Tin filter

NCI Dose Team response

One quick approach would be using CTDIvol with a Tin filter and entering the values into NCICT. This approach is based on the assumption that when organ doses are normalized by CTDIvol, dose differences would reduce to less than 5% (validated by several papers to date).

Another approach is implementing nCTDIw data into NCICT. NCICT uses normalized CTDIw data from several sources (e.g., NRPB national survey). To collect nCTDIw from new scanners that are not currently available in NCICT, we would need the following data from your own measurements or vendors.

Measurement of CTDIw: For 16 cm and 32 cm CTDI phantoms For 80, 100, 120, and 140 kVp or other kV settings available on your scanners For head and body bowtie filters or other filters available For 1 cm collimation width (not sure if this is available. We had to use a service mode for our measurements with Siemens Sensation 16) Divide CTDIw by mAs to obtain nCTDIw (mGy/mAs) If these data are available, we can include them in the NCICT nCTDIw library. If you can create two sets of nCTDIw measurements with and without a Tin filter (not sure if you can do this since we're not familiar with how the filter is installed), we should be able to add them and see how organ dose changes with and without the filter.

NCI Dose Team response

Luckily, Siemens includes extensive sets of measurements in their system owner manual (SOM). We have attached the two relevant tables for the Force that you will need for NCICT implementation. The 0.6 mm Sn filter has a pronounced effect on beam quality and dose. Like the NCI Dose Team said, most of this will be reflected in the CTDI(vol), but there may be some other dose distribution effects from the beam spectra. Let us know if there is anything else we can do to help.

-Seth Siemens-Force-dosimetry-tables.pdf

NCI Dose Team response

Thank you Seth for uploading the data sheet. We left this on feature request post.