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SU‐E‐T‐464: On the Equivalence of the Quality Correction Factor for Pencil Beam Scanning Proton Therapy
Author(s) -
Sorriaux J,
Paganetti H,
Testa M,
Giantsoudi D,
Schuemann J,
Bertrand D,
Orban de Xivry J.,
Lee J,
Palmans H,
Vynckier S,
Sterpin E
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 - 10.1118/1.4888797
Subject(s) - pencil beam scanning , proton therapy , dosimetry , imaging phantom , beam (structure) , laser beam quality , bragg peak , monte carlo method , optics , physics , calibration , proton , monitor unit , range (aeronautics) , nuclear medicine , ionization chamber , materials science , mathematics , ion , statistics , nuclear physics , medicine , laser , quantum mechanics , laser beams , composite material , ionization
Purpose: In current practice, most proton therapy centers apply IAEA TRS‐398 reference dosimetry protocol. Quality correction factors (kQ) take into account in the dose determination process the differences in beam qualities used for calibration unit and for treatment unit. These quality correction factors are valid for specific reference conditions. TRS‐398 reference conditions should be achievable in both scattered proton beams (i.e. DS) and scanned proton beams (i.e. PBS). However, it is not a priori clear if TRS‐398 kQ data, which are based on Monte Carlo (MC) calculations in scattered beams, can be used for scanned beams. Using TOPAS‐Geant4 MC simulations, the study aims to determine whether broad beam quality correction factors calculated in TRS‐398 can be directly applied to PBS delivery modality. Methods: As reference conditions, we consider a 10×10×10 cm 3 homogeneous dose distribution delivered by PBS system in a water phantom (32/10 cm range/modulation) and an air cavity placed at the center of the spread‐out‐Bragg‐peak. In order to isolate beam differences, a hypothetical broad beam is simulated. This hypothetical beam reproduces exactly the same range modulation, and uses the same energy layers than the PBS field. Ion chamber responses are computed for the PBS and hypothetical beams and then compared. Results: For an air cavity of 2×2×0.2 cm 3 , the ratio of ion chamber responses for the PBS and hypothetical beam qualities is 0.9991 ± 0.0016. Conclusion: Quality correction factors are insensitive to the delivery pattern of the beam (broad beam or PBS), as long as similar dose distributions are achieved. This investigation, for an air cavity, suggests that broad beam quality correction factors published in TRS‐398 can be applied for scanned beams. J. Sorriaux is financially supported by a public‐private partnership involving the company Ion Beam Applications (IBA).