PHOTODYNAMIC
THERAPY [PDT] |
Photodynamic
therapy [PDT]
is used for a variety of malignant and pre-malignant skin disorders
including actinic keratosis, Bowen's disease and superficial
basal cell carcinoma. A haem precursor 5-aminolaevulenic acid
[5-ALA] or the methyl ester of 5-ALA [MAL] is applied to the
treatment area in a cream base for three to six hours and is
taken up by the keratinocytes and converted by the haem biosynthetic
pathway to protoporphyrin IX. Further conversion of protoporphyrin
IX is a rate limited process and protoporphyrin IX accumulates
in the cells [fluoresces under UV light]. Protoporphyrin IX
is a photoactive molecule and when activated by red light in
the presence of oxygen causes cell destruction. 5-ALA or MAL
are preferentially taken up in diseased tissue but low level
accumulation of protoporphyrin IX does occur in normal skin
following ALA application. This preferential accumulation of
protoporphyrin IX in abnormal cells facilitates selectivity
of treatment for diseased tissue. |
| Superficial
basal cell carcinoma before application of 5-ALA |
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Accumulation
of protoporphyrin IX in a skin cancer 6 hours after application
of 5-ALA |
PDT |
| On
the day of treatment patients attend in the morning when any crusts
are gently removed from lesions and 5-ALA [or MAL] cream is applied
to the lesion. The area is covered with an occlusive dressing
and the patient returns three to six hours later. The dressing
is removed, the area gently cleaned and the light treatment applied.
The duration of treatment is determined by the lamp output and
the maximum diameter of the lesion. |
Adverse
effects of PDT |
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During
treatment patients generally experience a burning discomfort
where the light is applied. If this proves very uncomfortable
we offer a local anaesthetic injection or gel. Pain and itch
may persist following treatment and symptoms are usually maximal
in the first one to two days after therapy and rapidly resolve
thereafter. The area will become inflamed for a few days after
treatment but rarely ulcerates or scars. Lesions are routinely
treated twice at a two to three month interval, although sometimes
more treatments are needed.
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| Alternative
therapy |
- cryotherapy
- Efudix
cream [5-fluorouracil]
- surgery
- imiquimod
- Solareze
gel [diclofenac]
- radiotherapy
|
Our
experience in Dundee |
| Topical
PDT was introduced as part of the Barbara Stewart PDT cancer centre.
We have performed about3000 treatments with PDT in the last seven
years, with response rates of approximately 80 - 90%. Most of
the lesions we have treated have been superficial skin cancers
and areas of sun damage. Treatment is well tolerated and it has
proved to be a very popular service. |
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Superficial basal cell
carcinoma before PDT
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Clearance
3 months after a single PDT treatment |
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Bowen's disease on the lower
leg before PDT |
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Clearance
3 months after a single PDT treatment |
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