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SU‐FF‐I‐67: Converting CT Dose Length Product (DLP) to Kerma Area Product (KAP)
Author(s) -
Ogden K,
Huda W
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3181187
Subject(s) - isocenter , kerma , nuclear medicine , medicine , fluoroscopy , radiography , computed radiography , dosimetry , scanner , radiology , optics , imaging phantom , physics , image quality , artificial intelligence , computer science , image (mathematics)
Purpose: The amount of radiation that is incident on patients in CT is measured using the Dose Length Product (DLP mGy‐cm) which is not commensurate with the corresponding quantity currently used in radiography and fluoroscopy, namely the Kerma Area Product [KAP]. This study computed DLP to KAP conversion factors that will enable patient exposures in CT to be compared with radiography and fluoroscopy. Method and Materials: We computed the DLP and KAP values for head and abdominal CT examinations on a GE LS 16 CT scanner for the same examination. Scan DLP data were obtained using the ImPACT spreadsheet. Average CT Kerma values were obtained from the free‐in‐air intensity of the CT at the scanner isocenter and relative intensities within the fan beam plane. Average x‐ray beam areas were obtained using the focal isocenter distance (541 mm) and modeling adult patients as ellipses (heads radii of 7.38 cm/9.47; abdomens radii of 11.25 cm/15.5 cm). Values of KAP were computed per 100 mGy‐cm for head and abdominal CT scanning computed in 16 cm and 32 cm diameter acrylic cylinders, respectively. Results: In head and body CT, a DLP of 100 mGy‐cm corresponds to a KAP incident on the patient of 1.9 Gy‐cm 2 and 5.4 Gy‐cm 2 , respectively. Conclusion: Conversion of DLP into KAP permit patient exposures in CT to be compared to exposures in radiography and fluoroscopy including head and chest radiography (∼1 Gy‐cm 2 ), abdominal radiography (∼5 Gy‐cm 2 ), barium studies (∼20 Gy‐cm 2 ) and interventional procedures (∼100 Gy‐cm 2 ).