Analysis of Potential Collisions of Elements of Therapeutic Accelerator on the Basis of the System of Virtual Visualization of Radiation Therapy

Purpose: Analysis of potential collisions of elements of the therapeutic complex with the patient on the basis of linear electron accelerator (LEA) using the system of virtual visualization of radiation therapy (VVLT). Material and methods: The research was conducted in the system of virtual visualization of radiation therapy, in which the acceptable positions of the elements of the LEA complex (position of the head part of the LEA at a certain gantry angle and of the therapy table) that do not lead to patient collision were evaluated. The system is a simulation software for radiotherapy procedures. Seven models of therapeutic LEAs (manufacturers Varian, Elekta and Siemens) and 4 patient models of different localizations (prostate tumor, lung tumor, breast tumor, head and neck tumor) with an appropriate set of immobilizing devices were selected for the analysis. Results: The results are presented in the form of graphs of the critical value of the gantry rotation angle at different transverse and vertical displacements of the therapy table for each localization. In the case of lung cancer, it was found that a transverse displacement of the table by 10 cm from the initial position (the position at which the patient model was centered relative to the isocenter of the LEA) resulted in a 15° difference in the gantry rotation angles at which collisions occur. Collisions occur at 90° on Elekta LEA, on Varian CX and iX at 96°, and on Varian TrueBeam at 105°. When the table height is increased by 10 cm, the difference increases to 20° with the same statistics for the transversal bias between linear accelerators. In general, increasing the lateral offset or table elevation results in a reduced range of gantry rotation before collision for all LEA models. Conclusion: Based on experimental simulation using the VVLT system, the values of the critical gantry rotation angle at transverse and vertical displacements of the therapy table were obtained. The obtained results can be used to develop collision prevention algorithms, thus improving the safety of radiation therapy procedures, allowing more accurate prediction and avoidance of possible obstacles during treatment.