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Monte Carlo dosimetry for 103 Pd, 125 I, and 131 Cs ocular brachytherapy with various plaque models using an eye phantom
Author(s) -
Lesperance Marielle,
Martinov M.,
Thomson R. M.
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4864474
Subject(s) - brachytherapy , dosimetry , imaging phantom , collimated light , monte carlo method , materials science , nuclear medicine , silicone , biomedical engineering , optics , radiation therapy , physics , medicine , radiology , mathematics , composite material , laser , statistics
Purpose: To investigate dosimetry for ocular brachytherapy for a range of eye plaque models containing 103 Pd, 125 I, or 131 Cs seeds with model‐based dose calculations.Methods: Five representative plaque models are developed based on a literature review and are compared to the standardized COMS plaque, including plaques consisting of a stainless steel backing and acrylic insert, and gold alloy backings with: short collimating lips and acrylic insert, no lips and silicone polymer insert, no lips and a thin acrylic layer, and individual collimating slots for each seed within the backing and no insert. Monte Carlo simulations are performed using the EGSnrc user‐code BrachyDose for single and multiple seed configurations for the plaques in water and within an eye model (including nonwater media). Simulations under TG‐43 assumptions are also performed, i.e., with the same seed configurations in water, neglecting interseed and plaque effects. Maximum and average doses to ocular structures as well as isodose contours are compared for simulations of each radionuclide within the plaque models.Results: The presence of the plaque affects the dose distribution substantially along the plaque axis for both single seed and multiseed simulations of each plaque design in water. Of all the plaque models, the COMS plaque generally has the largest effect on the dose distribution in water along the plaque axis. Differences between doses for single and multiple seed configurations vary between plaque models and radionuclides. Collimation is most substantial for the plaque with individual collimating slots. For plaques in the full eye model, average dose in the tumor region differs from those for the TG‐43 simulations by up to 10% for 125 I and 131 Cs, and up to 17% for 103 Pd, and in the lens region by up to 29% for 125 I, 34% for 103 Pd, and 28% for 131 Cs. For the same prescription dose to the tumor apex, the lowest doses to critical ocular structures are generally delivered with plaques containing 103 Pd seeds.Conclusions: The combined effects of ocular and plaque media on dose are significant and vary with plaque model and radionuclide, suggesting the importance of model‐based dose calculations employing accurate ocular and plaque media and geometries for eye plaque brachytherapy.