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Saturday, May 17, 2008

Photodynamic therapy (PDT)

This information is about photodynamic therapy (PDT). PDT is a treatment for some types of cancer. It may also be used to treat some non-cancerous conditions of the skin or eye.

How PDT works

PDT uses laser, or other light sources, combined with a light-sensitive drug (sometimes called a photosensitising agent) to destroy cancer cells.

A photosensitising agent is a drug that makes cells more sensitive to light. Once in the body, the drug is attracted to cancer cells. It does not do anything until it is exposed to a particular type of light. When the light is directed at the area of the cancer, the drug is activated and the cancer cells are destroyed. Some healthy, normal cells in the body will also be affected by PDT, although these cells will usually heal after the treatment.

When PDT is used

PDT may be used to treat cancers of the skin (but not melanoma), or those that are on, or near, the lining of internal organs, such as cancers of:

  • the head and neck area
  • the lining of the mouth
  • the lining of the lung
  • the lining of the gullet (oesophagus)
  • the lining of the stomach
  • the lining of the bladder
  • the lining of the bile ducts.

Doctors are working to identify the types of cancer for which it is most effective. Research trials are taking place to look at new photosensitising agents, new laser and non-laser light treatments and ways of reducing the side effects.

Your doctor can advise you whether PDT is an appropriate treatment in your situation, and whether you may be able to take part in any research trials.

In cancers that are being treated at an early stage, the aim of treatment may be to try to cure the cancer.

The aim of PDT for advanced cancer is usually to reduce symptoms by shrinking the tumour. In this situation PDT cannot cure a cancer.

Photodynamic therapy treatments for some cancers, such as prostate and pancreas, are still the subjects of research. Some research studies have used PDT to treat conditions that may develop into a cancer, including one which affects the vulva known as vulval intraepithelial neoplasia (VIN).

PDT can safely be given to patients who have had other cancer treatments such as surgery, radiotherapy and chemotherapy.

How PDT is given

The treatment is normally in two stages.

Stage 1 A light-sensitive drug is given. For cancers of the skin, the drug is usually applied to the skin as a cream.

For cancers that are inside the body, the drug is usually given by injection into a vein.

There is a delay between the cream being applied, or the drug being given, and the next stage of treatment. This allows time for the drug to concentrate in the cancer cells.

Stage 2 The second stage of treatment involves shining light directly on to the cancer. A laser delivers energy in the form of light in a very precise way. Special non-laser lamps may also be used in some situations. For skin cancers, the light is shone directly onto the skin. For internal cancers, a flexible tube (an endoscope) may need to be passed into your body to deliver the light to the tumour.

PDT and possible side effects

As with all kinds of treatment, the experience of PDT can vary from person to person. How the treatment is given and the side effects that it may cause vary, according to:

  • the area of the body affected by the cancer
  • the type of photosensitising drug given
  • the time between giving the drug and applying the light
  • the amount of skin sensitivity to light following treatment.

When PDT is used to treat skin cancer, the side effects are different to when PDT is used for a cancer elsewhere in the body. For this reason we have divided this information into two: firstly for people being treated for skin cancers, and secondly for people with cancer in any other part of the body.

PDT for skin cancer

A photosensitising cream will be applied to the affected area of skin. You will then need to wait for approximately 4–6 hours before being treated. Treatment with the PDT light will last 20–45 minutes, after which a dressing will be put on to cover the area and protect it from light. Usually only one treatment is needed, but occasionally two or three further treatments may be given.

Possible side effects of PDT for skin cancer

  • Pain You will be given a local anaesthetic before your PDT, to prevent pain. For many people this is all that they will need. You may be given steroid cream to apply to the area if it hurts when you are at home.
  • Sensitivity to light The treated area of skin will be sensitive to daylight and bright, indoor lighting. This effect will probably last for between 24–36 hours. You will need to keep the treated area of skin covered during this time. After that you can wash, bathe or shower as usual, but you will still need to treat your skin gently and not rub the area until it has healed.
  • Healing – a scab will form on the treated area The scab usually falls off after about three weeks. As PDT heals quickly without scarring, the appearance after treatment is usually very good.

PDT for cancers of the head and neck

The photosensitising drug is given as an injection through a small tube (cannula) inserted into a vein. This takes a few minutes and then the tube is removed.

You will then have to wait up to about four days before the light treatment is given. The length of time varies depending upon the particular photosensitising drug you've been given. Generally, only one treatment is given, although it is possible to have a second treatment a few weeks after the first.

Possible side effects of PDT for head and neck cancers

Sensitivity to light Although photosensitising drugs are mostly taken up by the cancer cells and are concentrated there, they can also make your ordinary skin cells, or your eyes, highly sensitive to light. People who have had PDT are advised to protect themselves from exposure to sunlight and bright indoor lighting. The duration of sensitivity to light (photosensitivity) varies depending upon which drug is used. The drug temoporfin (Foscan®) is commonly used to treat head and neck cancers and will make you sensitive to direct sunlight for up to two weeks.

While your skin is photosensitive, it is advisable to avoid going outside during the day. However, you do not need to stay in total darkness during this time. To start with you will need to stay in a darkened room, but you can gradually build-up the amount of light over two weeks. If you need to go out, use clothing to cover your skin: for example, wear a brimmed hat, scarf, long-sleeved shirt or blouse and trousers, gloves and dark glasses. Using sunscreens will not give you any additional protection.

You can go out uncovered very early in the morning or after sunset, and you can use low-level artificial light indoors (maximum 60W bulb). In the first few days it is possible to get ‘sunburn’ even on a dull winter day. You will not notice that you are getting burnt while you are out in the sun. As with sunburn, the damage to your skin can take a few hours to show up.

You can even get burnt through glass if the light is strong. Remember to draw curtains during the day if the sun is bright. Bright artificial lights can also cause a skin reaction, so spot lamps are best avoided. It is important to be aware of unexpected sources of light – for instance, warming your hands over a fire could result in being burnt. It is also a good idea not to use a computer during this time and not to watch the television from less than about 2 metres (6 feet) away. You may be given a light meter to use at home, to check that the light intensity is at a safe level.

It is advisable to avoid opticians’ appointments around the time of your treatment, as the retinas inside your eyes will be more vulnerable to light than usual, and you should not have light shone into your eyes.

Towards the end of the time of photosensitivity, a small area of skin can be exposed to brighter light for five minutes and the reaction assessed 24 hours later. Your doctors will advise you on how to do this. After this time, you will be able to gradually increase the amount of light you are exposed to and most people are able to go outside as usual after approximately three weeks. Your doctor or specialist nurse can let you know for exactly how long you will need to protect your skin.

Pain Treatment with PDT can cause pain in the tumour area. Your specialist nurse should be able to tell you how much pain you might expect and see that you are given appropriate painkillers. The amount of pain will vary according to where your tumour is and which light-sensitising drug has been used. Pain can range from mild to severe. For some treatments aspirin or paracetamol may be enough, however for others a morphine-type drug may be necessary. If you have pain, it is important to let your doctor know, so that you can be given effective and appropriate painkillers.

Swelling Some photosensitising drugs can cause swelling in the treated area. This varies from one person to another. If you have had treatment in your mouth or throat, the swelling may make it difficult to swallow. It is important to let your nurse or doctor know if swallowing becomes very difficult. The swelling is only temporary but can be treated with steroid injections or drugs that help to reduce inflammation.

Constipation This is a fairly common side effect of PDT and you may need to ask your doctor for medication.

Nausea Some people may feel sick, which can be controlled with mild anti-sickness tablets if necessary.

Healing PDT causes much less scarring than surgery. However, the time taken for PDT-treated areas to heal can vary a lot. It may be several weeks, depending on the area treated and how deeply the light has penetrated into the body tissues.

PDT for other cancers

Other than skin cancer, and cancers of the head and neck, the cancers most commonly treated with PDT are those found in the inner lining of the digestive system, the lungs and the bladder. However, as PDT is a new treatment, it may start to be used for other cancers. If the cancer is on the lining of an internal organ such as the gullet (oesophagus), stomach or lungs, it may be necessary for a thin, flexible tube to be passed into the windpipe or gullet to bring the laser light as close to the cancer as possible.

If the cancer is inside the bladder, a tube will be passed into the bladder. You would be given a drug to make you sleepy (sedated) while this part of the treatment is given.

There are several drugs that can be used as the photosensitising agent. The most common are 5-aminolevulinic acid (ALA), temoporfin (Foscan®) and porfimer sodium (Photofrin®). The drug used will depend on the type of cancer that you have and which is best for your situation. These drugs may be given as a drink or tablets or as an injection. The way that the drug is given will depend on which one is best for your treatment.

The length of time you need to wait for treatment after having the drug can vary from 90 minutes to four days. You will be told which drug will be used, how it will be given and whether your treatment is to be as an outpatient or if you will need to stay in hospital.

Possible side effects of PDT for other cancers

PDT drugs for cancers in other parts of the body are usually given by injection into a vein. Many of the side effects will be similar to those experienced by people who have had PDT for head and neck cancers. The time of sensitivity to light (photosensitivity) varies, ranging from one or two days to several months. This difference depends on which photosensitising drug is used. Your doctor or specialist nurse can let you know the length of time you will need to protect your skin.

You may also have some pain, nausea and constipation. Other side effects will depend upon the part of the body that is treated.

Cancer and pre-cancer of the gullet (oesophagus) Swelling and inflammation can occur around the treatment area and may cause nausea and chest pain. This may make swallowing difficult.

Cancer of the stomach The lining of the stomach may become inflamed and swollen, causing abdominal discomfort and nausea.

Cancer of the lung The PDT may cause swelling and inflammation in the lung which may cause some chest pain, a cough and breathlessness. You may notice that you are producing more sputum and rarely you may cough up blood-stained sputum. Occasionally there may be a build-up of fluid in the lining of the lung (a pleural effusion), which can be drained if necessary.

Cancer of the bladder It is likely that the PDT will cause symptoms of an inflamed bladder. Common problems include pain, the need to pass urine frequently, slight leakage of urine (incontinence), and passing small amounts of blood in the urine. These side effects usually last for only 2–4 weeks after treatment.

Cancer of the prostate PDT as a treatment for prostate cancer is still at an experimental stage. Possible side effects include mild incontinence of urine and difficulty passing urine.

Cancer of the pancreas PDT as a treatment for pancreatic cancer is still being researched and is not widely available. Possible side effects include abdominal pain and diarrhoea.

References

This section has been compiled using information from a number of reliable sources including:

  • Oxford Textbook of Oncology (2nd edition). Souhami et al. Oxford University Press, 2002.
  • Cancer and its Management (4th edition). Souhami and Tobias. Oxford Blackwell Scientific Publications, 2003.
  • The Textbook of Uncommon Cancers (2nd edition). Raghavan et al. Wiley, 1999.
  • British National Formulary (52nd edition). British Medical Association and Royal Pharmaceutical Society of Great Britain, September 2006.

For further references, please see the general bibliography.

Via: http://www.cancerbackup.org.uk

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