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SU‐E‐J‐19: An Intra‐Institutional Study of Cone‐Beam CT Dose for Image‐Guided Radiation Therapy
Author(s) -
Knutson N,
Rankine L,
Reilly M,
Li H
Publication year - 2015
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 - 10.1118/1.4924106
Subject(s) - truebeam , ionization chamber , imaging phantom , nuclear medicine , dosimetry , cone beam computed tomography , medicine , cone beam ct , computed tomography , beam (structure) , linear particle accelerator , physics , radiology , optics , ionization , ion , quantum mechanics
Purpose: To determine the variability of Cone‐Beam CT Dose Index (CB‐CTDI) across multiple on‐board imaging (OBI) systems within a single institution, and compare this to manufacturer provided data. Methods: The CB‐CTDI was measured on three Trilogy and three TrueBeam Varian OBI systems, for six different clinically used scan protocols. Measurements were taken using a 10 cm long CT ionization chamber in either a 16 cm (head‐simulating) or 32 cm (body‐simulating) diameter, acrylic, cylindrical, 15 cm long CTDI phantom. We assessed the variation in CB‐CTDI between the OBI systems and compared our measured values to the data provided by the manufacturer. Results: The standard error in the CB‐CTDI measured for all protocols was found to be within ±2% and ±5% of the mean for TrueBeam and Trilogy, respectively. For all head scan protocols, the measured TrueBeam values were lower than the manufacturer's reported values, with a maximum difference of 13.9% and an average difference of 11%. For the body scan protocols, the TrueBeam measured values were 3% and 13% greater than the manufacturer's reported values for two out of three protocols, and 38% lower than reported for the third protocol. In total, 7/18 CB‐CTDI measurements fell within the manufacturers specified range (±10%). Across all scans the Truebeam machines were found to have a lower CB‐CTDI than Trilogy, particularly the head scan protocols, which show decreases of up to 30% . Conclusion: The intra‐institutional variation of CB‐CTDI was found to be clinically acceptable at less than 5%. For the TrueBeam OBI system, over half of the measured scans failed to fall with in the manufactured quoted range of 10%, however, all measured values were within 15% of the manufacturer's reported values. For accurate assessment and reporting of imaging dose to radiotherapy patients, our results indicate a need for standardization in CB‐CTDI measurement technique.