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PHOTODYNAMIC THERAPY & OCT

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Photodynamic treatment (PDT) of skin cancers has been around for over 20 years (see a demonstration video here). The treatment involves loading the skin cancer cells with a photoactive drug (applied in a cream) and then activating the drug with a strong light source.

PDT is a remarkable non-invasive treatment but recurrences have been an issue with the conventional protocol. We think the conventional protocol is now out-dated. There are several reasons why conventional treatment fails, these include:

 

1. Failure in the assessment of appropriate lesions to treat (too often skin cancers are thicker than they appear).                 2. Inadequate delivery of light to tumour cells when using the standard red LED (Aktilite) lamp alone.                                 

 PDT can only be an effective treatment if light can reach all parts of the tumour. Adequate penetration of light will depend on the depth of the tumour, the optical properties of the tumour, and the optical properties of the overlying skin. It is our premise that the optical properties of the underlying skin (dermal tissue) will also influence the treatment outcome. Light that is reflected or "back-scattered" from underlying collagen will also increase the amount of light to tumour.

 

The OCT technology is extremely valuable for PDT:  Apart from measuring tumour depth, a scan can assess the optical properties of tumour and surrounding skin.

The depth obtained with OCT is a true depth measurement and in addition, the entire skin cancer can be scanned to obtain the point of maximum depth. A biopsy will not do this - a biopsy will only look at a small section of the cancer and the processing involved in preparing the tissue for histological analysis will distort the sample leading to a false depth reading. 

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The treatment protocol developed at our clinic is described below:

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1. ASSESSMENT

An OCT scan is performed to confirm a diagnosis of skin cancer - a biopsy is generally not required. The scan will show the precise depth of the cancer down to 1/100th of a millimetre (see the image above).  Other aspects of the tumour (that are recognisable on OCT) will determine if biphasic photodynamic treatment is suitable.

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2.  INCUBATION WITH PHOTOSENSITISER

A special photosensitising cream is applied to the tumour and this is left under a dressing for a few hours. The ingredient in the cream will be converted to a light-activated molecule which selectively accumulates in skin cancer cells. 

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3. ACTIVATION WITH LIGHT

Two types of intense light will then be used to illuminate the area ("biphasic activation"):

 The first light is a high intensity red LED lamp which is used for 5 - 8 minutes. The red light will begin activation but the skin often becomes flushed. Flushing is a good thing as the extra blood will deliver more oxygen to tumour (oxygen is essential for successful activation). A problem however with flushing is that the extra haemoglobin absorbs light in the underlying dermal tissue and thus interferes with the passage of back-scattered light to the tumour cells.  

This is the point when the light source is switched to an intense pulsed light device (IPL). Additional high fluence light is then delivered with mechanical pressure onto the skin. The mechanical pressure is in order to drain the skin of blood whilst light is being delivered. Removing blood at the tumour site will dramatically increase the passage of back-scattered light to tumour cells.  This second phase of light takes less than 30 seconds to complete. This is demonstrated in the video below.

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It is during the illumination process that a chemical reaction occurs within the tumour cells. They are destroyed. The normal healthy cells are spared. This means tumour removal with faster healing and less scarring.

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The OCT technology combined with biphasic PDT makes it possible for skin cancer diagnosis and removal on the same day...

without any needles, without any cutting, without any stitches and with minimal (if any) scarring.

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If the tumour is not suitable for biphasic PDT then we can still excise it in our rooms or we can map it out for excision by a plastic surgeon if you prefer. Some tumours are best treated by a combination of biphasic PDT followed by surgery.

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Please note that a referral to Dr Stephens or Dr Raychaudhury will be needed for biphasic PDT.

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