (n = 7, 29%), or circumpapillary (n = 8, 33%). Ultrasound revealed dome-shaped tumors in 79% of patients, collar-button tumors in 17% of patients, irregular tumor in 1 patient (4%), and intraneural invasion in 2 patients. Mean initial largest basal dimension was 11.0 mm (standard deviation [SD] ± 3.5 mm; median, 11.4 mm; range, 5.9-16.4 mm). Mean initial tumor thickness was 3.5 mm (SD ± 1.7 mm; median, 3.0 mm; range, 1.4-6.9 mm). Initial visual acuities were a median 20/25 (range, 20/20 to hand motions) and decreased to a median 20/40 (range, 20/20 to no light perception). At a mean follow-up of 23 months, 12 patients required periodic intravitreal bevacizumab to suppress radiation optic neuropathy (RON) or maculopathy. To date, there has been a 100% local control rate. No patients have required secondary enucleation for recurrence or neovascular glaucoma. No patients have developed metastasis. Slotted plaque radiation therapy allows peripapillary, juxtapapilary, and circumpapillary choroidal melanomas (and a safety margin) to be included in the radiation targeted zone. Normalization of the plaque position beneath the tumor appears to increase RON and improve local control.

Dosimetry verification in eye brachytherapy using silicon pixelated detectors

Abstract This study presents a high spatial resolution dosimetry system for quality assurance of I-125 eye plaques. The system is based on a silicon pixelated detector and is capable of deriving 3D dose distributions. A simple design was implemented, incorporating a movable eye plaque in a small water phantom above the silicon Medipix2 detector. It is designed for obtaining 2D dose distributions at different depths in water, for subsequent 3D dose mapping. The effect of backscattering in a medium placed behind the Medipix2 to simulate surrounding tissue has been studied in terms of dose distribution. Additionally, two modes of acquisition, event counting mode and the more complex time-over-threshold mode, were compared to the TG-43 protocol for the determination of their suitability for dosimetry.

Erratum to: ROPES eye plaque brachytherapy dosimetry for two models of 103Pd seeds

Erratum to: ROPES eye plaque brachytherapy dosimetry for two models of 103Pd seeds

Mathematical solutions of the TG-43 geometry function for curved line, ring, disk, sphere, dome and annulus sources, and applications for quality assurance

Analytic solutions for the TG-43 geometry function for curved line, ring, disk, sphere, dome and annulus shapes containing uniform distributions of air-kerma are derived. These geometry functions describe how dose distributions vary strictly due to source geometry and not including attenuation or scatter effects. This work extends the use of geometry functions for individual sources to applicators containing multiple sources. Such geometry functions may be used to verify dose distributions computed using advanced techniques, including QA of model-based dose calculation algorithms. The impact of source curvature on linear and planar implants is considered along with the specific clinical case of brachytherapy eye plaques. For eye plaques, the geometry function for a domed distribution is used with published Monte Carlo dose distributions to determine a radial dose function and anisotropy function which includes all the scatter and attenuation effects due to the phantom, eye plaque and sources. This TG-43 model of brachytherapy eye plaques exactly reproduces azimuthally averaged Monte Carlo calculations, both inside and outside the eye.

Improved Eye Plaque Brachytherapy Dosimetry Using Monte Carlo Methods

Eye plaque brachytherapy is a sight-preserving medical procedure in which radioactive sources are reproducibly arranged within a collimating source backing and temporarily sutured to the eye. The procedure was established as an alternative to enucleation or eye removal for the treatment ocular melanoma. The 1987 Collaborative Ocular Melanoma Study (COMS) standardized this treatment technique in a prospective, randomized clinical trial; however, dose calculations were performed using simple assumptions. These assumptions used the point-source dosimetry formalism, omitted dose anisotropy, and ignored the presence of dose perturbing material heterogeneities. Monte Carlo (MC) simulations from the mid-1980s to the present have critically evaluated these assumptions and indicated where improvements in practice could be made. Various investigators have used MC to evaluate plaque design, choice of source radionuclide, X-ray fluorescence from plaque components, plaque material heterogeneity attenuation, and patient tissue heterogeneity attenuation, among others. These publications are reviewed with emphasis on clinically relevant observations. In addition, MC simulations of standard COMS eye plaques using MCNP5 are made and compared to published data using other MC codes. Good agreement is observed between radiation transport codes with differences <2%, for points within the eye globe. These results indicate that historically delivered radiation doses were systematically lower than prescribed doses. Practical considerations for implementing MC calculations in the clinic are introduced, and the need for a heterogeneity-corrected treatment planning system to ensure treatment uniformity across medical centers and for different treatment techniques is discussed.

WE‐A‐BRB‐01: Accurate Dosimetric Characterization of a Fully Loaded 20 Mm COMS I‐125 Eye Plaque Using Specially Designed GAFCHROMICTM Film

Purpose: The majority of eye plaques used in the U.S. are of Collaborative Ocular Melanoma Study (COMS) design with I‐125 brachytherapy seeds. Treatment planning is usually done using the TG‐43 formalism, not accounting for the gold alloy backing and Silastic insert, which significantly reduce the dose, as calculated by BrachyDose Monte Carlo (MC) (www.physics.carleton.ca/clrp/eye_plaque/). Dosimetric characterization of a fully loaded 20 mm COMS plaque using radiochromic film is reported. Methods: A 20 mm COMS eye plaque was uniformly loaded with 24 6711 I‐125 seeds at 6.75 U/seed. Measurements were performed using specially designed single layer GAFCHROMIC EBT1 film sandwiched perpendicular to the plaqueˈs central axis at depths 0 – 19 mm between inserts of a Solid Water “eye” phantom located at the center of a 30×30×30 cm3 full scatter Solid Water phantom. The films were calibrated using a 6711 I‐125 seed in Solid Water, applying the TG‐43 formalism. Results: Dose distributions in planes perpendicular to the central axis of the plaque are radially isotropic and uniform. Measured depth dose on central axis as well as off‐axis profiles, agree well with the results of MC. At 3 mm from the inner sclera, the measured dose rate is 12.5% lower than TG‐43 dose rate in homogenous water, similar to 11.9% for MC. The thin flexible film enabled measurements of the dose at the surface of the plaque. Results on duplicate films agree within 5.5%. Conclusions: GAFCHROMIC film in a Solid Water phantom is a convenient, accurate, and reproducible dosimeter for I‐125 eye plaque dosimetry. Dose measurements on the inner surface of the plaque enable precise assessment of the scleral dose and its homogeneity, and of the active area of the plaque for coverage determination. This work validates the MC simulations about the dose reduction effect by the plaqueˈs backing and insert.In‐Kind support of materials provided by Oncura, Inc., Arlington Heights, IL and by International Specialty Products, Inc., Wayne, NJ

SU-E-T-751: Clinical Comparison of Point Source and Line Source Approximations for I-125 Brachytherapy Seeds

Purpose: Currently, the point source approximation is used in our institution to calculate the dose distribution of I‐125 seeds. The purpose of this study was to compare the isodose distributions of both point source and line source models in prostate implant and eye plaque procedures. Methods: Using Pinnacle Planning System (V8.0m, dose grid size 2×2×2 mm3), the point source and line source models for Iodine‐125 were commissioned according to the AAPM TG43 report. Values of function g(r) and F(r, &#952;) were obtained from reference tables inTG‐43. The CTimages for 3 post‐implant prostate cases were obtained in 3mm slices. In addition, the plans for 5 different sized eye plaques (diameters 12–20 mm) were used. The point source was positioned at the center of each seed, and the orientation of the line source was defined by both ends of the seed. Dose volume histograms for the prostate, bladder, and rectum were calculated for the prostate implants, while the dose at points 5mm and 10mm from the sclera were calculated for the eye plaque cases. Results: Target prescription dose coverage for the prostate post‐implants increased by ∼4% using the line source over the point source, while mean target dose decreased by ∼9.1%. D90 increased by ∼7.5%. Mean dose to rectum increased by as much as 6.5% and mean dose to the bladder decreased as much as 4Gy in one patient. For the eye plaque cases, a significant difference in dose at 5mm and 10mm existed between the point and line source models. This discrepancy can be explained by large differences in g(r), between the two models, at small distances. Conclusions: Further investigation is required to determine the extent to which the point source approximation can be implemented in clinical settings while ignoring the discrepancy between the two models.

SU-E-T-396: Heterogeneity Effect on Dose Distributions for COMS Eye Plaques with 125I Seeds (Model I25.S16): A Radiochromic EBT Film Dosimetry Study

Purpose: To study the heterogeneity effect on dose distributions in eye phantom for COMS eye plaques with 125I seeds using radiochromic EBT film dosimetry. Methods: COMS eye plaques (14,16,18 and 20mm in size) uniformly loaded with 125I seeds (model I25.S16) were studied. EBT film (lot #36076‐003AL) was positioned in a polystyrene eye phantom above the eye plaque, in two configurations: (1) in the plaque's central plane, (2) perpendicular to the central axis at depth=5 or 12mm (from inner sclera) in the eye phantom. With the seed air‐kerma‐strengths of 2.4–4U, the exposure times (3.5–8.7h) were adjusted to deliver ∼400cGy at 5mm depth. Calibration films were irradiated by a single 125I seed at ∼5mm distance, one at a time, for doses up to 1200cGy. All films were scanned using Epson 10000XL scanner and data were analyzed using Mephysto FilmCal Mc2 software. With the established calibration curve, dose conversion was performed. Central axis depth doses and off‐axis profiles were determined. Results: The film dose data were compared with the calculated doses using Plaque Simulator v5.3.9 with homogeneous assumption (Homo) and heterogeneity correction (Hetero). The dose ratio (film/Homo) and (film/Hetero) values were obtained. The dose ratio (film/Homo) values are substantially lower than unity (mostly between 0.8 and 0.9) for all plaque sizes studied, indicating dose reduction by COMS plaque compared with homogeneous assumption. The film dose data agree with the Hetero values within the uncertainty of measurement data. Conclusions: We found significant heterogeneity effect on the 125I (model I25.S16) dose distributions in an eye for COMS plaques using radiochromic EBT film dosimetry. The film data agree with the calculated doses using Plaque Simulator with heterogeneity correction. The dose reduction effect for COMS plaques uniformly loaded with 125I seed (model I25.S16) found in this study is similar to that for other 125I seed models.

SU‐E‐T‐387: A Biologically Effective Dose Volume Histogram for Optimizing Eye Plaque Brachytherapy

Purpose: Clinical optimization of eye plaque brachytherapy is currently limited to tumor coverage, standardized prescription dosage, and dose calculations to ocular structures. The biologically effective dose (BED) of brachytherapy treatments is a function of implant duration and chosen radionuclide. A novel method would propose to evaluate eye plaque brachytherapy implants based on BED delivered to the tumor volume and surrounding normal ocular structures.Methods: Using the equation introduced by Dale for temporary low dose rate (LDR) brachytherapy implants, 16 mm COMS‐eye plaque patient DVH data were converted to biologically‐effective dose volume histograms (BEDVH). These data were calculated for Pd‐103, I‐125, and Cs‐131 for different implant durations. Therapeutic ratios were derived from comparing BED results as a function of implant duration for tumors and normal ocular structures (lens, lacrimal gland, and optic nerve). Isobiologically‐effective physical doses were created for different implant durations and radionuclides. Results: The BEDVH curves were dependent on implant duration and less sensitive to radionuclide choice. In comparison to a 7‐day implant, maximum BED for a 1‐day implant increased by a factor of 2–3 for normal ocular structures; for the tumor, maximum BED increased by a factor of 4.5. These factors decreased with increasing implant duration, and were not significantly radionuclide‐dependent. Conclusions: A method was introduced to evaluate and further optimize eye plaque dosimetry through analysis of BED delivered to the tumor and adjacent normal tissue volumes. This method is readily adaptable to other temporary or permanent brachytherapy implants in a variety of clinical situations.

SU-E-T-385: Use of a Plastic Scintillation Detector for Calibration of a P32 Dura Plaque

Purpose: Radiochromic film has been used to calibrate 32P plaques, which are used to irradiate the dura for patients with sarcomas of the spine. Although this method has been successful, it is time consuming due to the characteristics of the film. A more efficient calibration method utilizing a miniature plastic scintillation detector has been investigated for this work. This new method provides an immediate readout which can be corrected with a factor to determine dose rate. Methods and Materials: The surface dose rate for a 1 cm2 flat 2.47 mCi 32P source was measured with radiochromic film. A calibration curve for the radiochromic film was determined using a 90Sr eye plaque of known output. A plastic 2 × 2 × 4 cm mini phantom with a channel through the long dimension to accommodate the plastic scintillation detector, which has a diameter of 5.0 mm and length of 23 mm, was used to measure the count rate at the surface of the 32P source. A multiplicative correction factor for the scintillation detector readout was determined by dividing the dose rate measured by radiochromic film by the count rate measured using the scintillation detector. Results: The radiochromic film measurements yielded a surface dose rate of 2.52 Gy/min. The scintillation detector yielded an average count rate of 2.3 × 106 counts/min. The correction factor from these measurements was determined to be 1.12 × 10‐6 Gy/min. Conclusion: The use of a plastic scintillation detector versus radiochromic film for the calibration of 32P plaques will greatly decrease the calibration time by providing an immediate readout of dose rate.

SU-E-T-589: IGRT-Assisted Episcleral Eye Plaque Brachytherapy

Purpose: The goal of episcleral eye plaque brachytherapy has been to deliver a prescribed dose to the apex of an intra‐ocular malignancy. Advances in dose calculation and image guidance allow for optimal plaque treatment planning. The BEBIG Plaque Simulator™ utilizes calibrated fundus collages to more precisely localize intra‐ocular tumors volumes, thus enabling physicists to plan plaque therapies that deliver the prescribed dose to the tumor while quantifying and limiting dose to critical optical structures, including the macula, optic disc, and lens. Methods and Materials: A retrospective study of 30 patients at our institution who previously received episcleral eye plaque brachytherapy based on conventional treatment planning techniques. For each patient, the originally defined Ultrasoundtumor dimensions, plaque specifications (COMS universal or notched), and treatment times were entered into Plaque Simulator. Fundus collages were calibrated and overlaid on a retinal diagram. The tumor was placed over the delineated tumor on the fundus collage. Doses to the tumor apex, macula, optic disc, and lens were calculated using TG‐43U1 formalism after assuming correct plaque placement. Results: Localization of intra‐ocular tumors allowed for accurate plaque placement and realistic dose calculation for critical structures. Recreated plans validated the original prescriptions while elucidating doses to critical structures. Doses to the macula and optic disc have been correlated to clinical outcomes, including radiation maculopathy and optic neuropathy, in an effort to evaluate dose thresholds that can be enforced in future plaque therapies. Conclusions: The use of image guidance gives radiationoncology‐ophthalmology teams the ability to deliver plaque therapy with the intent to control the tumor and spare critical structures. Dose determination may highlight the necessity of proper plaque placement, plaque size, source strength, and carrier angle optimization to deliver the prescribed dose while reducing dose to critical structures below suggested thresholds in order to preserve vision.

ROPES eye plaque brachytherapy dosimetry for two models of 103Pd seeds

Brachytherapy dose distributions are calculated for 15mm ROPES eye plaque loaded with model Theragenics200 and IR06-(103)Pd seeds. The effects of stainless steel backing and Acrylic insert on dose distribution along the central axis of the eye plaque and at critical ocular structure are investigated. Monte Carlo simulation was carried out with the Version 5 of the MCNP. The dose at critical ocular structure by considering the eye composition was calculated. Results are compared with the calculated data for COMS eye plaque loaded with Theragenics200 palladium-103 seeds and model 6711 iodine-125 seed. The air kerma strength of the IR06-(103)Pd seed to deliver 85Gy in apex of tumor in water medium was calculated to be 4.10 U/seed. Along the central axis of stainless steel plaque loaded with new (103)Pd seeds in Acrylic insert, the dose reduction relative to water is 6.9% at 5mm (apex). Removal of the Acrylic insert from the plaque (replacing with water) did not make significantly difference in dose reduction results (~0.2%). The presence of the stainless steel backing results in dose enhancement near the plaque relative to water. Doses at points of interest are higher for ROPES eye plaque when compared to COMS eye plaque. The dosimetric parameters calculated in this work for the new palladium seed, showed that in dosimetry point of view, the IR06-(103)Pd seed is suitable for use in brachytherapy. The effect of Acrylic insert on dose distribution is negligible and the main effect on dose reduction is due to the presence of stainless steel plaque backing.

Palladium-103 eye plaque brachytherapy for primary adenocarcinoma of the ciliary body epithelium

Purpose To present an interventional case report on the use of plaque brachytherapy for adenocarcinoma of the nonpigmented ciliary epithelium. Methods and materials A 36-year-old woman with unilateral right eye pain and finger counting vision was noted to have an anterior segment intraocular mass. It extended between the iris and lens and into the pupillary aperture. High-frequency ultrasound imaging revealed a ciliary body origin. A minimally invasive biopsy technique allowed for a cytology and histopathology diagnosis of primary adenocarcinoma of the ciliary epithelium. Treatment was performed with palladium-103 ophthalmic plaque brachytherapy (80-Gy apex). Main outcome measures include visual acuity, local control, radiation complications, and metastatic disease. Results The patient presented with counting fingers vision, focal angle closure, cataract, and a 5.5-mm thick ciliary body malignancy. At 3 years after radiation therapy and 2.5 years after cataract extraction, her visual acuity was improved to 20/30 and the tumor residua stabilized at 60% of its initial thickness. There has been neither radiation-related keratopathy, retinopathy, optic neuropathy nor metastatic disease. Conclusions Plaque brachytherapy was used to treat primary adenocarcinoma of the ciliary epithelium. With 3-year followup, there has been excellent local control, preservation of the eye, and recovery of vision.

A 17-year retrospective study of institutional results for eye plaque brachytherapy of uveal melanoma using 125I, 103Pd, and 131Cs and historical perspective

Purpose To compare overall survival, local and distant failure rates, ocular toxicity, and vision preservation in patients treated with eye plaque brachytherapy at Tufts Medical Center with those in the published literature. Methods and Materials Records were reviewed for 53 patients with the diagnosis of uveal melanoma treated with plaque brachytherapy at Tufts Medical Center over the past 17 years. American Joint Committee on Cancer staging (T1, T2, or T3) were 4, 39, and 10 patients, respectively. All the patients were treated using 125I ( n = 37), 103Pd ( n = 5), or 131Cs ( n = 11) to a dose of 85 Gy (documented as 100 Gy before 1996 for the same physical dose). Results With a mean followup of 75 months, 38 of 53 patients were still alive. Five patients (all 125I) developed liver metastases (9%) with no evidence of local failure. There were 10 definitive local failures and four additional transpupillary thermo-therapy procedures performed to ensure local control for lesions slow to respond. Twelve patients (23%) required enucleation. At most recent followup, 32 patients (71%) maintained 20/200 vision or better in the treated eye. In this first report of 131Cs plaque therapy with a mean followup of 20 months, there were two transpupillary thermo-therapy procedures and one definitive failure requiring enucleation after 10 months. Conclusions Our disease control and ocular results were comparable to those in the literature given the extended followup. We are developing a multi-institutional, prospective clinical protocol for considering radionuclide selection and other prescriptive criteria.

Comparison of dose calculation methods for brachytherapy of intraocular tumors

To investigate dosimetric differences among several clinical treatment planning systems (TPS) and Monte Carlo (MC) codes for brachytherapy of intraocular tumors using 125I or 103Pd plaques, and to evaluate the impact on the prescription dose of the adoption of MC codes and certain versions of a TPS (Plaque Simulator with optional modules). Three clinical brachytherapy TPS capable of intraocular brachytherapy treatment planning and two MC codes were compared. The TPS investigated were Pinnacle v8.0dp1, BrachyVision v8.1, and Plaque Simulator v5.3.9, all of which use the AAPM TG-43 formalism in water. The Plaque Simulator software can also handle some correction factors from MC simulations. The MC codes used are MCNP5 v1.40 and BrachyDose/EGSnrc. Using these TPS and MC codes, three types of calculations were performed: homogeneous medium with point sources (for the TPS only, using the 1D TG-43 dose calculation formalism); homogeneous medium with line sources (TPS with 2D TG-43 dose calculation formalism and MC codes); and plaque heterogeneity-corrected line sources (Plaque Simulator with modified 2D TG-43 dose calculation formalism and MC codes). Comparisons were made of doses calculated at points-of-interest on the plaque central-axis and at off-axis points of clinical interest within a standardized model of the right eye. For the homogeneous water medium case, agreement was within approximately 2% for the point- and line-source models when comparing between TPS and between TPS and MC codes, respectively. For the heterogeneous medium case, dose differences (as calculated using the MC codes and Plaque Simulator) differ by up to 37% on the central-axis in comparison to the homogeneous water calculations. A prescription dose of 85 Gy at 5 mm depth based on calculations in a homogeneous medium delivers 76 Gy and 67 Gy for specific 125I and 103Pd sources, respectively, when accounting for COMS-plaque heterogeneities. For off-axis points-of-interest, dose differences approached factors of 7 and 12 at some positions for 125I and 103Pd, respectively. There was good agreement (approximately 3%) among MC codes and Plaque Simulator results when appropriate parameters calculated using MC codes were input into Plaque Simulator. Plaque Simulator and MC users are perhaps at risk of overdosing patients up to 20% if heterogeneity corrections are used and the prescribed dose is not modified appropriately. Agreement within 2% was observed among conventional brachytherapy TPS and MC codes for intraocular brachytherapy dose calculations in a homogeneous water environment. In general, the magnitude of dose errors incurred by ignoring the effect of the plaque backing and Silastic insert (i.e., by using the TG-43 approach) increased with distance from the plaque's central-axis. Considering the presence of material heterogeneities in a typical eye plaque, the best method in this study for dose calculations is a verified MC simulation.

MONTE CARLO SIMULATION FOR TREATMENT PLANNING OPTIMIZATION OF THE COMS AND USC EYE PLAQUES USING THE MCNP4C CODE

Introduction: Ophthalmic plaque radiotherapy using I-125 radioactive seeds in removable episcleral plaques is often used in management of ophthalmic tumors. Radioactive seeds are fixed in a gold bowl-shaped plaque and the plaque is sutured to the scleral surface corresponding to the base of the intraocular tumor. This treatment allows for a localized radiation dose delivery to the tumor with a minimum target dose of 85 Gy. The goal of this study was to develop a Monte Carlo simulation method for treatment planning optimization of the COMS and USC eye plaques. Material and Methods: The MCNP4C code was used to simulate three plaques: COMS-12mm, COMS-20mm, and USC #9 with I-125 seeds. Calculation of dose was performed in a spherical water phantom (radius 12 mm) using a 3D matrix with a size of 12 voxels in each dimension. Each voxel contained a sphere of radius 1 mm. Results: Dose profiles were calculated for each plaque. Isodose lines were created in 2 planes normal to the axes of the plaque, at the base of the tumor and at the level of the 85 Gy isodose in a 7 day treatment. Discussion and Conclusion: This study shows that it is necessary to consider the following tumor properties in design or selection of an eye plaque: the diameter of tumor base, its thickness and geometric shape, and the tumor location with respect to normal critical structures. The plaque diameter is selected by considering the tumor diameter. Tumor thickness is considered when selecting the seed parameters such as their number, activity and distribution. Finally, tumor shape and its location control the design of following parameters: the shape and material of the plaque and the need for collimation.

Local control and visual acuity following treatment of medium-sized ocular melanoma using a contact eye plaque: A single surgeon experience

Purpose To evaluate the outcomes of choroidal melanoma in (CM) patients treated with 125I episcleral plaque brachytherapy and to compare our single surgeon results with the multi-institutional Collaborative Ocular Melanoma Study (COMS). Methods and Materials A review was performed of all CM patients treated with 125I episcleral plaque brachytherapy by ophthalmologist in accordance with established COMS guidelines. Results The records of 35 patients were reviewed. The median longest basal tumor diameter and apical tumor height was 13.5 and 7.8 mm, respectively. Median dose to the apex was 8609 cGy at a median dose rate of 92 cGy/h. At a median followup of 45 months, 35 patients had local control and 33 had successful organ preservation. At 5 years, the local control rate was 100%, and the eye preservation rate was 94%. Five patients developed hepatic metastasis at a median of 58 months, and 2 succumbed from disease. The 5-year survival rate was 84%, and the 5-year rate of death with histopathologically confirmed metastasis was 15%. Of the 22 patients with at least 3 years of followup, 68% had a visual acuity in the treated eye of 20/200 or worse. Conclusion Excellent local control, eye preservation rates, and survival outcomes following 125I episcleral plaque application for CM can be optimized by having an experienced ophthalmologist place the plaques. Additionally, hepatic metastasis can occur more than 5 years postimplant regardless of local control; therefore, longer systemic staging should be considered.

Eye Plaque Brachytherapy for the Treatment of Uveal Melanoma: The 2010 Tufts Medical Center Experience

Eye Plaque Brachytherapy for the Treatment of Uveal Melanoma: The 2010 Tufts Medical Center Experience

Three-dimensional dosimetry imaging of I-125 plaque for eye cancer treatment

Treatment of ocular cancers using eye plaque brachytherapy is now an established medical procedure. However, current QA for these eye plaques is quite rudimentary, limiting the opportunities for precise pre-tumour plaque customisation. This paper proposes and experimentally validates a new technique for imaging of eye plaque dose distributions using a high-resolution pixelated silicon detector. Results are presented demonstrating the 2D and 3D isodose surfaces produced using experimental data collected using this method.