Photodynamic Therapy (PDT)

Photodynamic therapy (PDT) kills cancer cells by using a combination of a light sensitising drug and a very bright light.

The doctor puts a cream that contains the light sensitising chemical to the skin cancer and surrounding area. Or, you might have the chemical as a tablet or injection. Your doctor then shines a special light on the treatment area which destroys the cancer cells. 

What is photodynamic therapy (PDT)?

Photodynamic therapy (PDT) is also called:

  • photoradiation therapy
  • phototherapy
  • photochemotherapy

PDT combines a drug that makes cells sensitive to light with exposure to a particular type of light. The drug is called a photosensitiser or photosensitising agent.

There are different types of sensitising drugs and each is activated by light of a specific wavelength. The type of photosensitiser and light wavelength you have depends on where the cancer is in your body.

How PDT works

When the sensitising drugs are exposed to their particular light, they produce a type of oxygen that kills nearby cells.

PDT directly kills cancer cells, but doctors think it also acts in other ways to shrink or destroy tumours. The sensitising drug may damage blood vessels in the tumour, and stop it from receiving nutrients that it needs. PDT may also trigger the immune system to attack the cancer cells.

When you have it

You might have PDT if you have a thin non melanoma skin cancer. You might have it to treat:

  • some basal cell cancers (BCC's)
  • Bowen's disease (squamous cell carcinoma in situ)
  • actinic keratosis (solar keratosis)

Your doctor might suggest PDT if surgery could cause changes to your appearance. So you might have it if you have a large skin cancer that is not too deep. Or if you have several cancers in an area. Clinical trials have shown that the appearance of the skin after PDT is better than after surgery.

PDT is not suitable for deep basal cell cancers or squamous cell skin cancers. This is because the light cannot go deeply enough into the skin.

For actinic keratosis you usually have one treatment. For basal cell cancer or Bowen’s disease you usually have two treatments 7 days apart. This is one cycle of treatment.

Your doctor will tell you what’s best for your situation. 

Before treatment

You have PDT treatment in the outpatient department at the hospital. 

Before treatment, the doctor cleans the area and removes any crust or scale from the top of the skin cancer. 

They apply a light sensitizing cream to the skin cancer and the surrounding skin. You have a dressing on top to keep the cream in the right spot and stop it from rubbing off. 

You do this for 3 to 6 hours before the PDT treatment.   

You might have the light sensitising drug as an injection into a vein instead.  

During the treatment

After 3 to 6 hours your doctor cleans the cream away.

You'll get a pair of sunglasses to wear during your treatment to protect your eyes from the light. 

Your doctor then shines the light on the treatment area. The light kills any cells that have absorbed the drug. The light is usually red in colour. They shine the light for about 10 to 15 minutes, depending on which light your doctor is using.

You might feel a stinging or burning sensation in the treatment area when the light is on. A fan, painkillers or numbing injection (local anaesthetic) can help ease the discomfort. Your doctor might pause the treatment for a short time. 

You can have more than one skin cancer treated at a time. 

After treatment

A scab forms where you had the treatment and you have a dressing in place to cover it. The dressing stays on for about 36 hours. Be careful not to bump or knock it. You need to also keep the dressing dry. 

The scab usually heals in about 3 weeks. 

The light sensitising drug makes the treated skin more sensitive to sunlight. Your doctor might recommend that you wear sunscreen of SPF 30 or more for a least 48 hours.  You'll get specific instructions about protecting your skin if you have the light sensitising drug into a vein. You might need to avoid bright light or sunlight for a time. This is because all of your skin may be more sensitive to sunlight.  

Ask the doctor or nurse if you are not sure about what to do after treatment. 

You might need another treatment about 4 weeks later if your skin cancer was thick or deep. 

Side effects of PDT

After PDT, it is common to have some pain and discomfort for a few days. Taking regular painkillers such as paracetamol can help.

The treated area might have some inflammation. It may look pink, red and swollen. The site might also ooze or develop a crust. This should get better after a few days. But if you are worried contact your advice line about this.

Ambulight guidance

The National Institute of Health and Care Excellence (NICE) published guidance on a particular type of PDT called Ambulight. You can have this photodynamic therapy in places outside hospitals, for example in your home. It is thought that it might cause less pain than normal photodynamic therapy.

But NICE said that although doctors can choose to use Ambulight PDT there is not much evidence about how well it works.

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