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Keywords:
Radioprotection / Radiation dose, Head and neck, Eyes, Cone beam CT, CT, Digital radiography, Diagnostic procedure, Radiobiology, Dosimetry, Biological effects, Dosimetric comparison, Pathology
Authors:
A. Stratis, G. Zhang, R. Jacobs, R. Bogaerts, H. Bosmans; Leuven/BE
DOI:
10.1594/ecr2015/B-0680
Conclusion
We calculated the dose to the eye lenses for different bone densities ranging from 2.2 g/cm3 (normal densities) to 1.2 g/cm3 (to account for variations in bone thickness,
density and pathologies across population).
The varying bone density has an immediate influence to the lens dose due to the bony orbit which encloses the eye bulb.
Jaw protocol analysis highlights the shielding role of the orbit against scatter radiation.
There is a substantial increase in the eye lens dose while density decreases from 2.2 to 1.2 g/cm3 (44% increase in Zubal phantom,
pearson-correlation-coefficient,
r= -0.978; 36% increase in ICRP phantom,
pearson-correlation-coefficient,
r= -0.989).
The so-called ‘face’ protocol which employs a larger in height FOV may result,
upon implementation,
in the exposure of the lenses by primary photons which have passed through the organs of the head behind the orbital bone as the x-ray tube crosses the posterior side of the patient.
The orbital bone in this case offers a protection shield against scatter and unattenuated primary photons.
Result analysis shows a 23% (r=-0.968) and 19% (r= -0.975) increase in the eye lens doses in Zubal and ICRP phantoms respectively when density decreases from 2.2 to 1.2 g/cm3.
The higher lens doses are observed in the skull protocol.
This is due to the fact that the tube performs a 360o rotation around the head and hence,
the eyes are exposed to the primary beam as the tube crosses the anterior side of the head.
There is a 18% (r=-0.963) and 12% (r=-0.976) increase in the lens dose in Zubal and ICRP phantoms respectively when density decreases from 2.2 to 1.2 g/cm3.
The two computational phantoms represent an adult male (Zubal) and an adult female (ICRP phantom).
The most realistic case is modeled when the bone density is equal to 1.92 g/cm3.
In such case,
the lens doses are 13.32 mGy and 18.35 mGy in the male and the female phantom respectively,
when the skull protocol is performed.
These doses are comparable to lens doses in head multislice CT9.