Commissioning of a Total Skin Electron Therapy (TSET) technique

Total skin electron therapy (TSET) is a special radiotherapeutic technique used to treat a variety of cutaneous malignancies where most or all of the skin is involved. The aim of the treatment is to irradiate the whole skin to a uniform dose profile within ±10%, both circumferentially around the patient as well as along the patient's length, while sparing the underlying organs. At King Fahd Specialist Hospital - Dammam, two irradiation techniques using a 6 MeV high dose rate (888 MU/min) electron beam from a Clinac 2300CD (Varian Medical Systems. Inc., Palo Alto, Ca, USA) are being investigated. For both techniques, the patient stands on a stationary platform 30 cm above the ground at a Source-to-Skin distance of 400 cm and is irradiated in six different positions to cover all parts of the body. Production of a flat beam profile in the first technique is based on a dual field irradiation with fields aiming above and below the mid-horizontal level. In the second technique, a flat beam is obtained using a custom made flattening filter with a single large field. We are in the process of designing and testing a filter for the production of flat beam profile. Percentage depth dose curves at 100 cm and at 400 cm were measured using a Markus parallel plate ionization chamber and beam profiles were measured using 20 MOSFET dosimeters. We have measured the beam output for the single stationary dual beams and the unfiltered single field beam. We have also measured an "effective" output correction factor that relates the output at a point from all 6 irradiation positions to that from a single irradiation position.