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OCT-GUIDED BIPHASIC PDT 

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SUMMARY: Sub-surface imaging technology (OCT) 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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 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 illumination is with red light (wavelength: 630nm), delivered by a bright LED lamp for 5 - 8 minutes. The red light will begin activation, inflammation then occurs and the skin often becomes flushed. Flushing is both advantageous and a problem! It is advantageous as more blood will deliver more oxygen to tumour and oxygen is absolutely essential for successful activation. A problem however is that more haemoglobin absorbs more light! This includes light which would otherwise have bounced off the underlying collagen and been redirected back to tumour. 

This problem is made worse because oxy-haemoglobin is converted to deoxy-haemoglobin which is a much stronger absorber of 630nm light.

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After 8 minutes of red light, or, at the point when flushing is noticeable, the light source is switched to an intense pulsed light device (IPL). High irradiance polychromatic 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 scattering of green, yellow, and red light photons.  Tumour cells will be hit by photons coming from different directions. Cells that may have been shadowed by small opacities above them (such as blood, melanin, or keratin) will now be vulnerable. Delivery of light to all parts of tumour will therefore be more thorough. This is in addition to there being a higher photodynamic dose. Removing blood does not immediately remove free-oxygen that has already dissociated from haemoglobin. There is likely to be an excess of free-oxygen. This is currently being investigated by our collaborators at the University of Malmö, Sweden.

This second phase of activation takes less than 30 seconds to complete. This is demonstrated in the video further 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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If the tumour is not suitable for biphasic PDT then we can still excise it in our rooms. Some tumours are best treated by having biphasic PDT prior to surgery. This is appropriate for tumours which have a broad superficial component and a smaller, deeper component. This can result in a much smaller cut and a simpler repair. This is known as "neoadjuvant treatment". It will often mean having a simple side-to-side closure rather than more complicated / more expensive or disfiguring surgery like a skin graft.

Sometimes only some spot cautery is needed for deeper tumour following biphasic treatment.​