At a Glance
IMRT (intensity modulated radiotherapy) is an advanced form of external beam radiotherapy that uses computer-guided dose shaping to target the prostate precisely while reducing radiation to the bladder and rectum. It is a well-established treatment for localised and locally advanced prostate cancer (NICE NG131) and is usually given as an outpatient over approximately four weeks. Men with localised disease may also wish to discuss focal therapy as an alternative.
Key takeaways
- What it is: IMRT varies radiation beam strength from multiple angles to deliver a high dose to the prostate while protecting nearby organs.
- Who it suits: Men with localised or some locally advanced prostate cancer, often combined with hormone therapy for higher risk disease.
- Main benefits include: strong cancer control data, no surgery or incisions, outpatient treatment, and reduced exposure to the bladder and rectum.
- Common side effects: Urinary frequency, bowel irritation and fatigue during treatment; longer-term risks include urinary, bowel, or erectile changes.
- Outpatient treatment: Typically 20 sessions over four weeks in England; no surgical incisions required.
- Compare your options: Men with localized disease may also be suitable for active surveillance, focal therapy (HIFU or NanoKnife) or surgery: a multi-disciplinary review helps weigh all options.
What is IMRT?
IMRT stands for intensity modulated radiotherapy. It is also sometimes written as intensity modulated radiation therapy.
It is a type of external beam radiotherapy. This means the radiation comes from a machine outside the body. The machine directs radiation towards the prostate to damage cancer cells and reduce their ability to grow.
The main difference between IMRT and older forms of radiotherapy is how carefully the dose can be shaped. IMRT allows the treatment team to vary the strength of the beam across different areas. This helps give a higher dose to the prostate, while aiming to lower the dose to nearby organs.
This matters because the prostate sits close to the bladder, rectum and nerves involved in erections. Careful planning is needed to treat the cancer while reducing avoidable side effects.
How does IMRT work?
Before IMRT starts, the radiotherapy team creates a treatment plan. This usually involves a planning CT scan. Some centres also use MRI to help define the prostate and surrounding tissues more clearly.
The plan shows exactly where the radiation should go. It also shows the areas where the team wants to keep the dose as low as possible, such as the bladder and rectum.
During treatment, the machine moves around the body and gives radiation from different angles. The patient does not feel the radiation itself. Each treatment session is carefully checked so that the prostate is lined up as accurately as possible.
Modern IMRT is often combined with image-guided radiotherapy. This means scans or images are taken before treatment sessions to check the prostate position. The prostate can move slightly from day to day, especially depending on bladder and bowel filling, so these checks are important.
Why is IMRT used for prostate cancer?
Prostate cancer often needs a carefully planned dose of radiotherapy to treat it effectively. IMRT helps doctors shape that dose more accurately than older radiotherapy methods.
IMRT may be used for men whose cancer is still inside the prostate. It may also be used for some men whose cancer has started to grow just outside the prostate, or where nearby lymph nodes need to be considered as part of the treatment plan.
Some men have IMRT alone. Others have IMRT with hormone therapy. Hormone therapy can make prostate cancer cells more sensitive to radiotherapy and may improve cancer control in the right patients. It is more commonly used for intermediate-risk, high-risk or locally advanced prostate cancer.
The decision depends on several factors, including:
- PSA level
- Cancer grade
- Cancer stage
- MRI and other scan findings
- Biopsy results
- Urinary symptoms
- General health
- Personal priorities about side effects and recovery
What are the Benefits of IMRT?
The main benefit of IMRT is improved dose control. It allows the treatment team to shape the radiation dose around the prostate more carefully than older forms of external beam radiotherapy.
Possible benefits include:
- No operation or surgical cuts
- Treatment usually given as an outpatient
- More accurate dose shaping than older radiotherapy techniques
- Reduced radiation dose to some nearby healthy tissues
- Ability to treat the prostate, and sometimes surrounding areas, in a planned way
- Strong evidence base for radiotherapy as a standard treatment for suitable men with localised or locally advanced prostate cancer
IMRT does not remove all risk of side effects. It is still a whole-prostate treatment in most cases, and nearby tissues can still be affected. However, compared with older 3D conformal radiotherapy, IMRT has been associated with better dose shaping and may reduce some bowel-related side effects.
Many men continue some usual activities during treatment, but this varies. Tiredness and urinary or bowel symptoms can make daily life harder for some patients, especially as treatment goes on.
What are the side effects?
Like all prostate cancer treatments, IMRT can cause side effects. These vary from person to person. Some side effects happen during treatment or soon after it finishes. Others may appear months or years later.
Short-term effects may include:
- Tiredness
- Passing urine more often
- A sudden need to pass urine
- Mild burning or discomfort when passing urine
- Getting up more often at night to pass urine
- Loose stools or bowel irritation / urgency
Long-term effects can include urinary changes, bowel symptoms, or erectile dysfunction. Risks depend on age, baseline function, and other health factors. Specialist review is important when discussing side effects of prostate cancer treatment.
Men should tell their treatment team about symptoms early. Urinary, bowel and sexual side effects are common topics in radiotherapy clinics, and support is often available.
How IMRT compares with older radiotherapy
Older radiotherapy techniques were less able to shape the dose around the prostate. This meant nearby tissues could receive more radiation than intended.
3D conformal radiotherapy improved this by using scans to shape the beams more closely. IMRT developed this further by varying the strength of the radiation beam across different parts of the treatment area.
Image-guided radiotherapy then added regular imaging checks to help make sure the prostate is in the correct position before treatment is given.
| Treatment type | How it works | Typical role |
|---|---|---|
| Older 2D methods | Simpler planning and beam arrangements | Largely replaced for curative prostate treatment in modern centres |
| 3D conformal radiotherapy | Scans to shape beams around the prostate | More precise than older 2D treatment |
| IMRT | Computer planning to vary and shape radiation dose | Modern approach for many men having external beam radiotherapy |
| Image-guided approaches | Uses imaging checks before and/or during treatment | Helps improve positioning accuracy |
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What happens before treatment starts?
Before treatment starts, the team will review the cancer details and general health. This usually includes PSA, biopsy results, MRI findings and any other scans.
A planning CT scan is usually needed. The scan helps the team map the prostate, bladder, rectum and nearby tissues. Some centres also use MRI to help with planning.
Patients may be asked to follow bladder and bowel instructions. For example, some centres ask patients to attend with a comfortably full bladder and an empty bowel. This can help keep the prostate in a more consistent position.
Some men may have small markers placed in the prostate before treatment, depending on local practice. These can help the team line up treatment accurately. Not every patient needs them. The team also usually explains how many treatments are planned, whether hormone therapy is needed, and who to contact if symptoms become difficult, for example.
What does a typical treatment session involve?
Most IMRT sessions are straightforward. The patient lies on a treatment couch in the same position each time. The team checks alignment carefully before treatment starts.
Images may be taken to confirm the prostate position. The machine then moves around the body and delivers radiation from different angles.
The treatment itself is painless. The patient does not feel or see the radiation. The machine may make noise, but it does not touch the body.
A session may take around 10 to 20 minutes, although the exact time varies. Much of this time is used for positioning and safety checks. The radiation delivery itself usually takes only a few minutes.
In England, many men having radical external beam radiotherapy for localised prostate cancer are treated over 20 sessions across 4 weeks. Some men need a different schedule depending on their cancer, previous treatment and local practice.
Is IMRT right for everyone?
IMRT is not the best option for every patient. Suitability depends on several medical and personal factors. Some men may benefit more from surgery or other approaches.
Important factors include:
- Cancer location within or beyond the prostate
- Stage and grade of the cancer
- MRI and biopsy findings
- Previous prostate treatments
- Existing urinary symptoms
- General health and fitness, other medical conditions
- Personal priorities around side effects and recovery
Men with localised disease may also wish to compare focal vs radiation approaches. Whole-gland radiation treats the prostate broadly, while targeted ablation may suit selected cases. A multidisciplinary review can help patients understand the pros and cons of each route before making a decision.
How Focal Therapy Clinic can help
The Focal Therapy Clinic provides specialist support for men exploring prostate cancer treatment after diagnosis. Its multidisciplinary team reviews each case in detail and discusses suitable options, including surgery, radiotherapy, and focal therapy. This helps patients understand the benefits and limitations of each approach.
The clinic’s urologists have more than 75 years of combined focal treatment experience, and more than 2000 patients have been treated. Selected men with localised disease may be suitable for HIFU or NanoKnife, which aim to treat only the cancerous area while preserving healthy tissue. These approaches may help reduce the risk of incontinence and erectile dysfunction in appropriate cases.
The team also offers second opinions for men considering IMRT radiotherapy or other treatments. Advice is based on clinical findings, scan results, and personal priorities. This can help patients make informed decisions with greater confidence.
FAQs
References
European Association of Urology. (2026). EAU Guidelines on Prostate Cancer. Available at: https://uroweb.org/guidelines/prostate-cancer
National Institute for Health and Care Excellence. (2019, updated 2021). Prostate cancer: diagnosis and management (NG131). Available at: https://www.nice.org.uk/guidance/ng131
Cancer Research UK. (2025). Having external radiotherapy for prostate cancer. Available at: https://www.cancerresearchuk.org/about-cancer/prostate-cancer/treatment/radiotherapy/external-radiotherapy/radiotherapy-treatment-external-for-prostate
Cancer Research UK. (2025). Planning radiotherapy for prostate cancer. Available at: https://www.cancerresearchuk.org/about-cancer/prostate-cancer/treatment/radiotherapy/external-radiotherapy/planning-radiotherapy
Cancer Research UK. (2025). Side effects of prostate cancer radiotherapy. Available at: https://www.cancerresearchuk.org/about-cancer/prostate-cancer/treatment/radiotherapy/external-radiotherapy/side-effects-external-radiotherapy
Prostate Cancer UK. (2022). External beam radiotherapy. Available at: https://prostatecanceruk.org/prostate-information-and-support/treatments/external-beam-radiotherapy
