title: Tissue composition and density impact on the clinical parameters for (125)I prostate implants dosimetry.
abstract: The MCNPX code was used to calculate the TG-43U1 recommended parameters in water and prostate tissue in order to quantify the dosimetric impact in 30 patients treated with (125)I prostate implants when replacing the TG-43U1 formalism parameters calculated in water by a prostate-like medium in the planning system (PS) and to evaluate the uncertainties associated with Monte Carlo (MC) calculations. The prostate density was obtained from the CT of 100 patients with prostate cancer. The deviations between our results for water and the TG-43U1 consensus dataset values were -2.6% for prostate V100, -13.0% for V150, and -5.8% for D90; -2.0% for rectum V100, and -5.1% for D0.1; -5.0% for urethra D10, and -5.1% for D30. The same differences between our water and prostate results were all under 0.3%. Uncertainties estimations were up to 2.9% for the gL(r) function, 13.4% for the F(r,θ) function and 7.0% for Λ, mainly due to seed geometry uncertainties. Uncertainties in extracting the TG-43U1 parameters in the MC simulations as well as in the literature comparison are of the same order of magnitude as the differences between dose distributions computed for water and prostate-like medium. The selection of the parameters for the PS should be done carefully, as it may considerably affect the dose distributions. The seeds internal geometry uncertainties are a major limiting factor in the MC parameters deduction.
authors.affiliation: Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Campo Mártires da Pátria, 130, 1169-056 Lisbon, Portugal; Quadrantes Faro - Unidade de Radioterapia do Algarve, Rua da Associação Oncológica do Algarve, 8000-316 Faro, Portugal; MedicalConsult, SA, Campo Grande, 56-8°A, 1700-093 Lisbon, Portugal. Electronic address: susana.alegre.oliveira@medicalconsult.pt.
authors.forename: Susana Maria
authors.initials: SM
authors.lastname: Oliveira
authors.affiliation: Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Campo Mártires da Pátria, 130, 1169-056 Lisbon, Portugal; Escola Superior de Tecnologia da Saúde de Lisboa, Instituto Politécnico de Lisboa, Av. D. João II, lote 4.69.01, 1900-096 Lisbon, Portugal.
authors.forename: Nuno José
authors.initials: NJ
authors.lastname: Teixeira
authors.affiliation: Escola Superior de Tecnologia da Saúde de Lisboa, Instituto Politécnico de Lisboa, Av. D. João II, lote 4.69.01, 1900-096 Lisbon, Portugal; Instituto Gulbenkian de Ciência, Rua da Quinta Grande, 6, 2780-156 Oeiras, Portugal; Centro de Biodiversidade, Genómica Integrativa e Funcional, Faculdade de Ciências, Universidade de Lisboa, Edifício ICAT, Campus FCUL, Campo Grande, 1740-016 Lisbon, Portugal.
authors.forename: Lisete
authors.initials: L
authors.lastname: Fernandes
authors.affiliation: IST/ITN, Instituto Superior Técnico, Universidade Técnica de Lisboa, Estrada Nacional 10, 2695-006 Bobadela LRS, Portugal.
authors.forename: Pedro
authors.initials: P
authors.lastname: Teles
authors.affiliation: Quadrantes Faro - Unidade de Radioterapia do Algarve, Rua da Associação Oncológica do Algarve, 8000-316 Faro, Portugal.
authors.forename: Guy
authors.initials: G
authors.lastname: Vieira
authors.affiliation: IST/ITN, Instituto Superior Técnico, Universidade Técnica de Lisboa, Estrada Nacional 10, 2695-006 Bobadela LRS, Portugal.
authors.forename: Pedro
authors.initials: P
authors.lastname: Vaz
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D009010:Monte Carlo Method; D058958:Organs at Risk / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012007:Rectum / Q000528:radiation effects; D035501:Uncertainty; D014521:Urethra / Q000528:radiation effects
chemical_list: D007457:Iodine Radioisotopes
keywords: Brachytherapy; Monte Carlo simulations; Prostate cancer; Uncertainties