I have heard that the proton therapy requires the use of an inflatable bladder that they insert rectally each day of treatment; that doesn't sound like much fun. But it is probably worth the fewer side effects.
The more correct term is "rectal balloon" and it serves the dual purpose of helping to hold the prostate in a constant position each day for delivery of the proton beam, plus also shielding the majority of the rectum from the beam itself. It does not hurt and in fact is another safeguard used in proton treatment that most photon facilities could use, but choose not to. Here is a reference to a study that confirms the effectiveness of the balloon: http://ptcog.web.psi.ch/PTCOG45/Monday%20
Age at time of diagnosis: 61, psa 4.6, 30 days cipro, psa 4.3, biopsy 4/28/11, 2 of 12 cores positive, Gleason 6
Approved (insurance) for Proton Therapy at IU @ Bloomington 7/14/2011
8/17/2011 Proton Therapy Treatment begins
10/19/2011 Proton Therapy Treatment Completed!
IU Health Proton Therapy Center: http://iuhealthprotontherapy.org/about
1/24/2012 psa 0.8