My RO hasn't seen lymphocyte reduction post-RT. RT has a stimulatory effect on the immune system, and there is a lot of research into how best to take advantage of this effect. It has long been known that radiation in one place may result in tumor killing in a completely different place - this is called the "abscopal" effect and is thought to be a product of immune stimulation. When cancer cells are destroyed by radiation, they present cancer antigens to the immune system, which reacts by seeking out and destroying any such cells elsewhere. ADT pretreatment is thought to be effective because it augments this process. Eventually, the immune system adapts to the cancer cells, and they are no longer destroyed. There are new immunotherapies (called immune checkpoint blockade) being tested that will prevent such adaptation.
This abscopal effect may be enhanced by hypofractionation (i.e., SBRT and HDR brachy), and may be minimal with normal fractionation.
Radiation as an immunological adjuvant: current evidence on dose and fractionationRT of bone marrow can deplete lymphocyte production, but this does not seem to occur with present day prostate radiation. As you can read in the following reference, "There is not significant systemic lymph
openia from prostate cancer EBRT, our group has observed."
Clinical opportunities in combining immunotherapy with radiation therapyEarly studies have observed some suppression, but at sub-clinical levels: "Low CBC levels during radiation therapy are likely to be the result of other medical problems that cancer patients face." It seems that leukocyte suppression was more common in the pre-IGRT era, possibly as a result of incidental bone irradiation. But with better imaging techniques, that's no longer an issue. Perhaps stress, which is known to diminish white blood cell count, plays a role as well.
- Allen