IGRT and Fiducial Marker movements during treatment

I need some input information on the subject that I don't clearly understand. I am in the beginning of my second week of IMRT/IGRT treatment and prior to the start of treatment I had 4 fiducial marker placement done one week before first session. There is one question that seems logical to me but I could not find any meaningful information. From what I learned before, for people who choose LDR BT one of side effect is possible seeds migration. In other words seeds can MOVE inside prostate. If this is a possibility with radioactive seeds then this possibility exists for Fiducial Markers. Now, the treatment plan for IGRT rely on FM position and calculates distance from markers to the edges of prostate, then this information goes to the program and treatment plan is generated. If gold seeds slowly moves withing prostate over period of time then all data get skewed and healthy tissue get additional radiation while prostate get lower dose then planned. One of the factors that can cause markers to move is sex life, because of prostate expanding during the process. My question should I avoid any sex life for treatment period (2,5 month) to minimize possibility of FM movements or it does not make any difference. I asked this question to one of the assistance during treatment and the answer was: the sex life does not have any impact on treatment process. I still concern and would like to have more detailed explanation if possible.

I understand the difference when markers move with prostate (rectum gas problem) and when markers move within prostate.

Thank you Andrew. I thought it should be some sort of double checking system in place. Otherwise it would be know by now with 20 years records.