Hello Cathy1919 ,
The side effects from radiotherapy really depend on what (so organs such as the heart, lungs, stomach, bowel, etc, etc) is in the radiation field and the total dose of radiation you are treated with. In terms of late effects, in addition to the radiation field and radiation dosage, age at the time of treatment is an important factor to consider (particularly where radiation treatment occurs before the age of 30yrs).
Have your doctors discussed how they plan to manage side effects should they occur? Do they plan to protect your lungs, heart and remaining breast tissue while you undergo radiotherapy? When I underwent mantle radiotherapy, lead shields were used to reduce radiation exposure to my heart, lungs and breast tissue.
It is also worth asking the doctor what late effects are associated with the radiotherapy regime you are undergoing and how will you be monitored for the development of late effects once treatment is completed.