科研之友
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摘要
Determination of dose error margins in radiation therapy planning due to variations in Hounsfield Units (HU) values dependent on the use of different CT scanning protocols. %26lt;br%26gt;Based on a series of different CT scanning protocols used in clinical practice, conversion tables for radiation dose calculations were generated and subsequently tested on a phantom. These tables were then used to recalculate the radiation therapy plans of 28 real patients after an incorrect scanning protocol had inadvertently been used for these patients. %26lt;br%26gt;Different CT parameter settings resulted in errors of HU values of up to 2.6 % for densities of %26lt; 1.1 g/cm(3), but up to 25.6 % for densities of %26gt; 1.1 g/cm(3). The largest errors were associated with changes in the tube voltage. Tests on a virtual water phantom with layers of variable thickness and density revealed a sawtooth-shaped curve for the increase of dose differences from 0.3 to 0.6 % and 1.5 % at layer thicknesses of 1, 3, and 7 cm, respectively. Use of a beam hardening filter resulted in a reference dose difference of 0.6 % in response to a density change of 5 %. The recalculation of data from 28 patients who received radiation therapy to the head revealed an overdose of 1.3 +/- 0.4 % to the bone and 0.7 +/- 0.1 % to brain tissue. On average, therefore, one monitor unit (range 0-3 MU) per 100 MU more than the correct dose had been given. %26lt;br%26gt;Use of different CT scanning protocols leads to variations of up to 20 % in the HU values. This can result in a mean systematic dose error of 1.5 %. Specific conversion tables and automatic CT scanning protocol recognition could reduce dose errors of these types.
- 出版日期2014-1
