Comparison of scatter doses from a multislice and a single slice CT scanner

Area of Science:

• Medical Physics
• Radiological Sciences
• Imaging Technology

Background:

• Manufacturer data suggested significantly higher external scatter doses for multislice CT (MSCT) compared to single slice CT (SSCT).
• This discrepancy contradicted expectations and UK ImPACT group statements regarding scatter dose equivalence when accounting for beam width.

Purpose of the Study:

• To investigate and compare external scatter doses between MSCT and SSCT scanners.
• To validate manufacturer's scatter dose data and assess shielding adequacy for a new MSCT installation.

Main Methods:

• Scatter dose measurements were conducted at three points using a standard perspex CTDI phantom for both MSCT (40 mm beam width) and SSCT (10 mm beam width).
• CT dose indices were measured to compare scanner outputs.
• A film badge survey was performed post-installation to evaluate room shielding effectiveness.

Main Results:

• Measured MSCT scatter doses were lower than manufacturer's predictions.
• MSCT scatter doses were approximately 4 times higher than SSCT doses, consistent with the difference in beam widths.
• CT dose indices were comparable between the two scanner types.
• The existing lead shielding was found to be adequate for the MSCT scanner.

Conclusions:

• Manufacturer's data for MSCT external scatter doses may be overestimated.
• Measured scatter dose increases with MSCT are attributable to wider beam widths, not disproportionately higher scatter.
• Existing shielding protocols are sufficient for MSCT, provided they were adequate for SSCT.