Feasibility study on pre-treatment quality assurance using the EPID system of the uRT-linac 506c.

Purpose: With the rapid development of computer technology, techniques with high modulation capabilities, such as Intensity Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT), have been widely applied in radiotherapy. As a result, it has become essential to perform Pre-treatment Quality Assurance (PQA) for each treatment plan to prevent radiation accidents. We aim to validate the novel uRT-linac 506c's EPID system as an alternative method for PQA by comparing the performance with IMatriXX.

Method: 30 IMRT and 30 VMAT treatment plans were selected, and the Gamma Index (GI) criterion was used to assess the agreement between the predicted and measured dose distributions. Under different GI standards, the verification passing rate of two verification systems was obtained. Then, deliberate errors, including changes in the positions of the MLC banks, collimator rotations, and variations in dose delivery to the target, were incorporated into the plans to rigorously evaluate the sensitivity of two PQA systems.

Result: The mean (± standard deviation) γ passing rates for the IMatriXX and EPID systems, assessed with a 3 mm/2 % gamma criteria, were 99.73 % ± 0.77 % and 99.91 % ± 0.15 %, for IMRT plans, respectively. For VMAT plans, the corresponding rates were 98.65 % ± 1.13 % and 99.81 % ± 0.32 %, respectively. The IMatriXX and EPID verification systems are capable of detecting MLC shift errors of 1.0 mm, collimator rotation errors of 3° for IMatriXX and 2° for EPID, and dose errors of 2 % for both systems, respectively.

Conclusion: The EPID system integrated with the uRT-linac 506c demonstrates a high degree of correlation with the conventional IMatriXX PQA method, suggesting that it may be a promising and potentially comparable alternative to the conventional IMatriXX system. Further studies with larger sample sizes and more comprehensive statistical analyses are needed to fully assess its non-inferiority.