USE OF RECTAL SPACER IN LOW DOSE BRACHYTHERAPY.

I didn't have LDR (I had HDR and EBRT) and I studied physics.

The strength of radiation falls off very rapidly with increasing distance from the radioactive source. For LDR seeds the effective range of radiation is about 4mm. Your bowel will be outside that range.

I know there are warnings about having pets or children on your lap, so you are probably thinking the radiation at about 15cm from your prostate is still dangerous, but the reality is that the radiation dose a child on your lap would receive is about 0.1% of the dose in your prostate (no point in exposing a child to that completely avoidable risk though). Your bowel at about 1cm from your prostate is probably getting about 5% the dose your prostate is getting.

With EBRT the figures are quite different. As your bowel is near your prostate it will be getting exactly the same dose as your prostate (100%). By firing at different angles they can get this down to about 20% the dose. By using a rectal spacer they can get it to about 10% the dose.

Even with EBRT it is considered the benefit of a rectal spacer is not worth while, or to put it another way, your bowel can tolerate 20% of radiation, and bringing that down to 10% doesn't make a significant improvement. So with LDR which is only getting 5% the dose the operation to insert the spacer would probably be more dangerous than the benefit you would get.