International Journal of Hematology and Oncology 2021, Vol 31, Num 3 Page(s): 192-198
Determination of Tumor Size and Hounsfield Unit/Electron Density Values in Three Different CT Scans for Lung SBRT Planning

Ayse OKUMUS1, Ismail Faruk DURMUS2

1Yeni Yüzyıl University Gaziosmanpasa Hospital, Department of Radiation Oncology, Istanbul, TURKEY
2Nisantasi University, Department of Radiotherapy, Istanbul, TURKEY

Keywords: Lung SBRT, Breath Hold,SGRT, Hounsfield Unit, Electron Density
The success of Radiotherapy treatment depends on the accurate calculation of dose distributions. The calculation algorithms calculate the dose distributions according to the physical properties of the materials in which the radiation interacts. In our study, the effects of different CT scanning techniques for tumor and healthy organ’s physical properties were investigated in lung SBRT treatments. We performed Normal-CT, Deep Insprium Breath Hold-CT (DIBH-CT) and Average-CT scans for 18 lung SBRT patients. Eighteen patients were scanned by each technique; Gross Tumor Volumes (GTV) were examined. Hounsfield Unit (HU) and Electron Density (ED) values, the most important parameters in dose calculation, were compared for three scan techniques. HU and ED values were examined for a spherical area of 10 cm diameter around of GTV and 1 cm outer of GTV. According to DIBH-CT, GTV was determined 18.4% (p< 0.001) greater in Normal-CT and 31.8% (p< 0.001) greater in Average-CT. Density of GTV decreased in Normal-CT and Average-CT, but healthy lung tissue’s density around GTV increased. The biggest differences for HU, ED and GTV volume were obtained in the Average-CT. Distortion and artefacts caused by respiratory motion were minimized with DIBH-CT. The ED/HU values were determined more accurately without respiratory motion with DIBH-CT. Thus, GTV can be determined in real dimensions with sharp limits and dose distributions can be calculated more accurately.