TG 142 Imaging Modalities QA - Three Year Experience
T Lin*, M Hossain, C Ma, Fox Chase Cancer Center, Philadelphia, PASU-D-103-1 Sunday 2:05PM - 3:00PM Room: 103
Purpose: This study is initiated to check if the frequency of imaging QA suggested by AAPM Task Group Report 142(TG142) is necessary. TG142 presents recommendations for QA criteria of IGRT treatment. It is an update to AAPM TG40 and has added recommendations for imaging devices that are integrated with IGRT Linacs. The imaging devices studied include kilovoltage(KV) X-ray imaging, megavoltage(MV) portal imaging, and cone-beam CT(CBCT) with kV CBCT for Varian and MV CBCT for Siemens.
Method and Materials: This study uses VarianIX2100 and Siemens Artiste Linacs to perform QAs on KV,MV,CBCT modalities. The QA was designed following under the recommendations of TG142. This study reports the daily imaging positioning/repositioning and imaging and treatment coordinate coincidence. QA results on kV, MV and CBCT from 4/7/2010~12/14/2012 are analyzed. A radio opaque marker was implanted into the center of a 5cm cube. KV,MV,CBCT images are taken with the cube localized at the isocenter. Digital graticule is used in the software to verify the isocenter position. Another image is taken with the cube placed at 1cm superior, lateral and anterior of the isocenter. In-line fusion software is used to verify the contrived shift. Digital ruler provided at the on-board-imaging software or adaptive-targeting software was used to measure the position differences. The position differences were recorded at AP,LR,SI directions.
Results: Thirty-two-month records on kV,MV,CBCT show the shifts in all three directions are within the tolerance of 1mm suggested in TG142 for stereotactic radiation treatment(SRS/SRT). There is no occasion where shifts are outside 1mm tolerance.
Conclusions: The daily imaging QA suggested in TG142 is useful in ensuring the accuracy needed for SRS/SRT in IGRT. Thirty-two-month measurements presented suggest that decreasing the frequency of imaging QA may be acceptable, in particular for institutions reporting no violation of tolerance over periods of few years.