This work is a comparative study of the dosimetry calculated by Plaque Simulator, a treatment planning system for eye plaque brachytherapy, to the dosimetry calculated using Monte Carlo simulation for an Eye Physics model EP917 eye plaque. Monte Carlo (MC) simulation using MCNPX 2.7 was used to calculate the central axis dose in water for an EP917 eye plaque fully loaded with 17 IsoAid Advantage  125I seeds. In addition, the dosimetry parameters normalΛ, gLfalse(rfalse), and Ffalse(r,θfalse) were calculated for the IsoAid Advantage model IAI‐125  125I seed and benchmarked against published data. Bebig Plaque Simulator (PS) v5.74 was used to calculate the central axis dose based on the AAPM Updated Task Group 43 (TG‐43U1) dose formalism. The calculated central axis dose from MC and PS was then compared. When the MC dosimetry parameters for the IsoAid Advantage  125I seed were compared with the consensus values, Λ agreed with the consensus value to within 2.3%. However, much larger differences were found between MC calculated gL(r) and Ffalse(r,θfalse) and the consensus values. The differences between MC‐calculated dosimetry parameters are much smaller when compared with recently published data. The differences between the calculated central axis absolute dose from MC and PS ranged from 5% to 10% for distances between 1 and 12 mm from the outer scleral surface. When the dosimetry parameters for the  125I seed from this study were used in PS, the calculated absolute central axis dose differences were reduced by 2.3% from depths of 4 to 12 mm from the outer scleral surface. We conclude that PS adequately models the central dose profile of this plaque using its defaults for the IsoAid model IAI‐125 at distances of 1 to 7 mm from the outer scleral surface. However, improved dose accuracy can be obtained by using updated dosimetry parameters for the IsoAid model IAI‐125  125I seed.PACS number: 87.55.K‐

The purpose of this work was to develop a method for easily verifying that the activity or air kerma strength of pre‐assembled eye plaques, used in the treatment of ocular melanomas, agrees with the activity or air kerma strength called for in the treatment plan. A Capintec CRC‐7 Dose Calibrator with its standard vial/syringe sample holder was used to measure the activity of pre‐assembled COMS and Eye Physics EP917 eye plaques using IsoAid Advantage I‐125 seeds. Plaque activity measurements were made by placing the plaque face up in the center of a 5 cm tall Styrofoam insert in the source holder. Activity measurements were made with the source holder rotated to four angles (0°, 90°, 180°, and 270°). The average of these four values was converted to air kerma strength and divided by the assay air kerma strength, from the NIST traceable source calibration, and decayed to the plaque measurement date, to determine a plaque calibration factor. The average of the calibration factors for each plaque type was used to establish a calibration factor for each plaque type. Several partially loaded plaque configurations were included in this study and different methods were used to determine the effects of partial loading. This verification method is easy to implement with commonly available equipment and is effective in identifying possible errors. During this two‐year study, the air kerma strength of 115 eye plaques was checked and 11 possible errors were identified.PACS number: 87.55.Qr

Purpose: To compare the dosimetry calculated by the treatment planning software, Plaque Simulator™, to the dosimetry calculated using Monte Carlo methods. Methods: MCNPX 2.6.0 Monte Carlo Simulation (MC) code was used to model the Eye Physics model EP917 eye plaque. The IsoAid Advantage, IA1‐125A, 125I seed was also modeled using MCNPX and compared to published data by Meigooni et al. Energy deposition tally in unit of MeV/g was used to calculate the dose averaged over a cell.Bebig Plaque Simulator (PS) v574 treatment‐planning software was used to calculate the dose based on AAPM TG‐43U1 dose formalism; single factors are used to account for source collimation and backscattering from the gold alloy plaque.Relative doses, normalized to a prescription point of 6 mm (5 mm from the inner sclera surface), from MCNPX and PS, along the eye central axis from 1 mm to 12 mm from the scleral surface, were compared for a single seed in the plaque. Results: The IsoAid Advantage, IA1‐125A, 125I seed dose rate constant and radial dose function were calculated and agreed within 5% and 4% respectively with Meigooni et al. published data. For the central seed position, the dose differences between the MC simulation along the central axis of the eye at 1 mm and 2 mm from the scleral surface and the predicted doses by the Plaque Simulator were 32.4% and 15.2%, respectively. For distances from 3 mm to 12 mm from the scleral surface, MCNPX agreed with PS within 5%. Conclusion: For the first source position, Plaque Simulator underestimated the dose at 1 mm and 2 mm from the scleral surface by 32.4% and 12.5%. Beyond 3 mm, PS agrees within uncertainties with MCNPX results. Further investigation is needed to better identify the sources of these differences.

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Purpose: To develop a method of easily verifying the activity or air kerma strength of pre‐assembled COMS and Eye Physics EP917 eye plaques. Methods: A Capintec CRC‐7 Dose Calibrator with its standard vial/syringe sample holder was used to measure the activity of pre‐assembled eye plaques using IsoAid Advantage I‐125 seeds. Plaque activity measurements were made by placing the plaque face up in the center of a 10 cm tall Styrofoam insert in the source holder. The source holder was rotated to four angles (0°, 90°, 180°, and 270°). The average of these four values was compared to the assay air kerma strength, decayed to the plaque measurement date, to establish a plaque calibration factor. The average and standard deviation of several plaque measurements were then calculated to determine the repeatability of the process. Activity measurements were also made to determine the contribution of each seed position to the total measured activity of the EP 917 plaque. Results: Activity measurements were taken on seven vendor‐preloaded Eye Physics EP917 eye plaques. For the EP917, the average plaque calibration factor was 0.344 with a standard deviation of 0.012. For the COMS plaques with a silastic carrier, the plaque calibration factors ranged from 0.237 for a COMS 16N to 0.281 for a COMS 20. The average plaque calibration factor was 0.256 and the standard deviation was 0.015 The individual seed measurements were made using three different EP‐917 plaques. The data from these measurements show that the contribution of a single seed to the total plaque activity is approximately 5.9% or 1/17th of the total activity. Conclusions: Plaque calibration factors based on this methodology may be used to verify the activity of preassembled plaques to within 5%.