Volumen 23 (2017): Edición 1 (March 2017)

Aim: The aim of the study was to compare several methods of dose prescription, the mean dose, the median dose, the effective dose and the generalized Equivalent Uniform Dose (gEUD).

Background: The dose distribution in the planning target volume is never fully homogenous. Depending on the dose prescription method for the same prescribed dose different biologically equivalent doses are delivered. The latest ICRU Report 83 proposes to prescribe the dose to the median dose in the PTV. Several other methods are also in common use. It is important to know what are differences of doses actually delivered depending on the dose prescription method.

Materials and methods: The study was performed for three groups of patients treated radically with external beams in Brzozow, over the 2012-2013 period. The groups were of patients with breast, lung and prostate cancer. There were 10 patients in each group. For each patient all metrics, i.e. the mean dose, the median dose, the effective dose and the generalized Equivalent Uniform Dose, were calculated. The influence of the dose homogeneity in the PTV on the results is also evaluated. The gEUD was used as a reference dose prescription method.

Results: For all patients, an almost perfect correlation between the median dose and the gEUD was obtained. Worse correlation was obtained between other metrics and the gEUD. The median dose is almost always a little higher than the gEUD, but the ratio of these two values never exceeded 1.013.

Conclusion: The median dose seems to be a good and simple method of dose prescription.

Aim: In the current study, some imaging characteristics of AuNPs were quantitatively analyzed and compared with two conventional contrast media (CM) including Iodine and Gadolinium by using of a cylindrical phantom.

Methods: AuNPs were synthesized with the mean diameter of 16 nm and were equalized to the concentration of 0.5, 1, 2 and 4 mg/mL in the same volumes. A cylindrical phantom resembling the head and neck was fabricated and drilled to contain small tubes filled with Iodine, Gadolinium, and AuNPs as contrast media. The phantom was scanned in different exposure techniques and CT numbers of three studied contrast media inside test tubes were measured in terms of Hounsfield Unit (HU). The imaging parameters of the noise and contrast to noise ratios (CNR) were calculated for all studied CMs.

Results: AuNPs showed 128% and 166% higher CT number in comparison with Iodine and Gadolinium respectively. Also, Iodine had a greater CT number than Gadolinium for the same exposure techniques and concentration. The maximum CT number for AuNPs and studied contrast materials was obtained at the highest mAs and the lowest tube potential. The maximum CT number were 1033±11 (HU) for AuNP, 565±10 (HU) for Iodine, 458±11 for Gadolinium. Moreover, the maximum CNRs of 433±117, 203±53, 145±37 were found for AuNPs, Iodine and Gadolinium respectively.

Conclusion: The contrast agent based on AuNPs showed higher imaging quality in terms of contrast and noise relative to other iodine and gadolinium based contrast media in X-ray computed tomography. Application of the AuNPs as a contrast medium in x-ray CT is recommended.