Santos J, Silva S, Sarmento S. Optimized method for in vivo dosimetry with small films in pelvic IOERT for rectal cancer.
Phys Med 2020;
81:20-30. [PMID:
33338728 DOI:
10.1016/j.ejmp.2020.11.019]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Revised: 11/09/2020] [Accepted: 11/15/2020] [Indexed: 11/28/2022] Open
Abstract
PURPOSE
Intra-Operative Electron Radiation Therapy (IOERT) is used to treat rectal cancer at our institution, and in vivo measurements with Gafchromic EBT3® films were introduced as quality assurance. The purpose of this work was to quantify the uncertainties associated with digitization of very small EBT3 films irradiated simultaneously, in order to optimize in vivo dosimetry for IOERT.
METHODS
Film samples of different sizes - M1 (5×5cm2), M2 (1.5×1.5 cm2), M3 (1.0×1.5 cm2) and M4 (0.75×1.5 cm2) - were used to quantify typical variations (uncertainties) due to scanner fluctuations, misalignment, film inhomogeneity, long-term effect of film cutting, small rotations, film curling, edge effects and the influence of opaque templates. Fitting functions and temporal validity of sensitometric curves were also assessed.
RESULTS
Film curling, intra-film variability and scanner fluctuations are important effects that need to be minimized or considered in the uncertainty budget. Small rotations, misalignments and film cutting have little or no influence on the readings. Most fitting functions perform well, but the quantity used for dose quantification determines over- or under-valuation of dose in the long term. Edge effects and the influence of opaque templates need to be well understood, to allow optimization of methodology to the intended purpose.
CONCLUSION
The proposed method allows practical and simultaneous digitization of up to ten small irradiated film samples, with an experimental uncertainty of 1%.
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