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Keywords:
Radioprotection / Radiation dose, Professional issues, Radiation physics, CT, Experimental, Technical aspects, Technology assessment, Radiation safety, Occupational / Environmental hazards, Quality assurance, Dosimetric comparison
Authors:
R. Pescada, P. Sousa, A. F. Abrantes, L. P. V. Ribeiro, R. P. P. Almeida, S. Rodrigues, K. B. Azevedo, J. P. Pinheiro; Faro/PT
DOI:
10.1594/ecr2015/B-0869
Methods and materials
MATERIALS
The materials used in order to conduct this research were:
- 1 plain ionization chamber PTW®
- 1 electometer PTW® Unidos E®
- 16 optically stimulated luminescence (OSL) dosimeters
- 1 bismuth breast protection KIRAN®
- (equivalent to 0.08mm of lead)
- 1 lens barium protection GRAYSHIELD®
- (equivalent to 0.075mm of lead)
- 1 thyroid lead protection GUIDANT®
- (equivalent to 0.5mm of lead)
- 1 gonads lead apron protection GUIDANT®
- (equivalent to 0.25mm of lead)
- 1 anthropomorfic phantom ADAMROUILLY®
- 1 computed tomography (CT) equipment SIEMENS® SOMATOM® EMOTION® 16
- 1 image control phantom GAMMEX 464®
METHODS
The methods developed to achieve the purposes of this research started by choosing the acquisition protocols to use.
The chosen protocols were routine head CT,
routine thorax CT,
routine abdomen CT and routine lower limb CT.
One of the most important aspects were to check wich of the measuring instruments is more sensitive for primary or secundary radiation.
It is known that the plain ionization chamber only detects radiation that incides directly to it (anisotropic detection),
and the OSL dosimeters detect radiation from any direction (isotropic detection).
The dosimetry on the routine head CT was made according to the following protocol:
- The anthropomorphic phantom was positioned in the isocenter to the CT gantry;
- The plain ionization chamber was placed in the right eye (Fig. 1);
- 1 OSL dosimeter was placed in the left eye,
another was placed in the thyroid and another was placed in the thorax (Fig. 1);
- 5 sequential acquisitions of the head (routine head CT) were made,
angled by the orbitomeatal line (Fig. 2) with the tecnical parameters of Table 2;
- The Air Kerma values were anotated for each exposition;
- The OSL dosimeters were sent to reading;
- The barium,
lead and bismuth protections were placed in the lens,
thyroid and thorax,
respectively.
Also,
new OSL dosimeters were placed in the same positions as before (Fig. 3).
- 5 sequential acquisitions of the head (routine head CT) were repeated,
angled by the orbitomeatal line (Fig. 2) with the same technical parameters of Table 2;
The dosimetry on the routine thorax CT was made according to the following protocol:
- The anthropomorphic phantom was positioned in the isocenter to the CT gantry;
- The plain ionization chamber was placed in the middle anterior region of thorax,
at the breast level (Fig. 4);
- 1 OSL dosimeter was placed in the middle anterior region of thorax,
at the breast level,
another was placed in the left eye,
and another was placed in the thyroid (Fig. 4);
- 5 volumetric acquisitions of the thorax (routine thorax CT) were made (Fig. 5),
with the tecnical parameters of Table 2;
- The Air-Kerma values were anotated for each exposition;
- The OSL dosimeters were sent to reading;
- The barium,
lead and bismuth protections were placed in the lens,
thyroid and thorax,
respectivelly.
Also,
new OSL dosimeters were placed in the same positions as before (Fig. 6).
- 5 volumetric acquisitions of the thorax (routine thorax CT) were repeated (Fig. 5),
with the same technical parameters of Table 2;
The dosimetry on the routine abdomen CT was made according to the following protocol:
- The anthropomorphic phantom was positioned in the isocenter to the CT gantry;
- The plain ionization chamber was kept in the middle anterior region of thorax,
at the breast level (Fig. 4);
- 1 new OSL dosimeter was placed in the middle anterior region of thorax,
as in the previous dosimetru plan,
at the breast level (Fig. 4);
- 5 volumetric acquisitions of the abdomen (routine abdomen CT) were made (Fig. 7),
with the tecnical parameters of Table 3 ;
- The Air-Kerma values were anotated for each exposition;
- The OSL dosimeter were sent to reading;
- The bismuth protection were placed in the thorax.
Also,
1 new OSL dosimeter were placed in the same position as before (Fig. 8).
- 5 volumetric acquisitions of the abdomen (routine abdomen CT) were repeated (Fig. 7),
with the same tecnical parameters of Table 3;
The dosimetry on the routine lower limb CT was made according to the following protocol:
- The anthropomorphic phantom was positioned in the isocenter to the CT gantry,
at the knees level;
- The plain ionization chamber was placed in the pelvic region,
at the female gonads level (Fig. 9);
- 1 OSL was placed in the pelvic region,
at the female gonads level (Image 9);
- 5 volumetric acquisitions of the left knee (routine lower limb CT of the knee) were made (Fig. 10),
with the tecnical parameters of Table 4;
- The Air-Kerma values were anotated for each exposition;
- The OSL dosimeter was sent to reading;
- The lead apron was placed over the pelvic region.
Also,
1 new OSL dosimeter were placed in the same position as before (Fig. 11).
- 5 volumetric acquisitions of the left knee (routine lower limb CT of the knee) were repeated (Fig. 10),
with the same tecnical parameters of Table 4;
To check the image quality the following steps were undertaken:
- The GAMMEX 464® was positioned in the isocenter to the CT gantry,
aligned according to the sagital,
axial and coronal lines (Fig. 12);
- The axial laser was positioned in the indicated module of the phantom (this phantom has 4 modules);
- The routine abdomen CT examination protocol was used,
but with several adjustments for image quality control purposes and there was produced just one slice.
This protocol can be seen in Table 5;
- The previous step was repeated,
with exactly the same protocol,
but adding a sponge over the phantom (to reduce beam hardenning artifacts) and with the bismuth protection over the sponge (Fig. 13);
- For each of the other 3 modules od the phantom,
the previous steps were repeated;