Your father is perhaps having what is known as castrate resistant prostate cancer
with disease progression. i presume that what you are mentioning to as chemotherapy
taken 2 years ago actually is hormone therapy
. Even if he has taken chemotherapy the first time, and had responded to it then, we could safely consider chemotherapeutic re-challenge in his present clinical context.
Unlike chemotherapy for many diseases, only a single drug is employed as chemotherapy in prostate cancer. there are two drugs, both being relatively safe and with minimal side effect profile.
a newer hormonal
agent called Abiraterone
is now available in India and could be considered as an alternative if your father cannot tolerate chemotherapy or fails to respond to the given therapy.
i am sure your doctors have considered your father's overall condition before recommending you this treatment option. go ahead and get it done. your father should do well with that.