TH‐AB‐BRA‐04: A Physical Phantom for Experimental Commissioning and Performance Testing of 192Ir MBDCAs

Abstract

Purpose:To present a phantom‐based methodology for the experimental commissioning and performance testing of model‐based dose calculation algorithms (MBDCAs), which have been recently introduced in 192Ir HDR brachytherapy treatment planning systems (TPSs).Methods:The phantom was constructed from PMMA slabs properly machined to accommodate material and density inhomogeneity inserts, as well as TLD detectors (TLD‐100, 1×1×1 mm3), radiochromic films (Gafchromic EBT‐3) and a cylindrical Presage dosimeter (d=6cm, h=8cm). The spatial arrangement of the different dosimeters within the phantom permitted measurements at regions of scatter conditions departing from TG43 assumptions (e.g., at phantom boundary) and/or close to the inhomogeneity inserts. The phantom was CT‐imaged and a multiple 192Ir source position treatment plan was prepared using the Oncentra Brachy v4.5 TPS. Dose calculations of the Oncentra‐ACE MBDCA were exported in DICOM‐RT for further evaluation. The plan was delivered using a microSelectron v.2 192Ir source and 4 plastic catheters embedded in PMMA slabs. The treatment plan data were subsequently imported into an in‐house developed software tool (BrachyGuide) used to obtain corresponding Monte Carlo (MC) simulation dosimetry results with the MCNP code. Detectors’ measurements were compared to both MBDCA‐ and MC‐calculated results in terms of absolute point dose differences, 2D and 3D relative dose and gamma index distributions.Results:Experimental dosimetry results and MC calculations were found in agreement within uncertainties. The corresponding dosimetry comparison between detector measurements and ACE‐calculations showed also a good agreement which deteriorated with increasing distance from the implant due, mainly, to MBDCA assumptions and optimization settings. The latter was highlighted in the comparison of the 3D dose distribution measured by the Presage dosimeter to corresponding ACE calculations.Conclusion:The proposed phantom/methodology can be used for both commissioning and quality assurance of MBDCA‐based TPSs, as well as for benchmarking MC‐calculated reference dose distributions.Research co‐financed by the ESF and Greek funds through the Operational Program Education and Lifelong Learning Investing in Knowledge Society of the NSRF. Research Funding Program: Aristeia.Nucletron, an Elekta company (Veenendaal, The Netherlands) is gratefully acknowledged for providing Oncentra Brachy v4.5 for research purposes.