Measurement and analysis of surface dose for flattening filter free medical accelerator using advanced markus chamber

Surface dose plays a significant role in radiotherapy. Doses received by the basal skin layer can result in complications such as skin erythema, epilation, dry desquamation, wet desquamation, necrosis etc depending on the magnitude of doses received.(1) Hence, accurate measurement of dose at the surface is essential for proper treatment of patients. Surface dose is machine dependent and can be affected by many parameters such as field size, source-to-surface distance (SSD), beam energy, materials present in the beam line, type of dosimeter used for its measurement etc.(2). Recently, flattening filter-free (FFF) medical linear accelerator (linac) has been introduced in radiotherapy. With the filter removed, this low-energy component is allowed to pass through to the patient and will act to increase the surface dose. Energy spectrum and electron contamination are the two factors, which can change the surface dose in FFF. In this study, the relative surface dose has been studied for two different linac models in FF and FFF mode for 6 MV beam energy considering the fact that 6 MV is the beam of choice for various clinical cases