Is it beneficial to use fiducial markers if you are using daily cone-beam CT for prostate localization?

The answer to this question will be self-evident if one ever tries to align the prostate to the CBCT at the linac console. It's tough enough to contour the prostate on a planning CT, and the inferior quality of CBCT images only makes it harder to know where the base or apex are. This latter point can be cause for anxiety when using tight margins <=5mm, especially for therapists who often have to do these alignments without physician supervision. Worse is when a therapist uses the bony structures on the CBCT to make the alignment with the false assurance that it's more accurate then kV or MV imaging of bones. For us, fiducials are simple, safe, and effective. They replace the need for CBCT, unless one needs to see bladder filling. They can a...

IGRT questions are, to me, the most mathematically interesting questions in radiation oncology and relatively understudied. They involve things like systematic error, random error, spatial calculations, mathematical "margin recipes," etc.

Let's perform what Einstein called a gedankenexperiment. We are going to take 10 patients with fiducials and do a fiducial-based match (either via kV or CBCT using the fiducials instead of soft tissue, it doesn't matter) and 10 patients sans fiducials and do a CBCT match using whatever the matcher-in-charge wishes (rectum, bone, calcifications, whatever). We will set the first 10 patients up on the table, do our fiducial match, and shift. Now we will re-image after the shift. We will have a different human...

I agree with @Dr. First Last. I try to use fiducial markers for all prostate patients. For those few patients who refuse, typically those who have had a bad experience with a biopsy, I use CBCT but have less confidence in the alignment. I don't have experience placing fiducials myself, but instead have my urologist colleagues place them.