Giving pelvic RT to a man with PCa mets is relatively new and not available to all men in all areas of the country so there is little data on the impact of getting the full dose, let alone what the impact might be of getting half of it and then stopping - I don't think anyone will have answers to your question about effectiveness.
On the basis that if you lived elsewhere or were under a different oncologist he might not have been offered this treatment at all you could -
- clarify with the oncologist / RT team whether a break in the treatment means it can't be started up again later
- clarify whether, with advanced PCa, compromised post chemo and on HT, it is wise to be visiting a hospital every day for 7 weeks