Sonodynamic therapy (SDT)
Photodynamic therapy (PDT) is a treatment that involves the use of a light-sensitive medication and a light source to destroy abnormal cells.
It can be used to treat some skin and eye conditions, as well as certain types of cancer.
On their own, the medication and light source are harmless, but when the medication is exposed to the light, it activates and causes a reaction that damages nearby cells.
This allows small abnormal areas of tissue to be treated without the need for surgery.
Uses of PDT
PDT can be used to treat abnormalities in parts of the body a light source can most easily reach, such as the skin, eyes, mouth, oesophagus (gullet) and lungs.
Conditions sometimes treated with PDT include:
actinic keratoses – dry scaly patches of skin caused by damage from years of sun exposure that could become cancerous if not treated
Bowen's disease – a very early form of skin cancer
basal cell carcinoma – a type of skin cancer
macular degeneration – an eye condition that can lead to vision loss
Barrett's oesophagus – changes in the cells in the lining of your lower oesophagus that could become cancerous if not treated
oesophageal cancer, mouth cancer and lung cancer – PDT can cure some cancers if used in the early stages, or offer relief from symptoms in more advanced cases
PDT also shows promise in treating other conditions, such as warts, acne and some other types of cancer.
Despite the claims relating to unproven “alternative” forms of PDT, such as next-generation PDT and sonodynamic therapy, PDT is not effective at treating widespread conditions or those affecting deeper parts of the body where a light source cannot reach.
In these cases, surgery, radiotherapy, and/or chemotherapy may be recommended instead.
PDT is carried out in two stages.
First, you will need to come into the hospital or clinic to be given the light-sensitive medication. Depending on the area of the body being treated, this can be a cream, injection or special drink.
Once the medication has been applied or given, you may be asked to go home and return in a few hours or days. This will give the medication a chance to build-up in the abnormal or cancerous cells that are going to be treated.
Later, you will need to return to the hospital or clinic for the light treatment. This will involve a lamp or laser being shone onto the treatment area for around 10-45 minutes. To treat abnormal cells inside your body, such as in your lungs, an endoscope (flexible tube) will be passed into your body to deliver the light.
You will usually be able to go home the same day you have the light treatment.
If your skin was treated, it will be covered by a dressing that will need to remain in place for at least two days. You should try to avoid scratching or knocking the treated area, and keep it as dry as possible.
Once you are advised to remove the dressing, you should be able to wash and bathe as normal, although you should make sure you pat the treated area dry gently.
A follow-up appointment at the hospital or clinic will be arranged to assess whether the treatment has been effective and decide if it needs to be repeated.
It will usually take around two to six weeks for the area to heal completely.
Risks and side effects
PDT is generally a very safe treatment. However, it’s common to experience a burning or stinging sensation while the light treatment is being carried out. This will usually pass soon after the treatment finishes.
PDT can also make your skin or eyes sensitive to light for up to six weeks, even if the area treated was inside your body. This means they may become red and sore when exposed to direct sunlight or bright indoor lights. Your treatment team will advise you about things you should do to protect your eyes and skin.
Other potential side effects will depend on the area treated.
For example, if your skin is treated, it may crust over, and become temporarily red, swollen or blistered after treatment.
Your skin may also become slightly darker or lighter than it was before and there may be some hair loss. This is usually temporary, but it can sometimes be permanent.
Treatment of the mouth, oesophagus and lungs can cause temporary coughing, difficulty swallowing, painful breathing, or breathlessness.
If your eyes are treated, there is a small risk of permanent vision loss.
Make sure you talk to your doctors about the possible risks and benefits of PDT before you agree to treatment.
Next-generation PDT (NGPDT) and sonodynamic therapy (SDT)
PDT as described above is an effective and licensed treatment for a number of conditions. It should not be confused with the unproven, unlicensed versions sold by some private clinics in the UK and overseas.
Clinics promoting these so-called "advanced" versions of PDT, called "next-generation PDT" (NGPDT) and "sonodynamic therapy" (SDT) claim they can treat deep or widespread cancers, but these claims aren't supported by scientific evidence and these treatments aren't recommended.
Sonodynamic therapy (SDT)