Program Information
Uncertainty in Positioning Ion Chamber at Reference Depth for Various Water Phantoms
N Kinoshita1, 2*, H Oguchi2 , Y Nishimoto1 , T Adachi1 , H Shioura3 , H Kimura3 , (1) Radiological Center, University of Fukui Hospital (2) Department of Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine (3) Department of Radiology, University of Fukui Hospital
Presentations
SU-I-GPD-T-450 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: We evaluated the uncertainties in positioning a cylindrical chamber at the reference depth for seven phantoms as well as the uncertainties in the chamber reading from the positioning uncertainties. The aim was to investigate the major contributions to the positioning uncertainty in order to reduce measurement uncertainty for external photon beam radiotherapy calibration.
Methods: The following the seven phantoms were used: DoseView 1D, WP1D, 1D SCANNER, and QWP-07 as one-dimensional (1D) phantoms for a vertical-beam geometry; GRI-7632 as a phantom for a fixed waterproofing sleeve; and PTW type 41023 and QWP-04 as 1D phantoms for a horizontal-beam geometry. The uncertainties were analyzed and estimated according to the recommendations of the ISO Guide on the Uncertainty in Measurement.
Results: The uncertainties in positioning the chamber at the reference depth and the resultant uncertainties in the chamber reading ranged from 0.15 mm to 0.40 mm and 0.09% to 0.24%, respectively, among the seven phantoms (k = 1 in both cases). The major components of positioning uncertainty were as follows: non-applied correction attributable to water density and determination of origin for phantom positioning among users for DoseView 1D, movement distance from the origin to the reference depth for WP1D, non-applied correction attributable to water density for 1D SCANNER, non-applied correction attributable to water density for QWP-07, water level of a 10-cm adjustment among users for GRI-7632, deformation of the phantom window and non-water material of the window for PTW type 41023, and non-water material of the phantom window and determination of origin for phantom positioning among users for QWP-04.
Conclusion: The major uncertainty components in the chamber reading resulting from the positioning uncertainty were different among the seven phantoms studied here. Thus, users need to consider the major components that correspond to the phantom used.
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