Radiotherapy for Lentigo Maligna
Radiotherapy for Lentigo Maligna
These recommendations have been based on the preceding review and supplemented by our initial experience from our new multidisciplinary LM clinic at the Melanoma Institute Australia, the largest melanoma unit in the world. The recommendations coming from the review would be at best level 3, those from our experience at best level 4.
The RT field treated for LM has traditionally been determined by treating the visible lesion with a margin. This practice assumes that the nonvisible extensions of LM around the visible lesions extend equally in all directions. The review suggested to us that in the three studies (Table 2) with sufficient data, the greater is the margin between the visible lesion and the treatment field edge, the fewer are the out-of-field recurrences. It is now possible to define the treatment volume more accurately by using in vivo reflectance confocal microscopy (RCM).
For LM treatment in our new clinic, the area marked as involved by RCM is further expanded by 1 cm all around, if anatomically possible, to define the treated area. These areas are photographed and recorded. Future events, e.g. recurrence, can then be recorded as in-field or out-of-field. In RT planning terminology, the RCM-defined field will be the gross tumour volume (GTV), and the clinical target volume will be a 1-cm expansion on GTV.
Depth of treatment should be determined by the depth of extension of LM. LM can migrate down skin appendages that are in direct continuity with the overlying epidermis (where LM arises). Kopf et al. reports in case 12 recurrent LM in a sweat gland, which may have been physically below the effective dose given by Grenz rays. There is little documentation of the actual depth of skin appendageal involvement in the LM literature to date. The review suggested to us that in five studies with sufficient data, the more penetrating radiation was associated with less in-field recurrence (Table 3). Based on a small study at our institution, RT treatment should extend to a depth of 5 mm to treat LM adequately (R.A. Scolyer, unpublished data). The depth actually treated will be determined by the RT modality used. Beams that attenuate too superficially may result in geographical miss at depth.
Dose parameters include total dose, dose per fraction and number of fractions given per week. It is not possible to give a dose response from the review except to say that 20 Gy in one fraction is insufficient based on one case. Doses as low as 35 Gy in five fractions were associated with long-term control. Our practice has been to prescribe 50 Gy for adjuvant treatment, with 54 Gy for definitive treatment; and no more than 60 Gy in 2 Gy fractions or equivalent in greater fraction sizes.
In the review, dose per fraction varied from 20 Gy in one fraction with superficial RT, to 160 Gy in six fractions at two treatments per week using Grenz rays. A conclusion on this issue could not be made from the review. There was one ectropion possibly caused by fibrosis from high dose per fraction. We use a dose per fraction of 2 Gy to decrease potential late effects but a higher dose per fraction of up to 4 Gy is reasonable if patient factors require this.
Radiotherapy Techniques Recommended for the Treatment of Lentigo Maligna
These recommendations have been based on the preceding review and supplemented by our initial experience from our new multidisciplinary LM clinic at the Melanoma Institute Australia, the largest melanoma unit in the world. The recommendations coming from the review would be at best level 3, those from our experience at best level 4.
Field
The RT field treated for LM has traditionally been determined by treating the visible lesion with a margin. This practice assumes that the nonvisible extensions of LM around the visible lesions extend equally in all directions. The review suggested to us that in the three studies (Table 2) with sufficient data, the greater is the margin between the visible lesion and the treatment field edge, the fewer are the out-of-field recurrences. It is now possible to define the treatment volume more accurately by using in vivo reflectance confocal microscopy (RCM).
For LM treatment in our new clinic, the area marked as involved by RCM is further expanded by 1 cm all around, if anatomically possible, to define the treated area. These areas are photographed and recorded. Future events, e.g. recurrence, can then be recorded as in-field or out-of-field. In RT planning terminology, the RCM-defined field will be the gross tumour volume (GTV), and the clinical target volume will be a 1-cm expansion on GTV.
Treatment Depth
Depth of treatment should be determined by the depth of extension of LM. LM can migrate down skin appendages that are in direct continuity with the overlying epidermis (where LM arises). Kopf et al. reports in case 12 recurrent LM in a sweat gland, which may have been physically below the effective dose given by Grenz rays. There is little documentation of the actual depth of skin appendageal involvement in the LM literature to date. The review suggested to us that in five studies with sufficient data, the more penetrating radiation was associated with less in-field recurrence (Table 3). Based on a small study at our institution, RT treatment should extend to a depth of 5 mm to treat LM adequately (R.A. Scolyer, unpublished data). The depth actually treated will be determined by the RT modality used. Beams that attenuate too superficially may result in geographical miss at depth.
Dose
Dose parameters include total dose, dose per fraction and number of fractions given per week. It is not possible to give a dose response from the review except to say that 20 Gy in one fraction is insufficient based on one case. Doses as low as 35 Gy in five fractions were associated with long-term control. Our practice has been to prescribe 50 Gy for adjuvant treatment, with 54 Gy for definitive treatment; and no more than 60 Gy in 2 Gy fractions or equivalent in greater fraction sizes.
Dose Per Fraction
In the review, dose per fraction varied from 20 Gy in one fraction with superficial RT, to 160 Gy in six fractions at two treatments per week using Grenz rays. A conclusion on this issue could not be made from the review. There was one ectropion possibly caused by fibrosis from high dose per fraction. We use a dose per fraction of 2 Gy to decrease potential late effects but a higher dose per fraction of up to 4 Gy is reasonable if patient factors require this.
Source...