Implementation and Evaluation of WS531-2017 "Specification for Testing of Quality Control in Helical Tomotherapy Unit"

Abstract

Objective: To perform an annual test on the system stability of the first helical tomotherapy unit (Tomotherapy, TOMO) in Zhejiang province according to WS531-2017 "specification for testing of quality control in helical tomotherapy unit", and to further standardize the quality control operation, understand the properties of the system and ensure the accurate implementation of clinical radiotherapy. Methods: According to the requirements of WS531-2017, 8-channel measurement instrument (TomoElectrometer), ionization chamber A1SL (Standing Imaging, USA) and A17 (Standing Imaging, USA), cylindrical phantom (Cheese Phantom), equivalent rectangular solid water, two-dimensional water tank, EBT3 film, and Vidar film analyzer were used to detect 10 key indicators of TOMO. Results: The static output dose deviation was -0.6%, and the rotational output dose deviation was 1.4%. The difference between radiation quality and planned value was 0.8%. The symmetry of the horizontal dose curve of the radiation field was -1.2%; and the full width at half-maximum deviation of the longitudinal dose curve of the radiation field was 0.7mm. The horizontal offset of multi-leaf collimator was -0.6mm. The green laser offset in axial plane, sagittal plane and coronal plane were 0.08mm, 0.2mm and 0.2mm to the of virtual isocenter. The red laser light offset was -0.4mm. The movement deviation of the treatment bed was 0.3mm; and the synchronous deviation of the rotation of the treatment bed and frame was -0.6mm. Conclusion: All 10 key indicators of TOMO meet the requirement of WS531-2017. Some necessary testing items, such as MVCT image quality verification, should be added to the annual TOMO quality control in order to ensure the good stability and normal working of system.