One more comment - make sure to get a second opinion since iris cancer is so rare.
MJK MD
Sorry I have no experience with this type of treatment. Iris malignancy is extremely rare and I suspect you will not find many people who have undergone such therepy. The specialist where you are due to receive the treatment should be able to give you some advice. Cataract formation and catract surgery should be one of your lesser concerns since the surgery only take 10-20 minutes and has an extremely high success rate.
MJK MD
The doctor here is on vacation. You can post your question on the eye expert forum, I hope you also get an answer from a community member.