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kVCT, MVCT, and hybrid CT image studies—Treatment planning and dose delivery equivalence on helical tomotherapy
Author(s) -
Martin Spencer,
Yartsev Slav
Publication year - 2010
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 - 10.1118/1.3432566
Subject(s) - tomotherapy , imaging phantom , nuclear medicine , radiation treatment planning , quality assurance , dosimetry , medical imaging , medicine , ionization chamber , image quality , dose profile , materials science , biomedical engineering , radiation therapy , radiology , computer science , image (mathematics) , physics , artificial intelligence , ion , external quality assessment , pathology , quantum mechanics , ionization
Purpose To determine the equivalence of radiation therapy treatment planning and delivery for various imaging options on helical tomotherapy. Methods Seven treatment plans using identical anatomy and planning parameters were created based on the following CT studies: Standard kilovoltage CT (kVCT); 2, 4, and 6 mm spacing megavoltage CT (MVCT); and 2, 4, and 6 mm hybrid MVCT/kVCT studies. In addition, two kVCT based plans were created to explore the effect of the choice of dose calculation grid for optimization. Calculated and measured dose distributions were compared via volumetric and dosimetric analysis at the planning stage, point dose measurements with ion chamber, along with EDR2 film data for gamma function analysis for distance to agreement of 3 mm and dose differences of 3%, 5%, and 7% using both the commercially available “cheese” phantom and the new QUASAR Verification (QVer) phantom. Results Plans created for each imaging option showed residual error increasing as image slice spacing increased and critical structure size decreased. With the exception of the low dose area in hybrid studies, point dose measurements were within the calculated/measured dose acceptance criteria of 5% on both the QVer and cheese phantoms. Gamma analysis for the original kVCT plan delivery showed an average of 98.5 % ± 0.5 % and 98.8 % ± 0.3 % of dose pixels passing kVCT study treatment and delivery quality assurance procedures, respectively. The QVer phantom allows for delivery quality assurance with simultaneous use of two films and more convenient gamma function assessment but shows some measurement discrepancy up to 10% compared to the cheese phantom. Conclusions The kVCT, MVCT, and kVCT/MVCT hybrid studies showed considerable agreement at both planning and delivery stages. The choice of calculation grid is more important when dealing with smaller anatomical structures.