Program Information
Accuracy of Kilovoltage X-Ray Beam Dosimetry Using a 0.6 Cc Ionization Chamber with An Absorbed Dose to Water Calibration Factor
Y Uchida1*, H Tachibana1 , T Kogure2 , (1) National Cancer Center, Kashiwa, ,(2) Chiba Tokushukai Hospital, Funabashi, Chiba
Presentations
TU-C3-GePD-I-5 (Tuesday, August 1, 2017) 10:30 AM - 11:00 AM Room: Imaging ePoster Lounge
Purpose: For image guidance using x-ray fluoroscopic imaging, entrance skin dose for x-ray fluoroscopic imaging should be carefully managed. AAPM task group 142 recommends a direct measure of imaging dose from kilovoltage x-ray beam at least annually. Kilovoltage x-ray beam dosimetry using a 0.6 cc farmer-type ionization chamber would be effective in radiotherapy department. In this study we investigated the dosimetry of kilovoltage x-ray beam using the chamber with a ND,w (absorbed dose to water calibration factor).
Methods: Our protocol for kilovoltage dose measurement uses 0.6 cc farmer-type ionization chamber with ND,w. To determine the quality conversion factor, kQ-kV, which converts the absorbed-dose to water calibration factor for a 60Co beam into the calibration factor for an arbitrary beam of quality Q-kV which can be for kilovoltage photon, the ratio of mean mass energy-absorption coefficient for water to air and the ratio of mean restricted collision mass stopping power for water to air in PTW30013 for 60Co converted kQ,Q0 for a 60Co beam into kQ-kV after half value layer was measured. Comparison in kilovoltage x-ray dose between using the chamber and using a commercially available semiconductor device (RaySafe ThinX RAD) was performed.
Results: The results showed good agreement between using the chamber and using the device for kilovoltage x-ray beam. The agreement was worse when measuring low energy x-ray beams. Compared to the measurement of the semiconductor device, dose deviations with and without kQ-kV showed 0.25 ± 1.71 % and 9.72 ± 2.05 %, respectively.
Conclusion: It would be useful to measure imaging dose for kilovoltage x-ray with tolerable measurement accuracy using the 0.6 cc farmer-type chamber in department of radiation oncology when quality assurance for image guidance using kilovoltage x-ray is performed.
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