The Effect of Misalignment on Precision of CT Quality Control Dosimetry Tests

سال انتشار: 1397
نوع سند: مقاله کنفرانسی
زبان: انگلیسی
مشاهده: 393

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شناسه ملی سند علمی:

RSMED01_010

تاریخ نمایه سازی: 30 دی 1397

چکیده مقاله:

Objective: To investigate the effect of misalignment (defined as difference between isocenter and phantom or pencil ion chamber central axis respectively for in phantom and air measurements) on precision of Computed Tomography (CT) quality control (QC) dosimetry tests.25Methods: A GE Light Speed 16 slice CT scanner was modeled by using GATE toolkit. This model consisted of: (1) CT x-ray source with head scan field of view and beam collimation of 10 mm and its flat and bowtie filters rotating around the isocenter; (2) the head standard dosimetry phantom; (3) a pencil ion camber. The CT scanner model was validated by comparison with measurement results. The misalignment of pencil ion chamber or head phantom was verified in CT dose index (CTDI) measurements by increasing their central axis from the isocenter toward edges of the table.Results: With increasing the misalignment: (1) No significantly variation was observed in CTDI measured in air. (2) Large difference observed in the peripheral CTDI with the maximum of ~11.5 mGy occurred at 4 cm from the isocenter. (3) An average increase of ~2% and ~9% were occurred in CTDI for central and peripheral holes of phantom. (4) The CTDIW was decreased by ~1 mGy.Conclusion: The misalignment at 4 cm from the isocenter starts affecting the precision of CTDI values required for QC tests. This effect should be taking into consideration in QC set up since the QC reports are the base of CT scanner output consistency and dose data base shown on the console.

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نویسندگان

Masoud Masoudi

Department of Ray-Medical Engineering, Shiraz University, Shiraz, Iran