My father will have radiotherapy is there any effect of the radiation on the persons in contact with my father

Absolutely Not.

However, depending on the RT dosage and location it will probably have an effect on your father's immune system and therefore it is important to consider any possible adverse effects others may have on your father.

As such it is important that anyone that may have a cold or ailment of any kind be kept away so as not to inadvertently infect him whilst his immune system is at a low.

Your question is somewhat not clear. I think you mean that is there any affect of the radiation if others come into contact with the radiated person.

Please note the Radiation therapy does not make the person having the treatments radioactive. During the radiation ONLY the High-energy radiation sent to the affected part of the patient, kills cells by damaging their DNA. Generally the radiologist involved in giving the therapy does not stay at the place when the patient receive the therapy. They will go near the patient only after radiation is done.

So when you or someone else come in contact with your father after radiation will not have any effect. -

No, none at all.