Radiotherapy for Prostate Cancer

Radiotherapy uses high-energy radiation to treat prostate cancer, and is one of the main curative-intent options for localised disease, alongside surgery and, in selected cases, active surveillance.^1,17 It can be delivered in three main ways:¹

• External beam radiation - radiation delivered from a machine outside the body.
• High dose rate (HDR) brachytherapy - a radioactive source placed temporarily inside the prostate. See our page on brachytherapy.
• Low dose rate (seed) brachytherapy - small radioactive seeds implanted permanently in the prostate. See our page on seed radiotherapy.

The sections below focus mainly on external beam radiotherapy. The right approach for any individual depends on the cancer’s stage and grade, prostate size, urinary symptoms, general health and personal preference, and is best decided after discussion with a urologist and a radiation oncologist.¹⁷

How external beam radiotherapy works

External beam radiotherapy is delivered as an outpatient. Patients lie on a machine and receive focused radiation daily, Monday to Friday, for around 20 minutes per session, over roughly seven weeks on a conventional schedule. Most patients are able to continue working during the treatment course.

Before treatment starts there is a planning stage, which usually involves a CT scan (and sometimes an MRI) so the radiation can be shaped to the prostate. Some men have small markers (fiducials) placed in the prostate, or a rectal spacer inserted, to help target the radiation accurately from day to day.^12,13

Radiotherapy techniques and dose

External beam radiotherapy⁸ is an accepted, effective treatment, but the technique and dose delivered can vary between centres. Modern conformal techniques, such as intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT), shape the radiation to the prostate and allow a higher dose to be delivered to the gland while limiting the dose to nearby organs.^1,8 Image guidance (IGRT) is used to check the position of the prostate at each session. When considering radiotherapy, it’s worth asking the treating institution exactly what technique and dose they plan to use.

Treatment schedules: conventional and hypofractionation

Traditionally, external beam radiotherapy was given as a large number of small daily treatments (fractions) over about seven to eight weeks. Large randomised trials have since shown that giving a slightly higher dose per session over a shorter overall course (moderate hypofractionation, typically around four weeks) produces similar cancer-control and side-effect outcomes.⁹ Because of this, shorter schedules have become widely used.

Even shorter courses are also used in selected patients. Ultra-hypofractionated radiotherapy delivers treatment in only a handful of sessions; the HYPO-RT-PC trial reported that an ultra-hypofractionated schedule was non-inferior to conventional fractionation for intermediate-risk disease at five years.¹⁰ Stereotactic body radiotherapy (SBRT), which delivers a small number of highly focused treatments, was found to be non-inferior to conventionally or moderately hypofractionated radiotherapy for low- and intermediate-risk prostate cancer in the five-year results of the PACE-B trial.¹¹ Not every schedule is suitable for every man, and the choice depends on the cancer’s risk category and individual factors, which a radiation oncologist can explain.

Side effects

Short-term side effects can include lethargy and occasional nausea. Because radiation inevitably affects some of the adjacent organs (bladder and rectum), a small percentage of patients experience more serious long-term effects such as rectal bleeding, and urinary or bowel urgency and frequency.^2,4 Radiotherapy can also affect erectile function and fertility over time. As with any treatment, the benefits need to be weighed against these risks, and side effects vary from person to person.

Protecting the rectum: rectal spacers

Because the rectum sits directly behind the prostate, it can receive some radiation dose during treatment. A rectal spacer is a soft gel injected between the prostate and the rectum to push the rectal wall further from the high-dose area. Randomised trials of hydrogel and hyaluronic acid spacers have shown that they reduce the radiation dose reaching the rectum and can lower the risk of certain bowel side effects.^12,13 A spacer is not required for every patient, and its insertion is a minor procedure that carries its own small risks; whether it is appropriate is a decision made with the treating team. Patient information on one such device is available in the brochures below.

Combining with hormone therapy

For more active or aggressive cancers, radiotherapy is usually combined with a period of hormone therapy (androgen deprivation therapy), often around 12 months, as this combination can improve outcomes for higher-risk disease.³ Hormone therapy itself has side effects, such as hot flushes, fatigue, loss of libido and effects on bone density, which need to be factored into the decision. More detail is on our hormone treatment page.

Comparing radiotherapy and surgery

Surgery after radiotherapy is generally not possible - radiation causes significant scarring which makes a subsequent operation very difficult.⁴

Most studies show that radiotherapy and surgery offer equivalent results up to around 10 years, though data beyond 10 years is more contested.^5,6 For this reason, younger patients or those with a long life expectancy are generally steered towards surgery rather than external beam radiotherapy. The ProtecT trial, which randomised men between monitoring, surgery and radiotherapy, found that the different treatments affected urinary, bowel and sexual function in different ways: surgery had a greater early effect on urinary continence and erectile function, while radiotherapy was more associated with bowel symptoms.¹⁵ Understanding these trade-offs is an important part of choosing between treatments.

Radiotherapy after surgery

Radiotherapy is sometimes used after a radical prostatectomy if there is a higher risk of, or evidence of, cancer returning. The RADICALS-RT trial compared giving radiotherapy routinely soon after surgery with waiting and giving it only if the PSA starts to rise (early salvage radiotherapy), and found that an observation policy with early salvage radiotherapy avoids over-treating men who may never need it, without compromising cancer control.¹⁴ Whether and when radiotherapy is needed after surgery is guided by the pathology results and PSA monitoring.

Secondary cancers

There is some concern about a slightly increased incidence of bladder cancer and other secondary cancers after radiotherapy, although this remains contentious and the absolute risk is small.⁷

Follow-up after radiotherapy

After radiotherapy the PSA is monitored over time rather than expected to fall immediately. Unlike after surgery, the PSA falls gradually to a low point (nadir) and can fluctuate. Treatment is generally considered to have failed only when the PSA rises to more than 2 ng/mL above that nadir - the widely used “Phoenix” definition of biochemical failure.¹⁶ A temporary rise in PSA (a “bounce”) can occur after radiotherapy and does not necessarily indicate that the cancer has returned, which is why ongoing follow-up is important.

Making a decision

Radiotherapy is one of several effective options for localised prostate cancer, and the best choice depends on the individual. If you would like to discuss whether radiotherapy is appropriate in your situation, or want a further opinion on a treatment plan, you are welcome to request a second opinion.