In reply to the Letter to the Editor titled:
“Comments on: Clinical implementation of a new electronic brachytherapy system for skin brachytherapy”

To the Editor:

We have read with an interest the letter to the Editor titled “New technologies for non-melanoma skin cancer”. In this letter, the authors comment on our article [1] about the clinical implementation of a new system for skin brachytherapy (Esteya® electronic brachytherapy by Elekta, Stockholm, Sweden) and they asked for a reply to their letter. We would like to thank the authors for their interest in our publication and would like to respond to their letter.
First of all we need to clarify that in our study we chose to exclude irregularly shaped lesions, lesions with a diameter > 2 cm, and lesions with a depth larger than 4 mm because of the design of the radiation therapy system that was used. Lesions included in our work using the specific features of the Esteya® device, in fact represent the vast majority of non-melanoma skin cancer primary presentations.
The Esteya® electronic brachytherapy system (E-eBT) is delivered with a set of applicators up to 3 cm in diameter. When treating non-melanoma skin cancer, typically a margin of 0.5 cm is added to the GTV. Consequently, the maximum diameter of lesions to be treated is 2 cm. The system has a dose-gradient of about 8% per mm, therefore with lesions deeper than 0.4 cm, the overdose at the first skin layers will exceed 130% and this might impact cosmetic outcome. This is the reason we limited inclusion to lesions with a depth of 4 mm or less. Finally, E-eBT applicators are designed with a flat surface to allow full contact with the skin. Avoiding air gaps between applicator and skin is a prerequisite because of the significant impact of air gaps on the dose to the lesion. Nowadays, we have the possibility to use a new set of more precise applicators for treatment of lesions in difficult areas.
When we say that irregular areas are not suitable for EBT, we only mean those locations that, despite applying some pressure, are not entirely in contact with the applicator. These cases should be treated with other types of brachytherapy/radiotherapy. In our experience there are only a few locations where one cannot get a flat surface by applying mild pressure. Only larger lesions in areas with angled surfaces result in bone or cartilage, for example impeding/preventing a flat surface being obtained; this can be on the inner canthus of the eye, or for example on the pinna, and on the peri-alar nose groove. We have, however, successfully treated several “difficult cases”...


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