Abstract
In this study, the Plaque SimulatorTM eye plaque brachytherapy planning system was commissioned for ROPES eye plaques and Amersham Health model 6711 Iodine 125 seeds, using TG43-UI data. The brachytherapy module of the RADCALC® independent checking program was configured to allow verification of the accuracy of the dose calculated by Plaque SimulatorTM. Central axis depth dose distributions were compared and observed to agree to within 2% for all ROPES plaque models and depths of interest. Experimental measurements were performed with a customized PRESAGEm 3-D type dosimeter to validate the calculated depth dose distributions. Preliminary results have shown the effect of the stainless steel plaque backing decreases the measured fluorescence intensity by up to 25%, and 40% for the 15 mm and 10 mm diameter ROPES plaques respectively. This effect, once fully quantified should be accounted for in the Plaque SimulatorTM eye plaque brachytherapy planning system.
Highlights
Choroidal melanoma is the most common primary intraocular malignancy [1] and is commonly treated using plaque brachytherapy, external beam charged particle therapy, surgical resection or enucleation
Radiation Oncology Physics and Engineering Services Australia (ROPES) Eye Plaques loaded with I-125 Seeds (Amersham Health type 6711) The ROPES eye plaques consist of an acrylic carrier with holes for the I-125 seeds combined with a stainless steel backing shield to place the acrylic insert in
3.2. 3-D PRESAGEm Central Axis Measurements Figure 2 shows the eye plaque central axis fluorescence intensity curves measured by the gel dosimeters for the 15 mm diameter plaque (10 seeds), both with and without the plaque stainless steel backing
Summary
Choroidal melanoma is the most common primary intraocular malignancy [1] and is commonly treated using plaque brachytherapy, external beam charged particle therapy, surgical resection or enucleation. The Collaborative Ocular Melanoma Study (COMS) trial began in 1986 [2], comparing enucleation against a minimum of 100 Gy I-125 plaque radiation therapy for medium-sized choroidal melanomas. With 12 years follow up, no significant difference in survival was found, establishing eye plaque brachytherapy as an effective treatment modality for choroidal melanoma [3]. LiF TLD remains the method of choice recommended in the AAPM TG43-UI report [6], and Monte Carlo codes are often used as benchmarks for any experimental measurements [7]
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