Study of Radiation dose perturbation by near metallic stents and its measurement

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15591296
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Radiation science
• Research Institution: Nara Medical University
• Principal Investigator: YOSHIMURA Hitoshi Nara Medical University, Associate Professor, 医学部, 助教授 (60167012)
• Project Period (FY): 2003 – 2004
• Keywords: High-energy X-ray irradiation / Metallic stent / Dose perturbation / Dose measurement / TL sheet / TLD / 2-dimensional read-out system / CCD camera

Research Abstract

We developed a 2-dimensional read-out system for thermoluminescent(TL) sheets using a cooled CCD camera, and measured the dose perturbation by metallic stents(MS) (for the trachea, esophagus, and blood vessels) of various shapes and materials.
<Read-out system> Concerning the luminescence-dose relationship, the characteristics of TL sheets with a wide dynamic range could not be utilized efficiently in the I.I.method, but reading out in a wide dynamic range became possible, and linearity was maintained over a range of 10-5,000 cGy, with the cooled CCD camera. Image data with a low noise level could be obtained by cooling the CCD. These results indicate that the new system is superior to the conventional I.I.method.
<Dose perturbation> Metallic stents for the trachea (stainless steel), esophagus (nytinol), lower limb artery (cobalt alloy, stainless steel), and coronary artery (stainless steel) and metal for spinal fixation (6.2 mmφ, high-purity titanium rod) were irradiated externally with 10 MV X-ray and intraluminally with ^<192>Ir-HDR at 6 Gy by contacting TL sheets on the metallic stents. The irradiated TL sheets were read out as images using a 2-dimensional read-out system using a cooled CCD camera, and absorption and backscatter (dose perturbation) were measured. The measurement was performed by the composite method, i.e., each stent was irradiated at least 5 times, and multiple images were over laid. The dose was reduced due to absorption by 2.2-8.1% in stainless steel, 3.4% in cobalt alloy, and 14% in the metal for spinal fixation. Measurement was impossible in nytinol. The dose was increased due to backscatter by 3.2-8.8% in stainless steel and 21% in the metal for spinal fixation, and measurement was impossible in cobalt alloy and nytinol. By intraluminal irradiation, the dose was reduced due to absorption by 8.7% in stainless steel, 1.8% in nytinol, and 2.4% in cobalt alloy. Thus, dose perturbation by metal stents in high-energy X-ray irradiation was restricted to an increase or a decrease at the surface of 8-9% at the maximum, which would pose no clinical problem, but a maximum increase of 21% was observed on the surface of the metal for spinal fixation, and dose evaluation in consideration of this effect was suggested to be necessary.