A Pioneer at Measuring CT Dose

The RTI CT Dose Profiler for Barracuda and Piranha has taken the CT quality assurance to the next level. Because of its revolutionary design it has transformed the CTDI measurement from being inaccurate due to underestimation of the dose for wide beams to be more exact. It also has the ability to further analyze the result – all in one shot.

The rapid advancements in CT technology are placing new demands on methods and equipment used for quality assurance. The wide beam widths found in CT scanners with multiple beam apertures make it difficult to use existing CT dose ionization chambers to measure the total dose given to the patient. Using a standard 10 cm CT ionization chamber may result in inaccurate measurements due to underestimation of the dose profile for wide beams. The CT Dose Profiler was developed to solve this problem.

This new type of CT probe has a very thin detector chip. The detector is completely irradiated when the table is moving and the CT beam scans over the probe. The dose is measured in every point of the X-ray beam and the total dose profile is acquired regardless of how wide the beam is. There is no limitation of the beam width.

With the CT Dose Profiler you can avoid more expensive methods that require both preparation before and read-out after each scan (like TLD and X-ray film). The CT Dose Profiler is also ideal for measuring point dose and dose rate in the CT beam.

Methods and exposure

The wide beam widths found in CT scanners with multiple beam apertures make it impossible to use existing CT ionization chambers to measure the total dose given to the patient. Using a standard 10 cm CT ionization chamber may result in inaccurate measurements due to underestimation of the dose profile for wide beams. The CT Dose Profiler Probe is a new type of CT detector that does not have this limitation. It can be used with the Barracuda or the Piranha and a PC running the CT Dose Profile Analyzer Software.

The conventional method to measure CT dose profile is using TLDs. The TLD method is very time-consuming and expensive since it requires both preparation before and read-out after each scan.

Another method used today is the use of X-ray film for profile measurements that has some of the same disadvantages as the TLD. The CT Dose Profiler from RTI Electronics has no such limitations, the dose profile is given in a matter of seconds.

The CT Dose Profiler is based on solid-state technology. It is robust and it fits into existing standard phantoms used for CTDI measurements. The sensitive part of the detector chip is very thin (width 0.3 mm). Thanks to the small width, the detector is completely irradiated when the table is moving and the CT scans over the probe. The dose is measured in every point of the X-ray beam and the total dose profile is acquired regardless of beam width. This makes it possible to measure without the drawbacks of traditional CT probes.

Following parameters are achieved from a single exposure:

CTDI100
Point Dose
CT dose profile
CTDIw
CTDIvol
DLP
Performance of the AEC	(Geometric efficiency %)
FWHM	(Full width at half maximum of the dose profile.)
Scatter Index	(An index for checking how much of the total dose that is not measured by a standard CT ionization chamber.)

Specifications

Dose rate:	40 nGy/s-760 mGy/s
	0.26 mR/min-5200 R/min
Inaccuracy:	±5 % or ±10 nGy/s
Spatial resolution:	0.25 mm

Wite papers and documentation 

CT Dose Profiler Documentation and Summary.
Absorbed dose and dose rate using the Varian OBI 1.3 and 1.4 CBCT system