a Linear accelerator dosimetry method with point-to-point measurements and 3D automated system

Abstract

     Good Radiotherapy requires the ability to determine the absorbed dose at any point of interest in the patient with a minimum accuracy of 95%. Data are needed to enable proper planning and delivery of radiation dose. The most convenient equipment for carrying out the measurements that result in these data is an 3D automatic radiation field scanning system. Such a system requires the use of signal integrating methods with integration times that are long relative to the field sweeping time. The objective of this work was to develop a point-to-point measurement system to obtain dosimetric parameters of linear accelerator beams used in radiotherapy. For this, a water phantom was built, named phantom-Telles, being composed by an automated system for detector positioning and a calculation model identified as FOCAL. The model uses the transport equation with approximations to interpolate data measured in the phantom-Telles in order to simulate continuous scan measurements made by commercial phantoms. The new phantom was constructed at the Federal University of Rio Grande do Norte, updated programmed, and calibrated at the Federal University of Sergipe, and validated at the Real Hospital Português in Recife, Brazil, through comparisons between dose depth percentage (PDD) and dose profile curves in radiation fields of 6 MV beams from a Varian-TrueBeam linear accelerator measured with a 3D Blue Phantom (IBA). The results of the PDD and Profile measurements showed that the data obtained with the phantom-Telles conformed to those obtained with the Blue Phantom. The simulated and measured point-to-point data in the new phantom differed by up to 2% from those obtained by scanning in the Blue Phantom in region of high dose gradient and around 1% elsewhere. The data set obtained in this work indicates that the phantom Telles has potential for use in quality control and commissioning of linear accelerators.