How do you manage significant gas in patients undergoing pelvic radiotherapy?
This is tough, especially once the simulation is completed, the patient comes in for treatments and now you see very different anatomy.
The one thing that I have changed in practice - and I'm aware this is not always possible at higher volume centers - is to have the simulation at about the same time of day as the treatment will be (within about 30 minutes). This requires planning. There is a rhythm to our bowel gas patterns and anecdotally, I have found that scheduling it like this makes it more reproducible and I have noticed much less of this issue.
If there was no gas at simulation and then at treatment there is, this may be a time of day issue. Can consider changing the treatment time to match when the simulation was. If this isn't possible/doesn't work, take the time to discuss diet and gas-producing foods. There is a lot of this on the internet, so I won't type it all. Preferably, this discussion was had prior to simulation and treatment, but does not always happen and it may be worthwhile to happen ex post facto.
Other options
- "Red Robin" rectal tube. Occasionally, I have heard the gas release. I don't know that this has data behind it, but you know what does? A finger in the rectum. Worth a try, I suppose.
- Fiber supplementation to start before simulation and continue during treatment (this is dietary, I guess, but I think of it as something different than the actual foods the patient eats, as it can be done with pills and powders).
- Re-simulation if it is drastic
- Gas-X (simethicone). Have not had much luck with this. Limited evidence, as well.
- Maybe not worry about it very much. IGRT/IMRT for prostate cancer is remarkably safe, has very low toxicity, and patients typically do well no matter what. I tend not to worry too much about it.
YMMV
I think the need to worry about this issue depends on what you're treating. If you are treating just the prostate +/- the proximal seminal vesicles, you are aligning the fields to the prostate and this is generally a non-issue. If you are including the prostate, SVs, and pelvic nodes, it can create major alignment problems. In that case, I will ask the patient to avoid foods that cause them to develop gas. This can vary from person to person, for example, as some people may be lactose intolerant and others are not, but most people know what causes them to get gassy. I've also had some success with simethicone as a gas-reducing agent (GasX and similar products). If I detect an alignment problem before treatment, I will generally ask the patient to try to have a bowel movement. Sometimes that helps. I've used rectal tubes, too, like Dr. @Dr. First Last, as a last resort.
If the patient is gassy at CT sim, unless it's in the rectum for a prostate patient, don't 'fix' it. All you're doing is setting yourself up for issues down the line. This mentality is also why I dislike enemas prior to CT sim because unless you're going to ask them to do it prior to each treatment, you're setting up each day to be a slog. Work with the patient's anatomy, within reason.
Low residue diet to start can be helpful. If insufficient, Gas-X and/or Beano at escalating doses as per packaging. I recommend that if one doesn't work, try the other. Has not been a common issue.
Pelvic nodal volumes are generally not overtly affected and can be ameliorated with appropriate PTV margins given only going to 45 Gy. Have PTVs generous enough that allow for variations in anatomy without requiring re-sim.
For lower dose EBRT (gyn/GI), same as nodal volumes.
For prostate patients where the EBRT dose is higher, the gas in the rectum (ONLY) can be an issue given tighter PTVs given higher EBRT dose. That may require patients to get off the table, or try to pass some on the table.
I have not personally placed a red rubber or finger in the rectum on the RT table for a patient coming in for EBRT. I would not ask my therapists to do that either.
Red rubber catheter. Our therapists are adept at recognizing the need and at inserting a rectal tube to relieve the gas. Then, they repeat the cone beam. The difference is readily apparent!