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Direct Calculation of Patient Absorbed Dose From X-Ray Beam Variables and Anatomy

F Soares

F Soares*, A Borba, T Moreira, Instituto Federal de Santa Catarina, Florianopolis, Brasil

SU-E-I-97 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Develop a direct equation to estimate patient absorbed dose under x-ray exams using electrical, geometrical and filtration parameters combined with anatomy data. The equation can further be used in radiology departments to record patient dose data and help to decide the best parameters set for each patient exam.

Methods:To determine the absorbed dose received by patients, Entrance Skin Dose (ESD) is used with the irradiated area and patient mean thickness for specific anatomy. ESD is calculated from a developed equation, where entrance surface air-KERMA (ESAK) and backscatter factor are taking into account, with air-to-skin coefficient conversion. Air-KERMA rate has its equation derived from IPEN/UK simulation data. The input variables in ESD equation are: voltage and its ripple, total bean filtration, anode angle, current, time, distance, patient area under irradiation and patient thickness. We developed specific Lambert-Beer attenuation equations derived from mass energy-absorption coefficients data (NIST/USA), for each anatomy: chest, upper arm, hand and thigh. The anatomy mean thickness was estimate by summing skin, muscle, fat and bone thickness at central ray location, in antero-posterior incidence, for standard male.

Results:The final equations, one for each anatomy, although complex in its whole format, simplifies the direct determination of absorbed dose from the variables involved. There is no need to look up tables, interpolation, or restrictions due to small ranges of variables. After one time input data, total absorbed dose (mGy) is calculated instantaneously. The final result mean error, compare to available data, was equal to 5%.

Conclusion:The complex equations developed has its use simplified by one time input data, with no look up tables or data interpolation. Besides dose calculation for a given exam and patient, the operator can chose the best variables that will deposit less radiation into patient by means of a previous analysis of each variables combination.

Funding Support, Disclosures, and Conflict of Interest: This research is support by CNPq, the Federal research supporting agency of Brazil.

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