Depth of ionization chamber in water

Abstract

The device developed by the authors and described here enables the user to measure the depth from the water surface to the point of measurement for a cylindrical ion chamber with a waterproof plastic cap in a water phantom, free of surface-tension error with a high precision. The device seeks vertical orientation and provides the convenience of hands-free operation. The measurement process is simple and quick with a precision of 0.1 mm. (The device is currently available as a 'water phantom depth gauge' from Nuclear Associates, Division of Victoreen Inc., Clare Place, NY, USA.)

Quantitative ionization chamber alignment to a water surface: Performance of multiple chambers

“…Given the 0.07 mm accuracy of the telescopic standard (see Data ) the conclusion is that the gCAP method accurately reproduces the point at which the IC touches the water surface with an uncertainty of approximately 0.1 mm. This is significantly less than the 0.33 mm to 0.5 mm estimated by the AAPM TG‐51 addendum and is similar to that reported for specialized mechanical devices …”

“…This paper experimentally demonstrates a method to quantitatively set or confirm IC positioning with respect to a water surface to within an uncertainty of approximately 0.1 mm. This is significantly less than the 0.33–0.5 mm uncertainty estimated for the TG‐106 reflection method and is similar to the 0.1 mm reported for specialized mechanical devices . Since the gCAP method relies only on knowledge of the IC OR and the measured depth‐dose data to define the position, unlike other methods, it can be retrospectively applied to a given scan to confirm IC positioning.…”

“…This is significantly less than the 0.33-0.5 mm uncertainty estimated for the TG-106 reflection method 2 and is similar to the 0.1 mm reported for specialized mechanical devices. 3 Since the gCAP method relies only on knowledge of the IC OR and the measured depth-dose data to define the position, unlike other methods, it can be retrospectively applied to a given scan to confirm IC positioning. The gCAP method requires no specialized devices, is easy to implement, is independent of incident beam parameters, and provides a standard quantitative procedure for localizing an IC at a water surface.…”

“…This is significantly less than the 0.33 mm to 0.5 mm estimated by the AAPM TG-51 addendum 2 and is similar to that reported for specialized mechanical devices. 3 3.C. Commercial scanning system…”

“…The AAPM TG‐51 Addendum analysis of the TG‐106 method estimates that it results in 0.33–0.5 mm position uncertainty, 1 standard deviation . Mechanical add‐ons have been suggested or are available from water phantom manufacturers with claimed or demonstrated accuracies at the 0.1 mm level. However, all of these techniques suffer from the same common failure mode, in that once the alignment has been set, there is no validation or record of this crucial step.…”