External beam radiotherapy – prostate cancer

External beam radiotherapy is widely used is widely used in the treatment of prostate cancer. It involves directing high energy radiation rays at the prostate gland to destroy the cancer cells in the prostate and spare the healthy tissues.

The are two different ways to give radiation, external beam radiotherapy (conformal or Intensity Modulated Radiotherapy – IMRT) and brachytherapy. A machine called a Linear Accelerator or LINAC (pictured right) is used to deliver external beam radiation.

Is this the right treatment for me?

External beam radiotherapy is mainly used to treat localised prostate cancer. This means the cancer cells have not spread beyond your prostate into the rest of your body. External beam radiotherapy is also used to treat locally advanced prostate cancer. This means the prostate cancer has started to spread from the prostate into nearby tissues, but has not spread to other parts of the body. External beam radiotherapy is also used to treat bone pain caused by advanced prostate cancer.

There are two different indications for external beam radiotherapy:

1. Radical radiotherapy: When external beam radiotherapy is used to treat early cancers confined to the prostate or locally advanced prostate cancer, where the cancer cells has spread to the area just outside the prostate but has not yet reached the lymph nodes or bones.
2. Palliative radiotherapy: When external beam radiotherapy is used to help symptoms caused by prostate cancer that has spread to the bones or lymph glands.

What does external beam radiotherapy involve?

Pre-treatment planning

Before you are treated, you will have an appointment for a radiotherapy planning session. At the initial appointment you will have a CT-scan of the area to be treated. This is done in order to determine the treatment field and exactly where the beams will be aimed. Planning is a very important part of radiotherapy and may take one or two visits. Before your scan, you will be asked to have a comfortably full bladder and have an empty bowel. This will help in targeting the treatment area more accurately. If you suffer from constipation, you need to tell your oncologist at the initial consultation. Pinpoint dots (tattoos) are marked on the skin in the centre at the level of the prostate and on each side at this level. These are barely visible but will help the radiographers to position you accurately and to show where the rays will be directed.

The CT-images are downloaded into the radiotherapy planning computer and your oncologist will localise the prostate gland, seminal vesicles, bladder, bowels and bones in order to target the cancer accurately and spare the normal tissues. A team of medical physicists will then produce a treatment plan which is authorised by your oncologist.

The planning process can take up to two weeks.

The treatment

External beam radiotherapy is given on an out-patient basis. The treatment is given daily, Monday to Friday, over six to eight weeks. Radiographers will position you carefully on a special bed and make sure you are comfortable. The radiation machine (linear accelerator) moves around the bed to deliver beams from different angles. During your treatment you will be left alone in the room but you are watched through cameras and will be able to talk to the radiographer. Radiotherapy is not painful but you have to lie still for a few minutes while the treatment is being given. Each daily treatment takes approximately 20 minutes, which include time to position you on the treatment couch.

How does external beam radiotherapy work?

External beam radiotherapy uses high-energy X-rays to kill cancer cells in the prostate to eradicate the disease. A special attachment to the radiotherapy machine carefully shapes X-ray beams to the size and shape of the prostate to target the cancer cells and minimise damage to healthy cells and nearby organs such as the bladder and bowels. This technique is known as conformal radiotherapy.

Intensity Modulated Radiotherapy (IMRT)

Intensity modulated radiotherapy is a relatively new approach, first introduced in the UK in 2002. The aim is to increase the dose of radiation to the prostate while sparing normal tissue. A device called “multi-leaf collimator” in the radiotherapy machine adjusts the size and shape of the radiation beams. There are 80–120 tiny lead "leaves" on each side of the beam that are moved in and out of the radiation field while the beam is on, to vary the beam intensity and precisely distribute the radiation dose.

To date, there is no evidence that IMRT is more effective than conformal radiotherapy. Clinical trials to determine the benefit of IMRT are ongoing.

Image-Guided Radiotherapy (IGRT)

IGRT takes IMRT one step further. Newer radiotherapy machines enable the oncologist to both scan and treat the patient at the same time, in the treatment room. The aim is to detect any slight change in the position of the prostate gland that may result from variation in the filling of the bladder or rectum. Using this information, the radiation beams can be adjusted in order to precisely target the treatment to the cancer.

Possible short term side-effects

There are a number of side-effects which you may experience during treatment, which normally disappear once treatment has finished. Most patients will continue with their normal activities during the treatment. You will be reviewed by your oncologist on regular basis during the treatment to assess and treat the side effects.

Radiotherapy may cause cystitis, making you want to pass urine more often and causing a burning sensation as you pass urine. This is treated with medications and sometimes requires a course of antibiotics. During radiotherapy, you may feel more tired than usual. Regular gentle exercise, such as walking, can help to prevent and improve tiredness.

Your treatment may cause irritation, resulting in soreness and diarrhea. Medicines can be prescribed to reduce these symptoms and you may be advised to change your diet during the course of your radiotherapy.

The radiographers will give you advice on skin care during radiotherapy. You may lose the pubic hair in the treatment area. This usually grows back but can be permanent.

Possible long-term side effects

Most side effects will settle down after your course of radiotherapy treatment has finished. However some side effects can become long term or permanent. These include long term bowel and urinary side effects such as chronic diarrhoea, rectal bleeding, cystitis, narrowing of the urethra and incontinence. With the new radiotherapy techniques, the risk of significant long-term side effects is very small (less than 5 per cent). If these side effects occur, you will be referred to a specialist for treatment.

External beam radiotherapy can cause impotence or erectile dysfunction (ED) in 40–60 per cent of men. The risk is higher in patients receiving hormonal treatment and those who suffer from diabetes or hypertension. There are special clinics called ED-clinics for patients who become impotent after treatment for prostate cancer.

Hormone therapy

You may be started on hormonal treatment to stop the production or block the action of testosterone before external beam radiotherapy. The duration of the treatment will depend on the stage of your cancer and is usually started three months before starting external beam radiotherapy. Patients with locally advanced prostate cancer may need to take the hormones for up to three years.

The main benefits of hormonal treatment are:

1. To reduce the size of the prostate gland and the cancer which in turn reduce the radiation fields and the side effects.
2. Hormones combined with radiotherapy have been shown to increase the cure rates in patients with the more aggressive forms of prostate cancer and in cases where the cancer has spread to the area just outside the gland.

Hormones can either be given as a daily tablet to block the action of testosterone or as an injection, known as LHRH-analogue, that produce a reversible castration. The main side effects of hormonal treatments include hot flushes, loss of sexual desire. They can occasionally cause impotence, breast tenderness and enlargement.

Evidence for hormone therapy

The addition of radiation therapy to hormone therapy for the treatment of locally advanced prostate cancer reduces prostate cancer deaths by 50%, according to the results of a Scandinavian study published in the Lancet.^[1]

In 1996 researchers from the Scandinavian Prostate Cancer Group and the Swedish Association for Urological Oncology initiated a Phase III trial to evaluate the benefits of adding radiation to hormone therapy. The trial involved 875 patients who were randomized to receive either hormone therapy alone (439) or combined hormone/radiation therapy (436). After nearly eight years of follow-up, 79 men in the hormone-only group had died of prostate cancer compared with 37 in the combination group. Furthermore, the rate of recurrence was substantially higher in the hormone-only group: 74.7% versus 25.9% in the combination group. After five years urinary, rectal, and sexual problems were slightly more frequent in the combination group.

The researchers concluded that the combination of radiation therapy and hormone therapy was superior to hormone therapy alone and cut the rate of prostate cancer deaths in half. Furthermore, the side-effect profile for the combination therapy was acceptable.

The Birmingham Prostate Clinic is a centre of excellence for external beam radiotherapy and we would be happy to discuss your needs and treatment options with you.

[1] Widmark A, Klepp O, Solberg A, et al. Endocrine treatment, with or without radiotherapy, in locally advanced prostate cancer (SPCG-7/SFUO-3): An open randomized phase III trial. The Lancet . December 16, 2008.