A Simple Technique for Quick In-Vivo Dose Measurements for KV CBCT and Diagnostic X-Ray Planar Imaging Using MicroMOSFET Dosimeters
P Charpentier*, P Chan, T Neicu, S Kaplan, S Li, Temple University Hospital, Phila., PASU-E-J-160 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: To present a practical method for dose measurement of kV CBCT scans and diagnostic X-ray planar imaging according to typical IGRT in radiotherapy and chest and pelvis diagnostic imaging protocols by using microMOSFET dosimeters. Once calibrated, in-vivo measurements can be easily performed on patients on surface and/or in internal cavities.
Methods:The calibration procedure uses two ADCL calibrated ion chambers for diagnostic kV X-ray beams, one 6 cc farm chamber and one large parallel plane chamber for absolute dose references, and the microMOSFET with high sensitivity settings for calibration in air and in phantom. The calibration covered the possible dose range from 1 to 25 mGy. The calibrated dosimeters were then placed at anterior, posterior, right lateral and center of an anthromorphic phantom to measure the dose for CBCT scans using the appropriate calibration file according to kVp and dose range. Also, the dosimeters were placed inside two cadavers for internal dose measurement for typical x-ray imaging.
Results: Our measured results showed that the dose from CBCT scans were typically 16% - 39% higher than the nominal dose presented by the vendor per protocol. The dose from 4D CBCT scan, 2.16 cGy, was approximately 39.4% higher than the nominal dose of 1.55 cGy. The Prostate M10 scan of 3.458 cGy was approximately 16.8% higher than the nominal dose of 2.96 cGy. The Pelvis/Chest M20 scan 2.972 cGy, was approximately 35.1% higher than the nominal dose of 2.2 cGy. Large variation was observed for planar X-ray imaging due to use of shielding and tissue attenuations.
Conclusion:The ease of implementation and using microMOSFETs for CBCT scans and X-ray imaging allows quick and accurate in-vivo dose measurements. Vendor specified doses are verified by this technique and should be added to increase patient quality assurance and safety.