Dosimetric evaluation of photon use in whole body skin irradiation

Radiotherapy is one of the main options used in the treatment of mycosis fungoides and sezary syndrome, which are the most known subtypes of cutaneous T-cell lymphoma. Total body skin electron irradiation is a special radiotherapy technique that has been used for many years in the treatment of mycosis fungoides. In our study, in addition to the compatibility of critical organ doses, homogeneity index and conformity index dosimetric values by using total body skin helical irradiation in the treatment of mycosis fungoides, the advantages of total body skin helical irradiation over Total body skin electron irradiation in terms of patient, employe and physical conditions during treatment were investigated. Images of a male patient were taken from the computed tomography device in our institution and transferred to the MIM® contouring system of the helcal tomotherapy device. Patient's critical organs, planned target volume and optimizations were determined in the MIM® contouring system. Patient data were transferred to treatment planning system and the patient was prescribed a dose of 36 Gy in 24 fractions and 1.5 Gy per fraction. The patient's treatment dose plan is prepared and critical organ, homogeneity index and conformity index values were analyzed dosimetrically. The unique irradiation technique of the helical tomotherapy device and the drawn optimizations allowed us to reduce the doses of both critical organs and all structures 0.5 cm deep from the skin. D95, D90, Dmax, Dmin and Dmean values for planned target volume in dose volume histogram were 34.33 Gy, 35.06 Gy, 42.65 Gy, 11.32 Gy, 36.93 Gy, respectively. The mean doses of the right and left parotid in our study were measured as 19.34 Gy and 18.76 Gy, respectively. The mean doses of critical organs in the head and neck, thorax, abdomen and pelvic region were between 2.98 Gy and 19.34 Gy, 3.73 and 8.20 Gy, 6.56 Gy and 9.30 Gy, 2.78 Gy and 6.76 Gy, respectively. The homogeneity index value was calculated as 0.15 according to the ICRU 83 report, and the conformity index value as 0.95 according to the ICRU 62 report. It was seen that total body skin helical irradiation could be an alternative to total body skin electron irradiation in terms of values such as the comfort of the patient during the treatment, the lack of initial measurements (dose profile measurements, percent deep dose measurements, absorbed dose calibration, combined dose measurements, determination of treatment depth, determination of treatment duration, measurement of X-ray contamination energy and amount), radiotherapy with imaging at the beginning of the treatment, and improvement in dose homogeneity. Keywords: Mycosis Fungoides, Total Body Skin Helical Irradiation, Total Body Skin Electron Irradiation, Helical Tomotherapy