Performance comparison of four common LINAC daily QA instruments / 中华放射医学与防护杂志

ABSTRACT

Objective To compare the performances of four commercially available LINAC daily QA instruments.Methods The dosimetric stability of a LINAC including central axis output,flatness and symmetry were verified and fine-tuned using a 3-dimensional water phantom,dosimeters and ionization chambers.The baseline of the four instruments including LINA-C,QUICK-C,BEAM-C and QA3 were set thereafter.Daily measurements of LINAC were conducted with these instruments respectively and the results were compared.Arbitrary errors (CAX and SYM) beyond TG-142 tolerances were introduced to the LINAC to test the sensibilities of each instrument in detecting these changes.Results Relative to the baseline that were measured by the 3-dimensional water phantom and dosimeters,the results monitored by the four instruments were comparable.The maximum disparities of the CAX,FLAT,and SYM were 0.5％ (LINA-C),-0.45％ (QUICK-C),and 0.5％ (BEAM-C),respectively.All checkers detected the known errors successfully.Conclusions The stabilities of all the four evaluated instruments met the requirements of daily QA for LINAC.LINA-C verifies CAX only.QUICKE-C,BEAM-C and QA3 can be used to perform all the daily QA protocols as suggested by AAPM TG 142 report.They also provide unique additional functions.The setup of baseline determines if the morning checkers could measure the LINAC dosimetric parameters correctly.When an error is alarmed by the morning checker,it is recommended to verify the performance of the instrument first rather than recalibrating the LINAC immediately.