(Tuesday, 7/16/2019) 1:15 PM - 1:45 PM
Room: Exhibit Hall | Forum 4
Purpose: To report on the dosimetric and radiobiological doses in LDR eye plaque brachytherapy for the purpose of preparing a clinical outcome analysis.
Methods: Data from 157 patients treated from 2014 to 2018 with low dose rate (LDR) brachytherapy were used for this investigation. Treatments used a collaborative ocular melanoma study (COMS) eye plaques and Iodine-125 radioactive seeds. The seed activities were chosen to deliver 85 Gy to the tumor apex or to a prescription point (if the apex <5mm) within 96 hours. The plaque sizes used were 10, 12, 14, 16, 18, 20, and 22mm including notched and deep notched. The plaques were modeled in Varian BrachyVision (Varian Medical Systems) with seed coordinates from AAPM Task Group 129. The treatment planning calculations used TG-43 protocol and did not include plaque heterogeneities, seed carrier attenuation, or special collimation protecting the optic nerve. Dose data were extracted for the apex, prescription point, sclera, opposite retina, lens, macula, and optic disk. The radiobiological dosimetry (biological equivalent doses, BED) was calculated using appropriate α/β ratios found in the literature.
Results: The mean BED for tumor apex (>5mm in depth) was 99.34 Gy (range: 92.87 – 110 Gy), and for the prescription point (if apex ≤5mm in depth) was 100.27 Gy (range: 92.61 – 109.14 Gy). The mean BED for opposite retina (10.31 Gy, range: 6.18 – 34.19 Gy), inner sclera (1043.50 Gy, range: 280.32 – 3742.49 Gy), macula (247.84 Gy, range: 7.53 – 3142.81 Gy), optic disk (259.58 Gy, range: 7.51 – 4162.04 Gy), and lens (49.16 Gy, range: 10.42 – 573.42 Gy) were also calculated.
Conclusion: The BED mean results were comparable to published single institution studies (Miguel et al.) in spite of not accounting for heterogeneities in the calculations. The clinical outcomes related to the BED doses will be further researched.
Keywords
Eye Plaques, Brachytherapy, Radiobiology
Taxonomy
Not Applicable / None Entered.
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