There are two ways that prostate motion is tracked inter-
fractionally -- only once at the beginning of each session. Often that's done with cone-beam CTs. The other way is intra-
fractionally -- continually throughout each treatment. Intra-fractional tracking is more precise and gives fewer SEs. Both of these are called "IGRT" - image guided radiation therapy.
Image guidance is achieved in one of 3 ways:
- tracking the position of gold fiducials with X-rays (cone beam CT or stereo X-rays)
- radio transponders (Calypso)
- continuous CT scanning (Tomotherapy)
I just read that the cone beam CTs can add up to 1 Gy on an 80 Gy treatment. Probably not enough to worry about
As for your other question about
whether combo therapy (BT+IMRT) is better than dose-escalated IMRT for intermediate risk PC...
In a recently completed randomized prospective trial, the only one ever done that I know of, they found in an interim unpublished analysis that there were superior outcomes with combination of EBRT plus brachy boost as compared with EBRT alone.
Retrospective analyses are unclear. At Sloan Kettering they found that an HDR brachy boost+IMRT had better results than ultrahigh dose-escalated (86 Gy) IMRT:Comparison of PSA relapse-free survival in patients treated with ultra-high-dose IMRT versus combination HDR brachytherapy and IMRT.
However a retrospective analysis from UC Irvine found no difference between HDR brachy boost+IMRT compared to high dose IMRT alone:Preliminary results in prostate cancer patients treated with high-dose-rate brachytherapy and intensity modulated radiation therapy (IMRT) vs. IMRT alone.
Both HDR brachy and SBRT have been used as monotherapies for intermediate risk with excellent results:High dose brachytherapy as monotherapy for intermediate risk prostate cancer.
Intermediate-Risk Patients With Organ-Confined Prostate Cancer Have High Cancer-Free Survival Rate After Stereotactic Body Radiation Therapy
It seems like you have several good choices.