How to Prepare for Prostate SBRT Treatment

By: David Grew MD MPH

"Preparing for prostate SBRT is mostly about consistency."

If you are getting ready for SBRT for prostate cancer, your care team may give you specific instructions about your bowels and bladder before your planning scan and each treatment.

These steps may seem minor, but they are an important part of delivering radiation accurately. The prostate sits between the bladder and rectum, and changes in either organ can slightly shift its position from day to day.

The goal of preparation is to keep your anatomy as consistent as possible so your radiation team can target the prostate precisely while limiting radiation exposure to nearby healthy tissues.

What is a simulation appointment?

Before prostate SBRT begins, you will usually have a planning visit called a simulation.

During simulation, imaging is used to show the exact position of the prostate, bladder, rectum, and nearby tissues. Your radiation team uses these images to design your treatment plan.

Because this scan becomes the roadmap for your radiation treatment, your care team may ask you to prepare your bowel and bladder in the same way you will before future treatment sessions.

Why does bowel preparation matter?

The rectum sits directly behind the prostate.

If the rectum contains stool or a large amount of gas, it can expand and change the position of the prostate. This can make it harder to reproduce the same anatomy from one treatment to the next.

Keeping the rectum relatively empty can help:

• keep the prostate in a more consistent position
• improve treatment accuracy
• reduce unnecessary radiation exposure to nearby healthy tissue

Your center may use medications, dietary changes, enemas, or a combination of these approaches.

What medications might be used for bowel preparation?

Some treatment centers recommend medications such as bisacodyl and simethicone before simulation and during prostate radiation therapy.

Bisacodyl is a laxative that helps promote regular bowel movements.

Simethicone helps reduce gas and bloating.

For example, some prostate SBRT programs ask patients to begin these medications several days before simulation, stop them while the treatment plan is being created, and then restart them several days before the first radiation treatment.

The exact doses and schedule are not the same everywhere, so follow the instructions from your own care team rather than starting these medicines on your own.

Why might I need an enema?

A saline enema may be used to help empty the rectum before simulation or treatment.

Some centers routinely give an enema before the simulation scan. During treatment, patients may be asked to use one if they have not had a bowel movement shortly before their appointment.

The goal is not to completely empty the entire digestive system. It is simply to reduce stool and gas in the rectum so the prostate and nearby tissues are positioned as consistently as possible.

If your care team recommends an enema, follow their instructions about when to use it and whether you should eat afterward.

What should I do before each SBRT treatment?

Many centers ask patients to have a bowel movement shortly before treatment.

You may be told to try to have one within about one to two hours before your appointment. If you cannot, your care team may recommend an enema.

If you are following the bowel preparation instructions but are still having trouble emptying your bowels, tell your radiation team. They can adjust the plan rather than having you repeatedly struggle on your own.

What if bowel preparation causes diarrhea?

Tell your care team. Because bisacodyl is a laxative, it can sometimes cause loose stools or diarrhea. That does not mean you should simply keep taking the same amount regardless of your symptoms.

Your radiation team may be able to reduce or adjust the dose so that your bowels remain regular without causing unnecessary discomfort.

The goal is consistency, not diarrhea.

Can diet help reduce gas during prostate SBRT?

Yes. Gas can enlarge the rectum and make the prostate position less predictable. Small changes in how you eat may help reduce bloating during treatment.

Helpful strategies may include:

• eating slowly
• chewing food thoroughly
• avoiding drinking through straws
• avoiding carbonated drinks
• limiting foods that you know cause gas
• choosing cooked vegetables instead of raw vegetables if raw foods make you bloated

Foods such as onions, garlic, cruciferous vegetables, dried fruit, and dairy products can cause more gas in some people.

There is no single perfect “radiation diet.” Different people react differently to different foods.

If gas or bloating is becoming a problem, keeping a simple food diary can help identify patterns. Your treatment center may also have a dietitian who can help.

Why does my bladder need to be full?

Bladder preparation is just as important as bowel preparation. For prostate radiation, many treatment centers ask patients to arrive with a comfortably full bladder.

A fuller bladder can help move parts of the bladder and nearby bowel away from the highest-dose treatment area. It also helps reproduce the anatomy that was used when your radiation plan was created.

The goal is not to make yourself painfully uncomfortable. Your bladder should generally feel full enough to reproduce your treatment position, but not so full that you cannot comfortably remain still.

How much water should I drink?

Your treatment center should give you specific instructions. Some centers encourage patients to stay well hydrated throughout the day and then drink a certain amount of water at a specific time before simulation or treatment.

For example, a center may suggest drinking roughly 64 ounces of fluid over the course of the day for general hydration, unless another healthcare provider has told you to restrict fluids.

The amount you drink immediately before treatment is different and should come directly from your radiation team.

Do not force large amounts of water if you have been told to restrict fluids because of heart, kidney, or another medical condition.

What happens if my bladder is too full or not full enough?

This happens. Your treatment team can check your anatomy with imaging before radiation is delivered. If your bladder is not full enough, you may be asked to drink more water and wait.

If it is too full and you are uncomfortable, the team may ask you to empty part of your bladder and then recheck your position.

This is one reason treatment appointments can occasionally take longer than expected.

It does not mean anything has gone wrong. The team is trying to reproduce the anatomy used to create your treatment plan.

Why consistency matters so much with SBRT

SBRT delivers a high dose of radiation during each treatment, usually over a small number of sessions. That makes precision especially important.

Your radiation team uses imaging before treatment to verify the position of the prostate and surrounding organs. Bowel and bladder preparation help make those images more consistent from one visit to the next.

These preparation steps may feel repetitive, but they are an important part of helping your team deliver radiation where it is intended while protecting nearby healthy tissues as much as possible.

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Preparing for prostate SBRT is mostly about consistency.

Keeping your rectum relatively empty, limiting excess gas, and arriving with a comfortably full bladder can help your care team reproduce the same anatomy used to design your radiation plan.

Your treatment center may have a very specific bowel and bladder routine. Follow those instructions even if they differ from general guidance you read elsewhere.

And if the preparation is not working for you—whether because of constipation, diarrhea, bloating, difficulty holding your bladder, or another concern—tell your care team. These are common issues, and the preparation plan can often be adjusted.

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To learn more, watch this video we made on How to Prepare for Prostate SBRT Treatment.

To learn more about prostate cancer, browse our dedicated prostate cancer education library for more information.

Hire PRIMR to create custom video content for your clinical trial or medical product today.

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FAQs:

Do I need to follow the bowel preparation instructions even if I normally have regular bowel movements?

Yes, if your radiation team has prescribed them. The goal is not simply to prevent constipation. It is to keep the rectum and prostate in a consistent position for planning and treatment. Follow your center's instructions, and let your care team know if the routine causes diarrhea, cramping, or other problems.

Should my bladder be as full as possible before treatment?

No. The goal is usually a comfortably full bladder, not an uncomfortably full one. Being too full can make it difficult to lie still during treatment. Your radiation team will tell you how much water to drink and when. If you are having trouble reaching the right level of fullness, tell them so they can adjust the routine.

Can I eat normally during my course of prostate SBRT?

Usually, yes. Most patients do not need a highly restrictive diet, but your care team may recommend limiting foods or drinks that cause gas or bloating. If you notice certain foods repeatedly causing problems before treatment, discuss them with your care team or a dietitian.

Do I need to use an enema before every SBRT treatment?

Not necessarily. Some centers recommend an enema routinely, while others use one only if you have not had a bowel movement close to your appointment or if imaging shows that the rectum is too full. Follow the instructions from your own treatment center rather than using an enema automatically.

What happens if I cannot complete the bowel or bladder preparation correctly one day?

Treatment may still be possible, but your team may need extra time to adjust. They may ask you to drink more water, empty part of your bladder, have a bowel movement, or use an enema before repeating the imaging. Do not feel embarrassed if this happens. Contact or tell your radiation team rather than trying to improvise on your own.

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