Dose estimation in multislice CT scan exam

Doses delivered in CT exams are relatively high compared to other medical explorations using X rays and radioactive elements. If we want to use a CT scanner with medical interventions, we must take care about the staff radioprotection. This study consists on dose estimation anywhere in the space around the scanner where a member of the medical staff might be. To achieve this purpose, Monte Carlo calculations of X rays interactions with a patient, especially scattered rays, have been computed. The computer simulation takes in account the source construction, photon transport inside the patient body assimilated as a cylinder, and dose calculation in the environment of the patient. The main results are the dose distribution and the energy spectrum in any point around the patient. Experimental measurements of these two results have been done and have shown a good correlation with the simulation. We have also computed the dose distribution in the patient and the depth distribution of the dose in the physician working close to the patient. We found that energy spectrum does not depend on physician position and dimensions of the patient. The dose is not monotonous decreasing, maximums in the dose distribution appear. The results may be used to calculate, for any exam on any patient, the dose absorbed by a person surrounding the scanner. As an example, 0.3 mSv is a typical dose for an exam on a normally sized man with 400 mA tube current, 120 kV and 15 s duration. To calculate these doses, isodose curves have been drawn and an easy calculation protocol is given