I need a sample CT DICOM data of a head. Where can I find it?
Search for head and neck.
Also on the same site the CPTAC-GBM dataset includes some head CTs.
This data is in TCIA format. How do I convert it to DICOM or is any there any way to load it in Slicer?
Most of the data on TCIA is in dicom, you just need to download it.
I have downloaded it but how do I import it in Slicer. I tried to drag and drop but it shows nothing.
Did you use the download manager? https://wiki.cancerimagingarchive.net/display/NBIA/Download+Manager+7.0
You might also try https://www.slicer.org/wiki/Documentation/Nightly/Extensions/TCIABrowser