Methods For Monitoring And Evaluation Of The Personal Dose For Staff During Interventional Procedures

Objective Radiological staff in interventional procedures usually perform interventional operation or diagnosis in the widely distributed X-ray scattered field, and they receive a high ionization radiation dose and risk. So monitoring personal dose to these staff must be strengthened. However, staff are exposed to an extremely non-uniform scattered field which brings difficulty in the accurate assessment of effective dose. Moreover, existed dose monitoring methods are not unified which also brings large discrepancy in dose assessment. So it is necessary to carry out in-depth study in more accurate methods for personal dose monitoring and evaluation. Therefore, through Monte Carlo (MC) simulations and field measurement, radiation fields in interventional workplaces were firstly studied, then staff’s surface doses were obtained, and finally correlations between effective doses and surface doses were studied. This study aims to establish more accurate methods for monitoring and evaluation of the personal dose for staff during interventional procedures and to provide the basis for normalizing personal dose monitoring work.Methods For scattered field in interventional room, firstly, as the source of scattered field, X-ray spectra were calculated under common conditions with the X-ray generation geometrical model in MC simulation. Then based on space geometry of operating room, scattered radiation fields were calculated in various common exposure conditions. Detailed investigation on radiation fields at staff’s common positions was done. Then measurements of radiation field in an X-ray room were carried out to verify the reliability of simulation results. For doses at surface of staff, firstly, based on interventional common conditions, MC simulations on surface doses of primary operators were carried out and then verified through field measurements. Anaesthetists doses during interventional procedures were also measured. Additionally, dose affect factors were analyzed, which could provide the basis for instructing radiation protection. To study monitoring and evaluation methods, organ doses of staff under various common conditions were then simulated by using ICRP male voxel phantom, and effective doses were summed up according to ICRP 103 organ weighting factors. Then with surface doses results, correlations between effective doses and surface doses at common dosemeter worn positions were then dissussed quantitively, and single dosimetry and double dosimetry methods were obtained with linear regression methods. Moreover, this study also discussed eye lens and thyroid doses, and their dose evaluation methods were also proposed.Results Interventional scattered fields were complex, radiation dose rates and their distributions closely correlated with beam projections and protection shields. The range of scattered air kerma (Ka) at staff’s usual positions under both head & neck and thorax irradiation regions of patient were:0.00～28.77 μGy/(Gy·cm2), at the height of eye were: 0.00～8.45 μGy/(Gy·cm2); and about 99% of Ka can be reduced by table curtain and 67% at the height of eye from ceiling shield. From both measurement and simulation results, beam projections and standing positions were key factors that influence surface doses mostly. Usually, doses were higher with the tube aside the staff, and lower with it at opposite side, different beam projections can cause dose differences by a factor of 30 in average. Doses were also higher when staff were closer to the beam, different positons could lead to difference by a factor of 8 in average. Additionally seen from simulation results, doses were highly influenced by tube voltages(kVp), they increased maximally by a factor of 3～4 as increase of kVp. Table curtain and ceiling shield can both reduce doses, and maximally reduce about 50% of surface doses at staff’s usual positions. From comparisons, double dosimetry (DD) can evaluate effective doses more stable and accurately than single dosimetry. The accurate DD method can be obtained through dosemeters at left collar over apron and right chest under apron with coefficients, by differentiating conditions with thyroid shield or not. Compared with other researches, our method was still optimum. Based on our DD methods, without adding additional dosemeters, left and right eye lens dose could be estimated with dose at left collar over apron respectively with different coefficients. Thyroid dose could also be evaluated with that dose by differentiating conditions with thyroid shield or not.Conclusions For interventional procedures, radiation field and staff’s surface doses closely correlate with X-ray beam projections, X-ray systems and shield facilities. Monitoring methods suggested by this work could not only provide accurate evaluations on effective doses of interventional staff, but also assist to estimate their eye lens and thyroid doses. The application of the results provides the important scientific basis for normalizing monitoring work of interventional staff in our country.