browntrout,
There is more to toxicity than just dose decreases (although they are correlated to some extent). There is more to patient-perceived harms than just toxicity data (although they are correlated to some extent). You are quite right to look to patient-reported outcomes on validated surveys as the best source of data, but we have none yet on rectal spacers.
FYI - here's the best data we have so far on the use of rectal spacers:
Hydrogel Spacer Prospective Multicenter Randomized Controlled Pivotal Trial: Dosimetric and Clinical Effects of Perirectal Spacer Application in Men Undergoing Prostate Image Guided Intensity Modulated Radiation TherapyThere were no differences in
acute rectal toxicity whether the spacer was used or not. Adverse acute (earlier than 3 months) rectal events were noted in 34 percent of those who got the SpaceOAR gel, and 32 percent of those who did not —
no difference.
As far as incidents of rectal toxicity that occurred between 3 and 15 months after treatment, there were only 5 cases of rectal symptoms (7 percent) at all in the group that did not have the spacer, and 4 of the 5 were mild — Grade 1 bleeding and urgency. It should be noted that Grade 1 symptoms are so mild that they are often not even reported, so I like to group Grade 0 and 1 together. There was only one serious rectal event (Grade 3 proctitis) in one man who did not get a spacer. There was a single late-term Grade 1 rectal adverse event in a man who got a spacer.
I also notice very serious use of anesthesia with the rectal spacer, including general (36 percent), monitored (25 percent), local (31 percent), conscious sedation (6 percent) and other (11 percent). This increases the cost, and raises safety concerns (there were no anesthesia-related incidents), and limits the number of patients who are eligible for it. Antibiotic prophylaxis is required with it as well.
This reinforces my point that
late-term rectal events are not a serious problem with modern radiation techniques.
Acute rectal adverse events are a much bigger problem, but the SpaceOAR gel did not help
at all with that. True, there will always be that residual 1 or 2 percent who are sensitive to radiation for some reason, and who may benefit. I’m glad that there is this option for those few who may benefit from it, and for whom it may be worth the additional $3000 cost. Men with a history of inflammatory bowel disease should definitely consider it.
- Allen