A Study Of Rapid Quality Control Method For Helical Tomotherapy

Helical Tomotherapy is the combination of CT and medical linear accelerator,and has new image-guide radiation equipment and intensity-modulated radiotherapy.Compared with traditional medical accelerators,there is no filter,but it has small source distance,high output dose rate,and clinically obtained.The dosimetric significant advantages such as dose uniformity,dose gradient and normal organ protection have been widely recognized and applied.As a new medical device,TOMO has strict requirements for quality control.At present,the TOMO annual performance test adopts the Cheese phantom and Tomoscanner water tank provided by the manufacturer.With the implementation of the National Health Standard WS 531-2017 Code for Quality Control Testing of Helical Tomotherapy Devices,it is urgent to develop a special TOMO phantom and water tank for testing.The home-made TOMO phantom and TOMO scanning water tank were developed here.In this study,the home-made TOMO phantom and the TOMO scanning water tank were used for dose measurement,off-axis dose distribution,and percent depth dose measurement,respectively.The two instruments were used to establish a rapid quality control method for helical tomotherapy.Firstly,the difference of dose measurement between home-made TOMO phantom and Cheese phantom combined with A1SL type ionization chamber under TOMO static field conditions;Secondly,the home-made TOMO phantom combined with A1SL type ionization chamber and PTW30012 ionization chamber for dose measurement under static field conditions;Then,the home-made TOMO phantom combined with EBT3 film was used to verify the patient’s intensity modulated plan.The test results were compared with the Cheese phantom and the ArcCheck three-dimensional semiconductor matrix;Finally,the home-made TOMO phantom and the Cheese phantom combined with the A1SL type ionization verify the difference of point absorbed dose of patient’s intensity modulated planThe TOMO scanning water tank performed beam scanning and data collection according to AAPM TG-148 and 106 reports,respectively obtaining lateral and longitudinal field width,penumbra value and lateral field symmetry,and percent depth dose value under longitudinal field conditions.Compared the above test values with the manufacturer’s values and analyzed the differencesUnder the static field conditions,the relative deviations of absorbed doses of home-made TOMO phantom and Cheese phantom at different depths were 0.35%,0.3%,0.3%,0.34%and 0.0%.The results were in good agreement.The home-made TOMO phantom combined with the A1SL type ionization chamber and the PTW30012 ionization chamber respectively under static conditions.The relative deviations of absorbed dose were-0.52%,-0.60%,-0.50%,-0.58%,-1.00%.The home-made TOMO phantom combined with EBT3 film was used to verify the patient’s intensity modulated plan.The average y pass rate was greater than 92%.There was no statistically significant of the test results between the home-made TOMO phantom and Cheese phantom and ArcCheck three-dimensional semiconductor matrix(P>0.05).The two phantoms combined with the A1SL type ionization chamber to measure the dose deviation of the region of interest within 3%,and the deviation was not statistically significant(P>0.05).For the lateral field,the TOMO scanning tank measured the field width difference compared with manufacturer value was 5 mm,the penumbra deviation in the range of 7 mm,the symmetry difference was less than 2%.For the longitudinal field,the deviation of the TOMO scanning tank measures the field width compared with the manufacturer value was within 1 mm,the field width deviation index was within 5 mm,the penumbra deviation was within 1 mm;Percent depth dose 1,measurement results have a PDD10 deviation of less than 1%and a PDD15 deviation of less than 2%In conclusion,the results of the home-made TOMO phantom compared with the results of the Cheese phantom or the manufacturer’s value and the results were in good consistent.The home-made TOMO phantom can be used for the static and rotational mode dose measurement of the helical tomotherapy.The development of this phantom is filled the blank of the domestic phantom;the TOMO scanning water tank needs further improvement and upgrade,and further research is continued.The home-made TOMO phantom and TOMO scanning water tank completed the test of WS 531-2017 Code for Quality Control Testing of Helical Tomotherapy Devices for the annual inspection items of the helical tomotherapy and the related indicators of dosimetry,and lays the foundation of my unit establish TOMO rapid quality control methods based on the industry standard.