Estimating brain radiation dose to the main operator in interventional radiology

Estimating brain and eye lens dose for the cardiologist in interventional cardiology-are the dose levels of concern?

OBJECTIVES

To establish conversion coefficients (CCs), between mean absorbed dose to the brain and eye lens of the cardiologist and the air kerma-area product, PKA, for a set of projections in cardiac interventional procedures. Furthermore, by taking clinical data into account, a method to estimate the doses per procedure, or annual dose, is presented.

METHODS

Thermoluminescence dosimeters were used together with anthropomorphic phantoms, simulating a cardiologist performing an interventional cardiac procedure, to estimate the CCs for the brain and eye lens dose for nine standard projections, and change in patient size and x-ray spectrum. Additionally, a single CC has been estimated, accounting for each projections fraction of use in the clinic and associated PKA using clinical data from the dose monitoring system in our hospital.

RESULTS

The maximum CCs for the eye lens and segment of the brain, is 5.47 μGy/Gycm2 (left eye lens) and 1.71 μGy/Gycm2 (left brain segment). The corresponding weighted CCs: are 3.39 μGy/Gycm2 and 0.89 μGy/Gycm2, respectively.

CONCLUSIONS

Conversion coefficients have been established under actual scatter conditions, showing higher doses on the left side of the operator. Using modern interventional x-ray equipment, interventional cardiac procedures will not cause high radiation dose levels to the operator when a ceiling mounted shield is used, otherwise there is a risk that the threshold dose values for cataract will be reached.

ADVANCE IN KNOWLEDGE

In addition to the CCs for the different projections, methods for deriving a single CC per cardiac interventional procedure and dose per year were introduced.

Editor's Choice - Estimated Radiation Dose to the Operator During Endovascular Aneurysm Repair

OBJECTIVE

To estimate operator organ doses from fluoroscopically guided infrarenal endovascular aneurysm repair (EVAR) procedures, using the detailed exposure information contained in radiation dose structured reports.

METHODS

Conversion factors relating kerma area product (PKA) to primary operator organ doses were calculated using Monte Carlo methods for 91 beam angles and seven x-ray spectra typical of clinical practice. A computer program was written, which selects the appropriate conversion factor for each exposure listed in a structured report and multiplies it by the respective PKA. This system was used to estimate operator doses for 81 EVAR procedures for which structured reports were available. The impact of different shielding scenarios and variations in operator position was also investigated.

RESULTS

Without any shielding, the median estimated effective dose was 113 μSv (interquartile range [IQR] 71, 252 μSv). The highest median organ doses were for the colon (154 μSv, IQR 81, 343) and stomach (133 μSv, IQR 76, 307). These dose estimates represent all exposures, including fluoroscopy and non-fluoroscopic digital acquisitions. With minimal shielding provided by 0.25 mm of Pb covering the torso and upper legs, the effective dose was reduced by a factor of around 6. With additional shielding from ceiling and table shields, a 25 to 50 fold reduction in dose is achievable. Estimated doses were highest where the primary beam was pointed directly away from the operator.

CONCLUSION

The models suggest that with optimal use of shielding, operator doses can be reduced to levels equivalent to one to two days of natural background exposure and well below statutory dose limits.

Evaluation of operator eye exposure and eye protective devices in interventional radiology: Results on clinical staff and phantom

PURPOSE

To assess occupational eye lens dose based on clinical monitoring of interventional radiologists and to assess personal protective eyewear (PPE) efficacy through measurements with anthropomorphic phantom.

METHODS

Two positions of the operator with respect to X-ray beam were simulated with phantom. Dose reduction factor (DRF) of four PPE was assessed, as well as correlation between eye lens and whole-body doses. Brain dose was also assessed. Five radiologists were monitored for one-year clinical procedures. All subjects were equipped with whole-body dosimeter placed over lead apron at the chest level and eye lens dosimeter placed over the left side of the PPE. Kerma-Area Product (KAP) of procedures performed during the monitoring period was recorded. The correlation of eye lens dose with whole-body dose and KAP was assessed.

RESULTS

DRF was 4.3/2.4 for wraparound glasses, 4.8/1.9 for fitover glasses, 9.1/6.8 for full-face visor in radial/femoral geometries. DRF of half-face visor depended on how it is worn (range 1.0-4.9). Statistically significant correlation between dose value over the PPE and chest dose was observed, while there was no correlation between eye lens dose and chest dose. The results on clinical staff showed statistically significant correlation between dose values over the PPE and KAP.

CONCLUSIONS

All PPE showed significant DRF in all configurations, provided they were worn correctly. Single DRF value is not applicable to all clinical situations. KAP is a valuable tool for determining appropriate radiation protection measures.

CORRELATION BETWEEN ROUTINE PERSONAL DOSIMETRY READING AND THE DOSE TO THE BRAIN OF INTERVENTIONAL STAFF

This study aimed to evaluate the relationship between the brain absorbed dose and personal dosimetry readings in interventional cardiologists. Interventional procedures were replicated using Monte Carlo simulations (MCNP 6) with anthropomorphic phantoms representing both operator and patient. Absorbed doses were evaluated for 10 predefined regions of the operator's brain as well as for dosemeters at chest and neck level. One beam quality (HVL = 6.2 mm Al) and nine beam projections were considered. A significant bias in the laterality of brain dose was found with doses at the left side of the brain being up to 2.8 times higher compared with the right. The correlation between brain dose and dosemeter reading was found to be dependent on beam projection. Yet, a generalized conversion factor (brain dose normalized by Hp(10)), averaged over all considered beam projections, could be proposed for (retrospective) brain dose estimation from routinely measured dosimetry data.

Clinical evaluation of a novel head protection system for interventional radiologists

PURPOSE

A novel two-part protective system consisting of a modified thyroid collar and a head protection is intended to reduce the radiation dose to the examiners head during fluoroscopy-guided interventions. In this pilot study, we tested this protection system under real-life conditions in general radiological and neuroradiological interventions.

METHODS

Two sets of the protection system (set A and B) were equipped with 12 thermoluminiscence detectors (TLD). For simultaneous measurement of radiation exposure and dose-reduction, each six TLDs were fixed to the inner side and on the corresponding outer side of the protection system. Set A was used exclusively for general radiological interventions and set B exclusively for neuroradiological interventions. To compare the staff exposure in general radiology and neuroradiology, dose values were normalized to a DAP of 10 000 µGy∙m².

RESULTS

The sets were tested during 20 general radiological interventions and 32 neuroradiological interventions. In neuroradiology, the mean normalized radiation exposure was 13.44 ± 1.36 µSv/10000 µGy∙m² at the head protection and 22.27 ± 2.09 µSv/10 000 µGy∙m² at the thyroid collar. In general radiology, the corresponding results were 29.91 ± 4.19 µSv/10 000 µGy∙m² (head protection) and 68.07 ± 17.25 µSv/10 000 µGy∙m² (thyroid collar). Thus, mean dose exposure was 2.5 times higher in general radiological interventions (p = 0.016). The use of the protection system resulted in a mean dose reduction of 81.2 ± 11.1 % (general radiology) and 92.1 ± 4.2 % (neuroradiology; p = 0.016).

CONCLUSION

Fluoroscopy-guided interventions lead to significant radiation exposure of the head area for the examiner. The novel protection system tested led to a significant dose reduction of 80-90%, depending on the type of intervention.