Dosimetric characteristics of a new unit for electronic skin brachytherapy.
OBJECTIVE
Brachytherapy with radioactive high dose rate (HDR) (192)Ir source is applied to small skin cancer lesions, using surface applicators, i.e. Leipzig or Valencia type. New developments in the field of radiotherapy for skin cancer include electronic brachytherapy. This technique involves the placement of an HDR X-ray source close to the skin, therefore combining the benefits of brachytherapy with the reduced shielding requirements and targeted energy of low energy X-rays. Recently, the Esteya(®) Electronic Brachytherapy System (Esteya EBS, Elekta AB-Nucletron, Stockholm, Sweden) has been developed specifically for HDR brachytherapy treatment of surface lesions. The system provides radionuclide free HDR brachytherapy by means of a small 69.5 kV X-ray source. The purpose of this study is to obtain the dosimetric characterization required for clinical implementation, providing the detailed methodology to perform the commissioning.


METHODS
Flatness, symmetry and penumbra, percentage of depth dose (PDD), kV stability, HVL, output, spectrum, linearity, and leakage have been evaluated for a set of applicators (from 10 mm to 30 mm in diameter).


RESULTS
Flatness and symmetry resulted better than 5% with around 1 mm of penumbra. The depth dose gradient is about 7%/mm. A kV value of 68.4 ± 1.0 kV (k = 1) was obtained, in good agreement with manufacturer data (69.5 kV). HVL was 1.85 mm Al. Dose rate for a typical 6 Gy to 7 Gy prescription resulted about 3.3 Gy/min and the leakage value was < 100 µGy/min.


CONCLUSIONS
The new Esteya(®) Electronic Brachytherapy System presents excellent flatness and penumbra as with the Valencia applicator case, combined with an improved PDD, allowing treatment of lesions of up to a depth of 5 mm in combination with reduced treatment duration. The Esteya unit allows HDR brachytherapy superficial treatment within a minimally shielded environment due its low energy.
Department of Radiation Oncology, La Fe University and Polytechnic Hospital, Valencia, Spain.
Teresa
T
Garcia-Martinez
PANalytical B.V., Eindhoven, the Netherlands.
Jan-Pieter
JP
Chan
Department of Radiation Oncology, La Fe University and Polytechnic Hospital, Valencia, Spain ; Department of Radiotherapy, Clínica Benidorm, Benidorm, Spain.
Jose
J
Perez-Calatayud
Department of Atomic, Molecular and Nuclear Physics, University of Valencia. Burjassor, Spain.
Facundo
F
Ballester
electronic brachytherapy; nonmelanoma skin-cancer; skin brachytherapy; superficial radiotherapy