Evaluation of Non-inferiority and Tolerability of the Device PHOS-ISTOS

Inclusion Criteria:

* Clinical diagnosis of minimum 10 previously untreated not pigmented, non-hyperkeratotic AK lesions of Grade I and II of the forehead and/or scalp (according to Olsen et Al. JAAD 1991, cf. REF 31) where other therapies are unacceptable or considered medically less appropriate with a symmetrical repartition on both side of the forehead and/or scalp. The diagnosis of AK will be determined upon clinical evaluation (i.e. visual inspection and palpation) by the investigator.
* No treatment for the AKs in the previous 30 days.
* Symmetrical areas in terms of number and severity of lesions. The axis of symmetry between the two areas will be defined by the investigator according to the distribution of lesions.
* The two areas to be treated should not be coalescing. A minimum distance of 10 mm is required between the lesions located on the 2 symmetrical areas. A minimum distance of 2 mm is required between the lesions on the same side.
* Minimum 5 lesions with similar dimensions at both symmetrical areas will be treated. If the number of lesions is \>7, only 7 lesions on each side will be considered.

Exclusion Criteria:

* Patients with porphyria.
* Patients immunosuppressed for idiopathic, disease specific or therapeutic reasons.
* Use of topical corticosteroids to lesional areas within 2 weeks before PDT.
* Patients receiving local treatment (including cryotherapy and curettage-electrocoagulation, any PDT treatment) in face / scalp area within the last 30 days.
* Patients receiving topical treatment (including imiquimod, 5-FU and diclofenac, Picato) in face / scalp area within the last 30 days.in
* Use of topical retinoids or alpha-hydroxy acids, systemic retinoids, chemotherapy or immunotherapy within 30 days of PDT.
* Pigmented AK lesion(s).
* Known allergy to Metvixia/Metvix, a similar PDT compound or excipients of the cream including arachis oil, or to peanut or soya.
* Participation in other clinical studies either currently or within the last 30 days.
* Female subjects must be of either:

  * Non-childbearing potential, i.e. post-menopausal or have a confirmed clinical history of sterility (e.g. the subject is without a uterus) or,
  * Childbearing potential, provided there is a confirmed negative urine pregnancy test or blood analysis prior to study treatment, to rule out pregnancy.
* Any condition which may be associated with a risk of poor protocol compliance.
* Patients currently receiving regular ultraviolet radiation therapy.