SU-GG-I-38: A Direct Skin Dose Calculation Method in CT Scans without Table Motion: Influence of Patient Size and Beam Collimation

CT Dose Index and Patient Dose: They AreNotthe Same Thing

“…With use of technique charts and diagnostic reference levels, CTDI vol can be used to prescribe the right dose for a specifi c patient size and diagnostic task. However, CTDI vol cannot be used as a surrogate for patient dose, either in epidemiologic assessments of potential late effects or for potential deterministic effects (eg, skin injury) ( 17,18 ). Neither CTDI vol nor its derivative, dose-length product (DLP, which is the product of CTDI vol and the irradiated scan length), should be used to estimate effective dose or potential cancer risk for any individual patient.…”

“…To achieve similar image quality, the scanner output (CTDI vol ) should be increased by about a factor of two as patient size changes from a typical adult abdomen (lateral dimension, 35-40 cm) to an obese adult abdomen (lateral width, 45-50 cm) (35)(36)(37). Even though the scanner output increases by a factor of two, the dose to many of the radiosensitive internal organs used in the calculation of effective dose does not with an accuracy of approximately 10% ( 19,(22)(23)(24)(25)(26)(27). Thus, as long as scanner output continues to be measured and reported by using a standardized, highly reproducible, and pragmatic measurement technique, such as the CTDI vol method, patient dose can be accurately estimated.…”

“…The CTDI vol tells the medical physicist precisely how the machine was operated, and it can be used, in conjunction with information regarding patient size and the scanned anatomy, to estimate patient dose ( 19,(23)(24)(25). Dose estimates can be for organ dose, skin dose, or a mean dose in the center of the scan volume ( 17,19,(23)(24)(25)57 ). The CTDI values are not, however, patient dose estimates.…”

“…The long scan times necessitated use of dosimeters that could integrate dose accurately over several minutes, such as fi lm or thermoluminescent dosimeters. Conversely, the (16)(17)(18)(19). These criticisms, however, are based on the belief that CTDI should estimate the patient dose, as opposed to quantifying the radiation output of CT systems.…”

Lateral Decubitus Positioning for Cervical Nerve Root Block Using CT Image Guidance Minimizes Effective Radiation Dose and Procedural Time

“…20 It has been demonstrated that during simulated brain perfusion procedures, the dose to the skin may vary from 53% to 89% of the CTDI vol , while the dose to the eye lens is approximately 62% of the CTDI vol . 21,22 If one assumes an average dose reduction by 75%, the product of this factor by the increase due to the 12-cm neck size results in a net overestimate of the true CTDI vol and DLP of approximately 10%-12%.…”