To understand the functional status and radiation protection requirements of helical tomotherapy (TOMO) unit when it is applied in clinic treatment so as to promote the construction of TOMO quality control system.

A helical tomotherapy unit with a type of tomotherapy Hi-Art was employed as the radiotherapy unit. A series of tests and analyses on dosimetric and radiation safety performance parameters of the TOMO unit were conducted with the use of a A1SL ionization chamber, a set of solid water equivalent phantoms and other test equipments. The performance parameters were compared with that of a conventional 6 MV accelerator with a type of ARTISTE.

The deviations of static and dynamic output dose were -1.51% and 1.18%, respectively. The values of PDD₁₀/PDD_1.5 and PDD₂₀/PDD_1.5 were 0.608 and 0.318 within the range of X-ray quality parameters calibration. Under the different field conditions of 40 cm×5 cm, 40 cm×2.5 cm and 40 cm×1 cm, the stability of transverse/longitudinal dose distribution curve was no more than 1.20% and the offset distance of Jaw width was smaller than 0.5 mm. Radiation leakage ratio of the treatment rotating center from the multileaf collimator (MLC) was 0.20%. No matter the average or the maximum value of the leakage radiation from couch plane was less than 0.02%.

The performances and testing requirements of TOMO unit are different from a conventional electron linear accelerator, the quality control index of TOMO unit should be set seperately and tested strictly in terms of the specific requirements of the unit by complying with the QC programme. The reliable quality control system should be established and effectively implemented to serve the radiotherapy quality and radiation safety effectively in the tomotherapy.