The rotary dual technique for total skin irradiation in the treatment of mycosis fungoides – a description of the applied method

Abstract

Background

The aim of total skin electron irradiation in the therapy of mycosis fungoides is to obtain total or partial remission of the disease while concurrently lowering the toxicity level. Total skin electron radiotherapy should fulfill the EORTC requirements from the year 2002.

Aim

The aim of this work is to present the rotary dual method for total skin electron irradiation used in the Great Poland Cancer Centre including its specific technical and physical aspects. These aspects include the parameters and conditions for the treatment (geometrical conditions of the technique, homogeneity of the dose, patient's positioning, additional fields and the method of dose fractionation), the absolute dosimetry (parameters and functions characterizing the electron irradiation beam used in the rotary dual method of the rotary dual method of the total skin electron irradiation) and in-vivo dosimetry conducted during the therapy with rotary dual fields, which allowed to control the dose distribution and to indicate additional skin areas, which should be irradiated with local fields.

Materials/Methods

The rotary dual method of the Total Skin Electron Irradiation proposed by the author, is based on the combination of the two most frequently used methods: 1) six dual fields’ method and 2) rotary method. The original, calculation algorithm elaborated by the author was based on the two dimensional algorithm proposed by Podgorsak et al.

Results

The new algorithm, proposed by the author takes into the changes in doses along the vertical and horizontal axis of the object. Moreover the elliptical; shape of the object proposed by the author, is more approximated to the shape of the patient than the cylindrical object proposed by Podgorsak et al.

Discussion

Parameters used by authors: nominal energy – 6 MeV, mean energy at the skin surface – 2.8 MeV, values of the PDD (at the skin surface – 100%, at the 4 mm – 83.6% and at the 20 mm – 1.8%), SSD – 300 cm, field size equal to 230 cm by 115 cm, fraction dose – 1.5Gy, total time of treatment from 6 to 7 weeks were compatibility with EORTC recommendations.

The elaboration of the rotary – dual method of total skin electron irradiation allowed to reduce SSD distance compared to irradiation with the rotary method. Moreover the dimension of most therapeutic rooms is usually too small to realize the total skin electron irradiation methods with SSD distance higher than 350 cm. Patient set-up and rotation during irradiation (based on rotary method) allow to reduce the number of dual fields used in Stanford method from six fields to one dual field (rotary-dual method). This modification leads to reduction of time assigned for set-up verification). Presented results of in-vivo dosimetry for selected patients treated in Great Poland Cancer Centre confirm the needfulness for using additional local for areas of perineum, scalp vertex, hands, neck-shoulders, plants.

Moreover, obtained results indicate that total dose prescribed for additional fields depends on height and obesity and should be prescribed individually for each patient.