Measuring the Vertical Profile of Electron Fields for Total Skin Electron Irradiation using Radiochromic Film
Total skin electron irradiation (TSEI) is a radiotherapeutic technique used in the treatment of mycosis fungoides. The treatment involves the delivery of a uniform radiation dose at an extended source to surface distance by using 80×200 cm2 uniform electron fields. To ensure the accurate delivery of radiation to the patient, it is necessary to conduct regular quality assurance of the TSEI technique through the measurement of relevant dosimetric data. One of the most time consuming measurements is quantifying the vertical profile of the electron field using ion chambers. Radiochromic film presents a new method of measuring vertical profiles and has the potential to replace the use of ion chambers. Recent advancements in dose calibration in the software FilmQA Pro have finally allowed for reliable film dosimetry. The vertical profile of the electron field described above was measured using both ion chambers and film for two linear accelerators. Several profiles measured over multiple days were compared to each other, as well as to the original data from commissioning, in order to test the accuracy and stability of the film. The results demonstrate the stability of the film measurements and increased accuracy of dose measurements when compared to ion chamber data. As such, a procedure for measuring the vertical profile of the large electron fields used during TSEI with GafChromic EBT-XD radiochromic film was developed. Overall, using radiochromic film to measure vertical profiles saves time, improves the accuracy of dose measurements, and ultimately ensures the reliable delivery of radiation to patients.