Simplified method for determining dose to a non-water phantom through the use of ND,w and IAEA TRS 483 for the GammaPod |
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| Institution: | 1. Department of Computer Science, Shantou University, Shantou, Guangdong, China;2. College of Computer Science and Software Engineering, Shenzhen University, Shenzhen, Guangdong, China;1. Fondazione Policlinico Universitario A. Gemelli IRCCS, Roma, Italy;2. Medical Physics, San Raffaele Scientific Institute, Milano, Italy;3. Prostate Cancer Program, Fondazione IRCCS Istituto Nazionale dei Tumori, Milano, Italy;4. Health Physics Unit, ASST Santi Paolo e Carlo, Milan, Italy;5. Department of Experimental and Clinical Biomedical Sciences “Mario Serio”, University of Florence, Florence, Italy;6. Università di Napoli Federico II, Dipartimento di Fisica “Ettore Pancini”, Napoli, Italy;7. Medical Physics Unit, Azienda Ospedaliera Universitaria Integrata – Verona, Italy;8. Unit of Radiation Research, IEO European Institute of Oncology, IRCCS, Milano, Italy;1. Dept. of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany;2. German Consortium for Translational Cancer Research Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany;3. Alaxo GmbH, Krün, Germany;4. Clinic for Diagnostic and Interventional Radiology, Saarland University Medical Center, Homburg, Saar, Germany;1. Department of Medical Physics, Institute of Radiation Protection and Dosimetry (IRD), Av. Salvador Allende, 3773, Barra da Tijuca, Rio de Janeiro, RJ CEP 22783-127, Brazil;2. Nuclear Engineering Department (DNC), Federal University of Rio de Janeiro (UFRJ), sala 206, Centro de Tecnologia, Av. Horácio Macedo, 2030, Bloco G, Fundão, Rio de Janeiro, RJ CEP 21941-941, Brazil;3. Department of Cell Biology, University of the State of Rio de Janeiro (UERJ), Pavilhão Haroldo Lisboa da Cunha, LabAngio, Rua São Francisco Xavier, 524, Maracanã, Rio de Janeiro, RJ CEP 20550-900, Brazil;4. CGMI/DRS, Brazilian National Nuclear Energy Comission (CNEN), Rua General Severiano, 90, Botafogo, Rio de Janeiro, RJ CEP 22290-901, Brazil;5. Department of Radiological Sciences (LCR), State University of Rio de Janeiro (UERJ), Pavilhão Haroldo Lisboa da Cunha, Rua São Francisco Xavier, 524, Maracanã, Rio de Janeiro, RJ CEP 20550-900, Brazil;6. Department of General Biology, Federal Fluminense University, Niterói, RJ CEP 21045-900, Brazil;1. Medical Physics Program, Department of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, MA 01854, United States;2. Landauer Medical Physics, 2 Science Road, Glenwood, IL 60425, United States;3. Department of Medical Physics and Radiation Safety, Rhode Island Hospital, Providence, RI 02903, United States;4. Department of Electrical and Computer Engineering, University of Massachusetts Lowell, Lowell, MA 01854, United States |
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| Abstract: | PurposeGammaPod, a breast stereotactic radiosurgery device, utilizes 25 rotating Co-60 sources to deliver highly conformal dose distributions. The GammaPod system requires that reference dosimetry be performed in a specific vendor-supplied poly-methylmethacrylate (PMMA) phantom. The nonstandard nature of GammaPod dosimetry, in both the phantom material and machine-specific reference (msr), prohibits use of the American Association of Physicists in Medicine Task Group 51 (TG-51) protocol. This study proposes a practical method using TRS 483 to make the reference dosimetry procedure simpler and to reduce overall uncertainties.MethodsThe dose to PMMA (DPMMA) is determined under msr conditions using TRS 483 with an Exradin A1SL chamber placed in a PMMA phantom. The conversion factor, which converts from the dose-to-water (Dw) in broad-beam Co-60 reference geometry to DPMMA in the msr small field Co-60 (Qmsr) geometry, is derived using the Monte Carlo simulations and procedure described in TRS 483.ResultsThe new conversion factor value for an Exradin A1SL chamber is 0.974. When combined with ND,w, DPMMA differs by 0.5% from the TG-21/Nx method and 0.2% from the IROC values. Uncertainty decreased from 2.2% to 1.6%.ConclusionWe successfully implemented TRS 483 reference dosimetry protocols utilizing ND,w for the GammaPod in the PMMA phantom. These results show not only agreement between measurements performed with the previously published method and independent thermoluminescent dosimetry measurements but also reductions in uncertainty. This also provides readers with a pathway to develop their own IAEA TRS 483 factor for any new small field machine that may be developed. |
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| Keywords: | IAEA TRS 483 TG-21 TG-51 GammaPod Reference dosimetry |
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