Help with no gas, empty bowel diet during RT.

I used these guidelines for 30 sessions of IMRT last fall. Didn't miss a session.
https://www.nutrition.va.gov/docs/Oncology/RadiationTherapyforProstateCancerNutritionMar2025.pdf
Only other thing I did was not eat anything past 6PM and only a slice of dry toast to take meds with before treatment. Good luck! 👍

I also got each week’s schedule the Friday before; that allowed me to plan not only my meals, but also my full bladder/empty bowel routine as well as my regular schedule around the appointments. (My appointments were always scheduled at 2:00PM or 2:40PM.)

Diet-wise —> I decreased red meats; increased fish, salads; added more fruits, vegetables, and grains/nuts; cut out soft drinks; cut back on processed foods, and made other tweaks here and there. I also added a protein/fruit smoothie every morning, and a protein bar & two energy bars every day. (I think that was helpful in sustaining energy and endurance during the months of low-testosterone due to ADT.)

I also exercised (lifted weights and ran 5Ks or swam) daily.

In the weeks leading up to my radiation treatments, I practiced the full bladder/empty bowel routine every day. By the time of my first treatment, I had the routine down to a ritual.

A FODMAP diet will definitely help; it limits the amount of fermentable foods you eat, so gas is drastically reduced.
Phil

I finished my 20 sessions of external beam recently. I am 76. I haven't had any previous surgery on my bowels. Prior to the external beam sessions I had one treatment of HDR, i.e. High Dose rate Brachytherapy. As I understand things, my external beam treatments were not as intense as they would have been if I had not already had the HDR. The HDR had already hit my prostate with a very high dose of radiation. The external beam was intended to add a bit to that as well as hit areas the HDR could not do, like some lymph nodes in my pelvis.

I knew nothing about how external beam treatment rooms operate. I had no idea how long the beam would be on during each session. I had no idea what the particular machine they would be using was capable of.

My understanding was that whatever the machine operators did to position me prior to treatment, by adjusting my position with lasers on my tattoos, and with whatever imaging scan their machine could provide while I was on the table, once they turned the beam on, the assumption was, everything is going to stay the same, and they just blast away.

Things do not necessarily stay the same. Gas and feces can move once the beam is on. If I couldn't hold all the water they want me to drink, I could piss myself right on the table which would also move the prostate. If the beam doesn't hit its intended target, it hits normal tissue. Too much radiated normal tissue leads to side effects - some of which are extremely not desirable.

I worried quite a bit about all this.

Prior to this treatment I was producing a lot of gas, and it seemed my rectum would always have something in it or something moving into it, which produced a number of small bowel movements during a typical day.

I experimented at home with drinking the amount of water I would be required to drink prior to each treatment and found I could not hold it for the length of time they were going to ask me to hold it. Great.

I consulted a dietitian and read whatever I could find that the cancer center I was to be treated at had published on how to prepare for external beam treatment. Basically the contradictions in the material and between the dietitian's advice and the material, plus the results of whatever I tried given my own unique situation, left me quite doubtful and confused. Don't change your diet. Change your diet. Get rid of insoluble fiber. Don't go low fiber. Don't eat [insert a favorite food here]. Eat [insert previously said to be verboten food here]. Etc.

I made it through the 20 sessions. The RO said things went well. My decision to be treated at this center, with this doctor supervising, was based on the respect I had developed by meeting and discussing things with him. All the other considerations, like should I have gone to one of the more distant centers where they had an MRI-Linac had faded away.

What would have helped me prepare for these treatments was to know more about what machine they would be using, and how they would be using it.

This center had an Ethos Hypersight. It has a cone beam CT that gives operators a high quality image they use to make sure they have things set up to hit the right target, just before they turn the beam on. A feature that made my treatments more bearable, and in my mind more likely to be successful, was the fact the machine could change the direction its radiation hits the patient from very quickly. Treatments can be short.

The plan when treating me was to blast away for about 3 minutes each session. Once I saw this, a lot of my worries disappeared. Their assumption that things could stay the same looked a lot more reasonable.

@heavyphil thanks, I was able to download and print a FODMAP food list. Easy now to understand why I have been so gassy. I have been eating a slice of 21 grain bread toasted with half an avocado every morning for years. Lunch is a smoothie with protein powder with frozen mango and frozen ripe banana. Dinner was lean meat or fish with rice or potato and always a large bowl of raspberries, blackberries, strawberries, peaches, etc. Pretty much everything I have been eating is on the restricted FODMAP list. We grocery shop on Fridays, so I will be drastically changing my diet starting Friday night.

@mjp0512 thank you, great to have the VA's recommendations and I printed out all 5 pages. I will cross reference this with @heavyphil's suggestion of a low FODMAP diet and hopefully come up with a diet that will work. We usually eat dinner at 6pm, and don't snack afterwards. I can handle a slice of sourdough dry toast with morning meds and the required amount of water to fill my bladder until my treatment time, I'm guessing this would work for me pretty well.

@climateguy thanks for your detailed reply. Yes, I have read a lot of contradictory information as well regarding which foods were good and which foods you should avoid. In my case, I think @heavyphil's suggestion of a low FODMAP diet might be a really good choice. I'm not sure what type of CT my RO uses, but I have the utmost confidence in his and his teams expertise. I just want to give them as stable a target as possible.

PS. What helped me a lot was that they happened to schedule almost all of my treatments for the same time each day. I felt that the 12:45 time that 19 of the 20 treatments were scheduled for was just about perfect for me. I would get up around 5 a.m. and have a light breakfast, then nothing until after the treatment for the day was over. I was able to establish a routine.

A big worry for me was how to arrive at the treatment table with a full bladder. I'd ask after each treatment for the operators to tell me how full my bladder was that day. They'd give me a number, like 80, which meant my bladder was 80% as full as it was when they did the CT-Sim session to plan the treatments in the first place. The ideal would be 100. Given the abilities of the machine they were using, they said 80s were acceptable, but that 100% or fuller than at the CT-Sim would be better.

An operator clued me in to how I might learn how to arrive in optimum shape. He said things didn't just depend on drinking the two cups of water "x" number of minutes prior to getting on the table. How hydrated was I when I drank the 2 cups of water? One day I squeezed in my daily visit to the YMCA prior to the treatment and worked out for an hour with weights. My bladder was its lowest number that day even though I drank 3 cups of water at the prescribed time.

The routine I eventually developed was to drink 2 cups of water 2 hours before presenting for treatment, then 2 more cups 1 hour before, then the prescribed 2 cups at the prescribed time. I think I tended to be dehydrated compared to most patients most of the time. I had to learn to pay attention to signals my body was producing indicating I was dehydrated. I also did not visit the gym prior to any more radiation treatments. This routine had me quite often hearing my bladder was exactly as full as it was during the CT-Sim.

Things fell apart around treatment 17. Side effects were setting in. I was fending off extreme fatigue, and fairly severe diarrhea. The bladder prep still worked, but bowel prep, which had not been a problem until then, became the problem.

They'd say they couldn't do the treatment and send me off to the bathroom while they treated another patient to see if I could clear my rectum. How was I supposed to clear my rectum and still hold a full bladder for an extra 15 minutes? Things went very far south when I tried holding my penis closed by hand while trying to take a crap only to watch blood dripping out of my penis as a result. I don't know how I made it through the last 3 treatments.

One thing I tried early on was to fast prior to the treatment, i.e. no breakfast. The nurse later explained as I told her how big my headache was after that treatment was it was a bad idea to suddenly subject my system to a fast during the stress of radiation treatment at my age. I didn't try that again.

I finished my 28 treatments back in 02/2026. I'm 9 months into ADT - with 9 months remaining.

For RT - I had a lovely 35 minute drive each day down to Rancho Bernardo (I live up in Fallbrook). I got into a routine of coffee when I woke up, bowel movement after coffee, and then I'd take a water bottle for the ride down there and take a few sips before going in for treatment. That ensured a bladder at the right level and a bowel they could work around. Nothing more embarrassing than having the nurse come in and tell me I need to go have a bowel movement. lol. That happened one time...and I was able to manage it. I may be different than you in that I had no diet restrictions over those 28 teartments. They just wanted the bladder at approx the same level each time and the bowels cleared.

Best of luck!

@jbristow3682

Thanks for sharing since our RO also told us that my husband should not change diet, that they do not do that with their patients since it brings more "unknowns" into equation and that it can cause digestive system to go berserk with so many changes.
They just want BM happening the morning of treatment and a full bladder.
Maybe it is California thing lol 🤷‍♀️ ! We are in the Bay Area - "Chill bro " lol lol