TECHNIQUE OF ESTIMATION OF ERROR IN THE REFERENCE VALUE OF THE DOSE DURING THE LINEAR ACCELERATOR RADIATION OUTPUT CALIBRATION PROCEDURE. PART 1. DEPENDANCE OF THE MECHANICAL PARAMETERS OF LINAC’S GANTRY

To ensure the safety of radiation oncology patients needed to provide a consistent functional characteristics of the medical linear electron accelerators, which affect the accuracy of dose delivery. To this end, their quality control procedures, which include the calibration of radiation output of the linear accelerator, the error in determining the dose reference value during which must not exceed 2 %, is provided. The aim is to develop a methodology for determining the error in determining this value, depending on the mechanical charachteristics of the linac’s gantry. To achieve the objectives have been carried out dosimetric measurements of Trilogy S/N 3567 linac dose distributions, on the basis of which dose errors depending on the accuracy setting the zero position of the gantry and the deviation of the gantry rotation isocenter were obtained. It was found that the greatest impact on the value of the error has gantry rotation isocenter deviation in a plane perpendicular to the plane of incidence of the radiation beam (up to 3,64% for the energy of 6 MeV). Dose errors caused by tilting the gantry and its isocenter deviation in the plane of incidence of the beam were highest for 18 MeV energy and reached –0,7 % and –0,9 % respectively. Thus, it is possible to express the results of periodic quality control of the linear accelerator ganty in terms of dose and use them to conduct a comprehensive assessment of the possibility of clinical use of a linear accelerator for oncology patients irradiation in case of development of techniques that allow to analyze the influence of the rest of its technical and dosimetric parameters for error in dose.

radiation therapy, linear accelerator radiation output calibration procedure, error in the reference value of the absorbed dose, linac’s gantry

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