I have small red veins on my neck and collarbone due to having radiation.

It is important to get an evaluation to make sure there is no upper extremity DVT by venous Duplex scan before any treatment is initiated. Radiation therapy can cause deep vein thrombosis 0f the SVC, jugular veins, subcalvian veins, etc. Access ports from chemotherapy also cause deep vein clots of the upper extremities ... 

It is difficult to give a definitive recommendation without seeing these veins and knowing how long it has been since the radiation.  Usually neck veins are not treated.  Small veins (hemangioma or telangiectasia) can probably be treated with Ohmic Thermolysis (VeinGogh) or micro needle radio frequency. For small superficial veins, sclerotherapy in low concentrations may also be possible.