Abstract
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
Highlights
The most common radiation treatment for ocular melanomas is episcleral plaque brachytherapy in which a small eye plaque containing radioactive seeds is sutured to the scleral surface over the tumor base
As with other forms of brachytherapy, quality assurance measures are needed to minimize the risk of treatment delivery errors
This paper describes this method of verifying the activity or air kerma strength of COMS and Eye Physics EP917 eye plaques
Summary
The most common radiation treatment for ocular melanomas is episcleral plaque brachytherapy in which a small eye plaque containing radioactive seeds (usually Iodine-125 and Palladium-103 in the USA) is sutured to the scleral surface over the tumor base. The plaque is left in place for a few days and removed. In comparison to enucleation (removal of eye), plaque brachytherapy offers equivalent tumor control while allowing eye preservation and the possibility of vision retention.[1]. For plaques that are to be assembled in-house, it is good practice, as well as mandated by regulation, that at least 10% of the seeds be assayed to confirm the source strength. Our practice is to assay at least 25% and usually 100% of the sources prior to loading them into eye plaques
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