Dosimetric comparison and quality assurance of different techniques in total skin electron irradiation (TSEI)

Total Skin Electron Irradiation (TSEI) using the Stanford technique typically requires an extended source-to-skin distance (SSD) of 400 cm. This study introduces a modified Stanford technique employing three fields at a reduced SSD of 310 cm and compares its dosimetric performance with the conventional approach. Dosimetric measurements were conducted at 310 cm SSD to obtain vertical and horizontal dose profiles. Percentage depth dose (PDD) curves were recorded from 0 to 40 mm depth at a gantry angle of 90°, and key parameters (d_max, R_p, R₅₀, E₀, cGy/MU) were derived. Field factors (12FF and 18FF) and treatment depth were assessed using an anthropomorphic phantom. X-ray contamination and its percentage were determined with lead and copper plates. To achieve profile uniformity, Stanford techniques used gantry angles of ±19°, and modified Stanford techniques used ±36° (in addition to 90°) from the horizontal. The 12FF-18FF values were 2.30 and 2.43, with total X-ray contamination measured at 2.84% and 2.68%. Required MUs were 768 for the Stanford and 1098 for the modified technique. Both techniques yielded similar dosimetric parameters (d_max: 1.3 cm; R_p: 2.91 cm; R₅₀: 2.27 cm; E₀: 5.30 MeV), while X-ray contamination energies were 1320 keV (lead) and 1360 keV (copper). Film analysis indicated superior dose homogeneity with the Stanford technique. Both techniques are dosimetrically viable for TSEI at reduced SSDs; however, the Stanford technique offers improved dose uniformity and lower monitor unit requirements, making it the more advantageous option.